Dating lacustrine episodes in the eastern Sahara by the epimerization of isoleucine in ostrich eggshells

USGS Publications Warehouse

Miller, G.H.; Wendorf, F.; Ernst, R.; Schild, R.; Close, A.E.; Friedman, I.; Schwarcz, H.P.

1991-01-01

The eggshell of the African ostrich, Struthio camelus, closely approximates a closed system for the retention of indigenous proteinaceous residues. Epimerization of the protein amino acid isoleucine follows linear first-order kinetics in laboratory simulations nearly to racemic equilibrium, and the variation in D/L ratio within a single fragment, or between fragments of the same age, is significantly less than in other carbonate systems. These observations suggest that the extent of isoleucine epimerization (aIle/Ile ratio) in ostrich eggshell offers the potential for high-resolution geochronology of Quaternary deposits. From the simulation experiments, and dated early Holocene samples for which we have in situ mean annual sediment temperature measurements, Arrhenius parameters have been calculated; the activation energy is 30.33 kcal mol-1, similar to that of other carbonate systems. We have measured the aIle/Ile ratio in ostrich eggshell associated with lacustrine episodes at Bir Tarfawi and Bir Sahara East, two depressions in what is currently the hyperarid eastern Sahara. The ratios can be used directly to indicate qualitatively the time represented by each series of lake sediment, and to correlate disjunct lacustrine deposits within and between the basins. Uranium-series disequilibrium dating of algal mats contained within some of the lake beds indicate that a major wet interval occurred about 130 ka ago. Using the U-series date for calibration, the amino acid ratios are used to date the most recent lacustrine interval to about 100 ka B.P., and two older intervals, one about 200 ?? 25 ka B.P., and an older interval that occurred prior to 250 ka ago. ?? 1991.

Reading a 400,000-year record of earthquake frequency for an intraplate fault

NASA Astrophysics Data System (ADS)

Williams, Randolph T.; Goodwin, Laurel B.; Sharp, Warren D.; Mozley, Peter S.

2017-05-01

Our understanding of the frequency of large earthquakes at timescales longer than instrumental and historical records is based mostly on paleoseismic studies of fast-moving plate-boundary faults. Similar study of intraplate faults has been limited until now, because intraplate earthquake recurrence intervals are generally long (10s to 100s of thousands of years) relative to conventional paleoseismic records determined by trenching. Long-term variations in the earthquake recurrence intervals of intraplate faults therefore are poorly understood. Longer paleoseismic records for intraplate faults are required both to better quantify their earthquake recurrence intervals and to test competing models of earthquake frequency (e.g., time-dependent, time-independent, and clustered). We present the results of U-Th dating of calcite veins in the Loma Blanca normal fault zone, Rio Grande rift, New Mexico, United States, that constrain earthquake recurrence intervals over much of the past ˜550 ka—the longest direct record of seismic frequency documented for any fault to date. The 13 distinct seismic events delineated by this effort demonstrate that for >400 ka, the Loma Blanca fault produced periodic large earthquakes, consistent with a time-dependent model of earthquake recurrence. However, this time-dependent series was interrupted by a cluster of earthquakes at ˜430 ka. The carbon isotope composition of calcite formed during this seismic cluster records rapid degassing of CO2, suggesting an interval of anomalous fluid source. In concert with U-Th dates recording decreased recurrence intervals, we infer seismicity during this interval records fault-valve behavior. These data provide insight into the long-term seismic behavior of the Loma Blanca fault and, by inference, other intraplate faults.

Belgian speleothems from the Last Interglacial: insights in the onset of glacial conditions in north western Europe.

NASA Astrophysics Data System (ADS)

Vansteenberge, Stef; Verheyden, Sophie; Cheng, Hai; Edwards, Lawrence R.; Keppens, Eddy; Claeys, Philippe

2015-04-01

Currently, a dataset combining at least four speleothems from two different cave systems in southern Belgium (Han-sur-Lesse and Remouchamps) is being constructed to improve the understanding of the termination of the Eemian and the millennial to decadal variability of the Early Glacial times in north western Europe. Here, one of those speleothems is presented. The Han-stm-9 (or 'Triptyque') speleothem is a broken, 68 cm long and candle-shaped stalagmite from the Han-sur-Lesse cave system. The stalagmite was collected in summer 2013 within the southern part of the cave network and was dated between ~126 and ~99ka. Most likely, climate optimum conditions during the 130-125ka interval are linked to the growth of this and other speleothems from Belgian caves. This particular speleothem gained interest because of the partial conformity with the continental interglacial period in northern western Europe (130 - 118ka) and its dense calcite composition with visible layering, excluding post-depositional deformation. Furthermore, the stalagmite displays a complex growth history, with large variations in growth rates (ranging from and periods of ceased speleothem formation. Two hiatuses, with a distinct macroscopic expression, occur. The first one starts at 118.4ka and lasts until 113.0ka. A second hiatus is situated between ~108ka and 103.7ka. A trend in growth rate, consisting of slow growth gradually increasing towards very fast speleothem formation before both hiatuses, is observed. These intervals with very high growth rates, for instance around 118ka, enable high-resolution climate reconstructions via stable isotopes (δ18O and δ13C) and trace elements (Mg, Sr, Ba and P), down to centennial and decadal scale. The timing of the first hiatus corresponds with Greenland Stadial 26 and with the generally accepted termination of the Eemian in northern Europe at 119-118ka. Also, preliminary stable isotope studies have indicated a large detoriation of δ13C occurring right before the second hiatus, while δ18O increases only gradually. This could indicate drastic vegetation changes in the area occurring around the timing of GS25. Furthermore, both δ18O and δ13C time series clearly display millennial to centennial scaled variability during the onset of the Last Glacial. These proxies thus indicate a rather complex glacial-interglacial transition, which is in line with other archives from different locations in Belgium and Europe. Eventually, integrating these findings into a more regional dataset can lead to an improved knowledge of continent-scaled tendencies, such as previously suggested N-S gradients in the onset of Interglacial and Glacial conditions.

Timing of wet episodes in Atacama Desert over the last 15 ka. The Groundwater Discharge Deposits (GWD) from Domeyko Range at 25°S.

NASA Astrophysics Data System (ADS)

Sáez, Alberto; Godfrey, Linda V.; Herrera, Christian; Chong, Guillermo; Pueyo, Juan J.

2016-08-01

A chronologically robust reconstruction of timing and dynamics of millennial time scale wet episodes encompassing the entire Atacama Desert during the last 15 ka has been constructed. To accomplish this, a new composite paleoclimatic record from Groundwater Discharge Deposits (GWD) in the Sierra de Varas (Domeyko Range, southern Atacama in Chile at 25°S) has been compiled and compared with other published paleohydrologic records from the Atacama region. In Sierra de Varas (SV), three millennial timescale wet climate phases have been characterized: around 14.5 ka cal BP, 12.2-9.8 ka cal BP, and 4.7 ka cal BP to the present day. These wet phases are interpreted from intervals of GWD facies formed during periods when the springs were active. GWD facies include: (1) black organic peat, rooted mudstones and sandstones formed in local wetland environments, and (2) gypsum-carbonate rich layers formed by interstitial growth. GWD intervals alternate with gravelly alluvial material deposited during arid phases. A trend towards less humid conditions during the Late Holocene wet episode characterizes GWD sedimentary series in Sierra the Varas, suggesting the onset of a dry episode over the last few centuries. Around 0.7 ka BP a very short wet episode is recorded in the central part of the desert suggesting this was the time of maximum humidity for the entire late Holocene wet period. A brief arid phase occurred between 1.5 and 2.0 ka BP indicated by the absence of GWD in the Domeyko Range. The paleoclimatic reconstruction encompassing the entire Atacama region shows that both the intensity and occurrence of wetter conditions were governed mainly by the distance to the source of moisture, and secondarily by the elevation of the sites. In the northern Atacama (16-20°S), four wet phases fed by N-NE summer monsoon precipitations have been proposed: Tauca phase (18-14 ka cal BP) and Coipasa phase (13-10 ka cal BP) during the Late Glacial, followed by Early Holocene and Late Holocene phases. In contrast, southern Atacama records (23-28°S) display only three pluvial periods which result from SE summer monsoon precipitation and outbreaks from the Westerlies during wintertime. The Early Holocene in the southern Atacama was a period of aridity, generating important landscape differences to those in the Northern Atacama where conditions were wetter. The core of Atacama (20-23°S) is the overall driest part of the desert because it is located in the distal limits of both N-NE and SE sources of moisture, the Amazon Basin and Gran Chaco areas, respectively.

A MIS 15-MIS 12 record of environmental changes and Lower Palaeolithic occupation from Valle Giumentina, central Italy

NASA Astrophysics Data System (ADS)

Villa, Valentina; Pereira, Alison; Chaussé, Christine; Nomade, Sébastien; Giaccio, Biagio; Limondin-Lozouet, Nicole; Fusco, Fabio; Regattieri, Eleonora; Degeai, Jean-Philippe; Robert, Vincent; Kuzucuoglu, Catherine; Boschian, Giovanni; Agostini, Silvano; Aureli, Daniele; Pagli, Marina; Bahain, Jean Jacques; Nicoud, Elisa

2016-11-01

An integrated geological study, including sedimentology, stable isotope analysis (δ18O, δ13C), geochemistry, micromorphology, biomarker analysis, 40Ar/39Ar geochronology and tephrochronology, was undertaken on the Quaternary infill of the Valle Giumentina basin in Central Italy, which also includes an outstanding archaeological succession, composed of nine human occupation levels ascribed to the Lower and Middle Palaeolithic. 40Ar/39Ar dating, and other palaeoenvironmental and tephrochronological data, constrain the sedimentary history of the whole succession to the MIS 15-MIS 12 interval, between 618 ± 13 ka and 456 ± 2 ka. Palaeoenvironmental proxies suggest that over this time interval of about 150 ka, sedimentary and pedogenic processes were mainly influenced by climatic changes, in particular by the pulsing of local mountain glaciers of the Majella massif. Specifically, the Valle Giumentina succession records glacio-fluvial and lacustrine sedimentation during the colder glacial periods and pedogenesis and/or alluvial sedimentation during the warmer interglacial and/or interstadial periods. During this interval, tectonics played a negligible role as a driving factor of local morphogenesis and sedimentation, whereas the general regional uplift experienced in the Middle Pleistocene led to capture of the basin and its definitive extinction after MIS 12. These data substantially improve previous knowledge of the chronology and sedimentary evolution of the succession, providing for the first time, a well constrained chronological and palaeoenvironmental framework for the archaeological and human palaeoecological record of Valle Giumentina.

Post-glacial variability of sea ice cover, river run-off and biological production in the western Laptev Sea (Arctic Ocean) - A high-resolution biomarker study

NASA Astrophysics Data System (ADS)

Hörner, T.; Stein, R.; Fahl, K.; Birgel, D.

2016-07-01

Multi-proxy biomarker measurements were applied on two sediment cores (PS51/154, PS51/159) to reconstruct sea ice cover (IP25), biological production (brassicasterol, dinosterol) and river run-off (campesterol, β-sitosterol) in the western Laptev Sea over the last ∼17 ka with unprecedented temporal resolution. The absence of IP25 from 17.2 to 15.5 ka, in combination with minimum concentration of phytoplankton biomarkers, suggests that the western Laptev Sea shelf was mostly covered with permanent sea ice. Very minor river run-off and restricted biological production occurred during this cold interval. From ∼16 ka until 7.5 ka, a long-term decrease of terrigenous (riverine) organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western Laptev Sea, caused by the onset of the post-glacial transgression. Intensified river run-off and reduced sea ice cover characterized the time interval between 15.2 and 12.9 ka, including the Bølling/Allerød warm period (14.7-12.9 ka). Prominent peaks of the DIP25 Index coinciding with maximum abundances of subpolar foraminifers, are interpreted as pulses of Atlantic water inflow on the western Laptev Sea shelf. After the warm period, a sudden return to severe sea ice conditions with strongest ice-coverage between 11.9 and 11 ka coincided with the Younger Dryas (12.9-11.6 ka). At the onset of the Younger Dryas, a distinct alteration of the ecosystem (reflected in a distinct drop in terrigenous and phytoplankton biomarkers) was detected. During the last 7 ka, the sea ice proxies reflect a cooling of the Laptev Sea spring/summer season. This cooling trend was superimposed by a short-term variability in sea ice coverage, probably representing Bond cycles (1500 ± 500 ka) that are related to solar activity changes. Hence, atmospheric circulation changes were apparently able to affect the sea ice conditions on the Laptev Sea shelf under modern sea level conditions.

The environmental context for the origins of modern human diversity: a synthesis of regional variability in African climate 150,000-30,000 years ago.

PubMed

Blome, Margaret Whiting; Cohen, Andrew S; Tryon, Christian A; Brooks, Alison S; Russell, Joellen

2012-05-01

We synthesize African paleoclimate from 150 to 30 ka (thousand years ago) using 85 diverse datasets at a regional scale, testing for coherence with North Atlantic glacial/interglacial phases and northern and southern hemisphere insolation cycles. Two major determinants of circum-African climate variability over this time period are supported by principal components analysis: North Atlantic sea surface temperature (SST) variations and local insolation maxima. North Atlantic SSTs correlated with the variability found in most circum-African SST records, whereas the variability of the majority of terrestrial temperature and precipitation records is explained by local insolation maxima, particularly at times when solar radiation was intense and highly variable (e.g., 150-75 ka). We demonstrate that climates varied with latitude, such that periods of relatively increased aridity or humidity were asynchronous across the northern, eastern, tropical and southern portions of Africa. Comparisons of the archaeological, fossil, or genetic records with generalized patterns of environmental change based solely on northern hemisphere glacial/interglacial cycles are therefore imprecise. We compare our refined climatic framework to a database of 64 radiometrically-dated paleoanthropological sites to test hypotheses of demographic response to climatic change among African hominin populations during the 150-30 ka interval. We argue that at a continental scale, population and climate changes were asynchronous and likely occurred under different regimes of climate forcing, creating alternating opportunities for migration into adjacent regions. Our results suggest little relation between large scale demographic and climate change in southern Africa during this time span, but strongly support the hypothesis of hominin occupation of the Sahara during discrete humid intervals ~135-115 ka and 105-75 ka. Hominin populations in equatorial and eastern Africa may have been buffered from the extremes of climate change by locally steep altitudinal and rainfall gradients and the complex and variable effects of increased aridity on human habitat suitability in the tropics. Our data are consistent with hominin migrations out of Africa through varying exit points from ~140-80 ka. Copyright © 2012 Elsevier Ltd. All rights reserved.

Lacustrine Records of Holocene Mountain Glacier Fluctuations from Western Greenland

NASA Astrophysics Data System (ADS)

Schweinsberg, A.; Briner, J. P.; Bennike, O.

2014-12-01

Recent studies have focused on documenting fluctuations of the Greenland Ice Sheet margin throughout the Holocene but few data exist that constrain past changes of local glaciers independent of the ice sheet. Our research combines proglacial lake sediment analysis with cosmogenic 10Be dating of Holocene moraines and radiocarbon dating of ice-cap-killed vegetation with an overall objective to use this multi-proxy approach to generate a detailed record of the coupled climate-glacier system through the Holocene. Here, we present lacustrine records of mountain glacier variability from continuous pro-glacial lake sediment sequences recovered from two glaciated catchments in northeastern Nuussuaq, western Greenland. We use radiocarbon-dated sediments from Sikuiui and Pauiaivik lakes to reconstruct the timing of advance and retreat of local glaciers. Sediments were characterized with magnetic susceptibility (MS), gamma density, Itrax XRF and visible reflectance spectroscopy at 0.2 cm intervals and sediment organic matter at 0.5 cm intervals. Basal radiocarbon ages provide minimum-age constraints on deglaciation from Sikuiui and Pauiaivik lakes of ~9.6 and 8.7 ka, respectively. Organic-rich gyttja from deglaciation until ~5.0 ka in Pauiaivik Lake suggests minimal glacial extent there while slightly elevated MS values from ~9.0 - 7.0 ka in Sikuiui Lake may reflect early Holocene glacial advances. Minerogenic sediment input gradually increases starting at ~5.0 ka in Pauiaivik Lake, which we interpret as the onset of Neoglaciation in the catchment. Furthermore, a distinct episode of enhanced glacial activity from ~4.0 - 2.2 ka in Sikuiui Lake may be correlative to a period of persistent snowline lowering evidenced by radiocarbon dates of ice-killed vegetation from nearby ice cap margins. Results from these lacustrine records and our ice-killed vegetation dataset suggest a middle Holocene onset of Neoglaciation ~5.0 - 4.0 ka in this region. We are supplementing these records with cosmogenic 10Be exposure dating to further constrain the timing of deglaciation. In addition, these sedimentary archives will continue to be compared to radiocarbon dates of ice-killed vegetation along adjacent ice cap margins to determine if times of persistent snowline lowering are correlative to periods of glacier advance.

The Record of Geomagnetic Excursions from a ~150 m Sediment Core: Clear Lake, Northern California

NASA Astrophysics Data System (ADS)

Levin, E.; Byrne, R.; Looy, C. V.; Wahl, D.; Noren, A. J.; Verosub, K. L.

2015-12-01

We are studying the paleomagnetic properties of a new ~150 meter drill core from Clear Lake, CA. Step-wise demagnetization of the natural remanent magnetism (NRM) yields stable directions after 20 mT, implying that the sediments are reliable recorders of geomagnetic field behavior. Several intervals of low relative paleointensity (RPI) from the core appear to be correlated with known geomagnetic excursions. At about 46 m depth, and ~33 ka according to an age model based on radiocarbon dates obtained from pollen and the Olema ash bed, a low RPI zone seems to agree with the age and duration of the Mono Lake Excursion, previously identified between 32 and 35 ka. Slightly lower in the core, at about 50 m depth and ~40 ka, noticeably low RPI values seem to be coeval with the Laschamp excursion, which has been dated at ~41 ka. A volcanic ash near the bottom of the core (141 mblf) is near the same depth as an ash identified in 1988 by Andrei Sarna-Wojcicki and others as the Loleta ash bed in a previous Clear Lake core. If the basal ash in the new core is indeed the, Loleta ash bed, then the core may date back to about 270-300 ka. Depending on the age of the lowest ash, a sequence of low RPI intervals could correlate with the Blake (120 ka), Iceland Basin (188 ka), Jamaica/Pringle Falls (211 ka), and CR0 (260 ka) excursions. Correlation of the low RPI intervals to these geomagnetic excursions will help in the development of a higher resolution chronostratigraphy for the core, resolve a long-standing controversy about a possible hiatus in the Clear Lake record, and provide information about climatically-driven changes in sedimentation.

Quaternary climate change on the northern margins of Saharo-Arabian Desert with possible impact on human evolution, evidence from Negev Desert speleothems, Israel

NASA Astrophysics Data System (ADS)

Vaks, A.; Bar-Matthews, M.; Ayalon, A.; Matthews, A.; Halicz, L.; Frumkin, A.

2006-12-01

The Saharo-Arabian Desert belt is the largest and driest desert in the world and its margins are vulnerable to climatic change. The paleoclimate of the northern margins of Saharo-Arabian Desert is not yet fully understood, and it is the subject of our study. The Negev Desert, southern Israel, located in the northern part of the Saharo-Arabian Desert is ideal for paleoclimate research, because of its very steep north-south precipitation gradient and numerous caves rich with carbonate cave deposits (speleothems). Speleothems grow only when precipitation is high enough to enable meteoric water to reach the caves. No present day speleothem deposition occurs in the Negev Desert. The aims of the study were: timing of the humid periods by U-Th dating of the speleothem deposition periods; origin of the rainfall by speleothem δ18O and fluid inclusions δ2H; correlations between local and global climate changes and between the climate changes to out of Africa dispersals of Early Modern Humans (EMH). Speleothems were collected from 7 caves located on the north-south transect of the Negev Desert, between 300 mm to 30 mm isohyets. Whereas in the Mediterranean climate zone (>350 mm) of central and northern Israel the speleothem deposition was continuous, in the Negev Desert periods of speleothem deposition alternated with multiple hiatuses. In the mildly arid transition zone of northern Negev (300 to 150 mm) speleothem deposition occurred most of the time during the last 210 ka, with hiatuses at 150-144 ka, ~140 ka, 117-96 ka, 93-85 ka, 25- 23 ka, and 14-0 ka. In present-day arid and hyper-arid zone of central and southern Negev (150 to 30 mm) no speleothem deposition occurred most of the last 350 ka, with humid intervals at 350-290 ka, 220-190 ka, 137- 110 ka, and ~85 ka. The origin of the precipitation in the Negev Desert during these intervals was from Eastern Mediterranean Sea, i. e. mid-latitude cyclones (as present day). The latter conclusion is based on three evidences: thinning laminae width of dateable speleothems from few tens of cm in northern Negev to less than 2 cm in the south; similarity of oxygen isotopic trends between desert speleothems and speleothems from Mediterranean climate; and δ18O - δ2H relationships of speleothem fluid inclusions that follow usually the Mediterranean Meteoric Water Line. The intensification of the mid-latitude cyclones that caused increased rainfall in northern Saharo-Arabian desert at 350-290 ka, 220-190 ka, 137-110 ka, and ~85 ka correlate to the peaks of monsoon activity in southern and central parts of the desert belt. We assume that during these events the Saharo-Arabian Desert significantly reduced its size, opening climatic windows for hominids and African animals to get out of the African continent. One of the evidences supporting this hypothesis is first appearance of the EMH out of the Africa at ~130 ka in Israeli caves Skhul and Qafzeh, during the peak of the humid period of 137-110 ka. The expanding aridity after 110 ka blocked the way back to Africa and may have driven the EMH further east and north.

Geomagnetic excursions in the Brunhes and Matuyama Chrons: Do they come in bunches?

NASA Astrophysics Data System (ADS)

Channell, J. E. T.

2012-04-01

Geomagnetic excursions, defined here as brief directional aberrations of the main dipole field outside the range of expected secular variation, remain controversial. Poorly-correlated records of apparent excursions from lavas and sediments can often be assigned to sampling artifacts, sedimentological phenomena, volcanic terrane effects, or local secular variation, rather than behavior of the main dipole field. Although records of magnetic excursions date from the 1960s, the number of Brunhes excursions in recent reviews of the subject have reached the 12-17 range, of which only about ~7 are adequately and/or consistently recorded. For the Matuyama Chron, the current inventory of excursions stands at about 10. The better quality excursion records, with reasonable age control, imply millennial-scale or even sub-millennial-scale durations. When "adequately" recorded, excursions are manifest as paired polarity reversals flanking virtual geomagnetic poles (VGPs) that reach high latitudes in the opposite hemisphere. At the young end of the excursion record, the Mono Lake (~33 ka) and Laschamp (~41 ka) excursions are well documented, although records of the former are not widely distributed. Several excursions younger than the Mono Lake excursion (at 17 ka and 25 ka) have recently been recorded in lavas and sediments, respectively. Is the 17-41 ka interval characterized by multiple excursions? Similarly, multiple excursions have been recorded in the 188-238 ka interval that encompasses records of the Iceland Basin excursion (~188 ka) and the Pringle Falls (PF) excursion. The PF excursion has been assigned ages in the 211-238 ka range. Does this mean that this interval is also characterized by several discrete excursions? The 500-600 ka interval incorporates not only the Big Lost excursion at ~565 ka, but also anomalous magnetization directions from lava flows, particularly in the West Eifel volcanics that yield mid-latitude northern-hemisphere VGPs with a range of Ar/Ar ages. The key question is whether such intervals of mid-latitude VGPs denote high-amplitude secular variation or inadequately recorded magnetic excursions. We propose that excursions characterized by high VGP latitudes in the opposite hemisphere should be termed Category 1 excursions, and those manifest by low/mid-latitude VGPs should be termed Category 2 excursions. In the future, improved records may "elevate" Category 2 excursions to Category 1. We do not view this subdivision of Category 1 and Category 2 excursions as necessarily a geomagnetic distinction, but possibly a distinction based on recording fidelity.

Paleoearthquake recurrence on the East Paradise fault zone, metropolitan Albuquerque, New Mexico

USGS Publications Warehouse

Personius, Stephen F.; Mahan, Shannon

2000-01-01

A fortuitous exposure of the East Paradise fault zone near Arroyo de las Calabacillas has helped us determine a post-middle Pleistocene history for a long-forgotten Quaternary fault in the City of Albuquerque, New Mexico. Mapping of two exposures of the fault zone allowed us to measure a total vertical offset of 2.75 m across middle Pleistocene fluvial and eolian deposits and to estimate individual surface-faulting events of about 1, 0.5, and 1.25 m. These measurements and several thermoluminescence ages allow us to calculate a long-term average slip rate of 0.01 ± 0.001 mm/yr and date two surface-faulting events to 208 ± 25 ka and 75 ± 7 ka. The youngest event probably occurred in the late Pleistocene, sometime after 75 ± 7 ka. These data yield a single recurrence interval of 133 ± 26 ka and an average recurrence interval of 90 ± 10 ka. However, recurrence intervals are highly variable because the two youngest events occurred in less than 75 ka. Offsets of 0.5-1.25 m and a fault length of 13-20 km indicate that surface-rupturing paleoearthquakes on the East Paradise fault zone had probable Ms or Mw magnitudes of 6.8-7.0. Although recurrence intervals are long on the East Paradise fault zone, these data are significant because they represent some of the first published slip rate, paleoearthquake magnitude, and recurrence information for any of the numerous Quaternary faults in the rapidly growing Albuquerque-Rio Rancho metropolitan area.

Holocene thermal optimal and climate variability of East Asian monsoon inferred from forest reconstruction of a subalpine pollen sequence, Taiwan

NASA Astrophysics Data System (ADS)

Liew, P. M.; Lee, C. Y.; Kuo, C. M.

2006-10-01

The East Asian monsoon Holocene optimal period has been debated both about duration and whether conditions were a maximum in thermal conditions or in precipitation. In this study we show Holocene climate variability inferred by a forest reconstruction of a subalpine pollen sequence from peat bog deposits in central Taiwan, based on modern analogues of various altitudinal biomes in the region. A warmer interval occurred between 8 and 4 ka BP (calibrated 14C years) when the subtropical forests were more extensive. The Holocene thermal optimum is represented by an altitudinal tropical forest at 6.1-5.9 ka BP and 6.9 ka BP and only the latter was accompanied by wet conditions, indicating decoupling of thermal and precipitation mechanism in the middle Holocene. Abrupt and relative severe cold phases, shown by biome changes, occurred at about 11.2-11.0 ka BP; 7.5 ka BP; 7.2 ka BP; 7.1 ka BP; 5.2 ka BP, 5.0 ka BP and 4.9 ka BP. A spectral analysis of pollen of a relatively cold taxon — Salix, reveals that the time series is dominated by a 1500 yr periodicity and similar to the cold cycle reported in the marine records of Indian and western Pacific Oceans. The cold-warm conditions inferred by the change of forests show close relationship to solar energy in comparison with the production rate of Be-10.

Drastic lake level changes of Lake Van (eastern Turkey) during the past ca. 600 ka: climatic, volcanic and tectonic control

NASA Astrophysics Data System (ADS)

Cukur, D.; Krastel, S.; Schmincke, H.; Sumita, M.; Tomonaga, Y.; Damci, E.

2013-12-01

Lake Van is the largest soda lake in the world with a present surface of 3,574 km2 and a maximum water depth of 450 m. Sedimentary deposits in the lake preserve one of the most complete record of continental climate in the Middle East since the Middle Pleistocene. We studied these deposits to characterize the evolution of the lake level and its possible relationships with changes in climate, volcanic, and regional tectonics since the formation of the lake ca. 600 ka ago. Changes in lake level were determined based on high-resolution seismic reflection profiles showing erosional surfaces, changes in stratal geometries such as downward shifts in coastal onlap, and recognition of distinctive stratigraphic features such as prograding delta clinoforms. Our results show that Lake Van has undergone drastic changes in surface elevation by as much as 600 meters over the past ca. 600 ka. Five major lowstands occurred at ca. ~600 ka, ca. 365-340 ka, ca 290-230 ka; ca. 150-130 ka; and ca. 30-14 ka. During a first period (A) (ca. 600-ca 230 ka) lake levels changed drastically by hundreds of m but at longer time intervals between low and high stands. Changes occurred more frequently but mostly by a few tens of m during the past ca. 230 ka years where we can distinguish a first period (B1) of stepwise transgressions between ca. 230 and 150 ka followed by a short regression between ca. 150 and 130 ka. Lake level rose stepwise again during period B2 lasting until ca 30 ka. During the past 30 ka a regression and a final transgression each lasted ca. 15 ka years. The major lowstand periods in Lake Van occurred during glacial periods, arguing for a climatic control of these lake-level fluctuations (i.e., significantly reduced precipitation leading to lake level low stands). Although climate forcing may have been the dominant cause for the drastic lake level changes of Lake Van, volcanic and tectonic forcing factors are also invoked. For example, the number of distinct tephra layers, some several meters thick, has drastically increased in the upper ca 100 m (the past ca. 230 ka). The highest density of excellent reflectors occurs in this interval. Tectonic activity evidenced by extensional and/or compressional faults across the basin margins may have also affected the lake level fluctuations in Lake Van. This series of reconstructions using seismic stratigraphy from this study enlighten the understanding of tectonically-active lacustrine basins and provide a model for similar basins elsewhere.

Evidence of resilience to past climate change in Southwest Asia: Early farming communities and the 9.2 and 8.2 ka events

NASA Astrophysics Data System (ADS)

Flohr, Pascal; Fleitmann, Dominik; Matthews, Roger; Matthews, Wendy; Black, Stuart

2016-03-01

Climate change is often cited as a major factor in social change. The so-called 8.2 ka event was one of the most pronounced and abrupt Holocene cold and arid events. The 9.2 ka event was similar, albeit of a smaller magnitude. Both events affected the Northern Hemisphere climate and caused cooling and aridification in Southwest Asia. Yet, the impacts of the 8.2 and 9.2 ka events on early farming communities in this region are not well understood. Current hypotheses for an effect of the 8.2 ka event vary from large-scale site abandonment and migration (including the Neolithisation of Europe) to continuation of occupation and local adaptation, while impacts of the 9.2 ka have not previously been systematically studied. In this paper, we present a thorough assessment of available, quality-checked radiocarbon (14C) dates for sites from Southwest Asia covering the time interval between 9500 and 7500 cal BP, which we interpret in combination with archaeological evidence. In this way, the synchronicity between changes observed in the archaeological record and the rapid climate events is tested. It is shown that there is no evidence for a simultaneous and widespread collapse, large-scale site abandonment, or migration at the time of the events. However, there are indications for local adaptation. We conclude that early farming communities were resilient to the abrupt, severe climate changes at 9250 and 8200 cal BP.

Global climate simulations at 3000-year intervals for the last 21 000 years with the GENMOM coupled atmosphere–ocean model

USGS Publications Warehouse

Alder, Jay R.; Hostetler, Steven W.

2015-01-01

We apply GENMOM, a coupled atmosphere–ocean climate model, to simulate eight equilibrium time slices at 3000-year intervals for the past 21 000 years forced by changes in Earth–Sun geometry, atmospheric greenhouse gases (GHGs), continental ice sheets, and sea level. Simulated global cooling during the Last Glacial Maximum (LGM) is 3.8 ◦C and the rate of post-glacial warming is in overall agreement with recently published temperature reconstructions. The greatest rate of warming occurs between 15 and 12 ka (2.4 ◦C over land, 0.7 ◦C over oceans, and 1.4 ◦C globally) in response to changes in radiative forcing from the diminished extent of the Northern Hemisphere (NH) ice sheets and increases in GHGs and NH summer insolation. The modeled LGM and 6 ka temperature and precipitation climatologies are generally consistent with proxy reconstructions, the PMIP2 and PMIP3 simulations, and other paleoclimate data–model analyses. The model does not capture the mid-Holocene “thermal maximum” and gradual cooling to preindustrial (PI) global temperature found in the data. Simulated monsoonal precipitation in North Africa peaks between 12 and 9 ka at values ∼ 50 % greater than those of the PI, and Indian monsoonal precipitation peaks at 12 and 9 ka at values ∼ 45 % greater than the PI. GENMOM captures the reconstructed LGM extent of NH and Southern Hemisphere (SH) sea ice. The simulated present-day Antarctica Circumpolar Current (ACC) is ∼ 48 % weaker than the observed (62 versus 119 Sv). The simulated present-day Atlantic Meridional Overturning Circulation (AMOC) of 19.3 ± 1.4 Sv on the Bermuda Rise (33◦ N) is comparable with observed value of 18.7 ± 4.8 Sv. AMOC at 33◦ N is reduced by ∼ 15 % during the LGM, and the largest post-glacial increase (∼ 11 %) occurs during the 15 ka time slice.

The importance of independent chronology in integrating records of past climate change for the 60-8 ka INTIMATE time interval

NASA Astrophysics Data System (ADS)

Brauer, Achim; Hajdas, Irka; Blockley, Simon P. E.; Bronk Ramsey, Christopher; Christl, Marcus; Ivy-Ochs, Susan; Moseley, Gina E.; Nowaczyk, Norbert N.; Rasmussen, Sune O.; Roberts, Helen M.; Spötl, Christoph; Staff, Richard A.; Svensson, Anders

2014-12-01

This paper provides a brief overview of the most common dating techniques applied in palaeoclimate and palaeoenvironmental studies including four radiometric and isotopic dating methods (radiocarbon, 230Th disequilibrium, luminescence, cosmogenic nuclides) and two incremental methods based on layer counting (ice layer, varves). For each method, concise background information about the fundamental principles and methodological approaches is provided. We concentrate on the time interval of focus for the INTIMATE (Integrating Ice core, MArine and TErrestrial records) community (60-8 ka). This dating guide addresses palaeoclimatologists who aim at interpretation of their often regional and local proxy time series in a wider spatial context and, therefore, have to rely on correlation with proxy records obtained from different archives from various regions. For this reason, we especially emphasise scientific approaches for harmonising chronologies for sophisticated and robust proxy data integration. In this respect, up-to-date age modelling techniques are presented as well as tools for linking records by age equivalence including tephrochronology, cosmogenic 10Be and palaeomagnetic variations. Finally, to avoid inadequate documentation of chronologies and assure reliable correlation of proxy time series, this paper provides recommendations for minimum standards of uncertainty and age datum reporting.

Lacustrine Basal Ages Constrain the Last Deglaciation in the Uinta Mountains, Utah, USA

NASA Astrophysics Data System (ADS)

Munroe, Jeffrey; Laabs, Benjamin

2013-04-01

Basal radiocarbon ages from 21 high-elevation lakes limit the timing of final Pleistocene deglaciation in the Uinta Mountains of northeastern Utah, USA. The lakes are located in glacial valleys and cirques 5 to 20 km upstream from LGM terminal moraines at elevations from 2830 to 3475 m. Many are impounded behind recessional moraines. Cores were retrieved from a floating platform with a percussion corer driven to the point of refusal. All penetrated inorganic silty clay beneath gyttja. AMS radiocarbon analyses were made on terrestrial macrofossils, daphnia ephippia, pollen concentrates, and bulk sediment retrieved from the base of each core. No radiocarbon reservoir effect was observed when bulk dates were checked against terrestrial material. Radiocarbon results were converted to calendar years using the IntCal09 calibration curve in OxCal 4.1. Given the stratigraphy observed in the cores, these calibrated basal ages are considered close limits on the timing of the local deglaciation and lake formation. The oldest three lakes have basal radiocarbon ages that calibrate to a few centuries after the Bölling/Alleröd warming, indicating that the landscape was becoming ice free at this time. These are followed by an overlapping group of five lakes with basal ages between 13.5 and 13.0 ka BP. Five more cores, from four separate lakes, have basal ages tightly clustered between 13.0 and 12.5 ka BP. Three of these lakes are dammed by moraines, suggesting glacial activity during the early part of the Younger Dryas interval. The lone kettle lake in the study yielded a basal age of 12.3 ka BP, considerably younger than the basal age of 13.9 ka BP from a nearby lake filling a bedrock basin, indicating that buried ice may have been locally stable for more than a millennium after deglaciation. The remaining seven lakes have basal ages between 12.0 and 11.0 ka BP. Four of these lakes are also dammed by moraines. These two non-overlapping clusters of basal ages for moraine-dammed lakes, with maximum probabilities ca. 12.7 and 11.3 ka BP, suggest that active glaciers were present in the Uinta Mountains during the Younger Dryas, and that Younger Dryas glacier activity was concentrated in two separate intervals.

Paleohydrology and paleochemistry of Lake Manitoba, Canada: the isotope and ostracode records

USGS Publications Warehouse

Last, W.M.; Teller, J.T.; Forester, R.M.

1994-01-01

Lake Manitoba, the largest lake in the Prairie region of North America, contains a fine-grained sequence of late Pleistocene and Holocene sediment that documents a complex postglacial history. This record indicates that differential isostatic rebound and changing climate have interacted with varying drainage basin size and hydrologic budget to create significant variations in lake level and limnological conditions. During the initial depositional period in the basin, the Lake Agassiz phase (???12-9 ka), ??18O of ostracodes ranged from -16??? to -5??? (PDB), implying the lake was variously dominated by cold, dilute glacial meltwater and warm to cold, slightly saline water. Candona subtriangulata, which prefers cold, dilute water, dominates the most negative ??18O intervals, when the basin was part of proglacial Lake Agassiz. At times during this early phase, the ??18O of the lake abruptly shifted to higher values; euryhaline taxa such as C. rawsoni or Limnocythere ceriotuberosa, and halobiont taxa such as L. staplini or L. sappaensis are dominant in these intervals. This positive covariance of isotope and ostracode records implies that the lake level episodically fell, isolating the Lake Manitoba basin from the main glacial lake. ??18O values from inorganic endogenic Mg-calcite in the post-Agassiz phase of Lake Manitoba trend from -4??? at 8 ka to -11??? at 4.5 ka. We interpret that this trend indicates a gradually increasing influence of isotopically low (-20??? SMOW) Paleozoic groundwater inflow, although periods of increased evaporation during this time may account for zones of less negative isotopic values. The ??18O of this inorganic calcite abruptly shifts to higher values (-6???) after ???4.5 ka due to the combined effects of increased evaporative enrichment in a closed basin lake and the increased contribution of isotopically high surface water inflow on the hydrologic budget. After ???2 ka, the ??18O of the Mg-calcite fluctuates between -13??? and -7???, implying short-term variability in the lake's hydrologic budget, with values indicating the lake varied from outflow-dominated to evaporation-dominated. The ??13C values of Mg-calcite remain nearly constant from 8 to 4.5 ka and then trend to higher values upward in the section. This pattern suggests primary productivity in the lake was initially constant but gradually increased after 4.5 ka. ?? 1994 Kluwer Academic Publishers.

Reappraisal of Los Humeros Volcanic Complex by New U/Th Zircon and 40Ar/39Ar Dating: Implications for Greater Geothermal Potential

NASA Astrophysics Data System (ADS)

Carrasco-Núñez, G.; Bernal, J. P.; Dávila, P.; Jicha, B.; Giordano, G.; Hernández, J.

2018-01-01

Longevity and size of magmatic systems are fundamental factors for assessing the potential of a geothermal field. At Los Humeros volcanic complex (LHVC), the first caldera-forming event was reported at 460 ± 40 ka. New zircon U/Th and plagioclase 40Ar/39Ar dates of pre-, syn- and postcaldera volcanics allow a reappraisal of the evolution of the geothermally active LHVC. The age of the voluminous Xaltipan ignimbrite (115 km3 dense rock equivalent [DRE]) associated with the formation of the Los Humeros caldera is now constrained by two geochronometers (zircon U/Th and plagioclase 40Ar/39Ar dating) to 164 ± 4.2 ka, which postdates a long episode of precaldera volcanism (rhyolitic domes), the oldest age of which is 693.0 ± 1.9 ka (40Ar/39Ar). The inferred short residence time (around 5 ka) for the paroxysmal Xaltipan ignimbrite is indicative of rapid assembly of a large magma body and rejuvenation of the system due to recurrent recharge magmas, as it has been occurred in some other large magmatic systems. Younger ages than previously believed have been obtained also for the other voluminous explosive phases of the Faby fall tuff at ˜70 ka and the second caldera-forming Zaragoza ignimbrite with 15 km3 DRE, which erupted immediately after. Thus, the time interval that separates the two caldera-forming episodes at Los Humeros is only 94 kyr, which is a much shorter interval than suggested by previous K-Ar dates (410 kyr). This temporal proximity allows us to propose a caldera stage encompassing the Xaltipan and the Zaragoza ignimbrites, followed by emplacement at 44.8 ± 1.7 ka of rhyolitic magmas interpreted to represent a postcaldera, resurgent stage. Rhyolitic eruptions have also occurred during the Holocene (<7.3 ± 0.1 ka) along with olivine-rich basalts that suggest recharge of the system. The estimated large volume magmatic reservoir for Los Humeros (>˜1,200 km3) and these new ages indicating much younger caldera-forming volcanism than previously believed are fundamental factors in the application of classical conductive models of heat resource, enhancing the heat production capacity and favor a higher geothermal potential.

The Younger Dryas phase of Great Salt Lake, Utah, USA

USGS Publications Warehouse

Oviatt, Charles G.; Miller, D.M.; McGeehin, J.P.; Zachary, C.; Mahan, S.

2005-01-01

Field investigations at the Public Shooting Grounds (a wildlife-management area on the northeastern shore of Great Salt Lake) and radiocarbon dating show that the Great Salt Lake rose to the Gilbert shoreline sometime between 12.9 and 11.2 cal ka. We interpret a ripple-laminated sand unit exposed at the Public Shooting Grounds, and dated to this time interval, as the nearshore sediments of Great Salt Lake deposited during the formation of the Gilbert shoreline. The ripple-laminated sand is overlain by channel-fill deposits that overlap in age (11.9-11.2 cal ka) with the sand, and by wetland deposits (11.1 to 10.5 cal ka). Consistent accelerator mass spectrometry radiocarbon ages were obtained from samples of plant fragments, including those of emergent aquatic plants, but mollusk shells from spring and marsh deposits yielded anomalously old ages, probably because of a variable radiocarbon reservoir effect. The Bonneville basin was effectively wet during at least part of the Younger Dryas global-cooling interval, however, conflicting results from some Great Basin locations and proxy records indicate that the regional effects of Younger Dryas cooling are still not well understood. ?? 2005 Elsevier B.V. All rights reserved.

A MIS 9/MIS 8 speleothem record of hydrological variability from Macedonia (F.Y.R.O.M.)

NASA Astrophysics Data System (ADS)

Regattieri, Eleonora; Zanchetta, Giovanni; Isola, Ilaria; Bajo, Petra; Perchiazzi, Natale; Drysdale, Russell N.; Boschi, Chiara; Hellstrom, John C.; Francke, Alexander; Wagner, Bernd

2018-03-01

The period corresponding to Marine Isotope Stages 9 (MIS 9) offers the opportunity to study orbital and sub-orbital scale climate variability under boundary conditions different from those of better studied intervals such as the Holocene and the Last Interglacial. Yet, it is poorly represented in independently-dated continental archives around the Mediterranean Region. Here, we present a speleothem stable isotope record (δ18O and δ13C) from the Former Yugoslavian Republic of Macedonia (F.Y.R.O.M., southern Balkans), which consists of two periods of growth broadly covering the ca. 332 to 292 ka and the ca. 264 to 248 ka intervals (MIS 9e-b and late MIS 8). We interpret the speleothem δ18O as mostly related to regional hydrology, with variations that can be interpreted as due to changes in rainfall amount, with higher/lower values associated to drier/wetter condition. This interpretation is corroborated by a change in mineralogical composition between aragonite and calcite at ca. 328 ka, which marks increasing precipitation at the onset of MIS 9 and occurs within a trend of decreasing δ18O values. Also the comparison with the multiproxy climate record available from the nearby Lake Ohrid seems to support the proposed interpretation. The MIS 9e interglacial appears to be characterized by wettest conditions between ca. 326 and 321 ka, i.e. lasting ca. 5 kyr. Decreasing precipitation and enhanced millennial scale variability matches the glacial inception (MIS9 d to b), with drier events at ca. 319 ka (ca. 2 kyr long) and 310 ka (ca. 1 kyr long), and a major rainfall reduction between 306 and 298 ka. The latter is followed by a prominent wetter period between 298 and 295 ka, for which carbon data values suggest high infiltration rate. Rainfall decreases again after 295 ka, and remain low until the growth interruption at ca. 292 ka. Resumption of the growth and progressive soil development, expressed by the carbon isotope record, occurred during the late part of MIS 8. Despite the rather high temporal uncertainty (average 6 ka), the speleothem hydrological record complements the environmental information provided by the Lake Ohrid record and also fits well to the framework of regional and extra-regional variability, showing similarities with pollen records from southern and western Europe, both at orbital and at sub-orbital time scale.

Reconstructing Atmospheric CO2 Through The Paleocene-Eocene Thermal Maximum Using Stomatal Index and Stomatal Density Values From Ginkgo adiantoides

NASA Astrophysics Data System (ADS)

Barclay, R. S.; Wing, S. L.

2013-12-01

The Paleocene-Eocene Thermal Maximum (PETM) was a geologically brief interval of intense global warming 56 million years ago. It is arguably the best geological analog for a worst-case scenario of anthropogenic carbon emissions. The PETM is marked by a ~4-6‰ negative carbon isotope excursion (CIE) and extensive marine carbonate dissolution, which together are powerful evidence for a massive addition of carbon to the oceans and atmosphere. In spite of broad agreement that the PETM reflects a large carbon cycle perturbation, atmospheric concentrations of CO2 (pCO2) during the event are not well constrained. The goal of this study is to produce a high resolution reconstruction of pCO2 using stomatal frequency proxies (both stomatal index and stomatal density) before, during, and after the PETM. These proxies rely upon a genetically controlled mechanism whereby plants decrease the proportion of gas-exchange pores (stomata) in response to increased pCO2. Terrestrial sections in the Bighorn Basin, Wyoming, contain macrofossil plants with cuticle immediately bracketing the PETM, as well as dispersed plant cuticle from within the body of the CIE. These fossils allow for the first stomatal-based reconstruction of pCO2 near the Paleocene-Eocene boundary; we also use them to determine the relative timing of pCO2 change in relation to the CIE that defines the PETM. Preliminary results come from macrofossil specimens of Ginkgo adiantoides, collected from an ~200ka interval prior to the onset of the CIE (~230-30ka before), and just after the 'recovery interval' of the CIE. Stomatal index values decreased by 37% within an ~70ka time interval at least 100ka prior to the onset of the CIE. The decrease in stomatal index is interpreted as a significant increase in pCO2, and has a magnitude equivalent to the entire range of stomatal index adjustment observed in modern Ginkgo biloba during the anthropogenic CO2 rise during the last 150 years. The inferred CO2 increase prior to the CIE coincides in part with the 'pre-warming' interval documented from δ18O in mammalian tooth enamel from the Bighorn Basin. Stomatal density values increase ~30ka prior to the CIE, suggesting a decrease in cell size from water stress, a change that closely matches the timing of a trend towards drier paleosols in the same region of the Bighorn Basin. All evidence collected to date suggests a long-term rise in pCO2 and temperature, and drying of soils prior to the prominent CIE. Presumably the source for CO2 released prior to the CIE did not significantly alter the isotopic value of atmospheric CO2. As suggested by previous authors, warming prior to the CIE may have triggered the release of carbon from a source depleted in 13C at the onset of the PETM. Well-preserved dispersed cuticle has been extracted from stratigraphic levels within the CIE, and may permit reconstruction of changes in pCO2 during the PETM.

Environmental history and tephrostratigraphy at Carp Lake, southwestern Columbia Basin, Washington, USA

USGS Publications Warehouse

Whitlock, C.; Sarna-Wojcicki, A. M.; Bartlein, P.J.; Nickmann, R.J.

2000-01-01

Sediment cores from Carp Lake provide a pollen record of the last ca. 125,000 years that helps disclose vegetational and climatic conditions from the present day to the previous interglaciation (120-133 ka). The core also contained 15 tephra layers, which were characterised by electron-microprobe analysis of volcanic glass shards. Identified tephra include Mount St. Helens Ye, 3.69 ka; Mazama ash bed, 7.54 ka; Mount St. Helens layer C, 35-50 ka; an unnamed Mount St. Helens tephra, 75-150 ka; the tephra equivalent of layer E at Pringle Falls, Oregon, <218 ka; and an andesitic tephra layer similar to that at Tulelake, California, 174 ka. Ten calibrated radiocarbon ages and the ages of Mount St. Helens Ye, Mazama ash, and the unnamed Mount St. Helens tephra were used to develop an age-depth model. This model was refined by also incorporating the age of marine oxygen isotope stage (IS) boundary 4/5 (73.9 ka) and the age of IS-5e (125 ka). The justification for this age-model is based on an analysis of the pollen record and lithologic data. The pollen record is divided into 11 assemblage zones that describe alternations between periods of montane conifer forest, pine forest, and steppe. The previous interglacial period (IS-5e) supported temperate xerothermic forests of pine and oak and a northward and westward expansion of steppe and juniper woodland, compared to their present occurrence. The period from 83 to 117 ka contains intervals of pine forest and parkland alternating with pine-spruce forest, suggesting shifts from cold humid to cool temperate conditions. Between 73 and 83 ka, a forest of oak, hemlock, Douglas-fir, and fir was present that has no modem analogue. It suggests warm wet summers and cool wet winters. Cool humid conditions during the mid-Wisconsin interval supported mixed conifer forest with Douglas-fir and spruce. The glacial interval featured cold dry steppe, with an expansion of spruce in the late-glacial. Xerothermic communities prevailed in the early Holocene, when temperate steppe was widespread and the lake dried intermittently. The middle Holocene was characterised by ponderosa pine forest, and the modem vegetation was established in the last 3900 yr, when ponderosa pine, Douglas-fir, fir, and oak were part of the local vegetation.

Hominin expansion into Central Asia during the last interglacial

NASA Astrophysics Data System (ADS)

Asmerom, Yemane; Polyak, Victor J.; Wagner, Jennifer D. M.; Jonathan Patchett, P.

2018-07-01

Central Asia was a likely gateway for hominin expansion. Obi-Rakhmat Grotto, northeastern Uzbekistan, has a deposit that contains the remains of a hominin child (OR-1) and more than 60,000 Paleolithic artifacts, making it one of the most important archaeological sites in Central Asia. Regionally, genetic data suggest hominin presence and human-Neanderthal interbreeding as far back as 100 ka, although, to date, absolute ages of hominin remains that old have not been known in the region. We present new uranium-series dates that constrain the age of the Obi-Rakhmat deposit to 98 ka towards the top and 109 ka for the layer containing OR-1, pushing hominin expansion into Central Asia minimally to 109 ± 2 ka, to a time, based on the genetic clock, of Neanderthal-modern human interbreeding. Our chronology establishes a minimum age of 98 ka for the well-developed lithic industry in Central Asia. The period covering the deposition of the sediments containing the artifacts and specimen OR-1 coincides with a warm and one of the most humid intervals of Marine Isotope Stage (MIS) 5 and last glacial period in the region, providing support for climate-driven hominin expansion.

Mauna Loa lava accumulation rates at the Hilo drill site: Formation of lava deltas during a period of declining overall volcanic growth

USGS Publications Warehouse

Lipman, P.W.; Moore, J.G.

1996-01-01

Accumulation rates for lava flows erupted from Mauna Loa, as sampled in the uppermost 280 m of the Hilo drill hole, vary widely for short time intervals (several thousand years), but overall are broadly similar to those documented elsewhere on this volcano since 100 ka. Thickness variations and accumulation rates for Mauna Loa lavas at the Hilo drill site have been strongly affected by local paleotopography, including funneling and ponding between Mauna Kea and Kilauea. In addition, gentle submerged slopes of Mauna Kea in Hilo Bay have permitted large shoreline displacements by Mauna Loa flows. Ages of eruptive intervals have been determined from published isotopic data and from eustatic sea level curves modified to include the isostatic subsidence of the island of Hawaii at 2.2-2.6 mm/yr. Prior to 10 ka, rates of Mauna Loa lava accumulation at the drill site varied from 0.6 to 4.3 mm/yr for dateable intervals, with an overall rate of 1.8 mm/yr. Major eruptive pulses at about 1.3 and 10 ka, each probably representing a single long-lived eruption based on lack of weathering between flow units, increase the overall accumulation rate to 2.4 mm/yr. The higher rate since 10 ka reflects construction of thick near-shoreline lava deltas as postglacial sea levels rose rapidly. Large lava deltas form only along coastal segments where initially subaerial slopes have been submerged by the combined effects of eustatic sea level rise, isostatic subsidence, or spreading of volcano flanks. Overall accumulation of 239 m of lava at the drill site since 100-120 ka closely balances submergence of the Hilo area, suggesting that processes of coastal lava deposition have been modulated by rise in sea level. The Hilo accumulation rate is slightly higher than average rates of 1-2 mm/yr determined elsewhere along the Mauna Loa coast, based on rates of shoreline coverage and dated sea cliff and fault scarp exposures. Low rates of coastal lava accumulation since 100 ka, near or below the rate of island-wide isostatic subsidence, indicate that Mauna Loa is no longer growing vigorously or even maintaining its size above sea level.

Rapamycin has paradoxical effects on S6 phosphorylation in rats with and without seizures.

PubMed

Chen, Linglin; Hu, Lin; Dong, Jing-Yin; Ye, Qing; Hua, Nan; Wong, Michael; Zeng, Ling-Hui

2012-11-01

  Accumulating data have demonstrated that seizures induced by kainate (KA) or pilocarpine activate the mammalian target of rapamycin (mTOR) pathway and that mTOR inhibitor rapamycin can inhibit mTOR activation, which subsequently has potential antiepileptic effects. However, a preliminary study showed a paradoxical exacerbation of increased mTOR pathway activity reflected by S6 phosphorylation when rapamycin was administrated within a short period before KA injection. In the present study, we examined this paradoxical effect of rapamycin in more detail, both in normal rats and KA-injected animals.   Normal rats or KA-treated rats pretreated with rapamycin at different time intervals were sacrificed at various time points (1, 3, 6, 10, 15, and 24 h) after rapamycin administration or seizure onset for western blotting analysis. Phosphorylation of mTOR signaling target of Akt, mTOR, Rictor, Raptor, S6K, and S6 were analyzed. Seizure activity was monitored behaviorally and graded according to a modified Racine scale (n = 6 for each time point). Neuronal cell death was detected by Fluoro-Jade B staining.   In normal rats, we found that rapamycin showed the expected dose-dependent inhibition of S6 phosphorylation 3-24 h after injection, whereas a paradoxical elevation of S6 phosphorylation was observed 1 h after rapamycin. Similarly, pretreatment with rapamycin over 10 h before KA inhibited the KA seizure-induced mTOR activation. In contrast, rapamycin administered 1-6 h before KA caused a paradoxical increase in the KA seizure-induced mTOR activation. Rats pretreated with rapamycin 1 h prior to KA exhibited an increase in severity and duration of seizures and more neuronal cell death as compared to vehicle-treated groups. In contrast, rapamycin pretreated 10 h prior to KA had no effect on the seizures and decreased neuronal cell death. The paradoxical effect of rapamycin on S6 phosphorylation was correlated with upstream mTOR signaling and was reversed by pretreatment of perifosine, an Akt inhibitor.   These data indicate the complexity of S6 regulation and its effect on epilepsy. Paradoxical effects of rapamycin need to be considered in clinical applications, such as for potential treatment for epilepsy and other neurologic disorders. Wiley Periodicals, Inc. © 2012 International League Against Epilepsy.

Rapamycin has Paradoxical Effects on S6 Phosphorylation in Rats With and Without Seizures

PubMed Central

Chen, Linglin; Hu, Lin; Dong, Jing-Yin; Ye, Qing; Hua, Nan; Wong, Michael; Zeng, Ling-Hui

2012-01-01

Summary Purpose Accumulating data have demonstrated that seizures induced by kainate (KA) or pilocarpine activate the mammalian target of rapamycin (mTOR) pathway and mTOR inhibitor rapamycin can inhibit mTOR activation which subsequently has potential anti-epileptic effects. However, a preliminary study showed a paradoxical exacerbation of increased mTOR pathway activity reflected by S6 phosphorylation when rapamycin was administrated within a short period before KA injection. In the present study, we examined this paradoxical effect of rapamycin in more detail, both in normal rats and KA-injected animals. Methods Normal Rats or KA-treated rats pretreated with rapamycin at different time interval were sacrificed at various time points (1h, 3h, 6h, 10h, 15h and 24h) after rapamycin administration or seizure onset for Western blotting analysis. Phosphorylation of mTOR signaling target of Akt, mTOR, Rictor, Raptor, S6K and S6 were analyzed. Seizure activity was monitored behaviorally and graded according to a modified Racine scale (n=6 for each time point). Neuronal cell death was detected by Fluoro-Jade B staining. Key findings In normal rats, we found that rapamycin showed the expected dose-dependent inhibition of S6 phosphorylation 3–24 h after injection, while a paradoxical elevation of S6 phosphorylation was observed 1 hour after rapamycin. Similarly, pretreatment with rapamycin over 10 h prior to KA inhibited the KA seizure induced mTOR activation. In contrast, rapamycin administered 1 to 6 hours before KA caused a paradoxical increase in the KA seizure-induced mTOR activation. Rats pretreated with rapamycin 1 h prior to KA exhibited an increase in severity and duration of seizures and more neuronal cell death as compared to vehicle treated groups. In contrast, rapamycin pretreated 10 h prior to KA had no effect on the seizures and decreased neuronal cell death. The paradoxical effect of rapamycin on S6 phosphorylation was correlated with upstream mTOR signaling and was reversed by pre-treatment of perifosine, an Akt inhibitor. Significance These data indicate the complexity of S6 regulation and its effect on epilepsy. Paradoxical effects of rapamycin need to be considered in clinical applications, such as for potential treatment for epilepsy and other neurological disorders. PMID:23145776

An ultra-high resolution last deglacial marine sediment records of the Northwest Atlantic Ocean

NASA Astrophysics Data System (ADS)

Rashid, H.; Piper, D.; Marche, B.; Vermooten, M.; Lazar, K.; Brockway, B.

2016-12-01

Lack of high sedimentation rate records of past changes pertaining to the late Pleistocene Laurentide ice-sheet (LIS) dynamics has prevented efforts to differentiate the various forcings in modulating abrupt climate changes. Here, we present an ultra-high resolution sediment record spanning approximately 1,500 km of the Eastern Canadian continental margin. The new record comprises four sediment cores which were collected from the northwest Labrador Sea (i.e., Saglek Bank) to southwestern Flemish Pass to the southeast Grand Banks in outer shelf and slope settings. Fifty new 14C-accelerator mass spectrometric dates were obtained to construct the stratigraphy. The total sediment thickness of the new record is 41 m covering the past 26 ka with 1.58/ka mean sediment rate, the highest sediment rate ever reported from the Northwest Atlantic Ocean for this time interval. Further, the temporal resolution of the record varies from a couple of decades to centuries depending on the time interval. X-ray fluorescence (XRF) data in conjunction with physical properties of sediments and petrology allowed us to distinguish sediment delivered by major ice-streams of the LIS namely the Hudson Strait, Hopedale Saddle, and Cumberland Sound ice streams. Heinrich layers 1 and 2 are well identified by their Labrador Sea specific characteristics. The so-called Younger Dryas equivalent Heinrich layer H0 was identified in these cores but the timing of onset of H0 has an offset by nearly 1,000 years with that of the 12.9 ka, suggesting that the YD event was not initiated by the Hudson Strait compared to other Heinrich events.

A record of more than 500,000 years of large-volume travertine formation in the southwestern United States and links between paleohydrology, paleoclimate, and landscape evolution

NASA Astrophysics Data System (ADS)

Priewisch, A.; Crossey, L. J.; Embid, E.; Karlstrom, K. E.; Polyak, V.; Asmerom, Y.; Ricketts, J. W.

2011-12-01

CO2 springs and associated travertine deposits offer a unique tool to better understand Cenozoic paleohydrology and paleoclimate in the context of geomorphic and neotectonic evolution of the southwestern United States. Travertine accumulations represent places of persistent and significant mantle CO2 degassing in high discharge spring systems that are found along faults and above magmatic systems. They complement speleothem records from the same regions in that they can provide better links to the surface geomorphic and neotectonic systems. New Mexico and Arizona host several exceptionally well-preserved, large-volume travertine deposits that extend from 10 - 60 km2, with thicknesses ranging from 15 to more than 60 m. Precise U-series and stable isotope analyses are underway for large travertine platforms at Mesa del Oro, NM (~27 km2), Riley North and South Mesa, NM (~60 km2), Mesa Aparejo/Belen Quarries, NM (~13 km2), and Springerville, AZ (~30 km2). New ages for the travertine deposits at Mesa del Oro are 56 ka, 253 ka, 361 ka, and more than 500 ka. The travertine deposits at Riley North and South Mesa are older than 500 ka and 207/287 ka, respectively. At Mesa Aparejo, travertine ages are 312 ka and more than 500 ka. U/Th dates from Springerville, AZ show that major travertine accumulations occurred over several time intervals: 36-100 ka, 200-280 ka and 300-350 ka. Stable isotope analyses overlap substantially, exhibiting high δ13C values, +2.0% to +8.3%, and δ18O values that range from -13.5% to -4%. High δ13C values are interpreted to be caused by rapid CO2 degassing while the range of δ18O values is interpreted to represent changing water temperatures and mixing trends of groundwater. U-series data show that travertine deposition at all of these localities overlapped temporally and that major aggradation and high volume deposition was not steady, but occurred episodically at 36-100, 200-280, and 300-380 ka. Times of high accumulation rates are interpreted as times of high groundwater flow and hence as a proxy for regional paleohydrology/paleoclimate controls while the locations of the travertine occurrences (along faults of the Jemez lineament and Rio Grande rift) reflect more local CO2-discharge (tectonic) controls. These travertine occurrences are important indicators of the extent of past natural CO2 leakage that can inform carbon sequestration models both in areas of modern CO2 gas fields (Springerville) and at sites of potential paleo-gas fields. The travertine platforms now occupy positions high in the landscape (inverted topography) and also provide data on the scales and timing of regional landscape denudation.

Volcanic geology and eruption frequency, São Miguel, Azores

USGS Publications Warehouse

Moore, Richard B.

1990-01-01

Six volcanic zones comprise São Miguel, the largest island in the Azores. All are Quaternary in age except the last, which is partly Pliocene. From west to east the zones are (1) the trachyte stratovolcano of Sete Cidades, (2) a field of alkali-basalt cinder cones and lava flows with minor trachyte, (3) the trachyte stratovolcano of Agua de Pau, (4) a field of alkali-basalt cinder cones and lava flows with minor trachyte and tristanite, (5) the trachyte stratovolcano of Furnas, and (6) the Nordeste shield, which includes the Povoação caldera and consists of alkali basalt, tristanite, and trachyte. New radiocarbon and K-Ar ages augment stratigraphic data obtained during recent geologic mapping of the entire island and provide improved data to interpret eruption frequency. Average dormant intervals for the past approximately 3000 years in the areas active during that time are about 400 years for Sete Cidades, 145 for zone 2, 1150 for Agua de Pau, and 370 for Furnas. However, the average dormant interval at Sete Cidades increased from 400 to about 680 years before each of the past two eruptions, and the interval at Furnas decreased from 370 to about 195 years before each of the past four eruptions. Eruptions in zone 4 occurred about once every 1000 years during latest Pleistocene and early Holocene time; none has occurred for about 3000 years. The Povoação caldera truncates part of the Nordeste shield and probably formed during the middle to late Pleistocene. Calderas formed during latest Pleistocene time at the three younger stratovolcanoes in the sequence: outer Agua de Pau (between 46 and 26.5 ka), Sete Cidades (about 22 ka), inner Agua de Pau (15.2 ka), and Furnas (about 12 ka). Normal faults are common, but many are buried by Holocene trachyte pumice. Most faults trend northwest or west-northwest and are related to the Terceira rift, whose most active segment on São Miguel passes through Sete Cidades and zone 2. A major normal fault displaces Nordeste lavas 150–250 m and may mark the location of an ancestral Terceira rift. Recent seismicity (e.g., in the 1980s) generally has been scattered, but some small earthquake swarms have occurred beneath the north-eastern flank of Agua de Pau.

High resolution paleoceanography of the Guaymas Basin, Gulf of California, during the past 15 000 years

USGS Publications Warehouse

Barron, J.A.; Bukry, D.; Bischoff, J.L.

2004-01-01

Deep Sea Drilling Project Site 480 (27??54.10???N, 111??39.34???W; 655 m water depth) contains a high resolution record of paleoceanographic change of the past 15 000 years for the Guaymas Basin, a region of very high diatom productivity within the central Gulf of California. Analyses of diatoms and silicoflagellates were completed on samples spaced every 40-50 yr, whereas ICP-AES geochemical analyses were completed on alternate samples (sample spacing 80-100 yr). The B??lling-Aller??d interval (14.6-12.9 ka) (note, ka refers to 1000 calendar years BP throughout this report) is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals, suggesting conditions somewhat similar to those of today. The Younger Dryas event (12.9-11.6 ka) is marked by a major drop in biogenic silica and an increase in calcium carbonate. Increasing relative percentage contributions of Azpeitia nodulifera and Dictyocha perlaevis (a tropical diatom and silicoflagellate, respectively) and reduced numbers of the silicoflagellate Octactis pulchra are supportive of reduced upwelling of nutrient-rich waters. Between 10.6 and 10.0 ka, calcium carbonate and A. nodulifera abruptly decline at DSDP 480, while Roperia tesselata, a diatom indicative of winter upwelling in the modern-day Gulf, increases sharply in numbers. A nearly coincident increase in the silicoflagellate Dictyocha stapedia suggests that waters above DSDP 480 were more similar to the cooler and slightly more saline waters of the northern Gulf during much of the early and middle parts of the Holocene (???10 to 3.2 ka). At about 6.2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom A. nodulifera marks a major change in oceanographic conditions in the Gulf. A winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions (El Nin??o-driven?) of the North Equatorial Countercurrent during the summer. Beginning between 2.8 and 2.4 ka, the amplitude of biogenic silica and wt% Fe, Al, and Ti (proxies of terrigenous input) increase, possibly reflecting intensification of ENSO cycles and the establishment of modern oceanographic conditions in the Gulf. Increased numbers of O. pulchra after 2.8 ka suggest enhanced spring upwelling. ?? 2003 Elsevier B.V. All rights reserved.

The rise and fall of Lake Bonneville between 45 and 10.5 ka

USGS Publications Warehouse

Benson, L.V.; Lund, S.P.; Smoot, J.P.; Rhode, D.E.; Spencer, R.J.; Verosub, K.L.; Louderback, L.A.; Johnson, C.A.; Rye, R.O.; Negrini, R.M.

2011-01-01

A sediment core taken from the western edge of the Bonneville Basin has provided high-resolution proxy records of relative lake-size change for the period 45.1-10.5 calendar ka (hereafter ka). Age control was provided by a paleomagnetic secular variation (PSV)-based age model for Blue Lake core BL04-4. Continuous records of ??18O and total inorganic carbon (TIC) generally match an earlier lake-level envelope based on outcrops and geomorphic features, but with differences in the timing of some hydrologic events/states. The Stansbury Oscillation was found to consist of two oscillations centered on 25 and 24 ka. Lake Bonneville appears to have reached its geomorphic highstand and began spilling at 18.5 ka. The fall from the highstand to the Provo level occurred at 17.0 ka and the lake intermittently overflowed at the Provo level until 15.2 ka, at which time the lake fell again, bottoming out at ~14.7 ka. The lake also fell briefly below the Provo level at ~15.9 ka. Carbonate and ??18O data indicate that between 14.7 and 13.1 ka the lake slowly rose to the Gilbert shoreline and remained at about that elevation until 11.6 ka, when it fell again. Chemical and sedimentological data indicate that a marsh formed in the Blue Lake area at 10.5 ka.Relatively dry periods in the BL04-4 records are associated with Heinrich events H1-H4, suggesting that either the warming that closely followed a Heinrich event increased the evaporation rate in the Bonneville Basin and (or) that the core of the polar jet stream (PJS) shifted north of the Bonneville Basin in response to massive losses of ice from the Laurentide Ice Sheet (LIS) during the Heinrich event. The second Stansbury Oscillation occurred during Heinrich event H2, and the Gilbert wet event occurred during the Younger Dryas cold interval. Several relatively wet events in BL04-4 occur during Dansgaard-Oeschger (DO) warm events.The growth of the Bear River glacier between 32 and 17 ka paralleled changes in the values of proxy indicators of Bonneville Basin wetness and terminal moraines on the western side of the Wasatch Mountains have ages ranging from 16.9 to 15.2 ka. This suggests a near synchroneity of change in the hydrologic and cryologic balances occurring in the Bonneville drainage system and that glacial extent was linked to lake size. ?? 2010.

Limnological and climatic environments at Upper Klamath Lake, Oregon during the past 45 000 years

USGS Publications Warehouse

Bradbury, J.P.; Colman, Steven M.; Dean, W.E.

2004-01-01

Upper Klamath Lake, in south-central Oregon, contains long sediment records with well-preserved diatoms and lithological variations that reflect climate-induced limnological changes. These sediment archives complement and extend high resolution terrestrial records along a north-south transect that includes areas influenced by the Aleutian Low and Subtropical High, which control both marine and continental climates in the western United States. The longest and oldest core collected in this study came from the southwest margin of the lake at Caledonia Marsh, and was dated by radiocarbon and tephrochronology to an age of about 45 ka. Paleolimnological interpretations of this core, based upon geochemical and diatom analyses, have been augmented by data from a short core collected from open water environments at nearby Howards Bay and from a 9-m core extending to 15 ka raised from the center of the northwestern part of Upper Klamath Lake. Pre- and full-glacial intervals of the Caledonia Marsh core are characterized and dominated by lithic detrital material. Planktic diatom taxa characteristic of cold-water habitats (Aulacoseira subarctica and A. islandica) alternate with warm-water planktic diatoms (A. ambigua) between 45 and 23 ka, documenting climate changes at millennial scales during oxygen isotope stage (OIS) 3. The full-glacial interval contains mostly cold-water planktic, benthic, and reworked Pliocene lacustrine diatoms (from the surrounding Yonna Formation) that document shallow water conditions in a cold, windy environment. After 15 ka, diatom productivity increased. Organic carbon and biogenic silica became significant sediment components and diatoms that live in the lake today, indicative of warm, eutrophic water, became prominent. Lake levels fell during the mid-Holocene and marsh environments extended over the core site. This interval is characterized by high levels of organic carbon from emergent aquatic vegetation (Scirpus) and by the Mazama ash (7.55 ka), generated by the eruption that created nearby Crater Lake. For a brief time the ash increased the salinity of Upper Klamath Lake. High concentrations of molybdenum, arsenic, and vanadium indicate that Caledonia Marsh was anoxic from about 7 to 5 ka. After the mid-Holocene, shallow, but open-water environments returned to the core site. The sediments became dominated (>80%) by biogenic silica. The open-water cores show analogous but less extreme limnological and climatic changes more typical of mid-lake environments. Millennial-scale lake and climate changes during OIS 3 at Upper Klamath Lake contrast with a similar record of variation at Owens Lake, about 750 km south. When Upper Klamath Lake experienced cold-climate episodes during OIS 3, Owens Lake had warm but wet episodes; the reverse occurred during warmer intervals at Upper Klamath Lake. Such climatic alternations apparently reflect the variable position and strength of the Aleutian Low during the mid-Wisconsin.

Equilibrium and Disequilibrium of 230Th-238U in Zircon from the Minoan Eruption, Santorini, Aegean Sea, Greece

NASA Astrophysics Data System (ADS)

Schmitt, A. K.; Stockli, D. F.; Song, E. J.; Storm, S.

2016-12-01

The Minoan eruption (ca. 1600 BCE; 40-80 km3 dense rock equivalent) occurred after a ca. 18 ka period of dormancy followed by rapid reinvigoration through arrival of new magma from deep reservoirs colliding with evolved magmas in shallow storage. Although zoned phenocrysts indicate brief timescales ranging between years to decades for final pre-eruptive magma recharge and mixing, it remains unclear how magma accumulation vs. crystallization were balanced in the subvolcanic reservoir during the preceding inter-eruptive cycle. To directly probe magma presence over the repose interval prior to the Minoan eruption and further back in time, we reconnoitered the potential of U-Th zircon geochronology to date the crystallization of individual zircon crystals from pumice from the Minoan eruption. Zircon crystals were extracted from composite pumice samples (several kg each) from basal fall out deposits using gravity and magnetic separation. Etching in cold HF removed adherent glass and revealed the shape of crystals, which were pressed into indium metal to expose unpolished rims to the ion beam of a CAMECA IMS 1270 secondary ionization mass spectrometer. Adherent glass was ubiquitous, indicating that crystals were in contact with melt at the time of eruption. Six of 18 crystals were in 230Th/238U secular equilibrium, two crystals yielded ages of ca. 160 ka, and the remaining rims dated between eruption age and ca. 20 ka. Low Th/U of some secular equilibrium zircon suggests recycling of metamorphic basement zircon, which is also indicated by the presence of rutile in heavy mineral separates. U-Th dates also reveal recycling of zircon from Pleistocene intrusions that likely represent left-over magma from antecedent eruption cycles. We tentatively interpret the dominant zircon population with near-eruption to ca. 20 ka ages to indicate continuous melt presence underneath Santorini during the last repose interval. Distinguishing a hiatus in zircon crystallization between 20 ka and 160 ka from continuous presence of a crystal mush capable of crystallizing zircon throughout the late Pleistocene requires further analyses. A corollary of mixed zircon populations of heterogeneous provenance in Minoan pumice is that the age significance of U-series data for major phases analyzed in bulk is suspect.

Attaining high-resolution eruptive histories for active arc volcanoes with argon geochronology

NASA Astrophysics Data System (ADS)

Calvert, A. T.

2012-04-01

Geochronology of active arc volcanoes commonly illuminates eruptive behavior over tens to hundreds of thousands of years, lengthy periods of repose punctuated by short eruptive episodes, and spatial and compositional changes with time. Despite the >1 Gyr half-life of 40K, argon geochronology is an exceptional tool for characterizing Pleistocene to Holocene eruptive histories and for placing constraints on models of eruptive behavior. Reliable 40Ar/39Ar ages of calc-alkaline arc rocks with rigorously derived errors small enough (± 500 to 3,000 years) to constrain eruptive histories are attainable using careful procedures. Sample selection and analytical work in concert with geologic mapping and stratigraphic studies are essential for determining reliable eruptive histories. Preparation, irradiation and spectrometric techniques have all been optimized to produce reliable, high-precision results. Examples of Cascade and Alaska/Aleutian eruptive histories illustrating duration of activity from single centers, eruptive episodicity, and spatial and compositional changes with time will be presented: (1) Mt. Shasta, the largest Cascade stratovolcano, has a 700,000-year history (Calvert and Christiansen, 2011 Fall AGU). A similar sized and composition volcano (Rainbow Mountain) on the Cascade axis was active 1200-950 ka. The eruptive center then jumped west 15 km to the south flank of the present Mt. Shasta and produced a stratovolcano from 700-450 ka likely rivaling today's Mt. Shasta. The NW portion of that edifice failed in an enormous (>30 km3) debris avalanche. Vents near today's active summit erupted 300-135 ka, then 60-15 ka. A voluminous, but short-lived eruptive sequence occurred at 11 ka, including a summit explosion producing a subplinian plume, followed by >60 km3 andesite-dacite Shastina domes and flows, then by the flank dacite Black Butte dome. Holocene domes and flows subsequently rebuilt the summit and flowed to the north and east. (2) Mt. Veniaminof on the Alaska Peninsula is a ~350 km3 tholeiitic arc volcano with basalt early in its history (~250 ka) and basaltic andesite to dacite currently. Chemical variation is due principally to crystallization differentiation with little or no evidence for crustal contamination. The smooth increase with time of Veniaminof's most silicic products chronicles the development of an intrusive complex, also reflected in granitoid blocks expelled during Holocene explosive eruptions (Bacon et al., 2007 Geology). (3) The Three Sisters in the central Oregon Cascades are a cluster of small volcanoes with remarkable chemical diversity (basalt to high silica rhyolite) that mainly erupted in a short interval between 40-15 ka. This eruptive interval was unusual in its chemical diversity beginning bimodal (basaltic andesite and rhyolite), progressing to dacite then andesite, and back to basaltic andesite. Over eighty percent of mapped units are dated, enabling time-series displays of the chemical and spatial evolution of the volcanic field (Calvert et al., 2010 Fall AGU).

South Asian climate change at the end of urban Harappan (Indus valley) civilization and mechanisms of Holocene monsoon variability

NASA Astrophysics Data System (ADS)

Staubwasser, M.; Sirocko, F.; Erlenkeuser, H.; Grootes, P. M.; Segl, M.

2003-04-01

Planktonic oxygen isotope ratios from the well-dated laminated sediment core 63KA off the river Indus delta are presented. The record reveals significant climate changes in the south Asian monsoon system throughout the Holocene. The most prominent event of the early-mid Holocene occurred after 8.4 ka BP and is within dating error of the GISP/GRIP event centered at 8.2 ka BP. The late Holocene is generally more variable and the largest change of the entire Holocene occurred at 4.2 ka BP. This event is concordant with the end of urban Harappan civilization in the Indus valley. Opposing isotopic trends across the northern Arabian Sea surface indicate a reduction in Indus river discharge at that time. Consequently, sustained drought may have initiated the archaeologically recorded interval of southeastward habitat tracking within the Harappan cultural domain. The hemispheric significance of the 4.2 ka BP event is evident from concordant climate change in the eastern Mediterranean and the Middle East. The remainder of the late Holocene shows drought cycles of approximately 700 years that are coherent with the evolution of cosmogenic radiocarbon production rates in the atmosphere. This suggests that solar variability is one fundamental cause behind late Holocene rainfall changes over south Asia.

Radiocarbon age-offsets in an arctic lake reveal the long-term response of permafrost carbon to climate change

USGS Publications Warehouse

Gaglioti, Benjamin V.; Mann, Daniel H.; Jones, Benjamin M.; Pohlman, John W.; Kunz, Michael L.; Wooller, Matthew J.

2014-01-01

Continued warming of the Arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon (OC), thereby accentuating global warming. However, it is unclear if recent warming has raised the current rates of permafrost OC release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing. Here we use a time series of radiocarbon age-offsets (14C) between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost OC release over the last 14,500 years. The lake traps and archives OC imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age-offsets. Today, the age-offset (2 ka; thousand of calibrated years before A.D. 1950) and the depositional rate of ancient OC from the watershed into the lake are relatively low and similar to those during the Younger Dryas cold interval (occurring 12.9–11.7 ka). In contrast, age-offsets were higher (3.0–5.0 ka) when summer air temperatures were warmer than present during the Holocene Thermal Maximum (11.7–9.0 ka) and Bølling-Allerød periods (14.5–12.9 ka). During these warm times, permafrost thaw contributed to ancient OC depositional rates that were ~10 times greater than today. Although permafrost OC was vulnerable to climate warming in the past, we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release. As a result, the temperature threshold to trigger widespread permafrost OC release is higher than during previous warming events.

Late quaternary paleoseismology of the southern Steens fault zone, northern Nevada

USGS Publications Warehouse

Personius, S.F.; Crone, A.J.; Machette, M.N.; Mahan, S.A.; Kyung, J.B.; Cisneros, H.; Lidke, D.J.

2007-01-01

The 192-km-long Steens fault zone is the most prominent normal fault system in the northern Basin and Range province of western North America. We use trench mapping and radiometric dating to estimate displacements and timing of the last three surface-rupturing earthquakes (E1-E3) on the southern part of the fault south of Denio, Nevada. Coseismic displacements range from 1.1 to 2.2 ?? 0.5 m, and radiometric ages indicate earthquake times of 11.5 ?? 2.0 ka (E3), 6.1 ?? 0.5 ka (E2), and 4.6 ?? 1.0 ka (E1). These data yield recurrence intervals of 5.4 ?? 2.1 k.y. between E3 and E2, 1.5 ?? 1.1 k.y. between E2 and E1, and an elapsed time of 4.6 ?? 1.0 k.y. since E1. The recurrence data yield variable interval slip rates (between 0.2 ?? 0.22 and 1.5 ?? 2.3 mm/yr), but slip rates averaged over the past ???18 k.y. (0.24 ?? 0.06 mm/year) are similar to long-term (8.5-12.5 Ma) slip rates (0.2 ?? 0.1 mm /yr) measured a few kilometers to the north. We infer from the lack of significant topographic relief across the fault in Bog Hot Valley that the fault zone is propagating southward and may now be connected with a fault at the northwestern end of the Pine Forest Range. Displacements documented in the trench and a rupture length of 37 km indicate a history of three latest Quaternary earthquakes with magnitudes of M 6.6-7.1 on the southern part of the Steens fault zone.

Holocene and latest Pleistocene climate and glacier fluctuations in Iceland

NASA Astrophysics Data System (ADS)

Geirsdóttir, Áslaug; Miller, Gifford H.; Axford, Yarrow; Ólafsdóttir, Sædís

2009-10-01

Multiproxy climate records from Iceland document complex changes in terrestrial climate and glacier fluctuations through the Holocene, revealing some coherent patterns of change as well as significant spatial variability. Most studies on the Last Glacial Maximum and subsequent deglaciation reveal a dynamic Iceland Ice Sheet (IIS) that responded abruptly to changes in ocean currents and sea level. The IIS broke up catastrophically around 15 ka as the Polar Front migrated northward and sea level rose. Indications of regional advance or halt of the glaciers are seen in late Alleröd/early Younger Dryas time and again in PreBoreal time. Due to the apparent rise of relative sea level in Iceland during this time, most sites contain evidence for fluctuating, tidewater glacier termini occupying paleo fjords and bays. The time between the end of the Younger Dryas and the Preboreal was characterized by repeated jökulhlaups that eroded glacial deposits. By 10.3 ka, the main ice sheet was in rapid retreat across the highlands of Iceland. The Holocene thermal maximum (HTM) was reached after 8 ka with land temperatures estimated to be 3 °C higher than the 1961-1990 reference, and net precipitation similar to modern. Such temperatures imply largely ice-free conditions across Iceland in the early to mid-Holocene. Several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8.5 and 8 ka, but no moraines have been detected from that time. Termination of the HTM and onset of Neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4.5 and 4.0 ka, intensifying between 3.0 and 2.5 ka. Although a distinct warming during the Medieval Warm Period is not dramatically apparent in Icelandic records, the interval from ca AD 0 to 1200 is commonly characterized by relative stability with slow rates of change. The literature most commonly describes Little Ice Age moraines (ca AD 1250-1900) as representing the most extensive ice margins since early Holocene deglaciation, with temperature depressions of 1-2 °C compared to the AD 1961-1990 average. Steep north-south and west-east temperature gradients are reconstructed in the Holocene records of Iceland, suggesting a strong maritime influence on the terrestrial climate of Iceland.

Effect of Kuanxiong Aerosol () on Patients with Angina Pectoris: A Non-inferiority Multi-center Randomized Controlled Trial.

PubMed

Yang, Qiao-Ning; Bai, Rui-Na; Dong, Guo-Ju; Ge, Chang-Jiang; Zhou, Jing-Min; Huang, Li; He, Yan; Wang, Jun; Ren, Ai-Hua; Huang, Zhan-Quan; Zhu, Guang-Li; Lu, Shu; Xiong, Shang-Quan; Xian, Shao-Xiang; Zhu, Zhi-Jun; Shi, Da-Zhuo; Lu, Shu-Zheng; Li, Li-Zhi; Chen, Ke-Ji

2018-05-01

To evaluate the effect and safety of Kuanxiong Aerosol (, KA) on patients with angina pectoris. Block randomization was performed to randomly allocate 750 patients into KA (376 cases) and control groups (374 cases). During an angina attack, the KA group received 3 consecutive sublingual sprays of KA (0.6 mL per spray). The control group received 1 sublingual nitroglycerin tablet (NT, 0.5 mg/tablet). Log-rank tests and Kaplan-Meier estimations were used to estimate the angina remission rates at 6 time-points after treatment (1, 2, 3, 4, 5, and >5 min). Logistic regression analysis was performed to observe the factors inflfluencing the rate of effective angina remission, and the remission rates and incidences of adverse reactions were compared for different Canadian Cardiovascular Society (CCS) classes of angina. The 5-min remission rates in the KA and control groups were not signifificantly different (94.41% vs. 90.64%, P>0.05). The angina CCS class signifificantly inflfluenced the rate of remission (95% confidence interval = 0.483-0.740, P<0.01). In the CCS subgroup analysis, the 3-and 5-min remission rates for KA and NT were similar in the CCSII and III subgroups (P>0.05), while they were signifificantly better for KA in the CCSI and II subgroups (P<0.05 or P<0.01). Furthermore, the incidence of adverse reactions was signifificantly lower in the KA group than in the control group for the CCSII and III subgroups (9.29% vs. 26.22%, 10.13% vs. 20.88%, P<0.05 or P<0.01). KA is not inferior to NT in the remission of angina. Furthermore, in CCSII and III patients, KA is superior to NT, with a lower incidence of adverse reactions. (Registration No. ChiCTRIPR-15007204).

28-ka History of Sea Surface Temperature, Primary Productivity and Planktonic Community Variability in the Western Arabian Sea

NASA Astrophysics Data System (ADS)

Pourmand, A.; Marcantonio, F.; Bianchi, T.

2006-12-01

Uranium-series radionuclides and organic compounds, which represent major groups of planktonic organisms, have been measured in western Arabian Sea sediments that span the past 28 ka. Variability of the Indian Ocean monsoons and their influence on primary productivity, sea surface temperature (SST), and planktonic community structure has been investigated. The average alkenone-derived SST for the glacial was ~3°C lower than that measured for the Holocene. We also identify, for the first time, an interval of exceptionally low SSTs between 19-18.1 ka BP (15.3°C at 18.5 ka). During this time, the low SSTs coincide with high cumulative biomarker fluxes (CBF). We propose that intensification of winter northeast monsoon winds during the glacial period resulted in cold SSTs, deep convective mixing, and enhanced primary productivity. Following the last termination, and within the Holocene, SSTs vary by ~2°C with high CBFs occurring at times of relatively warmer SSTs. The fluxes of dinoflagellates and zooplankton relative to the total flux of organisms remain constant throughout the record. However, transitioning from the glacial to the Holocene, diatom fluxes comparatively increase relative to the total flux of organisms, while those of coccolithophorids decrease. Considering that the Indian Ocean monsoons are an important component of the global climate system, a shift in the planktonic ecosystem structure in the Arabian Sea may have important implications for the global biogeochemical cycle of carbon.

Fitful and protracted magma assembly leading to a giant eruption, Youngest Toba Tuff, Indonesia

USGS Publications Warehouse

Reid, Mary R; Vazquez, Jorge A.

2017-01-01

The paroxysmal eruption of the 74 ka Youngest Toba Tuff (YTT) of northern Sumatra produced an extraordinary 2800 km3 of non-welded to densely welded ignimbrite and co-ignimbrite ash-fall. We report insights into the duration of YTT magma assembly obtained from ion microprobe U-Th and U-Pb dates, including continuous age spectra over >50% of final zircon growth, for pumices and a welded tuff spanning the compositional range of the YTT. A relatively large subpopulation of zircon crystals nucleated before the penultimate caldera-related eruption at 501 ka, but most zircons yielded interior dates 100-300 ka thereafter. Zircon nucleation and growth was likely episodic and from diverse conditions over protracted time intervals of >100 to >500 ka. Final zircon growth is evident as thin rim plateaus that are in Th/U chemical equilibrium with hosts, and that give crystallization ages within tens of ka of eruption. The longevity and chemical characteristics of the YTT zircons, as well as evidence for intermittent zircon isolation and remobilization associated with magma recharge, is especially favored at the cool and wet eutectoid conditions that characterize at least half of the YTT, wherein heat fluxes could dissolve major phases but have only a minor effect on larger zircon crystals. Repeated magma recharge may have contributed to the development of compositional zoning in the YTT but, considered together with limited allanite, quartz, and other mineral dating and geospeedometry, regular perturbations to the magma reservoir over >400 ka did not lead to eruption until 74 ka ago.

Impact of diagenesis on the environmental magnetic record from a Holocene sedimentary sequence from the Chukchi-Alaskan margin, Arctic Ocean

NASA Astrophysics Data System (ADS)

Brachfeld, Stefanie; Barletta, Francesco; St-Onge, Guillaume; Darby, Dennis; Ortiz, Joseph D.

2009-07-01

We present a high-resolution Holocene sedimentary record of environmental variability from the eastern Chukchi Sea. An ice-rafted debris bearing silty-clay marks the deglacial to post-glacial Holocene transition at this site and is dated at 9.7 ka. An interval of oscillating magnetic parameters from 9.5 to 8.7 ka coincides with the Holocene Thermal Maximum in the western Arctic, and is manifested at the study area as pulses of fine-grained magnetite input every 180-230 years, possibly from increased river discharge or stronger currents flowing over the core site. The magnetic mineral assemblage is very uniform over the last 8.2 ka and consists of a mixture of magnetite, titanomagnetite, and a magnetic phase that we tentatively identify as the magnetic iron sulfide greigite. The amount of magnetic iron sulfides increases up through the Holocene, a trend that is controlled by the amount of marine organic matter available to fuel bacterial sulfate reduction. The median destructive field of the Natural Remanent Magnetization (MDF NRM) displays centennial to millennial scale cycles with significant variance at periods of 900-1300 and 1700-2700 years, with intervals of high MDF NRM values coinciding with indicators of greater sea ice cover [McKay, J., de Vernal, A., Hillaire-Marcel, C., Not, C., Polyak, L., Darby, D., 2008. Holocene fluctuations in Arctic sea-ice cover: Dinocyst-based reconstructions for the eastern Chukchi Sea. Can. J. Earth Sci. 45, 1399-1415]. The MDF NRM is controlled by the variable abundance of iron sulfides formed during early diagenesis. We interpret intervals of high MDF NRM values as times of stronger water column stratification, during which the pyritization process was interrupted by the lack of marine organic matter and lack of reactive iron. Intervals of low MDF NRM values, which coincide with indicators of reduced sea ice cover, are interpreted as times of stronger vertical mixing of the water column, which allows fresh marine organic matter and reactive iron to reach the seafloor, driving the pyritization process to completion.

Annual, orbital, and enigmatic variations in tropical oceanography recorded by the Equatorial Atlantic amplifier

NASA Technical Reports Server (NTRS)

Mcintyre, Andrew

1992-01-01

Equatorial Atlantic surface waters respond directly to changes in zonal and meridional lower tropospheric winds forced by annual insolation. This mechanism has its maximum effect along the equatorial wave guide centered on 10 deg W. The result is to amplify even subtle tropical climate changes such that they are recorded by marked amplitude changes in the proxy signals. Model realizations, NCAR AGCM and OGCM for 0 Ka and 126 Ka (January and July), and paleoceanographic proxy data show that these winds are also forced by insolation changes at the orbital periods of precession and obliquity. Perhelion in boreal summer produces a strengthened monsoon, e.g., increase meridional and decrease zonal wind stress. This reduces oceanic Ekman divergence and thermocline/nutricline shallowing. The result, in the equatorial Atlantic, is reduced primary productivity and higher euphotic zone temperatures; vice versa for perihelion in boreal winter. Perihelion is controlled by precession. Thus, the dominant period in spectra from a stacked SST record (0-252 Ka BP) at the site of the equatorial Atlantic amplifier is 23 Ky (53 percent of the total variance). This precessional period is coherent (k = 0.920) and in phase with boreal summer insolation. Oscillations of shorter period are present in records from cores sited beneath the amplifier region. These occur between 12.5 and 74.5 Ka BP, when eccentricity modulation of precession is at a minimum. Within this time interval there are 21 cycles with mean periods of 3.0 plus or minus 0.5 Ky. Similar periods have been documented from high latitude regions, e.g., Greenland ice cores from Camp Century. The Camp Century signal in this same time interval contains 21 cycles. A subjective correlation was made between the Camp Century and the equatorial records; the signals were statistically similar, r = 0.722 and k = 0.960.

Limiting age for the Provo shoreline of Lake Bonneville

USGS Publications Warehouse

Miller, David; Wahl, David B.; McGeehin, John; Rosario, Jose J.; Oviatt, Charles G.; Anderson, Lysanna; Presnetsova, Liubov S.

2015-01-01

Pluvial Lake Bonneville features a prominent shoreline at the Provo level, which has been interpreted as having formed during a period of threshold-stabilized overflow. The timing of Provo shoreline development is important for paleoclimate interpretations and for inferences on geomorphic process rates. Estimates for the timing of the shoreline formation, based on radiocarbon measurements from gastropod shells, are from approximately 18 to 15 cal ka. One key radiocarbon age on plant fragments from Swan Lake, which formed in the threshold spillway after overflow ceased, has been taken as a young limiting age. The conventional age of 12090 ± 300 14C when calibrated at 2σ has large uncertainty (13375–15103 cal BP). We report six new AMS radiocarbon ages recovered from new Swan Lake sediment cores. A twig near the base of lacustrine muds was dated at 11,615 ± 40 14C yr (13,350 to 13,560 cal BP). Age determinations on roots in that interval and deeper in the core are somewhat younger. These ages limit the last overflow of the Provo stand to earlier than ∼13.5 cal ka BP, consistent with the younger bound of the imprecise age reported by Bright. If conservative interpretations of sedimentation rates for the thick well-sorted sand interval below the lacustrine muds are correct and landscape change that resulted in damming of Swan Lake is accounted for, cessation of flow probably occurred before ∼14.5 cal ka BP.

A 130 ka reconstruction of rainfall on the Bolivian Altiplano

NASA Astrophysics Data System (ADS)

Placzek, C. J.; Quade, J.; Patchett, P. J.

2013-02-01

New efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the Bolivian Altiplano. On the Southern Altiplano, 10 lake oscillations have been identified from this new unified chronology, each coincident with North Atlantic cold events such as Heinrich Events H5, H2, H1, and the Younger Dryas. By coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the Southern Bolivian Altiplano over the last 130 ka. These modeling efforts underscore the relative aridity of the Altiplano during the rare and small lake cycles occurring between 80 and 20 ka, when colder temperatures combined with little or no change in rainfall produced smaller paleolakes. Relative aridity between 80 and 20 ka contrasts with the immense Tauca lake cycle (18.1-14.1 ka), which was six times larger than modern Lake Titicaca and coincided with Heinrich Event 1. This improved paleolake record from the Southern Altiplano reveals a strong link between central Andean climate and Atlantic sea-surface temperature gradients during the late Pleistocene, even though today rainfall variability is driven mostly by Pacific sea-surface temperature anomalies associated with El Niño/Southern Oscillation. However, not all Heinrich Events appear to result in lake expansions, most conspicuously during the global cold interval between 80 and 20 ka when the Altiplano and Amazon Basin were relatively arid.

Hydroclimatic variability in the Levant during the early last glacial (∼ 117-75 ka) derived from micro-facies analyses of deep Dead Sea sediments

NASA Astrophysics Data System (ADS)

Neugebauer, I.; Schwab, M. J.; Waldmann, N. D.; Tjallingii, R.; Frank, U.; Hadzhiivanova, E.; Naumann, R.; Taha, N.; Agnon, A.; Enzel, Y.; Brauer, A.

2015-08-01

The new sediment record from the deep Dead Sea basin (ICDP core 5017-1) provides a unique archive for hydroclimatic variability in the Levant. Here, we present high-resolution sediment facies analysis and elemental composition by μXRF scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca 117-75 ka, i.e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a) up to several meters thick, greenish sediments of alternating aragonite and detrital marl laminae (aad) and (b) thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at ∼110-108 ± 5 and ∼93-87 ± 7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio) and low global sea levels during MIS 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in-situ beach deposit. Two intervals of higher lake stands at ∼108-93 ± 6 and ∼87-75 ± 7 ka correspond to interstadial conditions in the central Mediterranean, i.e. pollen zones St. Germain I and II in Monticchio, and GI 24 + 23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These apparent correlations suggest a close link of the climate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern Hemisphere ice shields in the early last glacial period.

Atmospheric CO2 and abrupt climate change on submillennial timescales

NASA Astrophysics Data System (ADS)

Ahn, Jinho; Brook, Edward

2010-05-01

How atmospheric CO2 varies and is controlled on various time scales and under various boundary conditions is important for understanding how the carbon cycle and climate change are linked. Ancient air preserved in ice cores provides important information on past variations in atmospheric CO2. In particular, concentration records for intervals of abrupt climate change may improve understanding of mechanisms that govern atmospheric CO2. We present new multi-decadal CO2 records that cover Greenland stadial 9 (between Dansgaard-Oeschger (DO) events 8 and 9) and the abrupt cooling event at 8.2 ka. The CO2 records come from Antarctic ice cores but are well synchronized with Greenland ice core records using new high-resolution CH4 records,precisely defining the timing of CO2 change with respect to abrupt climate events in Greenland. Previous work showed that during stadial 9 (40~38 ka), CO2 rose by about 15~20 ppm over around 2,000 years, and at the same time temperatures in Antarctica increased. Dust proxies indicate a decrease in dust flux over the same period. With more detailed data and better age controls we now find that approximately half of the CO2 increase during stadial 9 occurred abruptly, over the course of decades to a century at ~39.6 ka. The step increase of CO2 is synchronous with a similar step increase of Antarctic isotopic temperature and a small abrupt change in CH4, and lags after the onset of decrease in dust flux by ~400 years. New atmospheric CO2 records at the well-known ~8.2 ka cooling event were obtained from Siple Dome ice core, Antarctica. Our preliminary CO2 data span 900 years and include 19 data points within the 8.2 ka cooling event, which persisted for ~160 years (Thomas et al., Quarternary Sci. Rev., 2007). We find that CO2 increased by 2~4 ppm during that cooling event. Further analyses will improve the resolution and better constrain the CO2 variability during other times in the early Holocene to determine if the variations observed during at 8.2 ka event are significant.

Persistence of the North American Monsoon over the last 50,000 years in Arizona, USA

NASA Astrophysics Data System (ADS)

Cole, K. L.; Ironside, K. E.; Cobb, N. S.

2012-12-01

Reconstruction of monsoon rainfall in the American southwest over the last 50,000 years has been complicated by past massive shifts in temperature and winter precipitation, as well as the rarity of proxy sources. Paleogeographical analysis of plant species distributions from plant macrofossils contained within packrat middens and sediment cores portray substantial shifts that are most easily attributed to these larger changes in temperature and winter precipitation. But some species can be more reliably associated with summer precipitation through spatial analyses of their climate space within their contemporary habitat. For example, warm-season C4 grasses and summer annuals were infrequent in southern Arizona throughout the late Wisconsinan, likely because of much lower temperatures and much higher levels of winter rainfall. But other species, today typical of summer precipitation regions further north, were especially abundant during selected intervals. Macrofossils of Arizona single-leaf pinyon (Pinus edulis var. fallax) and one seed juniper (Juniperus monosperma) are abundant in middens from northern Arizona and southern Utah ranging from 30,400 to > 50,000 C14 yr BP, suggesting at least 200% of the current summer precipitation. The abundance of Arizona single-leaf pinyon throughout Arizona during the Allerød Interval (~13.9 ka to ~12.9 ka) suggests that summer precipitation was at least 120% of modern. The rapid expansion and dominance of the southwestern interior race of Ponderosa pine (Pinus ponderosa), as well as increases in Rocky Mountain Juniper (Juniperus scopulorum), during the earliest Holocene (~11.7 ka to ~10.2 Ka) portray summer precipitation somewhat greater than that of today. These paleobotanical conclusions are supported by a recent analysis of Deuterium isotopes from 120 middens in 5 regional series. These isotopic values should reflect the relative frequency of precipitation originating from Pacific winter cyclonic storms versus sub-tropical summer monsoonal convective precipitation. This correlation was supported by the analysis of 41 modern samples from throughout the region. Higher values, similar to modern levels, were recorded during the Allerød Interval and earliest Holocene. Much lower levels were recorded during the Full-glacial Wisconsinan and the Younger Dryas Period. These paleogeograpic records and isotopic analyses are temporally and spatially consistent. They suggest that the climate mechanisms responsible transport of summer moisture into Arizona have persisted at various times during the late Wisconsinan, although the amounts, transport dynamics, and moisture sources may have shifted from time to time.

Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

USGS Publications Warehouse

Matthews, Naomi E.; Vazquez, Jorge A.; Calvert, Andrew T.

2015-01-01

The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff. Tephra from the Lava Creek eruption is a key Quaternary chronostratigraphic marker, in particular for dating the deposition of mid Pleistocene glacial and pluvial deposits in western North America. To resolve the timing of eruption and crystallization history for the Lava Creek magma, we performed (1) 40Ar/39Ar dating of single sanidine crystals to delimit eruption age and (2) ion microprobe U-Pb and trace-element analyses of the crystal faces and interiors of single zircons to date the interval of zircon crystallization and characterize magmatic evolution. Sanidines from the two informal members composing Lava Creek Tuff yield a preferred 40Ar/39Ar isochron date of 631.3 ± 4.3 ka. Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 626.5 ± 5.8 ka, and have trace element concentrations that vary with the eruptive stratigraphy. Zircon interiors yield a mean 206Pb/238U date of 659.8 ± 5.5 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high U concentration cores that likely grew from highly evolved melt. The occurrence of distal Lava Creek tephra in stratigraphic sequences marking the Marine Isotope Stage 16–15 transition supports the apparent eruption age of ∼631 ka. The combined results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103−104 year interval before eruption.

Propagation of current pulses with an amplitude of up to 85 kA in soil over distances of several tens of meters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smirnov, V. P.; Fortov, V. E.; Bykov, Yu. A.

Conditions for the propagation in soil of current pulses with an amplitude of up to 85 kA and temporal characteristics typical of a lightning stroke are studied with the help of a specially designed mobile test complex on the basis of a 4-MJ capacitive energy storage with an output voltage of up to 2 MV. In contrast to the conventional opinion that the ionization processes in highly conductive soils are weakly pronounced, a dramatic reduction in the grounding resistance at a resistivity of about 100 Ω m and currents above 10 kA was observed. A time interval in which themore » grounding resistance is determined by the skin effect in soil is revealed. It is shown that the grounding resistance continues to decrease behind the front of the current pulse due to the continuous growth of spark channels in soil. Time variations in the grounding resistance cannot be related to the formation of a continuous ionization zone near the grounding electrodes and are explained only by the simultaneous growth of several long spark channels extending from the grounding device.« less

Accessory mineral U-Th-Pb ages and 40Ar/39Ar eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California

USGS Publications Warehouse

Simon, J.I.; Vazquez, J.A.; Renne, P.R.; Schmitt, A.K.; Bacon, C.R.; Reid, M.R.

2009-01-01

We determined Ar/Ar eruption ages of eight extrusions from the Pleistocene Coso volcanic field, a long-lived series of small volume rhyolitic domes in eastern California. Combined with ion-microprobe dating of crystal ages of zircon and allanite from these lavas and from granophyre geothermal well cuttings, we were able to track the range of magma-production rates over the past 650 ka at Coso. In ??? 230 ka rhyolites we find no evidence of protracted magma residence or recycled zircon (or allanite) from Pleistocene predecessors. A significant subset of zircon in the ???85 ka rhyolites yielded ages between ???100 and 200 Ma, requiring that generation of at least some rhyolites involves material from Mesozoic basement. Similar zircon xenocrysts are found in an ???200 ka granophyre. The new age constraints imply that magma evolution at Coso can occur rapidly as demonstrated by significant changes in rhyolite composition over short time intervals (???10's to 100's ka). In conjunction with radioisotopic age constraints from other young silicic volcanic fields, dating of Coso rhyolites highlights the fact that at least some (and often the more voluminous) rhyolites are produced relatively rapidly, but that many small-volume rhyolites likely represent separation from long-lived mushy magma bodies. ?? The Author(s) 2009.

Holocene South Asian Monsoon Climate Change - Potential Mechanisms and Effects on Past Civilizations

NASA Astrophysics Data System (ADS)

Staubwasser, M.; Sirocko, F.; Grootes, P. M.; Erlenkeuser, H.; Segl, M.

2002-12-01

Planktonic oxygen isotope ratios from the laminated sediment core 63KA off the river Indus delta dated with 80 AMS radiocarbon ages reveal significant climate changes in the south Asian monsoon system throughout the Holocene. The most prominent event of the early-mid Holocene occurred after 8.4 ka BP and is within dating error of the GISP/GRIP event centered at 8.2 ka BP. The late Holocene is generally more variable, and shows non-periodic cycles in the multi-centennial frequency band. The largest change of the entire Holocene occurred at 4.2 ka BP and is concordant with the end of urban Harappan civilization in the Indus valley. Opposing isotopic trends across the northern Arabian Sea surface indicate a reduction in Indus river discharge at that time. Consequently, sustained drought may have initiated the archaeologically recorded interval of southeastward habitat tracking within the Harappan cultural domain. The hemispheric significance of the 4.2 ka BP event is evident from concordant climate change in the eastern Mediterranean and the Middle East. The late Holocene cycles in South Asia, which most likely represent drought cycles, vary between 250 and 800 years and are coherent with the evolution of cosmogenic radiocarbon production rates in the atmosphere. This suggests that solar variability is the fundamental cause behind late Holocene rainfall changes at least over south Asia.

Mid-Holocene drying of the U.S. Great Basin recorded in Nevada speleothems

NASA Astrophysics Data System (ADS)

Steponaitis, Elena; Andrews, Alexandra; McGee, David; Quade, Jay; Hsieh, Yu-Te; Broecker, Wallace S.; Shuman, Bryan N.; Burns, Stephen J.; Cheng, Hai

2015-11-01

Lake level records point to dramatic changes in Great Basin water balance over the last 25 ka, but the timing and pace of Holocene drying in the region remains poorly documented. Here we present stable isotope and trace metal data from two Lehman Caves, NV speleothems that provide a well-dated record of latest Pleistocene to mid-Holocene hydroclimate in the U.S. Great Basin. Together the stalagmites span the interval between 16.4 ka and 3.8 ka, with a hiatus from 15.0 ka to 12.7 ka. Mg/Ca and δ13C covary throughout the records, consistent with control by the extent of degassing and prior calcite precipitation (PCP); measurements of modern cave and soil waters support PCP as the primary control on drip-water trace-element composition. We therefore interpret Mg/Ca and δ13C as reflecting infiltration rates, with higher values corresponding to drier periods. Both Mg/Ca and δ13C indicate a wet period at the beginning of the record (12.7-8.2 ka) followed by pronounced drying after 8.2 ka. This mid-Holocene drying is consistent with records from around the western United States, including a new compilation of Great Basin lake-level records. The strong temporal correspondence with the collapse of the Laurentide ice sheet over Hudson Bay suggests that this drying may have been triggered by northward movement of the winter storm track as a result of ice sheet retreat. However, we cannot rule out an alternative hypothesis that wet early Holocene conditions are related to equatorial Pacific sea-surface temperature. Regardless, our results suggest that Great Basin water balance in the early Holocene was driven by factors other than orbital changes.

Paleoclimate in continental northwestern Europe during the Eemian and early Weichselian (125-97 ka): insights from a Belgian speleothem

NASA Astrophysics Data System (ADS)

Vansteenberge, Stef; Verheyden, Sophie; Cheng, Hai; Edwards, R. Lawrence; Keppens, Eddy; Claeys, Philippe

2016-07-01

The last interglacial serves as an excellent time interval for studying climate dynamics during past warm periods. Speleothems have been successfully used for reconstructing the paleoclimate of last interglacial continental Europe. However, all previously investigated speleothems are restricted to southern Europe or the Alps, leaving large parts of northwestern Europe undocumented. To better understand regional climate changes over the past, a larger spatial coverage of European last interglacial continental records is essential, and speleothems, because of their ability to obtain excellent chronologies, can provide a major contribution. Here, we present new, high-resolution data from a stalagmite (Han-9) obtained from the Han-sur-Lesse Cave in Belgium. Han-9 formed between 125.3 and ˜ 97 ka, with interruptions of growth occurring at 117.3-112.9 and 106.6-103.6 ka. The speleothem was investigated for its growth, morphology and stable isotope (δ13C and δ18O) composition. The speleothem started growing relatively late within the last interglacial, at 125.3 ka, as other European continental archives suggest that Eemian optimum conditions were already present during that time. It appears that the initiation of Han-9 growth is caused by an increase in moisture availability, linked to wetter conditions around 125.3 ka. The δ13C and δ18O proxies indicate a period of relatively stable conditions after 125.3 ka; however, at 120 ka the speleothem δ18O registered the first signs of regionally changing climate conditions, being a modification of ocean source δ18O linked to an increase in ice volume towards the Marine Isotope Stage (MIS) 5e-5d transition. At 117.5 ka, drastic vegetation changes are recorded by Han-9 δ13C immediately followed by a cessation of speleothem growth at 117.3 ka, suggesting a transition to significantly dryer conditions. The Han-9 record covering the early Weichselian displays larger amplitudes in both isotope proxies and changes in stalagmite morphology, evidencing increased variability compared to the Eemian. Stadials that appear to be analogous to those in Greenland are recognized in Han-9, and the chronology is consistent with other European (speleothem) records. Greenland Stadial 25 is reflected as a cold/dry period within Han-9 stable isotope proxies, and the second interruption in speleothem growth occurs simultaneously with Greenland Stadial 24.

PaleoClim: new datasets to quantify the impact of past climate changes on modern biodiversity

NASA Astrophysics Data System (ADS)

Hill, D. J.; Brown, J. T.; Carnaval, A. C.; Haywood, A. M.

2017-12-01

Palaeoclimate history is an important driver of modern patterns of biodiversity and many ecological modelling studies have shown the predictive power of palaeoclimate information. However, a major limiting factor to such studies is the availability of global palaeoclimate reconstructions in the relevant bioclim layers. The primary source of such fields is from climate model simulations, which are currently limited to the key PMIP (Paleoclimate Modelling Intercomparison Project) intervals of the mid-Holocene (6ka), the Last Glacial Maximum (21ka) and the Last Interglaciation (130ka). The PaleoClim project will significantly increase the availability of pre-processed palaeoclimate bioclim information and provide a new platform for accessing the information. The first new PaleoClim time period will be the mid-Pliocene Warm Period (3Ma). This is the last period of sustained globally warmer than modern climate in Earth history and represents the last global warmth before the cooling into the Pleistocene ice ages. Being 3 million years ago this represents a significant lengthening of the time range of available bioclim layers and the first time these have been available over evolutionary timescales. PaleoClim will also greatly expand the available Pleistocene time periods, looking to both quantify the differences between the late Pleistocene interglacial periods and understand the role of orbital changes in modulating tropical precipitation and driving modern biodiversity patterns.

Human responses to Middle Holocene climate change on California's Channel Islands

NASA Astrophysics Data System (ADS)

Kennett, Douglas J.; Kennett, James P.; Erlandson, Jon M.; Cannariato, Kevin G.

2007-02-01

High-resolution archaeological and paleoenvironmental records from California's Channel Islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses. Available climate records in western North America (7-3.8 ka) indicate a severe dry interval between 6.3 and 4.8 ka embedded within a generally warm and dry Middle Holocene. Very dry conditions in western North America between 6.3 and 4.8 ka correlate with cold to moderate sea-surface temperatures (SST) along the southern California Coast evident in Ocean Drilling Program (ODP) Core 893A/B (Santa Barbara Basin). An episode of inferred high marine productivity between 6.3 and 5.8 ka corresponds with the coldest estimated SSTs of the Middle Holocene, otherwise marked by warm/low productivity marine conditions (7.5-3.8 ka). The impact of this severe aridity on humans was different between the northern and southern Channel Islands, apparently related to degree of island isolation, size and productivity of islands relative to population, fresh water availability, and on-going social relationships between island and continental populations. Northern Channel Islanders seem to have been largely unaffected by this severe arid phase. In contrast, cultural changes on the southern Channel Islands were likely influenced by the climatically induced environmental changes. We suggest that productive marine conditions coupled with a dry terrestrial climate between 6.3 and 5.8 ka stimulated early village development and intensified fishing on the more remote southern islands. Contact with people on the adjacent southern California Coast increased during this time with increased participation in a down-the-line trade network extending into the western Great Basin and central Oregon. Genetic similarities between Middle Holocene burial populations on the southern Channel Islands and modern California Uto-Aztecan populations suggest Middle Holocene movement of people at this time from southern California desert environs westward to the southern islands, a migration perhaps stimulated by increased continental aridity.

Holocene surface-faulting earthquakes at the Spring Lake and North Creek Sites on the Wasatch Fault Zone: Evidence for complex rupture of the Nephi Segment

USGS Publications Warehouse

Duross, Christopher; Hylland, Michael D.; Hiscock, Adam; Personius, Stephen; Briggs, Richard; Gold, Ryan D.; Beukelman, Gregg; McDonald, Geg N; Erickson, Ben; McKean, Adam; Angster, Steve; King, Roselyn; Crone, Anthony J.; Mahan, Shannon

2017-01-01

The Nephi segment of the Wasatch fault zone (WFZ) comprises two fault strands, the northern and southern strands, which have evidence of recurrent late Holocene surface-faulting earthquakes. We excavated paleoseismic trenches across these strands to refine and expand their Holocene earthquake chronologies; improve estimates of earthquake recurrence, displacement, and fault slip rate; and assess whether the strands rupture separately or synchronously in large earthquakes. Paleoseismic data from the Spring Lake site expand the Holocene record of earthquakes on the northern strand: at least five to seven earthquakes ruptured the Spring Lake site at 0.9 ± 0.2 ka (2σ), 2.9 ± 0.7 ka, 4.0 ± 0.5 ka, 4.8 ± 0.8 ka, 5.7 ± 0.8 ka, 6.6 ± 0.7 ka, and 13.1 ± 4.0 ka, yielding a Holocene mean recurrence of ~1.2–1.5 kyr and vertical slip rate of ~0.5–0.8 mm/yr. Paleoseismic data from the North Creek site help refine the Holocene earthquake chronology for the southern strand: at least five earthquakes ruptured the North Creek site at 0.2 ± 0.1 ka (2σ), 1.2 ± 0.1 ka, 2.6 ± 0.9 ka, 4.0 ± 0.1 ka, and 4.7 ± 0.7 ka, yielding a mean recurrence of 1.1–1.3 kyr and vertical slip rate of ~1.9–2.0 mm/yr. We compare these Spring Lake and North Creek data with previous paleoseismic data for the Nephi segment and report late Holocene mean recurrence intervals of ~1.0–1.2 kyr for the northern strand and ~1.1–1.3 kyr for the southern strand. The northern and southern strands have similar late Holocene earthquake histories, which allow for models of both independent and synchronous rupture. However, considering the earthquake timing probabilities and per-event vertical displacements, we have the greatest confidence in the simultaneous rupture of the strands, including rupture of one strand with spillover rupture to the other. Ultimately, our results improve the surface-faulting earthquake history of the Nephi segment and enhance our understanding of how structural barriers influence normal-fault rupture.

Biogenic sedimentation beneath the California Current system for the past 30 kyr and its paleoceanographic significance

USGS Publications Warehouse

Gardner, J.V.; Dean, W.E.; Dartnell, P.

1997-01-01

A north-south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33?? to 42?? N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, Corg, and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time-space maps reveal a complex pattern of changes that do not follow a simple glacial-interglacial two-mode model. Biogenic sedimentation shows responses that are sometimes time-transgressive and sometimes coeval, and most of the responses show more consistency within a limited geographic area than any temporal consistency. Reconstructed conditions during late oxygen isotope stage 3 were more like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased during the last glacial interval in the central California region, and the waters of the southern California margin had relatively low productivity. Productivity on the southern Oregon margin was relatively low at the beginning of the last glacial interval, but by about 20 ka, productivity in this area significantly increased. This change suggests that the center of the divergence of the West Wind Drift shifted south at this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increased upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (<300 years) decrease in CaCO3, Corg, and biogenic opal occurred at 13 ka. The changes suggest a major reorientation of the atmospheric circulation in the North Pacific and western North America and the establishment of a strong seasonality in the central California region. A carbonate preservation event occurred at 10 ka that appears to reflect the uptake of CO2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers. The Holocene has been a period of relatively high productivity in the southern California margin, relatively strong coastal upwelling along the central California margin, relatively weak upwelling along the northern California margin, and the northward migration of the divergence zone of the West Wind Drift.

Mid-Brunhes magnetic excursions in marine isotope stages 9, 13, 14, and 15 (286, 495, 540, and 590 ka) at North Atlantic IODP Sites U1302/3, U1305, and U1306

NASA Astrophysics Data System (ADS)

Channell, J. E. T.

2017-02-01

Integrated Ocean Drilling Program (IODP) Site U1302/3 (Orphan Knoll, off Newfoundland) recorded magnetic excursions in marine isotope stages (MIS) 9a (at 286 ka) and 13a (at 495 ka). Sites U1306 and U1305 (Eirik Drift, off SE Greenland) record excursions in MIS 14a/b (at 540 ka) and 15b/c (at 590 ka). In the excursion intervals, magnetic measurements of continuous "u-channel" samples from multiple holes within site are augmented by measurements of cubic (8 cm3) discrete samples. The excursions lie in relative paleointensity (RPI) minima at each site and in RPI reference stacks, and correspond to dated intervals of 10Be overproduction in other deep-sea sediment records. Although observed at multiple holes at each site, and from u-channel and discrete samples, the excursions are not observed at all three sites, and often at only one of the three sites. Sporadic recording of these magnetic excursions, and excursions in general, is attributed to a combination of filtering by the process of acquisition of detrital remanent magnetization (DRM), postdepositional overprint of weak excursion magnetizations, the millennial or even centennial duration of directional excursions, and nonuniform sedimentation rates at these timescales in North Atlantic sediment drifts.

Vegetation Response to Climatic Variations in the southern African tropics during the Late- Pleistocene and Holocene

NASA Astrophysics Data System (ADS)

Beuning, K. R.; Zimmerman, K. A.; Ivory, S. J.; Cohen, A. S.

2007-12-01

Pollen records from Lake Malawi, Africa spanning the last 135 kyr show substantial and abrupt vegetation response to multiple episodes of extreme aridity during the mega-drought period (130-90 ka). In contrast, vegetation composition and relative abundance remained fairly constant throughout the last 75 ka with no significant change during the Last Glacial Maxima (LGM) (35-15 ka). During the extremely arid mega-drought time period, fluctuations in pollen production define three distinct zones. The first zone, from 123-117 ka, is characterized by increasing amounts of grass, and decreasing amounts of both Podocarpus and evergreen forest taxa (i.e. Celtis, Ixora, Myrica, Macaranga), which, when matched with charcoal data, suggests a short period of extreme aridity. The disappearance of Brachystegia in this interval in conjunction with a peak in Amaranthaceae suggests conversion of the surrounding miombo woodland to an open grassland community probably caused by increased seasonality with a more prolonged and arid dry season. Peak amounts of Podocarpus (30-40%) along with diminishing levels of grass distinguish zone two (117-105 ka). This assemblage defines zone 2 as a period marked by a cool, dry climate resulting in expansion of montane forest taxa to lower elevations. Marine palynological records from the Angola Margin and Congo Fan show similar peak Podocarpus percentages at this time (oxygen isotope stage 5d) indicating similar latitudinal climates across the African continent. Zone three (105-75 ka) shows the highest and most consistent levels of Poaceae. This evidence, along with markedly low levels of most other taxa, indicates that this period contained the most sustained long-lasting dry spells during the past 135 ka. This episode in African history was severe enough as to cause the disappearance of forest taxa such as Uapaca and Brachystegia as well as montane taxa ( Podocarpus, Olea spp. and Ericaceae) within the pollen source area of Lake Malawi. The resultant semi-desert vegetation would have been inhospitable for early humans living within or traveling through the Lake Malawi region.

Cold climate deglaciation prior to termination 2 implied by new evidence for high sea-levels at 132 KA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, R.G.

1992-01-01

Radioisotope dating of corals from reefs and beaches suggests a high sea stand just prior to termination 2. Lack of precision in the ages, stratigraphic uncertainties, and possible diagenetic alterations in the corals have prevented a widespread acceptance of this sea stand. These disadvantages can be avoided by an approach that uses differential uplift measurements to determine the duration of the interval of generally high sea-levels. The last interglacial terrace on Barbados has features indicating two intervals of constant sea-level: an older wave-cut at the inshore edge of the terrace, and a younger cut formed near present eustatic sea-level, belowmore » the crest, and just before the earliest Wisconsin glacial buildup. The differential uplift between these two features, measured at five locations having uplift rates between 0.18 and 0.39m/ka, yields a eustatic sea-level differences of 5.4m and a minimal duration of 12.1 [+-] 0.6ka between the two still stands. The assigned age of the younger wave-cut is 120 [+-] 0.5ka, based on sea-level regression due to ice sheet buildup implied by a Little Ice Age analog and rapidly falling Milankovitch summer insolation. The resulting minimal age of the first high sea-stand is 132.1 [+-] 1.1ka, about 7ka before termination 2. This age implies a major early deglaciation caused by a deficit of moisture transported to the great ice sheets, and occurring under relatively cold climate conditions.« less

Sediment geochemical records of productivity and oxygen depletion along the margin of western North America during the past 60,000 years: teleconnections with Greenland Ice and the Cariaco Basin

USGS Publications Warehouse

Dean, W.E.

2007-01-01

Many sediment records from the margins of the Californias (Alta and Baja) collected in water depths between 60 and 1200 m contain anoxic intervals (laminated sediments) that can be correlated with interstadial intervals as defined by the oxygen-isotope composition of Greenland ice (Dansgaard-Oeschger, D-O, cycles). These intervals include all or parts of Oxygen Isotope Stage 3 (OIS3; 60-24 cal ka), the Bo??lling/Allero??d warm interval (B/A; 15-13 cal ka), and the Holocene. This study uses organic carbon (Corg) and trace-element proxies for anoxia and productivity, namely elevated concentrations and accumulation rates of molybdenum and cadmium, in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom-water oxygen (BWO) conditions on open, highly productive continental margins. The main conclusion from these proxies is that during the last glacial interval (LGI; 24-15 cal ka) and the Younger Dryas cold interval (YD; 13-11.6 cal ka) productivity was lower and BWO levels were higher than during OIS3, the B/A, and the Holocene on all margins of the Californias. The Corg and trace-element profiles in the LGI-B/A-Holocene transition in the Cariaco Basin on the margin of northern Venezuela are remarkably similar to those in the transition on the northern California margin. Correlation between D-O cycles in Greenland ice with gray-scale measurements in varved sediments in the Cariaco Basin also is well established. Synchronous climate-driven changes as recorded in the sediments on the margins of the Californias, sediments from the Cariaco Basin, and in the GISP-2 Greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka. Millennial-scale cycles in productivity and oxygen depletion on the margins of the Californias demonstrate that the California Current System was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern North Pacific Ocean. It is likely that the Pacific and Atlantic Oceans were linked through the atmosphere. Warmer air temperatures during interstadials would have strengthened Hadley and Walker circulations, which, in turn, would have strengthened the subtropical high pressure systems in both the North Pacific and the North Atlantic, producing increased rainfall over the Cariaco Basin and increased upwelling along the margins of the Californias. ?? 2006 Elsevier Ltd. All rights reserved.

cyclostratigraphy, sequence stratigraphy and organic matter accumulation mechanism

NASA Astrophysics Data System (ADS)

Cong, F.; Li, J.

2016-12-01

The first member of Maokou Formation of Sichuan basin is composed of well preserved carbonate ramp couplets of limestone and marlstone/shale. It acts as one of the potential shale gas source rock, and is suitable for time-series analysis. We conducted time-series analysis to identify high-frequency sequences, reconstruct high-resolution sedimentation rate, estimate detailed primary productivity for the first time in the study intervals and discuss organic matter accumulation mechanism of source rock under sequence stratigraphic framework.Using the theory of cyclostratigraphy and sequence stratigraphy, the high-frequency sequences of one outcrop profile and one drilling well are identified. Two third-order sequences and eight fourth-order sequences are distinguished on outcrop profile based on the cycle stacking patterns. For drilling well, sequence boundary and four system tracts is distinguished by "integrated prediction error filter analysis" (INPEFA) of Gamma-ray logging data, and eight fourth-order sequences is identified by 405ka long eccentricity curve in depth domain which is quantified and filtered by integrated analysis of MTM spectral analysis, evolutive harmonic analysis (EHA), evolutive average spectral misfit (eASM) and band-pass filtering. It suggests that high-frequency sequences correlate well with Milankovitch orbital signals recorded in sediments, and it is applicable to use cyclostratigraphy theory in dividing high-frequency(4-6 orders) sequence stratigraphy.High-resolution sedimentation rate is reconstructed through the study interval by tracking the highly statistically significant short eccentricity component (123ka) revealed by EHA. Based on sedimentation rate, measured TOC and density data, the burial flux, delivery flux and primary productivity of organic carbon was estimated. By integrating redox proxies, we can discuss the controls on organic matter accumulation by primary production and preservation under the high-resolution sequence stratigraphic framework. Results show that high average organic carbon contents in the study interval are mainly attributed to high primary production. The results also show a good correlation between high organic carbon accumulation and intervals of transgression.

Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

USGS Publications Warehouse

Muhs, Daniel R.; Simmons, Kathleen R.; Schumann, R. Randall; Groves, Lindsey T.; Mitrovica, Jerry X.; Laurel, Deanna

2012-01-01

San Nicolas Island, California has one of the best records of fossiliferous Quaternary marine terraces in North America, with at least fourteen terraces rising to an elevation of ~270 m above present-day sea level. In our studies of the lowest terraces, we identified platforms at 38-36 m (terrace 2a), 33-28 m (terrace 2b), and 13-8 m (terrace 1). Uranium-series dating of solitary corals from these terraces yields three clusters of ages: ~120 ka on terrace 2a (marine isotope stage [MIS] 5.5), ~120 and ~100 ka on terrace 2b (MIS 5.5 and 5.3), and ~80 ka (MIS 5.1) on terrace 1. We conclude that corals on terrace 2b that date to ~120 ka were reworked from a formerly broader terrace 2a during the ~100 ka sea stand. Fossil faunas differ on the three terraces. Isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding San Nicolas Island. A mix of extralimital southern and extralimital northern species is found on terrace 2b, and extralimital northern species are on terrace 1. On terrace 2b, with its mixed faunas, extralimital southern species, indicating warmer than present waters, are interpreted to be from the ~120 ka high sea stand, reworked from terrace 2a. The extralimital northern species on terrace 2b, indicating cooler than present waters, are interpreted to be from the ~100 ka sea stand. The abundant extralimital northern species on terrace 1 indicate cooler than present waters at ~80 ka. Using the highest elevations of the ~120 ka platform of terrace 2a, and assuming a paleo-sea level of +6 m based on previous studies, San Nicolas Island has experienced late Quaternary uplift rates of ~0.25-0.27 m/ka. These uplift rates, along with shoreline angle elevations and ages of terrace 2b (~100 ka) and terrace 1 (~80 ka) yield relative (local) paleo-sea level elevations of +2 to +6 m for the ~100 ka sea stand and -11 to -12 m for the ~80 ka sea stand. These estimates are significantly higher than those reported for the ~100 ka and ~80 ka sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure.

Insights from a synthesis of old and new climate-proxy data from the Pyramid and Winnemucca lake basins for the period 48 to 11.5 cal ka

USGS Publications Warehouse

Benson, Larry; Smoot, J.P.; Lund, S.P.; Mensing, S.A.; Foit, F.F.; Rye, R.O.

2013-01-01

A synthesis of old and new paleoclimatic data from the Pyramid and Winnemucca lake basins indicates that, between 48.0 and 11.5·103 calibrated years BP (hereafter ka), the climate of the western Great Basin was, to a degree, linked with the climate of the North Atlantic. Paleomagnetic secular variation (PSV) records from Pyramid Lake core PLC08-1 were tied to the GISP2 ice-core record via PSV matches to North Atlantic sediment cores whose isotopic and(or) carbonate records could be linked to the GISP2 δ18O record. Relatively dry intervals in the western Great Basin were associated with cold Heinrich events and relatively wet intervals were associated with warm Dansgaard-Oeschger (DO) oscillations. The association of western Great Basin dry events with North Atlantic cold events (and vice versa) switched sometime after the Laurentide Ice Sheet (LIS) reached its maximum extent. For example, the Lahontan highstand, which culminated at 15.5 ka, and a period of elevated lake level between 13.1 and 11.7 ka were associated with cold North Atlantic conditions, the latter period with the Youngest Dryas event. Relatively dry periods were associated with the Bølling and Allerød warm events. A large percentage of the LIS may have been lost to the North Atlantic during Heinrich events 1 and 2 and may have resulted in the repositioning of the Polar Jet Stream over North America. The Trego Hot Springs, Wono, Carson Sink, and Marble Bluff tephras found in core PLC08-1 have been assigned GISP2 calendar ages of respectively, 29.9, 33.7, 34.1, and 43.2 ka. Given its unique trace-element chemistry, the Carson Sink Bed is the same as Wilson Creek Ash 15 in the Mono Lake Basin. This implies that the Mono Lake magnetic excursion occurred at approximately 34 ka and it is not the Laschamp magnetic excursion. The entrance of the First Americans into the northern Great Basin is dated to approximately 14.4 ka, a time when the climate was relatively dry. Evidence for human occupation of the Great Basin is lacking for the next 1100 years (y); i.e., the oldest western stemmed point site in the Great Basin dates to 13.3 ka. Two hypotheses are suggested for this cultural hiatus: (1) the climate had deteriorated to the point that people vacated the Great Basin, or (2) people moved to basin-bottom wetlands that persisted during the dry period, and then the subsequent Younger Dryas wet event erased the archaeological evidence deposited around the low-elevation wetland sites.

Denudational slope processes on weathered basalt in northern California: 130 ka history of soil development, periods of slope stability and colluviation, and climate change

NASA Astrophysics Data System (ADS)

McDonald, Eric; Harrison, Bruce; Baldwin, John; Page, William; Rood, Dylan

2017-04-01

The geomorphic history of hillslope evolution is controlled by multiple types of denudational processes. Detailed analysis of hillslope soil-stratigraphy provides a means to identify the timing of periods of slope stability and non-stability, evidence of the types of denudational processes, and possible links to climatic drivers. Moreover, the degree of soil formation and the presence of buried or truncated soils provide evidence of the relative age of alternating periods of colluviation and stability. We use evaluation of soil stratigraphy, for a small forested hillslope (<500 m of slope length) located in the Cascades of northern California, to elucidate both the timing and processes controlling 130 ka of hillslope evolution. The soils and slope colluvium are derived from highly weathered basalt. Stratigraphic interpretation is reinforced with soil profile development index (PDI) derived age estimates, tephrochronology, luminescence ages on colluvium, and He3 nuclide exposure dates. Soils formed along hilltop ridges are well developed and reflect deep (>2-3 m) in-situ weathering of the basalt bedrock. PDI age estimates and He3 exposure dates indicate that these hilltop soils had been in place for 100-130 ka, implying a long period of relative surface stability. At about 40-30 ka, soil stratigraphy indicates the onset of 3 distinct cycles of denudation of the hilltop and slopes. Evidence for changes in stability and onset of soil erosion is the presence of several buried soils formed in colluvium downslope of the hilltop. These buried soils have formed in sediment derived from erosion of the hilltop soils (i.e. soil parent material of previously weathered soil matrix and basalt cobbles). The oldest buried soil indicates that slope stability was re-established between 32-23 ka, with stability and soil formation lasting to about 10 ka. Soil-stratigraphy indicates that two additional intervals of downslope transport of sediment between 6-10 ka, and 2-5 ka. Soil properties indicate that the primary method of downslope transport is largely due to tree throw and faunal burrowing. Onset of slope instability at 40-30 ka appears to be related to changes in vegetation with establishment of a pine dominated forest (increase in tree throw) and/or onset of local faulting. By comparison, slope stability from 30-10 ka appears to be a related to the formation of a shrub dominated steppe and a decrease in tree throw. The two periods of slope erosion after 10 ka appear related to regional periods of pronounced channel incision. Results indicate that soil stratigraphy can provide a key record of slope evolution and related paleoenvironmental changes.

Comparison of Holocene marine paleoseismic records of two sectors of the Algerian margin: what's the reason for different responses from turbidites?

NASA Astrophysics Data System (ADS)

Cattaneo, Antonio; Babonneau, Nathalie; Ratzov, Gueorgui; Yelles, Karim; Bracène, Rabah; Bachir, Roza Si; Déverchere, Jacques

2016-04-01

The Algerian margin is at the slow convergence (~3mm/yr) of the African and European plates and it is affected by seismic activity linked to the presence of faults located in the coastal region and/or offshore. The historical seismicity record includes earthquakes located all along the margin from the west (1954 Orléansville M6.7; 1980 El Asnam M7.3), to the central area offshore Algiers (2003 Boumerdès M6.9, and also earthquakes of 1847, 1716 et 1365 AD), to the eastern area (two events offshore Djidjelli in 1856). Thanks to recent work on the signature of earthquakes in the deep offshore domain inferred from the analysis of successions of alternating turbidites and hemipelagites, the record of earthquakes could be extended back in time over most of the Holocene, at least in two analysed sectors offshore Kramis and Algiers. Offshore Kramis, thirteen coastal paleoquakes over the last 8 ka support clusters of 3 to 6 events with mean recurrence intervals of ˜300-600 years, separated by two periods of quiescence of ˜1.7 ka without major events on any fault. They imply alternation of broad phases of strain loading and shorter phases of strain release along the fault network (Ratzov et al., 2015). Offshore Algiers, thirty-six events are identified along the Algiers margin segment over the last 9 kyr and are tentatively interpreted as seismically triggered, including the historical events of 2003, 1716 and 1365 AD. The recurrence interval of events varies from 50 to 900 years with three quiescence periods of 800, 1400 and 500 years (7-6.2 ka BP, 5.4-4 ka BP, and 1.5-1 ka BP), supporting an irregular earthquake cyclicity. Overall, the marine paleosesimicity record of the two study areas appears rather different. In particular, slope failures offshore Algiers could occur more frequently because of the proximity of lower magnitude earthquakes, explaining the high occurrence of turbiditic events, while the recurring interval of stronger earthquakes could be more easily comparable in the two margin sectors. Other possible explanations include: i) difference in the tectonic behavior of distinct margin sectors; (ii) temporal and spatial variability in sedimentary processes, possibly due to changes in sediment availability; (iii) different distance of the seismic sources from the areas of sediment destabilisation on the continental slope. Ref. 
Ratzov et al. (2015) Geology 43,4,331-334.

Global diversity and oceanic divergence of humpback whales (Megaptera novaeangliae).

PubMed

Jackson, Jennifer A; Steel, Debbie J; Beerli, P; Congdon, Bradley C; Olavarría, Carlos; Leslie, Matthew S; Pomilla, Cristina; Rosenbaum, Howard; Baker, C Scott

2014-07-07

Humpback whales (Megaptera novaeangliae) annually undertake the longest migrations between seasonal feeding and breeding grounds of any mammal. Despite this dispersal potential, discontinuous seasonal distributions and migratory patterns suggest that humpbacks form discrete regional populations within each ocean. To better understand the worldwide population history of humpbacks, and the interplay of this species with the oceanic environment through geological time, we assembled mitochondrial DNA control region sequences representing approximately 2700 individuals (465 bp, 219 haplotypes) and eight nuclear intronic sequences representing approximately 70 individuals (3700 bp, 140 alleles) from the North Pacific, North Atlantic and Southern Hemisphere. Bayesian divergence time reconstructions date the origin of humpback mtDNA lineages to the Pleistocene (880 ka, 95% posterior intervals 550-1320 ka) and estimate radiation of current Northern Hemisphere lineages between 50 and 200 ka, indicating colonization of the northern oceans prior to the Last Glacial Maximum. Coalescent analyses reveal restricted gene flow between ocean basins, with long-term migration rates (individual migrants per generation) of less than 3.3 for mtDNA and less than 2 for nuclear genomic DNA. Genetic evidence suggests that humpbacks in the North Pacific, North Atlantic and Southern Hemisphere are on independent evolutionary trajectories, supporting taxonomic revision of M. novaeangliae to three subspecies. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Global diversity and oceanic divergence of humpback whales (Megaptera novaeangliae)

PubMed Central

Jackson, Jennifer A.; Steel, Debbie J.; Beerli, P.; Congdon, Bradley C.; Olavarría, Carlos; Leslie, Matthew S.; Pomilla, Cristina; Rosenbaum, Howard; Baker, C. Scott

2014-01-01

Humpback whales (Megaptera novaeangliae) annually undertake the longest migrations between seasonal feeding and breeding grounds of any mammal. Despite this dispersal potential, discontinuous seasonal distributions and migratory patterns suggest that humpbacks form discrete regional populations within each ocean. To better understand the worldwide population history of humpbacks, and the interplay of this species with the oceanic environment through geological time, we assembled mitochondrial DNA control region sequences representing approximately 2700 individuals (465 bp, 219 haplotypes) and eight nuclear intronic sequences representing approximately 70 individuals (3700 bp, 140 alleles) from the North Pacific, North Atlantic and Southern Hemisphere. Bayesian divergence time reconstructions date the origin of humpback mtDNA lineages to the Pleistocene (880 ka, 95% posterior intervals 550–1320 ka) and estimate radiation of current Northern Hemisphere lineages between 50 and 200 ka, indicating colonization of the northern oceans prior to the Last Glacial Maximum. Coalescent analyses reveal restricted gene flow between ocean basins, with long-term migration rates (individual migrants per generation) of less than 3.3 for mtDNA and less than 2 for nuclear genomic DNA. Genetic evidence suggests that humpbacks in the North Pacific, North Atlantic and Southern Hemisphere are on independent evolutionary trajectories, supporting taxonomic revision of M. novaeangliae to three subspecies. PMID:24850919

Hydroclimatic variability in the Levant during the early last glacial (˜ 117-75 ka) derived from micro-facies analyses of deep Dead Sea sediments

NASA Astrophysics Data System (ADS)

Neugebauer, I.; Schwab, M. J.; Waldmann, N. D.; Tjallingii, R.; Frank, U.; Hadzhiivanova, E.; Naumann, R.; Taha, N.; Agnon, A.; Enzel, Y.; Brauer, A.

2016-01-01

The new sediment record from the deep Dead Sea basin (ICDP core 5017-1) provides a unique archive for hydroclimatic variability in the Levant. Here, we present high-resolution sediment facies analysis and elemental composition by micro-X-ray fluorescence (µXRF) scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca. 117 to 75 ka, i.e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a) up to several metres thick, greenish sediments of alternating aragonite and detrital marl laminae (aad) and (b) thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at ˜ 110-108 ± 5 and ˜ 93-87 ± 7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio) and low global sea levels during Marine Isotope Stage (MIS) 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in situ beach deposit. Two intervals of higher lake stands at ˜ 108-93 ± 6 and ˜ 87-75 ± 7 ka correspond to interstadial conditions in the central Mediterranean, i.e. pollen zones St. Germain I and II in Monticchio, and Greenland interstadials (GI) 24+23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These apparent correlations suggest a close link of the climate in the Levant to North Atlantic and Mediterranean climates during the time of the build-up of Northern Hemisphere ice shields in the early last glacial period.

Heinrich Events in the Southern Hemisphere: A Tropical Trigger?

NASA Astrophysics Data System (ADS)

Farmer, E. C.; Choi, W. S.; Quadri, M.

2006-12-01

Heinrich events, or periodic pulses of ice-rafted debris into the North Atlantic, have long been envisioned as having a high-latitude trigger. This trigger is most often cited as internal ice-sheet dynamics. McIntyre and Molfino (1996) proposed a tropical trigger for Heinrich Events: they suggested that precession-related strengthening of the North African monsoonal atmospheric circulation would alter oceanic circulation in such a way as to reduce heat transport to the high latitudes. Discovery of possible evidence (Mg/Ca ratios and faunal abundance) for Heinrich Event 1 (H1) in the Benguela upwelling region (Farmer et al. 2005) stimulated a search for a Heinrich Event 2 (H2) signal. From the review by Hemming (2004), we estimated the time horizon in which we would expect to find H2 as 22.4 - 26.8 ka. We extrapolated the published ODP1084B age model (Farmer et al. 2005) to estimate the depth interval of this time horizon, and counted the relative abundance of the four dominant species of planktonic foraminifera (G. inflata, G. bulloides, N. pachyderma right- and left-coiling) in each sample within this interval. We found an interval spanning five centimeters, or approximately 22.9 to 23.1 ka, in which the relative abundance of N. pachyderma (left-coiling) rose to a an average of 31.5%. Compared to the average level of 23.5% in the surrounding samples, and our pooled standard deviation of 3.4%, this shift appears significant. Increases in relative abundance of N. pachyderma (left-coiling) in earlier intervals are associated with decreased Mg/Ca-based sea surface temperatures (SSTs) and are inferred to be a likely result of increased upwelling (Farmer et al. 2005). Although this new interval is shorter than would be expected from Heinrich event studies elsewhere, the shift in relative abundance of N. pachyderma (left-coiling) is consistent with an H2 signal. Better age control is needed to constrain the timing of this event, however, and data from an additional proxy such as Mg/Ca is needed to confirm the signal.

Sedimentary record on the Indian Summer Monsoon since the Last Glacial Maximum: Evidence from the southeastern Andaman Sea

NASA Astrophysics Data System (ADS)

Shi, Xuefa; Liu, Shengfa; Cao, Peng; Khokiattiwong, Somkiat; Kornkanitnan, Narumol

2016-04-01

The Indian Summer Monsoon (ISM) generated by across-equatorial pressure gradient between the Asian continent and the southern Indian Ocean is a major component of the Asian monsoon system and establishes interactions among the ocean, land and atmosphere. Provenance and paleoclimate changes in the Andaman Sea during the last 26 ka were reconstructed from high-resolution records of grain-size, major elements and Sr-Nd isotopes in core ADM-9. The values of ɛNd(0) and 87Sr/86Sr were in good agreement with those of Irrawaddy River sediments, indicating a common source of origin. Two sensitive grain-size intervals (3.4-7.5 and 16.8-21.2 μm) were identified; the former was controlled primarily by sea-level change, whereas the latter was related to Irrawaddy River discharge and South-west Current transport driven by the ISM. Proxies of chemical weathering (K/Al) and terrigenous input (Ti/Ca) coupled with sensitive grain-size interval (16.8-21.2 μm population) revealed that the ISM was weak during ~15-26 ka BP and then strengthened gradually to a maximum during ~7-9 ka BP; subsequently, the ISM exhibited a generally declining trend to ~2 ka BP. The variation of the ISM recorded in this work is consistent with ISM variations observed in an open area in the northern Indian Ocean and in adjacent continents, implying the evolution of the Asia summer monsoon since 26 ka.

Last Deglaciation Events (16.1-11.4 cal-Ka) Recorded in a Speleothem from DeSoto Caverns, Alabama, U.S.A.

NASA Astrophysics Data System (ADS)

Lambert, W. J.; Aharon, P.; Hellstrom, J.

2007-12-01

Whereas the rapid climate swings that occurred during the last deglaciation have been well documented in the Greenland ice cores, their cause/s continue to be a subject of heated debate. Clearly, more geographically dispersed records are required in order to provide better insight into the history of deglaciation, and by extension into the cause/s of the abrupt climate shifts. Particularly scarce are continental deglaciation records from the southeast North America whose atmospheric conditions were controlled by the retreating Laurentide Ice Sheet to the north and the Gulf of Mexico warm waters to the south. In order to remedy the absence of deglaciation records in the Southeast USA in general, and the Gulf Coast in particular, we have initiated a study of a 55-cm long stalagmite (DSSG-2) from the DeSoto Caverns in Childersburg, Alabama (33° 18'N, 86° 17'W). Seven radiocarbon AMS and eighteen U/Th TIMS dates reveal that the continuously layered stalagmite covers the time interval 31 to 11.4 cal-Ka at growth rates varying from 61 μm/decade at the start of deglaciation and up to 2700 μm/decade close to its termination. The combination of unusually high growth rates, pristine aragonite mineralogy and tight sampling (n=602) afforded generation of high fidelity δ13C and δ18O records from about 16.1 to 11.4 cal-Ka whose high resolution is comparable with the contemporaneous Greenland ice core records. The stalagmite δ18O record shows excellent agreement in relative amplitude shifts and timing of abrupt and brief cold reversals (Oldest Dryas, Older Dryas, Inter-Allerød Cold Period) that punctuated the overall trend of deglaciation warming (Bølling/Allerød period). The succeeding Younger Dryas is depicted in the stalagmite by rapid positive shifts in δ18O and δ13C of 1.3‰ and 2.3‰ (V-PDB) relative to the baseline mean value and its start and termination (12.7-11.8 Ka) are concordant within error with the dates reported from GISP2 ice core (12.82-11.60 Ka). We interpret the negative isotope shifts during the warm B/A interval and the positive shifts during the cold ODs and YD intervals as being primarily an expression of rapid shifts in rainfall amount alternating between excessive floods and severe droughts. The excellent correspondence observed between the DeSoto stalagmite and the GISP2 isotope records further suggests that disturbances in thermohaline circulation caused by repeated fresh water discharge episodes into the North Atlantic from the retreating American and European ice sheets were the principal governing factors controlling the documented isotope shifts in the Southeastern USA and Greenland.

Mechanisms that triggered hydrological changes in the tropical lowlands of northern Central America during the past 85 ka

NASA Astrophysics Data System (ADS)

Sylvestre, Florence; Perez, Liseth; Paillès, Christine; Schwalb, Antje; Kutterolf, Steffen; Brenner, Mark; Curtis, Jason; Ariztegui, Daniel; Anselmetti, Flavio; Hodell, David

2016-04-01

Orbital precession is thought to have been the major mechanism that drove precipitation and temperature changes in the tropics during the Quaternary. Other mechanisms, however, such as the rate of meridional overturning of the ocean, tropical carbon production, atmospheric methane and water vapour, and hence the modes of tropical ocean-atmosphere interactions, need to be considered. Few sites are suitable to explore the sensitivity of these different components of the climate system or their relative contributions to climate conditions through time. We present new, continuous, high-resolution paleoenvironmental and paleoclimate results from a long sediment sequence collected in Lake Petén Itzá, northern Guatemala. The composite core (PI-6) was dated using radiocarbon and tephra stratigraphy and spans the last ~85 ka. We inferred past conditions using aquatic bioindicators (diatoms, ostracods) that are abundant in the sediment and respond rapidly to climate and environmental changes, especially lake-level changes. Lake-level highstands occurred during the intervals 80-61 ka, 40-32 ka, 23-16 ka, and with a lower-amplitude episode between 47 and 45 ka. Sharp transitions from humid to arid, and arid to humid conditions are recorded during Heinrich events H1, H2, H3, and H4, whereas H5 and H6 correspond to persistent low lake levels. Lake-level fluctuations are largely in phase with precession cycles, except before 50 ka. Lake status, however, is not always in phase with expectations from insolation forcing. For instance, during MIS 4 (ca. 71-57 ka) and the Last Glacial Maximum (ca. 23-19 ka), lake level was high in Petén Itzá, implying moister conditions, whereas low lake level would be expected because of the southerly position of the ITCZ during those times. The moist conditions are attributed to intensified cold air masses during glacial stages, coming mainly from the North American interior and bringing precipitation during winter (Hodell et al., 2008). Moreover, between 80 and 61 ka, fresher sea surface waters are inferred from the adjacent oceans, associated with globally warmer temperatures, implying moister conditions for the Yucatán Peninsula (Leduc et al., 2007). Our results highlight shifts through time in the major forcing mechanisms that triggered water-level changes in Lake Petén Itzá. These new paleoenvironmental proxy data will be useful for selecting parameters to be included in future modelling experiments that test forcing of tropical climatic changes during the late Quaternary. Hodell, D.A., Anselmetti, F.S., Ariztegui, D., Brenner, M., Curtis, J.H., Gilli, A., Grzesik, D.A., Guilderson, T.J., Muller, A.D., Bush, M.B., Correa-Metrio, Y.A., Escobar, J., and Kutterolf, S., 2008. An 85-ka Record of Climate Change in Lowland Central America, Quaternary Science Reviews, 27, 1152- 1165. Leduc, G., Vidal, L., Tachikawa, K., Rostek, F., Sonzogni, C., Beaufort, L., Bard, E., 2007. Moisture transport across Central America as a positive feedback on abrupt climatic changes. Nature, 445, 908-911.

Paleoclimate change in the Nakuru basin, Kenya, at 119 - 109 ka derived from δ18Odiatom and diatom assemblages and 40Ar/39Ar geochronology

NASA Astrophysics Data System (ADS)

Bergner, Andreas; Deino, Alan; Leng, Melanie; Gasse, Francoise

2016-04-01

A 4.5m-thick diatomite bed deposited during the cold interval of the penultimate interglacial at ~119 - 109 ka documents a period in which a deep freshwater lake filled the Nakuru basin in the Central Kenya Rift (CKR), East Africa. Palaeohydrological conditions of the basin are reconstructed for the paleolake highstand using δ18Odiatom and characterization of diatom assemblages. The age of the diatomite deposit is established by precise 40Ar/39Ar-dating of intercalated pumice tuffs. The paleolake experienced multiple hydrological fluctuations on sub-orbital (~1,500 to 2,000 years) time scales. The magnitude of the δ18Odiatom change (+/- 3‰) and significant changes in the plankton-littoral ratio of the diatom assemblage (+/- 25%) suggest that the paleolake record can be interpreted in the context of long-term climatic change in East Africa. Using 40Ar/39Ar age control and nominal diatomite-sedimentation rates we establish a simplified age model of paleohydrological vs. climatic change, from which we conclude that more humid conditions prevailed in equatorial East Africa during the late Pleistocene over a relatively long time interval of several thousands years. Then, extreme insolation at eccentricity maximum and weakened zonal air-pressure gradients in the tropics favored intensified ITCZ-like convection over East Africa and deep-freshwater lake conditions.

Last interglacial plant macrofossils and climates from Ziegler Reservoir, Snowmass Village, Colorado, USA

USGS Publications Warehouse

Strickland, Laura E.; Baker, Richard G.; Thompson, Robert S.; Miller, Dane M.

2014-01-01

Ninety plant macrofossil taxa from the Ziegler Reservoir fossil site near Snowmass Village, Colorado, record environmental changes at high elevation (2705 m asl) in the Rocky Mountains during the Last Interglacial Period. Present-day vegetation is aspen forest (Populus tremuloides) intermixed with species of higher (Picea, Abies) and lower (Artemisia, Quercus) elevations. Stratigraphic units 4–13 contain montane forest taxa found near the site today and several species that today generally live at lower elevations within (Abies concolor, Lycopus americanus) and outside Colorado (Najas flexilis). These data suggest near-modern climatic conditions, with slightly warmer summer and winter temperatures. This montane forest period was succeeded by a shorter treeless interval (Unit 14) representing colder and/or drier conditions. In units 15–16, conifer trees reoccur but deciduous and herb taxa are lacking, suggesting a return to warmer conditions, although cooler than during the earlier forest period. Comparison of these inferred paleoclimatic changes with the site's geochronologic framework indicates that the lower interval of sustained warmth correlates with late MIS 6–early 5b (~ 138–94 ka), the cold interval with MIS 5b (~ 94–87 ka), and the uppermost cool assemblages with MIS 5a (~ 87–77 ka).

Evidence for insolation and Pacific forcing of late glacial through Holocene climate in the Central Mojave Desert (Silver Lake, CA)

NASA Astrophysics Data System (ADS)

Kirby, Matthew E.; Knell, Edward J.; Anderson, William T.; Lachniet, Matthew S.; Palermo, Jennifer; Eeg, Holly; Lucero, Ricardo; Murrieta, Rosa; Arevalo, Andrea; Silveira, Emily; Hiner, Christine A.

2015-09-01

Silver Lake is the modern terminal playa of the Mojave River in southern California (USA). As a result, it is well located to record both influences from the winter precipitation dominated San Bernardino Mountains - the source of the Mojave River - and from the late summer to early fall North American monsoon at Silver Lake. Here, we present various physical, chemical and biological data from a new radiocarbon-dated, 8.2 m sediment core taken from Silver Lake that spans modern through 14.8 cal ka BP. Texturally, the core varies between sandy clay, clayey sand, and sand-silt-clay, often with abrupt sedimentological transitions. These grain-size changes are used to divide the core into six lake status intervals over the past 14.8 cal ka BP. Notable intervals include a dry Younger Dryas chronozone, a wet early Holocene terminating 7.8 - 7.4 cal ka BP, a distinct mid-Holocene arid interval, and a late Holocene return to ephemeral lake conditions. A comparison to potential climatic forcings implicates a combination of changing summer - winter insolation and tropical and N Pacific sea-surface temperature dynamics as the primary drivers of Holocene climate in the central Mojave Desert.

Advantages of Repeated Low Dose against Single High Dose of Kainate in C57BL/6J Mouse Model of Status Epilepticus: Behavioral and Electroencephalographic Studies

PubMed Central

Beamer, Edward; Sills, Graeme J.; Thippeswamy, Thimmasettappa

2014-01-01

A refined kainate (KA) C57BL/6J mouse model of status epilepticus (SE) using a repeated low dose (RLD) of KA (5 mg/kg, intraperitoneal; at 30 min intervals) was compared with the established single high dose (SHD) of KA (20 mg/kg, intraperitoneal) model. In the RLD group, increased duration of convulsive motor seizures (CMS, Racine scale stage ≥3) with a significant reduction in mortality from 21% to 6% and decreased variability in seizure severity between animals/batches were observed when compared to the SHD group. There was a significant increase in the percentage of animals that reached stage-5 seizures (65% versus 96%) in the RLD group. Integrated real-time video-EEG analysis of both groups, using NeuroScore software, revealed stage-specific spikes and power spectral density characteristics. When the seizures progressed from non-convulsive seizures (NCS, stage 1–2) to CMS (stage 3–5), the delta power decreased which was followed by an increase in gamma and beta power. A transient increase in alpha and sigma power marked the transition from NCS to CMS with characteristic ‘high frequency trigger’ spikes on the EEG, which had no behavioral expression. During SE the spike rate was higher in the RLD group than in the SHD group. Overall these results confirm that RLD of KA is a more robust and consistent mouse model of SE than the SHD of KA mouse model. PMID:24802808

Lake Level Changes in the Mono Basin During the Last Deglacial Period

NASA Astrophysics Data System (ADS)

Wang, X.; Ali, G.; Hemming, S. R.; Zimmerman, S. R. H.; Stine, S. W.; Hemming, G.

2014-12-01

Mono Basin, located in the southwestern corner of the US Great Basin, has long been known to have experienced large lake level changes, particularly during the last deglaciation. But until recently it was not possible to establish a reliable lake level time series. We discovered many visually clean, white, shiny, dense calcite samples in the basin, associated with tufa deposits from high terraces. Their low thorium, but high uranium contents allow precise and reproducible U/Th age determinations. A highly resolved history of a minimum lake level through the last deglaciation can therefore be inferred based on sample locations and their ages. We found that the lake level reached ~2030 m asl at ~20.4 ka, evidenced by calcite coatings on a tufa mound at the upper Wilson Creek. The lake then rose to ~2075 m by ~19.1 ka, shown by calcite cements on conglomerates from the Hansen Cut terrace. The lake climbed to at least ~2140 m at ~15.9 ka, indicated by beach calcites from the east Sierra slope. Such timing of the highest lake stand, occurring within Heinrich Stadial 1, is reinforced by U/Th dates on calcite coatings from widespread locations in the basin, including the Bodie Hills and Cowtrack Mountains. The lake then dropped rapidly to ~2075 m at ~14.5 ka. It stood near this height over the next ~300 years, evidenced by a few-centimeter thick, laminated calcite rims on the Goat Ranch tufa mounds. It subsequently plunged to ~2007 m at ~13.8 ka, indicated by calcite coatings from cemetery road tufa mounds. The lake level came back to ~2030 m at ~12.9 ka, as seen in upper Wilson Creek tufa mounds. The lake level had a few fluctuations within the Younger Dryas, and even shot up to ~2075 m at ~12.0 ka. It then fell to levels in accord with Holocene climatic conditions. Relative to the present lake level of ~1950 m, Mono Lake broadly stood high during Heinrich Stadial 1 and Younger Dryas, when the climate was extremely cold over the North Atlantic, and the Asian monsoon was much weakened. When the climate shifted from cold to warm, the lake dropped significantly, during the transition between Heinrich Stadial 1 and the Bølling time interval, and then during the Allerød period. The U/Th ages on the tufa samples therefore not only establish a highly resolved chronology of hydroclimate history in the Mono Basin, but also put the lake level oscillations in a global context.

Unusually low rates of slip on the Santa Rosa Range fault zone, northern Nevada

USGS Publications Warehouse

Personius, S.F.; Mahan, S.A.

2005-01-01

The Santa Rosa Range fault zone (SRRFZ) is one of the most topographically prominent normal fault systems in the northern Basin and Range province of the western United States. It has been assigned high rates of vertical slip by others and has been identified as a possible site of the future extension of the central Nevada seismic belt (CNSB). We use detailed trench mapping and luminescence dating to estimate displacements and timing of the last several large-magnitude paleoearthquakes on the southern part of the SRRFZ at a trench site near Orovada, Nevada. Coseismic vertical displacements ranged from 1 to 2.8 m for each of the last four events. Luminescence ages provide time limits for the last three events of 125-155 ka, 90-108 ka, and 11-16 ka. These data yield recurrence intervals of 17-65 k.y. and 74-97 k.y. and an elapsed time of 11-16 k.y. since the youngest event. Slip-rate determinations at the Orovada site are complicated by multiple fault strands, but rates calculated from a variety of data are surprisingly low (0.01-0.16 mm/yr), given the topographic prominence of the Santa Rosa Range. A lack of compelling patterns in a comparison of paleoseismic parameters indicate that the SRRFZ is no more likely a location for a large-magnitude earthquake than previously identified seismic gaps or along faults that lie directly north of the CNSB.

Piezomagnetic behavior of Fe-Al-B alloys

NASA Astrophysics Data System (ADS)

Bormio-Nunes, Cristina; Hubert, Olivier

2015-11-01

For the first time, the piezomagnetic behavior of polycrystalline Fe-Al-B alloys is accessed. Piezomagnetic factors of up to 4.0 kA m-1/MPa were reached for an interval of applied compressive stresses between 0 and -140 MPa. The experimental results together with a powerful multiscale and biphasic modeling allowed the general understanding of the magnetostrictive and piezomagnetic behaviors of these materials. The magnetic and mechanical localizations as well as homogeneous stresses were considered in the modeling and are associated to the intrinsic presence of the Fe2B phase. The interplay of the magnetocrystalline anisotropy, initial susceptibility, saturation magnetostriction and texture were quantified by the model and compared to the experimental results. An improvement of the piezomagnetic factor to 15 kA m-1/MPa is predicted, for an alloy containing 20% of aluminum, by getting an adequate texture near < 100 > directions.

Development of In Vitro Correlate Assays of Immunity to Infection with Yersinia Pestis

DTIC Science & Technology

2007-05-01

cynomolgus macaques (CM) and African green (Chlorocebus aethiops) monkeys (AGM) vaccinated s.c. three times at 4-week intervals with the F1-V fusion...Yersinia pestis in African green monkeys . Arch. Pathol. Lab. Med. 120:156–163. 15. Faure, K., J. Fujimoto, D. W. Shimabukuro, T. Ajayi, N. Shime, K...A. Kuwae, C. Sasakawa, and S. Imajoh-Ohmi. 1999. Shigella flexneri YSH6000 induces two types of cell death, apoptosis and oncosis, in the

The Preboreal-like Asian monsoon climate in the early last interglacial period recorded from the Dark Cave, Southwest China

NASA Astrophysics Data System (ADS)

Jiang, Xiuyang; He, Yaoqi; Wang, Xiaoyan; Sun, Xiaoshuang; Hong, Hui; Liu, Juan; Yu, Tsai-Luen; Li, Zhizhong; Shen, Chuan-Chou

2017-08-01

Transitions of glacial-interglacial cycles are critical periods for Quaternary climate shifts. Here, we present new, decadal resolution Asian summer monsoon (ASM) record from three stalagmites obtained from the Dark Cave in southwestern China over 130-114 thousand years ago (ka, before CE 1950). Chronology was anchored by 28 230Th dates with typical uncertainties of ±0.3-1.0 kyr, allowing an assessment of timing and transition of climate changes during the onset and end of the last interglacial. An agreement between this new and previous stalagmite δ18O records supports that summer insolation predominates orbital-scale ASM evolution. A 2-3 kyr-long gradually increasing ASM period, analogous to the classical Preboreal episode in the early Holocene, follows the termination of a weak monsoon interval at 129.0 ± 0.8 ka. This finding suggests a strong influence of high-latitude ice-sheet dynamics on Asian monsoonal conditions during the early interglacial period. An abrupt end of the marine isotope stage 5e at 118.8 ± 0.6 ka was probably caused by the internal climate system threshold effects.

Chronostratigraphy in karst records from the Epipaleolithic to the Mid/Early Neolithic (c. 13.0-6.0 cal ka BP) in the Catalan Coastal Ranges of NE Iberia: environmental changes, sedimentary processes and human activity

NASA Astrophysics Data System (ADS)

Bergadà, M. Mercè; Cervelló, Josep M.; Edo, Manel; Cebrià, Artur; Oms, F. Xavier; Martínez, Pablo; Antolín, Ferran; Morales, Juan Ignacio; Pedro, Mireia

2018-03-01

The stratigraphic, sedimentary and palaeoenvironmental features reflected in cavities in the Catalan Coastal Ranges of NE Iberia (Can Sadurní and Guineu caves) characterize the periods of pronounced climatic and human complexity that occurred c. 13.0-6.0 cal ka BP. This includes the stages of the Younger Dryas and Mid/Early Holocene, the latter being one of the periods of so-called Rapid Climatic Changes (RCCs). These caves, like others in Mediterranean contexts, are the result of an old duct originating in the saturated zone of the karst system and open to the outside; recording a succession of different detrital and anthropic episodes of the Epipaleolithic, Mesolithic and Neolithic communities. From this study it can be seen that paleoclimatic events do not always present clear signals in the karst records, especially c. 12.7-7.4 cal ka BP, corresponding to the Epipaleolithic and Mesolithic. It is characterized by a stratigraphic discontinuity in which there are phases with predominantly detrital sedimentation alternating with hiatus intervals. Detrital sedimentation formed by fine material colluvium with gravitational movements or solifluction processes in fresh and humid conditions. It appears in the following chronological intervals: 12.7-12.2 cal ka BP, 11.5/11.1-10.7/10.4 cal ka BP and 8.2-8.0 cal ka BP (less humid). Hiatus phases are represented in the rest of the sequence up to c. 7.4 cal ka BP. From the sedimentary point of view these stages of hiatus are indicative of phases of stability or lack of episodes with seasonal contrasts; a fact that would cause interruptions to detrital deposition in the interior of the caves. In contrast, in the period c. 7.4 to 6.0 cal ka BP, attributed to the Middle and Early Neolithic, there is a certain stratigraphic continuity. From the sedimentary point of view it is distinguished by a variability of processes that responds to accumulative episodes of short duration characteristic of morphogenesis of the slopes in an arid Mediterranean environment, identified in our records as RCCs, (c. 7.4-7.2 cal ka BP- Cardial Neolithic; c. 6.8-6.3 cal ka BP-Early Postcardial Middle Neolithic and c. 6.2-5.7 cal ka BP- Late Postcardial Middle Neolithic) alternating with episodes of stability, more humid and coinciding with a better sedimentary record of the pastoral activity in the cavities during Epicardial and Late Cardial Neolithic (c. 7.1-6.7 cal ka BP) and Postcardial Middle Neolithic (c. 6.6-5.9 cal ka BP). It is during this period that Holocene climate variability has better resolution in caves in the Catalan Coastal Ranges of NE Iberia.

Late Quaternary tephrostratigraphy of Baegdusan and Ulleung volcanoes using marine sediments in the Japan Sea/East Sea

NASA Astrophysics Data System (ADS)

Lim, Chungwan; Toyoda, Kazuhiro; Ikehara, Ken; Peate, David W.

2013-07-01

Only Ulleung and Baegdusan volcanoes have produced alkaline tephras in the Japan Sea/East Sea during the Quaternary. Little is known about their detailed tephrostratigraphy, except for the U-Oki and B-Tm tephras. Trace element analysis of bulk sediments can be used to identify alkaline cryptotephra because of the large compositional contrast. Five sediment cores spanning the interval between the rhyolitic AT (29.4 ka) and Aso-4 (87 ka) tephras were analyzed using an INAA scanning method. Source volcanoes for the five detected alkaline cryptotephra were identified from major element analyses of hand-picked glass shards: Ulleung (U-Ym, and the newly identified U-Sado), and Baegdusan (B-J, and the newly identified B-Sado and B-Ym). The eruption ages of the U-Ym, U-Sado, B-J, B-Sado, and B-Ym tephras are estimated to be 38 ka, 61 ka, 26 ka, 51 ka, 68-69 ka, and 86 ka, respectively, based on correlations with regional-scale TL (thinly laminated) layer stratigraphy (produced by basin-wide changes in bottom-water oxygen levels in response to millennium-scale paleoclimate variations). This study has allowed construction of an alkaline tephrostratigraphical framework for the late Quaternary linked to global environmental changes in the Japan Sea/East Sea, and improves our knowledge of the eruptive histories of Ulleung and Baegdusan volcanoes.

The timing and duration of the Last Interglacial Asian Monsoon

NASA Astrophysics Data System (ADS)

Yuan, D.; Cheng, H.; Edwards, R.; Kelly, M.; Qing, J.; Lin, Y.; Zhang, M.

2002-12-01

An accurate estimate for the timing and duration of regional and global climate change associated with the Last Interglacial is important for elucidating climate change mechanisms. We present a 230Th-dated δ18O record of 2 stalagmites (D3 and D4) from Dongge Cave, southern China (25°N, 109°E, an area affected by East Asian and Indian Monsoons), which record Asian Monsoon history over 3 periods, 160-110 ka, 65-43 ka and 15.5 ka - present. The stalagmites have different precipitation environments and water flow paths as indicated by different growth histories, growth rates and δ234U values. D3 grew faster between 123-118 ka (12 vs. 0.4 cm/ka), but D4 grew faster between 138-126 ka (3.4 vs. 0.7 cm/ka). The mean initial δ234U value of D3 is -272 (range of -261 to -287). D4 values are higher (mean = -78, range of -27 to -160). Despite these differences, both have similar large δ18O variations for the interval over which both were active (148 to 113 ka), suggesting that water-rock interactions and kinetic fractionation did not affect δ18O values significantly. Dongge Cave stalagmites exhibit features similar to the Younger Dryas (YD) and the Bolling/Allerod as recorded in Greenland ice cores (GISP, 1997) and stalagmites from Hulu Cave, eastern China (Wang et al., 2001). The Dongge YD lies between 12640 +/-140 and 11550 +/-80 years BP, synchronous with Greenland and Hulu Cave YD analogues. Similar to Hulu Cave, light Dongge Cave δ18O excursions correspond to heavy isotopic excursions in Greenland, consistent with a positive correlation between the intensity of the Asian summer monsoon and Greenland temperature. The most prominent feature in the Dongge record is a peak that approximates a square wave and is contemporaneous with at least portions of the Last Interglacial sea level high. Dongge Termination II is a large, abrupt negative shift in δ18O (>3 per mil). The mid-point is at 129.3 +/-0.9 ka, based on direct dating of D4. D3 gives an age indistinguishable from this value. If D4 growth rate is linear over the transition, as implied by long term stable growth rates (from 144 to 124 ka), the transition takes less than 500 y, with most of it taking less than 200 y. The Dongge Last Interglacial also ends with an abrupt δ18O shift (about 4 per mil). The midpoint is at 119.6 +/-0.6 ka based on direct dating of D3. D4 gives an age indistinguishable from this value. Assuming linear growth, the main portion of the transition took less than 700 y. Combining the onset and end ages of the Dongge Last Interglacial, the duration is 9.7 +/-1.1 ka, from 129.3 +/-0.9 ka to 119.6 +/-0.6 ka, remarkably similar to some estimates of full Last Interglacial sea levels. The timing is broadly consistent with orbital forcing of the Monsoon, although the abrupt shifts require the involvement of other mechanisms (e.g. changes in circulation). Dongge Termination II lags Devils Hole Termination II, some fraction of sea level Termination II, and likely Vostok temperature, Vostok CO2, and eastern Pacific sea surface temperature. However, there is some evidence that it coincides within error with the final rise in sea level to full Last Interglacial elevations. It may well be that Monsoon Termination II is an orbitally-forced event at the end of a sequence of events not directly caused by orbital forcing. As such it may mark the inception of full interglacial conditions world-wide. Orbital forcing may be necessary for full interglacial conditions, but not for many of the shifts toward interglacial conditions observed to prior to Dongge Termination II.

Late Pleistocene climate change and landscape dynamics in the Eastern Alps: the inner-alpine Unterangerberg record (Austria)

PubMed Central

Starnberger, Reinhard; Drescher-Schneider, Ruth; Reitner, Jürgen M.; Rodnight, Helena; Reimer, Paula J.; Spötl, Christoph

2013-01-01

Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ∼120–110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ∼70–60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ∼55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ∼45 ka and/or was truncated by ice during the Last Glacial Maximum. PMID:23805019

Geochronology and paleoenvironment of pluvial Harper Lake, Mojave Desert, California, USA

USGS Publications Warehouse

Garcia, Anna L.; Knott, Jeffrey R.; Mahan, Shannon; Bright, Jordan

2014-01-01

Accurate reconstruction of the paleo-Mojave River and pluvial lake (Harper, Manix, Cronese, and Mojave) system of southern California is critical to understanding paleoclimate and the North American polar jet stream position over the last 500 ka. Previous studies inferred a polar jet stream south of 35°N at 18 ka and at ~ 40°N at 17–14 ka. Highstand sediments of Harper Lake, the upstream-most pluvial lake along the Mojave River, have yielded uncalibrated radiocarbon ages ranging from 24,000 to > 30,000 14C yr BP. Based on geologic mapping, radiocarbon and optically stimulated luminescence dating, we infer a ~ 45–40 ka age for the Harper Lake highstand sediments. Combining the Harper Lake highstand with other Great Basin pluvial lake/spring and marine climate records, we infer that the North American polar jet stream was south of 35°N about 45–40 ka, but shifted to 40°N by ~ 35 ka. Ostracodes (Limnocythere ceriotuberosa) from Harper Lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the Mojave River, thus confirming the lake was fed by the Mojave River. The ~ 45–40 ka highstand at Harper Lake coincides with a shallowing interval at downstream Lake Manix.

Timescales of magmatic processes prior to the ˜4.7 ka Agnano-Monte Spina eruption (Campi Flegrei caldera, Southern Italy) based on diffusion chronometry from sanidine phenocrysts

NASA Astrophysics Data System (ADS)

Iovine, Raffaella Silvia; Fedele, Lorenzo; Mazzeo, Fabio Carmine; Arienzo, Ilenia; Cavallo, Andrea; Wörner, Gerhard; Orsi, Giovanni; Civetta, Lucia; D'Antonio, Massimo

2017-02-01

Barium diffusion chronometry applied to sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (˜4.7 ka) constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera. Backscattered electron imaging and quantitative electron microprobe measurements on 50 sanidine phenocrysts from representative pumice samples document core-to-rim compositional zoning. We focus on compositional breaks near the crystal rims that record magma mixing processes just prior to eruption. Diffusion times were modeled at a magmatic temperature of 930 °C using profiles based on quantitative BaO point analyses, X-ray scans, and grayscale swath profiles, yielding times ≤60 years between mixing and eruption. Such short timescales are consistent with volcanological and geochronological data that indicate that at least six eruptions occurred in the Agnano-San Vito area during few centuries before the Agnano-Monte Spina eruption. Thus, the short diffusion timescales are similar to time intervals between eruptions. Therefore, the rejuvenation time of magma residing in a shallow reservoir after influx of a new magma batch that triggered the eruption, and thus pre-eruption warning times, may be as short as years to a few decades at Campi Flegrei caldera.

Ocean forcing of Ice Sheet retreat in central west Greenland from LGM to the early Holocene

NASA Astrophysics Data System (ADS)

Jennings, Anne E.; Andrews, John T.; Ó Cofaigh, Colm; Onge, Guillaume St.; Sheldon, Christina; Belt, Simon T.; Cabedo-Sanz, Patricia; Hillaire-Marcel, Claude

2017-08-01

Three radiocarbon dated sediment cores from trough mouth fans on the central west Greenland continental slope were studied to determine the timing and processes of Greenland Ice Sheet (GIS) retreat from the shelf edge during the last deglaciation and to test the role of ocean forcing (i.e. warm ocean water) thereon. Analyses of lithofacies, quantitative x-ray diffraction mineralogy, benthic foraminiferal assemblages, the sea-ice biomarker IP25, and δ18 O of the planktonic foraminifera Neogloboquadrina pachyderma sinistral from sediments in the interval from 17.5-10.8 cal ka BP provide consistent evidence for ocean and ice sheet interactions during central west Greenland (CWG) deglaciation. The Disko and Uummannaq ice streams both retreated from the shelf edge after the last glacial maximum (LGM) under the influence of subsurface, warm Atlantic Water. The warm subsurface water was limited to depths below the ice stream grounding lines during the LGM, when the GIS terminated as a floating ice shelf in a sea-ice covered Baffin Bay. The deeper Uummannaq ice stream retreated first (ca. 17.1 cal ka BP), while the shallower Disko ice stream retreated at ca. 16.2 cal ka BP. The grounding lines were protected from accelerating mass loss (calving) by a buttressing ice shelf and by landward shallowing bathymetry on the outer shelf. Calving retreat was delayed until ca. 15.3 cal ka BP in the Uummannaq Trough and until 15.1 cal ka BP in the Disko Trough, during another interval of ocean warming. Instabilities in the Laurentide, Innuitian and Greenland ice sheets with outlets draining into northern Baffin Bay periodically released cold, fresh water that enhanced sea ice formation and slowed GIS melt. During the Younger Dryas, the CWG records document strong cooling, lack of GIS meltwater, and an increase in iceberg rafted material from northern Baffin Bay. The ice sheet remained in the cross-shelf troughs until the early Holocene, when it retreated rapidly by calving and strong melting under the influence of atmosphere and ocean warming and a steep reverse slope toward the deep fjords. We conclude that ocean warming played an important role in the palaeo-retreat dynamics of the GIS during the last deglaciation.

Coarse-grained sediment delivery and distribution in the Holocene Santa Monica Basin, California: Implications for evaluating source-to-sink flux at millennial time scales

USGS Publications Warehouse

Romans, B.W.; Normark, W.R.; McGann, M.M.; Covault, J.A.; Graham, S.A.

2009-01-01

Utilizing accumulations of coarse-grained terrigenous sediment from deep-marine basins to evaluate the relative contributions of and history of controls on sediment flux through a source-to-sink system has been difficult as a result of limited knowledge of event timing. In this study, six new radiocarbon (14C) dates are integrated with five previously published dates that have been recalibrated from a 12.5-m-thick turbidite section from Ocean Drilling Program (ODP) Site 1015 in Santa Monica Basin, offshore California. This borehole is tied to high-resolution seismic-reflection profiles that cover an 1100 km2 area of the middle and lower Hueneme submarine fan and most of the basin plain. The resulting stratigraphic framework provides the highest temporal resolution for a thick-bedded Holocene turbidite succession to date, permitting an evaluation of source-to-sink controls at millennial (1000 yr) scales. The depositional history from 7 ka to present indicates that the recurrence interval for large turbidity-current events is relatively constant (300-360 yr), but the volume of sediment deposited on the fan and in the basin plain has increased by a factor of 2 over this period. Moreover, the amount of sand per event on the basin plain during the same interval has increased by a factor of 7. Maps of sediment distribution derived from correlation of seismic-reflection profiles indicate that this trend cannot be attributed exclusively to autogenic processes (e.g., progradation of depocenters). The observed variability in sediment accumulation rates is thus largely controlled by allogenic factors, including: (1) increased discharge of Santa Clara River as a result of increased magnitude and frequency of El Ni??o-Southern Oscillation (ENSO) events from ca. 2 ka to present, (2) an apparent change in routing of coarse-grained sediment within the staging area at ca. 3 ka (i.e., from direct river input to indirect, littoral cell input into Hueneme submarine canyon), and (3) decreasing rates of sea-level rise (i.e., rate of rise slowed considerably by ca. 3 ka). The Holocene history of the Santa Clara River-Santa Monica Basin source-to-sink system demonstrates the ways in which varying sediment flux and changes in dispersal pathways affect the basinal stratigraphic record. ?? 2009 Geological Society of America.

Late quaternary changes in lakes, vegetation, and climate in the Bonneville Basin reconstructed from sediment cores from Great Salt Lake: Chapter 11

USGS Publications Warehouse

Thompson, Robert S.; Oviatt, Charles G.; Honke, Jeffrey S.; McGeehin, John

2016-01-01

Sediment cores from Great Salt Lake (GSL) provide the basis for reconstructing changes in lakes, vegetation, and climate for the last ~ 40 cal ka. Initially, the coring site was covered by a shallow saline lake and surrounded by Artemisia steppe or steppe-tundra under a cold and dry climate. As Lake Bonneville began to rise (from ~ 30 to 28 cal ka), Pinus and subalpine conifer pollen percentages increased and Artemisia declined, suggesting the onset of wetter conditions. Lake Bonneville oscillated near the Stansbury shoreline between ~ 26 and ~ 24 cal ka, rose to the Bonneville shoreline by ~ 18 cal ka, and then fell to the Provo shoreline, which it occupied until ~ 15 cal ka. Vegetation changed during this time span, albeit not always with the same direction or amplitude as the lake. The pollen percentages of Pinus and subalpine conifers were high from ~ 25 to 21.5 cal ka, indicating cool and moist conditions during the Stansbury oscillation and for much of the rise toward the Bonneville shoreline. Pinus percentages then decreased and Artemisia became codominant, suggesting drier and perhaps colder conditions from ~ 21 to ~ 15 cal ka, when Lake Bonneville was at or near its highest levels.Lake Bonneville declined to a low level by ~ 13 cal ka, while Pinus pollen percentages increased, indicating that conditions remained cooler and moister than today. During the Younger Dryas interval, the brief Gilbert episode rise in lake level was followed by a shallow lake with a stratified water column. This lake rise occurred as Pinus pollen percentages were declining and those of Artemisia were rising (reflecting increasingly dry conditions), after which Artemisia pollen was at very high levels (suggesting cold and dry conditions) for a brief period.Since ~ 10.6 cal ka lacustrine conditions have resembled those of present-day GSL. Pollen spectra for the period from ~ 10.6 to 7.2 cal ka have low levels of conifer pollen and high (for the Holocene) levels of desert and steppe taxa, suggesting generally dry conditions with maximum aridity occurring prior to the deposition of the Mazama tephra (~ 7.6 cal ka). After ~ 10.6 cal ka, Juniperus pollen percentages began to increase and by ~ 7.2 cal ka juniper woodlands were well established on lower mountain slopes. From ~ 7 to 4 cal ka, pollen percentages fluctuated near their mean values for the entire Holocene. The neopluvial (~ 4 to 2 cal ka) was the wettest part of the Holocene, with higher levels of Juniperus pollen and lower levels for steppe and desert taxa than in older Holocene sediments. Pollen percentages for the last ~ 2 cal ka are variable, but generally indicate a return to drier conditions.

Deglacial climate variability in central Florida, USA

USGS Publications Warehouse

Willard, D.A.; Bernhardt, C.E.; Brooks, G.R.; Cronin, T. M.; Edgar, T.; Larson, R.

2007-01-01

Pollen and ostracode evidence from lacustrine sediments underlying modern Tampa Bay, Florida, document frequent and abrupt climatic and hydrological events superimposed on deglacial warming in the subtropics. Radiocarbon chronology on well-preserved mollusk shells and pollen residue from core MD02-2579 documents continuous sedimentation in a variety of non-marine habitats in a karst-controlled basin from 20 ka to 11.5 ka. During the last glacial maximum (LGM), much drier and cooler-than-modern conditions are indicated by pollen assemblages enriched in Chenopodiaceae and Carya, with rare Pinus (Pinus pollen increased to 20–40% during the warming of the initial deglaciation (∼ 17.2 ka), reaching near modern abundance (60–80%) during warmer, moister climates of the Bølling/Allerød interval (14.7–12.9 ka). Within the Bølling/Allerød, centennial-scale dry events corresponding to the Older Dryas and Intra-Allerød Cold Period indicate rapid vegetation response (

Quaternary Sea-ice history in the Arctic Ocean based on a new Ostracode sea-ice proxy

USGS Publications Warehouse

Cronin, T. M.; Gemery, L.; Briggs, W.M.; Jakobsson, M.; Polyak, L.; Brouwers, E.M.

2010-01-01

Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon. ?? 2010.

Rapid directional changes associated with a 6.5 kyr-long Blake geomagnetic excursion at the Blake-Bahama Outer Ridge

NASA Astrophysics Data System (ADS)

Bourne, Mark; Mac Niocaill, Conall; Thomas, Alex L.; Knudsen, Mads Faurschou; Henderson, Gideon M.

2012-06-01

Geomagnetic excursions are recognized as intrinsic features of the Earth's magnetic field. High-resolution records of field behaviour, captured in marine sedimentary cores, present an opportunity to determine the temporal and geometric character of the field during geomagnetic excursions and provide constraints on the mechanisms producing field variability. We present here the highest resolution record yet published of the Blake geomagnetic excursion (∼125 ka) measured in three cores from Ocean Drilling Program (ODP) Site 1062 on the Blake-Bahama Outer Ridge. The Blake excursion has a controversial structure and timing but these cores have a sufficiently high sedimentation rate (∼10 cm ka-1) to allow detailed reconstruction of the field behaviour at this site during the excursion. Palaeomagnetic measurements of the cores reveal rapid transitions (<500 yr) between the contemporary stable normal polarity and a completely reversed state of long duration which spans a stratigraphic interval of 0.7 m. We determine the duration of the reversed state during the Blake excursion using oxygen isotope stratigraphy, combined with 230Th excess measurements to assess variations in the sedimentation rates through the sections of interest. This provides an age and duration for the Blake excursion with greater accuracy and with constrained uncertainty. We date the directional excursion as falling between 129 and 122 ka with a duration for the deviation of 6.5±1.3 kyr. The long duration of this interval and the fully reversed field suggest the existence of a pseudo-stable, reversed dipole field component during the excursion and challenge the idea that excursions are always of short duration.

Pleistocene to Holocene contrasts in organic matter production and preservation on the California continental margin

USGS Publications Warehouse

Dean, W.E.; Gardner, J.V.

1998-01-01

Organic matter in sediments from cores collected from the upper continental slope (200-2700 m) off California and southern Oregon shows marked differences in concentration and marine character between the last glacial interval (ca. 24-10 ka) and either Holocene time or last interstadial (oxygen isotope stage 3, ca. 60-24 ka). In general, sediments deposited during Holocene time and stage 3 contain higher amounts of marine organic matter than those deposited during the last glacial interval, and this contrast is greatest in cores collected off southern California. The most profound differences in stage 3 sediments are between predominantly bioturbated sediments and occasional interbeds of laminated sediments. The sediments are from cores collected within the present oxygen minimum zone on the upper continental slope from as far north as the Oregon-California border to as far south as Point Conception. These upper Pleistocene laminated sediments contain more abundant hydrogen-rich (type II) marine algal organic matter than even surface sediments that have large amounts of nonrefractory organic matter. The stable carbon-isotopic composition of the organic matter does not change with time between bioturbated and laminated sediments, indicating that the greater abundance of type II organic matter in the laminated sediments is not due to a change in source but rather represents a greater degree of production and preservation of marine organic matter. The presence of abundant, well-preserved organic matter supports the theory that the oxygen minimum zone in the northeastern Pacific Ocean was more intense, and possibly anoxic, during late Pleistocene time as a result of increased coastal upwelling that enhanced algal productivity.

Pollen-based evidence of extreme drought during the last Glacial (32.6-9.0 ka) in coastal southern California

NASA Astrophysics Data System (ADS)

Heusser, Linda E.; Kirby, Matthew E.; Nichols, Jonathan E.

2015-10-01

High resolution pollen analyses of sediment core LEDC10-1 from Lake Elsinore yield the first well-dated, terrestrial record of sub-centennial-scale ecologic change in coastal southern California between ˜32 and 9 ka. In the Lake Elsinore watershed, the initial, mesic montane conifer forests dominated by Pinus, and Cupressaceae with trace amounts of Abies and Picea were replaced by a sequence of multiple, extended severe mega-droughts between ˜27.5 and ˜25.5 ka, in which halophytic and xerophytic herbs and shrubs occupied an ephemeral lake. This prolonged and extended dry interval, which corresponds with warm waters offshore, imply strengthening of the North Pacific High and persistent below-average winter precipitation. The subsequent, contrasting monotonic occurrence of montane conifers reflects little variation in cold, mesic climate until ˜15 ka. Postglacial development of Quercus woodland and chaparral mark the return to more xeric, warmer conditions at this time. A brief reversal at ˜13.1-˜12.1 ka, as reflected by an expansion of Pinus, is correlative with the Younger Dryas and interrupts development of warm, postglacial climate. Subsequent gradual expansion of xeric vegetation post - Younger Dryas denotes the establishment of a winter hydroclimate regime in coastal southern California that is more similar to modern conditions. Pollen-based reconstructions of temperature and precipitation at Lake Elsinore are generally correlative with pollen-based paleoclimatic reconstructions and foraminifera-based sea surface temperatures from Santa Barbara Basin in marine core ODP 893. The conspicuous absence of the ˜27.5-˜25.5 ka glacial "mega-drought" in the Santa Barbara Basin pollen record highlights the sensitivity of Lake Elsinore to hydroclimate change, and thus, the importance of this new record that indicates that mega-drought can occur during the full glacial when climatic boundary conditions and forcings differed substantially from the present.

Sedimentary constraints on late Quaternary lake-level fluctuations at Bear Lake, Utah and Idaho

USGS Publications Warehouse

Smoot, J.P.; Rosenbaum, J.G.

2009-01-01

A variety of sedimentological evidence was used to construct the lake-level history for Bear Lake, Utah and Idaho, for the past ???25,000 years. Shorelines provide evidence of precise lake levels, but they are infrequently preserved and are poorly dated. For cored sediment similar to that in the modern lake, grain-size distributions provide estimates of past lake depths. Sedimentary textures provide a highly sensitive, continuous record of lake-level changes, but the modern distribution of fabrics is poorly constrained, and many ancient features have no modern analog. Combining the three types of data yields a more robust lake-level history than can be obtained from any one type alone. When smooth age-depth models are used, lake-level curves from multiple cores contain inconsistent intervals (i.e., one record indicates a rising lake level while another record indicates a falling lake level). These discrepancies were removed and the multiple records were combined into a single lake-level curve by developing age-depth relations that contain changes in deposition rate (i.e., gaps) where indicated by sedimentological evidence. The resultant curve shows that, prior to 18 ka, lake level was stable near the modern level, probably because the lake was overflowing. Between ca. 17.5 and 15.5 ka, lake level was ???40 m below the modern level, then fluctuated rapidly throughout the post-glacial interval. Following a brief rise centered ca. 15 ka ( = Raspberry Square phase), lake level lowered again to 15-20 m below modern from ca. 14.8-11.8 ka. This regression culminated in a lowstand to 40 m below modern ca. 12.5 ka, before a rapid rise to levels above modern ca. 11.5 ka. Lake level was typically lower than present throughout the Holocene, with pronounced lowstands 15-20 m below the modern level ca. 10-9, 7.0, 6.5-4.5, 3.5, 3.0-2.5, 2.0, and 1.5 ka. High lake levels near or above the modern lake occurred ca. 8.5-8.0, 7.0-6.5, 4.5-3.5, 2.5, and 0.7 ka. This lake-level history is more similar to records from Pyramid Lake, Nevada, and Owens Lake, California, than to those from Lake Bonneville, Utah. Copyright ?? 2009 The Geological Society of America.

Holocene evolution of diatom and silicoflagellate paleoceanography in Slocum Arm, a fjord in southeastern Alaska

USGS Publications Warehouse

Barron, John A.; Bukry, David; Addison, Jason A.; Ager, Thomas A.

2016-01-01

Diatom and silicoflagellate assemblages in cores EW0408-47JC, -47TC, -46MC (57° 34.5278′ N, 136° 3.7764′ W, 114 m water depth) taken from the outer portion of Slocum Arm, a post-glacial fjord in southeastern Alaska, reveal the paleoclimatic and paleoceanographic evolution of the eastern margin of the Gulf of Alaska (GoA) during the past 10,000 years. Between ~ 10 and 6.8 cal ka, periods of low salinity and cool water conditions alternated with brief intervals marked by the increased influx of oceanic, more saline and likely warmer waters. Increased surface water stability characterized by a middle Holocene interval between ~ 6.8 and 3.2 cal ka is typified by increased abundances of northeastern Pacific Thalassiosira spp. that are indicative of spring coastal blooms and decreased abundances of warm and higher salinity oceanic diatoms. At ~ 3.2 cal ka, an abrupt increase in both the relative contribution of oceanic diatoms and silicoflagellates suggestive of cooler upwelling conditions occurred in the -47JC record. A stepwise increase in alkenone sea surface temperature in northern GoA core EW0408-85JC and increase in southern sourced precipitation in the carbonate δ18O record of Jellybean Lake (Yukon) present evidence that this ~ 3.2 cal ka event coincided with the onset of enhanced positive Pacific Decadal Oscillation-like (PDO) conditions in the GoA. These positive PDO-like conditions persisted until ~ 1.0 cal ka and were followed by high amplitude fluctuations in the relative abundance of diatom and silicoflagellate assemblages.

Integration of paleoseismic data from multiple sites to develop an objective earthquake chronology: Application to the Weber segment of the Wasatch fault zone, Utah

USGS Publications Warehouse

DuRoss, Christopher B.; Personius, Stephen F.; Crone, Anthony J.; Olig, Susan S.; Lund, William R.

2011-01-01

We present a method to evaluate and integrate paleoseismic data from multiple sites into a single, objective measure of earthquake timing and recurrence on discrete segments of active faults. We apply this method to the Weber segment (WS) of the Wasatch fault zone using data from four fault-trench studies completed between 1981 and 2009. After systematically reevaluating the stratigraphic and chronologic data from each trench site, we constructed time-stratigraphic OxCal models that yield site probability density functions (PDFs) of the times of individual earthquakes. We next qualitatively correlated the site PDFs into a segment-wide earthquake chronology, which is supported by overlapping site PDFs, large per-event displacements, and prominent segment boundaries. For each segment-wide earthquake, we computed the product of the site PDF probabilities in common time bins, which emphasizes the overlap in the site earthquake times, and gives more weight to the narrowest, best-defined PDFs. The product method yields smaller earthquake-timing uncertainties compared to taking the mean of the site PDFs, but is best suited to earthquakes constrained by broad, overlapping site PDFs. We calculated segment-wide earthquake recurrence intervals and uncertainties using a Monte Carlo model. Five surface-faulting earthquakes occurred on the WS at about 5.9, 4.5, 3.1, 1.1, and 0.6 ka. With the exception of the 1.1-ka event, we used the product method to define the earthquake times. The revised WS chronology yields a mean recurrence interval of 1.3 kyr (0.7–1.9-kyr estimated two-sigma [2δ] range based on interevent recurrence). These data help clarify the paleoearthquake history of the WS, including the important question of the timing and rupture extent of the most recent earthquake, and are essential to the improvement of earthquake-probability assessments for the Wasatch Front region.

Integration of paleoseismic data from multiple sites to develop an objective earthquake chronology: Application to the Weber segment of the Wasatch fault zone, Utah

USGS Publications Warehouse

DuRoss, C.B.; Personius, S.F.; Crone, A.J.; Olig, S.S.; Lund, W.R.

2011-01-01

We present a method to evaluate and integrate paleoseismic data from multiple sites into a single, objective measure of earthquake timing and recurrence on discrete segments of active faults. We apply this method to the Weber segment (WS) of the Wasatch fault zone using data from four fault-trench studies completed between 1981 and 2009. After systematically reevaluating the stratigraphic and chronologic data from each trench site, we constructed time-stratigraphic OxCal models that yield site probability density functions (PDFs) of the times of individual earthquakes. We next qualitatively correlated the site PDFs into a segment-wide earthquake chronology, which is supported by overlapping site PDFs, large per-event displacements, and prominent segment boundaries. For each segment-wide earthquake, we computed the product of the site PDF probabilities in common time bins, which emphasizes the overlap in the site earthquake times, and gives more weight to the narrowest, best-defined PDFs. The product method yields smaller earthquake-timing uncertainties compared to taking the mean of the site PDFs, but is best suited to earthquakes constrained by broad, overlapping site PDFs. We calculated segment-wide earthquake recurrence intervals and uncertainties using a Monte Carlo model. Five surface-faulting earthquakes occurred on the WS at about 5.9, 4.5, 3.1, 1.1, and 0.6 ka. With the exception of the 1.1-ka event, we used the product method to define the earthquake times. The revised WS chronology yields a mean recurrence interval of 1.3 kyr (0.7-1.9-kyr estimated two-sigma [2??] range based on interevent recurrence). These data help clarify the paleoearthquake history of the WS, including the important question of the timing and rupture extent of the most recent earthquake, and are essential to the improvement of earthquake-probability assessments for the Wasatch Front region.

Crustal subsidence rate off Hawaii determined from sup 234 U/ sup 238 U ages of drowned coral reefs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ludwig, K.R.; Szabo, B.J.; Simmons, K.R.

1991-02-01

A series of submerged coral reefs off northwestern Hawaii was formed during (largely glacial) intervals when the rate of local sea-level rise was less than the maximum upward growth rate of the reefs. Mass-spectrometric {sup 234}U/{sup 238}U ages for samples from six such reefs range from 17 to 475 ka and indicate that this part of the Hawaiian Ridge has been subsiding at a roughly uniform rate of 2.6 mm/yr for the past 475 ka. The {sup 234}U/{sup 238}U ages are in general agreement with model ages of reef drowning (based on estimates of paleo-sea-level stands derived from oxygen-isotope ratiosmore » of deep-sea sediments), but there are disagreements in detail. The high attainable precision ({plus minus}10 ka or better on samples younger than {approximately}800 ka), large applicable age range, relative robustness against open-system behavior, and ease of analysis for this technique hold great promise for future applications of dating of 50-1,000 ka coral.« less

Biomarker reconstruction of phytoplankton productivity and community structure changes in the mud area southwest off Cheju Island during the past 9 ka

NASA Astrophysics Data System (ADS)

Wang, Z. C.; Xiao, X.; Yuan, Z. N.; Wang, F.; Xing, L.; Li, L.; Zhao, M.

2017-12-01

High-resolution biomarker records from the mud area southwest off Cheju Island in the East China Sea reveal the variabilities of the phytoplankton productivity and community structure during the past 9 ka. This area has undergone dramatic environmental changes during the last glacial cycle, as eustatic sea-level fluctuations resulting in major migration of the coastline. We use the brassicasterol, dinosterol and alkenones records in three sediment cores (B3-1: 31.62°N, 125.75°E; F10: 31.75°N, 126.11°E; F11: 31.88°N, 126.35°E) to reconstruct diatom community, dinoflagellate community and haptophyte community, respectively. The low content of alkenones and relative high contents of brassicasterol and dinosterol of the three sediment cores indicated that diatoms and dinoflagellates were the main marine productivity during the Holocene. The phytoplankton productivity was generally low during the early-Holocene (9-5 ka BP) because of the low input of nutrient. The phytoplankton productivity increased during the mid-Holocene (5-3 ka BP) in response to the upwelling which complemented the nutrient to the upper layer. High content of alkenones in F11 during this period caused by the establishment of the modern circulation pattern around 5-6 ka BP because the intrusion of the Yellow Sea Warm Current (YSWC) brought the high-temperature and high-salinity waters to the core site which provide the suitable living conditions for the haptophytes growth in the east of the mud area. In contrast, the decreased trend of alkenones in F11 around 4 ka BP revealed a weakened YSWC. During the late-Holocene (3-1 ka BP), the phytoplankton productivity showed increasing trend in three sediment cores. The inverse relationships of SST and brassicasterol/dinosterol between B3-1 and F11 indicated the migration of the cold center in this area during this time interval. The hydrology change resulted in a spatial difference in the mud area during the late Holocene.

Age and isotopic constraints on pleistocene pluvial episodes in the Western Desert, Egypt.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crombie, M. K.; Arvidson, R. E.; Sturchio, N. C.

1997-01-01

North Africa has undergone drastic climatic changes over the past several hundred thousand years. The timing of humid intervals called pluvials was investigated by uranium-series disequilibrium dating of travertines from the Kurkur Oasis, Western Desert, Egypt. The youngest and best dated travertines (70-160 ka) are found in Wadi Kurkur and include spring and lacustrine units exposed as 2 to 3 m high terraces. Travertines having an age of approximately 191-220 ka are exposed by differential erosion as linear mounds produced by spring systems over fracture zones in ancient wadis. The oldest travertines, having ages >260 ka, are extensive, cap limestonemore » units above the oasis, and were deposited in paludal and lacustrine environments. Oxygen isotope ratios were measured for the wadi travertines ({delta}{sup 18}O values ranging from 16.7 to 19.1{per_thousand} SMOW) and for spring mound travertines (18.5-20.5{per_thousand}). Equilibrium oxygen isotope fractionation calculations indicate that the Kurkur travertines were deposited from waters having {delta}{sup 18}O values similar to ancient Western Desert groundwaters ({approx} -11{per_thousand}). The ages of the travertines correspond to times of monsoonal maxima, eustatic sea level high stands and interglacial maxima. Rainfall producing these groundwaters (and travertines) was significantly fractionated during atmospheric transport, in contrast to modern meteoric waters (-2.09{per_thousand}), implying a distant source for the pluvial waters. Increased precipitation, recharge of Western Desert groundwaters, and resultant travertine deposition are interpreted to be consequences of Milankovitch insolation cycle forcing, through enhanced Atlantic and Indian Ocean monsoons during interglacial time periods.« less

Disentangling the impacts of climate and human colonization on the flora and fauna of the Australian arid zone over the past 100 ka using stable isotopes in avian eggshell

NASA Astrophysics Data System (ADS)

Miller, Gifford H.; Fogel, Marilyn L.; Magee, John W.; Gagan, Michael K.

2016-11-01

Throughout the Quaternary, the flora and fauna of Australia evolved and adapted to the high-amplitude, low- and high-frequency climate changes that characterized the ice-age cycles. However, during the last glacial cycle, between ∼120 and 15 ka, unprecedented irreversible changes in flora and fauna occurred, and in that same interval modern humans established their first firm presence in the landscape. Disentangling the impacts of the first-order trend toward a colder, drier planet through the Late Quaternary from the impacts of human colonization has been challenging, from both the chronological and paleoenvironmental perspectives. We utilize the stable isotopes of carbon and oxygen preserved in near-continuous time series of Dromaius (emu) eggshell from five regions across Australia to provide independent reconstructions of ecosystem status and climate over the past 100 ka. Carbon isotopes are determined by the diet consumed by the female bird, whereas oxygen isotopes record the status of local moisture balance in the months prior to breeding. Together, δ13C and δ18O provide ecosystem status and climate from the same dated sample, reducing correlation uncertainties between proxies. Combined with recent improvements in the chronologies of Late Quaternary shorelines fringing inland lake basins and deflation during arid times, these data collectively reaffirm that Australia generally became increasingly, albeit irregularly, drier from the last interglaciation through to the last glacial maximum. Dromaius eggshell δ18O documents peak aridity between 30 and 15 ka, but shows no evidence of exceptional climate change between 60 and 40 ka. In contrast, Dromaius δ13Cdiet documents an irreversible loss of the majority of palatable summer-rainfall-related C4 grasses across the Australian arid zone between 50 and 45 ka, about the same time that the giant megafaunal bird, Genyornis, became extinct, and coincident with human dispersal across the continent. Our data indicate that changes unique to Australia occurred between 50 and 45 ka that led to a new climate-vegetation relationship and an overall reduction in effective moisture across much of the continent. The large summer-rainfall-dominated lakes of interior Australia failed to re-fill subsequently, despite a wide range of global climate states. A full explanation for the mechanisms behind these changes remains elusive, but they are almost certainly related to human agency. Plausible explanations include a change in fire regime resulting from human-lit fires, a change in fire regime following extinction of megafaunal browsers, and/or a threshold response to increasing aridity. Of these, the climate change explanation is least likely, given the lack of evidence for unprecedented aridity between 60 and 40 ka, and the successful adaptation of Australian ecosystems to 2.5 Ma of similar changes.

New K Ar age determinations of Kilimanjaro volcano in the North Tanzanian diverging rift, East Africa

NASA Astrophysics Data System (ADS)

Nonnotte, Philippe; Guillou, Hervé; Le Gall, Bernard; Benoit, Mathieu; Cotten, Joseph; Scaillet, Stéphane

2008-06-01

The Kilimanjaro is the African highest mountain and culminates at 5895 m high. This huge volcanic edifice is composed of three main centres along a N110°E-striking axis (Shira, Kibo and Mawenzi from W to E), and emplaced in a key area where a major N80°E-oriented volcanic lineament intersects a first-order NW-SE basement fault-like discontinuity. Seventeen K-Ar ages (on microcrystalline groundmass) acquired on lavas and intrusive facies from the three eruptive centres confirm that the Plio-Quaternary volcanicity of Kilimanjaro is clearly polyphased. The oldest phases of volcanic activity begun at ~ 2.5 Ma in the Shira vent and our data suggest that the latest important phases occurred around 1.9 Ma, just before the collapse of the Northern part of the edifice. Magmatic activity then shifted eastwards in the Mawenzi and Kibo twin centres where initial volcanism is dated at ~ 1 Ma. Two K-Ar ages obtained for the most recent Mawenzi rocks from the Neumann Tower-Mawenzi group (492 ka) and Mawenzi eruptive centre (448 ka), near the present summit, are linked to the final stage of edification for this centre. Whereas the eruptive activity ceased in the Mawenzi, it still continued on Kibo since sub-actual time. The oldest dated rocks from Kibo (482 ka) is obtained on a dyke from the Lava Tower group cropping out at 4600 m high. The main phase of magmatism on Kibo is recorded by two lava formations with a great spatial extension - the Rhomb Porphyry group and the Lent group - that have been emplaced in a short time interval at ~ 460-360 ka (including two erosive stages) and 359-337 ka, respectively. Based on the dating of Caldera rim group lavas, it is shown that the edification of the present cone was accomplished in a period ranging from 274 to 170 ka. The new ages obtained for the main episodes of volcanic activity on Kibo appear to roughly coincide with the oldest known Quaternary glaciations. The interaction between eruptive phenomena and the ice cover is assumed to have played an important role in triggering collapse processes and associated lahars deposits. The last volcanicity, around 200-150 ka, is marked by the formation of the present summit crater in Kibo and the development of linear parasitic volcanic belts, constituted by numerous Strombolian-type isolated cones on the NW and SE slopes of Kilimanjaro. These belts are likely to occur above deep-seated fractures that have guided the magma ascent, and the changes in their directions with time might be related to the rotation of recent local stress field.

Moderate rates of late Quaternary slip along the northwestern margin of the Basin and Range Province, Surprise Valley fault, northeastern California

USGS Publications Warehouse

Personius, Stephen F.; Crone, Anthony J.; Machette, Michael N.; Mahan, Shannon; Lidke, David J.

2009-01-01

The 86-km-long Surprise Valley normal fault forms part of the active northwestern margin of the Basin and Range province in northeastern California. We use trench mapping and radiocarbon, luminescence, and tephra dating to estimate displacements and timing of the past five surface-rupturing earthquakes on the central part of the fault near Cedarville. A Bayesian OxCal analysis of timing constraints indicates earthquake times of 18.2 ± 2.6, 10.9 ± 3.2, 8.5 ± 0.5, 5.8 ± 1.5, and 1.2 ± 0.1 ka. These data yield recurrence intervals of 7.3 ± 4.1, 2.5 ± 3.2, 2.7 ± 1.6, and 4.5 ± 1.5 ka and an elapsed time of 1.2 ± 0.1 ka since the latest surface-rupturing earthquake. Our best estimate of latest Quaternary vertical slip rate is 0.6 ?? 0.1 mm/a. This late Quaternary rate is remarkably similar to long-term (8-14 Ma) minimum vertical slip rates (>0.4-0.5 ± 0.3 mm/a) calculated from recently acquired seismic reflection and chronologic and structural data in Surprise Valley and the adjacent Warner Mountains. However, our slip rate yields estimates of extension that are lower than recent campaign GPS determinations by factors of 1.5-4 unless the fault has an unusually shallow (30°-35°) dip as suggested by recently acquired seismic reflection data. Coseismic displacements of 2-4.5 ± 1 m documented in the trench and probable rupture lengths of 53-65 km indicate a history of latest Quaternary earthquakes of M 6.8-7.3 on the central part of the. Surprise Valley fault.

Orbital forced frequencies in the 975000 year pollen record from Tenagi Philippon (Greece)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mommersteeg, H.J.P.M.; Young, R.; Wijmstra, T.A.

Frequency analysis was applied to different time series obtained from the 975 ka pollen record of Tenagi Philippon (Macedonia, Greece). These time series are characteristic of different vegetation types related to specific climatic conditions. Time control of the 196 m deep core was based on 11 finite {sup 14}C dates in the upper 17 m, magnetostratigraphy and correlation with the marine oxygen isotope stratigraphy. Maximum entropy spectrum analyses and thomson multi-taper spectrum analysis were applied using the complete time series. Periods of 95-99, 40-45. 24.0-25.5 and 19-21 ka which can be related to orbital forcing, as well as periods ofmore » about 68, 30 ka and of about 15.5, 13.5, 12 and 10.5 ka were detected. The detected periods of about 68, 30 ka and 16, 14, 12, 10.5 ka are likely to be harmonics and combination tones of the periods related to orbital forcing. The period of around 30 ka is possibly a secondary peak of obliquity. To study the stability of the detected periods through time, analysis with a moving window was employed. Signals in the eccentricity band were detected clearly during the last 650 ka. In the precession band, detected periods of about 24 ka show an increase in amplitude during the last 650 ka. The evolution of orbital frequencies during the last 1.0 Ma is in general agreement with the results of other marine and continental time series. Time series related to different climatic settings showed a different response to orbital forcing. Time series of vegetational elements sensitive to changes in net precipitation were forced in the precession and obliquity bands. Changes in precession caused changes in the monsoon system, which indirectly had a strong influence on the climatic history of Greece. Time series of vegetational elements which are more indicative of changes in annual temperature are forced in the eccentricity band. 54 refs., 12 figs., 3 tabs.« less

Holocene paleoclimatic evidence and sedimentation rates from a core in southwestern Lake Michigan

USGS Publications Warehouse

Colman, Steven M.; Jones, Glenn A.; Forester, R.M.; Foster, D.S.

1990-01-01

Preliminary results of a multidisciplinary study of cores in southwestern Lake Michigan suggest that the materials in these cores can be interpreted in terms of both isostatically and climatically induced changes in lake level. Ostracodes and mollusks are well preserved in the Holocene sediments, and they provide paleolimnologic and paleoclimatic data, as well as biogenic carbonate for stable-isotope studies and radiocarbon dating. Pollen and diatom preservation in the cores is poor, which prevents comparison with regional vegetation records. New accelerator-mass spectrometer 14C ages, from both carbon and carbonate fractions, provide basin-wide correlations and appear to resolve the longstanding problem of anomalously old ages that result from detrital organic matter in Great Lakes sediments. Several cores contain a distinct unconformity associated with the abrupt fall in lake level that occurred about 10.3 ka when the isostatically depressed North Bay outlet was uncovered by the retreating Laurentide Ice Sheet. Below the unconformity, ostracode assemblages imply deep, cold water with very low total dissolved solids (TDS), and bivalves have ?? 18O (PDB) values as light as - 10 per mil. Samples from just above the unconformity contain littoral to sublittoral ostracode species that imply warmer, higher-TDS (though still dilute) water than that inferred below the unconformity. Above this zone, another interval with ?? 18O values more negative than - 10 occurs. The isotopic data suggest that two influxes of cold, isotopically light meltwater from Laurentide ice entered the lake, one shortly before 10.3 ka and the other about 9 ka. These influxes were separated by a period during which the lake was warmer, shallower, but still very low in dissolved solids. One or both of the meltwater influxes may be related to discharge from Lake Agassiz into the Great Lakes. Sedimentation rates appear to have been constant from about 10 ka to 5 ka. Bivalve shells formed between about 8 and 5 ka have ?? 18O values that range from-2.3 to-3.3 per mil and appear to decrease toward the end of the interval. The ostracode assemblages and the stable isotopes suggest changes that are climatically controlled, including fluctuating water levels and increasing dissolved solids, although the water remained relatively dilute (TDS < 300 mg/l). A dramatic decrease in sedimentation rates occurred at about 5 ka, about the time of the peak of the Nippissing high lake stage. This decrease in sedimentation rate may be associated with a large increase in effective wave base as the lake approached its present size and fetch. A dramatic reduction in ostracode and mollusk abundances during the late Holocene is probably due to this decrease in sedimentation rates, which would result in increased carbonate dissolution. Ostracode productivity may also have declined due to a reduction in bottom-water oxygen caused by increased epilimnion algal productivity. 

Kuroshio variation near Taiwan during the past 6,000 years

NASA Astrophysics Data System (ADS)

Wei, K.; Lai, Y.; Lin, Y.; Shen, C.; Mii, H.

2013-12-01

The Holocene thermal optimum at about 6 ka is considered to be warmer and wetter than the present in northern subtropical regions, and the late Holocene is expected to show a generally cooling trend ever since, however, the exact pattern is not yet clear for the Taiwan region. New and published data of hydrological proxies of the Late Holocene collected from two marine sedimentary cores adjacent to Taiwan were compiled in an attempt to reconstruct hydrological conditions of the Kuroshio over the past 6000 years. Sea surface temperatures, salinities and potential densities were estimated from paired measurements of Mg/Ca ratio and δ18O of planktonic foraminfera Globigerinoides ruber. The SSTs from Core ORI715-21 (22.7°N, 121.5°E, water depth 760 m) varied between 26.0 and 29.0°C, showing three short cool intervals during 5.6 - 5.0, ~3,5 and 0.8-0.2 ka intercalated in generally warm late Holocene. Salinity shows a generally decreasing trend, decreasing particularly in the last 3000 years. Reconstructed water density follows mainly with salinity change, showing a clear decreasing trend over the past 3000 years. The SSTs from Core MD01-2403 (25.3°N, 123.2°E, water depth 1420 m) in the southern Okinawa Trough varied between 26.5 and 29.5°C, exhibiting a stable, mild warm period between 5.0 and 2.6 ka, The SSTs in 6.0 - 5.5 ka, as well as in 2.5-1.0 ka are relatively cooler than the rest of time in the late Holocene. The SSS shows a decreasing trend since 2.0 ka. The SSTs and SSSs reconstructed from the southern Okinawa site (MD01-2403) are in general higher than that from the southern site ORI-715-21 near Green Island, somewhat counter-intuitive. In viewing the high-speed flow of the Kuroshio, mixture pattern of waters and the life cycle length of G. ruber, we regard that the record of the southern site reflects sea-surface conditions of the tropical Pacific east of Luzon and that of the South China Sea, while the northern site record reflects the condition of the Kuroshio near Taiwan eastern coast. The hydrological gradients reflect the strength of the Upstream Kuroshio as well the degree to which it mixed with the South China Sea water masses. Three intervals, marked by strong negative S-N SST gradients, 5.6-5.1, 3.7-3.5 and 2.4-1.9 Ka, are interpreted as having strong winter monsoons and weak Upstream Kuroshio such that the Kuroshio intruded into SCS and formed prolonged Loop Currents, bringing out more cool and fresh surface sea waters. No systematic relationships can be found among the Upstream Kuroshio strength, Greenland atmospheric temperature (GISP II δ18O), Asian monsoon (Dongge cave carbonate δ18O) and ENSO activity (Moy et al.2002).

A multi-proxy record of MIS 11-12 deglaciation and glacial MIS 12 instability from the Sulmona basin (central Italy)

NASA Astrophysics Data System (ADS)

Regattieri, Eleonora; Giaccio, Biagio; Galli, Paolo; Nomade, Sebastien; Peronace, Edoardo; Messina, Paolo; Sposato, Andrea; Boschi, Chiara; Gemelli, Maurizio

2016-01-01

A multi-proxy record (lithology, XRF, CaCO3 content, carbonate δ18O and δ13C) was acquired from a sediment core drilled in the intermountain Sulmona basin (central Italy). Tephrostratigraphic analyses of three volcanic ash layers ascribe the investigated succession to the MIS 12-MIS 11 period, spanning the interval ca. 500-410 ka. Litho-pedo facies assemblage indicates predominant lacustrine deposition, interrupted by a minor sub-aerial and lake low stand episode. Variations in major and minor elements concentrations are related to changes in the clastic input to the lake. The oxygen isotopic composition of carbonate (δ18Oc) intervals is interpreted mainly as a proxy for the amount of precipitation in the high-altitude catchment of the karst recharge system. The record shows pronounced hydrological variability at orbital and millennial time-scales, which appears closely related to the Northern Hemisphere summer insolation pattern and replicates North Atlantic and west Mediterranean Sea Surface Temperature (SST) fluctuations. The MIS 12 glacial inception is marked by an abrupt reduction of precipitation, lowering of the lake level and enhanced catchment erosion. A well-defined and isotopically prominent interstadial with increased precipitation maybe related to insolation maxima-precession minima at ca. 465 ka. This interstadial ends abruptly at ca. 457 ka and it is followed by a phase of strong short-term instability. Drastic lake-level lowering and enhanced clastic flux characterized the MIS 12 glacial maximum. Lacustrine deposition restarted about 440 ka ago. The MIS 12-MIS 11 transition is characterized by a rapid increase in the precipitation, lake-level rise and reduction in the clastic input, interrupted by a short and abrupt return to drier conditions. Comparison with marine records from the Iberian margin and western Mediterranean suggests that major events of ice rafted debris deposition, related to southward migrations of the polar front, match the harshest periods in central Italy. This indicates strong teleconnections between Northern hemisphere ice sheet dynamics, North Atlantic oceanic conditions and Mediterranean continental hydrology.

Depositional environment, foraminifer content and ESR ages of Quaternary Gediz Delta Sediments (Eastern Aegean Sea, İzmir-Western Turkey)

NASA Astrophysics Data System (ADS)

Gökçe Benli, Ekin; Aydın, Hülya; İşintek, İsmail; Engin, Birol; Şengöçmen, Berna

2016-04-01

Sediments and fossil content of Gediz Delta (Eastern Aegean Sea - İzmir) were examined based on the drilling core samples of the YSK-C and SK-246 drilling. W-SW part of the Delta is represented by continental delta sediments up to 6 meters and shallow marine detritic sediments up to 35 meters in the YSK-C drilling. Continental part consists of an soiled, graveled, muddy and sandy sediment in terms of rich organic substance. As for marine part, it consists of bioclast, muddy, fine graveled sand and by repetition of pebble, sand and bioclast bearing mud layers. Bioclasts comprise of bivalvia, echinoid, ostracod, gastropod, foramifer and bryozoa fragments. Benthic foraminiferal fauna determinated in the marine levels are represented by 55 bethic, 2 planktonic species. These foraminifers and bioclasts reflect that the W-SW part of the delta, has been occured in marine conditions between 8-31m deep. E-NE part of the delta is generally represented by continental sediments up to 43.5m in SK-246 drilling. In addition, it includes marine levels in 18-19 m, 23-24 m and 36-37,5 m intervals. Continental sediments of E-NE part is generally represented by calcareous and sandy mud rocks which mostly includes ash, tuff, and pebble derived from Neogene volcanic rocks. As for marine levels, it is composed of calcareous mud stones and calcareous clay stones including very thin gastropod, bivalvia and ostracod in 18- 19 and 36-37.5 meters whereas it is represented by sandy mud stones including a great deal of bentic foraminifer, bivalvia, bryozoa, echinoid, gastropod in 23-24 metres. Thus show that E-NE part of the delta is usually in continental condition but it is occasionally covered by sea. In aging studies of YSK-C core done by ESR method, age of 8-9 m interval is determined to be 11. 376 ± 0,067 Ka; however ages of 10-11m and 24-25 m intervals are revealed to be 16.466 ± 0,016 Ka and 15.344 ± 0,021 Ka respectively; finally age of 25-26 m interval is found to be 19.995 ± 0,022 Ka. This results reflect while the W-SW part of the delta is in marine condition between 20 and 11 Ka, in the E-NE part of the delta, continental and marine conditions were repeated.

a Marine Record of Holocene Climate Events in Tropical South America

NASA Astrophysics Data System (ADS)

Haug, G. H.; Günther, D.; Hughen, K. A.; Peterson, L. C.; Röhl, U.

2002-12-01

Metal concentration data (Ti, Fe) from the anoxic Cariaco Basin off the Venezuelan coast record with subdecadal to seasonal resolution variations in the hydrological cycle over tropical South America during the last 14 ka. Following a dry Younger Dryas, a period of increased precipitation and riverine discharge occurred during the Holocene `thermal maximum'. Since ~5.4 ka, a trend towards drier conditions is evident from the data, with high amplitude fluctuations and precipitation minima during the time interval 3.8 to 2.8 ka and during the `Little Ice Age'. O pronouced increase in precipitation coincides with the phase sometimes referred to as the `Medieval Warm Period'. These regional changes in precipitation are best explained by shifts in the mean latitude of the Atlantic Intertropical Convergence Zone (ITCZ), potentially driven by Pacific-based climate variability. The variations recorded in Cariaco Basin sediments coincide with events in societal evolution that have been suggested previously to be motivated by environmental change. Regionally, the Cariaco record supports the notion that the collapse of this civilization between 800 and 1000 AD coincided with an extended period of drier conditions, implying that the rapid growth of Mayan culture from 600 to 800 AD may have resulted in a population operating at the fringes of the environment's carrying capacity. The Cariaco Basin record also hints at tropical climate events similar in timing to high latitude changes in the North Atlantic often invoked as pivotal to societal developments in Europe.

Palaeoseismology of the Vilariça segment of the Manteigas-Bragança fault in northeastern Portugal

USGS Publications Warehouse

Rockwell, Thomas; Fonseca, Joao; Madden, Chris; Dawson, Tim; Owen, Lewis A.; Vilanova, Susana; Figueiredo, Paula

2009-01-01

The Manteigas-Bragança fault is a major, 250-km-long, NNE-striking, sinistral strike-slip structure in northern Portugal. This fault has no historical seismicity for large earthquakes, although it may have generated moderate (M5+) earthquakes in 1751 and 1858. Evidence of continued left horizontal displacement is shown by the presence of Cenozoic pull-apart basins as well as late Quaternary stream deflections. To investigate its recent slip history, a number of trenches were excavated at three sites along the Vilariça segment, north and south of the Douro River. At one site at Vale Meão winery, the occurrence of at least two and probably three events in the past 14.5 ka was determined, suggesting an average return period of about 5–7 ka. All three events appear to have occurred as a cluster in the interval between 14.5 and 11 ka, or shortly thereafter, suggesting a return period of less than 2 ka between events within the cluster. In the same area, a small offset rill suggests 2–2.5 m of slip in the most recent event and about 6.1 m after incision below a c. 16 ka alluvial fill event along the Douro River. At another site along the Vilariça River alluvial plain, NE of the Vale Meão site, several trenches were excavated in late Pleistocene and Holocene alluvium, and exposed the fault displacing channel deposits dated to between 18 and 23 ka. In a succession of closely spaced parallel cuts and trenches, the channel riser was traced into and across the fault to resolve c. 6.5 m of displacement after 18 ka and c. 9 m of slip after c. 23 ka. These observations yield a slip rate of 0.3–0.5 mm/a, which is consistent with earlier estimates. Combining the information on timing at Vale Meão winery and displacement at Vilariça argues for earthquakes in the M7+ range, with coseismic displacements of 2–3 m. This demonstrates that there are potential seismic sources in Portugal that are not associated with the 1755 Lisbon earthquake or the Tagus Valley, and, although rare, large events on the Vilariça fault could be quite destructive for the region. This work provides an analogue for the study of active faulting in intracontinental settings and supports the view that earthquakes within intracontinental settings tend to cluster in time. In addition, this study highlights the usefulness and application of multiple field, remote sensing and geochronological techniques for seismic hazard mitigation.

Drastic shifts in the Levant hydroclimate during the last interglacial indicate changes in the tropical climate and winter storm tracks

NASA Astrophysics Data System (ADS)

Kiro, Y.; Goldstein, S. L.; Kushnir, Y.; Lazar, B.; Stein, M.

2017-12-01

Marine Isotope Stage (MIS) 5e was a warm interglacial with where with significantly varying insolation and hence varied significantly throughout this time suggesting highly variable climate. The ICDP Dead Sea Deep Drilling Project recovered a 460m record of the past 220ka, reflecting the variable climate along MIS 5e. This time interval is reflected by alternating halite and detritus sequences, including 20m of halite-free detritus during the peak insolation at 125 ka. The Dead Sea salt budget indicates that the Levant climate was extremely arid when halite formed, reaching 20% of the present runoff. The halite-free detritus layer reflects increased precipitation to levels similar to present day, assuming similar spatial and temporal rainfall patterns. However, the 234U/238U activity ratio in the lake, reflected by authigenic minerals (aragonite, gypsum and halite), shifts from values of 1.5 (reflecting the Jordan River, the present main water source) down to 1.3 at 125-122ka during the MIS5e insolation peak and 1.0 at 118-116ka. The low 234U/238U reflects increased flash floods and eastern water sources (234U/238U 1.05-1.2) from the drier part of the watershed in the desert belt. The intermediate 234U/238U of 1.3 suggests that the Jordan River, fed from Mediterranean-sourced storm tracks, continued to flow along with an increase in southern and eastern water sources. NCAR CCSM3 climate model runs for 125ka indicate increases in both Summer and Winter precipitation. The drastic decrease to 234U/238U 1.0 occurs during the driest period, indicating a near shutdown of Jordan River flow, and water input only through flash floods and southern and eastern sources. The 120ka climate model runs shows a decrease in Winter and increase in Fall precipitation as a result of an increased precipitation in the tropics. The extreme aridity, associated with increased flooding is similar to patterns expected due to future warming. The increase in aridity is the result of expansion of the desert-belt and increases in southern precipitation and indicates an important link between the tropical and mid-latitude climate.

No surface breaking on the Ecemiş Fault, central Turkey, since Late Pleistocene (~ 64.5 ka); new geomorphic and geochronologic data from cosmogenic dating of offset alluvial fans

NASA Astrophysics Data System (ADS)

Sarıkaya, M. A.; Yıldırım, C.; Çiner, A.

2015-05-01

The Ecemiş Fault Zone (EF) has been recognized as a major left lateral strike-slip fault in the Central Anatolian Fault Zone (CAFZ) of Turkey. However, its Quaternary slip-rate has been challenging to determine due to the difficulty of dating offset markers. Using high-precision offset measurements and 36Cl cosmogenic nuclide dating, we present the first geochronologically determined Late Quaternary slip-rate for the EF. Our study focuses on the excellent exposures of offset alluvial fan surfaces, originating from the Aladağlar, a Late Quaternary glaciated mountain. Analysis of airborne orthophotogrametry and GNSS (Global Navigation Satellite System) surveys indicates 168 ± 2 m left lateral and 31 ± 1 m vertical displacements. In-situ terrestrial cosmogenic 36Cl geochronology obtained from eleven surface boulders provides a minimum abandonment/incision age of 104.2 ± 16.5 ka for the oldest offset alluvial fan surface. Our geomorphic observations together with Self-potential geophysical surveys revealed the presence of an unfaulted alluvial fan terrace, which allows us to constrain the timing of deformation. The abandonment/incision age of this fan is 64.5 ± 5.6 ka based on thirteen 36Cl depth profile samples. Accordingly, we obtained a geologic fault slip-rate of 4.2 ± 1.9 mm a- 1 horizontally and 0.8 ± 0.3 mm a- 1 vertically for the time frame between 104.2 ± 16.5 ka and 64.5 ± 5.6 ka. Our analysis indicates that the EF has not been producing a major surface breaking earthquake on the main strand at least since 64.5 ± 5.6 ka (mid-Late Pleistocene). This could be the result of abandonment of the main strand and accommodation of deformation by other faults within the EF. Nevertheless, a recently occurred (30 September 2011) low magnitude (ML: 4.3) left lateral strike-slip earthquake indicates recent seismic activity of the EF. Comparison of the recent GPS velocity field with the longer slip history along the CAFZ indicates a constant but low strain release without surface breaking and very long large earthquake recurrence intervals.

Apparent late Quaternary fault slip rate increase in the southwestern Lower Rhine Graben, central Europe

USGS Publications Warehouse

Gold, Ryan D.; Friedrich, Anke M.; Kubler, Simon; Salamon, Martin

2017-01-01

In regions of low strain, long earthquake recurrence intervals (104–106  yrs) and erosive processes limit preservation of Quaternary markers suitable for distinguishing whether faults slip at uniform or secularly varying rates. The Lower Rhine graben in the border region of Germany, The Netherlands, and Belgium provides a unique opportunity to explore Quaternary slip‐rate variations in a region of low strain using the basal (2.29±0.29  Ma) and surface (700±80  ka) contacts of the regionally extensive main terrace (“Hauptterrasse”), deposited by the Rhine and Maas Rivers. These surfaces are vertically offset 3–140 m and 0–68 m, respectively, across individual fault strands within a distributed network of northwest‐trending, slow‐slipping (<0.1  mm/yr) normal faults. In this investigation, we construct Quaternary slip histories for the southern Lower Rhine graben faults using new main terrace surface vertical offset measurements made from light detection and ranging (lidar)‐derived bare‐earth digital terrain models, which we synthesize with existing constraints on the offset basal contact of this fluvial deposit (n=91 collocated sites with displacement constraints). We find that >80% of the sites record an apparent increase in slip rate for the more recent interval from 700 ka to present, which corresponds to a period of increased uplift of the nearby Rhenish Massif and regional volcanism. However, the apparent increase in slip rate could result, in part, from erosion of the footwall surface below the main terrace, leading to an apparent displacement that is smaller than the total vertical offset since the start of the Quaternary. Prior work focused on characterization of these faults as seismic sources in the Lower Rhine graben has preferentially relied on the average fault‐slip rate constrained using the base of the main terrace. We suggest that average fault‐slip rates calculated using the ∼700  ka main terrace surface are subjected to fewer uncertainties and sample a time interval that is more relevant for seismic‐hazard analysis.

Late Cenozoic lacustrine and climatic environments at Tule Lake, northern Great Basin, USA

USGS Publications Warehouse

Platt, Bradbury J.

1992-01-01

Cores of lake sediment to a depth of 334 m in the town of Tulelake, Siskiyou County, northern California, document the late Cenozoic paleolimnologic and paleoclimatic history of the northwestern edge of the Great Basin. The cores have been dated by radiometric, tephrochronologic and paleomagnetic analyses. Lacustrine diatoms are abundant throughout the record and document a nearly continuous paleolimnologic history of the Tule Lake basin for the last 3 Myr. During most of this time, this basin (Tule Lake) was a relatively deep, extensive lake. Except for a drier (and cooler?) interval recorded by Fragilaria species about 2.4 Ma, the Pliocene is characterized by a dominance of planktonic Aulacoseira solida implying a warm monomictic lake under a climatic regime of low seasonality. Much of the Pleistocene is dominated by Stephanodiscus and Fragilaria species suggesting a cooler, often drier, and highly variable climate. Benthic diatoms typical of alkaline-enriched saline waters commonly appear after 1.0 Ma, and tephrochronology indicates slow deposition and possible hiatuses between about 0.6 and 0.2 Ma. The chronology of even-numbered oxygen isotope stages approximately matches fluctuations in the abundance of Fragilaria since 800 ka indicating that glacial periods were expressed as drier environments at Tule Lake. Glacial and interglacial environments since 150 ka were distinct from, and more variable than, those occurring earlier. The last full glacial period was very dry, but shortly thereafter Tule Lake became a deep, cool lacustrine system indicating a substantial increase in precipitation. Aulacoseira ambigua characterized the latest glacial and Holocene record of Tule Lake. Its distribution indicates that warmer and wetter climates began about 15 ka in this part of the Great Basin. Diatom concentration fluctuates at 41 000 year intervals between 3.0 and 2.5 Ma and at approximately 100 000 year intervals after 1.0 Ma. In the late Pliocene and early Pleistocene, Aulacoseira solida percentages wax and wane in an approximately 400 000 year cycle. The possible response of Tule Lake diatom communities to orbitally-induced insolation cycles underscores the importance of this record for the study of late Cenozoic paleoclimate change. ?? 1992 Springer-Verlag.

Clastic sediment flux to tropical Andean lakes: records of glaciation and soil erosion

NASA Astrophysics Data System (ADS)

Rodbell, Donald T.; Seltzer, Geoffrey O.; Mark, Bryan G.; Smith, Jacqueline A.; Abbott, Mark B.

2008-08-01

We developed records of clastic sediment flux to 13 alpine lakes in Peru, Ecuador, and Bolivia, and compared these with independently dated records of regional glaciation. Our objectives are to determine whether a strong relationship exists between the extent of ice cover in the region and the rate of clastic sediment delivery to alpine lakes, and thus whether clastic sediment records serve as reliable proxies for glaciation during the late Pleistocene. We isolated the clastic component in lake sediment cores by removing the majority of the biogenic and authigenic components from the bulk sediment record, and we dated cores by a combination of radiocarbon and tephrochronology. In order to partially account for intra-basin differences in sediment focusing, bedrock erosivity, and sediment availability, we normalized each record to the weighted mean value of clastic sediment flux for each respective core. This enabled the stacking of all 13 lake records to produce a composite record that is generally representative of the tropical Andes. There is a striking similarity between the composite record of clastic sediment flux and the distribution of ˜100 cosmogenic radionuclide (CRN) exposure ages for erratics on moraine crests in the central Peruvian and northern Bolivian Andes. The extent of ice cover thus appears to be the primary variable controlling the delivery of clastic sediment to alpine lakes in the region, which bolsters the increasing use of clastic sediment flux as a proxy for the extent of ice cover in the region. The CRN moraine record and the stacked lake core composite record together indicate that the expansion of ice cover and concomitant increase in clastic sediment flux began at least 40 ka, and the local last glacial maximum (LLGM) culminated between 30 and 20 ka. A decline in clastic sediment flux that began ˜20 ka appears to mark the onset of deglaciation from the LLGM, at least one millennium prior to significant warming in high latitude regions. The interval between 20 and 18 ka was marked by near-Holocene levels of clastic sediment flux, and appears to have been an interval of much reduced ice extent. An abrupt increase in clastic sediment flux 18 ka heralded the onset of an interval of expanded ice cover that lasted until ˜14 ka. Clastic sediment flux declined thereafter to reach the lowest levels of the entire length of record during the early-middle Holocene. A middle Holocene climatic transition is apparent in nearly all records and likely reflects the onset of Neoglaciation and/or enhanced soil erosion in the tropical Andes.

Vegetation and climate history in the Laptev Sea region (arctic Siberia) during Late Quaternary inferred from pollen records

NASA Astrophysics Data System (ADS)

Andreev, A.; Schirrmeister, L.; Tarasov, P.

2009-04-01

A number of permafrost sections dated by 14C, TL, IRSL, and 230U/Th were analysed for pollen. Pollen spectra suggest that wet grass-sedge tundra habitats dominated during an interstadial c. 200-170 ka ago. The climate was rather wet and cold. The pollen spectra reflect sparser grass-sedge vegetation cover during the Late Saalian stadial, c. 170-130 ka BP. Environmental conditions were much more severe compared with the previous interstadial. Open Poaceae and Artemisia communities dominated at the beginning of the Last Interglacial. Some shrubs (Alnus fruticosa, Salix, Betula nana) grew in more protected and wetter places. Climate was rather warm (similar to modern conditions)during this time. Shrub tundra with Alnus fruticosa and Betula nana s.l. dominated in the area during the Eemian climatic optimum, when summer temperatures were 4-5°C higher than today. Early Weichselian pollen records reflect harsh environmental conditions; sparser vegetation (mostly grass and sedge communities) during this time. Middle Weichselian (Karginsky) Interstadial records with dominance of Cyperaceae and Poaceae with some Artemisia and Salix reflects tundra- and steppe-like associations with willow shrubs dominated the area. The climate was relatively moist and warm. A rather high content of algae colonies in the sediments indicates shallow water habitats (e.g. centres of ice wedge polygons). Dominance of Poaceae, Cyperaceae, Artemisia, and Caryophyllaceae pollen with some other herbs is typical for the 40-32 ka BP (climatic optimum) old sediments when open herb dominated the area. High pollen concentrations reflect that dense grass-sedge dominated vegetation; presence of Salix is also characteristic. The records point to climate amelioration during the Middle Weichselian compared to the Early Weichselian. Climate conditions became colder and drier c. 30-26 ka BP. Pollen spectra reflect that sedge-grass-Artemisia with some Caryophyllaceae and Asteraceae dominated the vegetation. Mostly grass conenoses with some Caryophyllaceae, Asteraceae, Cichoriaceae, Selaginella rupestris predominated during the late Weichselian (Sartan), ca 26-16 ka BP. Climate was very cold and dry. Later, 16-12 ka BP, grass and sedge associations with Caryophyllaceae, Asteraceae, and Cichoriaceae dominated the vegetation. Climate was significantly warmer and moister than during the previous interval. Accumulation of Ice Complex sediments stopped ca 12 ka BP, at the beginning of Allerød. Higher pollen concentration, the presence of willow and birch pollen points to a relatively warm climate between 12 and 11 ka BP reflecting significant climate amelioration. Pollen of shrubs disappeared from the Younger Dryas spectra pointing to the harsher climate. Early Holocene spectra are dominated by alder, birch, Poaceae, and Cyperaceae. Climate reconstruction inferred a temperature substantially warmer than present (up to 12°C). Shrubs gradually disappeared from the area after 7.6 14C ka BP and vegetation cover became similar to modern tundra.

Climatic variability during the penultimate interglacial (MIS 7) and glacial (MIS 6) periods recorded in a speleothem from Kanaan cave, Lebanon (Central Levant)

NASA Astrophysics Data System (ADS)

Nehme, Carole; Verheyden, Sophie; Breitenbach, Sebastian F. M.; Gillikin, David P.; Verheyden, Anouk; Cheng, Hai; Edwards, Laurence; Hellstrom, John; Noble, Stephen R.; Farrant, Andrew R.; Sahy, Diana; Goovaerts, Thomas; Salem, Ghada; Claeys, Philippe

2017-04-01

Little is known about terrestrial climate dynamics of the Levant during the penultimate interglacial-glacial period. A well-dated stalagmite ( 194 to 154 ka) from Kanaan cave, located near the Mediterranean in Lebanon, is examined for its petrography, growth history, and stable isotope geochemistry to answer the climate instability pattern of the glacial MIS 6 and possible wet phases. A highly resolved continental climate record from the northern Levant has been recovered from this precisely U-Th-dated speleothem, spanning the late penultimate interglacial (equivalent of the MIS 7) to the mid-penultimate glacial period ( MIS 6). The stalagmite grew slowly and discontinuously with an unstable isotopic pattern from 194 and at least up to 178 ka. Subsequently, the stalagmite ceased growing from 169.5 to 163.1 ka (interpolated ages) with a hiatus of ca. 6.24 ka according to the model age. However, low δ 18O and δ 13C values indicate generally cold, but overall more humid climate compared to the last glacial (MIS 3). Higher growth rates during the mid-penultimate glacial period ( 163-154 ka) are most probably linked to increased water recharge in the vadose zone. A short More distinct layering in the upper section compared to the basal part of the stalagmite suggests stronger seasonality from 163 ka to 154 ka. Negative oxygen and carbon isotope excursions were found at ˜155.5 ka, ˜156 ka, between ˜159.6 and ˜160.1 ka and at ˜162.6 ka. The inferred Kanaan cave humid intervals during the mid-penultimate period follow variations of pollen records in the Eastern and Western Mediterranean basins and correlate well with the synthetic Greenland records and East Asian Summer Monsoon Interstadials, indicating short warm/wet periods similar to the D-O events during MIS 4-3 in the Eastern Mediterranean region.

Danngarrd-Oscar events recorded in a terrestrial sequence in central British Columbia, Canada

NASA Astrophysics Data System (ADS)

Ward, B. C.; Geertsema, M.; Telka, A.; Mathewes, R.

2012-12-01

The Indianpoint section, 90 km southeast of Prince George, presents a >25 ka record of paleoenvironmental changes from non-glacial MIS 3 time to just before Late Wisconsinan (MIS2) ice from the Cordilleran Ice Sheet overran the site. Detailed plant and insect macrofossil and pollen analyses were carried out on a 5-6 m thick fine-grained unit. It represents a small lake, based on aquatic plants and insects, and taxa indicative of riparian or shoreline environments. A total of 11 radiocarbon ages, most obtained on willow (Salix) twigs provide chronological control for 8 levels. Radiocarbon ages of >44 ka (CAMS-96170) and 46.5 ka (CAMS 93938) were obtained near the base and are associated with spruce macrofossils (abundant needles, seeds and seed wings) and high spruce pollen. Between 37.0 ka (CAMS115785) and 25.9 ka (CAMS117312) alternations between open spruce forest and tundra with minor willow and birch occur. In the upper 2.5 m of the section, between 24.5 ka (CAMS 93940) and 20.4 ka (CAMS 93939), the vegetation changes to dry shrub tundra, dominated again by willow with minor birch. Most pollen from this interval comes from herbs such as sedges, grasses and Artemisia. Also present are characteristic insects such as the weevil Vitavitus thulius and the ground beetles Trichocellus mannerheimi, Pteriostichus (Cryobius) nivalis, and Amara alpina that are presently only found in dry tundra habitats. The decrease in the occurrence of willow and birch in the upper 40-50 cm reflects increasingly harsh conditions as glaciers approached the site. An age of 19.9 ka (AA44045) has been obtained on a willow twig 20-30 cm below where the unit is truncated by a Late Wisconsinan till. The lacustrine unit of the Indianpoint section spans >25 ka and records climatic variation during MIS 3 and deterioration associated with the growth of the Cordilleran Ice Sheet during the Late Wisconsinan (MIS 2). The alternations in the middle portion of the record are thought to represent Danngarrd-Oscar events recorded in the GISP2 Greenland Ice Core. The increasingly dry and cold conditions indicated by the macrofossil assemblage likely reflect the growth of ice in the Coast Mountains that would reduce the availability of moisture to the Interior Plateau from Pacific air masses. This is confirmed by reconstruction of the growth of the Cordilleran Ice Sheet during the Late Wisconsinan based on published radiocarbon dates.

Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

NASA Astrophysics Data System (ADS)

Ivanovic, R. F.; Gregoire, L. J.; Maycock, A.; Valdes, P. J.

2017-12-01

The Laurentide ice sheet, which covered Canada during glacial periods, had a major influence on atmospheric circulation and surface climate, but its role in climate during the early Holocene (9-7 ka), when it was thinner and confined around Hudson Bay, is unclear. It has been suggested that the demise of the ice sheet played a role in the 8.2 ka event (an abrupt 1-3 °C Northern Hemisphere cooling lasting 160 years) through the influence of changing topography on atmospheric circulation. To test this hypothesis, and to investigate the broader implications of changing ice sheet topography for climate, we analyse a set of equilibrium climate simulations with ice sheet topographies taken at 500 year intervals from 9.5 ka to 8.0 ka. Between 9.5 and 8.0 ka, our simulations show a 2 °C cooling south of Iceland and a 1 °C warming between 40-50° N in the North Atlantic. These surface temperature changes are associated with a weakening of the subtropical and subpolar gyres caused by a decreasing wind stress curl over the mid-North Atlantic as the ice sheet lowers. The climate response is strongest during the period of peak ice volume change (9.5 ka - 8.5 ka), but becomes negligible after 8.5 ka. The climatic effects of the Laurentide ice sheet lowering are restricted to the North Atlantic sector. Thus, topographic forcing did not play a significant role in the 8.2 ka event and had only a small effect on Holocene climate change compared to the effects of changes in greenhouse gases, insolation and ice sheet meltwater.

The 9.2 ka event in Asian summer monsoon area: the strongest millennial scale collapse of the monsoon during the Holocene

NASA Astrophysics Data System (ADS)

Zhang, Wenchao; Yan, Hong; Dodson, John; Cheng, Peng; Liu, Chengcheng; Li, Jianyong; Lu, Fengyan; Zhou, Weijian; An, Zhisheng

2018-04-01

Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric 14C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).

A Younger Dryas re-advance of local glaciers in north Greenland

NASA Astrophysics Data System (ADS)

Larsen, Nicolaj K.; Funder, Svend; Linge, Henriette; Möller, Per; Schomacker, Anders; Fabel, Derek; Xu, Sheng; Kjær, Kurt H.

2016-09-01

The Younger Dryas (YD) is a well-constrained cold event from 12,900 to 11,700 years ago but it remains unclear how the cooling and subsequent abrupt warming recorded in ice cores was translated into ice margin fluctuations in Greenland. Here we present 10Be surface exposure ages from three moraines in front of local glaciers on a 50 km stretch along the north coast of Greenland, facing the Arctic Ocean. Ten ages range from 11.6 ± 0.5 to 27.2 ± 0.9 ka with a mean age of 12.5 ± 0.7 ka after exclusion of two outliers. We consider this to be a minimum age for the abandonment of the moraines. The ages of the moraines are furthermore constrained using Optically Stimulated Luminescence (OSL) dating of epishelf sediments, which were deposited prior to the ice advance that formed the moraines, yielding a maximum age of 12.4 ± 0.6 ka, and bracketing the formation and subsequent abandonment of the moraines to within the interval 11.8-13.0 ka ago. This is the first time a synchronous YD glacier advance and subsequent retreat has been recorded for several independent glaciers in Greenland. In most other areas, there is no evidence for re-advance and glaciers were retreating during YD. We explain the different behaviour of the glaciers in northernmost Greenland as a function of their remoteness from the Atlantic Meridional Overturning Circulation (AMOC), which in other areas has been held responsible for modifying the YD drop in temperatures.

Terrestrial biosphere changes over the last 120 kyr and their impact on ocean δ 13C

NASA Astrophysics Data System (ADS)

Hoogakker, B. A. A.; Smith, R. S.; Singarayer, J. S.; Marchant, R.; Prentice, I. C.; Allen, J. R. M.; Anderson, R. S.; Bhagwat, S. A.; Behling, H.; Borisova, O.; Bush, M.; Correa-Metrio, A.; de Vernal, A.; Finch, J. M.; Fréchette, B.; Lozano-Garcia, S.; Gosling, W. D.; Granoszewski, W.; Grimm, E. C.; Grüger, E.; Hanselman, J.; Harrison, S. P.; Hill, T. R.; Huntley, B.; Jiménez-Moreno, G.; Kershaw, P.; Ledru, M.-P.; Magri, D.; McKenzie, M.; Müller, U.; Nakagawa, T.; Novenko, E.; Penny, D.; Sadori, L.; Scott, L.; Stevenson, J.; Valdes, P. J.; Vandergoes, M.; Velichko, A.; Whitlock, C.; Tzedakis, C.

2015-03-01

A new global synthesis and biomization of long (>40 kyr) pollen-data records is presented, and used with simulations from the HadCM3 and FAMOUS climate models to analyse the dynamics of the global terrestrial biosphere and carbon storage over the last glacial-interglacial cycle. Global modelled (BIOME4) biome distributions over time generally agree well with those inferred from pollen data. The two climate models show good agreement in global net primary productivity (NPP). NPP is strongly influenced by atmospheric carbon dioxide (CO2) concentrations through CO2 fertilization. The combined effects of modelled changes in vegetation and (via a simple model) soil carbon result in a global terrestrial carbon storage at the Last Glacial Maximum that is 210-470 Pg C less than in pre-industrial time. Without the contribution from exposed glacial continental shelves the reduction would be larger, 330-960 Pg C. Other intervals of low terrestrial carbon storage include stadial intervals at 108 and 85 ka BP, and between 60 and 65 ka BP during Marine Isotope Stage 4. Terrestrial carbon storage, determined by the balance of global NPP and decomposition, influences the stable carbon isotope composition (δ13C) of seawater because terrestrial organic carbon is depleted in 13C. Using a simple carbon-isotope mass balance equation we find agreement in trends between modelled ocean δ13C based on modelled land carbon storage, and palaeo-archives of ocean δ13C, confirming that terrestrial carbon storage variations may be important drivers of ocean δ13C changes.

A regional record of expanded Holocene wetlands and prehistoric human occupation from paleowetland deposits of the western Yarlung Tsangpo valley, southern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Hudson, Adam M.; Olsen, John W.; Quade, Jay; Lei, Guoliang; Huth, Tyler E.; Zhang, Hucai

2016-07-01

The Asian Monsoon, which brings ∼80% of annual precipitation to much of the Tibetan Plateau, provides runoff to major rivers across the Asian continent. Paleoclimate records indicate summer insolation and North Atlantic paleotemperature changes forced variations in monsoon rainfall through the Holocene, resulting in hydrologic and ecologic changes in plateau watersheds. We present a record of Holocene hydrologic variability in the Yarlung Tsangpo (YT) valley of the southern Tibetan Plateau, based on sedimentology and 14C dating of organic-rich 'black mats' in paleowetlands deposits, that shows changes in wetlands extent in response to changing monsoon intensity. Four sedimentary units indicate decreasing monsoon intensity since 10.4 ka BP. Wet conditions occurred at ∼10.4 ka BP, ∼9.6 ka BP and ∼7.9-4.8 ka BP, with similar-to-modern conditions from ∼4.6-2.0 ka BP, and drier-than-modern conditions from ∼2.0 ka BP to present. Wetland changes correlate with monsoon intensity changes identified in nearby records, with weak monsoon intervals corresponding to desiccation and erosion of wetlands. Dating of in situ ceramic and microlithic artifacts within the wetlands indicates Epipaleolithic human occupation of the YT valley after 6.6 ka BP, supporting evidence for widespread colonization of the Tibetan Plateau in the early and mid-Holocene during warm, wet post-glacial conditions.

Climatic implications of correlated upper Pleistocene glacial and fluvial deposits on the Cinca and Gallego rivers, NE Spain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewis, Claudia J; Mcdonald, Eric; Sancho, Carlos

We correlate Upper Pleistocene glacial and fluvial deposits of the Cinca and Gallego River valleys (south central Pyrenees and Ebro basin, Spain) using geomorphic position, luminescence dates, and time-related trends in soil development. The ages obtained from glacial deposits indicate glacial periods at 85 {+-} 5 ka, 64 {+-} 11 ka, and 36 {+-} 3 ka (from glacial till) and 20 {+-} 3 ka (from loess). The fluvial drainage system, fed by glaciers in the headwaters, developed extensive terrace systems in the Cinca River valley at 178 {+-} 21 ka, 97 {+-} 16 ka, 61 {+-} 4 ka, 47 {+-}more » 4 ka, and 11 {+-} 1 ka, and in the Gallego River valley at 151 {+-} 11 ka, 68 {+-} 7 ka, and 45 {+-} 3 ka. The times of maximum geomorphic activity related to cold phases coincide with Late Pleistocene marine isotope stages and heinrich events. The maximum extent of glaciers during the last glacial occurred at 64 {+-} 11 ka, and the terraces correlated with this glacial phase are the most extensive in both the Cinca (61 {+-} 4 ka) and Gallego (68 {+-} 7 ka) valleys, indicating a strong increase in fluvial discharge and availability of sediments related to the transition to deglaciation. The global Last Glacial Maximum is scarcely represented in the south central Pyrenees owing to dominantly dry conditions at that time. Precipitation must be controlled by the position of the Iberian Peninsula with respect to the North Atlantic atmospheric circulation system. The glacial systems and the associated fluvial dynamic seem sensitive to (1) global climate changes controlled by insolation, (2) North Atlantic thermohaline circulation influenced by freshwater pulses into the North Atlantic, and (3) anomalies in atmospheric circulation in the North Atlantic controlling precipitation on the Iberian peninsula. The model of glacial and fluvial evolution during the Late Pleistocene in northern Spain could be extrapolated to other glaciated mountainous areas in southern Europe.« less

Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2 cal ka, and Little Ice Age events

USGS Publications Warehouse

Benson, L.; Madole, R.; Kubik, P.; McDonald, R.

2007-01-01

Surface-exposure (10Be) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-m-long Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to ???3.0 10Be ka.11Surface-exposure ages in this paper are labeled 10Be; radiocarbon ages are labeled 14C ka, calendar and calibrated radiocarbon ages are labeled cal ka, and layer-based ice-core ages are labeled ka. 14C ages, calibrated 14C ages, and ice core ages are given relative to AD 1950, whereas 10Be ages are given relative to the sampling date. Radiocarbon ages were calibrated using CALIB 5.01 and the INTCAL04 data base Stuiver et al. (2005). Ages estimated using CALIB 5.01 are shown in terms of their 1-sigma range. Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 10Be ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0-11.7 10Be ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the Pinedale glacier and the advance of the Chicago Lakes glacier; in addition, bedrock in the Chicago Lakes cirque area may have remained covered with snow and ice during that interval, thus partially shielding the bedrock from cosmogenic radiation.

Glacial terminations and the Last Interglacial in the Okhotsk Sea; Their implication to global climatic changes

NASA Astrophysics Data System (ADS)

Gorbarenko, Sergey; Velivetskaya, Tatyana; Malakhov, Mikhail; Bosin, Aleksandr

2017-05-01

Paleoclimate data from the Okhotsk Sea (OS) over Terminations II and I (TII, TI), and the Last and Present Interglacial (LIG, PIG) periods were compiled in order to examine Northern Hemisphere climate and sea level changes. Based on records of four AMS 14C-dated OS cores over TI-PIG, it is argued that the OS productivity/climate, IRD (ice-rafted debris), and benthic foraminiferal oxygen isotope (δ18Obf) proxies provide representative and in-phase evidence of the Northern Hemisphere climate and continental ice sheet changes consistent with the LR 04 δ18Obf curve. Chronologies for two central OS cores over TII-LIG-cooling event 23 (C23) were constructed by correlating OS productivity proxies with well-dated δ18O records of Chinese speleothems because OS environment is modulated by East Asian Monsoon; and, as well as correlating measured magnetic paleointensity excursions with those in the dated PISO-1500 paleointensity stack. Results show several OS climatic and environment states, including TII coeval with Asian Weak Monsoon Interval (WMI) II since 136 ka, LIG with a sharp two-step transition (130.2-129 ka) and demise at С25 (116.5 ka), and last glaciation with coolings at C24 (111 ka) and C23. The OS productivity and IRD records demonstrate certain climate amelioration in the middle of WMI-II, and two insignificant cooling events inside the LIG marked by C27 (126 ka) and C26 (120.6 ka). OS δ18Obf records of both cores demonstrate a gradual trend of lighter values since around 131.5 ka BP, continuing from the onset of LIG (129 ka) to minimum values at 126 ka BP (C27), then nearly constant values until 121.5 ka, followed by a slight increase up to 120.6 ka (C26), and a subsequent strong increase up to 116.5 ka (C25). The magnitude of OS δ18Obf oscillations is 1.35‰, which is less than those in the N. Atlantic. It may therefore be suggested that this OS index probably tracks changes in continental ice sheet volume and sea level.

Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)

NASA Astrophysics Data System (ADS)

Svensson, A.; Bigler, M.; Blunier, T.; Clausen, H. B.; Dahl-Jensen, D.; Fischer, H.; Fujita, S.; Goto-Azuma, K.; Johnsen, S. J.; Kawamura, K.; Kipfstuhl, S.; Kohno, M.; Parrenin, F.; Popp, T.; Rasmussen, S. O.; Schwander, J.; Seierstad, I.; Severi, M.; Steffensen, J. P.; Udisti, R.; Uemura, R.; Vallelonga, P.; Vinther, B. M.; Wegner, A.; Wilhelms, F.; Winstrup, M.

2013-03-01

The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia, where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra and on accurately dated European stalagmites, the Toba event is known to occur between the onsets of Greenland interstadials (GI) 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 ka BP) before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM-19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. The bipolar linking gives no support for a long-term global cooling caused by the Toba eruption as Antarctica experiences a major warming shortly after the event. Furthermore, our bipolar match provides a way to place palaeo-environmental records other than ice cores into a precise climatic context.

Episodic Sediment Failure in Northern Flemish Pass, Eastern Canadian Margin: Interplay of Seismicity, Contour Current Winnowing, and Excess Pore Pressures

NASA Astrophysics Data System (ADS)

Piper, D.

2015-12-01

Episodic sediment failures are recognised on continental slopes around Flemish Pass and Orphan Basin from multibeam bathymetry, seismic reflection profiles and piston cores. Seismic stratigraphy is tied to published long cores with O-isotope data back to before MIS 6 and carbonate rich Heinrich layers in places produce marker reflections in high-resolution sparker profiles. Heinrich layers, radiocarbon dates and peaks in diatom abundance provide core chronology. Slope sedimentation was strongly influenced by the Labrador Current and the silty muds show architecture characteristic of contourites. Variation in Labrador Current strength is known from the sortable silt proxy over the past 125 ka. Large slope failures were mapped from seismic reflection profiles and their age estimated from seismic stratigraphy (3-5 ka resolution) and in some cases refined from cores (1-3 ka resolution). Large slope failures occurred apparently synchronously over margin lengths of 50-350 km. Such failures were earthquake triggered: other mechanisms for producing laterally extensive synchronous failure do not apply. Triaxial shear measurements show a Su/σ' ratio of typical slope sediment of 0.48, implying considerable stability. However, some silty muds have Atterberg limits that suggest susceptibility to liquefaction under cyclic loading, particularly in Holocene deposits and by analogy those of past full interglacials. Basal failure planes of some large failures correspond with either the last interglacial or the MIS 6 glacial maximum. Comparison with seismological models suggests that the observed slope failures represent earthquakes ranging from Mw ~5.6 to ~7.6. Mean recurrence interval of M = 7 earthquakes at any point on the margin is estimated at 30 ka from seismological models and 40 ka from the sediment failure record. In northern Flemish Pass, a spatial cluster of several failures over 30 ka preceded by a long interval with no failures suggests that some other mechanism has preconditioned the slope for earthquake triggering. There is circumstantial evidence that such preconditioning is related to excess pore pressures, released by fluid drainage at head scarps.

The marine isotope stage 1-5 cryptotephra record of Tenaghi Philippon, Greece: Towards a detailed tephrostratigraphic framework for the Eastern Mediterranean region

NASA Astrophysics Data System (ADS)

Wulf, Sabine; Hardiman, Mark J.; Staff, Richard A.; Koutsodendris, Andreas; Appelt, Oona; Blockley, Simon P. E.; Lowe, J. John; Manning, Christina J.; Ottolini, Luisa; Schmitt, Axel K.; Smith, Victoria C.; Tomlinson, Emma L.; Vakhrameeva, Polina; Knipping, Maria; Kotthoff, Ulrich; Milner, Alice M.; Müller, Ulrich C.; Christanis, Kimon; Kalaitzidis, Stavros; Tzedakis, Polychronis C.; Schmiedl, Gerhard; Pross, Jörg

2018-04-01

The iconic climate archive of Tenaghi Philippon (TP), NE Greece, allows the study of short-term palaeoclimatic and environmental change throughout the past 1.3 Ma. To provide high-quality age control for detailed palaeoclimate reconstructions based on the TP archive, (crypto)tephra studies of a peat core 'TP-2005' have been carried out for the 0-130 ka interval. The results show that the TP basin is ideally positioned to receive tephra fall from both the Italian and Aegean Arc volcanic provinces. Two visible tephra layers, the Santorini Cape Riva/Y-2 (c. 22 ka) and the Campanian Ignimbrite (CI)/Y-5 (c. 39.8 ka) tephras, and six primary cryptotephra layers, namely the early Holocene E1 tephra from the Aeolian Islands (c. 8.3 ka), the Campanian Y-3 (c. 29 ka) and X-6 tephras (c. 109.5 ka), as well as counterpart tephras TM-18-1d (c. 40.4 ka), TM-23-11 (c. 92.4 ka) and TM-33-1a (c. 116.7 ka) from the Lago Grande di Monticchio sequence (southern Italy), were identified along with repeatedly redeposited Y-2 and CI tephra material. Bayesian modelling of the ages of seven of the primary tephra layers, 60 radiocarbon measurements and 20 palynological control points have been applied to markedly improve the chronology of the TP archive. This revised chronology constrains the age of tephra TM-18-1d to 40.90-41.66 cal ka BP (95.4% range). Several tephra layers identified in the TP record form important isochrons for correlating this archive with other terrestrial (e.g., Lago Grande di Monticchio, Sulmona Basin and Lake Ohrid) and marine (e.g., Adriatic Sea core PRAD 1-2 and Aegean Sea core LC21) palaeoclimate records in the Mediterranean region.

Anticonvulsant effect of Uncaria rhynchophylla (Miq) Jack. in rats with kainic acid-induced epileptic seizure.

PubMed

Hsieh, C L; Chen, M F; Li, T C; Li, S C; Tang, N Y; Hsieh, C T; Pon, C Z; Lin, J G

1999-01-01

This study investigated the anticonvulsant effect of Uncaria rhynchophylla (UR) and the physiological mechanisms of its action in rats. A total of 70 male Sprague-Dawley (SD) rats were selected for study. Thirty four of these rats were divided into 5 groups as follows: 1) CONTROL GROUP (n = 6): received intraperitoneal injection (i.p.) of kainic acid (KA, 12 mg/kg); 2) UR1000 group (n = 10), 3) UR500 group (n = 6) 4) UR250 group, received UR 1000, 500, 250 mg/kg i.p. 30 min prior to KA administration, respectively; 5) Contrast group: received carbamazepine 20 mg/kg i.p. 30 min prior to KA administration. Behavior and EEG were monitored from 15 min prior to drug administration to 3 hours after KA administration. The number of wet dog shakes were counted at 10 min intervals throughout the experimental course. The remaining 36 rats were used to measure the lipid peroxide level in the cerebral cortex one hour after KA administration. These rats were divided into 6 groups of 6 rats as follows: 1) Normal group: no treatment was given; 2) CONTROL GROUP: received KA (12 mg/kg) i.p.; 3) UR1000 group, 4) UR500 group, 5) UR250 group, received UR 1000, 500, 250 mg/kg i.p. 30 min prior to KA administration, respectively; 6) Contrast group: received carbamazepine 20 mg/kg i.p. 30 min prior to KA administration. Our results indicated that both UR 1000 and 500 mg/kg decreased the incidence of KA-induced wet dog shakes, no similar effect was observed in the UR 250 mg/kg and carbamazepine 20 mg/kg group. Treatment with UR 1000 mg/kg, 500 mg/kg, or 250 mg/kg and carbamazepine 20 mg/kg decreased KA-induced lipid peroxide level in the cerebral cortex and was dose-dependent. These findings suggest that the anticonvulsant effect of UR possibly results from its suppressive effect on lipid peroxidation in the brain.

Impact of millennial-scale Holocene climate variability on eastern North American terrestrial ecosystems: Pollen-based climatic reconstruction

USGS Publications Warehouse

Willard, D.A.; Bernhardt, C.E.; Korejwo, D.A.; Meyers, S.R.

2005-01-01

We present paleoclimatic evidence for a series of Holocene millennial-scale cool intervals in eastern North America that occurred every ???1400 years and lasted ???300-500 years, based on pollen data from Chesapeake Bay in the mid-Atlantic region of the United States. The cool events are indicated by significant decreases in pine pollen, which we interpret as representing decreases in January temperatures of between 0.2??and 2??C. These temperature decreases include excursions during the Little Ice Age (???1300-1600 AD) and the 8 ka cold event. The timing of the pine minima is correlated with a series of quasi-periodic cold intervals documented by various proxies in Greenland, North Atlantic, and Alaskan cores and with solar minima interpreted from cosmogenic isotope records. These events may represent changes in circumpolar vortex size and configuration in response to intervals of decreased solar activity, which altered jet stream patterns to enhance meridional circulation over eastern North America. ?? 2004 Elsevier B.V. All rights reserved.

High resolution sedimentary record from the Cocos Ridge: evidence of land-ocean linkages in the Eastern Equatorial Pacific over the last 70 ka

NASA Astrophysics Data System (ADS)

Murdmaa, I.; Ivanova, E.; Leduc, G.; Beaufort, L.; Peresypkin, V.; Vidal, L.; Ovsepyan, E.; Alekhina, G.; Kravtsov, V.; Vasileva, V.

2009-04-01

We analyzed n-alkanes spectra, TOC content, and C/N ratio in the upper 12 m of the giant IMAGES Core MD02-2529 from the Cocos Ridge (08°12.33'N; 84°07.32'W; 1619 m w.d.) to estimate terrestrial organic matter (TOM) and marine organic matter (MOM) contribution to the total organic matter budget in sediments. Multi-proxy studies of nannofossils, benthic and planktic foraminifers reveal productivity variations during the time interval of the last ~ 70 ka recovered by the upper part of the core according to the age model based on AMS-14C dates and benthic oxygen isotope record. According to the shipboard core description, the slightly calcareous hemipelagic mud recovered by Core MD02-2529 contains a considerable admixture of terrestrial plant remains. This is confirmed by optical microscopic and SEM studies which reveal a strong pyritization of the particular terrestrial organic matter. As estimated by the proportion of the mainly terrestrial long-molecular alkanes (C23 - C38) relative to mainly planktic short-molecular ones (C10 - C22), the TOM input largely controls variations in the TOC content throughout the studied core interval, possibly except for the Upper Holocene, where higher TOC values correspond to relatively increased MOM content. TOM strongly dominates over the MOM content in sediments of the beginning of Termination 1, most enriched in total organic matter (up to 3.4% TOC). High content of the TOM is also fixed by n-alkane data over the Younger Dryas and H-events. Mass accumulation rates (MAR) of TOC, as well as terrestrial and marine organic matter, generally support the data on percentages, but show that the MOM flux was considerable even during the maximum TOM input at the beginning of Termination I. We suggest that this abundant TOM flux was related to the glacioeustatic sea level lowstand at the LGM, during which the emerged shelf became a vegetated coastal plain affected by seasonally humid tropical monsoon climate. The terrestrial organic debris was most intensely washed off the coastal plain at the beginning of post-glacial transgression ~17 cal. ka BP. Glacioeustatic sea level oscillations, along with climate and river runoff changes, controlled variations in the TOM flux throughout the studied interval. The MOM commonly prevails in intervals with a low TOC content, although its relatively high MAR values may also coincide with TOC maxima, as at the beginning of Termination I. The MOM contribution to the total organic matter increased in the Early Holocene, at ~ 8 cal. ka, and especially at ~ 60 cal. ka (possibly coeval with the H-6 event). Relatively low and less variable accumulation rates of MOM, as compared to those of TOM may be explained by the location of the site MD02-2529 between the two high-productivity areas associated with coastal upwellings in the Panama Bight and Gulf of Papagayo. The paleoproductivity estimates based on coccolithophoride counts show a short-term variability with the extremal values during the Termination I. This high-productivity event corresponds to the highest planktic foraminiferal abundance and the maximum values of foraminiferal productivity index. The productivity increase at 16-14 cal ka BP might result from the nutrient rearrangement related to reorganization of the thermohaline circulation over the termination. However, high total abundance of benthic foraminifera and maximum values of several productivity-related benthic species are found at MIS 2, from ~ 25 to 22 cal ka BP. MOM export from the upper continental slope by the bottom nepheloid layer during the LGM sea level lowstand might serve as the food source for this benthic production pulse. Meanwhile, calcareous phytoplankton production seems to remain rather high through the late MIS3 - Termination I and decreased during the Holocene. The low total abundance of planktic foraminifera and an enhanced content of oligotrophic mixed-layer dwelling planktic foraminiferal species in the Holocene sediments confirm the productivity decrease. The low productivity might result from a pycnocline deepening due to abundant moisture supply from the Caribbean and corresponding surface water freshening at site MD02-2529.

Synchrotron Radiation and the Far-Infrared and Mid-Infrared Spectra of Ncncs

NASA Astrophysics Data System (ADS)

Winnewisser, Manfred; Winnewisser, Brenda P.; De Lucia, Frank C.; Tokaryk, Dennis; Ross, Stephen Cary; Billinghurst, Brant E.

2014-06-01

The large-amplitude in-plane bending vibration of NCNCS at 85 wn has a potential energy function which includes a barrier to linearity with a height of about 285 wn. The topology of the surface of the space defined by this two-dimensional potential function exhibits non-trivial monodromy. Therefore an energy/momentum map for a quantum system with its motion determined by such a potential takes the form of a lattice which contains a defect associated with the top of the barrier. In NCNCS, the wavenumber values of the fundamental vibrational excitation and the barrier height mean that easily accessible energy levels allow us to observe 3 bending vibrational levels below and 3 above the barrier, yet still below all of the other vibrational levels, allowing the study of all the levels in the neighborhood of the defect. In three measuring campaigns at the Canadian Light Source in May of the years 2011, 2012, and 2013 we have now obtained 8 of the 9 fundamental vibrational band systems of NCNCS in high resolution, in particular that of the large-amplitude bend in the FIR. So far only a-type spectra have been assigned. Thus we have now determined the Δvb = 1, and ΔKa = 0 vibrational intervals (using bent molecule notation) but do not yet have experimental values for either rotational ΔKa = +/- 1 intervals nor ro-vibrational Δvb = 1, ΔKa = +/- 1 intervals. In May of 2014 we will have our last measuring campaign and hope to observe the more elusive b-type transitions.

Cogenetic late Pleistocene rhyolite and cumulate diorites from Augustine Volcano revealed by SIMS 238U-230Th dating of zircon, and implications for silicic magma generation by extraction from mush

USGS Publications Warehouse

Coombs, Michelle L.; Vazquez, Jorge A.

2014-01-01

Augustine Volcano, a frequently active andesitic island stratocone, erupted a late Pleistocene rhyolite pumice fall that is temporally linked through zircon geochronology to cumulate dioritic blocks brought to the surface in Augustine's 2006 eruption. Zircon from the rhyolite yield a 238U-230Th age of ∼25 ka for their unpolished rims, and their interiors yield a bimodal age populations at ∼26 ka and a minority at ∼41 ka. Zircon from dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption, have interiors defining a ∼26 ka age population that is indistinguishable from that for the rhyolite; unpolished rims on the dioritic zircon are dominantly younger (≤12 ka) indicating subsequent crystallization. Zircon from rhyolite and diorite overlap in U, Hf, Ti, and REE concentrations although diorites also contain a second population of high-U, high temperature grains. Andesites that brought dioritic blocks to the surface in 2006 contain zircon with young (≤9 ka) rims and a scattering of older ages, but few zircon that crystallized during the 26 ka interval. Both the Pleistocene-age rhyolite and the 2006 dioritic inclusions plot along a whole-rock compositional trend distinct from mid-Holocene–present andesites and dacites, and the diorites, rhyolite, and two early Holocene dacites define linear unmixing trends often oblique to the main andesite array and consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate amphibole-bearing residue (diorites). Rare zircon antecrysts up to ∼300 ka from all rock types indicate that a Quaternary center has been present longer than preserved surficial deposits.

Geochronology and paleoclimatic implications of the last deglaciation of the Mauna Kea Ice Cap, Hawaii

USGS Publications Warehouse

Anslow, Faron S.; Clark, P.U.; Kurz, M.D.; Hostetler, S.W.

2010-01-01

We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5??2.5ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3km upslope for ~4.5-5.0kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ~15.4ka corresponds to a large reduction of the Atlantic meridional overturning circulation (AMOC) following Heinrich Event 1. Subsequent ice-margin retreat began at 14.6??1.9ka, corresponding to a rapid resumption of the AMOC and onset of the B??lling warm interval, with the ice cap melting rapidly to complete deglaciation. Additional 3He ages obtained from a flood deposit date the catastrophic outburst of a moraine-dammed lake roughly coeval with the Younger Dryas cold interval, suggesting a more active hydrological cycle on Mauna Kea at this time. A coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of LLGM and readvance sizes. The depression of the LLGM equilibrium line altitude requires atmospheric cooling of 4.5??1??C, whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present. We hypothesize (1) that the LLGM temperature depression was associated with global cooling, (2) that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the North Atlantic, and (3) that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter-tropical convergence zone (ITCZ). Such a shift in the ITCZ would have allowed midlatitude cyclones to reach Mauna Kea more frequently which would have increased precipitation at high elevations and caused additional cooling. ?? 2010 Elsevier B.V.

The Role of Middle and Late Holocene North Pacific Sea Surface Temperatures on Precipitation Patterns in the Western United States

NASA Astrophysics Data System (ADS)

Barron, J. A.; Anderson, L.; Starratt, S.; Wahl, D.; Anderson, L.; Addison, J. A.

2015-12-01

Comparative analyses of marine and terrestrial proxy records reveal regional changes in precipitation seasonality and relationships with sea surface temperatures (SSTs) as indicators of ocean-atmosphere dynamics. Enhanced La Niña-like conditions and cooler SSTs characterized the middle Holocene (~8.O to 4.0 ka) waters off northern California and in the eastern equatorial Pacific. Terrestrial records suggest that winters in the western US were generally dry, although wetter intervals attributed to winter precipitation beginning at ~5.5 ka are documented in coastal Oregon and Washington and in the northern Great Basin. Proxy studies suggest that the North American Monsoon (NAM) intensified beginning at ~7.5 ka, coinciding with warming Gulf of California SSTs coupled with a more northerly position of the Intertropical Convergence Zone (ITCZ). If monsoonal precipitation spread northward into the eastern Great Basin and the western Rockies of Colorado, it is possible that wetter intervals of the middle Holocene in Nevada, Utah, and western Colorado may reflect increases in both summer and winter precipitation. El Niño event frequency and intensity began increasing between 4.0 and 3.0 ka, when modern ocean-atmosphere dynamics appear to have been established along the California coastal margin. Effects included cool, wet winters, enhanced spring coastal upwelling that extended into the summer, and higher September-October SSTs corresponding with the end of the coastal upwelling season. Winters became wetter in both the coastal and interior regions of the western US, while spring and summers generally became drier. The intensity of NAM precipitation also declined due to a more southerly mean position of the ITCZ. By ~3.0 cal ka the modern climatology of the margins of eastern North Pacific was established, resulting in intensification of the northwest-southwest precipitation dipole and the development of distinct Pacific Decadal Oscillation cycles.

Geochemical and Sedimentological Records of Late Quaternary Climate Change, Lake Tanganyika, Tropical East Africa

NASA Astrophysics Data System (ADS)

Felton, A. A.; Russell, J. M.; Cohen, A. S.; Baker, M. E.; McGlue, M. M.; Lezzar, K. E.

2005-12-01

We have analyzed piston core records from Lake Tanganyika (western Tanzania, East African Rift Valley) to investigate possible signals of tropical paleoclimate change during the Late Quaternary. Long paleoclimate records from East Africa are of importance for understanding climatic processes such as the role of solar variability in regulating tropical climates at Milankovitch time scales, and the relationship between abrupt climate changes, migration of Intertropical Convergence Zone, and regional climate variability (Nicholson, 2000). However, records of pre-Holocene climate variability from tropical African lakes (>25ka) are still quite rare. Long records from Lake Tanganyika are of particular interest given the lake's antiquity and its demonstrated potential for producing high resolution (frequently annually laminated) sedimentary records (Cohen et al., 1993). We analyzed physical properties, grain size, total organic carbon, major, minor and trace element variability, and biogenic silica data for a 7.75 m core from the Kalya slope and horst region of central Lake Tanganyika at 640m water depth. Nine 14C dates provide an age model for the core, which spans ~62 cal kyr. Elemental concentrations preserved in Lake Tanganyika sediments record variability in deposition and runoff into the lake basin. Under conditions of rapid erosion, exposure and rapid weathering of bedrock has been shown to generate high concentrations of original silicate minerals enriched in soluble cations such as sodium and potassium, elements that are also biologically conservative. Prior to 40ka cal yr. core sediments are characterized by high magnetic susceptibility, intermediate levels of organic carbon, low to intermediate levels of biogenic silica, and fine grain size, indicative of relatively high precipitation. There is a profound decrease in magnetic susceptibility, a decrease in organic carbon and an increase in grain size at 40ka cal yr, which persists until ~16ka cal yr. Seismic reflection profiles demonstrate the existence of paleodeltas at ~360m below modern lake level that may have formed during this period, although it is unclear whether this deposit represents a Late Quaternary (OIS 2) or earlier (OIS 6) event. Maximum aridity occurred at about 20-20.5ka cal yr, consist with earlier interpretations of lake lowstands (Gasse et al., 1989, Scholz et al., 1997). The late Pleistocene and earliest Holocene sediments in our record are characterized by generally rising magnetic susceptibility, declining organic carbon and biogenic silica, and finer grain size. However during this period there are marked fluctuations in magnetic susceptibility and biogenic silica at millennial time-scales. These indicate intervals of fluctuating precipitation, productivity, and possibly windiness and are particularly prominent during the Pleistocene-Holocene transition. Massive clays, rising magnetic susceptibility, low biogenic silica and low organic carbon mark the early Holocene, indicative of increased rainfall during a regionally wet interval. These sediments are capped by a laminated ooze, indicative of drier conditions and a more stratified water body.

The description of a method for accurately estimating creatinine clearance in acute kidney injury.

PubMed

Mellas, John

2016-05-01

Acute kidney injury (AKI) is a common and serious condition encountered in hospitalized patients. The severity of kidney injury is defined by the RIFLE, AKIN, and KDIGO criteria which attempt to establish the degree of renal impairment. The KDIGO guidelines state that the creatinine clearance should be measured whenever possible in AKI and that the serum creatinine concentration and creatinine clearance remain the best clinical indicators of renal function. Neither the RIFLE, AKIN, nor KDIGO criteria estimate actual creatinine clearance. Furthermore there are no accepted methods for accurately estimating creatinine clearance (K) in AKI. The present study describes a unique method for estimating K in AKI using urine creatinine excretion over an established time interval (E), an estimate of creatinine production over the same time interval (P), and the estimated static glomerular filtration rate (sGFR), at time zero, utilizing the CKD-EPI formula. Using these variables estimated creatinine clearance (Ke)=E/P * sGFR. The method was tested for validity using simulated patients where actual creatinine clearance (Ka) was compared to Ke in several patients, both male and female, and of various ages, body weights, and degrees of renal impairment. These measurements were made at several serum creatinine concentrations in an attempt to determine the accuracy of this method in the non-steady state. In addition E/P and Ke was calculated in hospitalized patients, with AKI, and seen in nephrology consultation by the author. In these patients the accuracy of the method was determined by looking at the following metrics; E/P>1, E/P<1, E=P in an attempt to predict progressive azotemia, recovering azotemia, or stabilization in the level of azotemia respectively. In addition it was determined whether Ke<10 ml/min agreed with Ka and whether patients with AKI on renal replacement therapy could safely terminate dialysis if Ke was greater than 5 ml/min. In the simulated patients there were 96 measurements in six different patients where Ka was compared to Ke. The estimated proportion of Ke within 30% of Ka was 0.907 with 95% exact binomial proportion confidence limits. The predictive accuracy of E/P in the study patients was also reported as a proportion and the associated 95% confidence limits: 0.848 (0.800, 0.896) for E/P<1; 0.939 (0.904, 0.974) for E/P>1 and 0.907 (0.841, 0.973) for 0.95 ml/min accurately predicted the ability to terminate renal replacement therapy in AKI. Include the need to measure urine volume accurately. Furthermore the precision of the method requires accurate estimates of sGFR, while a reasonable measure of P is crucial to estimating Ke. The present study provides the practitioner with a new tool to estimate real time K in AKI with enough precision to predict the severity of the renal injury, including progression, stabilization, or improvement in azotemia. It is the author's belief that this simple method improves on RIFLE, AKIN, and KDIGO for estimating the degree of renal impairment in AKI and allows a more accurate estimate of K in AKI. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Geologic Map of the Craters of the Moon 30' x 60' Quadrangle, Idaho

USGS Publications Warehouse

Kuntz, Mel A.; Skipp, Betty; Champion, Duane E.; Gans, Philip B.; VanSistine, D. Paco; Snyders, Scott R.

2007-01-01

The Craters of the Moon 30 x 60 minute quadrangle shows the geology of the northern two-thirds of the Craters of the Moon (COM) lava field and volcanic structures of the northern and central parts of the Great Rift volcanic rift zone. The COM lava field is the largest, predominantly Holocene lava field in the conterminous United States. The northwest corner of the map shows older sedimentary, intrusive, and volcanic rocks that range in age from Ordovician to Miocene. These rocks provide evidence of compressional fold and thrust events of the Antler and Sevier orogenies. Compression was followed by voluminous volcanism represented by the Challis Volcanic Group. Basin-and-Range faulting followed in Neogene time. The COM lava field covers about 1,600 square kilometers and contains about 30 cubic kilometers of lava flows and associated vent deposits. Stratigraphic relationships, paleomagnetic studies, and radiocarbon ages indicate that the field formed during eight eruptive periods designated as H, the oldest, to A, the youngest. Each eruptive period was several hundred years or less in duration and separated from other eruptive periods by non-eruptive recurrence intervals of several hundred to about 3,000 years. The first eruptive period began about 15,000 carbon-14 years ago and the latest one ended about 2,100 carbon-14 years ago. All available field, paleomagnetic, radiocarbon, and argon-40/argon-39 data are incorporated in this map and they quantitatively refine the volcanic and paleomagnetic history of the pre-Holocene lava fields and the COM lava field. In a sense, these data determine the 'pulse rate' for Pleistocene and Holocene basaltic volcanism in the area of this map. Twenty-three new argon-40/argon-39 geochronologic data reveal a fairly complete and continuous record of basaltic volcanism in the Craters of the Moon 30 x 60 minute quadrangle for the last 500 ka. The ages cluster into age groupings at ~30 ka, 50-70 ka, 100-125 ka, 260-290 ka, 320-340 ka, and 475 ka. There are apparent periods of ~30 to 60 ka duration when little or no volcanic activity took place between groups. Magnetic polarity and remanent inclination and declination directions for most lava flows in the quadrangle have normal magnetic polarity; they were emplaced during the Brunhes Normal Polarity Chron and are younger than 780,000 years. Directions of remanent magnetization and the new argon-40/argon-39 ages were used to correlate and approximately date lava flows and lava fields for this map.

New constraints on late Holocene eustatic sea-level changes from Mahé, Seychelles

NASA Astrophysics Data System (ADS)

Woodroffe, Sarah A.; Long, Antony J.; Milne, Glenn A.; Bryant, Charlotte L.; Thomas, Alexander L.

2015-05-01

This study provides new estimates of globally integrated ice sheet melt during the late Holocene (since 4 ka BP) from Seychelles in the western Indian Ocean, a tectonically stable, far field location where the necessary Glacial-Isostatic Adjustment (GIA) correction is small and is relatively insensitive to predictions using different Earth viscosity profiles. We compare sea level data from Seychelles to estimates of eustasy from two GIA models, ICE-5G and EUST3, which represent end-members in the quantity of global melt during the late Holocene. We use data from a range of coastal environments including fringing reef, present day beaches, fossil plateau and mangrove deposits on the largest island of the Seychelles archipelago, Mahé to reconstruct relative sea-level changes. Our data suggest that extensive coastal deposits of carbonate-rich sands that fringe the west coast formed in the last 2 ka and the horizontal nature of their surface topography suggests RSL stability during this period. Mangrove sediments preserved behind these deposits and in river mouths date to c. 2 ka and indicate that RSL was between -2 m and present during this interval. Correcting the reconstructed sea level data using a suite of optimal GIA models based on the two ice models mentioned above and a large number (c. 350) of Earth viscosity models gives a result that is consistent with the sedimentological constraints. When uncertainties in both model results and data are considered, it is possible to rule out eustatic sea levels below c. 2 m and more than a few decimetres above present during the past two millennia. This uncertainty is dominated by error in the reconstructions rather than the model predictions. We note, however, that our estimates of eustasy are more compatible with the EUST3 model compared to the ICE-5G model during the late Holocene (2-1 ka BP). Our evidence from Seychelles shows that the timing of when eustatic sea level first rose close to present is between the predictions of the two end-member GIA models presented here (4 ka BP for ICE-5G and 1 ka BP for EUST3). Using all lines of evidence currently available from Mahé we suggest that the eustatic contribution during the last 2 ka has been less than 2 m . This conclusion is drawn from a tectonically stable, far-field region that is relatively insensitive to earth and ice model uncertainties, and implies that global eustasy has been relatively insensitive to climate fluctuations over the pre-industrial part of the last 2 ka.

Characteristics of NLDN-Reported Radio Frequency Emissions Associated with Terrestrial Gamma-ray Flashes

NASA Astrophysics Data System (ADS)

Mailyan, B. G.; Nag, A.; Murphy, M. J.; Briggs, M. S.; Dwyer, J. R.; Cramer, E.; Stanbro, M.; Roberts, O. J.; Rassoul, H.

2017-12-01

Electric and magnetic field signals in the radio frequency range associated with Terrestrial Gamma-ray Flashes (TGFs) have become important measurements for studying this high-energy atmospheric phenomenon. These signals can be used to geolocate the source of TGFs, but they also provide insights into the TGF production mechanism, and the relationship between particle fluxes and lightning. In this study, we analyze 32 TGFs detected by the Fermi Gamma-ray Burst Monitor (GBM) occurring in 2014-2016 in conjunction with data from the U.S. National Lightning Detection Network (NLDN). We examine the characteristics of magnetic field waveforms measured by NLDN sensors for 48 pulses occurring within 5 ms of the peak-time of the gamma-ray photon flux. The -3 dB bandwidth of the NLDN sensors are from about 400 Hz to 400 KHz. For 15 (out of 32) TGFs, the associated NLDN pulse occurred almost simultaneously with (that is, within 300 μs of) the TGF. It is possible that these near-simultaneous low frequency magnetic field pulses were produced by relativistic electron beams. The median time interval between the beginning of these near-simultaneous NLDN pulses and the peak-times of the TGF flux is 38 μs. 3 out of 16 ( 19%) of these pulses had negative initial polarity. The absolute value of NLDN-estimated peak currents, which can be viewed as a quantity proportional to the peak magnetic radiation field of these pulses, ranges from 17 kA to 166 kA, with the median being 32 kA. Twelve pulses had peak currents less than 50 kA. Additionally, we will compare the characteristics of GBM-reported gamma-ray signatures of the two categories of TGFs, those with a near-simultaneous NLDN-detected pulse and those with no such pulse (but with other pulses detected by the NLDN occurring within 5 ms of the TGF). Also, one of the TGFs occurred within the coverage region of the Kennedy Space Center Lightning Mapping Array (LMA). We will examine in detail the LMA, NLDN, and NEXRAD radar data for this TGF.

Declining growth of Mauna Loa during the last 100,000 years: Rates of lava accumulation vs. gravitational subsidence

NASA Astrophysics Data System (ADS)

Lipman, Peter W.

Long-term growth rates of Hawaiian volcanoes are difficult to determine because of the short historical record, problems in dating tholeiitic basalt by K-Ar methods, and concealment of lower volcanic flanks by 5 km of seawater. Combined geologic mapping, petrologic and geochemical studies, geochronologic determinations, marine studies, and scientific drilling have shown that, despite frequent large historical eruptions (avg. 1 per 7 years since mid 19th century), the lower subaerial flanks of Mauna Loa have grown little during the last hundred thousand years. Coastal lava-accumulation rates have averaged less than 2 mm/year since 10 to 100 ka along the Mauna Loa shoreline, slightly less than recent isostatic subsidence rates of 2.4-2.6 mm/yr. Since 30 ka, lava accumulation has been greatest on upper flanks of the volcano at times of summit caldera overflows; rift eruptions have been largely confined to vents at elevations above +2,500 m, and activity has diminished lower along both rift zones. Additional indicators of limited volcanic construction at lower levels and declining eruptive activity include: (1) extensive near-surface preservation of Pahala Ash along the southeast coast, dated as older than about 30 ka; (2) preservation in the Ninole Hills of block-slumped ancestral Mauna Loa lavas erupted at 100-200 ka; (3) preservation low in the subaerial Kealakekua landslide fault scarp of lavas newly dated by K-Ar as 166±53 ka; (4) preservation of submerged coral reefs (150 m depth) dated at 14 ka and fossil shoreline features (as much as 350-400 m depth), with estimated ages of 130-150 ka, that have survived without burial by younger Mauna Loa lavas and related ocean-entry debris; (5) incomplete filling of old landslide breakaway scars; (6) limited deposition of post-landslide lava on lower submarine slopes (accumulation mostly <1,000 m depth); and (7) decreased deformation and gravitational instability of the volcanic edifice. In addition, the estimated recent magma-supply rate for Mauna Loa, about 28×106 m3/yr since 4 ka (including intrusions), is inadequate to have constructed the present-day edifice (80×103 km3) within a geologically feasible interval (0.6-1.0 m.y.); higher magma supply (100×106 m3/yr?, comparable to present-day Kilauea) must have prevailed during earlier times of more rapid volcano growth. Interpreted collectively, these features indicate that the emerged area of Mauna Loa and its eruptive vigor were greater in the past than at present. Volcanic growth due to lava accumulation has been offset by subsidence and by landsliding on the lower Hanks of the volcano. Along with the apparent "drying up" of distal parts of the rift zones, these features suggest that Mauna Loa is nearing the end of the tholeiitic shield-building stage of Hawaiian volcanism.

From Lake Malawi Drilling: East African Climate May Have Caused Major Evolutionary Turnover in Mammalian Species During MIS 14

NASA Astrophysics Data System (ADS)

Johnson, Thomas; Werne, Josef

2016-04-01

Hominin evolution underwent important changes in the last 1.3 million years, including the extinction of Paranthropus at about 1.2 Ma, leaving Homo as the sole hominin genus. Our genus experienced a major increase in cranial capacity at about 500 ka, and our species, H. sapiens, first appeared at ~200 ka. There was a major turnover in mammalian species in East Africa between 540 and 400 ka, favoring descendants of smaller size and less specialized diet. An understanding of what drove evolution in these directions is fundamental to understanding the development of modern H. sapiens. Climate certainly played a role, for it is the principal factor that influences the distribution of vegetation and habitability on the landscape. We present a 1.3 million year record of temperature and hydroclimate in the basin of Lake Malawi, the second deepest lake in Africa, derived from a 380 m sediment sequence taken from a water depth of 590 m by the Lake Malawi Drilling Project. Seismic reflection profiles used to select the site portray an undisturbed sedimentary section that was not impacted by erosion, turbidity currents or mass wasting events. Sediment samples were analyzed to produce records of temperature (TEX86) and aridity (Ca content and leaf wax δ13C). The temperature record displays progressively larger amplitude glacial-interglacial variations from MIS 13 (~500 ka) to MIS 5 (~125 ka). Intervals of low Ca abundance, which reflect lake high stands, correlate with times of depleted δ13Cwax and relatively warm temperatures. The Malawi basin experienced warm, wet interglacials and cooler (by about 2 - 4°C), dry glacial periods, with roughly a 100 ky periodicity since the Mid-Pleistocene Transition (MPT), about 900 ka. The paleoclimate record from Lake Malawi sediments portrays a transition from a highly variable and predominantly arid climate prior to 900 ka to a progressively more humid environment after the MPT dominated by 100 ky cycles consisting of warm, wet interglacial periods alternating with relatively cool, dry glacial periods. One of the coldest, and most prolonged dry periods of the last million years in the Malawi basin occurred around 540 ka (MIS 14). This perturbation in the climate may have been a factor in the substantial mammalian extinctions and increased cranial capacity of Homo that occurred during this time. As more long-term, high-resolution histories of climate are recovered from the other great lakes of East Africa, we will be able to address key questions raised by the Malawi record, e.g., the extent of the rift valley that shifted to wetter conditions over the past million years, and whether MIS 14 was an unusually cold ice age throughout the region. Future drilling campaigns on the East African Great Lakes will offer unique opportunities to understand the changing landscape where our ancestors evolved, migrated, and advanced their cultures.

Increased production of cosmogenic 10Be recorded in oceanic sediment sequences: Information on the age, duration, and amplitude of the geomagnetic dipole moment minimum over the Matuyama-Brunhes transition

NASA Astrophysics Data System (ADS)

Simon, Quentin; Thouveny, Nicolas; Bourlès, Didier L.; Bassinot, Franck; Savranskaia, Tatiana; Valet, Jean-Pierre; Aster Team

2018-05-01

New high-resolution authigenic 10Be/9Be ratio (Be-ratio) records covering the last geomagnetic reversal, i.e. the Matuyama-Brunhes transition (MBT), have been obtained and set on a time scale using benthic δ18O (Cibicides wuellerstorfi) records. The geographic distribution of the four studied sites allows global comparison between the North Atlantic, Indian and Pacific Oceans. All Be-ratio records contain a two-fold increase triggered by the geomagnetic dipole moment (GDM) collapse associated with the MBT. The stratigraphic position of the Be-ratio spike, relative to marine isotope stages, allows establishment of a robust astrochronological framework for the MBT, anchoring its age between 778 and 766 ka (average mid-peaks at 772 ka), which is consistent with all other available 10Be-proxy records from marine, ice and loess archives. The global 10Be atmospheric production doubling represents an increase of more than 300 atoms m-2 s-1 that is compatible with the increased magnitude of atmospheric 10Be production obtained by simulations between the present GDM and a null-GDM. The minimum 10Be-derived GDM average computed for the 776-771 ka interval is 1.7 ± 0.4 ×1022 Am2, in agreement with model simulations and absolute paleointensities of transitional lava flows.

Hydroclimate of the Last Glacial Maximum and deglaciation in southern Australia's arid margin interpreted from speleothem records (23-15 ka)

NASA Astrophysics Data System (ADS)

Treble, Pauline C.; Baker, Andy; Ayliffe, Linda K.; Cohen, Timothy J.; Hellstrom, John C.; Gagan, Michael K.; Frisia, Silvia; Drysdale, Russell N.; Griffiths, Alan D.; Borsato, Andrea

2017-06-01

Terrestrial data spanning the Last Glacial Maximum (LGM) and deglaciation from the southern Australian region are sparse and limited to discontinuous sedimentological and geomorphological records with relatively large chronological uncertainties. This dearth of records has hindered a critical assessment of the role of the Southern Hemisphere mid-latitude westerly winds on the region's climate during this time period. In this study, two precisely dated speleothem records for Mairs Cave, Flinders Ranges, are presented, providing for the first time a detailed terrestrial hydroclimatic record for the southern Australian drylands during 23-15 ka. Recharge to Mairs Cave is interpreted from the speleothem record by the activation of growth, physical flood layering, and δ18O and δ13C minima. Periods of lowered recharge are indicated by 18O and 13C enrichment, primarily affecting δ18O, argued to be driven by evaporation of shallow soil/epikarst water in this water-limited environment. A hydrological driver is supported by calcite fabric changes. These include the presence of laminae, visible organic colloids, and occasional dissolution features, related to recharge, as well as the presence of sediment bands representing cave floor flooding. A shift to slower-growing, more compact calcite and an absence of lamination is interpreted to represent reduced recharge. The Mairs Cave record indicates that the Flinders Ranges were relatively wet during the LGM and early deglaciation, particularly over the interval 18.9-15.8 ka. This wetter phase ended abruptly with a shift to drier conditions at 15.8 ka. These findings are in agreement with the geomorphic archives for this region, as well as the timing of events in records from the broader Australasian region. The recharge phases identified in the Mairs Cave record are correlated with, but antiphase to, the position of the westerly winds interpreted from marine core MD03-2611, located 550 km south of Mairs Cave in the Murray Canyons region. The implication is that the mid-latitude westerlies are located further south during the period of enhanced recharge in the Mairs Cave record (18.9-16 ka) and conversely are located further north when greater aridity is interpreted in the speleothem record. A further comparison with speleothem records from the northern Australasian region reveals that the availability of tropical moisture is the most likely explanation driving enhanced recharge, with further amplification of recharge occurring during the early half of Heinrich Stadial 1 (HS1), possibly influenced by a more southerly displaced Intertropical Convergence Zone (ITCZ). A rapid transition to aridity at 15.8 ka is consistent with a retraction of this tropical moisture source.

Coastal cliffs, rock-slope failures and Late Quaternary transgressions of the Black Sea along southern Crimea

NASA Astrophysics Data System (ADS)

Pánek, Tomáš; Lenart, Jan; Hradecký, Jan; Hercman, Helena; Braucher, Règis; Šilhán, Karel; Škarpich, Václav

2018-02-01

Rock-slope failures represent a significant hazard along global coastlines, but their chronology remains poorly documented. Here, we focus on the geomorphology and chronology of giant rockslides affecting the Crimean Mountains along the Black Sea coast. Geomorphic evidence suggests that high (>100 m) limestone cliffs flanking the southern slopes of the Crimean Mountains are scarps of rockslides nested within larger deep-seated gravitational slope deformations (DSGSDs). Such pervasive slope failures originated due to lateral spreading of intensively faulted Late Jurassic carbonate blocks moving atop weak/plastic Late Triassic flysch and tuff layers. By introducing a dating strategy relying on the combination of the uranium-thorium dating (U-Th) of exposed calcareous speleothems covering the landslide scarps with the 36Cl exposure dating of rock walls, we are able to approximate the time interval between the origin of incipient crevices and the final collapse of limestone blocks that exposed the cliff faces. For the three representative large-scale rockslides between the towns of Foros and Yalta, the initiation of the DSGSDs as evidenced by the widening of crevices and the onset of speleothem accumulation was >300 ka BP, but the recent cliff morphology along the coast is the result of Late Pleistocene/Holocene failures spanning ∼20-0.5 ka BP. The exposures of rockslide scarps occurred mostly at ∼20-15, ∼8, ∼5-4 and ∼2-0.5 ka, which substantially coincide with the last major Black Sea transgressions and/or more humid Holocene intervals. Our study suggests that before ultimate fast and/or catastrophic slope failures, the relaxation of rock massifs correlative with karstification, cracks opening, and incipient sliding lasted on the order of 104-105 years. Rapid Late Glacial/Holocene transgressions of the Black Sea likely represented the last impulse for the collapse of limestone blocks and the origin of giant rockslides, simultaneously affecting the majority of the SW coast of the Crimean Peninsula.

Geomagnetic Dipole Lows and Excursions of the last 800 ka : connection with Interglacials and/or low Obliquity Times?

NASA Astrophysics Data System (ADS)

Thouveny, N.

2006-12-01

Paleomagnetic directions, relative paleointensities (RPI) and authigenic 10Be/9Be ratio were measured along sedimentary clayey-carbonate sequences in high accumulation rate sites of the Portuguese margin (0-400 ka BP) and West-Equatorial Pacific (600-1300 ka BP. Series of high and low RPI features are placed on the chronological scale using C-14 ages, using correlations with of delta O-18 records with the Greenland ice cores and SPECMAP records, and using the ages of polarity reversals. During the time intervals of dramatically low RPI anomalous paleodirections document excursions or polarity reversals. Significant peaks of the authigenic 10Be/9Be ratio point in stratigraphic layers recording all low RPI phases. Plotted against RPI data the 10Be/9Be ratios statistically follow the expected power law (Elsasser et al. ,1958 and Lal, 1988), which strongly establishes the unique and direct link between the recorded cosmogenic enhancement and dipole moment loss, allowing us to univocally interpret our 10Be/9Be ratio and RPI records in terms of geomagnetic dipole moment lows and highs (DML and DMH) alternation. delta O-18 records of the same cores (e.g. Abreu et al. 2004), provide the frame to interpret dipole moment variations in a paleoclimatic context within strict stratigraphic terms. We note that most DML of the last 400 ka fall in the end of interglacial stages, while DMH are rather related with full glacials. We then confirm this coincidence, though whithout strict stratigraphic control, by comparing the SINT-800 curve (Guyodo and Valet, 1999) and the S. E. Pacific near Sea Floor mag. record (Gee et al., 2000), with the highest resolution 18O record yet available (Bassinot et al. 1994). Complex Wavelet analyses using modulus and phase reveal that the geomagnetic moment proxy records contain a maximum power for periods between 30 and 100 ka. DML do not occur in any fixed eccentricity context, but several DML fall at the time of obliquity minima. The comparison of phases of the SINT-800 and Indian Ocean 18O records, at the 100 ka period, indicates that the ice volume fluctuations lead the geomagnetic moment fluctuations. These observations shed the light on mechanical couplings via Earth's rotation rate and/or orbital changes : 1) Alternations of ice accretion/melting at high and mid-latitude may have resulted in acceleration/deceleration of the Earth's rotation (Doake, 1977), although the mass of the 130 m equivalent sea level only represents 7 ppm of the Earth mass. However, acceleration/braking effects generated by tides friction on large/reduced continental platform at low/high sea level conditions (in glacial/interglacial conditions resp.)may have contribute. A coupling between Earth's rotation and geomagnetic regime was suggested for the 20th century (Courtillot and Le Mouel, 1984; Jing, 1992). An alternative - or complementary- explanation can be envisaged: lots of DML occured at the time of low obliquity, i.e. at the time of low angle precession, (rejoining Fuller's (2006)observation and re-introducing the long standing debate about possible forcing by astronomical precession on the geodynamo (Malkus, 1963,1968, Rochester, 1976). It has to be emphasized that because deglaciation are explained by maximum summer insolation of the Northern hemisphere (i.e. at high obliquity), dipole lows occurring at low obliquity, would logically lagg the deglaciation by obliquity period (20.5 ka), and thus occur near the end of interglacials.

Geomagnetic field intensity determination from Pleistocene trachytic lava flows in Jeju Geopark

NASA Astrophysics Data System (ADS)

Jeong, Doohee; Yu, Yongjae; Liu, Qingsong; Jiang, Zhaoxia; Koh, Gi Won; Koh, Dong-Chan

2014-03-01

A composite of 28 trachytic lava flows were recovered from the Jeju Geopark Drilling Project (JGDP) in Jeju Geopark, one of the new seven wonders of Nature declared by UNESCO in 2011. Each trachytic lava flow has a tendency to increase in magnetic grain size from the rapidly cooled brecciated margin and vesicle streaked zone downward into the massive crystalline flow interiors. The brecciated margin and vesicle streaked zone of individual trachytic lava flow contains exclusively fine-grained magnetite as inclusions in plagioclase. High-fidelity paleointensity determinations were obtained from 26 (out of 224 examined) samples from JGDP cores. Temporal variation of virtual axial dipole moments (VADMs) calculated from the absolute paleointensity estimates follows the trend of sint-800 data for the interval from ˜80 to ˜360 ka. High VADM from flow 21 possibly represents real intensity peak, as previously recognized high VADM in Japan at ˜336 ka, in Trans-Mexican volcanism ˜339, and in Hawaii ˜340-350 ka. Perhaps such a strong magnetic intensity near ˜325-350 ka might be smoothed out in relative paleointensity records.

Ocean-atmosphere interactions as drivers of mid-to-late Holocene rapid climate changes: Evidence from high-resolution stalagmite records at DeSoto Caverns, Southeast USA

NASA Astrophysics Data System (ADS)

Aharon, Paul; Dhungana, Rajesh

2017-08-01

Oxygen and carbon isotope time-series derived from an actively growing aragonitic stalagmite in DeSoto Caverns exhibit with unusual clarity rapid hydroclimate changes in the mid-to-late Holocene. Data consist of 1884 δ18O and δ13C determinations whose chronology is anchored on 35 230Th/234U absolute dates in the interval 6.0-1.1 cal ka BP. Exceptional 18O and 13C-enrichments centered at 4.8 ± 0.14 cal ka BP likely represent the imprints of a severe drought. Isotope cycles from 4.7 to 1.3 cal ka BP, exhibit a dominant periodicity of 68 ± 4 yrs. A gradual cooling trend of ∼0.6 °C/103 yrs is attributed to a declining seasonal contrast in insolation. The synchronicity of the mega-drought in the Southeast US with the (1) termination of the African Humid Period; (ii) abrupt reduction of the North Atlantic Deep Water production, and (iii) rapid sea-ice expansion in the polar regions of both Hemispheres testifies to the global extent and rapidity of the "5 ka" event and points to the North Atlantic Deep Water variability as the likely controlling factor. The multidecadal cycles are consistent with alternating dry and wet summers occurring during a long-term switch in the seasonal rainfall amount dominance from winter to summer. The periodic summer droughts in the Southeast US support climate models that predict profound hydroclimate changes in the late Holocene governed by the Atlantic Multidecadal Oscillation. The relatively short and rapid hydroclimate phase transitions documented in this study introduce a complication in the correlation of late Holocene drought events that had significant societal impacts.

Sensitivity of sediment magnetic records to climate change during Holocene for the northern South China Sea

NASA Astrophysics Data System (ADS)

Ouyang, Tingping; Li, Mingkun; Zhao, Xiang; Zhu, Zhaoyu; Tian, Chengjing; Qiu, Yan; Peng, Xuechao; Hu, Qiao

2016-05-01

Magnetic property has been proved to be a sensitive proxy to climate change for both terrestrial and marine sediments. Based on the schedule frame established by AMS 14C dating of foraminifera, detail magnetic analyses were performed for core PC24 sediments at sampling intervals of 2 cm to discuss magnetic sensitivity of marine sediment to climate during Holocene for the northern South China Sea. The results indicated that: 1) Concentration dependent magnetic parameters are positive corresponding to variation of temperature. The frequency dependent susceptibility coefficient basically reflected the variation in humidity; 2) XARM/SIRM was more sensitive to detrital magnetite particles and SIRM/X was more effective to biogenic magnetite particles. Variations of XARM/SIRM and SIRM/X are corresponding to precipitation and temperature, respectively; 3) the Holocene Megathermal in the study area was identified as 7.5-3.4 cal. ka BP. The warmest stage of Holocene for the study area should be during 6.1 to 3.9 cal. ka BP; 4) The 8 ka cold event was characterized as cold and dry during 8.55 to 8.25 cal. ka BP; 5) During early and middle Holocene, the climate combinations were warm dry and cold wet. It turned to warm and wet after 2.7 cal. ka BP.

Early volcanic history of the Rabaul area

NASA Astrophysics Data System (ADS)

McKee, Chris O.; Duncan, Robert A.

2016-04-01

We conducted an extensive program of 40Ar-39Ar age determinations on a suite of 27 volcanic rock samples from key stratigraphic units at Rabaul, Papua New Guinea in order to improve understanding of the early eruption history of the multiple volcanic systems present in the area. Analyses of whole rock, plagioclase and groundmass separates yielded statistically significant ages for 24 samples. Replicate analyses (groundmass, plagioclase) for 17 of the samples provided concordant ages. The oldest systems in the Rabaul area (>1 Ma to ≈300 ka) are in the south, associated with the caldera-like Varzin Depression, and in the north, at the stratovolcanoes Watom and Tovanumbatir. The earliest known activity of the Rabaul system occurred between about 330 and 200 ka and involved emplacement of lava flows and scoria deposits. Major explosive activity at the Rabaul system commenced at about 200 ka and produced a sequence of dacitic ignimbrites that culminated with the emplacement of the large-volume Malaguna Pyroclastics at about 160 ka. Calderas may have been formed as a consequence of the large volumes of tephra produced during some of these eruptions. Products of the early activity are found in the northern and northeastern walls of Rabaul Caldera and on the northeastern flank of Tovanumbatir. This leads to the conclusion that the source of the early activity at Rabaul probably was located in the northern part of the present caldera complex. A shift in the focus of activity at the Rabaul system took place between about 160 and 125 ka. All of the younger (<125 ka) major pyroclastic formations, including the Karavia Welded Tuff, the Barge Tunnel Ignimbrite and the Latlat Pyroclastics, which make up the bulk of the exposure in the southern and western walls of Rabaul Caldera, were erupted from a source or sources in the south-central part of the complex. The stratovolcanoes Palangiangia and Kabiu, which flank the northeastern part of the complex, had commenced activity by about 100 ka while their neighbour to the southeast, Turagunan, was active by about 70 ka. There is little stratigraphic and chronological information about the Tavui system, immediately north of Rabaul. At present, the products of only two eruptions in the Rabaul area can be attributed to Tavui: the ≈79 ka Tokudukudu Ignimbrite and the ≈7 ka Raluan Ignimbrite. However, this evidence of activity and its timing is sufficient to show that the Tavui and Rabaul systems are co-eval. The average interval between major eruptions at the Rabaul system over the last ≈18 ky is in the range 2.6 to 6 ky. Eruption frequency likely varied over the life of the system; however, the return period during the early phase of ignimbrite eruptions appears to have been similar to that of the last ≈18 ky.

Radiolaria and pollen records from 0 to 50 ka at ODP Site 1233: Continental and marine climate records from the Southeast Pacific

USGS Publications Warehouse

Pisias, N.G.; Heusser, L.; Heusser, C.; Hostetler, S.W.; Mix, A.C.; Weber, M.

2006-01-01

Site 1233 drilled during Leg 202 of the Ocean Drilling Program provides a detailed record of marine and continental climate change in the Southeast Pacific and South American continent. Splits from over 500 samples taken at 20 cm intervals for quantitative analysis of radiolarian and pollen populations yield a temporal resolution of 200-400 years. In each sample, 39 pollen taxa and 40 radiolarian species and genera were evaluated. Age control is provided by 25 AMS 14C dates [Lamy, F., Kaiser, J., Ninnemann, U., Hebbeln, D., Arz, H.W., Stoner, J., 2004. Science 304, 1959-1962]. Multivariate statistical analyses of these data allow us to conclude the following: (1) During the past 50 ka, the region of the central Chile coast is not directly influenced by polar water from the Antarctic region. (2) Changes in ocean conditions off central Chile during this time interval primarily reflect north-south shifts in the position of the South Pacific transition zone. (3) Changes in Chilean vegetation reflect comparable latitudinal shifts in precipitation and the position of the southern westerlies. (4) The first canonical variate of radiolarian and pollen records extracted from Site 1233 are remarkably similar to each other as well as to temperature records from the Antarctic, which suggests that marine and continental climate variability in the region is tightly coupled at periods longer than 3000 years. (5) The phase coupling of these climate records, which lead variations of continental erosion based on iron abundance at the same site, are consistent with a hypothesis that erosion is linked to relatively long (i.e, few thousand years) response times of the Patagonian ice sheet, and thus is not a direct indicator of regional climate. ?? 2005 Elsevier Ltd. All rights reserved.

Coupled greenhouse warming and deep-sea acidification in the middle Eocene

NASA Astrophysics Data System (ADS)

Bohaty, Steven M.; Zachos, James C.; Florindo, Fabio; Delaney, Margaret L.

2009-06-01

The Middle Eocene Climatic Optimum (MECO) is an enigmatic warming event that represents an abrupt reversal in long-term cooling through the Eocene. In order to further assess the timing and nature of this event, we have assembled stable isotope and calcium carbonate concentration records from multiple Deep Sea Drilling Project and Ocean Drilling Program sites for the time interval between ˜43 and 38 Ma. Revised stratigraphy at several sites and compilation of δ18O records place peak warming during the MECO event at 40.0 Ma (Chron C18n.2n). The identification of the δ18O excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive. The total duration of the MECO event is estimated at ˜500 ka, with peak warming lasting <100 ka. Assuming minimal glaciation in the late middle Eocene, ˜4°-6°C total warming of both surface and deep waters is estimated during the MECO at the study sites. The interval of peak warming at ˜40.0 Ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth, reflecting a temporary shoaling of the calcite compensation depth. The synchroneity of deep-water acidification and globally extensive warming makes a persuasive argument that the MECO event was linked to a transient increase in atmospheric pCO2. The results of this study confirm previous reports of significant climatic instability during the middle Eocene. Furthermore, the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short-term climate variability during this critical period of Eocene climate evolution.

Quaternary paleoceanography of the central Arctic based on Integrated Ocean Drilling Program Arctic Coring Expedition 302 foraminiferal assemblages

USGS Publications Warehouse

Cronin, T. M.; Smith, S.A.; Eynaud, F.; O'Regan, M.; King, J.

2008-01-01

The Integrated Ocean Drilling Program (IODP) Arctic Coring Expedition (ACEX) Hole 4C from the Lomonosov Ridge in the central Arctic Ocean recovered a continuous 18 in record of Quaternary foraminifera yielding evidence for seasonally ice-free interglacials during the Matuyama, progressive development of large glacials during the mid-Pleistocene transition (MPT) ???1.2-0.9 Ma, and the onset of high-amplitude 100-ka orbital cycles ???500 ka. Foraminiferal preservation in sediments from the Arctic is influenced by primary (sea ice, organic input, and other environmental conditions) and secondary factors (syndepositional, long-term pore water dissolution). Taking these into account, the ACEX 4C record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages (MIS) 13-37, and although less precise dating is available for older sediments, these trends appear to continue through the Matuyama. The MPT is characterized by nearly barren intervals during major glacials (MIS 12, 16, and 22-24) and faunal turnover (MIS 12-24). Abundant calcareous planktonic (mainly Neogloboquadrina pachyderma sin.) and benthic foraminifers occur mainly in interglacial intervals during the Brunhes and very rarely in the Matuyama. A distinct faunal transition from calcareous to agglutinated foraminifers 200-300 ka in ACEX 4C is comparable to that found in Arctic sediments from the Lomonosov, Alpha, and Northwind ridges and the Morris Jesup Rise. Down-core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100-ka cycles, pore water dissolution, or both. Copyright 2008 by the American Geophysical Union.

The Antarctic ice core chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years

NASA Astrophysics Data System (ADS)

Veres, D.; Bazin, L.; Landais, A.; Toyé Mahamadou Kele, H.; Lemieux-Dudon, B.; Parrenin, F.; Martinerie, P.; Blayo, E.; Blunier, T.; Capron, E.; Chappellaz, J.; Rasmussen, S. O.; Severi, M.; Svensson, A.; Vinther, B.; Wolff, E. W.

2012-12-01

The deep polar ice cores provide reference records commonly employed in global correlation of past climate events. However, temporal divergences reaching up to several thousand years (ka) exist between ice cores over the last climatic cycle. In this context, we are hereby introducing the Antarctic Ice Core Chronology 2012 (AICC2012), a new and coherent timescale developed for four Antarctic ice cores, namely Vostok, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML) and Talos Dome (TALDICE), alongside the Greenlandic NGRIP record. The AICC2012 time scale has been constructed using the Bayesian tool Datice (Lemieux-Dudon et al., 2010) that combines glaciological inputs and data constraints, including a wide range of relative and absolute gas and ice stratigraphic markers. We focus here on the last 120 ka, whereas the companion paper by Bazin et al., (2012) focuses on the interval 120-800 ka. Compared to previous timescales, AICC2012 presents an improved timing for the last glacial inception respecting the glaciological constraints of all analyzed records. Moreover, with the addition of numerous new stratigraphic markers and improved calculation of the lock-in depth (LID) based on δ15N data employed as the Datice background scenario, the AICC2012 presents a new timing for the bipolar sequence of events over Marine Isotope Stage 3 associated with the see-saw mechanism, with maximum differences of about 500 yr with respect to the previous Datice-derived chronology of Lemieux-Dudon et al. (2010), hereafter denoted LD2010. Our improved scenario confirms the regional differences for the millennial scale variability over the last glacial period: while the EDC isotopic record (events of triangular shape) displays peaks roughly at the same time as the NGRIP abrupt isotopic increases, the EDML isotopic record (events characterized by broader peaks or even extended periods of high isotope values) reached the isotopic maximum several centuries before.

Cordilleran Ice Sheet meltwater delivery to the coastal waters of the northeast Pacific Ocean

NASA Astrophysics Data System (ADS)

Hendy, I. L.; Taylor, M.; Gombiner, J. H.; Hemming, S. R.; Bryce, J. G.; Blichert-Toft, J.

2014-12-01

Cordilleran Ice Sheet (CIS) delivered meltwater to the NE Pacific Ocean off BC and WA via glacial lake outburst floods (GLOFs), ice rafting and subglacial meltwater discharge. A deglacial glaciomarine sedimentation record is preserved in the well dated ~50-kyr core MD02-2496 (48˚58.47' N, 127˚02.14' W, water depth 1243 m), collected off Vancouver Island. To understand the history of the relationship between the CIS, climate and meltwater discharge, high resolution, multi-proxy geochemical records from the interval that captures the Fraser Glaciation (~30-10 ka) were generated. These proxies include Mg/Ca temperatures and δ18Oseawater from planktonic foraminiferal sp. N. pachyderma and G. bulloides, elemental and organic carbon (Corg) geochemistry of bulk sediments, ɛNd and K/Ar dating of the <63µm fraction. A detailed reconstruction of CIS retreat has been generated based on the source of glaciomarine sediments and ice rafted debris (IRD), as well as evidence for processes such as GLOF events and iceberg discharge. At the Fraser Glaciation initiation (~30 ka) <63µm glaciomarine sediments deposited at MD02-2496 had a ~100 Ma volcanic rock source. The CIS passed over the Vancouver Island continental shelf at Tofino at ~20 ka ~75 km from the site dramatically increasing sedimentation. From ~19 to 17.3 ka GLOFs created cyclic (~80 year) sedimentary packages of ~300 Ma (ɛNd of ~-8) shale associated with terrestrial Corg, and ~100 Ma (ɛNd of ~-3) volcanic sediment associated with marine Corg. The GLOFs were likely to be associated with glacial lake Missoula outburst flooding, occurring during the interval of the coolest ocean temperatures (2-4°C) and most depleted δ18Oseawater (-1.75‰). At 17.3 ka as ocean temperatures increased by ~3°C and δ18Oseawater increased to ~0‰, IRD deposition increased dramatically at the site, terminating abruptly at 16.2 ka. At the Bølling, ocean temperatures rose by > 3°C to 10-12°C in association with an additional IRD event at ~14.8 ka sourced from a ~75 Ma felsic volcanic source, likely the Southern Coast Plutonic Complex. At no point in the δ18Oseawater reconstruction is an obvious meltwater isotopic signature recorded despite the sedimentary evidence for both ice rafting and outburst flooding. Thus CIS meltwater likely entered the NE Pacific Ocean via hyperpycnal flow.

Foraminifera eco-biostratigraphy of the southern Evoikos outer shelf, central Aegean Sea, during MIS 5 to present

NASA Astrophysics Data System (ADS)

Drinia, Hara; Antonarakou, Assimina; Tsourou, Theodora; Kontakiotis, George; Psychogiou, Maria; Anastasakis, George

2016-09-01

The South Evoikos Basin is a marginal basin in the Aegean Sea which receives little terrigenous supply and its sedimentation is dominated by hemipelagic processes. Late Quaternary benthic and planktonic foraminifera from core PAG-155 are investigated in order to understand their response to the glacial-interglacial cycles in this region. The quantitative analysis of planktonic foraminifera, coupled with accelerator mass spectrometry (14C-AMS) radiocarbon date measurements, provide an integrated chrono-stratigraphic time framework over the last 90 ka (time interval between late Marine Isotopic Stages 5 and 1; MIS5-MIS1). The temporary appearance and disappearance as well as several abundance peaks in the quantitative distribution of selected climate-sensitive planktonic species allowed the identification of several eco-bioevents, useful to accurately mark the boundaries of the eco-biozones widely recognized in the Mediterranean records and used for large-scale correlations. The established bio-ecozonation scheme allows a detailed palaecological reconstruction for the late Pleistocene archive in the central Aegean, and furthermore provides a notable contribution for palaeoclimatic studies, facilitating intercorrelations between various oceanographic basins. The quantitative analyses of benthic foraminifera identify four distinct assemblages, namely Biofacies: Elphidium spp., Haynesina spp. Biofacies, characterized by neritic species, dominated during the transition from MIS 5 to MIS 4; Cassidulina laevigata/carinata Biofacies dominated till 42 ka (transgressive trend from MIS 4 to MIS 3); Bulimina gibba Biofacies dominated from 42 ka to 9.5 ka (extensive regression MIS 3,2 through lowstand and early transgression; beginning of MIS 1); Bulimina marginata, Uvigerina spp. Biofacies dominated from 9.5 ka to the present (late transgression through early highstand; MIS 1)., This study showed that the South Evoikos Basin which is characterized by its critical depths and connections to the open sea, and its small volume water masses that nourished foraminiferal assemblages, accurately records 5th-4th order sea level and climatic fluctuations. Especially, the basin's limited communication with the open ocean implies that any climatic signals will be recorded in an amplified fashion, and therefore this heightened sensitivity to the effects of climate variability further underlies the prominent role of such marginal basins in the understanding of the global climatic evolution.

Seawater-derived neodymium isotope records in the Chukchi Sea, western Arctic Ocean during Holocene: implications for oceanographic circulation

NASA Astrophysics Data System (ADS)

Lee, Borom; Nam, Seung-Il; Huh, Youngsook; Lee, Mi Jung

2015-04-01

Changes in oceanographic circulation in the Artic have a large influence on the global oceanic and climate system of the Earth through the geological times. In particular, freshwater input from the North Pacific to the western Arctic Ocean affects the Atlantic meridional overturning circulation (AMOC) after the opening of the Bering Strait. Seawater-derived neodymium isotope in marine sediments has been used as a proxy to trace the origin of water masses and oceanic circulation system. The global average residence time of Nd is shorter than the global ocean mixing time and dissolved Nd in seawater behaves quasi-conservatively. In the modern Arctic Ocean, the Nd isotope distribution is dominated by Atlantic source water, although the circum-Arctic riverine discharge and Pacific-derived waters also have noticeable impacts. In this study, we investigated seawater-derived neodymium isotope records from a sediment core recovered from the Chukchi Sea to understand the changes in hydrograhic circulation of the western Arctic during the Holocene. A gravity core, ARA02B 01A, was collected on the northern shelf of the Chukchi Sea (73°37.8939'N, 166°30.9838'W, ca. 111 m in water depth) during the RV Araon expedition in 2011. To obtain seawater-derived Nd records, we extracted Fe-Mn oxide coatings as an authigenic fraction from bulk sediments by leaching with acid-reducing solution after removing carbonate by leaching with acetic acid. Our preliminary results might show a general pattern of increasing radiogenic ɛNd values through Holocene intervals. Therefore, it implies that ɛNd results may be related with variations in the intensity of Bering Strait inflow during the last ~9.31 ka BP. The radiogenic trend was strongly pronounced from the late Holocene (ɛNd -7.23; ca. 8.84 ka BP) to the middle Holocene (ɛNd -4.78; ca. 6.18 ka BP) and vaguely during the middle Holocene. After 4.13 ka BP, ɛNd values were increased again from -4.86 to -4.03 at 0.57 ka BP. But 87Sr/86Sr values vary from 0.70929 to 0.70991 throughout the whole sediment core and they might be higher than the Sr isotopic value of modern seawater (0.70918). This implies that the leachates may not be preserved past seawater signal. Thus, our preliminary results indicate that further studies for assessment of leaching methods and for other reliable seawater-derived records (including authigenic carbonates, i.e., foraminiferal and bivalve shells which are found in sediment cores) are necessary.

High-resolution tephrochronology of the Wilson Creek Formation (Mono Lake, California) and Laschamp event using 238U-230Th SIMS dating of accessory mineral rims

NASA Astrophysics Data System (ADS)

Vazquez, Jorge A.; Lidzbarski, Marsha I.

2012-12-01

Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and tephras yield discordant results due to open-system effects and radiocarbon reservoir uncertainties as well as abundant xenocrysts. New ion microprobe 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yield ages that effectively date eruption of key tephra beds and delimit the timing of basal Wilson Creek sedimentation to the interval between 26.8±2.1 and 61.7±1.9 ka. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields an age of 40.8±1.9 ka, indicating that the event is instead the Laschamp excursion. The new ages support a depositional chronology from magnetostratigraphy that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to regional climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation.

High-resolution tephrochronology of the Wilson Creek Formation (Mono Lake, California) and Laschamp event using 238U-230Th SIMS dating of accessory mineral rims

USGS Publications Warehouse

Vazquez, Jorge A.; Lidzbarski, Marsha I.

2012-01-01

Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and tephras yield discordant results due to open-system effects and radiocarbon reservoir uncertainties as well as abundant xenocrysts. New ion microprobe 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yield ages that effectively date eruption of key tephra beds and delimit the timing of basal Wilson Creek sedimentation to the interval between 26.8±2.1 and 61.7±1.9 ka. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields an age of 40.8±1.9 ka, indicating that the event is instead the Laschamp excursion. The new ages support a depositional chronology from magnetostratigraphy that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to regional climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation.

The Rock Magnetic Record Across the 12.9 ka Younger Dryas Boundary: Evidence for Impact?

NASA Astrophysics Data System (ADS)

Nadel, M.; Feinberg, J. M.; Waters, M.

2012-12-01

The cause/s of the onset of the Younger Dryas (YD) climactic event at 12.9 ka and the corresponding extinction of Pleistocene megafauna and drastic changes in human subsistence patterns in the Americas remain a geologic mystery. Firestone et. al. (2007) proposed a bolide impact on the Laurentide ice sheet to explain these dramatic environmental changes, citing as evidence an increase in the concentration of magnetic spherules (MSp) and magnetic grains, among several other parameters. Over the five and a half years since the idea was first proposed it has evolved and matured, and many of the original lines of evidence are no longer argued. However, peaks in MSp concentrations (along with the presence of nanodiamonds) continue to be central to pro-impact arguments. Soils and lacustrine sediments are the most common recording media across the YD time interval, and the sample procedure used by previous workers to isolate the magnetic component is noteworthy. Disaggregated sediment was suspended in water and a plastic-covered hand magnet was used to stir the suspension and attract magnetic grains. Adhered grains were transferred into a separate container, and the process was repeated until grains were no longer attracted to the magnet. The total magnetic fraction was weighed and MSp were hand-picked under a microscope, to quantify concentration. Here we present an alternative approach that uses a comprehensive suite of highly sensitive rock magnetic measurements on in-situ samples to examine two early human archaeological sites: the Debra L. Friedkin site in central Texas and the Topper site in South Carolina (one of the original sites in the Firestone et al. (2007) study). The depositional history at both sites is constrained by optically stimulated luminescence ages, and the stratigraphic position of the 12.9 ka YD event is non-controversial. Two continuous soil profiles were collected at Friedkin, using 9 cm3 plastic boxes as well as a separate 20 cm U-channel core spanning the YD interval, later sub-sampled at 0.5 cm intervals. At Topper we collected bulk samples to be used in the hand magnet method described by Israde-Alcántara et al., (2012) and in 9 cm3 plastic boxes. Samples were analyzed for low- and high-field χ, frequency dependence of χ, NRM, ARM, and IRM intensities, and major hysteresis loops. The magnetic parameters collected from Friedkin provide a clear record of pedogenesis, but exhibit no obvious magnetic anomalies that can be correlated with either the onset of the YD or the potential environmental aftermath of a bolide impact. While we observe minor peaks in Hcr and the Mr/Ms ratio close to but not coincident with the YD, these peaks are no greater in magnitude than those in other portions of the profile. Analyses of the samples from the Topper site are not complete at the time of writing, but will provide a direct comparison between data acquired using the two competing methods. This additional data will allow us to evaluate the robustness of MSp concentrations as evidence for a bolide impact at 12.9 ka.

Relative paleointensity (RPI) and oxygen isotope stratigraphy at IODP Site U1308: North Atlantic RPI stack for 1.2-2.2 Ma (NARPI-2200) and age of the Olduvai Subchron

NASA Astrophysics Data System (ADS)

Channell, J. E. T.; Hodell, D. A.; Curtis, J. H.

2016-01-01

Integrated Ocean Drilling Program (IODP) Site U1308 (49°53‧N, 24°14‧W; water depth 3871 m) provides a record of relative paleointensity (RPI) and benthic stable isotope stratigraphy back to 3.2 Ma. The record since 1.5 Ma was published previously, and here we present the interval from 1.5 Ma to 3.2 Ma (Early Pleistocene-Late Pliocene). The benthic oxygen isotope record in this interval is correlated to Marine Isotope Stage (MIS) 51 to KM2, with an apparent hiatus that removed part of the interval spanning MIS 104-G2 (2.6-2.65 Ma), at the Gauss-Matuyama boundary. The mean sedimentation rate for the 1.5-3.2 Ma period is 8.5 cm/kyr. The age model was built by correlation of the benthic oxygen isotope record to a global stack (LR04). Apart from the expected polarity reversals, three magnetic excursions are recorded: Punaruu in MIS 31/32 at 1092 ka, Gilsa in MIS 54/55 at 1584 ka, and a newly recognized excursion labeled Porcupine (after the nearby Porcupine Abyssal Plain) in MIS G6/G7 at 2737 ka. The ages of polarity reversals at Site U1308, on the LR04 time scale, are consistent with the current geomagnetic polarity timescale (GPTS) with the exception of the base of the Olduvai Subchron that occurred in MIS 73, corresponding to 1925 ka on the LR04 time scale, 25 kyr younger than in the current GPTS. The RPI record at Site U1308 is calibrated using the oxygen isotope age model, and combined with four other North Atlantic records to obtain a North Atlantic RPI stack for 1.2-2.2 Ma (NARPI-2200) that is compared with published RPI stacks: Epapis, Sint-2000 and PADM2M. For 2.2-3.2 Ma, the Site U1308 RPI record is compared with a RPI record from North Atlantic IODP Site U1314, and with the Pacific Epapis stack. The mean sedimentation rates of the North Atlantic sites in NARPI-2200 are greater (by about an order of magnitude) than most of the records incorporated in other stacks. The comparison of Epapis and NARPI-2200 yields an apparent lag for NARPI-2200 relative to Epapis, attributed the Epapis age model constructed by correlation of magnetic concentration parameters (a proxy for carbonate percentage) to a calibrated oxygen isotope record. The long RPI record from Site U1308 yields a very similar mean value for the Brunhes and Matuyama virtual axial dipole moments (7.05 × 1022 Am2), implying no polarity bias in the strength of the main geomagnetic dipole, in contrast to interpretations from Sint-2000 and PADM2M. The results strengthen the case that RPI can be used to improve global stratigraphic correlation for sites with mean sedimentation rates up to several decimeters/kyr.

Meaningful Words and Non-Words Repetitive Articulatory Rate (Oral Diadochokinesis) in Persian Speaking Children.

PubMed

Zamani, Peyman; Rezai, Hossein; Garmatani, Neda Tahmasebi

2017-08-01

Repetitive articulatory rate or Oral Diadochokinesis (oral-DDK) shows a guideline for appraisal and diagnosis of subjects with oral-motor disorder. Traditionally, meaningless words repetition has been utilized in this task and preschool children have challenges with them. Therefore, we aimed to determine some meaningful words in order to test oral-DDK in Persian speaking preschool children. Participants were 142 normally developing children, (age range 4-6 years), who were asked to produce /motæka, golabi/ as two meaningful Persian words and /pa-ta-ka/ as non-word in conventional oral-DDK task. We compared the time taken for 10-times fast repetitions of two meaningful Persian words and the tri-syllabic nonsense word /pa-ta-ka/. Praat software was used to calculate the average time that subjects took to produce the target items. In 4-5 year old children, [Formula: see text] of time taken for 10-times repetitions of /pa-ta-ka, motæka, golabi/ were [Formula: see text], and [Formula: see text] seconds respectively, and in 5-6 year old children were [Formula: see text], and [Formula: see text] seconds respectively. Findings showed that the main effect of type of words on oral diadochokinesis was significant ([Formula: see text]). Children repeated meaningful words /motæka, golabi/ faster than the non-word /pa-ta-ka/. Sex and age factors had no effect on time taken for repetition of oral-DDK test. It is suggested that Speech Therapists can use meaningful words to facilitate oral-DDK test for children.

Glacial Cycles Influence Marine Methane Hydrate Formation

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A. E.; Daigle, H.; Oryan, B.

2018-01-01

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sediments with greater organic carbon content deposited during the penultimate glacial cycle ( 120-240 ka). The model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.

Using Grain-Size Distribution Methods for Estimation of Air Permeability.

PubMed

Wang, Tiejun; Huang, Yuanyang; Chen, Xunhong; Chen, Xi

2016-01-01

Knowledge of air permeability (ka ) at dry conditions is critical for the use of air flow models in porous media; however, it is usually difficult and time consuming to measure ka at dry conditions. It is thus desirable to estimate ka at dry conditions from other readily obtainable properties. In this study, the feasibility of using information derived from grain-size distributions (GSDs) for estimating ka at dry conditions was examined. Fourteen GSD-based equations originally developed for estimating saturated hydraulic conductivity were tested using ka measured at dry conditions in both undisturbed and disturbed river sediment samples. On average, the estimated ka from all the equations, except for the method of Slichter, differed by less than ± 4 times from the measured ka for both undisturbed and disturbed groups. In particular, for the two sediment groups, the results given by the methods of Terzaghi and Hazen-modified were comparable to the measured ka . In addition, two methods (e.g., Barr and Beyer) for the undisturbed samples and one method (e.g., Hazen-original) for the undisturbed samples were also able to produce comparable ka estimates. Moreover, after adjusting the values of the coefficient C in the GSD-based equations, the estimation of ka was significantly improved with the differences between the measured and estimated ka less than ±4% on average (except for the method of Barr). As demonstrated by this study, GSD-based equations may provide a promising and efficient way to estimate ka at dry conditions. © 2015, National Ground Water Association.

Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

NASA Astrophysics Data System (ADS)

Gregoire, Lauren J.; Ivanovic, Ruza F.; Maycock, Amanda C.; Valdes, Paul J.; Stevenson, Samantha

2018-02-01

The Laurentide ice sheet, which covered Canada during glacial periods, had a major influence on atmospheric circulation and surface climate, but its role in climate during the early Holocene (9-7 ka), when it was thinner and confined around Hudson Bay, is unclear. It has been suggested that the demise of the ice sheet played a role in the 8.2 ka event (an abrupt 1-3 °C Northern Hemisphere cooling lasting 160 years) through the influence of changing topography on atmospheric circulation. To test this hypothesis, and to investigate the broader implications of changing ice sheet topography for climate, we analyse a set of equilibrium climate simulations with ice sheet topographies taken at 500 year intervals from 9.5 to 8.0 ka. Between 9.5 and 8.0 ka, our simulations show a 2 °C cooling south of Iceland and a 1 °C warming between 40° and 50°N in the North Atlantic. These surface temperature changes are associated with a weakening of the subtropical and subpolar gyres caused by a decreasing wind stress curl over the mid-North Atlantic as the ice sheet lowers. The climate response is strongest during the period of peak ice volume change (9.5-8.5 ka), but becomes negligible after 8.5 ka. The climatic effects of the Laurentide ice sheet lowering during the Holocene are restricted to the North Atlantic sector. Thus, topographic forcing is unlikely to have played a major role in the 8.2 ka event and had only a small effect on Holocene climate change compared to the effects of changes in greenhouse gases, insolation and ice sheet meltwater.

Wetlands sediment record from the upper Yarlung Tsangpo valley, southwest Tibetan Plateau, reveals mid-Holocene Epipaleolithic human occupation coincident with increased early and mid-Holocene wetness driven by enhanced Indian Monsoon rainfall

NASA Astrophysics Data System (ADS)

Hudson, A. M.; Olsen, J. W.; Quade, J.; Lei, G.; Huth, T.; Zhang, H.; Perreault, C.

2016-12-01

The headwaters of the Yarlung Tsangpo river valley, located in the southwestern Tibetan Plateau, are characterized by a cold and dry climate, but contain abundant river-marginal wetlands environments, which fluctuate in extent in response to changes in local water table elevation. This region receives 80% of precipitation from the Indian Monsoon, which forms the dominant control on moisture availability, and hence wetlands extent. Our paleowetlands record, based on 14C dating of organic-rich paleowetlands deposits, provides a novel record of Holocene monsoon intensity. The wetlands deposits consist of four sedimentary units that indicate decreasing wetlands extent and monsoon intensity since 10.4 ka BP. Wet conditions occurred at ˜10.4 ka BP, ˜9.6 ka BP and ˜7.9-4.8 ka BP, with similar-to-modern conditions from ˜4.6-2.0 ka BP, and drier-than-modern conditions from ˜2.0 ka BP to present. Wetland changes correlate with monsoon intensity changes identified in nearby records, with weak monsoon intervals corresponding to desiccation and erosion of wetlands deposits. Dating of in situ ceramic and microlithic artifacts in wetlands sediments at multiple sites indicates Epipaleolithic human occupation of the YT valley after 6.6 ka BP. Artifact typology study reveals a similar microlithic technology was employed across the high plateau interior, but XRF obsidian provenance reveals separate northeast and southwest lithic conveyance zones. This indicates widespread colonization of the high, arid Tibetan Plateau interior by one or more highly mobile human populations during the early and mid-Holocene, coincident with favorable warm, wet climate conditions.

Abrupt hydroclimate disruption across the Australian arid zone 50 ka coincident with human colonization

NASA Astrophysics Data System (ADS)

Miller, G. H.; Fogel, M. L.; Magee, J. W.; Gagan, M. K.

2016-12-01

Although many studies focus on how climate change impacted ancient societies, in Australia a growing body of evidence indicates that activities of the earliest human colonizers in turn altered the Australian climate. We utilize the stable isotopes of carbon and oxygen preserved in near-continuous 100 ka time series of avian eggshell from five regions across the Australian arid zone to reconstruct ecosystem status (d13C) and effective moisture (d18O). Training sets of sub-modern samples provide the basis for the reconstructions. Together, d13C and d18O provide independent estimates of ecosystem status and climate over the past 100 ka from the same dated sample, reducing correlation uncertainties between proxies. Changes in eggshell d13C document a dramatic reduction of palatable summer-wet C4 grasses in all regions between 50 and 45 ka, that has persisted through to modern times. Continuous 100 ka records of effective moisture derived from eggshell d18O show moist conditions from 100 to 60 ka, with variable drying after 60 ka, but the strong shift toward greatest aridity is coincident with the onset of the last glacial maximum 30 ka ago, 15 ka after the observed ecosystem restructuring. Combining the d13C and d18O time-series shows that an abrupt and permanent restructuring of the moisture/ecosystem balance occurred between 50 and 45 ka. Additional studies show that most large monsoon-fed inland arid-zone lakes carried permanent water at least intermittently between 120 and 50 ka, but never experienced permanent deep-water status after 45 ka, despite a wide range of global climate states, including the early Holocene when most other monsoon systems were reinvigorated. The lack of exceptional climate shifts either locally or globally between 60 and 40 ka eliminates climate as the cause of the ecosystem restructuring and persistent lake desiccation. Collectively these data suggest the wave of human colonization across Australia in altered land surface characteristics in a way that reduced the efficiency of the climate system to deliver monsoon moisture to the continental interior. This explanation will now be tested with climate modeling.

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

NASA Astrophysics Data System (ADS)

Vetter, Lael; Spero, Howard J.; Eggins, Stephen M.; Williams, Carlie; Flower, Benjamin P.

2017-12-01

We present a new method that quantifies the oxygen isotope geochemistry of Laurentide ice-sheet (LIS) meltwater across the last deglaciation, and reconstruct decadal-scale variations in the δ18O of LIS meltwater entering the Gulf of Mexico between ∼18 and 11 ka. We employ a technique that combines laser ablation ICP-MS (LA-ICP-MS) and oxygen isotope analyses on individual shells of the planktic foraminifer Orbulina universa to quantify the instantaneous δ18Owater value of Mississippi River outflow, which was dominated by meltwater from the LIS. For each individual O. universa shell, we measure Mg/Ca (a proxy for temperature) and Ba/Ca (a proxy for salinity) with LA-ICP-MS, and then analyze the same O. universa for δ18O using the remaining material from the shell. From these proxies, we obtain δ18Owater and salinity estimates for each individual foraminifer. Regressions through data obtained from discrete core intervals yield δ18Ow vs. salinity relationships with a y-intercept that corresponds to the δ18Owater composition of the freshwater end-member. Our data suggest that from 15.5 through 14.6 ka, estimated δ18Ow values of Mississippi River discharge from discrete core intervals range from -11‰ to -21‰ VSMOW, which is consistent with δ18O values from both regional precipitation and the low-elevation, southern margin of the LIS. During the Bølling and Allerød (14.0 through 13.3 ka), estimated δ18Ow values of Mississippi River discharge from discrete core intervals range from -22‰ to -38‰ VSMOW. These values suggest a dynamic melting history of different parts of the LIS, with potential contributions to Mississippi River outflow from both the low-elevation, southern margin of the LIS and high-elevation, high-latitude domes in the LIS interior that were transported to the ablation zone. Prior to ∼15.5 ka, the δ18Owater value of the Mississippi River was similar to that of regional precipitation or low-latitude LIS meltwater, but the Ba concentration in the Mississippi basin was affected by changes in weathering within the watershed, complicating Ba-salinity relationships in the Gulf of Mexico. After 13 ka, our data suggest Mississippi River outflow did not influence surface salinity above our Gulf of Mexico Orca Basin core site. Rather, we hypothesize that open ocean conditions prevailed as sea level rose and the paleoshoreline at the southern edge of North America retreated northward.

A loess-paleosol record of climate and glacial history over the past two glacial-interglacial cycles (~140 ka), southern Jackson Hole, Wyoming

USGS Publications Warehouse

Pierce, Kenneth L.; Muhs, Daniel R.; Fosberg, Maynard A.; Mahan, Shannon; Rosenbaum, Joseph G.; Licciardi, Joseph M.; Pavich, Milan J.

2011-01-01

Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric Be-10 accumulation in soils, and cosmogenic Be-10 surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8,7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (similar to 76-69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (similar to 43-51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada. Published by Elsevier Inc. on behalf of University of Washington.

Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records

PubMed Central

Storey, Michael; Roberts, Richard G.; Saidin, Mokhtar

2012-01-01

The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated 40Ar/39Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our 40Ar/39Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard–Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our 40Ar/39Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of 14C dating. PMID:23112159

Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records

NASA Astrophysics Data System (ADS)

Storey, Michael; Roberts, Richard G.; Saidin, Mokhtar

2012-11-01

The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated 40Ar/39Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our 40Ar/39Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard-Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our 40Ar/39Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of 14C dating.

Astronomically calibrated 40Ar/39Ar age for the Toba supereruption and global synchronization of late Quaternary records.

PubMed

Storey, Michael; Roberts, Richard G; Saidin, Mokhtar

2012-11-13

The Toba supereruption in Sumatra, ∼74 thousand years (ka) ago, was the largest terrestrial volcanic event of the Quaternary. Ash and sulfate aerosols were deposited in both hemispheres, forming a time-marker horizon that can be used to synchronize late Quaternary records globally. A precise numerical age for this event has proved elusive, with dating uncertainties larger than the millennial-scale climate cycles that characterized this period. We report an astronomically calibrated (40)Ar/(39)Ar age of 73.88 ± 0.32 ka (1σ, full external errors) for sanidine crystals extracted from Toba deposits in the Lenggong Valley, Malaysia, 350 km from the eruption source and 6 km from an archaeological site with stone artifacts buried by ash. If these artifacts were made by Homo sapiens, as has been suggested, then our age indicates that modern humans had reached Southeast Asia by ∼74 ka ago. Our (40)Ar/(39)Ar age is an order-of-magnitude more precise than previous estimates, resolving the timing of the eruption to the middle of the cold interval between Dansgaard-Oeschger events 20 and 19, when a peak in sulfate concentration occurred as registered by Greenland ice cores. This peak is followed by a ∼10 °C drop in the Greenland surface temperature over ∼150 y, revealing the possible climatic impact of the eruption. Our (40)Ar/(39)Ar age also provides a high-precision calibration point for other ice, marine, and terrestrial archives containing Toba sulfates and ash, facilitating their global synchronization at unprecedented resolution for a critical period in Earth and human history beyond the range of (14)C dating.

Increased sedimentation following the Neolithic Revolution in the Southern Levant

NASA Astrophysics Data System (ADS)

Lu, Yin; Waldmann, Nicolas; Nadel, Dani; Marco, Shmuel

2017-05-01

The Dead Sea drainage basin offers a rare combination of well-documented substantial climate change, intense tectonics and abundant archaeological evidence for past human activity in the Southern Levant. It serves as a natural laboratory for understanding how sedimentation rates in a deep basin are related to climate change, tectonics, and anthropogenic impacts on the landscape. Here we show how basin-wide erosion rates are recorded by thicknesses of rhythmic detritus laminae and clastic sediment accumulation rates in a long core retrieved by the Dead Sea Deep Drilling Project in the Dead Sea depocenter. During the last 11.5 kyr the average detrital accumulation rate is 3-4 times that during the last two glacial cycles (MIS 7c-2), and the average thickness of detritus laminae in the last 11.6 kyr is 4.5 times that between 21.7 and 11.6 ka, implying an increased erosion rate on the surrounding slopes during the Holocene. We estimate that this intensified erosion is incompatible with tectonic and climatic regimes during the corresponding time interval and further propose a close association with the Neolithic Revolution in the Levant (beginning at 11.5 ka). We thus suggest that human impact on the landscape was the primary driver causing the intensified erosion and that the Dead Sea sedimentary record serves as a reliable recorder of this impact since the Neolithic Revolution.

Changes in sea ice cover and ice sheet extent at the Yermak Plateau during the last 160 ka - Reconstructions from biomarker records

NASA Astrophysics Data System (ADS)

Kremer, A.; Stein, R.; Fahl, K.; Ji, Z.; Yang, Z.; Wiers, S.; Matthiessen, J.; Forwick, M.; Löwemark, L.; O'Regan, M.; Chen, J.; Snowball, I.

2018-02-01

The Yermak Plateau is located north of Svalbard at the entrance to the Arctic Ocean, i.e. in an area highly sensitive to climate change. A multi proxy approach was carried out on Core PS92/039-2 to study glacial-interglacial environmental changes at the northern Barents Sea margin during the last 160 ka. The main emphasis was on the reconstruction of sea ice cover, based on the sea ice proxy IP25 and the related phytoplankton - sea ice index PIP25. Sea ice was present most of the time but showed significant temporal variability decisively affected by movements of the Svalbard Barents Sea Ice Sheet. For the first time, we prove the occurrence of seasonal sea ice at the eastern Yermak Plateau during glacial intervals, probably steered by a major northward advance of the ice sheet and the formation of a coastal polynya in front of it. Maximum accumulation of terrigenous organic carbon, IP25 and the phytoplankton biomarkers (brassicasterol, dinosterol, HBI III) can be correlated to distinct deglaciation events. More severe, but variable sea ice cover prevailed at the Yermak Plateau during interglacials. The general proximity to the sea ice margin is further indicated by biomarker (GDGT) - based sea surface temperatures below 2.5 °C.

Orbital-tuning of Marine Cyclic Sediments - Examples from the Neogene and Jurassic

NASA Astrophysics Data System (ADS)

Weedon, G. P.; Hall, I. R.; Wilson, G. S.

2001-12-01

Orbital-tuning of pre-Pleistocene sediments usually involves the use of variations in bulk compositional parameters, such as carbonate contents, rather than the oxygen-isotope time series available from Plio-Pleistocene marine strata. Consequently, ascertaining the relationship between orbital-climatic changes and sediment composition is not straightforward. Tuning is either conducted using a target curve (an orbital solution) for late Cenozoic records, or by using a sine wave with a specified period for earlier records - where a "floating" chronology is generated. Examples of each sort of tuning are discussed here. Drilling during Leg 181 of the Ocean Drilling Program yielded an essentially complete record of sediment-drift accumulation at Site 1123 off New Zealand for the past 20Ma. Dissolution of carbonate in the older part of the section precluded generation of isotopic records for tuning. Instead colour reflectance and magnetic susceptibility were used for tuning between 3 and 15Ma. Additionally, the mean size of sortable silt, a proxy for bottom-water flow speed, was used for orbital-tuning between 12 and 15Ma. Site 1123 possesses an exceptionally well-preserved record of geomagnetic reversals. Thus a preliminary time scale was established using the ages of 60 reversal events between 3 and 15.2Ma (based on Berggren et al., 1995). Since the sediment drift at this site accumulated under the influence of the Pacific deep western boundary current which incorporates circumpolar deep water, the sediment cyclicity is dominated by the 41ka orbital-tilt (obliquity) cycle. Tuning to the tilt cycle required relatively little revision to the ages of the magnetic reversals (maximum 65ka, average 23ka). Evolutionary spectra and band-pass filtering of the tuned reflectance time series reveal a pronounced increase in the amplitude of the stratigraphic record of the obliquity cycle after 7Ma. Eccentricity and precession cycles are evident for short intervals (less than one million years), but they are always subsidiary to the obliquity component - consistent with a high-latitude origin of the variability. The late Jurassic Kimmeridge Clay Formation is the principal oil-source rock in the North Sea Province. It is well-known for cyclic variations in organic-carbon contents linked to alternately oxic and anoxic bottom waters. During the Anatomy of a Source Rock Project, high-resolution (5-20cm) compositional records (e.g. carbonate, total organic carbon, magnetic susceptibility) were obtained from throughout the 550m Formation at the type section in Dorset, England. Spectral analysis indicates regular cyclicity in depth. The regular sedimentary cycles are interpreted as indirect climatic records of the Jurassic obliquity cycle and hence were tuned using a sine wave with a period of 38ka. Evolutionary spectral analysis of the tuned time series reveals small-amplitude 19ka precession cycles, but no evidence for 100 or 400ka orbital-eccentricity cycles. Hence, this record of Late Jurassic climatic variability in Britain implies a high-latitude forcing mechanism. The orbitally-tuned data indicate that ammonite zone durations ranged from 0.36 to 2.3Ma. Accumulation rates (post-compaction) ranged from 20-130m/Ma and organic carbon (post-diagenesis) had a flux of 0.2-2.25g/cm2/ka.

Controlling weathering and erosion intensity on the southern slope of the Central Himalaya by the Indian summer monsoon during the last glacial

NASA Astrophysics Data System (ADS)

Kuwahara, Yoshihiro; Masudome, Yukiko; Paudel, Mukunda Raj; Fujii, Rie; Hayashi, Tatsuya; Mampuku, Mami; Sakai, Harutaka

2010-03-01

This paper reports the results of clay mineral analysis (the amount of clay fraction, clay mineral assemblages, illite crystallinity) of samples collected from a drilled core (Rabibhawan (RB) core) located in the west-central part of the Kathmandu Basin on the southern slope of the Central Himalaya. The amount of clay fraction in the core sediments between 12 m and 45 m depth (corresponding to ca. 17-76 ka), which belong to the Kalimati Formation, is variable and shows three clay-poor zones (19-31 ka, 44-51 ka, and 66-75 ka). The variations correspond with those of illite crystallinity index (Lanson index (LI) and modified Lanson index (MLI)) and kaolinite/illite ratio as well as the fossil pollen and diatom records reported by previous workers. These data reveal the following transformations occurring during the weathering process in this area: micas(mainlymuscovite)→illite(→illite-smectitemixedlayermineral(R=1))→kaolinite The sedimentation rate (~ 50 cm/kyr) of clay-poor zones that correspond to dry climate intervals is only half that of clay-rich zones (~ 120 cm/kyr) that correspond to wet climate intervals, indicating weakened chemical weathering and erosion and low suspended discharge during dry climate intervals. The clay-poor zones commonly show unique laminite beds with very fine, authigenic calcite, which was probably precipitated under calm and high calcite concentration conditions caused by low precipitation and run-off. The variations between dry and wet conditions in this area as deduced from clay minerals appear to follow the Indian Summer Monsoon Index (ISMI) (30°N-30°S, 1 July) and northern hemisphere summer insolation (NHSI) signals (30°N) at 1 July, especially during the dry climate zones, whereas the wet maxima of the wet climate zones somewhat deviate from the strongest NHSI. On the other hand, the dry-wet records lead markedly the SPECMAP stack (by about 5000 years). These results suggest that the Indian summer monsoon precipitation was strongly controlled by the NHSI or summer insolation difference between the Himalayan-Tibetan Plateau and the subtropical Indian Ocean, showing a major fluctuation on the 23,000 years precessional cycle, and that it was not driven by changes in high-latitude ice volume, although the records of clay mineral indices during the wet intervals leave a question that other factors, in addition to insolation forcing, may play important roles in weathering, erosion, and sedimentation processes.

Fluoroscopically guided transforaminal epidural steroid injections at a quaternary-care teaching institution: effect of trainee involvement and patient body mass index on fluoroscopy time and patient dose.

PubMed

Tiegs-Heiden, C A; Murthy, N S; Geske, J R; Diehn, F E; Schueler, B A; Wald, J T; Kaufmann, T J; Lehman, V T; Carr, C M; Amrami, K K; Morris, J M; Thielen, K R; Maus, T P

2016-01-01

To investigate whether there are differences in fluoroscopy time and patient dose for fluoroscopically guided lumbar transforaminal epidural steroid injections (TFESIs) performed by staff radiologists versus with trainees and to evaluate the effect of patient body mass index (BMI) on fluoroscopy time and patient dose, including their interactions with other variables. Single-level lumbar TFESIs (n=1844) between 1 January 2011 and 31 December 2013 were reviewed. Fluoroscopy time, reference point air kerma (Ka,r), and kerma area product (KAP) were recorded. BMI and trainee involvement were examined as predictors of fluoroscopy time, Ka,r, and KAP in models adjusted for age and gender in multivariable linear models. Stratified models of BMI groups by trainee presence were performed. Increased age was the only significant predictor of increased fluoroscopy time (p<0.0001). Ka,r and KAP were significantly higher in patients with a higher BMI (p<0.0001 and p=0.0009). When stratified by BMI, longer fluoroscopy time predicted increased Ka,r and KAP in all groups (p<0.0001). Trainee involvement was not a statistically significant predictor of fluoroscopy time or Ka,r in any BMI category. KAP was lower with trainees in the overweight group (p=0.0009) and higher in male patients for all BMI categories (p<0.02). Trainee involvement did not result in increased fluoroscopy time or patient dose. BMI did not affect fluoroscopy time; however, overweight and obese patients received significantly higher Ka,r and KAP. Male patients received a higher KAP in all BMI categories. Limiting fluoroscopy time and good collimation practices should be reinforced in these patients. Copyright © 2015 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Late Pleistocene to Holocene paleoseismicity of the House Range fault from UAV photogrammetry and exposure-age dating

NASA Astrophysics Data System (ADS)

Niemi, N. A.; Stahl, T.; Andreini, J.; Wells, J.; Bunds, M. P.

2016-12-01

The western face of the House Range in Utah is one of the steepest normal fault-bounded blocks in the Basin and Range. In spite of this, clear evidence of recent faulting is limited to a single c. 10 km-long, 1-2 m high scarp at the surface. A drone-based photogrammetric DEM with <10 cm resolution reveals that the fault displaces transgressive Lake Bonneville (c. 20-18 ka) and Provo highstand shorelines (c. 17 cal. ka) by similar amounts, suggesting a single event displacement of c. 1.5 m. Elastic strain models that incorporate shoreline geometry are best-fit by a fault dip of 50-60° in the uppermost crust, whereas previous studies have noted that the fault becomes listric or is truncated by a low-angle fault at depth. Exposure-ages of surface clasts on undeformed alluvial fans suggest that regression from the Provo shoreline occurred rapidly and that the last surface-rupturing earthquake occurred during occupation of the Provo shoreline. This pattern is consistent with other areas in the Great Basin that observe enhanced seismic moment release and earthquake ruptures during late Pleistocene lake regression. We calculate a time-averaged slip rate of 0.1-0.2 mm/yr and minimum recurrence interval of 17 ka. This study highlights the utility of drone surveys and high-resolution geochronology in neotectonic studies and in defining paleoseismic fault parameters.

Quantitative reconstruction of summer precipitation using a mid-Holocene δ13C common millet record from Guanzhong Basin, northern China

NASA Astrophysics Data System (ADS)

Yang, Qing; Li, Xiaoqiang; Zhou, Xinying; Zhao, Keliang; Sun, Nan

2016-12-01

To quantitatively reconstruct Holocene precipitation for particular geographical areas, suitable proxies and faithful dating controls are required. The fossilized seeds of common millet (Panicum miliaceum) are found throughout the sedimentary strata of northern China and are suited to the production of quantitative Holocene precipitation reconstructions: their isotopic carbon composition (δ13C) gives a measure of the precipitation required during the growing season of summer (here the interval from mid-June to September) and allows these seeds to be dated. We therefore used a regression function, as part of a systematic study of the δ13C of common millet, to produce a quantitative reconstruction of mid-Holocene summer precipitation in the Guanzhong Basin (107°40'-107°49' E, 33°39'-34°45' N). Our results showed that mean summer precipitation at 7.7-3.4 ka BP was 353 mm, ˜ 50 mm or 17 % higher than present levels, and the variability increased, especially after 5.2 ka BP. Maximum mean summer precipitation peaked at 414 mm during the period 6.1-5.5 ka BP, ˜ 109 mm (or 36 %) higher than today, indicating that the East Asian summer monsoon (EASM) peaked at this time. This work can provide a new proxy for further research into continuous paleoprecipitation sequences and the variability of summer precipitation, which will promote the further research into the relation between early human activity and environmental change.

Stratigraphic and technological evidence from the Middle Palaeolithic-Châtelperronian-Aurignacian record at the Bordes-Fitte rockshelter (Roches d'Abilly site, Central France).

PubMed

Aubry, Thierry; Dimuccio, Luca Antonio; Almeida, Miguel; Buylaert, Jan-Pieter; Fontana, Laure; Higham, Thomas; Liard, Morgane; Murray, Andrew S; Neves, Maria João; Peyrouse, Jean-Baptiste; Walter, Bertrand

2012-01-01

This paper presents a geoarchaeological study of Middle and Upper Palaeolithic (Châtelperronian, Aurignacian and Solutrean) occupations preserved at the Bordes-Fitte rockshelter in Central France. The lithostratigraphic sequence is composed of near-surface sedimentary facies with vertical and lateral variations, in a context dominated by run-off and gravitational sedimentary processes. Field description and micromorphological analysis permit us to reconstruct several episodes of sediment slope-wash and endokarst dynamics, with hiatuses and erosional phases. The archaeostratigraphic succession includes Châtelperronian artefacts, inter-stratified between Middle Palaeolithic and Aurignacian occupations. Systematic refitting and spatial analysis reveal that the Châtelperronian point production and flake blanks retouched into denticulates, all recovered in the same stratigraphic unit, result from distinct and successive occupations and are not a 'transitional' Middle to Upper Palaeolithic assemblage. The ages obtained by (14)C place the Châtelperronian occupation in the 41-48 ka cal BP (calibrated thousands of years before present) interval and are consistent with the quartz optically stimulated luminescence age of 39 ± 2 ka and feldspar infra-red stimulated luminescence age of 45 ± 2 ka of the sediments. The Bordes-Fitte rockshelter sequence represents an important contribution to the debate about the characterization and timing of the Châtelperronian, as well as its affinities to earlier and later industries. Copyright © 2011 Elsevier Ltd. All rights reserved.

Volcanological perspectives on Long Valley, Mammoth Mountain, and Mono Craters: Several contiguous but discrete systems

USGS Publications Warehouse

Hildreth, W.

2004-01-01

The volcanic history of the Long Valley region is examined within a framework of six successive (spatially discrete) foci of silicic magmatism, each driven by locally concentrated basaltic intrusion of the deep crust in response to extensional unloading and decompression melting of the upper mantle. A precaldera dacite field (3.5-2.5 Ma) northwest of the later site of Long Valley and the Glass Mountain locus of >60 high-silica rhyolite vents (2.2-0.79 Ma) northeast of it were spatially and temporally independent magmatic foci, both cold in postcaldera time. Shortly before the 760-ka caldera-forming eruption, the mantle-driven focus of crustal melting shifted ???20 km westward, abandoning its long-stable position under Glass Mountain and energizing instead the central Long Valley system that released 600 km3 of compositionally zoned rhyolitic Bishop Tuff (760 ka), followed by ???100 km3 of crystal-poor Early Rhyolite (760-650 ka) on the resurgent dome and later by three separate 5-unit clusters of varied Moat Rhyolites of small volume (527-101 ka). West of the caldera ring-fault zone, a fourth focus started up ???160 ka, producing a 10??20-km array of at least 35 mafic vents that surround the trachydacite/alkalic rhyodacite Mammoth Mountain dome complex at its core. This young 70-vent system lies west of the structural caldera and (though it may have locally re-energized the western margin of the mushy moribund Long Valley reservoir) represents a thermally and compositionally independent focus. A fifth major discrete focus started up by ???50 ka, 25-30 km north of Mammoth Mountain, beneath the center of what has become the Mono Craters chain. In the Holocene, this system advanced both north and south, producing ???30 dike-fed domes of crystal-poor high-silica rhyolite, some as young as 650 years. The nearby chain of mid-to-late Holocene Inyo domes is a fault-influenced zone of mixing where magmas of at least four kinds are confluent. The sixth and youngest focus is at Mono Lake, where basalt, dacite, and low-silica rhyolite unrelated to the Mono Craters magma reservoir have erupted in the interval 14 to 0.25 ka. A compelling inference is that mantle-driven magmatic foci have moved repeatedly, allowing abandoned silicic reservoirs, including the formerly vigorous Long Valley magma chamber, to crystallize. A 100-fold decline of intracaldera eruption rate after 650 ka, lack of crystal-poor rhyolite since 300 ka, limited volumes of moat rhyolite (most of it crystal-rich), absence of postcaldera mafic volcanism inside the structural caldera (or north and south adjacent to it), low thermal gradients inside the caldera, and sourcing of hydrothermal underflow within the western array well outside the ring-fault zone all suggest that the Long Valley magma reservoir is moribund. ?? 2004 Published by Elsevier B.V.

Phase Diagram of Kob-Andersen-Type Binary Lennard-Jones Mixtures

NASA Astrophysics Data System (ADS)

Pedersen, Ulf R.; Schrøder, Thomas B.; Dyre, Jeppe C.

2018-04-01

The binary Kob-Andersen (KA) Lennard-Jones mixture is the standard model for computational studies of viscous liquids and the glass transition. For very long simulations, the viscous KA system crystallizes, however, by phase separating into a pure A particle phase forming a fcc crystal. We present the thermodynamic phase diagram for KA-type mixtures consisting of up to 50% small (B ) particles showing, in particular, that the melting temperature of the standard KA system at liquid density 1.2 is 1.028(3) in A particle Lennard-Jones units. At large B particle concentrations, the system crystallizes into the CsCl crystal structure. The eutectic corresponding to the fcc and CsCl structures is cutoff in a narrow interval of B particle concentrations around 26% at which the bipyramidal orthorhombic PuBr3 structure is the thermodynamically stable phase. The melting temperature's variation with B particle concentration at two constant pressures, as well as at the constant density 1.2, is estimated from simulations at pressure 10.19 using isomorph theory. Our data demonstrate approximate identity between the melting temperature and the onset temperature below which viscous dynamics appears. Finally, the nature of the solid-liquid interface is briefly discussed.

40Ar/39Ar dating of tuff vents in the Campi Flegrei caldera (southern Italy): Toward a new chronostratigraphic reconstruction of the Holocene volcanic activity

USGS Publications Warehouse

Fedele, L.; Insinga, D.D.; Calvert, A.T.; Morra, V.; Perrotta, A.; Scarpati, C.

2011-01-01

The Campi Flegrei hosts numerous monogenetic vents inferred to be younger than the 15 ka Neapolitan Yellow Tuff. Sanidine crystals from the three young Campi Flegrei vents of Fondi di Baia, Bacoli and Nisida were dated using 40Ar/39Ar geochronology. These vents, together with several other young edifices, occur roughly along the inner border of the Campi Flegrei caldera, suggesting that the volcanic conduits are controlled by caldera-bounding faults. Plateau ages of ∼9.6 ka (Fondi di Baia), ∼8.6 ka (Bacoli) and ∼3.9 ka (Nisida) indicate eruptive activity during intervals previously interpreted as quiescent. A critical revision, involving calendar age correction of literature 14C data and available 40Ar/39Ar age data, is presented. A new reference chronostratigraphic framework for Holocene Phlegrean activity, which significantly differs from the previously adopted ones, is proposed. This has important implications for understanding the Campi Flegrei eruptive history and, ultimately, for the evaluation of related volcanic risk and hazard, for which the inferred history of its recent activity is generally taken into account.

The 40Ar/39Ar and K/Ar dating of lavas from the Hilo 1-km core hole, Hawaii Scientific Drilling Project

USGS Publications Warehouse

Sharp, W.D.; Turrin, B.D.; Renne, P.R.; Lanphere, M.A.

1996-01-01

Mauna Kea lava flows cored in the HilIo hole range in age from <200 ka to about 400 ka based on 40Ar/39Ar incremental heating and K-Ar analyses of 16 groundmass samples and one coexisting plagioclase. The lavas, all subaerially deposited, include a lower section consisting only of tholeiitic basalts and an upper section of interbedded alkalic, transitional tholeiitic, and tholeiitic basalts. The lower section has yielded predominantly complex, discordant 40Ar/39Ar age spectra that result from mobility of 40Ar and perhaps K, the presence of excess 40Ar, and redistribution of 39Ar by recoil. Comparison of K-Ar ages with 40Ar/39Ar integrated ages indicates that some of these samples have also lost 39Ar. Nevertheless, two plateau ages of 391 ?? 40 and 400 ?? 26 ka from deep in the hole, combined with data from the upper section, show that the tholeiitic section accumulated at an average rate of about 7 to 8 m/kyr and has an mean recurrence interval of 0.5 kyr/flow unit. Samples from the upper section yield relatively precise 40Ar/39Ar plateau and isotope correlation ages of 326 ?? 23, 241 ?? 5, 232 ?? 4, and 199 ?? 9 ka for depths of -415.7 m to -299.2 m. Within their uncertainty, these ages define a linear relationship with depth, with an average accumulation rate of 0.9 m/kyr and an average recurrence interval of 4.8 kyr/flow unit. The top of the Mauna Kea sequence at -280 m must be older than the plateau age of 132 ?? 32 ka, obtained for the basal Mauna Loa flow in the corehole. The upward decrease in lava accumulation rate is a consequence of the decreasing magma supply available to Mauna Kea as it rode the Pacific plate away from its magma source, the Hawaiian mantle plume. The age-depth relation in the core hole may be used to test and refine models that relate the growth of Mauna Kea to the thermal and compositional structure of the mantle plume.

10Be exposure dating of the timing of Neoglacial glacier advances in the Ecrins-Pelvoux massif, southern French Alps

NASA Astrophysics Data System (ADS)

Le Roy, Melaine; Deline, Philip; Carcaillet, Julien; Schimmelpfennig, Irene; Ermini, Magali; Aster Team

2017-12-01

Alpine glacier variations are known to be reliable proxies of Holocene climate. Here, we present a terrestrial cosmogenic nuclide (TCN)-based glacier chronology relying on 24 new 10Be exposure ages, which constrain maximum Neoglacial positions of four small to mid-sized glaciers (Rateau, Lautaret, Bonnepierre and Etages) in the Ecrins-Pelvoux massif, southern French Alps. Glacier advances, marked by (mainly lateral) moraine ridges that are located slightly outboard of the Little Ice Age (LIA, c. 1250-1860 AD) maximum positions, were dated to 4.25 ± 0.44 ka, 3.66 ± 0.09 ka, 2.09 ± 0.10 ka, c. 1.31 ± 0.17 ka and to 0.92 ± 0.02 ka. The '4.2 ka advance', albeit constrained by rather scattered dates, is to our knowledge exposure-dated here for the first time in the Alps. It is considered as one of the first major Neoglacial advance in the western Alps, in agreement with other regional paleoclimatological proxies. We further review Alpine and Northern Hemisphere mid-to-high latitude evidence for climate change and glacier activity concomitant with the '4.2 ka event'. The '2.1 ka advance' was not extensively dated in the Alps and is thought to represent a prominent advance in early Roman times. Other Neoglacial advances dated here match the timing of previously described Alpine Neoglacial events. Our results also suggest that a Neoglacial maximum occurred at Etages Glacier 0.9 ka ago, i.e. during the Medieval Climate Anomaly (MCA, c. 850-1250 AD). At Rateau Glacier, discordant results are thought to reflect exhumation and snow cover of the shortest moraine boulders. Overall, this study highlights the need to combine several sites to develop robust Neoglacial glacier chronologies in order to take into account the variability in moraine deposition pattern and landform obliteration and conservation.

Magnetic Mineral diagenesis in changing water environments in the Black Sea since ˜41.6 ka

NASA Astrophysics Data System (ADS)

Liu, Jiabo; Nowaczyk, Norbert; Frank, Ute; Arz, Helge

2017-04-01

Magnetic mineral diagenesis plays a key role in the global iron cycle. To understand the authigenic magnetic mineral formation by diagenesis is also fundamentally important for the interpretation of environmental magnetic as well as paleomagnetic signals. Core MSM33-55-1, recovered from the SW Black Sea, was subjected to rock-magnetic and SEM studies. The results demonstrate that four different magnetic mineral assemblages associated to specific water conditions can be observed. Between ˜41.6 ka and ˜19 ka, magnetite and greigite are alternatively in dominance in the sediment. Due to low organic matter input during the late MIS 3 and the last glacial maximum (LGM), oxygenated bottom water in the Black Sea was favourable for preserving detrital magnetite. Greigite in this interval have irregular shapes and assemble in spots, which were formed in a micro environment with limited sulfate availability. Between ˜19 ka and ˜16.5 ka, black layers were deposited as a result of organic matter accumulation induced by productivity blooming and riverine discharge soaring after the LGM. Hence less oxygenated bottom water conditions developed, and more fine grained greigite was formed. After melt-water pulse (MWP) events (˜16.5 ka), both primary productivity and the sea level were continuously rising until ˜8.3 ka, leading to the depletion of oxygen in bottom water. In addition to greigite, pyrite was also formed and gradually in dominance as approaching the Holocene. The influx of salt water masses from the Mediterranean Sea after ˜8.3 ka contributed to the establishment of the anoxic Black Sea, which resulted in the formation of ubiquitous frambiods of pyrite. Additionally, bacterial magnetic minerals are likely present in the sediment younger than ˜8.3 ka as indicated by rock magnetic results. In this paper, four different magnetic mineral assemblages, reflecting gradual changes from an oxic to an anoix Black Sea, were identified, yielding insights into the relation between magnetic minerals diagenesis and bottom water conditions.

Astronomical Pacing of Relative Sea Level through OAE2 from the Expanded SH#1 Core, Southern Utah

NASA Astrophysics Data System (ADS)

Jones, M. M.; Sageman, B. B.; Oakes, R. L.; Bralower, T. J.; Parker, A. L.; Leckie, R. M.

2017-12-01

Proximal marine strata of the North American Western Interior Basin (WIB) preserve a rich record of faunal turnover linked to Oceanic Anoxic Event 2 (OAE2 - 94 Ma), a pronounced Late Cretaceous carbon cycle perturbation interpreted to reflect global warming and possible ocean acidification. To develop a more robust synthesis of paleobiologic and geochemical datasets spanning this major Earth-life transition, we drilled a 131-meter core (SH#1) on the Kaiparowits Plateau of southern Utah, recovering the Cenomanian-Turonian Boundary (CTB) interval of the Tropic Shale. A 17.5-meter positive excursion in high-resolution bulk carbon isotope chemostratigraphy (δ13Corg) of SH#1 characterizes the most expanded and detailed record of OAE2 recovered from the WIB. Additionally, we detect statistically significant evidence for astronomical cycles in a companion δ13Ccarb dataset, using advanced spectral techniques (evolutive average spectral misfit). Bandpass filtering and tracing of the short eccentricity cycle (97 ka) permit development of a floating astronomical time scale (ATS) for the CTB interval. The presence of radioisotopic dates within the time series provides an independent check on astrochronologic interpretations. We attribute some depleted δ13Ccarb values in SH#1, which cyclically punctuate the OAE2 excursion, to preferential carbonate diagenesis driven by periodic sea level oscillations. Accordingly, major flooding surfaces in SH#1 correlate well to an existing sequence stratigraphic framework from shoreface facies of the Markagunt Plateau ( 100 km west). Comparing the ATS and sequence stratigraphic surfaces in SH#1, we observe that stable eccentricity cycles (405 ka) pace stratigraphic sequences and associated saw-toothed trends in sedimentation rate estimates through OAE2. Furthermore, short eccentricity cycles pace nested parasequences. These results confirm astronomical and, therefore, climatic pacing of relative sea level trends during OAE2 in the WIB. The ATS, δ13C chemostratigraphy, and basin-wide correlation of the CTB interval provide an expanded, temporally-resolved record of OAE2 within the chronostratigraphic framework of the WIB, and help to resolve rates of paleobiologic and paleoenvironmental change in the context of oscillating relative sea levels.

Lateglacial and Holocene climatic changes in south-eastern Patagonia inferred from carbonate isotope records of Laguna Potrok Aike (Argentina)

NASA Astrophysics Data System (ADS)

Oehlerich, M.; Mayr, C.; Gussone, N.; Hahn, A.; Hölzl, S.; Lücke, A.; Ohlendorf, C.; Rummel, S.; Teichert, B. M. A.; Zolitschka, B.

2015-04-01

First results of strontium, calcium, carbon and oxygen isotope analyses of bulk carbonates from a 106 m long sediment record of Laguna Potrok Aike, located in southern Patagonia are presented. Morphological and isotopic investigations of μm-sized carbonate crystals in the sediment reveal an endogenic origin for the entire Holocene. During this time period the calcium carbonate record of Laguna Potrok Aike turned out to be most likely ikaite-derived. As ikaite precipitation in nature has only been observed in a narrow temperature window between 0 and 7 °C, the respective carbonate oxygen isotope ratios serve as a proxy of hydrological variations rather than of palaeotemperatures. We suggest that oxygen isotope ratios are sensitive to changes of the lake water balance induced by intensity variations of the Southern Hemisphere Westerlies and discuss the role of this wind belt as a driver for climate change in southern South America. In combination with other proxy records the evolution of westerly wind intensities is reconstructed. Our data suggest that weak SHW prevailed during the Lateglacial and the early Holocene, interrupted by an interval with strengthened Westerlies between 13.4 and 11.3 ka cal BP. Wind strength increased at 9.2 ka cal BP and significantly intensified until 7.0 ka cal BP. Subsequently, the wind intensity diminished and stabilised to conditions similar to present day after a period of reduced evaporation during the "Little Ice Age". Strontium isotopes (87Sr/86Sr ratio) were identified as a potential lake-level indicator and point to a lowering from overflow conditions during the Glacial (∼17 ka cal BP) to lowest lake levels around 8 ka cal BP. Thereafter the strontium isotope curve resembles the lake-level curve which is stepwise rising until the "Little Ice Age". The variability of the Ca isotope composition of the sediment reflects changes in the Ca budget of the lake, indicating higher degrees of Ca utilisation during the period with lowest lake level.

Comparison of Glacial Records From 10°S and 11°S in the Peruvian Andes Suggests Similar Forcings but Different Local Influences

NASA Astrophysics Data System (ADS)

Smith, J. A.; Rodbell, D. T.

2010-12-01

Moraine records of glaciation from three sites in the central Peruvian Andes are broadly consistent over the last glacial cycle (since MIS 5). Surface-exposure dating (10Be) of moraines east and west of Lake Junin (11°00'S, 76°00'W, 4082 masl) and 180 km northwest at the Nevado Jeulla Rajo (NJR) massif (10°00'S, 77°16'W) at the southern end of the Cordillera Blanca suggests a link between glacial advances and increased precipitation associated with Heinrich events. On the eastern side of Lake Junin, the most extensive moraines are >150 ka, but end moraines farther upvalley date to the local last glacial maximum (LLGM, 25-30 ka) and a late-glacial stillstand or readvance (14-18 ka). Surface-exposure ages on a moraine and bedrock in the Santuario Nacional Bosque de Piedras de Huayllay (BPH) on the western side of Lake Junin (10°59'S, 76°20'W) are consistent with 10Be ages on younger moraines on the eastern side: ~26 and ~20 ka on two quartz boulders, ~14-15 ka on four ignimbrite boulders, and ~45 ka on bedrock below a trimline in the valley wall. The NJR massif (ca. 5600 masl) hosts a number of small glaciers within a cirque on its southwestern face; large lateral moraines extend onto the Conococha Plain (ca. 4050 masl) from west-facing valleys. Fault scarps on moraines and valley floors on the western side of NJR show the trace of the active, west-dipping Cordillera Blanca Normal Fault (CBNF). At NJR, 10Be ages indicate that the largest lateral moraines were deposited during similar intervals (27-32 ka and 15-18 ka) to the younger moraines in the eastern Junin valleys and BPH. Differences between the Junin/BPH and NJR records are intriguing. NJR lacks the morphologically distinct pre-MIS 5 moraines that are present in valleys east of Lake Junin, although the Conococha Plain adjacent to NJR is underlain by till and outwash that is likely >50 ka, based on 10Be ages of surface cobbles. At NJR, avulsion of two glacial valleys preserved older, smaller pairs of lateral moraines that are cross-cut by larger, younger moraines. One pair of cross-cut moraines has been dated (56-65 ka) and may be the first geomorphologically distinct evidence of an advance during MIS 4 identified in the region; correlative moraines were apparently not preserved in the Junin valleys. The changes in ice-flow direction at NJR may be related to movement on the CBNF that changed the slope of the Conococha Plain onto which ice flowed. We are in the process of dating additional cross-cutting moraines and moraines offset by the CBNF to gain a better understanding of the timing of the ice-flow shifts. Numerical dating of faulted moraines also provides a means of determining apparent slip rates on a fault. Preliminary results at NJR suggest an apparent slip rate of 2.2-2.8 mm/yr for the CBNF where it offsets one of the late-glacial moraines (15-18 ka).

A 150-ka-long record for the volcano-tectonic deformation of Central Anatolian Volcanic Province

NASA Astrophysics Data System (ADS)

Karabacak, Volkan; Tonguç Uysal, I.; Ünal-İmer, Ezgi; Mutlu, Halim; Zhao, Jian-xin

2017-04-01

The Anatolian Block represents one of the most outstanding examples of intra-plate deformation related to continental collision. Deformation related to the convergence of the Afro-Arabian continent toward north gives rise to widespread and intense arc volcanism in the Central Anatolia. All the usual studies on dating the volcano-tectonic deformation of the region are performed entirely on volcanic events of the geological record resulted in eruptions. However, without volcanic eruption, magma migration and related fluid pressurization also generate crustal deformation. In the current study has been funded by the Scientific and Technological Research Council of Turkey with the project no. 115Y497, we focused on fracture systems and their carbonate veins around the Ihlara Valley (Cappadocia) surrounded by well-known volcanic centers with latest activities of the southern Central Anatolian Volcanic Province. We dated 37 samples using the Uranium-series technique and analyzed their isotope systematics from fissure veins, which are thought to be controlled by the young volcanism in the region. Our detailed fracture analyses in the field show that there is a regional dilatation as a result of a NW-SE striking extension which is consistent with the results of recent GPS studies. The Uranium-series results indicate that fracture development and associated carbonate vein deposition occurred in the last 150 ka. Carbon and oxygen isotope systematics have almost remained unchanged in the studied time interval. Although veins in the region were precipitated from fluids primarily of meteoric origin, fluids originating from water-rock interaction also contribute for the deposition of carbonate veins. The age distribution indicates that the crustal deformation intensified during 7 different period at about 4.7, 34, 44, 52, 83, 91, 149 ka BP. Four of these periods (4.7, 34, 91, 149 ka BP) correspond to the volcanic activities suggested in the previous studies. The three crustal deformation periods occurred at 44, 52, and 83 ka BP were dated in addition to the known. They are interpreted to have possibly occurred without any eruption in the late Pleistocene and were controlled by magma movements and/or associated fluid pressure. Such crustal deformation controlled by volcanism is dated for the first time in the literature with a sampling other than extrusive material. The obtained age data revealed that crustal deformation linked to the young volcanism in the Central Anatolian Volcanic Province was repeated in short-term strain cycles of 8-10 ka and that the duration of activity lasted approximately 1100 ± 1000 years in each period, possibly triggered fracture development without any eruption in some periods.

Expectations of younger patients concerning activities after knee arthroplasty: are we asking the right questions?

PubMed

Witjes, Suzanne; van Geenen, Rutger C I; Koenraadt, Koen L M; van der Hart, Cor P; Blankevoort, Leendert; Kerkhoffs, Gino M M J; Kuijer, P Paul F M

2017-02-01

Indications for total and unicondylar knee arthroplasty (KA) have expanded to younger patients, in which Patient-Reported Outcome Measures (PROMs) often show ceiling effects. This might be due to higher expectations. Our aims were to explore expectations of younger patients concerning activities in daily life, work and leisure time after KA and to assess to what extent PROMs meet and evaluate these activities of importance. Focus groups were performed among osteoarthritis (OA) patients <65 years awaiting KA, in which they indicated what activities they expected to perform better in daily life, work and leisure time after KA. Additionally, 28 activities of daily life, 17 of work and 27 of leisure time were depicted from seven PROMS, which were rated on importance, frequency and bother. A total score, representing motivation for surgery, was also calculated. Data saturation was reached after six focus groups including 37 patients. Younger OA patients expect to perform better on 16 activities after KA, including high-impact leisure time activities. From the PROMs, daily life and work activities were rated high in both importance and motivation for surgery, but for leisure time activities importance varied highly between patients. All seven PROMs score activities of importance, but no single PROM incorporates all activities rated important. Younger patients expect to perform better on many activities of daily life, work and leisure time after KA, and often at demanding levels. To measure outcomes of younger patients, we suggest using PROMs that include work and leisure time activities besides daily life activities, in which preferably scored activities can be individualized.

Resolving the age of Wilson Creek Formation tephras and the Mono Lake excursion using high-resolution SIMS dating of allanite and zircon rims

NASA Astrophysics Data System (ADS)

Vazquez, J. A.; Lidzbarski, M. I.

2012-12-01

Sediments of the Wilson Creek Formation surrounding Mono Lake preserve a high-resolution archive of glacial and pluvial responses along the eastern Sierra Nevada due to late Pleistocene climate change. An absolute chronology for the Wilson Creek stratigraphy is critical for correlating the paleoclimate record to other archives in the western U.S. and the North Atlantic region. However, multiple attempts to date the Wilson Creek stratigraphy using carbonates and interbedded rhyolitic tephras yield discordant 14C and 40Ar/39Ar results due to open-system effects, carbon reservoir uncertainties, as well as abundant xenocrysts entrained during eruption. Ion microprobe (SIMS) 238U-230Th dating of the final increments of crystallization recorded by allanite and zircon autocrysts from juvenile pyroclasts yields ages that effectively date eruption of key tephra beds and resolve age uncertainties about the Wilson Creek stratigraphy. To date the final several micrometers of crystal growth, individual allanite and zircon crystals were embedded in soft indium to allow sampling of unpolished rims. Isochron ages derived from rims on coexisting allanite and zircon (± glass) from hand-selected pumiceous pyroclasts delimit the timing of Wilson Creek sedimentation between Ashes 7 and 19 (numbering of Lajoie, 1968) to the interval between ca. 27 to ca. 62 ka. The interiors of individual allanite and zircon crystals sectioned in standard SIMS mounts yield model 238U-230Th ages that are mostly <10 k.y. older than their corresponding rim age, suggesting a relatively brief interval of allanite + zircon crystallization before eruption. A minority of allanite and zircon crystals yield rim and interior model ages of ca. 90-100 ka, and are likely to be antecrysts recycled from relatively early Mono Craters volcanism and/or intrusions. Tephra (Ash 15) erupted during the geomagnetic excursion originally designated the Mono Lake excursion yields a rim isochron age of ca. 41 ka indicating that the recorded event is instead the Laschamp excursion. The results are consistent with a depositional chronology from correlation of relative paleointensity (Zimmerman et al., 2006) that indicates quasi-synchronous glacial and hydrologic responses in the Sierra Nevada and Mono Basin to climate change, with intervals of lake filling and glacial-snowpack melting that are in phase with peaks in spring insolation. Moreover, the results demonstrate that high-spatial resolution SIMS dating of accessory mineral rims is an alternative and promising approach for resolving the depositional ages of silicic tephras containing minerals that crystallized over protracted intervals or that are plagued by incorporation of xenocrysts and/or antecrysts. References: Lajoie, K., 1968, PhD Dissertation, UC Berkeley; Zimmerman et al., 2006, EPSL 252: 94-106.

Determination of pK(a) of felodipine using UV-Visible spectroscopy.

PubMed

Pandey, M M; Jaipal, A; Kumar, A; Malik, R; Charde, S Y

2013-11-01

In the present study, for the first time, experimental pKa value of felodipine is reported. Dissociation constant, pKa, is one of the very important physicochemical properties of drugs. It is of paramount significance from the perspective of pharmaceutical analysis and dosage form design. The method used for the pKa determination of felodipine was essentially a UV-Visible spectrophotometric method. The spectrophotometric method for the pKa determination was opted by acknowledging the established fact that spectrophotometric determination of pKa produces most precise values. The pKa of felodipine was found to be 5.07. Furthermore, the ruggedness of the determined value is also validated in this study in order to produce exact pKa of the felodipine. Copyright © 2013 Elsevier B.V. All rights reserved.

Milankovitch and sub-Milankovitch cycles of the Early Triassic Daye Formation, South China and their geochronological and paleoclimatic implications

NASA Astrophysics Data System (ADS)

Wu, H.; Zhang, S.; Feng, Q.; Jiang, G.; Li, H.; Yang, T.

2011-12-01

The most profound mass extinction in the Phanerozoic occurred at the end of the Permian, with global loss of nearly 90% of marine invertebrate species and 70% of terrestrial vertebrate genera. Recent studies suggested that volcanisms represented by the Siberian Trap were most likely cause of the end-Permian extinction. The post-extinction periods in the Early Triassic was characterized by low biodiversity, reduced abundance and size of invertebrates, hiatus in coal deposition, anomalously high sediment fluxes, and large perturbations of the carbon cycle, which have been interpreted as the consequence of persistently unfavorable environmental conditions. However, the time framework for the Early Triassic geological, biological and geochemical events is traditionally established by conodont biostratigraphy, but the absolute duration of condont biozones are not well constrained. In this study, a rock magnetic cyclostratigraphy, based on high-resolution analysis (2440 samples) of magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) intensity variations, was developed for the 55.1-m-thick, Early Triassic Daye Formation at the Daxiakou section, Hubei province in South China. The Daye Formation shows exceptionally well-preserved lithological cycles with alternations of thin-bedded mudstone, marl and limestone, which are closely tracked by the MS and ARM variations. Power spectral, wavelet and amplitude modulation (AM) analysis of the ARM and MS series reveal strong evidence for the presence of Milankovitch to sub-Milankovitch frequencies dominated by precession index signal and 4-5 ka cycles. Cycles expressed by variations in MS and ARM were likely controlled by the input of fine-grained detrital magnetite, which in turn may be driven by astronomically induced changes in monsoon intensity in the equatorial eastern Tethys during the Early Triassic greenhouse period. On the basis of the 100-ka tuning results, the astronomically constrained duration of the Induan stage is 1.162 Ma, with the Griesbachian and Dienerian substage of 491ka and 671 ka, respectively. The new astronomical time scale also provides time constraints for the conodont and bivalve biozones, the carbonate carbon isotope (δ13C) records and magnetic polarity zones of the Lower Triassic Daye Formation. Time constraints for the conodont biozones include 34 ka for Hindeodus parvus , 24 ka for Isarcicella stachei-I. isarcica, 367 ka for Neogondolella planate-Ng. carinata, 66 ka for Neogondolella discreta, 255 ka for Neospathodus kummeli and 416 ka for Neospathodus dieneri. The Early Smithian negative δ13C shift near the Indun/Olenekian boundary may have happened within 430 ka. Global comparison indicates that Milankovitch and 4-5 ka sub-Milankovitch forcing depositional rhythms may have been common in tropical and sub-tropical carbonate platforms during Early and Middle Triassic time. The ultimate control on the 4-5 ka cycles may have been millennial-scale fluctuations in solar insolation.

Late Holocene earthquake history of the Brigham City segment of the Wasatch fault zone at the Hansen Canyon, Kotter Canyon, and Pearsons Canyon trench sites, Box Elder County, Utah

USGS Publications Warehouse

DuRoss, Christopher B.; Personius, Stephen F.; Crone, Anthony J.; McDonald, Greg N.; Briggs, Richard W.

2012-01-01

Of the five central segments of the Wasatch fault zone (WFZ) having evidence of recurrent Holocene surface-faulting earthquakes, the Brigham City segment (BCS) has the longest elapsed time since its most recent surface-faulting event (~2.1 kyr) compared to its mean recurrence time between events (~1.3 kyr). Thus, the BCS has the highest time-dependent earthquake probability of the central WFZ. We excavated trenches at three sites––the Kotter Canyon and Hansen Canyon sites on the north-central BCS and Pearsons Canyon site on the southern BCS––to determine whether a surface-faulting earthquake younger than 2.1 ka occurred on the BCS. Paleoseismic data for Hansen Canyon and Kotter Canyon confirm that the youngest earthquake on the north-central BCS occurred before 2 ka, consistent with previous north-central BCS investigations at Bowden Canyon and Box Elder Canyon. At Hansen Canyon, the most recent earthquake is constrained to 2.1–4.2 ka and had 0.6–2.5 m of vertical displacement. At Kotter Canyon, we found evidence for two events at 2.5 ± 0.3 ka and 3.5 ± 0.3 ka, with an average displacement per event of 1.9–2.3 m. Paleoseismic data from Pearsons Canyon, on the previously unstudied southern BCS, indicate that a post-2 ka earthquake ruptured this part of the segment. The Pearsons Canyon earthquake occurred at 1.2 ± 0.04 ka and had 0.1–0.8 m of vertical displacement, consistent with our observation of continuous, youthful scarps on the southern 9 km of the BCS having 1–2 m of late Holocene(?) surface offset. The 1.2-ka earthquake on the southern BCS likely represents rupture across the Weber–Brigham City segment boundary from the penultimate Weber-segment earthquake at about 1.1 ka. The Pearsons Canyon data result in a revised length of the BCS that has not ruptured since 2 ka (with time-dependent probability implications), and provide compelling evidence of at least one segment-boundary failure and multi-segment rupture on the central WFZ. Our paleoseismic investigations of the BCS clarify the timing, displacement, and extent of late Holocene earthquakes on the segment, and importantly, confirm the long elapsed time since the most recent earthquake on most of the BCS.

Sub-decadal turbidite frequency during the early Holocene: Eel Fan, offshore northern California

USGS Publications Warehouse

Paull, Charles K.; McGann, Mary L.; Sumner, Esther J; Barnes, Philip M; Lundsten, Eve M.; Anderson, Krystle; Gwiazda, Roberto; Edwards, Brian D.; Caress, David W

2014-01-01

Remotely operated and autonomous underwater vehicle technologies were used to image and sample exceptional deep sea outcrops where an ∼100-m-thick section of turbidite beds is exposed on the headwalls of two giant submarine scours on Eel submarine fan, offshore northern California (USA). These outcrops provide a rare opportunity to connect young deep-sea turbidites with their feeder system. 14C measurements reveal that from 12.8 ka to 7.9 ka, one turbidite was being emplaced on average every 7 yr. This emplacement rate is two to three orders of magnitude higher than observed for turbidites elsewhere along the Pacific margin of North America. The turbidites contain abundant wood and shallow-dwelling foraminifera, demonstrating an efficient connection between the Eel River source and the Eel Fan sink. Turbidite recurrence intervals diminish fivefold to ∼36 yr from 7.9 ka onward, reflecting sea-level rise and re-routing of Eel River sediments.

Th-230 - U-238 series disequilibrium of the Olkaria rhyolites Gregory Rift Valley, Kenya: Residence times

NASA Technical Reports Server (NTRS)

Black, S.; Macdonald, R.; Kelly, M.

1993-01-01

U-series disequilibrium analyses have been conducted on samples from Olkaria rhyolite centers with ages being available for all but one center using both internal and whole rock isochrons. 67 percent of the rhyolites analyzed show U-Th disequilibrium, ranging from 27 percent excess thorium to 36 percent excess uranium. Internal and whole rock isochrons give crystallization/formation ages between 65 ka and 9 ka, in every case these are substantially older than the eruptive dates. The residence times of the rhyolites (U-Th age minus the eruption date) have decreased almost linearly with time, from 45 ka to 7 Ka suggesting a possible increase of activity within the system related to increased basaltic input. The long residence times are mirrored by large Rn-222 fluxes from the centers which cannot be explained by larger U contents.

Lateglacial and Holocene climate, disturbance and permafrost peatland dynamics on the Seward Peninsula, western Alaska

USGS Publications Warehouse

Hunt, Stephanie D.; Yu, Zicheng; Jones, Miriam C.

2013-01-01

Northern peatlands have accumulated large carbon (C) stocks, acting as a long-term atmospheric C sink since the last deglaciation. How these C-rich ecosystems will respond to future climate change, however, is still poorly understood. Furthermore, many northern peatlands exist in regions underlain by permafrost, adding to the challenge of projecting C balance under changing climate and permafrost dynamics. In this study, we used a paleoecological approach to examine the effect of past climates and local disturbances on vegetation and C accumulation at a peatland complex on the southern Seward Peninsula, Alaska over the past ∼15 ka (1 ka = 1000 cal yr BP). We analyzed two cores about 30 m apart, NL10-1 (from a permafrost peat plateau) and NL10-2 (from an adjacent thermokarst collapse-scar bog), for peat organic matter (OM), C accumulation rates, macrofossil, pollen and grain size analysis.A wet rich fen occurred during the initial stages of peatland development at the thermokarst site (NL10-2). The presence of tree pollen from Picea spp. and Larix laricinia at 13.5–12.1 ka indicates a warm regional climate, corresponding with the well-documented Bølling–Allerød warm period. A cold and dry climate interval at 12.1–11.1 ka is indicated by the disappearance of tree pollen and increase in Poaceae pollen and an increase in woody material, likely representing a local expression of the Younger Dryas (YD) event. Following the YD, the warm Holocene Thermal Maximum (HTM) is characterized by the presence of Populus pollen, while the presence of Sphagnum spp. and increased C accumulation rates suggest high peatland productivity under a warm climate. Toward the end of the HTM and throughout the mid-Holocene a wet climate-induced several major flooding disturbance events at 10 ka, 8.1 ka, 6 ka, 5.4 ka and 4.7 ka, as evidenced by decreases in OM, and increases in coarse sand abundance and aquatic fossils (algae Chara and water fleas Daphnia). The initial peatland at permafrost site (NL10-1) is characterized by rapid C accumulation (66 g C m−2 yr−1), high OM content and a peak in Sphagnum spp. at 5.8–4.6 ka, suggesting the lack of permafrost. A transition to extremely low C accumulation rates of 6.3 g C m−2 yr−1 after 4.5 ka at this site suggests the onset of permafrost aggradation, likely in response to Neoglacial climate cooling as documented across the circum-Arctic region. A similar decrease in C accumulation rates also occurred at non-permafrost site NL10-2. Time-weighted C accumulation rates are 21.8 g C m−2 yr−1 for core NL10-1 during the last ∼6.5 ka and 14.8 g C m−2 yr−1 for core NL10-2 during the last ∼15 ka. Evidence from peat-core analysis and historical aerial photographs shows an abrupt increase in Sphagnum spp. and decrease in area of thermokarst lakes over the last century, suggesting major changes in hydrology and ecosystem structure, likely due to recent climate warming.Our results show that the thermokarst–permafrost complex was much more dynamic with high C accumulation rates under warmer climates in the past, while permafrost was stabilized and C accumulation slowed down following the Neoglacial cooling in the late Holocene. Furthermore, permafrost presence at local scales is controlled by both regional climate and site-specific factors, highlighting the challenge in projecting responses of permafrost peatlands and their C dynamics to future climate change.

Climate Controls on Last Glacial Maximum to Early Holocene Glacier Extents in the Rwenzori Mountains, Uganda-Democratic Republic of Congo

NASA Astrophysics Data System (ADS)

Jackson, M. S.; Kelly, M. A.; Russell, J. M.; Baber, M.; Loomis, S. E.

2014-12-01

The climate controls on past and present tropical glacier fluctuations are unclear. Here we present a chronology of past glacial extents in the Rwenzori Mountains (~1ºN, 30ºE), on the border of Uganda and the Democratic Republic of Congo, and compare this with local and regional paleoclimate records to infer the climate controls on glaciation. The Rwenzori Mountains host the most extensive glacial system in Africa and are composed of quartz-rich bedrock lithologies, enabling 10Be dating. Our dataset includes thirty 10Be ages of boulders on moraines estimated to have been deposited between the end of the last glacial period and early Holocene time. In the Mubuku Valley, eight 10Be ages of large (~50-150 m relief) lateral moraines that extend down to ~2000 m asl indicate that deposition occurred at ~23.4 ka (n=4) and ~20.1 ka (n=4), contemporaneously with the global Last Glacial Maximum (LGM). Local and regional paleoclimate records document dry, cool conditions in East Africa during this time. Therefore, we suggest that cooler temperatures were a primary influence on the LGM glacial extents. Upvalley from these samples, six 10Be ages of boulders on moraines (between 3450 and 3720 m asl) document stillstands or readvances of glacier ice at ~14.3 ka (n=2), ~13.2 ka (n=2), and ~11.1 ka (n=2). In the nearby Nyagumasani Valley sixteen 10Be ages of boulders on moraines at similar elevations (3870-4020 m asl) indicate stillstands or readvances at ~11.5 ka (n=4), ~10.6 ka (n=4), and ~10.5 ka (n=4). Local and regional paleoclimate records indicate dry conditions during Younger Dryas time, wet conditions during early Holocene time, and no significant late-glacial temperature reversal. Thus, the relationship between glacier advance and climate conditions during late-glacial time remains enigmatic. We continue to develop the moraine chronology in order to improve our interpretations of climate controls on glacier fluctuations during late-glacial to early Holocene time.

The Mono Lake geomagnetic excursion recorded in loess: Its application as time marker and implications for its geomagnetic nature

NASA Astrophysics Data System (ADS)

Hambach, U.; Hark, M.; Zeeden, C.; Reddersen, B.; Zöller, L.; Fuchs, M.

2009-04-01

One of the youngest and worldwide documented geomagnetic excursions in the Brunhes Chron is the Mono Lake excursion (MLE). It has been detected in marine and terrestrial sedimentary archives as well as in lavas. Recent age determinations and age estimates for the MLE centre around an age interval of approximately 31 - 34 ka. Likewise the Laschamp excursion the MLE goes along with a distinct peak in cosmogenic radionuclides in ice cores and sedimentary archives. It provides therefore an additional geomagnetic time marker for various geoarchives to synchronise different climate archives. Here we report on a detailed record of the MLE from a loess site at Krems, Lower Austria. The site is situated on the southern slope of the Wachtberg hill in the vicinity of the old city centre of Krems. The archive comprises Middle to Upper Würmian (Late Pleistocene) loess in which an Upper Palaeolithic (Early Gravettian) cultural layer is embedded. The most spectacular finds are a double infant burial found in 2005 and a single burial discovered in 2006 (Einwögerer et al., 2006). Generally, archaeological findings show an extraordinarily good preservation due to embedding in rapidly sedimented loess (Händel et al., 2008). The about 10 m thick loess pile consists of calcareous sandy, coarse silt which is rich in mica indicating local sources. It is well stratified with brownish horizons representing embryonic soils pointing to incipient pedogenesis. Some of the pedo-horizons show occasionally indications of minor erosion and bedding-parallel sediment transport, but no linear erosional features. Pale greyish horizons are the result of partial gleying under permafrost conditions. No strong pedogenesis including decalcification and clay formation is present. The cultural layer is still covered by more than 5 m of loess, and dated by radiocarbon to ~27 ka 14C BP (Einwögerer et al., 2006). Below this layer up to 2.5 m of loess resting on Lower Pleistocene fluvial gravels are preserved. Thus, the loess section represents a palaeoclimatic record of alternating cold-dry and warm-humid conditions on millennial scale. Optical stimulated luminescence dating of aeolian loess around the cultural layer reveals ages of 30 to 32 ka which is supported by thermoluminesence dating of burnt loess from a hearth belonging to the archaeological living floor. In summer 2005 and 2006, two overlapping sections were continuously sampled in for palaeomagnetic investigations. The sampled sections are located outside the centre of the main archaeological occupation in the northwestern corner of the excavation pit. Sample spacing is strictly 2.1 cm, measured from centre to centre of the specimens. In total, 432 individually oriented specimens were recovered from the almost 8 m thick section. Magnetic susceptibility (MS) as function of depth resembles generally the lithology. Low MS-values represent pure unaltered or weakly gleyed loess, whereas higher values represent the enhancement of magnetic minerals caused by incipient soil formation. Anhysteretic remanent magnetisation (ARM) versus MS reveals an enhancement of super-paramagnetic particles where MS is increased. Consequently, the rock magnetic variations with depth can be taken as a palaeoclimatic record representing the climatic variations between drier and slightly more humid conditions at the transition from Middle to Upper Pleniglacial. Based on the ARM/MS record a correlation of the geoarchive at the Krems-Wachtberg site with the NORTH-GRIP isotopic record (NGRIP Members, 2004) and with sedimentological data from Maar-lake sediments of the Eifel area (ELSA; Schaber and Sirocko, 2005), Germany can be established. The general correlation suggests the dating of the loess at the excavation site to a time interval between approx. 20 to 40 ka, covering Greenland interstadials (GI) 2 to 8 and Heinrich Events 3 and 4 (top). The Gravettian living floor is assigned to the base of GI 5 and thus to an age of 32 to 33 ka. The directional palaeomagnetic record is of high quality and shows variations in the bandwidth of secular variation in the upper and in the lower part of the section, whereas in the central part shallow (? 30˚ ) and oversteep inclinations reveal the record of a geomagnetic excursion just above the find horizon. The shallow inclinations are preceded by and go along with westerly declinations, whereas the steep inclinations are preceded by easterly declinations. This directional pattern is similar to what was found at the Mono Lake in California (e.g. Liddicoat and Coe, 1979; Lund et al., 1988). A relative palaeointensity (RPI) record was constructed by using MS and ARM as normalisers. This record corresponds quite well to the GLOPIS (Laj et al., 2004) and thus provides additional dating. The peak of the directional excursion coincides with a relative minimum of RPI. The average RPI during the excursional interval, however, is significantly higher than during normal periods, contrary to what is usually reported. Furthermore, just before and after the directional excursion the highest values of RPI occur. The largest amplitude of the directional excursion does not correspond to the well defined minimum in RPI preceding this interval which is usually taken for the MLE in the marine RPI records. This offset between the RPI and the directional record may indicate the presence of strong non-dipole components and may also explain the blur in dating of the MLE. The calculated VGPs of the directional excursion lie over North America but do not correspond to the looping behaviour as reported from the Mono Lake VGPs itself (Liddicoat and Coe, 1979). The cultural layer at the Krems-Wachtberg site is located in the centre of the RPI minimum which is slightly older than the peak of the directional excursion. The radiocarbon ages from the cultural layer (~27 ka 14C age BP = ~32 ka calendric age calBP) fit well to the age estimates of the MLE at the Mono Lake based on radiocarbon dating and tephrochronology (31.5 - 33.3 ka; Benson et al., 2003). Furthermore, the recently published 40Ar/39Ar ages of one excursional group (Auckland cluster 1: 31.6 ± 1.8 ka) from the Auckland volcanic field, New Zealand correspond to the ages discussed above. Thus, the MLE is a perfect time marker occurring globally but is probably dominated by strong non-dipole components. Benson et al. (2003). Quaternary Science Reviews, 22,135-140; Cassata et al. (2008). Earth and Planetary Science Letters, 268, 76-88; Einwögerer et al. (2006). Nature, 444, 285; Händel et al. (in press). Quaternary International; Laj et al. (2004). Geophysical Monograph Series, 145, 255-265; Liddicoat and Coe (1979). Journal of Geophysical Research, 84, 261-271; Lund et al. (1988). Geophysical Research Letters,15,10, 1101-1104; North Greenland Ice Core Project Members (2004). Nature 431, 147-151; Schaber and Sirocko (2005). Mainzer geowiss. Mitt., 33, 295-340.

Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska continental slope

USGS Publications Warehouse

Addison, Jason A.; Finney, Bruce P.; Dean, Walter E.; Davies, Maureen H.; Mix, Alan C.; Jaeger, John M.

2012-01-01

Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W, 682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal changes in productivity and nutrient utilization over the last 17,000 years. Maximum values of opal concentration (∼10%) occur during the deglacial Bølling-Allerød (B-A) interval and earliest Holocene (11.2 to 10.8 cal ka BP), moderate values (∼6%) occur during the Younger Dryas (13.0 to 11.2 cal ka BP) and Holocene, and minimum values (∼3.5%) occur during the Late Glacial Interval (LGI). When converted to opal mass accumulation rates, the highest values (∼5000 g cm−2 kyr−1) occur during the LGI prior to 16.7 cal ka BP, which points to a strong influence by LGI glacimarine sedimentation regimes. Similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies. Mid-Holocene peaks in the terrestrial organic matter fraction at 5.5, 4.7, 3.5, and 1.2 cal ka BP indicate periods of enhanced delivery of glaciomarine sediments by the Alaska Coastal Current. The B-A and earliest Holocene intervals are laminated, and enrichments of redox-sensitive elements suggest dysoxic-to-anoxic conditions in the water column. The laminations are also associated with mildly enriched sedimentary δ15N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial δ15N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine δ15N (6.3 ± 0.4 ‰) ratios are consistent with either mild denitrification, or increased nitrate utilization. These findings can be explained by increased micronutrient (Fe) availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain; iron input from enhanced terrestrial runoff; and/or the intermittent presence of seasonal sea ice resulting from altered ocean/atmospheric circulation during the B-A in the Gulf of Alaska.

Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska continental slope

USGS Publications Warehouse

Addison, Jason A.; Finney, Bruce P.; Dean, Walter E.; Davies, Maureen H.; Mix, Alan C.; Stoner, Joseph S.; Jaeger, John M.

2012-01-01

Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W, 682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal changes in productivity and nutrient utilization over the last 17,000 years. Maximum values of opal concentration (∼10%) occur during the deglacial Bølling-Allerød (B-A) interval and earliest Holocene (11.2 to 10.8 cal ka BP), moderate values (∼6%) occur during the Younger Dryas (13.0 to 11.2 cal ka BP) and Holocene, and minimum values (∼3.5%) occur during the Late Glacial Interval (LGI). When converted to opal mass accumulation rates, the highest values (∼5000 g cm−2 kyr−1) occur during the LGI prior to 16.7 cal ka BP, which points to a strong influence by LGI glacimarine sedimentation regimes. Similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies. Mid-Holocene peaks in the terrestrial organic matter fraction at 5.5, 4.7, 3.5, and 1.2 cal ka BP indicate periods of enhanced delivery of glaciomarine sediments by the Alaska Coastal Current. The B-A and earliest Holocene intervals are laminated, and enrichments of redox-sensitive elements suggest dysoxic-to-anoxic conditions in the water column. The laminations are also associated with mildly enriched sedimentary δ15N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial δ15N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine δ15N (6.3 ± 0.4 ‰) ratios are consistent with either mild denitrification, or increased nitrate utilization. These findings can be explained by increased micronutrient (Fe) availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain; iron input from enhanced terrestrial runoff; and/or the intermittent presence of seasonal sea ice resulting from altered ocean/atmospheric circulation during the B-A in the Gulf of Alaska.

Sedimentological analysis and long term chronostratigraphy (> 30 ka) of turbidite record offshore the central Algerian margin

NASA Astrophysics Data System (ADS)

Bachir, Roza Si; Babonneau, Nathalie; Cattaneo, Antonio; Ratzov, Gueorgui; Déverchère, Jacques; Yelles, Karim

2016-04-01

The Algerian margin is a Cenozoic passive margin located at the diffuse plate boundary between Eurasia and Africa, presently reactivated in compression. It is among the most seismically active areas of the Western Mediterranean and it suffered from numerous devastating earthquakes, for example the El Asnam earthquake in 1980 (Ms = 7.3) and the Boumerdès earthquake in 2003 (Ms = 6.7). A consistent dataset of sediment cores was collected between 2003 and 2007 during the MARADJA and PRISME cruises. Previous work has focused on the Holocene and allowed to highlight a consistent paleosesimological record in the central area of the Algerian margin (Algiers area). The purpose of this work is to extend the sedimentary analysis of turbiditic deposits over longer periods of time (throughout the Last Glacial Maximum), in order to determine whether the record of seismic events is exploitable, or if the impact of climate-driven and eustatic variations is dominant in turbidite triggering and accumulation. A sedimentological and stratigraphic approach was performed on the three most distal sediment cores of the area: PSM-KS21, PSM-KS23 and PSM-KS27. The establishment of an age model is based on radiocarbon dating and measurements of oxygen stable isotopes on planktonic foraminifera collected from the pelagic intervals (hemipelagites) interfingered with the turbidites. A homogeneous clay bed identifiable by its grey colour is a marker to correlate the three cores and it is dated between 18 and 19 ka BP. The PSM-KS23 core has the longest sedimentary record, thus it was used as a reference. Preliminary results show a significant increase in the number and thickness of individual turbidites between 10 and 20 ka BP. The expected results of this work are: 1) to determine whether the number of turbidites is consistent and correlates among the three cores; 2) to assess if the paleo-earthquake signal related to turbidites can be extracted beyond the Holocene; 3) to identify the recurrence interval of recorded paleo-earthquake events.

Changes in the Thermohaline Flow due to changes in the WAIS and Astronomical Forcing during the MIS31 Superinterglacial

NASA Astrophysics Data System (ADS)

Justino, F. J.; Lindemann, D.; Kucharski, F.; Wilson, A.; Bromwich, D. H.; Stordal, F.

2017-12-01

The Marine Isotope Stage 31 (MIS31, between 1085 ka and 1055 ka) was characterised by higher extra-tropical air temperatures and a substantial recession of polar glaciers compared to today. Paleoreconstructions and model simulations have increased the understanding of the MIS31 interval, but questions remain regarding the role of the Atlantic and Pacific Oceans in modifying the climate associated with the variations in Earth's orbital parameters. Multi-century coupled climate simulations, with the astronomical configuration of the MIS31 and modified West Antarctic Ice Sheet (WAIS) topography, show an increase in the thermohaline flux and northward oceanic heat transport (OHT) in the Pacific Ocean. These oceanic changes are driven by anomalous atmospheric circulation and increased surface salinity in concert with a stronger meridional overturning circulation (MOC). The intensified northward OHT is responsible for up to 85% of the global OHT anomalies and contributes to the overall reduction in sea-ice in the Northern Hemisphere (NH) due to Earth's astronomical configuration. The relative contributions of the Atlantic Ocean to global OHT and MOC anomalies are minor compared to that of the Pacific. However, sea-ice changes are remarkable, highlighted by decreased (increased) cover in Ross (Weddell) Sea but widespread reductions of sea-ice across the NH. These modeling results have enormous implications for paleoreconstructions of the MIS31 climate that mostly assume overall ice free conditions in the vicinity of the Antarctic continent. Since these reconstructions may depict dominant signals in a particular time interval and locale, they cannot be assumed to geographically represent large-scale domains. Therefore, their ability to reproduce long-term environmental conditions should be considered with care. Finally, it is important to emphasize that understanding past interglacial intervals that are characterized by a depleted WAIS can shed light on the potential effects of increasing atmospheric CO2, as the stability of the WAIS will be a key climate factor in decades to come.

Geochemical record of Holocene to Recent sedimentation on the Western Indus continental shelf, Arabian Sea

NASA Astrophysics Data System (ADS)

Limmer, David R.; BöNing, Philipp; Giosan, Liviu; Ponton, Camilo; KöHler, Cornelia M.; Cooper, Matthew J.; Tabrez, Ali R.; Clift, Peter D.

2012-01-01

We present a multiproxy geochemical analysis of two cores recovered from the Indus Shelf spanning the Early Holocene to Recent (<14 ka). Indus-23 is located close to the modern Indus River, while Indus-10 is positioned ˜100 km further west. The Holocene transgression at Indus-10 was over a surface that was strongly weathered during the last glacial sea level lowstand. Lower Holocene sediments at Indus-10 have higherɛNdvalues compared to those at the river mouth indicating some sediment supply from the Makran coast, either during the deposition or via reworking of older sediments outcropping on the shelf. Sediment transport from Makran occurred during transgressive intervals when sea level crossed the mid shelf. The sediment flux from non-Indus sources to Indus-10 peaked between 11 ka and 8 ka. A hiatus at Indus-23 from 8 ka until 1.3 ka indicates non-deposition or erosion of existing Indus Shelf sequences. HigherɛNdvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building Holocene clinoforms. Chemical Index of Alteration (CIA), Mg/Al and Sr isotopes are all affected by erosion of detrital carbonate, which reduced through the Holocene. K/Al data suggest that silicate weathering peaked ca. 4-6 ka and was higher at Indus-10 compared to Indus-23. Fine-grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain. The Indus Shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings.

Role of the NH2-terminus of substance P in the inhibition by capsaicin of behavioral sensitization to kainic acid-induced activity in the adult mouse.

PubMed

Larson, A A; Sun, X

1994-01-01

Activation of primary afferent C-fibers by repeated intrathecal injection of kainic acid (KA) in mice is inhibited after pretreatment with capsaicin. The increased behavioral response to multiple injections of KA is thought to be brought about by an action of the NH2-terminus of substance P (SP). In light of our recent observation that the antinociceptive effect of capsaicin may also involve an action of the NH2-terminus of SP, we tested the hypothesis that capsaicin inhibits behavioral sensitization to KA by a desensitization to the action of the NH2-terminus of SP. Using adult mice, pretreatment (24 hr) with either capsaicin (0.8 micrograms) or SP(1-7) (1 and 10 nmol) attenuated sensitization of the behavioral response to four injections of 25 pmol of KA at 2-min intervals. Pretreatment with 10 nmol of the COOH-terminal SP fragment, SP(5-11), had no effect. [D-Pro2,D-Phe7]-SP(1-7), a SP NH2-terminal antagonist, injected 5 min before capsaicin or SP(1-7), inhibited the effects of both capsaicin and SP(1-7) on KA sensitization whereas the COOH-terminal neurokinin antagonist, [D-Pro2,D-Trp7,9]-SP, did not. The similarities in behavioral responses after treatment with SP(1-7) or capsaicin, together with the sensitivity of these effects to D-SP(1-7), suggest that SP released in response to capsaicin may inhibit subsequent KA-induced activity 24 hr later. This action of SP appears to be brought about by its NH2-terminus and/or an accumulation of its NH2-terminal metabolites after capsaicin treatment.

Late quaternary temperature record from buried soils of the North American Great Plains

USGS Publications Warehouse

Nordt, L.; Von Fischer, J.; Tieszen, L.

2007-01-01

We present the first comprehensive late Quaternary record of North American Great Plains temperature by assessing the behavior of the stable isotopic composition (δ13C) of buried soils. After examining the relationship between the δ13C of topsoil organic matter and July temperature from 61 native prairies within a latitudinal range of 46°–38°N, we applied the resulting regression equation to 64 published δ13C values from buried soils of the same region to construct a temperature curve for the past 12 k.y. Estimated temperatures from 12 to 10 ka (1 k.y. = 1000 14C yr B.P.) fluctuated with a periodicity of ∼1 k.y. with two cool excursions between −4.5 and −3.5 °C and two warmer excursions between −1 and 0 °C, relative to modern. Early Holocene temperatures from ca. 10–7.5 ka were −1.0 to −2.0 °C before rising to +1.0 °C in the middle Holocene between 6.0 and 4.5 ka. After a cool interlude from 4.2 to 2.6 ka, when temperatures dropped to slightly below modern, another warm interval ensued from 2.6 to 1 ka as temperatures increased to ∼+0.5 °C. A final decline in temperature to below modern occurred beginning ca. 0.5 ka. Cooler than present temperatures in the Great Plains indicate telecommunications with cool-water episodes in the Gulf of Mexico and North Atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance.

Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation.

PubMed

Bauska, Thomas K; Baggenstos, Daniel; Brook, Edward J; Mix, Alan C; Marcott, Shaun A; Petrenko, Vasilii V; Schaefer, Hinrich; Severinghaus, Jeffrey P; Lee, James E

2016-03-29

An understanding of the mechanisms that control CO2 change during glacial-interglacial cycles remains elusive. Here we help to constrain changing sources with a high-precision, high-resolution deglacial record of the stable isotopic composition of carbon in CO2(δ(13)C-CO2) in air extracted from ice samples from Taylor Glacier, Antarctica. During the initial rise in atmospheric CO2 from 17.6 to 15.5 ka, these data demarcate a decrease in δ(13)C-CO2, likely due to a weakened oceanic biological pump. From 15.5 to 11.5 ka, the continued atmospheric CO2 rise of 40 ppm is associated with small changes in δ(13)C-CO2, consistent with a nearly equal contribution from a further weakening of the biological pump and rising ocean temperature. These two trends, related to marine sources, are punctuated at 16.3 and 12.9 ka with abrupt, century-scale perturbations in δ(13)C-CO2 that suggest rapid oxidation of organic land carbon or enhanced air-sea gas exchange in the Southern Ocean. Additional century-scale increases in atmospheric CO2 coincident with increases in atmospheric CH4 and Northern Hemisphere temperature at the onset of the Bølling (14.6-14.3 ka) and Holocene (11.6-11.4 ka) intervals are associated with small changes in δ(13)C-CO2, suggesting a combination of sources that included rising surface ocean temperature.

Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation

PubMed Central

Bauska, Thomas K.; Baggenstos, Daniel; Brook, Edward J.; Mix, Alan C.; Marcott, Shaun A.; Petrenko, Vasilii V.; Schaefer, Hinrich; Lee, James E.

2016-01-01

An understanding of the mechanisms that control CO2 change during glacial–interglacial cycles remains elusive. Here we help to constrain changing sources with a high-precision, high-resolution deglacial record of the stable isotopic composition of carbon in CO2 (δ13C-CO2) in air extracted from ice samples from Taylor Glacier, Antarctica. During the initial rise in atmospheric CO2 from 17.6 to 15.5 ka, these data demarcate a decrease in δ13C-CO2, likely due to a weakened oceanic biological pump. From 15.5 to 11.5 ka, the continued atmospheric CO2 rise of 40 ppm is associated with small changes in δ13C-CO2, consistent with a nearly equal contribution from a further weakening of the biological pump and rising ocean temperature. These two trends, related to marine sources, are punctuated at 16.3 and 12.9 ka with abrupt, century-scale perturbations in δ13C-CO2 that suggest rapid oxidation of organic land carbon or enhanced air–sea gas exchange in the Southern Ocean. Additional century-scale increases in atmospheric CO2 coincident with increases in atmospheric CH4 and Northern Hemisphere temperature at the onset of the Bølling (14.6–14.3 ka) and Holocene (11.6–11.4 ka) intervals are associated with small changes in δ13C-CO2, suggesting a combination of sources that included rising surface ocean temperature. PMID:26976561

A robust, multisite Holocene history of drift ice off northern Iceland: Implications for North Atlantic climate

USGS Publications Warehouse

Andrews, John T.; Darby, D.; Eberle, D.; Jennings, A.E.; Moros, M.; Ogilvie, A.

2009-01-01

An important indicator of Holocene climate change is provided by evidence for variations in the extent of drift ice. A proxy for drift ice in Iceland waters is provided by the presence of quartz. Quantitative x-ray diffraction analysis of the < 2 mm sediment fraction was undertaken on 16 cores from around Iceland. The quartz weight (wt.)% estimates from each core were integrated into 250-yr intervals between ????'0.05 and 11.7 cal. ka BP. Median quartz wt.% varied between 0.2 and 3.4 and maximum values ranged between 2.8 and 11.8 wt.%. High values were attained in the early Holocene and minimum values were reached 6 - 7 cal. ka BP. Quartz wt.% then rose steadily during the late Holocene. Our data exhibit no correlation with counts on haematite-stained quartz (HSQ) grains from VM129-191 west of Ireland casting doubt on the ice-transport origin. A pilot study on the provenance of Fe oxide grains in two cores that cover the last 1.3 and 6.1 cal. ka BP indicated a large fraction of the grains between 1 and 6 cal. ka BP were from either Icelandic or presently unsampled sources. However, there was a dramatic increase in Canadian and Russian sources from the Arctic Ocean ???1 cal. ka BP. These data may indicate the beginning of an Arctic Oscillation-like climate mode. ?? 2009 SAGE Publications.

Magnetic and mineralogical properties of central Baffin Bay sediments since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Simon, Q.; St-Onge, G.; Hillaire-Marcel, C.

2011-12-01

Magnetic and mineralogical properties of terrigenous sediments from the deep central Baffin Bay (HU2008-029-016PC - 70°46,14N/-64°65,77W - 2063 m) were analyzed as a means of linking sedimentological changes to ice-margin dynamics along the surrounding coastlines of W. Greenland, E. Baffin Island and N.E. Ellesmere Island since the Last Glacial Maximum (LGM). A chronology based on relative paleointensity (RPI) and secular variation (PSV) in sections where magnetism properties were suitable has been set. The age-model yields a low mean sedimentation rate varying between 4 - 8 cm/kyr along the core and illustrates a significant increase during Termination 1. Carbonate content increases drastically from 16 ka due to increasing supplies of dolomitic material from dolostone rocks outcropping in the Canadian Arctic Archipelago and associated with inputs from the Innuitian Ice Sheet margin. The magnetic properties demonstrate major changes during the deglaciation and especially during Heinrich event 1 (H1), the Younger Dryas (YD) and throughout the Holocene. Very low median destructive field (MDF) of the natural remanent magnetization (NRM) values are observed during the 11.5 - 12.6 ka (YD) and 14.8 - 16 (H1) ka intervals, and are reflecting coarser magnetic grains. Similarly, the kARM/kLF grain-size ratio shows coarser magnetic grain size during the H1 and YD intervals, and finer magnetic grains during the LGM (19 - 22 ka). During the LGM, "glacial flour" formed by mechanical grinding of rocks by ice sheets released finer magnetic grains from lateral source (e.g., Greenland continental shelf). On the contrary, during the YD and H1 periods, icebergs released coarser magnetic grains from a northern source (axial source). The Holocene is marked by the highest median destructive field (MDF) and ARM20mT/ARM0mT values of the core, indicating an increased proportion of finer magnetic grains during this interval. Together with the large increase in the silt fraction, these different proxies tend to demonstrate the establishment of the modern Baffin Bay oceanic circulation that followed the deglaciation and the opening of Lancaster Sound, Jones Sound and Nares Strait, and the onset of the Western Greenland Current. These data provide strong marine evidence of 1) increasing supplies of sedimentary material coming from the rapid retreat of ice streams in the northern part of Baffin Bay starting at 16 ka and 2) the ice-margin dynamics (Innuitian vs. Greenland ice sheets) since the LGM. The study enables to document these sedimentological changes with regard to regional and Northern Hemisphere climatic variability, and highlights the importance of Baffin Bay for the establishment of modern oceanic circulation.

Large mammals from the Upper Neopleistocene reference sections in the Tunka rift valley, southwestern Baikal Region

NASA Astrophysics Data System (ADS)

Shchetnikov, A. A.; Klementiev, A. M.; Filinov, I. A.; Semeney, E. Yu.

2015-03-01

This work presents the data on new finds of fossil macrotheriofauna in the reference sections of the Upper Neopleistocene sediments in the Tunka rift valley (southwestern Baikal Region). The osteological material of a number of Late Neopleistocene mammals including extinct species rare for the Baikal region such as Crocuta spelaea, Panthera spelaea, and Spirocerus kiakhtensis (?) was directly dated with a radiocarbon (AMS) method. The obtained 14C data (18000-35000 years) allow one to rejuvenate significantly the upper limit of the common age interval of habitat of these animals in southern part of Eastern Siberia. Cave hyena and spiral-horned antelope lived in the Tunka rift valley in the Baikal region in Late Kargino time (37-24 ka), and cave lion survived the maximum in the Sartan cryochron in the region (21-20 ka). The study of collected paleontological collections provides a basis for selection of independent Kargino (MIS 3) faunal assemblages to use them for regional biostratigraphic analysis of Pleistocene deposits. Radiocarbon age dating of samples allows one to attribute confidently all paleofaunal remains available to the second half of the Late Pleistocene.

Selective cooling on land supports cloud formation by cosmic ray during geomagnetic reversals

NASA Astrophysics Data System (ADS)

Kitaba, I.; Hyodo, M.; Nakagawa, T.; Katoh, S.; Dettman, D. L.; Sato, H.

2017-12-01

On geological time scales, the galactic cosmic ray (GCR) flux at the Earth's surface has increased significantly during many short time intervals. There is a growing body of evidence that suggests that climatic cooling occurred during these episodes. Cloud formation by GCR has been claimed as the most likely cause of the linkage. However, the mechanism is not fully understood due to the difficulty of accurately estimating the amount of cloud cover in the geologic past. Our study focused on the geomagnetic field and climate in East Asia. The Earth's magnetic field provides a shield against GCR. The East Asian climate reflects the temperature balance between the Eurasian landmass and the Pacific Ocean that drives monsoon circulation.Two geomagnetic polarity reversals occurred at 780 ka and 1,070 ka. At these times the geomagnetic field decreased to about 10% of its present level causing a near doubling of the GCR flux. Temperature and rainfall amounts during these episodes were reconstructed using pollen in sediment cores from Osaka Bay, Japan. The results show a more significant temperature drop on the Eurasian continent than over the Pacific, and a decrease of summer rainfall in East Asia (i.e. a weakening of East Asian summer monsoon). These observed climate changes can be accounted for if the landmasses were more strongly cooled than the oceans. The simplest mechanism behind such asymmetric cooling is the so-called `umbrella effect' (increased cloud cover blocking solar radiation) that induces greater cooling of objects with smaller heat capacities.

Dead Sea pollen provides new insights into the paleoenvironment of the southern Levant during MIS 6-5

NASA Astrophysics Data System (ADS)

Chen, Chunzhu; Litt, Thomas

2018-05-01

The paleoclimate of the southern Levant, especially during the last interglacial (LIG), is still under debate. Reliable paleovegetation information for this period, as independent evidence to the paleoenvironment, was still missing. In this study, we present a high-resolution pollen record encompassing 147-89 ka from the Dead Sea deep drilling core 5017-1A. The sediment profile is marked by alternations of laminated marl deposits and thick massive halite, indicating lake-level fluctuations. The pollen record suggests that steppe and desert components predominated in the Dead Sea surroundings during the whole investigated interval. The late penultimate glacial (147.3-130.9 ka) and early last glacial (115.5-89.1 ka) were cool and relatively dry, with sub-humid conditions confined to the mountains that sustained moderate amounts of deciduous oaks. Prior to the LIG optimum, a prevalence of desert components and a concomitant increase in frost-sensitive pistachio trees demonstrate the occurrence of an arid initial warming phase (130.9-124.2 ka). The LIG optimum (124.2 ka-115.5 ka) was initiated by an abrupt grass expansion that was followed by a rapid spread of woodlands in the mountains due to increased moisture availability. The remarkable sclerophyllous expansion points to a strong seasonal moisture deficit. These results contradict previous Dead Sea lake-level investigations that suggested pluvial glacials and a warm, dry LIG in the southern Levant. Prominent discrepancies between vegetation and Dead Sea lake stands are also registered at 128-115 ka, and the potential causes are discussed. In particular, while the pollen spectra mirror increased effective moisture during the LIG optimum, the massive halite deposition is indicative of an extremely low lake level. Given that the climate amelioration triggered the migration of early modern humans to the southern Levant, we speculate that the diverse ecosystems in the region provided great potential for their residence. Across the eastern Mediterranean region, an analogous vegetation succession pattern is observed.

Holocene temperature variability revealed by brGDGTs in subtropical southwestern China

NASA Astrophysics Data System (ADS)

Feng, X.; Zhao, C.

2017-12-01

Subtropical areas are important source region of moisture and heat in global climate system. Paleoclimate reconstructions from these regions, especially quantitative records, would not only help to better understand the nature of climate system through time, but also provide important constraining dataset for long-term ecosystem variations in these ecological important areas. To date, quantitative climate records with reliable chronological controls are still limited from terrestrial archives in subtropical areas. Here we present a 50-year-resolution quantitative temperature record throughout the Holocene based on branched GDGTs at a small alpine lake, Tiancai Lake (26°38'E, 99°43'N, 3898 m.a.s.l) in southwestern China. The record is based on a temporal calibration between instrumental mean annual air temperature (MAAT) and brGDGT compounds (GDGT-IIIa, GDGT-IIa', GDGT-IIb, GDGT-Ia and GDGT-Ic). The MAAT was relatively low -0.6 ° between 11 and 7.5 ka, then abruptly increased 1 ° to 4 °until 7 ka. The MAAT was relatively warm 2° between 7 and 1 ka, then decreased to 1° over the last 1 ka. The Middle to Late Holocene was 3 ° warmer than the Early Holocene. The MAAT variation at Lake Tiancai is supported by changes in evergreen oaks and Tsuga from the same sediment core, suggesting that the growth of cold-tolerant forest in place of subtropical evergreen broadleaved forest has been driven by the decrease in MAAT. The early Holocene cold interval revealed by our record and pollen data is different with the chironomid-based summer temperature reconstruction from the same lake, the latter has been driven by summer insolation. This difference suggests that a pronounced winter contribution to the mean annual temperature during the early Holocene, which was probably caused by a low winter insolation, and strengthened by a sparse vegetation cover and influences of winter ice/snow cover in tropical high latitude regions.

Northern Hemisphere Influence on the Position of the SPCZ During MIS3: a High Resolution Glacial Rainfall Record from a Niuean Speleothem

NASA Astrophysics Data System (ADS)

Sinclair, D.; Sherrell, R. M.; Tremaine, D. M.; Sweeney, J. R.; Rowe, H.; Wright, J. D.; Mortlock, R. A.; Hellstrom, J. C.; Cheng, H.; Min, A.; Edwards, R. L.

2017-12-01

Here we present a high-resolution glacial paleorainfall record from the heart of the South Pacific Convergence Zone (SPCZ) extracted from a stalagmite from the remote island of Niue (19°03'S 169°52'W). The record spans much of MIS3 (25-45 ka) and captures rapid rainfall changes associated with shifts in the SPCZ. It is clear that rapid climate shifts in the Northern Hemisphere have a strong influence on the SPCZ. All of the warm Dansgaard-Oeschger (`D-O') interstadials across this period are represented by rainfall increases, with D-O Events 9-11 particularly strongly represented. Since Niue lies south of the core of the SPCZ, this implies that rather than shifting northwards (as the ITCZ does), the SPCZ instead rotates clockwise in response to northern Hemisphere warming (analogous to a shift between modern El Nino and La Nina states). We propose that changes to surface ocean temperature gradients in the Eastern Pacific modulate the strength of the Wind Evaporation SST feedback, changing the size and westward penetration of the eastern Pacific dry zone, resulting in changes to the diagonality of the SPCZ. Our record also captures a response to strong northern Hemisphere cooling. The 25-45 ka record is bounded by large hiatuses (inferred dry conditions) coincident with cold Heinrich Stadials (HS) 2 and 5, while HS3 and HS4 are captured as distinct reductions in speleothem growth rate and proxy evidence for declining rainfall. This is consistent with a counter-clockwise rotation of the SPCZ during Northern cooling, supporting our proposed mechanism. Interestingly, our record also captures several other (non-Heinrich) cooling events, including a strong 500-year dry interval at 26ka that is seen in Chinese and Brazilian speleothems and coincides with a strong cooling over Asia (inferred from Greenland dust records). We note the (possibly coincidental) timing between this event and the Oruanui super-eruption at 25.6 ka.

Late Quaternary sedimentation on the Leidy Creek fan, Nevada-California: Geomorphic responses to climate change

USGS Publications Warehouse

Reheis, M.C.; Slate, J.L.; Throckmorton, C.K.; McGeehin, J.P.; Sarna-Wojcicki, A. M.; Dengler, L.

1996-01-01

Well-dated surface and subsurface deposits in semiarid Fish Lake Valley, Nevada and California, demonstrate that alluvial-fan deposition is strongly associated with the warm dry climate of the last two interglacial intervals, and that fans were stable and (or) incised during the last glaciation. Fan deposition was probably triggered by a change from relatively moist to arid conditions causing a decrease in vegetation cover and increases in flash floods and sediment yield. We think that this scenario applies to most of the other valleys in the southern Basin and Range. Radiocarbon, tephra, and a few thermoluminescence and cosmogenic ages from outcrops throughout Fish Lake Valley and from cores on the Leidy Creek fan yield ages of > 100-50 ka and 11-0 ka for the last two periods of alluvial-fan deposition. Mapping, coring and shallow seismic profiling indicate that these periods were synchronous throughout the valley and on the proximal and distal parts of the fans. From 50 to 11 ka, fan deposition ceased, a soil formed on the older alluvium and the axial drainage became active as runoff and stream competence increased. Slow deposition due to sheet flow or aeolian processes locally continued during this interval, producing cumulic soil profiles. The soil was buried by debris-flow sediment beginning at about 11 ka, coincident with the onset of relatively dry and warm conditions in the region. However, ground-water discharge maintained a large freshwater marsh on the valley floor throughout the Holocene. Pulses of deposition during the Holocene are recorded in the marsh and fan deposits; some pulses coincided with periods of or transitions to warm, dry climate indicated by proxy climate records, whereas others may reflect local disturbances associated with volcanism and fires. Within the marsh deposits, much of the clastic material is probably desert loess. In addition, the deposition of coppice dunes within the fan deposits coincides with two dry periods during the late Holocene.

Subdecadal phytolith and charcoal records from Lake Malawi, East Africa imply minimal effects on human evolution from the ∼74 ka Toba supereruption.

PubMed

Yost, Chad L; Jackson, Lily J; Stone, Jeffery R; Cohen, Andrew S

2018-03-01

The temporal proximity of the ∼74 ka Toba supereruption to a putative 100-50 ka human population bottleneck is the basis for the volcanic winter/weak Garden of Eden hypothesis, which states that the eruption caused a 6-year-long global volcanic winter and reduced the effective population of anatomically modern humans (AMH) to fewer than 10,000 individuals. To test this hypothesis, we sampled two cores collected from Lake Malawi with cryptotephra previously fingerprinted to the Toba supereruption. Phytolith and charcoal samples were continuously collected at ∼3-4 mm (∼8-9 yr) intervals above and below the Toba cryptotephra position, with no stratigraphic breaks. For samples synchronous or proximal to the Toba interval, we found no change in low elevation tree cover, or in cool climate C 3 and warm season C 4 xerophytic and mesophytic grass abundance that is outside of normal variability. A spike in locally derived charcoal and xerophytic C 4 grasses immediately after the Toba eruption indicates reduced precipitation and die-off of at least some afromontane vegetation, but does not signal volcanic winter conditions. A review of Toba tuff petrological and melt inclusion studies suggest a Tambora-like 50 to 100 Mt SO 2 atmospheric injection. However, most Toba climate models use SO 2 values that are one to two orders of magnitude higher, thereby significantly overestimating the amount of cooling. A review of recent genetic studies finds no support for a genetic bottleneck at or near ∼74 ka. Based on these previous studies and our new paleoenvironmental data, we find no support for the Toba catastrophe hypothesis and conclude that the Toba supereruption did not 1) produce a 6-year-long volcanic winter in eastern Africa, 2) cause a genetic bottleneck among African AMH populations, or 3) bring humanity to the brink of extinction. Copyright © 2017 Elsevier Ltd. All rights reserved.

Imprint of Late Quaternary Climate Change on the Mid-Atlantic Landscape

NASA Astrophysics Data System (ADS)

Pavich, M.; Markewich, H.; Newell, W. L.; Litwin, R.; Smoot, J.; Brook, G.

2009-12-01

Recent geomorphic, lithostratigraphic, palynologic and chronostratigraphic investigations of the mid-Atlantic region show that much of the modern landscape flanking the Chesapeake Bay and the Potomac River is developed on late Quaternary sediments. These deposits, dated by OSL and 14C, include transgressive marine and estuarine sediments deposited between 120ka and 32ka, and parabolic dunes formed between 32ka and 15ka. The stacked estuarine units were deposited in a subsiding basin as eustatic sea level fell from +7m to -60m. The estuarine units contain pollen that provides evidence for millennial scale climate fluctuations. The dunes formed during the period of rapid expansion of the Laurentide Ice Sheet as sea level fell to -120m. Permafrost features such as frost wedges and periglacial “pots” formed during cold intervals associated with marine oxygen isotope stages 4 and 2. This periglacial climate, along with glacioisostatic adjustments to growth and decay of the Laurentide Ice Sheet, affected landscape processes at least as far south as the Potomac River valley. While many of these features were recognized in earlier mapping and stratigraphic investigations, OSL dating has greatly extended the range of available dates and significantly improved our understanding of the impacts of highly variable periglacial climate on this region.

Environmental magnetic record and paleosecular variation data for the last 40 kyrs from the Lake Biwa sediments, Central Japan

NASA Astrophysics Data System (ADS)

Hayashida, Akira; Ali, Mohammed; Kuniko, Yoshiki; Kitagawa, Hiroyuki; Torii, Masayuki; Takemura, Keiji

2007-07-01

We have conducted paleomagnetic and environmental magnetic analysis of a sediment piston core recovered from Lake Biwa, central Japan. Tephrochronology and AMS radiocarbon dating showed that this core covers the time period since about 40 kyr BP. The variation of paleomagnetic direction shows a good agreement with the PSV record for the last 10 kyrs from the deeper water site (BIWA SV-3; Ali et al., 1999), although the amplitudes are subdued probably due to the relatively lower accumulation rate at the shallower site. Inclination lows of the pre-Holocene interval are correlated to PSV records reported from the marine sediments off Shikoku and in the Japan Sea. In addition, the variation of magnetic mineral concentration reflects environmental changes during the last glacial period. It is suggested that the flux of fine-grained magnetite, probably associated with greater precipitation, was increased during interstadial periods. The variation of anhysteretic remanent magnetization is likely correlated to the Dansgaard-Oeschger (D-O) cycles recorded in Greenland ice cores. An apparent swing of the PSV curve is recognized at about 27 ka, but evidence for the Mono Lake excursion at 32 ka around the D-O events 6 and 7 is unclear. Combination of the detailed paleomagnetic record and the sub-Milankovitch climate cycles thus provides better resolution for understanding geomagnetic secular variation and polarity excursions in space and time.

Millimeter-Wave Radar Field Measurements and Inversion of Cloud Parameters for the 1999 Mt. Washington Icing Sensors Project

NASA Technical Reports Server (NTRS)

Pazmany, Andrew L.; Reehorst, Andrew (Technical Monitor)

2001-01-01

The Mount Washington Icing Sensors Project (MWISP) was a multi-investigator experiment with participants from Quadrant Engineering, NOAA Environmental Technology Laboratory (NOAA/ETL), the Microwave Remote Sensing Laboratory (MIRSL) of the University of Massachusetts (UMass), and others. Radar systems from UMass and NOAA/ETL were used to measure X-, Ka-, and W-band backscatter data from the base of Mt. Washington, while simultaneous in-situ particle measurements were made from aircraft and from the observatory at the summit. This report presents range and time profiles of liquid water content and particle size parameters derived from range profiles of radar reflectivity as measured at X-, Ka-, and W-band (9.3, 33.1, and 94.9 GHz) using an artificial neural network inversion algorithm. In this report, we provide a brief description of the experiment configuration, radar systems, and a review of the artificial neural network used to extract cloud parameters from the radar data. Time histories of liquid water content (LWC), mean volume diameter (MVD) and mean Z diameter (MZD) are plotted at 300 m range intervals for slant ranges between 1.1 and 4 km. Appendix A provides details on the extraction of radar reflectivity from measured radar power, and Appendix B provides summary logs of the weather conditions for each day in which we processed data.

Comparison Of The I-Gel Supraglottic And King Laryngotracheal Airways In A Simulated Tactical Environment.

PubMed

March, Juan A; Tassey, Theresa E; Resurreccion, Noel B; Portela, Roberto C; Taylor, Stephen E

2018-01-01

When working in a tactical environment there are several different airway management options that exist. One published manuscript suggests that when compared to endotracheal intubation, the King LT laryngotracheal airway (KA) device minimizes time to successful tube placement and minimizes exposure in a tactical environment. However, comparison of two different blind insertion supraglottic airway devices in a tactical environment has not been performed. This study compared the I-Gel airway (IGA) to the KA in a simulated tactical environment, to determine if one device is superior in minimizing exposure and minimizing time to successful tube placement. This prospective randomized cross over trial was performed using the same methods and tactical environment employed in a previously published study, which compared endotracheal intubation versus the KA in a tactical environment. The tactical environment was simulated with a one-foot vertical barrier. The participants were paramedic students who wore an Advanced Combat Helmet (ACH) and a ballistic vest (IIIA) during the study. Participants were then randomized to perform tactical airway management on an airway manikin with either the KA or the IGA, and then again using the alternate device. The participants performed a low military type crawl and remained in this low position during each tube placement. We evaluated the time to successful tube placement between the IGA and KA. During attempts, participants were videotaped to monitor their height exposure above the barrier. Following completion, participants were asked which airway device they preferred. Data was analyzed using Student's t-test across the groups for time to ventilation and height of exposure. In total 19 paramedic students who were already at the basic EMT level participated. Time to successful placement for the KA was 39.7 seconds (95%CI: 32.7-46.7) versus 14.4 seconds (95%CI: 12.0-16.9) for the IGA, p < 0.001. Maximum height exposure of the helmet above a one foot vertical barrier for the KA resulted in 1.42 inches of exposure (95%CI: 0.38-0.63) compared to the IGA with 1.42 inches, 95%CI:0.32-0.74, p = 0.99. On questioning 100% of the participants preferred the IGA device over the KA. In a simulated tactical environment placement of the IGA for airway management was faster than with the KA, but there was no difference in regard to exposure. Additionally, all the participants preferred using the IGA device over the KA.

Standard Observing Bands: Is Now the Time to Replace S/X with X/Ka?

NASA Technical Reports Server (NTRS)

Jacobs, C. S.; Lanyi, G. E.; Naudet, C. J.

2004-01-01

In this paper we will argue that the VLBI community should be developing a road map to transition from S/X to simultaneous X and Ka-band (32 GHz) observations. There are both negative and positive reasons for planning such a transition. On the negative side, we will outline concerns that S-band observations may be headed toward obsolescence. On the positive side, we will refer to evidence that X/Ka has potential for providing a more stable reference frame than S/X. We will propose timetables for a transition to X/Ka observing starting from the current status of X/Ka and plans that are now taking shape. First X/Ka fringes were obtained in 2001 with the Deep Space Network. Future plans will be discussed including a proposed X/Ka-band upgrade to the VLBA. Lastly, we will consider the need for a period of overlap between S/X and X/Ka so that the long and rich history of astrometric and geodetic VLBI is not compromised.

High-resolution climate of the past ∼7300 years of coastal northernmost California: Results from diatoms, silicoflagellates, and pollen

USGS Publications Warehouse

Barron, John A.; Bukry, David; Heusser, Linda E.; Addison, Jason A.; Alexander, Clark R.

2018-01-01

Piston core TN062-O550, collected about 33 km offshore of Eureka, California, contains a high-resolution record of the climate and oceanography of coastal northernmost California during the past ∼7.34 kyr. Chronology established by nine AMS ages on a combination of planktic foraminifers, bivalve shell fragments, and wood yields a mean sedimentation rate of 103 cm kyr−1. Marine proxies (diatoms and silicoflagellates) and pollen transported by the nearby Eel River reveal a stepwise development of both modern offshore surface water oceanography and coastal arboreal ecosystems. Beginning at ∼5.4 cal ka the relative abundance of coastal redwood pollen, a proxy for coastal fog, displays a two fold increase suggesting enhanced coastal upwelling. A decline in the relative contribution of subtropical diatoms at ∼5.0 cal ka implies cooling of sea surface temperatures (SSTs). At ∼3.6 cal ka an increase in the relative abundance of alder and oak at the expense of coastal redwood likely signals intensified riverine transport of pollen from inland environments. Cooler offshore SSTs and increased precipitation characterize the interval between ∼3.6 and 2.8 cal ka. A rapid, stepwise change in coastal climatology and oceanography occurs between ∼2.8 and 2.6 cal ka that suggests an enhanced expression of modern Pacific Decadal Oscillation-like (PDO) cycles. A three-fold increase in the relative abundance of the subtropical diatom Fragilariopsis doliolus at 2.8 cal ka appears to mark an abrupt warming of winter SSTs. Soon afterwards at 2.6 cal ka, a two fold increase in the relative abundance of coastal redwood pollen is suggestive of an abrupt intensification of spring upwelling. After ∼2.8 cal ka a sequence of cool-warm, PDO-like cycles occurs wherein cool cycles are characterized by relative abundance increases in coastal redwood pollen and decreased contributions of subtropical diatoms, whereas opposite proxy trends distinguish warm cycles.

Effects of kainic acid on rat body temperature: unmasking by dizocilpine.

PubMed

Ahlenius, S; Oprica, M; Eriksson, C; Winblad, B; Schultzberg, M

2002-07-01

The effects of intraperitoneal (i.p.) administration of kainic acid (KA) and dizocilpine, alone or in combination, on body temperature of freely moving rats were examined. Injection of saline or dizocilpine (3.0 or 5.0 mg/kg) was followed after an hour by injection of saline or KA (10 mg/kg) and the body temperature was measured at different time points during the first 5 h. KA alone produced an initial short-lasting hypothermia followed by a longer-lasting hyperthermic effect. Administration of dizocilpine alone produced an early increase in core temperature. Pretreatment of KA-injected rats with dizocilpine potentiated the KA-induced hypothermic effect at 30 min and dose-dependently reduced the temperature measured at 1 h after KA-injection without influencing the ensuing hyperthermia.These data suggest that the KA-induced changes in body temperature do not necessarily involve the activation of NMDA-receptors as opposed to KA-induced behavioural changes that are blocked by dizocilpine in a dose-dependent manner. It is unlikely, therefore, that the KA-induced hyperthermia is a result of the KA-induced seizure motor activity. Furthermore, our findings indicate that KA-induced changes in core temperature may be used as a criterion of drug-responsiveness when the behavioural changes are blocked, e.g. with dizocilpine.

The timing and cause of glacial activity during the last glacial in central Tibet based on 10Be surface exposure dating east of Mount Jaggang, the Xainza range

NASA Astrophysics Data System (ADS)

Dong, Guocheng; Zhou, Weijian; Yi, Chaolu; Fu, Yunchong; Zhang, Li; Li, Ming

2018-04-01

Mountain glaciers are sensitive to climate change, and can provide valuable information for inferring former climates on the Tibetan Plateau (TP). The increasing glacial chronologies indicate that the timing of the local Last Glacial Maximum (LGM) recorded across the TP is asynchronous, implying different local influences of the mid-latitude westerlies and Asian Summer Monsoon in triggering glacier advances. However, the well-dated sites are still too few, especially in the transition zone between regions controlled by the two climate systems. Here we present detailed last glacial chronologies for the Mount Jaggang area, in the Xainza range, central Tibet, with forty-three apparent 10Be exposure-ages ranging from 12.4 ± 0.8 ka to 61.9 ± 3.8 ka. These exposure-ages indicate that at least seven glacial episodes occurred during the last glacial cycle east of Mount Jaggang. These include: a local LGM that occurred at ∼61.9 ± 3.8 ka, possibly corresponding to Marine Isotope Stage 4 (MIS 4); subsequent glacial advances at ∼43.2 ± 2.6 ka and ∼35.1 ± 2.1 ka during MIS 3; one glacial re-advance/standstill at MIS3/2 transition (∼29.8 ± 1.8 ka); and three glacial re-advances/standstills that occurred following MIS 3 at ∼27.9 ± 1.7 ka, ∼21.8 ± 1.3 ka, and ∼15.1 ± 0.9 ka. The timing of these glacial activities is roughly in agreement with North Atlantic millennial-scale climate oscillations (Heinrich events), suggesting the potential correlations between these abrupt climate changes and glacial fluctuations in the Mount Jaggang area. The successively reduced glacial extent might have resulted from an overall decrease in Asian Summer Monsoon intensity over this timeframe.

230Th/U dating of a late Pleistocene alluvial fan along the southern San Andreas fault

USGS Publications Warehouse

Fletcher, Kathryn E.K.; Sharp, Warren D.; Kendrick, Katherine J.; Behr, Whitney M.; Hudnut, Kenneth W.; Hanks, Thomas C.

2010-01-01

U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ± 0.6 ka (2σ) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the “time lag” inherent to dating via U-series on pedogenic carbonate can be no larger than ∼10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ± 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ± 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development.

230Th/U dating of a late pleistocene alluvial fan along the southern san andreas fault

USGS Publications Warehouse

Fletcher, K.E.K.; Sharp, W.D.; Kendrick, K.J.; Behr, W.M.; Hudnut, K.W.; Hanks, T.C.

2010-01-01

U-series dating of pedogenic carbonate-clast coatings provides a reliable, precise minimum age of 45.1 ?? 0.6 ka (2??) for the T2 geomorphic surface of the Biskra Palms alluvial fan, Coachella Valley, California. Concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238U-234U-230Th system has remained closed since carbonate formation. The U-series minimum age is used to assess previously published 10Be exposure ages of cobbles and boulders. All but one cobble age and some boulder 10Be ages are younger than the U-series minimum age, indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine-grained matrix to expose them on the present fan surface. A comparison of U-series and 10Be ages indicates that the interval between final alluvial deposition on the T2 fan surface and accumulation of dateable carbonate is not well resolved at Biskra Palms; however, the "time lag" inherent to dating via U-series on pedogenic carbonate can be no larger than ~10 k.y., the uncertainty of the 10Be-derived age of the T2 fan surface. Dating of the T2 fan surface via U-series on pedogenic carbonate (minimum age, 45.1 ?? 0.6 ka) and 10Be on boulder-top samples using forward modeling (preferred age, 50 ?? 5 ka) provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development. ?? 2010 Geological Society of America.

Rapid cooling rates at an active mid-ocean ridge from zircon thermochronology

USGS Publications Warehouse

Schmitt, Axel K.; Perfit, Michael R.; Rubin, Kenneth H.; Stockli, Daniel F.; Smith, Matthew C.; Cotsonika, Laurie A.; Zellmer, Georg F.; Ridley, W. Ian

2011-01-01

Oceanic spreading ridges are Earth's most productive crust generating environment, but mechanisms and rates of crustal accretion and heat loss are debated. Existing observations on cooling rates are ambiguous regarding the prevalence of conductive vs. convective cooling of lower oceanic crust. Here, we report the discovery and dating of zircon in mid-ocean ridge dacite lavas that constrain magmatic differentiation and cooling rates at an active spreading center. Dacitic lavas erupted on the southern Cleft segment of the Juan de Fuca ridge, an intermediate-rate spreading center, near the intersection with the Blanco transform fault. Their U–Th zircon crystallization ages (29.3-4.6+4.8 ka; 1δ standard error s.e.) overlap with the (U–Th)/He zircon eruption age (32.7 ± 1.6 ka) within uncertainty. Based on similar 238U-230Th disequilibria between southern Cleft dacite glass separates and young mid-ocean ridge basalt (MORB) erupted nearby, differentiation must have occurred rapidly, within ~ 10–20 ka at most. Ti-in-zircon thermometry indicates crystallization at 850–900 °C and pressures > 70–150 MPa are calculated from H2O solubility models. These time-temperature constraints translate into a magma cooling rate of ~ 2 × 10-2 °C/a. This rate is at least one order-of-magnitude faster than those calculated for zircon-bearing plutonic rocks from slow spreading ridges. Such short intervals for differentiation and cooling can only be resolved through uranium-series (238U–230Th) decay in young lavas, and are best explained by dissipating heat convectively at high crustal permeability.

Patterns of hydroclimatic change in the Rocky Mountains and surrounding regions since the last glacial maximum

NASA Astrophysics Data System (ADS)

Shuman, Bryan N.; Serravezza, Marc

2017-10-01

The paleohydrologic record of western North America since the last glacial maximum reveals a wide range of hydroclimatic variability in time and space. To improve the understanding of abrupt hydroclimatic shifts and millennial-scale hydrologic changes in the central Rocky Mountains, we reconstruct the lake-level histories of two small lakes in the Beartooth and Bighorn Mountains in northern Wyoming over the past 17 ka. To do so, we use ground-penetrating radar (GPR) and sediment cores to track the elevations of shoreline sediments within the lakes through time. We compare the stratigraphies with those from four other lakes in Wyoming and Colorado, and find widespread evidence for a Terminal Pleistocene Drought from 15 to 11 ka, an early Holocene humid period from 11 to 8 ka, and mid-Holocene aridity from 8 to 5.5 ka. The northern Wyoming lakes also provide evidence of high levels in the Pleistocene, possibly before ca. 15 ka, and rapid hydroclimatic changes that may have correlated with Heinrich Event 1 (ca. 16.8 ka). We place the changes in a broad context by summarizing and mapping water-level changes from 107 additional, previously studied lakes. Important patterns include 1) extensive drying across the western U.S. after 15 ka; 2) sub-regional differences during the Pleistocene-Holocene transition; 3) a north-south contrast from 9 to 6 ka consistent with a northward shift in storm tracks as the influence of the Laurentide Ice Sheet diminished; and 4) rapid increases in effective moisture across much of western North America from 6 to 4 ka.

Glacial cycles influence marine methane hydrate formation

DOE PAGES

Malinverno, A.; Cook, A. E.; Daigle, H.; ...

2018-01-12

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sedimentsmore » with greater organic carbon content deposited during the penultimate glacial cycle (~120-240 ka). As a result, the model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.« less

Glacial cycles influence marine methane hydrate formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malinverno, A.; Cook, A. E.; Daigle, H.

Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sedimentsmore » with greater organic carbon content deposited during the penultimate glacial cycle (~120-240 ka). As a result, the model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.« less

IRD evidence for Heinrich Events H1 and H2 on the NJ Margin

NASA Astrophysics Data System (ADS)

Christensen, B. A.; Calabrese, J.; O'Neill, C.; Goff, J. A.

2011-12-01

Recent seismic reflection studies suggest icebergs grounded on the late Pleistocene New Jersey margin (Goff and Austin, 2009) during Heinrich events H1 (~17 cal Ka), H2 (~23 cal Ka), H3 (~30 cal Ka) and H4 (~37 cal Ka). We tested this hypothesis by analyzing sediments on the upper NJ continental slope, near the area where icebergs were found. Ocean Drilling Program Site 1073A is located at 39°13.5214'N, 72°16.5461'W in 639 m water depth. The greater water depth increases the likelihood of preservation and improves the stratigraphic control. We obtained elemental measurements for Site 1073A Cores 1-6 using the X-ray Fluorescence (XRF) Core Scanner at the MARUM IODP core repository, University of Bremen. Cores were scanned at 10kV and 30kV to obtain a full suite of elements for analysis, with XRF data collected between 1 and 10 cm intervals. The values are reported in areas for the elements and were then converted to elemental ratios (Ca/Sr, Si/Sr, K/Al, and Si/Ti) for analysis. The origin of a Heinrich layer within an IRD belt can be identified by geochemical measures along with magnetic susceptibility and the presence of detrital materials that reflect its provenance (Hemming, 2004). Following analyses for Atlantic Ocean IRD by Hodell et al. (2008), higher Si/Sr values indicate abundant detrital silicates and low biogenic carbonate. Abundant detrital carbonate is identified by higher Ca/Sr values. K/Al may be used as a proxy for weathered matter being deposited and is a good indicator of terrigenous material (Yarincik, 2000). Si/Ti ratios may be used as a proxy for organic and siliceous productivity (Agnihotri, 2008). The elemental analysis was ground-truthed with grain size analysis at 10 cm intervals. Grain size analysis reveals large particles in a finer matrix at 123 cm and 284 cm. We interpret these as IRD. A linear sedimentation age model places the IRD around the time of Heinrich events H1 and H2. Age control is provided for the late Pleistocene principally by radiocarbon methods (McHugh and Olsson, 2002); however, the age model is not unequivocal so we present results for a few interpretations (linear sedimentation rates, and modeled). Nonetheless, the IRD is consistent with the timing of H1 and H2. While the IRD are obvious from the grain size analysis, we were not able to identify IRD from XRF elemental analyses. This may because the sediments are derived locally rather than transported from the higher latitudes, rendering IRD identification a function of grain size (anomalously large particles in a marine setting) rather than geochemistry. Alternatively, the particles were not close enough to the surface to impact the XRF response. This study provides further evidence for the presence of icebergs on the late Pleistocene NJ margin.

Different structural requirements for functional ion pore transplantation suggest different gating mechanisms of NMDA and kainate receptors.

PubMed

Villmann, Carmen; Hoffmann, Jutta; Werner, Markus; Kott, Sabine; Strutz-Seebohm, Nathalie; Nilsson, Tanja; Hollmann, Michael

2008-10-01

Although considerable progress has been made in characterizing the physiological function of the high-affinity kainate (KA) receptor subunits KA1 and KA2, no homomeric ion channel function has been shown. An ion channel transplantation approach was employed in this study to directly test if homomerically expressed KA1 and KA2 pore domains are capable of conducting currents. Transplantation of the ion pore of KA1 or KA2 into GluR6 generated perfectly functional ion channels that allowed characterization of those electrophysiological and pharmacological properties that are determined exclusively by the ion pore of KA1 or KA2. This demonstrates for the first time that KA1 and KA2 ion pore domains are intrinsically capable of conducting ions even in homomeric pore assemblies. NMDA receptors, similar to KA1- or KA2-containing receptors, function only as heteromeric complexes. They are composed of NR1 and NR2 subunits, which both are non-functional when expressed homomerically. In contrast to NR1, the homomeric NR2B ion pore failed to translate ligand binding into pore opening when transplanted into GluR6. Similarly, heteromeric coexpression of the ion channel domains of both NR1 and NR2 inserted into GluR6 failed to produce functional channels. Therefore, we conclude that the mechanism underlying the ion channel opening in the obligatorily heterotetrameric NMDA receptors differs significantly from that in the facultatively heterotetrameric alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate and KA receptors.

Paleohydrologic record from lake brine on the southern High Plains, Texas

USGS Publications Warehouse

Sanford, W.E.; Wood, W.W.

1995-01-01

The timing of changes in the stage and salinity of Double Lakes of Lynn County, Texas, was estimated using dissolved-chloride profiles across an underlying shale layer. Lake conditions over the past 30 to 50 ka can be inferred from the chloride profiles by using the advective velocity of the pore water through the shale and an appropriate coefficient of molecular diffusion. The profiles suggest that net-evaporative conditions existed over the southern High Plains for the past 50 ka; a period of increasing salinity in the lake began at ~20 ka and reached current levels at ~5 ka. In addition, deflationary conditions were present for at least 4 ka, and likely began or were accelerated during the most recent altithermal period at ~5 ka. -from Authors

Geoacoustic character, sedimentology and chronology of a cross-shelf Holocene sediment deposit off Cabo Frio, Brazil (southwest Atlantic Ocean)

NASA Astrophysics Data System (ADS)

Mendoza, Ursula; Ayres Neto, Arthur; C. Abuchacra, Rodrigo; Fernandes Barbosa, Cátia; G. Figueiredo, Alberto; C. Gomes, Manoela; Belem, Andre L.; Capilla, Ramsés; S. Albuquerque, Ana Luiza

2014-08-01

The Cabo Frio region in the state of Rio de Janeiro, southeast coast of Brazil, is characterized by a local coastal upwelling system and converging littoral sediment transport systems that are deflected offshore at Cabo Frio, as a consequence of which a thick cross-shelf sediment deposit has developed over time. To investigate the evolution of this muddy deposit, geophysical, sedimentological and geochemical data from four sediment cores (3.8-4.1 m in length) recovered in water depths between 88 and 141 m were analyzed. The high-resolution seismic data show variable sediment thicknesses ranging from 1 to 20 m, comprising two sedimentary units separated by a high-impedance layer at a depth of about 10 m below the seafloor at the coring sites. According to the available age datings, the upper sedimentary unit is late Pleistocene to Holocene in age, whereas the lower unit (not dated) must, by implication, be entirely Pleistocene in age. The boomer-seismic reflection signal can be divided into three echo-types, namely transparent (inner shelf), stratified (middle shelf) and reflective (outer shelf), each type seemingly related to the local sediment composition. The upper 4 m of the upper sedimentary unit is dominated by silty sediment on the middle shelf, and by upward-fining sediments (silty sand to sandy silt) on the inner and outer shelf. The downcore trends of P-wave velocity, gamma-ray density and acoustic impedance are largely similar, but generally reversed to those of water and organic carbon contents. Total organic carbon contents increase with decreasing mean grain size, periodic fluctuations suggesting temporal changes in the regional hydrodynamics and primary productivity fuelled by the local upwelling system. The reconstruction of sedimentation rates in the course of the Holocene is based on 35 AMS age datings of organic material recovered from variable downcore depths. These range from a maximum of 13.3 cm/decade near the base of the inner shelf core (7.73-7.70 ka BP) to generally very low values (<0.11 cm/century) over the last thousand years in all cores. Over the last 6 ka there appear to have been three distinct sedimentation peaks, one between 6 and 5 ka BP, another between 4 and 3 ka PB, and one around 1 ka BP. Due to different time intervals between dates, not every peak is equally well resolved in all four cores. Based on the similar sedimentology of the inner and outer shelf cores, an essentially identical sedimentation model is proposed to have been active in both cases, albeit at different times. Thus, already during the last glacial maximum, alongshore sediment transport was deflected offshore by a change in shoreline orientation caused by the Cabo Frio structural high. The source of terrigenous material was probably a barrier-island complex that was subsequently displaced landward in the course of sea-level rise until it stabilized some 6.5 ka BP along the modern coast.

Timing of Glacial Lake Missoula Outburst Floods and the southwestern Cordilleran Ice Sheet retreat.

NASA Astrophysics Data System (ADS)

Hendy, I. L.; Bervid, H. D.; Carlson, A. E.

2017-12-01

Glacial Lake Missoula formed when the Purcell Trench Lobe dammed the Clark Fork River in Montana and catastrophically collapsed repeatedly through the last glacial period as the southern Cordilleran Ice Sheet advanced and retreated. A well-dated 50-kyr jumbo piston core MD02-2496 (48.97˚ N, 127.04˚ W, water depth of 1243 m) collected from the continental slope 75 km off Vancouver Island contains evidence of these floods. The in-situ bulk elemental composition of the 35-m core was determined at 1 mm intervals using an ITRAX X-ray Fluorescence (XRF) Core Scanner (Cox Analytical Instruments) at the Sediment Geochemistry Lab of the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University. With 40 mixed planktonic foraminifera and bulk organic carbon 14C ages, the core provides a high-resolution resolution record of glaciomarine sedimentation during deglaciation. A series of >81 layers of fine-grained sediments with ancient (K/Ar ages of 300 Ma and eNd of -8) shale-like (high Rb counts) composition can be found between 19.6 and 9.2 m below coretop. These layers are interspersed by coarser grained, young (K/Ar ages of 100 Ma and eNd of -3) sediments containing ice-rafted debris (IRD). The composition and age of the layers indicates the sediments originated in Glacial Lake Missoula and were transported by ocean currents 250 miles north along the west coast of North America. The flood layers begin at 19.5 ka with five thin (<5 cm thick) layers before thick flood layers (>5 cm thick) appear after 19.3 ka. At 17.1 ka, IRD concentrations increase from <1 grain g-1 to 20 grains g-1, and remain >50 grains g-1 from 16.5-16.35 ka, except in flood layers, as the Juan de Fuca Strait deglaciated. Another 16 flood layers occur from 16.3-15.65 ka; however, the base and top of these layers are diffuse rather than abrupt like earlier flood layers suggesting enhanced mixing between flood and melt waters. The final flood layers from 14.9-14.5 ka are thin (<2 cm thick) suggesting that the final floods were small events similar to the initial floods. This well-dated sequence displays how Glacial Lake Missoula flood sedimentation changed during the advance and retreat of the Cordilleran Ice Sheet.

Tilted lake shorelines record the onset of motion along the Hilton Creek fault adjacent to Long Valley caldera, CA, USA

NASA Astrophysics Data System (ADS)

Perkins, J. P.; Finnegan, N. J.; Cervelli, P. F.; Langbein, J. O.

2010-12-01

Prominent normal faults occur within and around Long Valley caldera, in the eastern Sierra Nevada of California. However, their relationship to both the magmatic and tectonic evolution of the caldera since the 760 ka eruption of the Bishop Tuff remains poorly understood. In particular, in the Mono-Inyo Craters north of Long Valley, extensional faulting appears to be replaced by dike intrusion where magma is available in the crust. However, it is unclear whether extensional faults in Long Valley caldera have been active since the eruption of the Bishop Tuff (when the current topography was established) or are a relatively young phenomenon owing to the cooling and crystallization of the Long Valley magma reservoir. Here we use GPS geodesy and geomorphology to investigate the evolution of the Hilton Creek fault, the primary range-front fault bounding Long Valley caldera to the southwest. Our primary goals are to determine how long the Hilton Creek fault has been active and whether slip rates have been constant over that time interval. To characterize the modern deformation field, we capitalize on recently (July, 2010) reoccupied GPS benchmarks first established in 1999-2000. These fixed-array GPS data show no discernible evidence for recent slip on the Hilton Creek fault, which further highlights the need for longer-term constraints on fault motion. To establish a fault slip history, we rely on a suite of five prominent shorelines from Pleistocene Long Valley Lake whose ages are well constrained based on field relationships to dated lavas, and that are tilted southward toward the Hilton Creek fault. A preliminary analysis of shoreline orientations using GPS surveys and a 5-m-resolution Topographic Synthetic Aperture Radar (TOPSAR) digital elevation model shows that lake shorelines tilt towards the Hilton Creek fault at roughly parallel gradients (~ 0.6%). The measured shorelines range in inferred age from 100 ka to 500 ka, which constrain recent slip on the Hilton Creek fault to the last 100 kyr and imply a late Pleistocene slip rate of ~0.8 mm/yr, consistent with shorter (~ 25 kyr) timescale estimates of ~1 mm/yr from displacement of LGM moraines and terraces along the active fault scarp. These data show that tilting in Long Valley caldera related to slip on the Hilton Creek fault commenced after 100 ka, and that slip rates are seemingly uniform over that time period. The 22 km-long trace of the Hilton Creek fault, with at least 1070 m of offset at McGee Mountain to the south, must have experienced significant pre-caldera slip. A lack of apparent tilting within Long Valley caldera from 500 ka to 100 ka may therefore be interpreted in one of two ways. Either extension ceased here for at least~ 400 kyr, or more likely, accommodation of Hilton Creek extension occurred either elsewhere (outside of the Caldera) or via a different physical mechanism, such as dike intrusion.

Spatial and temporal variations in the sediment state of North American dune fields

NASA Astrophysics Data System (ADS)

Halfen, Alan F.; Lancaster, Nicholas; Wolfe, Stephen

2015-04-01

This research evaluates geomorphic and chronologic data from the INQUA Dune Atlas for three areas of North America: 1) the Prairie, Parkland and Boreal ecozones of the northern Great Plains in Canada; 2) the Central Great Plains of the USA; and 3) the deserts of southwestern USA and northern Mexico. Chronometric data for periods of dune activity and stability are compared with palaeoenvironment reconstructions to assess dune system response to changes in sediment supply, availability, and mobility. Dune fields in the northern Great Plains were formed from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16-11 ka. Subsequent aeolian deposition occurred in Parkland and Prairie dune fields as a result of mid-Holocene (8-5 ka) and late-Holocene (< 3.5 ka) activity related to drought conditions. In the Central Great Plains, many dune fields are closely linked to fluvial sediment sources. Sediment supply was high in these dune fields during deglaciation of the Rocky Mountains and resulted in widespread dune construction 16-10 ka. Multiple periods of Holocene reactivation are recorded and reflect increased sediment availability during drought episodes. Dune fields in the southwestern deserts experienced periods of construction as a result of enhanced supply of sediment from fluvial and lacustrine sources during the period 11.8 - 8 ka and at short but repeated intervals during the late Holocene. Despite spatial and temporal gaps in chronometric data, the record from North American dune fields indicates the strong influence of sediment supply on dune construction, with changes in sediment availability, as a result of drought, being the primary driver of dune activity during the Holocene.

Improvement of Thermal Interruption Capability in Self-blast Interrupting Chamber for New 245kV-50kA GCB

NASA Astrophysics Data System (ADS)

Shinkai, Takeshi; Koshiduka, Tadashi; Mori, Tadashi; Uchii, Toshiyuki; Tanaka, Tsutomu; Ikeda, Hisatoshi

Current zero measurements are performed for 245kV-50kA-60Hz short line fault (L90) interruption tests with a self-blast interrupting chamber (double volume system) which has the interrupting capability up to 245kV-50kA-50Hz L90. Lower L90 interruption capability is observed for longer arcing time although very high pressure rise is obtained. It may be caused by higher blowing temperature and lower blowing density for longer arcing time. Interruption criteria and a optimization method of the chamber design are discussed to improve L90 interruption capability with it. The new chambers are designed at 245kV-50kA-60Hz to improve gas density in thermal volume for long arcing time. 245kV-50kA-60Hz L90 interruptions are performed with the new chamber. The suggested optimization method is an efficient tool for the self-blast interrupting chamber design although study of computing methods is required to calculate arc conductance around current zero as a direct criterion for L90 interruption capability with higher accuracy.

Assessing backscatter change due to backscatter gradient over the Greenland ice sheet using Envisat and SARAL altimetry

NASA Astrophysics Data System (ADS)

Su, Xiaoli; Luo, Zhicai; Zhou, Zebing

2018-06-01

Knowledge of backscatter change is important to accurately retrieve elevation change time series from satellite radar altimetry over continental ice sheets. Previously, backscatter coefficients generated in two cases, namely with and without accounting for backscatter gradient (BG), are used. However, the difference between backscatter time series obtained separately in these two cases and its impact on retrieving elevation change are not well known. Here we first compare the mean profiles of the Ku and Ka band backscatter over the Greenland ice sheet (GrIS), with results illustrating that the Ku-band backscatter is 3 ∼ 5 dB larger than that of the Ka band. We then conduct statistic analysis about time series of backscatter formed separately in the above two cases for both Ku and Ka bands over two regions in the GrIS. It is found that the standard deviation of backscatter time series becomes slightly smaller after removing the BG effect, which suggests that the method for the BG correction is effective. Furthermore, the impact on elevation change from backscatter change due to the BG effect is separately assessed for both Ku and Ka bands over the GrIS. We conclude that Ka band altimetry would benefit from a BG induced backscatter analysis (∼10% over region 2). This study may provide a reference to form backscatter time series towards refining elevation change time series from satellite radar altimetry over ice sheets using repeat-track analysis.

Rapid response of alpine timberline vegetation to the Younger Dryas climate oscillation in the Colorado Rocky Mountains, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reasoner, M.A.; Jodry, M.A.

2000-01-01

Paleobotanical records from two high-altitude (>3,300 m) sites in Colorado show a clear and immediate response to the Younger Dryas climate oscillation. The Black Mountain Lake and Sky Pond records indicate that alpine timberline migrated upslope to near-modern elevations during the late Bolling-Allerod (13.6--12.9 ka). Subsequent declines in arboreal pollen percentages and accumulation rates during the Younger Dryas interval (12.9--11.7 ka) reflect a downslope displacement of the alpine timberline ecotone of 60--120 m in elevation. This change translates to a cooling of summer temperature by {approximately}0.4--0.9 C and is consistent with proposed Younger Dryas advances of alpine glaciers in themore » Rocky Mountains to positions close to Little Ice Age maxima. Alpine timberline readvanced upslope to elevations above both sites between 11.7 and 11.4 ka. The concomitant response of temperature-sensitive alpine timberline vegetation in Colorado and late-glacial changes in North Atlantic thermohaline circulating implicates a rapid, widespread atmospheric transmission of the Younger Dryas climate oscillation.« less

Decoupling of monsoon activity across the northern and southern Indo-Pacific during the Late Glacial

NASA Astrophysics Data System (ADS)

Denniston, R. F.; Asmerom, Y.; Polyak, V. J.; Wanamaker, A. D.; Ummenhofer, C. C.; Humphreys, W. F.; Cugley, J.; Woods, D.; Lucker, S.

2017-11-01

Recent studies of stalagmites from the Southern Hemisphere tropics of Indonesia reveal two shifts in monsoon activity not apparent in records from the Northern Hemisphere sectors of the Austral-Asian monsoon system: an interval of enhanced rainfall at ∼19 ka, immediately prior to Heinrich Stadial 1, and a sharp increase in precipitation at ∼9 ka. Determining whether these events are site-specific or regional is important for understanding the full range of sensitivities of the Austral-Asian monsoon. We present a discontinuous 40 kyr carbon isotope record of stalagmites from two caves in the Kimberley region of the north-central Australian tropics. Heinrich stadials are represented by pronounced negative carbon isotopic anomalies, indicative of enhanced rainfall associated with a southward shift of the intertropical convergence zone and consistent with hydroclimatic changes observed across Asia and the Indo-Pacific. Between 20 and 8 ka, however, the Kimberley stalagmites, like the Indonesian record, reveal decoupling of monsoon behavior from Southeast Asia, including the early deglacial wet period (which we term the Late Glacial Pluvial) and the abrupt strengthening of early Holocene monsoon rainfall.

Tulelake, California: The last 3 million years

USGS Publications Warehouse

Adam, D.P.; Sarna-Wojcicki, A. M.; Rieck, Hugh J.; Bradbury, J.P.; Dean, W.E.; Forester, R.M.

1989-01-01

The Tulelake basin, formed by east-west extension and faulting during the past several million years, contains at least 550 m of lacustrine sediment. Interdisciplinary studies of a 334 m-long cored section from the town of Tulelake, California, near the center of the basin, document a 3-m.y. record of environmental changes. The core consists of a thick sequence of diatomaceous clayey, silty, and marly lacustrine sediments interbedded with numerous tephra layers. Paleomagnetic study puts the base of the core at about 3.0 Ma. Twelve widespread silicic tephra units provide correlations with other areas and complement age control provided by magnetostratigraphy; mafic and silicic tephra units erupted from local sources are also common in the core. Widespread tephra units include the Llao Rock pumice (=Tsoyawata, 7 ka), the Trego Hot Springs Bed (23 ka), and the Rockland (0.40 Ma), Lava Creek (0.62 Ma), and Rio Dell (1.5 Ma) ash beds, as well as several ash beds also found at Summer Lake, Oregon, and an ash bed originally recognized in DSDP hole 173 in the northeastern Pacific. Several tephra layers found in the core also occur in lacustrine beds exposed around the margins of the basin and elsewhere in the ancestral lacustrine system. Diatoms are present throughout the section. Pollen is present in most of the section, but some barren zones are found in the interval between 50 and 140 m; the greatest change in behavior of the pollen record takes place just above the top of the Olduvai Normal-Polarity Subchronozone. Ostracodes are present only in high-carbonate (>10% CaCO3) intervals. Evolutionary changes are found in the diatom and ostracode records. Bulk geochemical analyses show significant changes in elemental composition of the sediment through time. ?? 1989.

Paleoearthquakes and Eolian-dominated fault sedimentation along the Hubbell Spring fault zone near Albuquerque, New Mexico

USGS Publications Warehouse

Personius, S.F.; Mahan, S.A.

2003-01-01

The Hubbell Spring fault zone forms the modern eastern margin of the Rio Grande rift in the Albuquerque basin of north-central New Mexico. Knowledge of its seismic potential is important because the fault zone transects Kirtland Air Force Base/Sandia National Laboratories and underlies the southern Albuquerque metropolitan area. No earthquakes larger than ML 5.5 have been reported in the last 150 years in this region, so we excavated the first trench across this fault zone to determine its late Quaternary paleoseismic history. Our trench excavations revealed a complex, 16-m-wide fault zone overlain by four tapered blankets of mixed eolian sand and minor colluvium that we infer were deposited after four large-magnitude, surface-rupturing earthquakes. Although the first (oldest) rupture event is undated, we used luminescence (thermoluminescence and infrared-stimulated luminescence) ages to determine that the subsequent three rupture events occurred about 56 ?? 6, 29 ?? 3, and 12 ?? 1 ka. These ages yield recurrence intervals of 27 and 17 k.y. between events and an elapsed time of 12 k.y. since the latest surface-rupturing paleoearthquake. Slip rates are not well constrained, but our preferred average slip rate since rupture event 2 (post-56 ka) is 0.05 mm/yr, and interval slip rates between the last three events are 0.06 and 0.09 mm/yr, respectively. Vertical displacements of 1-2 m per event and probable rupture lengths of 34-43 km indicate probable paleoearthquake magnitudes (Ms or Mw) of 6.8-7.1. Future earthquakes of this size likely would cause strong ground motions in the Albuquerque metropolitan area.

Change in seasonality in the southwest tropical Pacific during the Holocene: a data -model comparison

NASA Astrophysics Data System (ADS)

Correge, T.; Deschamps, C.; Duprey, N.; Pujol, N.; Braconnot, P.; Charlier, K.; Lazareth, C. E.; Le Cornec, F.; Malaizé, B.

2012-12-01

Our ability to successfully predict future climate change relies heavily on the improvement of climate models. One way to do so is to compare model outputs with paleodata. The aim of the French ELPASO program (El Niño in the Past: Simulations and Observations) is to conduct such comparisons in the tropics to study the evolution of ENSO in the late Pleistocene, and more particularly during the Holocene, and the link to the background climate state (including the seasonal cycle). We generated multi-decadal time series of SST derived from Sr/Ca analyses of massive Porites corals from Vanuatu dating from 10 ka, 6.8 ka, 6.2 ka and 4.2 ka. For each time series, the mean seasonal cycle was calculated and compared to simulations from the IPSL-CM4 model (Braconnot et al., 2012; Luan et al., 2012). When insolation parameters (in particular precession) are taken into account for the 9.5 ka and 6 ka simulations, the model predicts that the seasonal cycle should be reduced in the southern hemisphere and enhanced in the northern hemisphere during the early and mid Holocene. In contrast, coral data from Vanuatu indicate enhanced mean seasonal cycles at 10 ka, 6.8 ka and 6.2 ka. The coral dating from 4.2 ka is the only one showing a reduced seasonal cycle compared to the present. Various scenarios will be proposed to reconcile this discrepancy. Braconnot, P. et al. Impact of Earth's orbit and freshwater fluxes on Holocene climate mean seasonal cycle and ENSO characteristics, Clim. Dynam., 38, 1081-1092, doi:10.1007/s00382-011-1029-x, 2012. Luan, Y. et al. 2012. Early and mid-Holocene climate in the tropical Pacific: seasonal cycle and interannual variability induced by insolation changes. Clim. Past, 8, 1093-1108 ; doi:10.5194/cp-8-1093-2012

Molecular weight dependent glucose lowering effect of low molecular weight Chitosan Oligosaccharide (GO2KA1) on postprandial blood glucose level in SD rats model.

PubMed

Jo, Sung-Hoon; Ha, Kyoung-Soo; Moon, Kyoung-Sik; Kim, Jong-Gwan; Oh, Chen-Gum; Kim, Young-Cheul; Apostolidis, Emmanouil; Kwon, Young-In

2013-07-09

This research investigated the effect of enzymatically digested low molecular weight (MW) chitosan oligosaccharide on type 2 diabetes prevention. Three different chitosan oligosaccharide samples with varying MW were evaluated in vitro for inhibition of rat small intestinal α-glucosidase and porcine pancreatic α-amylase (GO2KA1; <1000 Da, GO2KA2; 1000-10,000 Da, GO2KA3; MW > 10,000 Da). The in vitro results showed that all tested samples had similar rat α-glucosidase inhibitory and porcine α-amylase inhibitory activity. Based on these observations, we decided to further investigate the effect of all three samples at a dose of 0.1 g/kg, on reducing postprandial blood glucose levels in Sprague-Dawley (SD) rat model after sucrose loading test. In the animal trial, all tested samples had postprandial blood glucose reduction effect, when compared to control, however GO2KA1 supplementation had the strongest effect. The glucose peak (Cmax) for GO2KA1 and control was 152 mg/dL and 193 mg/dL, respectively. The area under the blood glucose-time curve (AUC) for GO2KA1 and control was 262 h mg/dL and 305 h mg/dL, respectively. Furthermore, the time of peak plasma concentration of blood glucose (Tmax) for GO2KA1 was significantly delayed (0.9 h) compared to control (0.5 h). These results suggest that GO2KA1 could have a beneficial effect for blood glucose management relevant to diabetes prevention in normal and pre-diabetic individuals. The suggested mechanism of action is via inhibition of the carbohydrate hydrolysis enzyme α-glucosidase and since GO2KA1 (MW < 1000 Da) had higher in vivo effect, we hypothesize that it is more readily absorbed and might exert further biological effect once it is absorbed in the blood stream, relevant to blood glucose management.

Influence of Large Lakes on Methane Greenhouse Forcing in the Early Eocene

NASA Astrophysics Data System (ADS)

Whiteside, J. H.; Granberg, D. L.; Kasprak, A. H.; Taylor, K. W.; Pancost, R. D.

2011-12-01

Long-duration elevated global temperatures and increased atmospheric pCO2 levels (~1000-2000 ppm) characterized the earliest portion of the Eocene (Ypressian; ~55 to 49 Ma). This extended period of global warmth was also punctuated by a series of short (sub-precessional) hyperthermal events in which atmospheric CO2 (>2000 ppm) and global temperatures rose with unprecedented and (as of yet) unexplained rapidity. This interval is perhaps the best temporal analog for assessing contemporary response of the biosphere and global carbon cycle to increased CO2 emissions. Although these hyperthermals appear paced by 100 Ka and 1 Ma scale orbital (eccentricity) cycles in the marine realm, high frequency forcing processes have not yet been examined, and long continental records have yet to be explored for their expression. To identify sub-eccentricity (<100,000 year) scale variability in Early Eocene carbon cycling, we examined lacustrine records of organic carbon isotopes and carbon content from a ~5 Ma record in the Green River Formation (GRF) in the Uinta Basin of Utah, U.S.A. and a ~1 Ma record from the Messel Shale, (Darmstadt, Germany.) We demonstrate that in addition to the expected 100 Ka eccentricity cycle, the 40 Ka cycle of obliquity is also an important component of climate variability as reflected in the lacustrine carbon cycle and hence a potential driver of global carbon cycling. We further investigated carbon cycle dynamics by examining biomarker evidence for changes in the terrestrial methane cycle during this time interval. Due to their increased volumes (>60,000 km2), highly stratified and cyclically anoxic lakes of the Eocene could have provided enough methane to alter global radiative forcing. This is consistent with our data, which demonstrate that the GRF and Messel Shale both exhibit strongly reducing conditions as well as abundant methanogen and methanotroph biomarkers. Further, the GRF lacustrine environment was highly stratified with, at times, euxinic waters extending into the photic zone, as inferred from the presence of isorenieratene derivatives. Thus, the GRF was likely an area of elevated methanogenic activity during this time. Increasing input of terrestrial matter into the GRF correlates with shifts in the pristane/phytane ratio and isorenieratane abundances, suggesting that increased runoff intensified the stratification of the lake with a transition to more anoxic conditions. Following this transition, it is likely that methane production in the GRF lake increased, which released more into the atmosphere. Our new results suggest that the global carbon cycle of the early Eocene greenhouse world was strongly mediated by both astronomical forcing (including obliquity) and increased methane production in large stratified lakes.

Environment and Climate Changes during the Holocene: Inferred from Sedimentary Record/Proxies of a Paleodelta Region, Southwest Coast of India

NASA Astrophysics Data System (ADS)

Allu, N. C.; Prakash, V.; Gautam, P. K.; Bera, S. K.

2014-12-01

This work explains the sedimentation history and environment and climate changes during the Holocene along the southwest coast of India. The area is characterized by various landforms such as lagoons, barrier islands, beach ridges, paleostrandlines, alluvial plains, marshy lands and flood plains. Paleodelta, located at the mouth of the modern Periyar River is an important geomorphic marker. A borehole of 40 m depth was drilled in the paleodelta and sediment samples were recovered at different depth intervals. Paleoclimate and paleo-environment were inferred based on geochronology, textural and geotechnical parameters, clay minerals, and pollen analysis results. The bottom of the borehole represents an age of ~ 12 ka BP. Sediments exhibit coarsening texture upwards of the borehole, with fine mud and peat intercalations at the bottom. Six litho facies - muddy sand, sand, sandy mud, silty sand, sandy silt, and mud - were recorded. Geotechnical properties comprising moisture content, organic carbon, plasticity index record high values, whereas low bulk density associated with a low critical shear stress, are recorded. An increase in illite and to a lesser degree smectite with concomitant decrease in kaolinite is observed. Sediment texture represents a major change of depositional environment from marine to fluvial sedimentary facies during the major sea level fall i.e., after 7 ka B.P. The present sea level attained during 4-5 ka B.P; major rise of sea level has taken place from 7-11 ka BP and regression during 7 - 5 ka B.P. These transgression and regression phases introduced the changes in the environment of deposition. The monsoon was dynamic and more intense after the major fall of sea level causing the fluctuations in the fluvial facies. Upward coarsening of grain size in the borehole indicates change in sediment deposition due to increased hydrodynamic conditions and strong fluvial action, which can be linked to marine regression. Geotechnical properties suggest textural changes and sedimentary facies. An upward increase in smectite and kaolinite and decreasing illite supports major fall in sea level and also the aridity. Pollen record of sediment strata supports the paleo-environment dominated by the presence of semi-evergreen type of mangrove plants during mid- to early-Holocene times.

Palaeoenvironmental conditions in the Gulf of Alaska (NE Pacific) during the Mid Pleistocene Transition

NASA Astrophysics Data System (ADS)

Müller, J.; Romero, O. E.; McClymont, E.; Stein, R. H.; Fahl, K.

2014-12-01

The Mid Pleistocene Transition (MPT) constitutes a fundamental shift in Earth's climate system from a 41 ka to a 100 ka periodicity in glacial oscillations. The exact timing and mechanism(s) that caused this change from a low- to high-amplitude glacial variability are still under debate and only recently Pena & Goldstein (2014) suggested that a disruption of the thermohaline circulation at about 900 ka BP and a subsequent change in ocean circulation might have acted as a trigger for the onset of 100 ka glacial-interglacial cycles. Most studies targeting the MPT are based on Atlantic sediment records whereas only few data sets are available from the North Pacific (see e.g. Clark et al., 2006 and McClymont et al., 2013 for reviews). IODP Expedition 341 distal deep-water site U1417 in the Gulf of Alaska (subpolar NE Pacific) now provided a continuous sediment record for reconstructing Miocene to Late Pleistocene changes in the sea surface conditions and how these relate to orbital and millennial scale climate variability. Here we present organic geochemical biomarker data covering the 1.5 Ma to 0.1 Ma time interval with special focus on the MPT. Alkenone, sterol, n-alkane and C25 highly branched isoprenoid data are used to reconstruct sea surface temperatures, primary productivity and terrigenous organic matter input (via sea ice, icebergs, meltwater discharge or aeolian transport). In addition, the diatom concentration and the species composition of the diatom assemblage deliver information on changes in palaeoproductivity and nutrient (silicate) availability. A major change in the environmental setting between 1.2 and 0.8 Ma is recorded by the biomarkers. This shift seems to be associated with a significant cooling of the surface waters in the Gulf of Alaska. Matching this shift, a significant change in the main components of the diatom community occurred between 1.2 and 0.8 Ma. References Clark, P.U., Archer, D., Pollard, D., Blum, J.D., Rial, J.A., Brovkin, V., Mix, A.C., Pisias, N.G., Roy, M., 2006. Quaternary Science Reviews, 25, (23-24), 3150-3184. McClymont, E.L., Sosdian, S.M., Rosell-Melé, A., Rosenthal, Y., 2013. Earth-Science Reviews, 123, 173-193. Pena, L.D. and Goldstein, S.L., 2014. Science, 345, 318-322.

Quaternary geology of the Duck Hawk Bluffs, southwest Banks Island, Arctic Canada: a re-investigation of a critical terrestrial type locality for glacial and interglacial events bordering the Arctic Ocean

NASA Astrophysics Data System (ADS)

Evans, David J. A.; England, John H.; La Farge, Catherine; Coulthard, Roy D.; Lakeman, Thomas R.; Vaughan, Jessica M.

2014-05-01

Duck Hawk Bluffs, southwest Banks Island, is a primary section (8 km long and 60 m high) in the western Canadian Arctic Archipelago exposing a long record of Quaternary sedimentation adjacent to the Arctic Ocean. A reinvestigation of Duck Hawk Bluffs demonstrates that it is a previously unrecognized thrust-block moraine emplaced from the northeast by Laurentide ice. Previous stratigraphic models of Duck Hawk Bluffs reported a basal unit of preglacial fluvial sand and gravel (Beaufort Fm, forested Arctic), overlain by a succession of three glaciations and at least two interglacials. Our observations dismiss the occurrence of preglacial sediments and amalgamate the entire record into three glacial intervals and one prominent interglacial. The first glacigenic sedimentation is recorded by an ice-contact sandur containing redeposited allochthonous organics previously assigned to the Beaufort Fm. This is overlain by fine-grained sediments with ice wedge pseudomorphs and well-preserved bryophyte assemblages corresponding to an interglacial environment similar to modern. The second glacial interval is recorded by ice-proximal mass flows and marine rhythmites that were glacitectonized when Laurentide ice overrode the site from Amundsen Gulf to the south. Sediments of this interval have been reported to be magnetically reversed (>780 ka). The third interval of glacigenic sedimentation includes glacifluvial sand and gravel recording the arrival of Laurentide ice that overrode the site from the northeast (island interior) depositing a glacitectonite and constructing the thrust block moraine that comprises Duck Hawk Bluffs. Sediments of this interval have been reported to be magnetically normal (<780 ka). The glacitectonite contains a highly deformed melange of pre-existing sediments that were previously assigned to several formally named, marine and interglacial deposits resting in an undeformed sequence. In contrast, the tectonism associated with the thrust block moraine imparted pervasive deformation throughout all underlying units, highlighted by a previously unrecognized raft of Cretaceous bedrock. During this advance, Laurentide ice from the interior of Banks Island coalesced with an ice stream in Amundsen Gulf, depositing the interlobate Sachs Moraine that contains shells as young as ˜24 cal ka BP (Late Wisconsinan). During deglaciation, meltwater emanating from these separating ice lobes deposited outwash that extended to deglacial marine limit (11 m asl) along the west coast of Banks Island. Our new stratigraphic synthesis fundamentally revises and simplifies the record of past Quaternary environments preserved on southwest Banks Island, which serves as a key terrestrial archive for palaeoenvironmental change.

Southern westerly winds: a pacemaker of Holocene glacial fluctuations in Patagonia?

NASA Astrophysics Data System (ADS)

Sagredo, E. A.; Reynhout, S.; Kaplan, M. R.; Patricio, M. I.; Aravena, J. C.; Martini, M. A.; Schaefer, J. M.

2017-12-01

A well-resolved glacial chronology is crucial to compare sequences of glacial/climate events within and between regions, and thus, to unravel mechanisms underlying past climate changes. Important efforts have been made towards understanding the Holocene climate evolution of the Southern Andes; however, the timing, patterns and causes of glacial fluctuations during this period still remain elusive. Recent advances in terrestrial cosmogenic nuclide surface exposure dating, together with the establishment of a Patagonian 10Be production rate, have opened new possibilities for establishing high-resolution glacial chronologies at centennial/decadal scale. Here we present a 10Be surface exposure chronology of fluctuations of a small, climate-sensitive mountain glacier at Mt. Fitz Roy area (49.3°S), spanning from the last glacial termination to the present. Thirty new 10Be ages show glacial advances and moraine building events at 17.1±0.9 ka, 13.5±0.5 ka, 10.2±0.7 ka or 9.9±0.5 ka, 6.9±0.2 ka, 6.1±0.3 ka, 4.5±0.2 ka and 0.5±0.1 ka. Similar to the pattern observed in New Zealand, this sequence features progressively less extensive glacial advances during the late-glacial and early Holocene, followed by advances of roughly similar extent during the mid- to late-Holocene. We suggest that while the magnitude of Holocene glacial fluctuations in Patagonia is modulated by SH summer insolation ("modulator"), the specific timing of these glacial events is influenced by centennial-scale shifts of the Southern Westerly Winds ("pacemaker").

Eruptive chronology of Tungurahua volcano (Ecuador) revisited based on new K-Ar ages and geomorphological reconstructions

NASA Astrophysics Data System (ADS)

Bablon, Mathilde; Quidelleur, Xavier; Samaniego, Pablo; Le Pennec, Jean-Luc; Lahitte, Pierre; Liorzou, Céline; Bustillos, Jorge Eduardo; Hidalgo, Silvana

2018-05-01

This study focuses on the evolution through time of Tungurahua volcano (Ecuador), and provides new information regarding its history. Eighteen new K-Ar ages constrain its construction and the activity of its three successive edifices. We show that the volcano is much younger than expected. Indeed, the older edifice activity only began around 293 ± 10 ka, and ended at 79 ± 3 ka. After 50 ka of quiescence, the second edifice started growing at 29 ± 2 ka after a major sector collapse, and itself collapsed at 3 ka. Since then, the third edifice filled the amphitheatre and is still active. Together with numerical reconstructions of the morphology of the three edifices flanks before erosion, these new ages allow us to quantify the magmatic productivity rates during their construction, from 0.6 ± 0.3 and 0.9 ± 0.2 km3/ka for the two older edifices to 2.5 ± 1.0 km3/ka for the youngest, as well as an erosion rate of 0.2 ± 0.1 km3/ka, occurring since the end of Tungurahua I construction. Major and trace element contents of lavas from the three edifices display rather similar trends. Combined with our new ages, the magmatic signature through time does not seem to have been significantly affected either by the sector collapses experienced by the volcano, or by changes of the deep magmatic source. Finally, our results show that the K-Ar dating method by the unspiked Cassignol-Gillot technique performed on groundmass can be successfully applied to lava flows older than the Holocene, while the uncertainties related to younger units can prevent an accurate age determination. Particularly, this method can be applied to Quaternary volcanoes from the Ecuadorian arc, with many of them remaining without knowledge of the timing of their past activity.

Late Pleistocene - Holocene surface processes and landscape evolution in the central Swiss Alps

NASA Astrophysics Data System (ADS)

Boxleitner, Max; Musso, Alessandra; Waroszewski, Jarosław; Malkiewicz, Małgorzata; Maisch, Max; Dahms, Dennis; Brandová, Dagmar; Christl, Marcus; de Castro Portes, Raquel; Egli, Markus

2017-10-01

The European Alps are a geomorphologically active region and experience a number of gravity-driven hillslope processes. Soil and landscape formation in the Alps has consequently undergone several minor and major traceable changes of developmental trajectories during the Holocene. Soil development is hypothesised to be often non-linear with time and characterised by stages of progressive and regressive evolution caused by upbuilding (formation, profile deepening) and erosion (profile shallowing). Several cold and warm climate phases are identified during the Holocene but it is largely unknown which effects these might have had on slope processes. By using datable moraines (10Be) and mires (14C), we have constructed a temporal framework for these processes. Using the geochemical imprint of mires in the Alpine setting of the Göschener-valley of the Central Swiss Alps, we reconstructed general (mostly erosional) landscape processes for the last ca. 10 ka. As this is the type locality for the Göschener cold phase, we assumed that this phase (Göschener cold phase I and II 1.5 and 2.5 ka BP) should have left easily recognizable traits. After deglaciation (11-12 ka BP), soil evolution was progressive. Beginning around 8 ka BP, we detect a distinct increase in erosion here, together with a vegetation change (towards tundra vegetation) and the highest measured rates of carbon sequestration. Other phases of high geomorphic activity were recognised ca. 5-6 ka BP, 4 ka BP and, to a lesser extent, 1-3 ka ago. The cold phase at 5-6 ka BP corresponds to a less distinct change in vegetation and lessened erosion. Human impact is increasingly obvious since about 2.4 ka BP which overlaps with the Göschener cold phase. Nonetheless, erosion processes were not extraordinarily high during this period and a climate effect cannot be distinguished. We detect evidence of increasing human disturbance (regressive soil evolution) for about the last 1 ka. We also detect an increase in dust flux during the last ca. 4-5 ka, presumably due to the landscape change(s) in the Sahara during this time.

Holocene landscape response to seasonality of storms in the Mojave Desert

USGS Publications Warehouse

Miller, D.M.; Schmidt, K.M.; Mahan, S.A.; McGeehin, J.P.; Owen, L.A.; Barron, J.A.; Lehmkuhl, F.; Lohrer, R.

2010-01-01

New optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the Mojave Desert are presented, which greatly improves the temporal resolution of surface processes. The new Mojave Desert climate-landscape record is particularly detailed for the late Holocene. Evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the Medieval Warm Period at ca. AD 1290 and during the Little Ice Age at ca. AD 1650. The former lakes postdate megadroughts of the Medieval Warm Period, whereas the latter match the Maunder Minimum of the Little Ice Age. Periods of alluvial fan aggradation across the Mojave Desert are 14-9 cal ka and 6-3 cal ka. This timing largely correlates to times of increased sea-surface temperatures in the Gulf of California and enhanced warm-season monsoons. This correlation suggests that sustained alluvial fan aggradation may be driven by intense summer-season storms. These data suggest that the close proximity of the Mojave Desert to the Pacific Ocean and the Gulf of California promotes a partitioning of landscape-process responses to climate forcings that vary with seasonality of the dominant storms. Cool-season Pacific frontal storms cause river flow, ephemeral lakes, and fan incision, whereas periods of intense warm-season storms cause hillslope erosion and alluvial fan aggradation. The proposed landscape-process partitioning has important implications for hazard mitigation given that climate change may increase sea-surface temperatures in the Gulf of California, which indirectly could increase future alluvial fan aggradation.

Reconstructing the Glacial Cycle of the Last 150 ka in the Southern Bay of Bengal

NASA Astrophysics Data System (ADS)

Holmes, B.; Dekens, P.; Weber, M. E.; Lantzsch, H.; Reilly, B. T.; Das, S. K.; Martos, Y. M.; Williams, T.

2017-12-01

The Himalayas and resulting monsoonal climate provide the source and mechanism for sediment deposition in the Bay of Bengal. Sediments from the distal Bengal Fan collected during IODP expedition 354, with the exception the westernmost Site U1454, show a several meter thick, hemipelagic top layer representing the Late Quaternary. This interval has abundant foraminifera throughout and therefore presents a unique opportunity to reconstruct oceanographic conditions, alongside records of terrestrial climate variability. We reconstructed oceanographic conditions at IODP site U1452 (8°N, 87°E, 3671 m water depth), in the southern Bay of Bengal. The age model was constructed by tuning the core's sediment lightness, L*, to the EDML ice core. The Toba Ash 1 (73.7 ka) is an additional constraint leading to an age model with a total of 35 tie points. We sampled the top 3.5 m of sediment at 2 cm resolution, and picked between 8 to 30 tests of the mixed surface layer planktonic foraminifera G. sacculifer from each sample. The tests were cracked open between two glass plates and the sample was homogenized before being split into separate aliquots for d18O and Mg/Ca analysis. Mg/Ca data range from 2.5 to 4.1 mmol/mol and show a SST change of 2-4°C between glacial and interglacial times. The δ18O data range from -2.63 to 0.17‰. The data shows the shift from the cooler glacial period into the warming interglacial period at 15 ka ending the LGM. The apparent late timing of the deglaciation in the record could be an artifact of lower resolution of the δ18O data (compared to the benthic stack). It is also possible the offset in the timing is due to the age model limitations and the assumption of linear sedimentation rates between tie points. We will further explore the age model implications by measuring d18O on benthic foraminifera where available in the sediment core. In collaboration with scientists from IODP Expedition 354, this data can be used to examine the link between tropical ocean conditions, monsoon strength, and glacial cycles.

Cova del Rinoceront (Castelldefels, Barcelona): a terrestrial record for the Last Interglacial period (MIS 5) in the Mediterranean coast of the Iberian Peninsula

NASA Astrophysics Data System (ADS)

Daura, J.; Sanz, M.; Julià, R.; García-Fernández, D.; Fornós, J. J.; Vaquero, M.; Allué, E.; López-García, J. M.; Blain, H. A.; Ortiz, J. E.; Torres, T.; Albert, R. M.; Rodríguez-Cintas, À.; Sánchez-Marco, A.; Cerdeño, E.; Skinner, A. R.; Asmeron, Y.; Polyak, V. J.; Garcés, M.; Arnold, L. J.; Demuro, M.; Pike, A. W. G.; Euba, I.; Rodríguez, R. F.; Yagüe, A. S.; Villaescusa, L.; Gómez, S.; Rubio, A.; Pedro, M.; Fullola, J. M.; Zilhão, J.

2015-04-01

The Cova del Rinoceront, a site in NE Iberia, contains a thick sedimentary fill preserving a faunal archive from the penultimate glacial and the the last interglacial periods. Layers I to III have been dated to between 74 and 147 ka, coinciding with MIS 5a to 5e, a period poorly represented in the Mediterranean terrestrial record. The results from Cova del Rinoceront are of broader interest for the reconstruction of ecological dynamics during warm stages and the understanding of the evolution and geographical variation of several taxa. The palaeoecological evidence suggests a landscape dominated by mixed wooded vegetation with mild climatic conditions, slightly more humid than today. Several vertebrate taxa, including Haploidoceros mediterraneus, Stephanorhinus hundsheimensis and Glis glis, are documented for the first time in the early Upper Pleistocene of Europe, showing that these species persisted across the region for longer than previously thought. In addition, the recovery of a small lithic assemblage indicates human presence in the surroundings of the site. The 11 m-thick stratigraphic section also provides an ideal setting in which to compare several geochronological methods. U-Th dating of the flowstones that cap the deposit, of speleothems formed along the cave walls, and of speleothems buried by the deposit at different elevations provides minimum and maximum ages of 74 and 175 ka, respectively, for the accumulation. The ages obtained by luminescence, electron spin resonance (ESR), amino acid racemisation (AAR), palaeomagnetism and U-series dating of bone are in good agreement with each other and are stratigraphically consistent. This well-dated faunal succession presents a unique opportunity to assess changes in the Pleistocene fauna of the Mediterranean coast over an interval of more than 100 ka.

Sr/Ca proxy sea-surface temperature reconstructions from modern and holocene Montastraea faveolata specimens from the Dry Tortugas National Park

USGS Publications Warehouse

Flannery, Jennifer A.; Poore, Richard Z.

2013-01-01

Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ~6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer-driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST + 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961-2008) and a 7-year Holocene (~6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ~0.3 and 0.5 mmol/mol. The amplitude of ~0.3 to 0.5 mmol/mol equates to a 10-15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s. The Holocene (~6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ~7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.

Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands

NASA Astrophysics Data System (ADS)

Dutton, Andrea; Webster, Jody M.; Zwartz, Dan; Lambeck, Kurt; Wohlfarth, Barbara

2015-01-01

In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ˜129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ˜5-8 m of polar ice sheet contribution, relative to today's volume, of which only ˜2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

New Insights into the 8.2 ka Cold Event and Subsequent Climate Recovery in Central Europe Provided by a Precisely Dated Ostracod δ18O Record from Mondsee (Austria)

NASA Astrophysics Data System (ADS)

Lauterbach, S.; Andersen, N.; Brauer, A.; Erlenkeuser, H.; Danielopol, D. L.; Namiotko, T.; Huels, M.; Belmecheri, S.; Nantke, C.; Meyer, H.; Chapligin, B.; von Grafenstein, U.

2015-12-01

As evidenced by numerous palaeoclimate records worldwide, the Holocene warm period has been interrupted by several short, low-amplitude cold episodes. Among these, the so-called 8.2 ka cold event is the most prominent Holocene climate perturbation but despite extensive studies, knowledge about its synchrony in different areas and particularly about the dynamics of subsequent climate recovery is still limited. As this is of crucial importance for understanding the complex mechanisms that trigger rapid climate fluctuations and for testing the performance of climate models, new data on the 8.2 ka cold event are needed. Here we present a new sub-decadally resolved, precisely dated oxygen isotope (δ18O) record for the interval 7.7-8.7 ka BP obtained from benthic ostracods preserved in the varved lake sediments of Mondsee (Austria), providing new insights into climate development around the 8.2 ka cold event in Central Europe. The new high-resolution δ18O data set reveals the occurrence of a pronounced cold spell around 8.2 ka BP, whose amplitude (~1.0 ‰, equivalent to a 1.5-2.0 °C cooling), total duration (151 a) and absolute dating (8231-8080 a BP, i.e. calendar years before AD 1950) perfectly agree with results from other Northern Hemisphere palaeoclimate archives, e.g. the precisely dated Greenland ice cores. In addition, the Mondsee δ18O record also indicates a 75-year-long air temperature overshoot of ~0.7 °C directly after the 8.2 ka event (between 8080 and 8005 a BP), which is so far only poorly documented in the mid-latitudes. However, this observation is consistent with results from coupled climate models and high-latitude proxy records, thus likely reflecting a hemispheric-scale climate signal driven by enhanced resumption of the Atlantic meridional overturning circulation (AMOC), which apparently also caused synchronous migrations of atmospheric and oceanic front systems in the North Atlantic realm.

Excess warming in Central Europe after the 8.2 ka cold event: evidence from a varve-dated ostracod δ18O record from Mondsee (Austria)

NASA Astrophysics Data System (ADS)

Lauterbach, Stefan; Andersen, Nils; Erlenkeuser, Helmut; Danielopol, Dan L.; Namiotko, Tadeusz; Hüls, Matthias; Belmecheri, Soumaya; Nantke, Carla; Meyer, Hanno; Chapligin, Bernhard; von Grafenstein, Uli; Brauer, Achim

2017-04-01

As evidenced by numerous palaeoclimate records worldwide, the Holocene warm period has been punctuated by several short, low-amplitude cold episodes. Among these, the so-called 8.2 ka cold event represents a particularly prominent climate anomaly. Accordingly, several proxy-based and modeling studies have addressed its causal mechanisms, absolute dating, duration, amplitude, spatio-temporal characteristics and environmental consequences so far. However, knowledge about the dynamics and causes of subsequent climate recovery is still limited although this is essential for understanding rapid climate change. Here we present a new sub-decadally resolved and precisely dated oxygen isotope (δ18O) record for the interval 7.7-8.7 ka BP derived from benthic ostracods preserved in the varved lake sediments of pre-Alpine Mondsee (Austria), providing new insights into climate development around the 8.2 ka cold event in Central Europe. The high-resolution Mondsee δ18O record reveals the occurrence of a pronounced cold spell around 8.2 ka BP, whose amplitude (˜1.0 ‰ , equivalent to a 1.5-2.0 ˚ C cooling), total duration (151 years) and absolute dating (8231-8080 varve years BP, i.e. calendar years before AD 1950) agrees well with results from other Northern Hemisphere palaeoclimate archives, e.g. the Greenland ice cores. In addition, the Mondsee data set provides evidence for a 75-year-long δ18O overshoot directly following the 8.2 ka event (between 8080 and 8005 varve years BP), which is interpreted as a period of excess warming (about 0.5-0.6 ˚ C above the pre-8.2 ka event level) in Central Europe. Though so far not been explicitly described elsewhere, this observation is consistent with evidence from other proxy records in the North Atlantic realm, therefore likely reflecting a hemispheric-scale signal rather than a local phenomenon. As a possible trigger we suggest an enhanced resumption of the Atlantic meridional overturning circulation (AMOC), supporting assumptions from climate model simulations.

Paleoseismic observations along the Langshan range-front fault, Hetao Basin, China: Tectonic and seismic implications

NASA Astrophysics Data System (ADS)

Dong, Shaopeng; Zhang, Peizhen; Zheng, Wenjun; Yu, Zhongyuan; Lei, Qiyun; Yang, Huili; Liu, Jinfeng; Gong, Huilin

2018-04-01

The Langshan range-front fault (LRF) is an active Holocene normal fault that borders Langshan Mountain and the Hetao Basin, northwest of the Ordos Plateau, China. In this study, paleoseismic trenching was undertaken at three sites (North-South): Dongshen village (TC1), Qingshan (TC2), and Wulanhashao (TC3). The paleoevents ED1, ED2, ED3 from TC1 were constrained to 6.0 ± 1.3, 9.6 ± 2.0, and 19.7 ± 4.2 ka, respectively. The single paleoevent (EQ1) from TC2 was constrained to about 6.7 ± 0.1 ka, and the paleoevents EW1, EW2, and EW3 from TC3 were constrained to 2.3 ± 0.4, 6.0 ± 1.0, and before 7.0 ka, respectively. With reference to previous research, the Holocene earthquake sequence of the LRF can be established as 2.30-2.43 (E1), 3.06-4.41 (E2), 6.71-6.80 (E3), 7.60-9.81 (E4), and 19.70 ± 4.20 (E5) ka BP. Events E1, E3, and E4 might have been caused by events with magnitudes of Mw 7.6-7.8 that ruptured the entire LRF. Event E2 might have been smaller magnitude, about M7.0, and ruptured only a portion of the fault. The vertical slip rate of the LRF at the Qingshan site is inferred as 0.9 or 1.4-1.6 mm/year in the last 6.8 ka. The slip rate at Wulanhashao is considered to have been close to, but not <0.66 mm/year since 15 ka BP. We deem the LRF is an unsegmented active fault. Although the possibility of missing events in Late Pleistocene can not be dismissed, we argue the Holocene paleoearthquake history is complete, indicating an average recurrence interval of 2500 years.

Termination-II interstadial/stadial climate change recorded in two stalagmites from the north European Alps

NASA Astrophysics Data System (ADS)

Moseley, Gina E.; Spötl, Christoph; Cheng, Hai; Boch, Ronny; Min, Angela; Edwards, R. Lawrence

2015-11-01

Understanding the sequence of events that take place during glacial-interglacial climate transitions is important for improving our knowledge of abrupt climate change. Here, we present a new stacked, high-resolution, precisely-dated speleothem stable isotope record from the northern Alps, which provides an important record of temperature and moisture-source changes between 134 and 111 ka for Europe and the wider North Atlantic realm. The record encompasses the penultimate deglaciation (Termination II (TII)), which lies beyond the limit of radiocarbon dating, thus providing an important new archive for a crucial period of rapid paleoclimate change. Warmer and wetter ice-free conditions were achieved by 134.1 ± 0.7 ka (modelled ages) as indicated by the presence of liquid water at the site. Temperatures warmed further at 133.7 ± 0.5 ka and led into an interstadial, synchronous with slightly elevated monsoon strength during the week monsoon interval. The interstadial experienced an unstable climate with a trough in temperature associated with a slowdown in Atlantic Meridional Overturning Circulation (AMOC) and a reduction in North Atlantic Deep Water (NADW) formation. The interstadial ended with a more extreme cold reversal lasting 500 years in which NADW formation remained active but the subpolar gyre weakened allowing cool polar waters to penetrate southwards. The main warming associated with TII was very rapid, taking place between 130.9 ± 0.9 and 130.7 ± 0.9 ka coeval with initial monsoon strengthening. Temperatures then plateaued before being interrupted by a 600-year cold event at 129.1 ± 0.6 ka, associated once again with penetration of polar waters southwards into the North Atlantic and a slowdown in monsoon strengthening. Sub-orbital climate oscillations were thus a feature of TII in the north Atlantic realm, which broadly resemble the Bølling/Allerød-Younger Dryas-8.2 ka event pattern of change observed in Termination I despite monsoon records indicating strong differences between the last and penultimate deglaciation.

A ~25 ka Indian Ocean monsoon variability record from the Andaman Sea

USGS Publications Warehouse

Rashid, H.; Flower, B.P.; Poore, R.Z.; Quinn, T.M.

2007-01-01

Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ18O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ18O of seawater (δ18Osw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ∼3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ18Osw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ18Osw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.

Centennial-scale vegetation dynamics and climate variability in SE Europe during Marine Isotope Stage 11 based on a pollen record from Lake Ohrid

NASA Astrophysics Data System (ADS)

Kousis, Ilias; Koutsodendris, Andreas; Peyron, Odile; Leicher, Niklas; Francke, Alexander; Wagner, Bernd; Giaccio, Biagio; Knipping, Maria; Pross, Jörg

2018-06-01

To better understand climate variability during Marine Isotope Stage (MIS) 11, we here present a new, centennial-scale-resolution pollen record from Lake Ohrid (Balkan Peninsula) derived from sediment cores retrieved during an International Continental Scientific Drilling Program (ICDP) campaign. Our palynological data, augmented by quantitative pollen-based climate reconstructions, provide insight into the vegetation dynamics and thus also climate variability in SE Europe during one of the best orbital analogues for the Holocene. Comparison of our palynological results with other proxy data from Lake Ohrid as well as with regional and global climate records shows that the vegetation in SE Europe responded sensitively both to long- and short-term climate change during MIS 11. The chronology of our palynological record is based on orbital tuning, and is further supported by the detection of a new tephra from the Vico volcano, central Italy, dated to 410 ± 2 ka. Our study indicates that MIS 11c (∼424-398 ka) was the warmest interval of MIS 11. The younger part of the interglacial (i.e., MIS 11b-11a; ∼398-367 ka) exhibits a gradual cooling trend passing over into MIS 10. It is characterized by considerable millennial-scale variability as inferred by six abrupt forest-contraction events. Interestingly, the first forest contraction occurred during full interglacial conditions of MIS 11c; this event lasted for ∼1.7 kyrs (406.2-404.5 ka) and was characterized by substantial reductions in winter temperature and annual precipitation. Most notably, it occurred ∼7 ka before the end of MIS 11c and ∼15 ka before the first strong ice-rafted debris event in the North Atlantic. Our findings suggest that millennial-scale climate variability during MIS 11 was established in Southern Europe already during MIS 11c, which is earlier than in the North Atlantic where it is registered only from MIS 11b onwards.

High-precision timeline for Earth’s most severe extinction

PubMed Central

Burgess, Seth D.; Bowring, Samuel; Shen, Shu-zhong

2014-01-01

The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms. PMID:24516148

Megadroughts and late Holocene dune activation at the eastern margin of the Great Plains, north-central Kansas, USA

NASA Astrophysics Data System (ADS)

Hanson, P. R.; Arbogast, A. F.; Johnson, W. C.; Joeckel, R. M.; Young, A. R.

2010-01-01

Optical and radiocarbon dating indicates that alluvium underlying dunes near Abilene was deposited at or before ˜45 ka, and that the overlying dunes were active at ˜1.1-0.5 ka. Geochemical data indicate that the Abilene dune sand is immature and was derived from the underlying Pleistocene alluvium, and not from Holocene age Smoky Hill River deposits. These findings suggest that dune activation was a response to increased aridity and local reduction in vegetation cover as opposed to changes in sediment availability from nearby rivers. The time interval of dune activation at Abilene overlaps Medieval Warm Period megadroughts, similar to the larger and more westerly dune fields on the Great Plains, including the Nebraska Sand Hills and the Great Bend Sand Prairie. The activation of smaller dune fields such as the Abilene dunes near the more humid eastern margin of the Great Plains shows the geographic extent and severity of paleodrought events. Unlike the Duncan dunes, another plains-marginal dune field, however, the Abilene dunes show no evidence for multiple drought events during the Holocene. This difference in dune activity, if it is not a result of sampling or preservation bias, indicates variations in the extent and severity of older drought events at the eastern margin of the Great Plains.

High-precision timeline for Earth's most severe extinction.

PubMed

Burgess, Seth D; Bowring, Samuel; Shen, Shu-zhong

2014-03-04

The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms.

A new sampling strategy for cosmogenic surface exposure dating of moraines: Amalgamated Boulder Chips (ABCs)

NASA Astrophysics Data System (ADS)

Akif Sarıkaya, M.; Çiner, Attila; Yıldırım, Cengiz

2017-04-01

Cosmogenic surface exposure dating has been applied to date numerous moraines worldwide. The geochronological data obtained from these studies have improved our knowledge on the timing of glaciation and allow us to reconstruct the paleoclimate. Due to the geomorphic complications after deposition, such as degradation, exhumation, bedrock erosion, snow cover and toppling of boulders, several (n>5) large boulder (>1-2 m) samples should be dated to obtain a reliable age distribution. Generally, the ages on a well-preserved moraine surface show unimodal normal distribution. Frequently, erosion, exhumation and boulder toppling are blamed for the younger outliers. On the other hand, although infrequent, older outliers will indicate inherited nuclide concentration from pre-exposure to cosmic radiation. To obtain the true age of a moraine deposit, one needs to collect several samples that not only greatly increases the budget of the project but also is time consuming. To overcome this problem, we developed a new sampling strategy for dating moraine surfaces by cosmogenic nuclides. We collected rock chips (each 20-50 grams) from large boulder (>1 m) tops located on the crest of moraines. Fourteen to 32 boulders were chosen for sampling every 20 m. All rock chips were amalgamated to make one sample. To test the suitability of the method, we also sampled 3 large boulders (>1 m), as it is done classically, from the same surface. The age results from the two Late Pleistocene moraines and one rock glacier surface show no difference in terms of boulder exposure ages. Three 36Cl ages from one single lateral moraine in Çimi Valley of Geyikdaǧ, central Taurus, Turkey, are 11.9±0.9 ka, 14.0±1.1 ka and 11.9±0.9 ka (all ages have no erosion corrections) and yield a mean age of 12.6±0.9 ka, while the amalgamated boulder chips' (ABCs) age is 12.0±0.9 ka. Another well developed terminal moraine (so called Zor Moraine) in the Güneycik Valley of Geyikdaǧ, yielded ages as 4.9±0.4 ka, 7.7±0.6 ka and 3.7±0.3 ka, while the ABCs' age is 6.4±0.6 ka. The rock glacier boulder samples yielded ages of 12.2±0.9 ka, 14.0±1.0 ka and 9.2±0.8 ka, while the rock glacier ABCs' age is 10.7±0.9 ka. These results clearly indicate that the age obtained from ABCs is reliable and can safely replace classical methodology that requires collection of several samples from a moraine surface. The use of ABCs sampling strategy will considerably decrease the time and budget allocated to date a landform. This work was supported by TUBITAK 112Y139 project.

Cosmogenic evidence for limited local LGM glacial expansion, Denton Hills, Antarctica

NASA Astrophysics Data System (ADS)

Joy, Kurt; Fink, David; Storey, Bryan; De Pascale, Gregory P.; Quigley, Mark; Fujioka, Toshiyuki

2017-12-01

The geomorphology of the Denton Hills provides insight into the timing and magnitude of glacial retreats in a region of Antarctica isolated from the influence of the East Antarctic ice sheet. We present 26 Beryllium-10 surface exposure ages from a variety of glacial and lacustrine features in the Garwood and Miers valleys to document the glacial history of the area from 10 to 286 ka. Our data show that the cold-based Miers, Joyce and Garwood glaciers retreated little since their maximum positions at 37.2 ± 6.9 (1σ n = 4), 35.1 ± 1.5 (1σ, n = 3) and 35.6 ± 10.1 (1σ, n = 6) ka respectively. The similar timing of advance of all three glaciers and the lack of a significant glacial expansion during the global LGM suggests a local LGM for the Denton Hills between ca. 26 and 51 ka, with a mean age of 36.0 ± 7.5 (1σ, n = 13) ka. A second cohort of exposure ages provides constraints to the behaviour of Glacial Lake Trowbridge that formerly occupied Miers Valley in the late Pleistocene. These data show active modification of the landscape from ∼20 ka until the withdrawal of ice from the valley mouths, and deposition of Ross Sea Drift, at 10-14 ka.

Timing and composition of continental volcanism at Harrat Hutaymah, western Saudi Arabia

USGS Publications Warehouse

Duncan, Robert A.; Kent, Adam J R; Thornber, Carl; Schliedler, Tyler D; Al-Amri, Abdullah M

2016-01-01

Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K–Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40Ar–39Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1–7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60–80 km).

Late Pleistocene shifts in Northeast African hydroclimate and the Out-of-Africa migration

NASA Astrophysics Data System (ADS)

Tierney, J. E.; deMenocal, P. B.; Zander, P. D.

2016-12-01

The major "Out-of-Africa" migration of modern humans is hypothesized to have occurred ca. 60,000-80,000 yr BP, with populations crossing the Red Sea via either the Bab al Mandeb strait or the Sinai Peninsula. The role of climatic and environmental pressures in driving the migration has long been a topic of debate. While paleoclimate data from southern East Africa generally show evidence for climatic instability during the Out-Of-Africa interval, no data has been available from northeast Africa, the region from which haplogroup L3, the most common parental lineage for humans outside Africa, dispersed. Here we present leaf wax hydrogen isotope data measured in a marine sediment core that provide a clear picture of how Northeast African climate has varied during the past 200,000 years. The data show that wet periods are generally in-phase with Northern hemisphere summer insolation, with MIS 7a emerging as the wettest "African Humid Period" of the last 200 ka. Interestingly, Stages 5e, 5c, and 5a are comparably wet. Last glacial aridity does not begin in earnest until ca. 75 ka, with an abrupt drop out of mesic Stage 5 conditions followed by a descent into very dry conditions during Stage 4. The timing of this wet-to-dry transition compares well with the estimated timing of Out-of-Africa migration from genetic data, suggesting that climatic deterioration could have been an impetus for early humans to leave northeast Africa.

Timing and composition of continental volcanism at Harrat Hutaymah, western Saudi Arabia

NASA Astrophysics Data System (ADS)

Duncan, Robert A.; Kent, Adam J. R.; Thornber, Carl R.; Schlieder, Tyler D.; Al-Amri, Abdullah M.

2016-03-01

Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K-Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40Ar-39Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1-7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60-80 km).

Episodes of environmental stability versus instability in Late Cenozoic lake records of Eastern Africa.

PubMed

Trauth, Martin H; Bergner, Andreas G N; Foerster, Verena; Junginger, Annett; Maslin, Mark A; Schaebitz, Frank

2015-10-01

Episodes of environmental stability and instability may be equally important for African hominin speciation, dispersal, and cultural innovation. Three examples of a change from stable to unstable environmental conditions are presented on three different time scales: (1) the Mid Holocene (MH) wet-dry transition in the Chew Bahir basin (Southern Ethiopian Rift; between 11 ka and 4 ka), (2) the MIS 5-4 transition in the Naivasha basin (Central Kenya Rift; between 160 ka and 50 ka), and (3) the Early Mid Pleistocene Transition (EMPT) in the Olorgesailie basin (Southern Kenya Rift; between 1.25 Ma and 0.4 Ma). A probabilistic age modeling technique is used to determine the timing of these transitions, taking into account possible abrupt changes in the sedimentation rate including episodes of no deposition (hiatuses). Interestingly, the stable-unstable conditions identified in the three records are always associated with an orbitally-induced decrease of insolation: the descending portion of the 800 kyr cycle during the EMPT, declining eccentricity after the 115 ka maximum at the MIS 5-4 transition, and after ∼ 10 ka. This observation contributes to an evidence-based discussion of the possible mechanisms causing the switching between environmental stability and instability in Eastern Africa at three different orbital time scales (10,000 to 1,000,000 years) during the Cenozoic. This in turn may lead to great insights into the environmental changes occurring at the same time as hominin speciation, brain expansion, dispersal out of Africa, and cultural innovations and may provide key evidence to build new hypotheses regarding the causes of early human evolution. Copyright © 2015 Elsevier Ltd. All rights reserved.

Palaeoenvironmental Transitions Between 22 ka and 8 ka in Monsoonally Influenced Namibia

NASA Astrophysics Data System (ADS)

Eitel, Bernhard; Blümel, Wolf Dieter; Hüser, Klaus

The paper presents a preliminary reconstruction of the development of different palaeoenvironments between the Last Glacial Maximum (LGM; c. 22 - 18 ka) and the Holocene Altithermal (HA; c. 8 ka - 4 ka) in Namibia. The synopsis is based on 36 optical datations of dune sands and fine-grained, silty deposits (OSL and TL). Most of the data were published by different research groups during the last decade. The synoptic view of all available optical age determinations is necessary because palaeoclimatic interpretations for southwestern Africa are not possible using results based only on local studies and on partly unreliable datations (e. g. 14C ages of calcretes). The compilation of all available datations and a synoptical interpretation such as the one presented here, show that gradual transitions and not abrupt changes from arid to more humid conditions occurred. These transitions did not affect all regions of Namibia at the same time and intensity. Differentiations in time and space are necessary for arriving a consistent model of the palaeoenvironmental transitions between LGM and HA.

Age and effects of the Odessa meteorite impact, western Texas, USA

NASA Astrophysics Data System (ADS)

Holliday, Vance T.; Kring, David A.; Mayer, James H.; Goble, Ronald J.

2005-12-01

The Odessa meteorite craters (Texas, United States) include a main crater (˜160 m diameter, ˜30 m deep) plus four smaller meteorite craters. The main crater was sampled by coring (to 22 m depth) to better understand its origin and history. Dating by optically stimulated luminescence indicates that it was produced immediately prior to ca. 63.5 ± 4.5 ka. Sediment filling the crater includes impact breccias produced at the time of impact; wind-dominated silts with minor amounts of pond sediments deposited ca. 63.5 ka, probably just after the impact, and ca. 53 ± 2 ka; wind-dominated silt ca. 38 ± 1.7 ka; and playa muds with a wind-blown silt component younger than 36 ka. The environment was arid or semiarid at the time of impact based on characteristics of soils on the surrounding landscape. The impact caused severe damage within 2 km and produced >1000 km/hr winds and thermal pulse. Animals within a 1 1.5-km-diameter area were probably killed. This is only the second well-dated Pleistocene hypervelocity impact crater in North America.

Late Quaternary environmental dynamics in the Atacama Desert reconstructed from rodent midden pollen records

USGS Publications Warehouse

de Porras, M.E.; Maldonado, A.; De Pol-Holz, R.; Latorre, C.; Betancourt, Julio L.

2017-01-01

In the past two decades, much has been learned about the late Quaternary climate history of the Atacama Desert with some details still unclear about the seasonality, timing and extent of wet and dry phases. Modern climate studies reveal that, far from exhibiting a unique pattern, seasonal precipitation originates from many sources and mechanisms. For the last 16 ka, we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22°–25°S in northern Chile. Widespread wet conditions prevailed during the late Pleistocene and early Holocene, particularly between 13 and 9 ka, evidenced by <400 m lowering of pollen zones (plant communities) compared to today. Regional differences in the timing and magnitude of this displacement may be related to the prevailing source (tropical/extra‐tropical) or mode (NNW/SE) of tropical precipitation through time. Wet conditions persisted well into the early Holocene, lasting ∼1–1.5 ka longer than previously suggested. The pollen record suggests extreme drying ∼8 ka, possibly associated with a northward shift of the Inter Tropical Convergence Zone, tracking minimum insolation values at subtropical latitudes during the austral summer. The establishment of conditions similar to today happened ∼4 ka. 

Late Quaternary eolian and alluvial response to paleoclimate, Canyonlands, southeastern Utah

USGS Publications Warehouse

Reheis, M.C.; Reynolds, R.L.; Goldstein, H.; Roberts, H.M.; Yount, J.C.; Axford, Y.; Cummings, L.S.; Shearin, N.

2005-01-01

In upland areas of Canyonlands National Park, Utah, thin deposits and paleosols show late Quaternary episodes of eolian sedimentation, pedogenesis, and climate change. Interpretation of the stratigraphy and optically stimulated luminescence ages of eolian and nearby alluvial deposits, their pollen, and intercalated paleosols yields the following history: (1) Eolian deposition at ca. 46 ka, followed by several episodes of alluviation from some time before ca. 40 ka until after 16 ka (calibrated). (2) Eolian deposition from ca. 17 ka to 12 ka, interrupted by periods of pedogenesis, coinciding with late Pleistocene alluviation as local climate became warmer and wetter. (3) A wetter period from 12 to 8.5 ka corresponding to the peak of summer monsoon influence, during which soils formed relatively quickly by infiltration of eolian silt and clay, and trees and grasses were more abundant. (4) A drier period between ca. 8.5 and 6 ka during which sheetwash deposits accumulated and more desertlike vegetation was dominant; some dunes were reactivated at ca. 8 ka. (5) Episodic eolian and fluvial deposition during a wetter, cooler period that began at ca. 6 ka and ended by ca. 3-2 ka, followed by a shift to drier modern conditions; localized mobilization of dune sand has persisted to the present. These interpretations are similar to those of studies at the Chaco dune field, New Mexico, and the Tusayan dune field, Arizona, and are consistent with paleoclimate interpretations of pollen and packrat middens in the region. A period of rapid deposition and infiltration of eolian dust derived from distant igneous source terranes occurred between ca. 12 and 8 ka. Before ca. 17 ka, and apparently back to at least 45 ka, paleosols contain little or no such infiltrated dust. After ca. 8 ka, either the supply of dust was reduced or the more arid climate inhibited translocation of dust into the soils. ?? 2005 Geological Society of America.

Characteristics of gas hydrate-bearing sediments of the northern South China Sea: insight into past hydrate episodic dissociations and intensities of seepage

NASA Astrophysics Data System (ADS)

Chen, F.; Su, X.; Zhou, Y.; Zhang, G.; Zhuang, C.; Lu, H.

2016-12-01

In 2013 the second China's major gas hydrate expedition, GMGS2, cored and recovered abundant gas hydrates at five sites, which were located in the South China Sea.Site GMGS08 (95m long) contained two gas hydrate intervals and five authigenic carbonate intervals. We analyzed carbon and oxygen isotopes of authigenic carbonates and foraminifera shells in sediments recovered at this site, in order to understanding of features of hydrate-bearing sediments and timing of gas hydrate dissociation and methane seepage at this site. An age of younger than 0.27 Ma was estimated for the 95 m sedimentary sequences at Site GMGS08. A detailed age model was further established by employing of U/Th and AMS14C dating of authigenic carbonates and seep bivalve fragments. These carbonates are featured by 13C-depleted (with a range from -38.9‰ to 56.7‰ δ13C) and positive δ18O (from 2.94‰ to 5.66‰ δ18O) values. A further analysis indicated the formation of carbonates were correlated to methane seepages derived from gas hydrate dissociation. Subsequently, these five authigenic carbonates intervals were seen as five hydrate episodic dissociation events since last 0.27Ma at this site. The most significant event during the period of 0.11 Ma to 0.13 Ma were account for the formation of thick authigenic carbonate (with the lowest -56.8‰ δ13C value) platform on paleo-seafloor at this site. The upmost authigenic carbonates interval is just overlying on the top of the upper gas hydrate occurrence zone, and it represents the latest methane seepage event with an age of 26ka to 36ka. Well correlated to these five events, it existed five intervals with strongly 13C-depleted carbon (-15.85‰ PDB) of foraminifera shells both from benthic and planktonic. The anomalous δ13C depletion records of planktonic G. ruber shells should be caused by formation of secondary authigenic carbonates on the shells, which were derived from the anaerobic oxidation of methane (AOM). The analyses on carbonate samples indicated varied intensity of methane flux in each event. The most intensive methane venting flux occurred during the event of 0.11 Ma to 0.13 Ma, which is correlated to a warm and relative high sea level period of MIS stage 5. These records obtained at Site GMGS08 implied much complicated causes for formation of authigenic carbonates and gas hydrate episodic dissociation.

Climate-driven sediment aggradation and incision since the late Pleistocene in the NW Himalaya, India

NASA Astrophysics Data System (ADS)

Dey, Saptarshi; Thiede, Rasmus C.; Schildgen, Taylor F.; Wittmann, Hella; Bookhagen, Bodo; Scherler, Dirk; Jain, Vikrant; Strecker, Manfred R.

2016-09-01

Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 103 to 105 yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives. New surface-exposure dating of six terrace levels with in-situ cosmogenic 10Be indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4 ± 3.2 ka and 43.0 ± 2.7 ka (1σ). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6 ± 1.2 ka and 15.3 ± 0.9 ka, while terraces sculpted into the upper Pleistocene-Holocene fan (AF2) provide ages of 9.3 ± 0.4 ka (T3), 7.1 ± 0.4 ka (T4), 5.2 ± 0.4 ka (T5) and 3.6 ± 0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision.

Millennial-scale variability to 735 ka: High-resolution climate records from Santa Barbara Basin, CA

NASA Astrophysics Data System (ADS)

White, Sarah M.; Hill, Tessa M.; Kennett, James P.; Behl, Richard J.; Nicholson, Craig

2013-06-01

Determining the ultimate cause and effect of millennial-scale climate variability remains an outstanding problem in paleoceanography, partly due to the lack of high-resolution records predating the last glaciation. Recent cores from Santa Barbara Basin provide 2500-5700 year "windows" of climate with 10-50 year resolution. Ages for three cores, determined by seismic stratigraphic correlation, oxygen isotope stratigraphy, and biostratigraphy, date to 293 ka (MIS 8), 450 ka (MIS 12), and 735 ka (MIS 18). These records sample the Late Pleistocene, during which the 100 kyr cycle strengthened and the magnitude of glacial-interglacial cyclicity increased. Thus, these records provide a test of the dependence of millennial-scale behavior on variations in glacial-interglacial cyclicity. The stable isotopic (δ18O) composition of planktonic foraminifera shows millennial-scale variability in all three intervals, with similar characteristics (duration, cyclicity) to those previously documented during MIS 3 at this site. Stadial G. bulloides δ18O values are 2.75-1.75‰ (average 2.25‰) and interstadial values are 1.75-0.5‰ (average 1‰), with rapid (decadal-scale) interstadial and stadial initiations of 1-2‰, as in MIS 3. Interstadials lasted 250-1600 years and occurred every 650-1900 years. Stadial paleotemperatures were 3.5-9.5°C and interstadial paleotemperatures were 7.5-13°C. Upwelling, evidenced by planktonic foraminiferal assemblages and δ13C, increased during interstadials, similar to MIS 3; high productivity during some stadials was reminiscent of the Last Glacial Maximum. This study builds upon previous records in showing that millennial-scale shifts were an inherent feature of Northern Hemisphere glacial climates since 735 ka, and they remained remarkably constant in the details of their amplitude, cyclicity, and temperature variability.

A six-stalagmite composite record of East Asian Summer Monsoon in northern China since 11.5 thousand years ago

NASA Astrophysics Data System (ADS)

Shen, C. C.; Dong, J.; Kong, X.; WU, C. C.; Ren, H. A.; Wang, Y.

2017-12-01

Here we present replicated carbonate δ18O records of six stalagmites with sub-decadal to multi-decadal resolutions from Lianhua Cave (38º10'N, 113º43'E), Shanxi Province, to reveal a detailed evolution of the East Asian Summer Monsoon (EASM) intensity in northern China since 11.5 thousand years ago (ka BP, before 1950 AD). This composite record shows that solar forcing dominated hydroclimatic changes, including an intensified monsoon at the Holocene Optimum from the termination of Younger Dryas to 6.5 ka BP, and a subsequent multi-millennial weakening of monsoon intensity, that agree with cave records in central and southern China. However, the EASM has retreated southwards more rapidly than the Indian summer monsoon after 6.5 ka BP, resulting in aridity conditions occurring at 4.0 ka BP in northern China, which is almost 2000-year earlier than in central and southern China. This asynchroneity may be related to the different regional responses among the coupling of the EASM, Indian summer monsoon, the solar forcing, and the differences in thermal forcing due to complex geographical configurations. In addition, a relative enrichment of 1‰ in 18O data of Lianhua record from 9.5 to 8.1 ka BP shows that the Holocene Optimum was punctuated by a millennial-long weak monsoon interval, which is not registered among previous cave records in central and southern China. The fresh water-induced cold climate conditions in the North Atlantic region could create stronger East Asian winter monsoon and induce a weakened EASM and a southward shift of rain belt in northern China. Therefore, it shall not be surprised that there are strong heterogeneities among regional hydroclimatic conditions across monsoonal China in the Holocene.

Alkenone-based reconstructions show four-phase Holocene temperature history for Arctic Svalbard

NASA Astrophysics Data System (ADS)

van der Bilt, W. G. M.; D'Andrea, W. J.; Bakke, J.; Balascio, N.; Werner, J.; Bradley, R. S.

2016-12-01

Situated at the crossroads of global oceanic and atmospheric circulation patterns, the Arctic is a key component of Earth`s climate system. Amplified by sea-ice feedbacks, even modest shifts in regional heat budget drive large climate responses. This is highlighted by the dramatic response of the Arctic to global warming. Assessing the signature of underlying forcings require paleoclimate records, allowing us to expand our knowledge beyond the short instrumental period and contextualize ongoing warming. However, such data are scarce and sparse in the Arctic, limiting our ability to address these issues. We present two quantitative Holocene-length summer temperature reconstructions from the Arctic Svalbard archipelago. Temperature estimates are based on alkenone unsaturation ratios measured on sediment cores from two lakes. Our data reveal a dynamic Holocene temperature history, with reconstructed lake water temperatures spanning a range of 6-8 °C, and characterized by four phases. The Early Holocene was marked by an early ( 10.5 ka cal. BP) onset of insolation-driven Hypsithermal conditions, likely compounded by strengthening oceanic heat transport. This warm interval was interrupted by cooling between 10.5-8.3 ka cal. BP that we attribute to cooling effects from the melting Northern Hemisphere ice sheets. Temperatures declined throughout the Middle Holocene, following a gradual trend that was accentuated by two cooling steps between 7.8-7 ka cal. BP and 4.4-3.5 ka cal. BP. These transitions coincide with a strengthening influence of Arctic water and sea-ice in the adjacent eastern Fram Strait. During the Late Holocene (past 4 ka), temperature change decoupled from the still-declining insolation, and fluctuated around cold mean conditions. This study improves our understanding of Arctic climate dynamics by demonstrating that Holocene Svalbard temperatures were governed by an alternation of forcing mechanism.

Boundary Conditions for Aeolian Activity in North American Dune Fields

NASA Astrophysics Data System (ADS)

Halfen, A. F.; Lancaster, N.; Wolfe, S.

2014-12-01

Geomorphic and chronological data for dune fields are evaluated for three contrasting areas of North America: 1) the Prairie-Parkland-Boreal ecozones of the northern Great Plains in Canada; 2) the Central Great Plains of the USA; and 3) the deserts of southwestern USA and northern Mexico. Luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply, availability, and mobility. Dune fields in the northern Great Plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16-11 ka. Subsequent aeolian deposition occurred in Parkland and Prairie dune fields as a result of mid-Holocene (8-5 ka) and late-Holocene (< 3.5 ka) activity related to drought conditions that reworked pre-existing aeolian sands. In the Central Great Plains, dune fields are closely linked to fluvial sediment sources. Sediment supply was high during deglaciation of the Rocky Mountains and resulted in widespread dune construction 16-10 ka. Multiple periods of Holocene reactivation are recorded and reflect increased sediment availability during drought episodes. Dune fields in the southwestern deserts experienced periods of construction as a result of enhanced supply of sediment from fluvial and lacustrine sources during the period 11.8-8 ka and at multiple intervals during the late Holocene. Despite spatial and temporal gaps in chronometric data as a result of sampling biases, the record from North American dune fields indicates the strong influence of sediment supply on dune construction, with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre-existing sediment.

Atmospheric changes in North America during the last deglaciation from dune-wetland records in the Midwestern United States

NASA Astrophysics Data System (ADS)

Wang, Hong; Stumpf, Andrew J.; Miao, Xiaodong; Lowell, Thomas V.

2012-12-01

Reconstructing moisture conditions during the early retreat of the Laurentide Ice Sheet (LIS) may help define the phase relationship of deglacial conditions and atmospheric changes over North America. Here, we report two sediment successions near the concurrent ice margins in the Midwest of the U.S.A. to show that dune formation was active from 17.7 to 14.7 and from 12.8 to 11.8 thousand years ago (ka) and lowland soils formed at 14.7 and wetland sediments developed from 13.5 to 12.8 ka. Our results suggest that moisture conditions in the Midwestern U.S.A. were inversely phased with those in the southwestern U.S.A. During the Heinrich event 1 (H1) and Younger Dryas (YD) stadials, the northern area became drier and southern area became wetter, whereas during the Bølling/Allerød (B/A) interstadials, the northern area became wetter and southern area became drier. This pattern is also observed on phase change levels within the H1 interval. In detail, from 17.7 to 16.5 ka during the H1b phase, major aridity in the Midwest corresponded to wet conditions in the Southwest U.S.A. From 16.5 to 15.0 ka during the H1a phase, climate reversed from dry to wet in the Midwest, whereas conditions went from wet to dry in the Southwest. From 15.0 to 14.7 ka during the transition to the Bølling/Allerød (t-B/A) phase, a return of aridity in the Midwest corresponded to a return of humidity in the Southwest.

The last interglacial period on the Pacific Coast of North America: Timing and paleoclimate

USGS Publications Warehouse

Muhs, D.R.; Simmons, K.R.; Kennedy, G.L.; Rockwell, T.K.

2002-01-01

New, high-precision U-series ages of solitary corals (Balanophyllia elegans) coupled with molluscan faunal data from marine terraces on the Pacific Coast of North America yield information about the timing and warmth of the last interglacial sea-level highstand. Balanophyllia elegans takes up U in isotopic equilibrium with seawater during growth and shortly after death. Corals from the second terrace on San Clemente Island (offshore southern California), the third terrace on Punta Banda (on the Pacific Coast of northern Baja California), and the Discovery Point Formation on Isla de Guadalupe (in the Pacific Ocean offshore Baja California) date to the peak of the last interglacial period and have U-series ages ranging from ca. 123 to 114 ka. The first terrace on Punta Banda has corals with ages ranging from ca. 83 to 80 ka, which corresponds to a sea-level highstand formed in the late last interglacial period. U-series analyses of corals from the Cayucos terrace (central California) and the Nestor terrace at Point Loma (southern California) show that these fossils have evidence of open-system history, similar to what has been reported by other workers for the same localities. Nevertheless, a model of continuous, secondary U and Th uptake shows that two ages of corals are likely present at these localities, representing the ca. 105 and ca. 120 ka sea-level highstands reported elsewhere. U-series ages of last interglacial corals from the Pacific Coast overlap with, but are on average younger than the ages of corals from Barbados, the Bahamas, and Hawaii. This age difference is explained by the nature of the geomorphic response to sea-level change: fringing or barrier reefs on low-latitude coastlines have an accretionary growth style that keeps pace with rising sea level, whether on a tectonically rising or stable coastline. In contrast, midlatitude, high-energy coastlines are sites of platform cutting during the early part of a sea-level high stand and terrace scouring and concomitant sediment and fossil deposition as sea level starts to recede. The youngest ages of corals from the Pacific Coast suggest that sea level was still relatively high at ca. 116 ka, which is not in agreement with other estimates of relatively large global ice volume at that time. Reliably dated, ca. 120 ka marine-terrace deposits on the Pacific Coast have fossil mollusks that indicate water temperatures as warm or warmer than at present. In contrast, ca. 80 ka marine deposits reported here and elsewhere have fossil mollusks indicating cooler-than-modern water temperatures. The presence of both ca. 105 ka and ca. 120 ka corals on the Nestor and Cayucos terraces explains a previously enigmatic mixture of warm-water and cool-water mollusks. At ca. 105 ka, a relatively high sea level with cool waters may have "captured" the terrace formed during the 120 ka sea-level highstand, in areas of low uplift rate. The inference of cooler-than-modern waters off the Pacific Coast of North America at ca. 80 ka and ca. 105 ka, based on marine-terrace faunas, does not agree with estimates of sea-surface temperatures derived from alkenone studies in the Santa Barbara Basin. However, cooler water temperatures at these times are in agreement with paleo-temperature estimates from planktonic foraminiferal data for the Santa Barbara Basin. All records, from central California to Baja California, whether from marine terraces or offshore cores, indicate at least seasonably warmer-than-modern waters during the peak of the last interglacial period at ca. 120 ka.

Dynamics of the earth magnetic field in the 10-75 kyr period comprising the Laschamp and Mono Lake excursions: New results from the French Chaîne des Puys in a global perspective

NASA Astrophysics Data System (ADS)

Laj, Carlo; Guillou, Hervé; Kissel, Catherine

2014-02-01

We report here on a new paleomagnetic (directions and intensities) and coupled K/Ar and 40Ar/39Ar analysis of 35 different flows, emplaced in the Chaîne des Puys during the 75 to 10 kyr interval, which contains the Mono Lake and Laschamp excursions. There is a remarkable agreement between the new set of absolute volcanic intensities and published sedimentary (GLOPIS-75) and cosmogenic (10Be and 36Cl) records. The Laschamp and Mono Lake excursions are clearly revealed by a very significant intensity drop at 41.2±1.6 ka and 34.2±1.2 ka respectively. The duration of the Laschamp excursion is ˜1500 yr and about 640 yr when the drop of paleointensity or the directional change are considered respectively. The intensity drop at the Mono Lake is twice as short. In the ˜7 ka interval separating the two excursions, the field intensity recovers to almost non-transitional values. The rate of decrease of the field intensity during these excursions attains 18 nT/yr for the Laschamp and even greater value (33 nT/yr) for the Mono Lake. This figure is, for the Laschamp excursion, similar to the present field intensity decrease in the last two centuries so that one may wonder whether such a high rate of change may be characteristic of an impending geomagnetic event (reversal or excursion). We suggest that the name Auckland excursion should be used for the present-day called Mono Lake.

Age of the Lava Creek supereruption and magma chamber assembly at Yellowstone based on 40Ar/39Ar and U-Pb dating of sanidine and zircon crystals

NASA Astrophysics Data System (ADS)

Vazquez, J. A.; Matthews, N. E.; Calvert, A. T.

2015-12-01

The last supereruption from the Yellowstone Plateau formed Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). Tephra from the eruption blanketed much of the western United States, and is a key Quaternary chronostratigraphic marker, in particular for dating deposition of mid-Pleistocene glacial and pluvial deposits in western North America. We performed 40Ar/39Ar dating of single sanidines to delimit eruption age, and ion microprobe U-Pb and trace-element analyses of crystal faces on single zircons to characterize magmatic evolution and date near-eruption crystallization, as well as analyses of crystal interiors to date the interval of zircon crystallization. Sanidines from the two LCT members A and B yield an 40Ar/39Ar isochron date of 631 ± 4 ka (2σ). Crystal faces on zircons from both members yield a weighted mean 206Pb/238U date of 627 ± 6 ka (2σ) and have trace element concentrations that vary with eruptive stratigraphy. Zircon interiors yield a weighted mean 206Pb/238U date of 660 ± 6 ka, and reveal reverse and/or oscillatory zoning of trace element concentrations, with many crystals containing high-U concentrations and dark cathodoluminescence (CL) cores. These crystals with high-U cores are possibly sourced from 'defrosting' of melt-impregnated margins of the growing subvolcanic reservoir. LCT sanidines mirror the variation of zircon composition within the eruptive stratigraphy, with crystals from upper LCT-A and basal LCT-B having bright-CL rims with high Ba concentrations, suggesting late crystallization after addition of less evolved silicic magma. The occurrence of distal LCT in stratigraphic sequences marking the Marine Isotope Stage 16-15 transition supports the apparent eruption age of ca. 631 ka. These results reveal that Lava Creek zircons record episodic heating, renewed crystallization, and an overall up-temperature evolution for Yellowstone's subvolcanic reservoir in the 103-104 year interval before eruption.

Deciphering the paleoseismic history of the central Dead Sea fault (Yammouneh fault, Lebanon) based on multiple luminescence dating techniques

NASA Astrophysics Data System (ADS)

Le Beon, M.; Tseng, Y. C.; Klinger, Y.; Elias, A.; Kunz, A.; Sursock, A.; Daeron, M.; Tapponnier, P.; Jomaa, R.

2017-12-01

The Yammouneh fault is the main strike-slip branch of the Dead Sea fault system in Lebanon. The morphology of the northern Yammouneh fault is characterized by a series of basins that represent archives for Late Pleistocene paleo-environments and paleo-earthquakes. We excavated a 4-m-deep trench across the fault in the Jbab el-Homr basin that revealed a succession of remarkable, very thin palustrine and lacustrine layers, ruptured by at least 17 earthquakes. Absolute ages of 4 samples from 0.5 to 3.7 m depth are obtained by optically stimulated luminescence dating on fine-grain quartz and on fine-grain K-feldspar using both infrared luminescence at 50˚C (IRSL50) and at a high temperature of 225˚C (pIRIR225). A fair agreement is obtained between the quartz ages (from 26.5 ± 3.1 ka at 0.5 m depth to 30.3 ± 3.4 ka at 3.7 m depth) and the pIRIR225 ages (from 26.2 ± 2.3 ka at 0.5 m depth to 25.8 ± 2.1 ka at 3.7 m depth), while the fading-corrected IRSL50 ages are systematically younger (from 18.3 ± 1.6 ka at 0.5 m depth to 21.4 ± 1.8 ka at 3.7 m depth). As proposed in earlier studies, we hypothesize that the IRSL50 fading rate is underestimated. The sedimentary sequence may reflect deposition in a marsh or shallow lake in a pro-glacial environment at a time when a glacier may have occupied the summits of Mount Lebanon. Erosion may have been dominant after the Last Glacial Maximum. Regarding paleo-earthquakes, 14 surface-rupturing events occurred during 3.8 ka with a mean return time of 270 years and probable clustering, while only 2-11 events occurred since 26.5 ka. Firstly, we explain the lack of events since 26.5 ka by the existence of another fault branch, which suggests that the active fault zone migrated with time. Secondly, the shorter mean recurrence time in Jbab compared to the Yammouneh site, located 30 km south may be explained by temporal variations in the earthquake cycle, different locations relative to fault segmentation, or by high-resolution of the stratigraphy in Jbab that allowed recording smaller-magnitude events that may have been missed in the thicker strata of Yammouneh.

Late Quaternary sedimentary features of Bear Lake, Utah and Idaho

USGS Publications Warehouse

Smoot, J.P.

2009-01-01

Bear Lake sediments were predominantly aragonite for most of the Holocene, reflecting a hydrologically closed lake fed by groundwater and small streams. During the late Pleistocene, the Bear River flowed into Bear Lake and the lake waters spilled back into the Bear River drainage. At that time, sediment deposition was dominated by siliciclastic sediment and calcite. Lake-level fluctuation during the Holocene and late Pleistocene produced three types of aragonite deposits in the central lake area that are differentiated primarily by grain size, sorting, and diatom assemblage. Lake-margin deposits during this period consisted of sandy deposits including well-developed shoreface deposits on margins adjacent to relatively steep gradient lake floors and thin, graded shell gravel on margins adjacent to very low gradient lake-floor areas. Throughout the period of aragonite deposition, episodic drops in lake level resulted in erosion of shallow-water deposits, which were redeposited into the deeper lake. These sediment-focusing episodes are recognized by mixing of different mineralogies and crystal habits and mixing of a range of diatom fauna into poorly sorted mud layers. Lake-level drops are also indicated by erosional gaps in the shallow-water records and the occurrence of shoreline deposits in areas now covered by as much as 30 m of water. Calcite precipitation occurred for a short interval of time during the Holocene in response to an influx of Bear River water ca. 8 ka. The Pleistocene sedimentary record of Bear Lake until ca. 18 ka is dominated by siliciclastic glacial fl our derived from glaciers in the Uinta Mountains. The Bear Lake deep-water siliciclastic deposits are thoroughly bioturbated, whereas shallow-water deposits transitional to deltas in the northern part of the basin are upward-coarsening sequences of laminated mud, silt, and sand. A major drop in lake level occurred ca. 18 ka, resulting in subaerial exposure of the lake floor in areas now covered by over 40 m of water. The subaerial surfaces are indicated by root casts and gypsum-rich soil features. Bear Lake remained at this low state with a minor transgression until ca. 15 ka. A new influx of Bear River water produced a major lake transgression and deposited a thin calcite deposit. Bear Lake quickly dropped to a shallow-water state, accumulating a mixture of calcite and siliciclastic sediment that contains at least two intervals of root-disrupted horizons indicating lake-level drops to more than 40 m below the modern highstand. About 11,500 yr B.P., the lake level rose again through an influx of Bear River water producing another thin calcite layer. The Bear River ceased to flow into the basin and the lake salinity increased, resulting in the aragonite deposition that persisted until modern human activity. The climatic record of Bear Lake sediment is difficult to ascertain by using standard chemical and biological techniques because of variations in the inflow hydrology and the significant amount of erosion and redeposition of chemical and biological sediment components. Copyright ?? 2009 The Geological Society of America.

New echocardiographic predictors of clinical outcome in patients presenting with heart failure and a preserved left ventricular ejection fraction: a subanalysis of the Ka (Karolinska) Ren (Rennes) Study.

PubMed

Donal, Erwan; Lund, Lars H; Oger, Emmanuel; Hage, Camilla; Persson, Hans; Reynaud, Amélie; Ennezat, Pierre-Vladimir; Bauer, Fabrice; Drouet, Elodie; Linde, Cecilia; Daubert, Claude

2015-07-01

To identify electrocardiographic and echocardiographic predictors of mortality and hospitalizations for heart failure (HF) in the KaRen study. KaRen is a prospective, observational study of the long-term outcomes of patients presenting with heart failure and a preserved ejection fraction (HFpEF). We identified 538 patients who presented with acute cardiac decompensation, a >100 pg/mL serum b-type natriuretic peptide (BNP) or >300 pg/mL N-terminal pro-brain natriuretic peptide (NT-proBNP) concentration and a left ventricular ejection fraction (LVEF) >45%. After 4-8 weeks of standard treatment, 413 patients (mean age = 76 ± 9 years, 55.9% women) returned for analyses of their clinical status, laboratory screen, and detailed electrocardiographic and Doppler echocardiographic recordings. They were followed for a mean of 28 months thereafter. The primary study endpoint was time to death from all causes or first hospitalization for heart failure. Mean LVEF was 62.4 ± 6.9% and median NT-proBNP 1410 pmol/L. PR interval >200 ms was present in 11.2% of patients and 14.9% had a >120 ms QRS duration, with left bundle branch block in only 6.3%. Over a mean follow-up of 28 months, 177 patients (42.9%) reached a primary study endpoint, including 61 deaths and 116 hospitalizations for heart failure. After adjustment for age, gender, New York Heart Association class, atrial fibrillation history, creatinine, sodium, BNP, ejection fraction, and right ventricular fractional shortening, only E/e' remained as a predictor, with a hazard ratio = 1.49 and P = 0.0012. The incidence of hospitalizations for HF and deaths in KaRen was high and E/e' predicted adverse clinical outcomes. These observations should help in the risk stratification and therapy of HFpEF. © 2015 The Authors. European Journal of Heart Failure © 2015 European Society of Cardiology.

Inverse stochastic-dynamic models for high-resolution Greenland ice core records

NASA Astrophysics Data System (ADS)

Boers, Niklas; Chekroun, Mickael D.; Liu, Honghu; Kondrashov, Dmitri; Rousseau, Denis-Didier; Svensson, Anders; Bigler, Matthias; Ghil, Michael

2017-12-01

Proxy records from Greenland ice cores have been studied for several decades, yet many open questions remain regarding the climate variability encoded therein. Here, we use a Bayesian framework for inferring inverse, stochastic-dynamic models from δ18O and dust records of unprecedented, subdecadal temporal resolution. The records stem from the North Greenland Ice Core Project (NGRIP), and we focus on the time interval 59-22 ka b2k. Our model reproduces the dynamical characteristics of both the δ18O and dust proxy records, including the millennial-scale Dansgaard-Oeschger variability, as well as statistical properties such as probability density functions, waiting times and power spectra, with no need for any external forcing. The crucial ingredients for capturing these properties are (i) high-resolution training data, (ii) cubic drift terms, (iii) nonlinear coupling terms between the δ18O and dust time series, and (iv) non-Markovian contributions that represent short-term memory effects.

Climate variability during the Holocene inferred from northeastern Iberian speleothems

NASA Astrophysics Data System (ADS)

Moreno, A.; Bartolomé, M.; Sancho, C.; Belmonte, Á.; Stoll, H.; Cacho, I.; Edwards, R. L.; Hellstrom, J.

2012-04-01

Although the general climate trends during the Holocene in the Iberian Peninsula have been well described after the study of marine and lacustrine records, many questions regarding the timing of some of the events together with the characterization of the higher-frequency climate variability are still poorly understood. New speleothem records from several caves in northeastern Iberia provide data to explore Holocene climate changes. The selected caves are located in a latitudinal transect from the Pyrenees to the Iberian Range and placed at different altitude. Two of them, 5 de Agosto and Pot au Feu, belong to the same karstic complex in Cotiella massif (Central Pyrenees, 1600 m asl). Seso Cave, also in the Central Pyrenees but at 781 m of altitude, and Molinos cave, a cavity very rich in speleothems located at 1040 m in the Iberian Range, complete the transect. Although in all the caves precipitation coming from Atlantic fronts dominates over the year, a significant Mediterranean influence, specially in summer months, is identified after rainfall monitoring. Speleothem formation during the Holocene occurred at a very low pace in 5 de Agosto cave (80yrs/mm) and increased dramatically at low-altitude caves and during particular periods proved to be wetter (eg. Early Holocene in Molinos cave, less than 10yr/mm). In Seso and Pot au Feu caves, up to seven studied speleothems only grew during short climatic events such as the Iron Cold Period (3000-2500 cal yr BP) or the Little Ice Age (1300-1850 yr AD) that, although cold, were particularly humid periods in northeastern Spain. First stable isotope results highlight the importance of comparing speleothems with similar growing rates and from the same cave to extract climate information and discard other influences. From the integration of four stalagmites from Molinos cave covering since the Holocene onset to 2000 cal yrs BP, the Early Holocene (11.7-8.5 ka BP) with d13C values between -11 and - 9‰ appears as the wetter interval. The highest isotopic values are reached during Middle Holocene (8.5-5.5 ka BP) while there is a tendency towards more negative values during Late Holocene (last 5000 yrs). The range of d18O values is low (about 2‰) but still lighter values during Early Holocene and heavier afterwards are well marked. Shorter events characterized by more negative d13C values are observed at 4 ka, 6 ka, 7.5 ka, 8.2, 8.7, 9.2, 10.3 ka and interpreted as cold but probably wetter periods with denser vegetation cover and soil development over the cave. However, changes in the source of precipitation (Atlantic vs Mediterranean) or the influence of fresh-water outbursts in North Atlantic can not be neglected.

Purge- and intensive-purge decontamination of dental units contaminated with biofilm

PubMed Central

Kramer, Axel; Assadian, Ojan; Bachfeld, Danny; Meyer, Georg

2012-01-01

Introduction: During hygienic-microbiological monitoring of the water quality in dental units, the total bacterial colony count was found to exceed the limits for drinking water quality; in addition, mold contamination was detected. The presumed cause was irregular decontamination of the units through purging and intensive decontamination. Methods: To decontaminate the units, the manufacturer’s recommended program for cleaning and intensive decontamination was intensified by shortened intervals over a 2-week period. For Sirona units, instead of once a day, the automatic purge program was run every morning and evening for 20 min each time, and instead of once a month, intensive decontamination was performed every two weeks; this schedule has been maintained since then. For KaVo units, cleaning with the hydroclean function was carried out for 2.5 min every morning and evening. The automatic intensive decontamination was run daily instead of weekly. A maintenance log book was introduced, in which decontamination/cleaning was confirmed by the operator’s signature. Results: Within 5 weeks, all previously contaminated units were decontaminated. Discussion: By shortening the cleaning and intensive decontamination intervals in a 2-week period with subsequent control that the recommended maintenance intervals were kept, it was possible to guarantee drinking-water quality in the dental units of both manufacturers. PMID:22558045

Long-Term ENSO Variation Over the Last 20,000 Years From the Peru Continental Margin

NASA Astrophysics Data System (ADS)

Skilbeck, G.; Fink, D.; Gagan, M.; Rein, B.

2006-12-01

Three ODP Leg 201 cores from the Peru continental margin comprise highly laminated diatomaceous ooze spanning Last Glacial Maximum to present. Geochemical proxy data, layer counting and spectral analysis of red color variation suggest the layers represent interannual accumulation under the influence tropical ENSO conditions, with darker layers representing El Niño events. AMS 14-C dating (Skilbeck &Fink, 2006) of bulk sediment from Sites 201-1228 and -1229 (~11°S) and comparison with Rein et al. (2005) Core SO147-106KL (~12°S) show that where the shelf is narrow south of ~10.5°S, regionally consistent rates of sediment accumulation have occurred over the late Deglaciation and Holocene, with high rates characterising the late (0-2.0 kyrBP, ~100 cm/ka) and the early (8.5-10 kyrBP, ~80 cm/ka) Holocene. Over these intervals laminae are of interannual resolution. Further north where the shelf is broader, Holocene-Late Deglaciation sediments are thin or absent, but the Early Deglaciation is well represented. In a core from ODP Site 201-1227 (~9°S, 427m water depth), the period 15.5-17.5 kyrBP is characterised by sediment accumulation rates in excess of 300 cm/ka, and interannual laminations are again present. Spectral analysis of the instrumental record of ENSO, the SOI, shows a relative stable mode of variation with an average frequency of about 5.5 yr for the past 130 years. Analysis of our ODP cores shows that the ENSO mode appears to be relatively stable for periods of 300-500 years throughout the Holocene with frequencies varying mostly between 5 and 8 years and relatively sudden mode switches, suggesting inter alia that the instrumental record is not long enough to test predictive models of ENSO variation. Throughout the Holocene, this pattern of variation transcends the sedimentation-rate zones identified above, with the inference that changes in the rate of sedimentation have not influenced the temporal pattern. The later part of the deglaciation period (10-14 kyrBP) appears to be a relatively long period of stable ENSO with a repeat frequency between 5 and 6 years. Layer variation over the interval between 14 to 15.5 yrBP loses interannual variability and is characterised by a dominant frequency of ~11-12 yr, but this may simply reflect the low sedimentation rate during this interval. During Early Deglaciation interannual- to decadal-scale layer variability is present, with over 600 discernable laminae recognisable across the ~1600 year interval represented in Core 210-1227B. ENSO during this time has multiple interannual frequency modes ranging between 4 and 10 yr, particularly over the interval 17.2- 16.2 kyrBP, with mode switches slightly more frequent than during the Holocene at between 200 and 300 years. In addition to the interannual laminations and the centennial-scale pattern of frequency mode variation described above, there is a regular oscillatory pattern in the contrast between dark and light laminations which can be traced to parasequence-like packets of laminations on a centimetre scale, and representing variability in the decadal to centennial range. References Rein, B., A. Luckge, et al. (2005). Paleoceanography 20(PA4003): 17p. Skilbeck, C.G. &D. Fink (2005). ODP Scientific Results 201.

Geology of the peralkaline volcano at Pantelleria, Strait of Sicily

USGS Publications Warehouse

Mahood, G.A.; Hildreth, W.

1986-01-01

Situated in a submerged continental rift, Pantelleria is a volcanic island with a subaerial eruptive history longer than 300 Ka. Its eruptive behavior, edifice morphologies, and complex, multiunit geologic history are representative of strongly peralkaline centers. It is dominated by the 6-km-wide Cinque Denti caldera, which formed ca. 45 Ka ago during eruption of the Green Tuff, a strongly rheomorphic unit zoned from pantellerite to trachyte and consisting of falls, surges, and pyroclastic flows. Soon after collapse, trachyte lava flows from an intracaldera central vent built a broad cone that compensated isostatically for the volume of the caldera and nearly filled it. Progressive chemical evolution of the chamber between 45 and 18 Ka ago is recorded in the increasing peralkalinity of the youngest lava of the intracaldera trachyte cone and the few lavas erupted northwest of the caldera. Beginning about 18 Ka ago, inflation of the chamber opened old ring fractures and new radial fractures, along which recently differentiated pantellerite constructed more than 25 pumice cones and shields. Continued uplift raised the northwest half of the intracaldera trachyte cone 275 m, creating the island's present summit, Montagna Grande, by trapdoor uplift. Pantellerite erupted along the trapdoor faults and their hingeline, forming numerous pumice cones and agglutinate sheets as well as five lava domes. Degassing and drawdown of the upper pantelleritic part of a compositionally and thermally stratified magma chamber during this 18-3-Ka episode led to entrainment of subjacent, crystal-rich, pantelleritic trachyte magma as crenulate inclusions. Progressive mixing between host and inclusions resulted in a secular decrease in the degree of evolution of the 0.82 km3 of magma erupted during the episode. The 45-Ka-old caldera is nested within the La Vecchia caldera, which is thought to have formed around 114 Ka ago. This older caldera was filled by three widespread welded units erupted 106, 94, and 79 Ka ago. Reactivation of the ring fracture ca. 67 Ka ago is indicated by venting of a large pantellerite centero and a chain of small shields along the ring fault. For each of the two nested calderas, the onset of postcaldera ring-fracture volcanism coincides with a low stand of sea level. Rates of chemical regeneration within the chamber are rapid, the 3% crystallization/Ka of the post-Green Tuff period being typical. Highly evolved pantellerites are rare, however, because intervals between major eruptions (averaging 13-6 Ka during the last 190 Ka) are short. Benmoreites and mugearites are entirely lacking. Fe-Ti-rich alkalic basalts have erupted peripherally along NW-trending lineaments parallel to the enclosing rift but not within the nested calderas, suggesting that felsic magma persists beneath them. The most recent basaltic eruption (in 1891) took place 4 km northwest of Pantelleria, manifesting the long-term northwestward migration of the volcanic focus. These strongly differentiated basalts reflect low-pressure fractional crystallization of partial melts of garnet peridotite that coalesce in small magma reservoirs replenished only infrequently in this continental rift environment. ?? 1986 Springer-Verlag.

Evidence for a new geomagnetic reversal from lava flows in Idaho: discussion of short polarity reversals in the Brunhes and late Matuyama Polarity Chrons

USGS Publications Warehouse

Champion, D.E.; Lanphere, M.A.; Kuntz, M.A.

1988-01-01

K-Ar ages and paleomagnetic data for basalt samples from a new core hole (site E) at the Idaho National Engineering Laboratory (INEL) indicate that the age of the reversed polarity event recorded in Snake River Plain lavas is older than 465 ?? 50 ka (1000 years before present) reported previously by Champion et al. (1981). A review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the Brunhes and two besides the Jaramillo in the late Matuyama. These 10 short subchrons begin to indicate the many short events that Cox (1968) hypothesized must exist if polarity interval lengths have a Poisson distribution. The mean sustained polarity interval length since late Matuyama Chron time is 90 000 years. The similarity of this number with the 105-year period of the Earth's orbital eccentricity suggests anew that linkage between geomagnetic, paleoclimatic, and possible underlying Earth orbital parameters should be evaluated. -from Authors

Late Pleistocene eruptive history of the Mono Craters rhyolites, eastern California, from U-Th dating of explosive and effusive products

NASA Astrophysics Data System (ADS)

Marcaida, M.; Vazquez, J. A.; Calvert, A. T.; Miller, J. S.

2016-12-01

During late Pleistocene-Holocene time, repeated explosive and effusive eruptions of high-silica rhyolite magma south of Mono Lake, California, have produced a chain of massive domes known as the Mono Craters and a time-series of tephra deposits preserved in sediments of the Wilson Creek formation of ancestral Mono Lake. The record of late Holocene volcanism at Mono Craters is relatively well constrained by tephrostratigraphy and 14C dating, and the timing of late Pleistocene eruptions is similarly well constrained by tephrochronology and magnetostratigraphy of the Wilson Creek formation. However, the chronology of eruptions for the Mono Craters chain, comprising at least 28 individual domes, has thus far been based on age estimates from hydration rind dating of obsidian that is highly dependent on local calibration. We constrain the timing of late Pleistocene dome emplacement by linking independently dated Wilson Creek tephras to their dome equivalents in the Mono Craters using combined titanomagnetite geochemistry and U-Th geochronology. Ion microprobe 238U-230Th dating of unpolished allanite and zircon rims gives isochron dates of ca. 42 ka, ca. 38 ka, ca. 26 ka, and ca. 20 ka for domes 19, 24, 31 (newly recognized), and 11 of the Mono Craters, respectively. These domes are biotite-bearing rhyolites with titanomagnetites that are compositionally identical to those from several Wilson Creek tephras. Specifically, we correlate Ash 15, Ash 7, and Ash 3 of the Wilson Creek formation to domes 19, 31, and 11 of the Mono Craters, respectively, based on matching titanomagnetite compositions and indistinguishable U-Th ages. 40Ar/39Ar dating of single sanidines from domes 19 and 31 yield mean dates that are 10 k.y. older than their corresponding U-Th dates, likely due to excess argon from melt inclusions and/or incompletely re-equilibrated antecrysts. Based on our new U-Th isochron date of ca. 34 ka for allanite-zircon from Ash 8 pumice and the ca. 26-27 ka age of Ash 7 and its extrusive equivalent dome 31, we infer that the stratigraphic position of the ca. 32 ka Auckland/Mono Lake geomagnetic excursion, if recorded in beds of the Wilson Creek formation, is between Ashes 7 and 8. Accordingly, the prominent geomagnetic excursion bisected by Ash 15 lower in the section is the ca. 41 ka global Laschamp event.

Concordant ages for the Lava Creek Tuff from high-spatial-resolution U-Pb dating of zircon rim faces and single-crystal sanidine 40Ar/39Ar dating

NASA Astrophysics Data System (ADS)

Matthews, N. E.; Vazquez, J. A.; Calvert, A. T.

2013-12-01

The last great explosive supereruption from the Yellowstone Plateau formed present-day Yellowstone caldera and ejected the >1000 km3 of rhyolite that composes the Lava Creek Tuff (LCT). The LCT eruption blanketed much of the western United States in ash, and consequently is a key chronostratigraphic marker bed for delimiting Quaternary uplift rates, the age of middle Pleistocene glacial and pluvial deposits, and tephra correlation in North America. Previous 40Ar/39Ar dating of the two mineralogically distinct LCT members (A & B) yield ages ranging from ca. 600 ka (Gansecki et al., 1998) to ca. 640 ka (Lanphere et al., 2002). To resolve the timing of eruption and crystallization timescale for the LCT magma, we dated both LCT members using a dual-method approach as follows: (1) ion microprobe (SHRIMP-RG) U-Pb dating and trace-element characterization of the final few micrometers of zircon crystallization by analysis of unpolished rims on indium-mounted crystals, and dating of the onset of zircon crystallization by traditional analysis of sectioned crystal interiors, and (2) laser-fusion 40Ar/39Ar dating of single sanidine crystals from bulk LCT ignimbrite and pumice. The unpolished rims of zircon from LCT members A & B yield indistinguishable ages, with a mean age of 621.8 × 2.5 ka (1σ) after correction for initial 230Th disequilibrium as constrained by ion-probe analyses of LCT melt inclusions. Single sanidine crystals from LCT-B yield a mean age of 624.9 × 2.6 ka (FCT=28.17 Ma) that is indistinguishable from the zircon rim ages for both members. These results indicate that LCT members A & B erupted over a geologically brief interval, which is supported by the direct and gradational contact of their equivalent fallout in distal lacustrine deposits and a lack of field evidence for a significant time-break between the LCT A & B in proximal deposits (Christiansen, 2001), but contrasts with older Yellowstone ignimbrite (e.g., Huckleberry Ridge) that may have erupted as multiple pulses over tens of kyr (Ellis et al., 2012). Both LCT members contain zircon whose interiors yield U-Pb ages that are mostly ca. 40 kyr older than their rims, suggesting a short timescale for assembly of the LCT magma chamber relative to some other voluminous bodies of silicic magma (e.g., Fish Canyon). Trace-element concentrations in zircon from Members A and B appear diagnostic, with the former containing higher U and REE concentrations. Our concordant results from U-Pb and 40Ar/39Ar dating indicating a ca. 625 ka age for the LCT eruption are supported by the stratigraphic position of LCT-B tephra at or near the top of Great Basin pluvial lake bed sequences associated with Marine Isotope Stage 16, whose termination is astronomically dated at 621 ka. Christiansen, 2001, USGS Prof. Pap. 729-G; Ellis et al., 2012, Quat Geochron 9: 31-41; Gansecki et al., 1998, Geology 26(4): 343-346; Lanphere et al., 2002, GSA Bull. 114(5): 559-568.

Progressive glacial retreat in the Southern Altiplano (Uturuncu volcano, 22°S) between 65 and 14 ka constrained by cosmogenic 3He dating

NASA Astrophysics Data System (ADS)

Blard, Pierre-Henri; Lave, Jérôme; Farley, Kenneth A.; Ramirez, Victor; Jimenez, Nestor; Martin, Léo C. P.; Charreau, Julien; Tibari, Bouchaïb; Fornari, Michel

2014-07-01

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65 ka, with an equilibrium line altitude (ELA) at 5280 m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at 5350 m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450 m after 14 ka, synchronously with the Bolling-Allerod.

Holocene fire activity and vegetation response in South-Eastern Iberia

NASA Astrophysics Data System (ADS)

Gil-Romera, Graciela; Carrión, José S.; Pausas, Juli G.; Sevilla-Callejo, Miguel; Lamb, Henry F.; Fernández, Santiago; Burjachs, Francesc

2010-05-01

Since fire has been recognized as an essential disturbance in Mediterranean landscapes, the study of long-term fire ecology has developed rapidly. We have reconstructed a sequence of vegetation dynamics and fire changes across south-eastern Iberia by coupling records of climate, fire, vegetation and human activities. We calculated fire activity anomalies (FAAs) in relation to 3 ka cal BP for 10-8 ka cal BP, 6 ka cal BP, 4 ka cal BP and the present. For most of the Early to the Mid-Holocene uneven, but low fire events were the main vegetation driver at high altitudes where broadleaved and coniferous trees presented a highly dynamic post-fire response. At mid-altitudes in the mainland Segura Mountains, fire activity remained relatively stable, at similar levels to recent times. We hypothesize that coastal areas, both mountains and lowlands, were more fire-prone landscapes as biomass was more likely to have accumulated than in the inland regions, triggering regular fire events. The wet and warm phase towards the Mid-Holocene (between ca 8 and 6 ka cal BP) affected the whole region and promoted the spread of mesophytic forest co-existing with Pinus, as FAAs appear strongly negative at 6 ka cal BP, with a less important role of fire. Mid and Late Holocene landscapes were shaped by an increasing aridity trend and the rise of human occupation, especially in the coastal mountains where forest disappeared from ca 2 ka cal BP. Mediterranean-type vegetation (evergreen oaks and Pinus pinaster- halepensis types) showed the fastest post-fire vegetation dynamics over time.

Holocene deglacial history of the northeast Antarctic Peninsula - A review and new chronological constraints

NASA Astrophysics Data System (ADS)

Johnson, Joanne S.; Bentley, Michael J.; Roberts, Stephen J.; Binnie, Steven A.; Freeman, Stewart P. H. T.

2011-12-01

The northeast Antarctic Peninsula (NEAP) region is currently showing signs of significant environmental change, evidenced by acceleration of glacial retreat and collapse of both Larsen-A and -B ice shelves within the past 15 years. However, data on the past extent of the eastern margin of the Antarctic Peninsula Ice Sheet (APIS) and its Holocene retreat history are sparse, and hence we cannot yet put the recent changes into a long-term context. In order to investigate the timing of deglaciation, we present 16 new cosmogenic 10Be surface exposure ages from sites on northern James Ross Island (Cape Lachman, Johnson Mesa and Terrapin Hill) and Seymour Island. The majority of the ages cluster around 6-10 ka, with three significantly older (25-31 ka). We combine these ages with existing terrestrial and marine radiocarbon deglaciation ages, and a compilation of existing swath bathymetry data, to quantify the temporal and spatial character of the regional glacial history. Ice had begun to retreat from the outer shelf by 18.3 ka, reaching Seymour Island by ˜8 ka. Northern James Ross Island began to deglaciate around the time of the Early Holocene Climatic Optimum (c. 11-9.5 ka). Deglaciation continued, and a transition from grounded to floating ice in Prince Gustav Channel occurred around 8 ka, separating the James Ross Island ice cap from the APIS. This occurred shortly before Prince Gustav Channel ice shelf began to disintegrate at 6.2 ka. Our results suggest there may be a bathymetric control on the spatial pattern of deglaciation in the NEAP.

Recent and Holocene Climate Change Controls on Vegetation and Carbon Accumulation in Alaskan Coastal Muskegs

NASA Technical Reports Server (NTRS)

Peteet, Dorothy M.; Nichols, Jonathan E.; Moy, Christopher M.; McGeachy, Alicia; Perez, Max

2015-01-01

Pollen, spore, macrofossil and carbon data from a peatland near Cordova, Alaska, reveal insights into the climate-vegetation-carbon interactions from the initiation of the Holocene, c. the last 11.5 ka, to the present (1 ka = 1000 calibrated years before present where 0 = 1950 CE). The Holocene period is characterized by early deposition of gyttja in a pond environment with aquatics such as Nuphar polysepalum and Potamogeton, and a significant regional presence of Alnus crispa subsp. sinuata. Carbon accumulation (50 g/m2/a) was high for a short interval in the early Holocene when Sphagnum peat accumulated, but was followed by a major decline to 13 g/m2/a from 7 to 3.7 ka when Cyperaceae and ericads such as Rhododendron (formerly Ledum) groenlandicum expanded. This shift to sedge growth is representative of many peatlands throughout the south-central region of Alaska, and indicates a drier, more evaporative environment with a large decline in carbon storage. The subsequent return to Sphagnum peat after 4 ka in the Neoglacial represents a widespread shift to moister, cooler conditions, which favored a resurgence of ericads, such as Andromeda polifolia, and increased carbon accumulation rate. The sustained Alnus expansion visible in the top 10 cm of the peat profile is correlative with glacial retreat and warming of the region in the last century, and suggests this colonization will continue as temperature increases and ice melts.

Obliquity-driven expansion of North Atlantic sea ice controls structure of the last glacial

NASA Astrophysics Data System (ADS)

Turney, Chris; Thomas, Zoe; Hutchinson, David; Bradshaw, Corey; Brook, Barry; England, Matthew; Fogwill, Christopher; Jones, Richard; Palmer, Jonathan; Hughen, Konrad; Cooper, Alan

2015-04-01

North Atlantic late-Pleistocene climate was characterised by a series of abrupt climate changes, the most extreme of which were the Dansgaard-Oeschger (D-O) events; millennial-scale oscillations that switched rapidly between cold and warm atmospheric conditions of up to Δ16°C, most strongly expressed during the period 60-30 ka. Time series analysis of palaeoclimate ice core records is one of the best ways to detect threshold behaviour in the climate system; however, some of these techniques can be age model dependent. Spectral analysis of a new Greenland-Cariaco GICC05 age model (GICC05-CB), generated by combining the GICC05 and Cariaco ∂18O chronologies, reveals a change in the dominant periodicities at ~31 ka, consistent with the cessation of the D-O events. While the GICC05-CB has the same ∂18O structure as GICC05, the different periodicity profile reveals a change in the climate system at 31 ka. Stability analysis of the ∂18O time series over the last 60 ka determines the number of states the climate experienced over time, and reveals a bifurcation in the climate system at 31 ka, switching from a bistable to a monostable state. Early warning signals of this bifurcation are also detected starting 10,000 years before the shift in the form of increasing autocorrelation and variance. This is consistent with the climate system experiencing a slow forcing towards a critical threshold. These signals are found in both the GICC05-CB and GICC05 chronologies, though the timing of the bifurcation point varies slightly. We suggest that this bifurcation is linked to a minima in obliquity, causing greatly expanded sea ice in the Labrador sea. Modelling runs from the CSIRO Mk3L Earth-system model indicates that extensive sea ice cover is established in the Labrador Sea and North Pacific at the obliquity minima centred on 28.5 ka. This expanded sea ice is thus responsible for shifting the Northern Hemisphere westerlies southwards and reducing the strength of the AMOC, preventing the establishment of the cold state from 31 ka.

Was millennial scale climate change during the Last Glacial triggered by explosive volcanism?

PubMed Central

Baldini, James U.L.; Brown, Richard J.; McElwaine, Jim N.

2015-01-01

The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal. Here we show that all eight known radiometrically-dated Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling (>95% confidence). Additionally, previous research reported a strong statistical correlation between the timing of Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99% confidence), but did not identify a causative mechanism. Volcanic aerosol-induced asymmetrical hemispheric cooling over the last few hundred years restructured atmospheric circulation in a similar fashion as that associated with Last Glacial millennial-scale shifts (albeit on a smaller scale). We hypothesise that following both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the stratosphere cooled the NH preferentially, inducing a hemispheric temperature asymmetry that shifted atmospheric circulation cells southward. This resulted in Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during the Last Glacial, the initial eruption-induced climate response was prolonged by NH glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling, and a consequent positive feedback. Conversely, preferential SH cooling following large SH eruptions shifted atmospheric circulation to the north, resulting in the characteristic features of DO events. PMID:26616338

Was millennial scale climate change during the Last Glacial triggered by explosive volcanism?

PubMed

Baldini, James U L; Brown, Richard J; McElwaine, Jim N

2015-11-30

The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal. Here we show that all eight known radiometrically-dated Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling (>95% confidence). Additionally, previous research reported a strong statistical correlation between the timing of Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99% confidence), but did not identify a causative mechanism. Volcanic aerosol-induced asymmetrical hemispheric cooling over the last few hundred years restructured atmospheric circulation in a similar fashion as that associated with Last Glacial millennial-scale shifts (albeit on a smaller scale). We hypothesise that following both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the stratosphere cooled the NH preferentially, inducing a hemispheric temperature asymmetry that shifted atmospheric circulation cells southward. This resulted in Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during the Last Glacial, the initial eruption-induced climate response was prolonged by NH glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling, and a consequent positive feedback. Conversely, preferential SH cooling following large SH eruptions shifted atmospheric circulation to the north, resulting in the characteristic features of DO events.

Measurement of time processing ability and daily time management in children with disabilities.

PubMed

Janeslätt, Gunnel; Granlund, Mats; Kottorp, Anders

2009-01-01

Improvement is needed in methods for planning and evaluating interventions designed to facilitate daily time management for children with intellectual disability, Asperger syndrome, or other developmental disorders. The aim of this study was to empirically investigate the hypothesized relation between children's time processing ability (TPA), daily time management, and self-rated autonomy. Such a relationship between daily time management and TPA may support the idea that TPA is important for daily time management and that children with difficulties in TPA might benefit from intervention aimed at improving daily time management. Participants were children aged 6 to 11 years with dysfunctions such as attention-deficit/hyperactivity disorder, autism, or physical or intellectual disabilities (N = 118). TPA was measured with the instrument KaTid. All data were transformed to interval measures using applications of Rasch models and then further analysed with correlation and regression analysis. The results demonstrate a moderate significant relation between the parents' ratings of daily time management and TPA of the children, and between the self-rating of autonomy and TPA. There was also a significant relation between self-ratings of autonomy and the parents' rating of the children's daily time management. Parents' ratings of their children's daily time management explain 25% of the variation in TPA, age of the children explains 22%, while the child's self-rating of autonomy can explain 9% of the variation in TPA. The three variables together explain 38% of the variation in TPA. The results indicate the viability of the instrument for assessing TPA also in children with disabilities and that the ability measured by KaTid is relevant for daily time management. TPA seems to be a factor for children's daily time management that needs to be taken into consideration when planning and evaluating interventions designed to facilitate everyday functioning for children with cognitive impairments. The findings add to the increasing knowledge base about children with time processing difficulties and contribute to better methods aimed at improving these children's daily time management. Further research is needed to examine if there are differences in TPA related to specific diagnosis or other child characteristics.

Glacial flour in lacustrine sediments: Records of alpine glaciation in the western U.S.A. during the last glacial interval

NASA Astrophysics Data System (ADS)

Rosenbaum, J. G.; Reynolds, R. L.

2010-12-01

Sediments in Bear Lake (UT/ID) and Upper Klamath Lake (OR) contain glacial flour derived during the last glacial interval from the Uinta Mountains and the southern Cascade Range, respectively. Magnetic properties provide measures of glacial-flour content and, in concert with elemental and grain-size analyses, yield high-resolution records of glacial growth and decay. Creation and preservation of such records requires that (1) properties of glacial flour contrast with those of other sedimentary components and (2) magnetic minerals are neither formed nor destroyed after deposition. In the Bear Lake watershed, glaciers were confined to a small headwater area of the Bear River underlain by hematite-rich rocks of the Uinta Mountain Group (UMG), which are not exposed elsewhere in the catchment. Because UMG detritus is abundant only in Bear Lake sediments of glacial age, hard isothermal remanent magnetization (a measure of hematite content) provides a proxy for glacial flour. In contrast, the entire Upper Klamath Lake catchment, which lies to the east of the Cascade Range in southern Oregon, is underlain largely by basalt and basaltic andesite. Magnetic properties of fresh titanomagnetite-rich rock flour from glaciers on a composite volcano contrast sharply with those of detritus from unglaciated areas in which weathering destroyed some of the titanomagnetite. Ideally, well-dated records of the flux of glacial flour can be compared to ages of glacial features (e.g., moraines). For Upper Klamath Lake, quantitative measures of rock-flour content (from magnetic properties) and excellent chronology allow accurate calculation of flux. However, ages of glacial features are lacking and mafic volcanic rocks, which weather rapidly in this environment, are not well suited for cosmogenic exposure dating. At Bear Lake, estimates of glacial-flour content are less quantitative and chronology within the glacial interval must be interpolated from radiocarbon ages above and below the glacial-age sediments, but cosmogenic dating (by Laabs et al.) of highly resistant quartzite boulders provide ages from terminal moraines in the Bear River drainage. Glacial flour appears abruptly at ~26 cal ka in Bear Lake, whereas it is present at the base of the Upper Klamath Lake core (~37 cal ka). Both glacial flour records (1) contain millennial-scale variations (uncertainties in chronology prevent precise correlation of these features), (2) attain maxima circa 19 cal ka, and (3) rapidly decline beginning prior to 18 cal ka. At Bear Lake the age of the decline in glacial flour coincides with cosmogenic exposure ages (18.1 - 18.7 ka) of terminal moraines in the upper Bear River valley. This concurrence supports the interpretation that the maximum amount and subsequent decrease in glacial flour are indicative of maximum glacial extent and glacial retreat, respectively, and more generally that increases and decreases in rock flour in these lake sediments represent waxing and waning of glaciers. Laabs, B,J.C., et al., 2007, Chronology of the last glacial maximum in the upper Bear River basin, Utah, Arctic and Alpine Research, v. 39, p. 537 - 548.

Pre-Flight Testing and Performance of a Ka-Band Software Defined Radio

NASA Technical Reports Server (NTRS)

Downey, Joseph A.; Reinhart, Richard C.; Kacpura, Thomas

2012-01-01

National Aeronautics and Space Administration (NASA) has developed a space-qualified, reprogrammable, Ka-band Software Defined Radio (SDR) to be utilized as part of an on-orbit, reconfigurable testbed. The testbed will operate on the truss of the International Space Station beginning in late 2012. Three unique SDRs comprise the testbed, and each radio is compliant to the Space Telecommunications Radio System (STRS) Architecture Standard. The testbed provides NASA, industry, other Government agencies, and academic partners the opportunity to develop communications, navigation, and networking applications in the laboratory and space environment, while at the same time advancing SDR technology, reducing risk, and enabling future mission capability. Designed and built by Harris Corporation, the Ka-band SDR is NASA's first space-qualified Ka-band SDR transceiver. The Harris SDR will also mark the first NASA user of the Ka-band capabilities of the Tracking Data and Relay Satellite System (TDRSS) for on-orbit operations. This paper describes the testbed's Ka-band System, including the SDR, travelling wave tube amplifier (TWTA), and antenna system. The reconfigurable aspects of the system enabled by SDR technology are discussed and the Ka-band system performance is presented as measured during extensive pre-flight testing.

Ka Band Objects: Observation and Monitoring (KaBOOM)

NASA Astrophysics Data System (ADS)

Geldzahler, B.

2012-09-01

NASA has embarked on a path that will enable the implementation of a high power, high resolution X/Ka band radar system using widely spaced 12m antennas to better track and characterize near Earth objects and orbital debris. This radar system also has applications for cost effective space situational awareness. We shall demonstrate Ka band coherent uplink arraying with real-time atmospheric compensation using three 12m antennas at the Kennedy Space Center (KSC). Our proposed radar system can complement and supplement the activities of the Space Fence. The proposed radar array has the advantages of filling the gap between dusk and dawn and offers the possibility of high range resolution (4 cm) and high spatial resolution (?10 cm at GEO) when used in a VLBI mode. KSC was chosen because [a] of reduced implementation costs, [b] there is a lot of water vapor in the air (not Ka band friendly), and [c] the test satellites have a low elevation adding more attenuation and turbulence to the demonstration. If Ka band coherent uplink arraying can be made to work at KSC, it will work anywhere. We expect to rebaseline X-band in 2013, and demonstrate Ka band uplink arraying in 2014.

Inorganic geochemical indicators of glacial-interglacial changes in productivity and anoxia on the California continental margin

USGS Publications Warehouse

Dean, W.E.; Gardner, J.V.; Piper, D.Z.

1997-01-01

Evidence from sediments in cores collected from within the present oxygen-minimum zone (OMZ; 600-1200 m) on the central and northern California margins record several episodes during the last interstadial (OIS-3, ca. 60-24 ka) of deposition of laminated sediments containing elevated concentrations of several trace elements indicative of anoxic conditions (e.g., Mo, Ni, Zn, and Cu). The presence of abundant well-preserved organic matter, as well as lack of bioturbation and the presence of elevated concentrations of Mo and other trace elements, all support the theory that the OMZ in the northeastern Pacific Ocean was more intense, possibly anoxic, at several times during the late Pleistocene. Sediments of all ages in cores from the southern California margin contain elevated concentrations of Mo, suggesting that this area has always had higher rates of sulfate reduction than either the central or northern California areas. Most of the Ba in sediments in all cores collected on the upper continental slope (200-2700 m) off California and southern Oregon is derived from detrital clastic material, and this source did not change much in time. However, the amount of biogenic Ba did vary with time, and these variations closely follow the temporal variations in organic C (Corg) mass accumulation rate. Using Ba and Corg mass accumulation rates as proxy variables for productivity, all cores show that organic productivity under the California Current upwelling system was highest during OIS-3 and the Holocene, and lowest during the last glacial interval (LGI, ca. 24-10 ka). All paleoproductivity proxy variables indicate that the southern California area has always experienced higher productivity than other areas under the California Current, at least over the last 50 ky. Copyright ?? 1997 Elsevier Science Ltd.

Anthropogenic-enhanced erosion following the Neolithic Revolution in the Southern Levant: Records from the Dead Sea deep drilling core

NASA Astrophysics Data System (ADS)

Lu, Yin; Waldmann, Nicolas; Nadel, Dani; Marco, Shmuel

2017-04-01

In addition to tectonics and climatic changes, humans have exerted a significant impact on surface erosion over timescales ranging from years to centuries. However, such kind of impact over millennial timescales remains unsubstantiated. The Dead Sea drainage basin offers a rare combination of well-documented substantial climate change, intense tectonics and abundant archaeological evidence for past human activity in the Southern Levant. It serves as a natural laboratory for understanding how sedimentation rates in a deep basin are related to climate change, tectonics, and anthropogenic impacts on the landscape. Here we show how basin-wide erosion rates are recorded by thicknesses of rhythmic detritus laminae and clastic sediment accumulation rates in a long core retrieved by the Dead Sea Deep Drilling Project in the Dead Sea depocenter. During the last 11.5 kyr the average detrital accumulation rate is 3-4 times that during the last two glacial cycles (MIS 7c-2), and the average thickness of detritus laminae in the last 11.6 kyr is 4.5 times that between 21.7 and 11.6 ka, implying an increased erosion rate on the surrounding slopes during the Holocene. We estimate that this intensified erosion is incompatible with tectonic and climatic regimes during the corresponding time interval and further propose a close association with the Neolithic Revolution in the Levant (beginning at 11.5 ka). We thus suggest that human impact on the landscape was the primary driver causing the intensified erosion and that the Dead Sea sedimentary record serves as a reliable recorder of this impact since the Neolithic Revolution.

Paleoceanographic history of the Lower Bengal Fan during the last glacial cycle - IODP Expedition 354

NASA Astrophysics Data System (ADS)

Dekens, P. S.; Weber, M. E.; Lantzsch, H.; Das, S. K.; Williams, T.; Adhikari, R. R.; Jia, G.; Fox, L. R.; Ge, J.; Manoj, M. C.; Savian, J. F.; Reilly, B. T.; Selkin, P. A.; Meynadier, L.; Spiess, V.; France-Lanord, C.; Sharma, B.

2015-12-01

IODP Expedition 354 drilled a ~320 km long transect of seven sites on the Lower Bengal Fan at 8o N in the Northern Indian Ocean. The sediments cores recovered record a complex relationship between turbiditic and hemipelagic environments. This variability offers a unique opportunity to link our understanding of tectonic and terrestrial processes with climate and oceanography. With the exception the westernmost Site U1454, all sites show a several meter thick, hemipelagic top layer, usually representing Late Quaternary sediment. We present physical, geochemical and stable isotopic properties of this interval to establish a time frame and assess the paleoceanographic development of the region during the last glacial cycle. We sampled Site U1452C-1H continuously for the uppermost 480 cm of hemipelagic sediment in 2-cm increments. Preliminary results indicate the Toba Ash 1 (0.74 ka) is a distinct time marker in all physical properties. Furthermore, wet-bulk density as well as color reflectance b* (the red-green component) and L* (the lightness) show a dominant precession cyclicity. Hence, we are able to provide an insolation-tuned chronology for the last 200 ka (MIS1 - 7) as a preliminary age model. These records agree well with d18O records retrieved from Chinese caves. We will present a preliminary paleoceanographic proxy data to reconstruct sea-surface temperature (SST), sea-surface salinity (SSS), ice volume, marine biological productivity, nutrient supply, and deep-water circulation. These oceanographic and climate conditions are linked to changes in monsoonal strength and terrestrial input using sedimentary proxies to reconstruct chemical weathering and sediment sources and transport time. This work addresses one of the primary cruise objectives - linking monsoon variability, regional and global climate, and Bay of Bengal sediment deposition.

A 20-15 ka high-resolution paleomagnetic secular variation record from Black Sea sediments - no evidence for the 'Hilina Pali excursion'?

NASA Astrophysics Data System (ADS)

Liu, Jiabo; Nowaczyk, Norbert R.; Frank, Ute; Arz, Helge W.

2018-06-01

A comprehensive magnetostratigraphic investigation on sixteen sediment cores from the southeastern Black Sea yielded a very detailed high-quality paleosecular variation (PSV) record spanning from 20 to 15 ka. The age models are based on radiocarbon dating, stratigraphic correlation, and tephrochronology. Further age constraints were obtained by correlating four meltwater events, described from the western Black Sea, ranging in age from about 17 to 15 ka, with maxima in K/Ti ratios, obtained from X-ray fluorescence (XRF) scanning, and minima in S-ratios, reflecting increased hematite content, in the studied cores. Since the sedimentation rates in the investigated time window are up to 50 cm ka-1, the obtained PSVs records enabled a stacking using 50-yr bins. A directional anomaly at 18.5 ka, associated with pronounced swings in inclination and declination, as well as a low in relative paleointensity (rPI), is probably contemporaneous with the Hilina Pali excursion, originally reported from Hawaiian lava flows. However, virtual geomagnetic poles (VGPs) calculated from Black Sea sediments are not located at latitudes lower than 60°N, which denotes normal, though pronounced secular variations. During the postulated Hilina Pali excursion, the VGPs calculated from Black Sea data migrated clockwise only along the coasts of the Arctic Ocean from NE Canada (20.0 ka), via Alaska (18.6 ka) and NE Siberia (18.0 ka) to Svalbard (17.0 ka), then looping clockwise through the Eastern Arctic Ocean.

Environment and paleoecology of a 12 ka mid-North American Younger Dryas forest chronicled in tree rings

USGS Publications Warehouse

Panyushkina, Irina P.; Leavitt, Steven W.; Thompson, Todd A.; Schneider, Allan F.; Lange, Todd

2008-01-01

Until now, availability of wood from the Younger Dryas abrupt cooling event (YDE) in N. America ca. 12.9 to 11.6 ka has been insufficient to develop high-resolution chronologies for refining our understanding of YDE conditions. Here we present a multi-proxy tree-ring chronology (ring widths, “events” evidenced by microanatomy and macro features, stable isotopes) from a buried black spruce forest in the Great Lakes area (Liverpool East site), spanning 116 yr at ca. 12,000 cal yr BP. During this largely cold and wet period, the proxies convey a coherent and precise forest history including frost events, tilting, drowning and burial in estuarine sands as the Laurentide Ice Sheet deteriorated. In the middle of the period, a short mild interval appears to have launched the final and largest episode of tree recruitment. Ultimately the tops of the trees were sheared off after death, perhaps by wind-driven ice floes, culminating an interval of rising water and sediment deposition around the base of the trees. Although relative influences of the continental ice sheet and local effects from ancestral Lake Michigan are indeterminate, the tree-ring proxies provide important insight into environment and ecology of a N. American YDE boreal forest stand.

The biogeophysical climatic impacts of anthropogenic land use change during the Holocene

NASA Astrophysics Data System (ADS)

Smith, M. Clare; Singarayer, Joy S.; Valdes, Paul J.; Kaplan, Jed O.; Branch, Nicholas P.

2016-04-01

The first agricultural societies were established around 10 ka BP and had spread across much of Europe and southern Asia by 5.5 ka BP with resultant anthropogenic deforestation for crop and pasture land. Various studies (e.g. Joos et al., 2004; Kaplan et al., 2011; Mitchell et al., 2013) have attempted to assess the biogeochemical implications for Holocene climate in terms of increased carbon dioxide and methane emissions. However, less work has been done to examine the biogeophysical impacts of this early land use change. In this study, global climate model simulations with Hadley Centre Coupled Model version 3 (HadCM3) were used to examine the biogeophysical effects of Holocene land cover change on climate, both globally and regionally, from the early Holocene (8 ka BP) to the early industrial era (1850 CE). Two experiments were performed with alternative descriptions of past vegetation: (i) one in which potential natural vegetation was simulated by Top-down Representation of Interactive Foliage and Flora Including Dynamics (TRIFFID) but without land use changes and (ii) one where the anthropogenic land use model Kaplan and Krumhardt 2010 (KK10; Kaplan et al., 2009, 2011) was used to set the HadCM3 crop regions. Snapshot simulations were run at 1000-year intervals to examine when the first signature of anthropogenic climate change can be detected both regionally, in the areas of land use change, and globally. Results from our model simulations indicate that in regions of early land disturbance such as Europe and south-east Asia detectable temperature changes, outside the normal range of variability, are encountered in the model as early as 7 ka BP in the June-July-August (JJA) season and throughout the entire annual cycle by 2-3 ka BP. Areas outside the regions of land disturbance are also affected, with virtually the whole globe experiencing significant temperature changes (predominantly cooling) by the early industrial period. The global annual mean temperature anomalies found in our single model simulations were -0.22 at 1850 CE, -0.11 at 2 ka BP, and -0.03 °C at 7 ka BP. Regionally, the largest temperature changes were in Europe with anomalies of -0.83 at 1850 CE, -0.58 at 2 ka BP, and -0.24 °C at 7 ka BP. Large-scale precipitation features such as the Indian monsoon, the Intertropical Convergence Zone (ITCZ), and the North Atlantic storm track are also impacted by local land use and remote teleconnections. We investigated how advection by surface winds, mean sea level pressure (MSLP) anomalies, and tropospheric stationary wave train disturbances in the mid- to high latitudes led to remote teleconnections.

Loess record of the Pleistocene-Holocene transition on the northern and central Great Plains, USA

USGS Publications Warehouse

Mason, J.A.; Miao, X.; Hanson, P.R.; Johnson, W.C.; Jacobs, P.M.; Goble, R.J.

2008-01-01

Various lines of evidence support conflicting interpretations of the timing, abruptness, and nature of climate change in the Great Plains during the Pleistocene-Holocene transition. Loess deposits and paleosols on both the central and northern Great Plains provide a valuable record that can help address these issues. A synthesis of new and previously reported optical and radiocarbon ages indicates that the Brady Soil, which marks the boundary between late Pleistocene Peoria Loess and Holocene Bignell Loess, began forming after a reduction in the rate of Peoria Loess accumulation that most likely occurred between 13.5 and 15 cal ka. Brady Soil formation spanned all or part of the B??lling-Aller??d episode (approximately 14.7-12.9 cal ka) and all of the Younger Dryas episode (12.9-11.5 cal ka) and extended at least 1000 years beyond the end of the Younger Dryas. The Brady Soil was buried by Bignell Loess sedimentation beginning around 10.5-9 cal ka, and continuing episodically through the Holocene. Evidence for a brief increase in loess influx during the Younger Dryas is noteworthy but very limited. Most late Quaternary loess accumulation in the central Great Plains was nonglacigenic and was under relatively direct climatic control. Thus, Brady Soil formation records climatic conditions that minimized eolian activity and allowed effective pedogenesis, probably through relatively high effective moisture. Optical dating of loess in North Dakota supports correlation of the Leonard Paleosol on the northern Great Plains with the Brady Soil. Thick loess in North Dakota was primarily derived from the Missouri River floodplain; thus, its stratigraphy may in part reflect glacial influence on the Missouri River. Nonetheless, the persistence of minimal loess accumulation and soil formation until 10 cal ka at our North Dakota study site is best explained by a prolonged interval of high effective moisture correlative with the conditions that favored Brady Soil formation. Burial of both the Brady Soil and the Leonard Paleosol by renewed loess influx probably represents eolian system response that occurred when gradual change toward a drier climate eventually crossed the threshold for eolian activity. Overall, the loess-paleosol sequences of the central and northern Great Plains record a broad peak of high effective moisture across the late Pleistocene to Holocene boundary, rather than well-defined climatic episodes corresponding to the B??lling-Aller??d and Younger Dryas episodes in the North Atlantic region. ?? 2008 Elsevier Ltd. All rights reserved.

Holocene environmental and climatic change in the Northern Great Plains as recorded in the geochemistry of sediments in Pickerel Lake, South Dakota

USGS Publications Warehouse

Dean, W.E.; Schwalb, A.

2000-01-01

The sediments in Pickerel Lake, northeastern South Dakota, provide a continuous record of climatic and environmental change for the last 12000 yr. Sediments deposited between 12 and 6 ka (radiocarbon) show extreme variations in composition, oxygen and carbon isotopic composition of bulk carbonate, carbon isotopic composition of organic matter, and magnetic susceptibility. These variations reflect changes in sources of moisture, regional vegetation types, precipitation-evaporation balance, ground- and surface-water influx, water residence time, erosion, lake productivity, water level, and water temperature. The total carbonate content of late Pleistocene sediments steadily increased from <20% at the base of the core to as much as 80% in sediments deposited between 11 and 9 ka. By about 8 ka, the total carbonate content of the sediments had declined to about 40% where it remained with little variation for the past 8 kyr, suggesting relatively stable conditions. There are marked increases in values of ??13C and ??18O in bulk carbonate, and ??13C of organic matter, in sediments deposited between 10 and 6 ka as evaporation increased, and the vegetation in the watershed changed from forest to prairie. This shift toward more 18O-enriched carbonate may also reflect a change in source or seasonality of precipitation. During this early Holocene interval the organic carbon (OC) content of the sediments remained relatively low (2-3%), but then increased rapidly to 4.5% between 7 and 6 ka, reflecting the rapid transition to a prairie lake. The OC content fluctuates slightly between 4 and 6% in sediments deposited over the past 6 kyr. Like OC and total carbonate, most variables measured show little variation in the 13 m of sediment deposited over the past 6 kyr, particularly when compared with early Holocene variations. Although the magnetic susceptibility of this upper 13 m of sediment is generally low (<10 SI units), the upper six meters of the section is marked by striking 1 m cycles (ca. 400-500 yr periodicity) in susceptibility. These cycles are interpreted as being due to variations in the influx of eolian detrital-clastic material. Century-scale cyclic variations in different proxy variables for aridity and eolian activity from sediments deposited over the past 2000 yr in other lakes in the northern Great Plains, as well as in sand dune activity, suggest that aridity cycles were the dominant feature of late Holocene climate of the northern Great Plains. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.

Coeval Formation of Zircon Megacrysts and Host Magmas in the Eifel Volcanic Field (Germany) Based on High Spatial Resolution Petrochronology

NASA Astrophysics Data System (ADS)

Schmitt, Axel; Klitzke, Malte; Gerdes, Axel; Ludwig, Thomas; Schäfer, Christof

2017-04-01

Zircon megacrysts (approx. 0.5-6 mm in diameter) from the Quaternary West and East Eifel volcanic fields, Germany, occur as euhedral crystals in porous K-spar rich plutonic ejecta clasts, and as partially resorbed xenocrysts in tephrite lava. Their relation to the host volcanic rocks has remained contentious because the dominantly basanitic to phonolitic magma compositions in the Eifel are typically zircon undersaturated. We carried out a detailed microanalytical study of zircon megacrysts from seven locations (Emmelberg and Rockeskyll in the West Eifel; Bellerberg, Laacher See, Mendig, Rieden, and Wehr in the East Eifel). Crystals were embedded in epoxy, sectioned to expose interiors through grinding with abrasives, diamond-polished, and mapped by optical microscopy, backscattered electron, and cathodoluminescence imaging. Subsequently, isotope-specific analysis using secondary ionization mass spectrometry (SIMS) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was carried out placing 100 correlated spots on 20 selected crystals. Concordant U-Th disequilibrium and U-Pb ages determined by SIMS are between ca. 430 ka (Rieden) and 170 ka (Mendig) and indicate that the megacryst zircons crystallized almost always briefly before eruption. A significant gap between zircon megacryst crystallization (ca. 230 ka) and eruption (ca. 45 ka) ages was only detected for the Emmelberg location. SIMS trace element abundances (e.g., rare earth elements) vary by orders-of-magnitude and correlate with domain boundaries visible in cathodoluminescence; trace element patterns match those reported for zircon from syenitic origins. Isotopic compositions are homogeneous within individual crystals, but show some heterogeneity between different crystals from the same locality. Average isotopic values (δ18O SMOW = +5.3±0.6 ‰ by SIMS; present-day ɛHf = +1.7±2.5 ‰ by LA-ICP-MS; 1 standard deviation), however, are consistent with source magmas being dominantly mantle-derived. The porous structure and relatively small grain size of the host enclaves suggests that they originated from subvolcanic intrusions. Moreover, the preservation of zircon in hot, zircon undersaturated magmas requires brief residence times. Zircon megacrysts thus appear to have crystallized in highly differentiated magmas or nearly solidified intrusions from which crystals or rock aggregates were incorporated into more primitive magmas en route to surface. This implies that chemical signatures of apparently primitive magmas in basaltic volcanic fields can be modified by interaction with evolved melts that differentiated prior to eruption, mostly within an interval less than the ca. 10-25 ka uncertainty range of the radiometric ages.

Quaternary Slip History for the Agua Blanca Fault, northern Baja California, Mexico

NASA Astrophysics Data System (ADS)

Gold, P. O.; Behr, W. M.; Rockwell, T. K.; Fletcher, J. M.

2017-12-01

The Agua Blanca Fault (ABF) is the primary structure accommodating San Andreas-related right-lateral slip across the Peninsular Ranges of northern Baja California. Activity on this fault influences offshore faults that parallel the Pacific coast from Ensenada to Los Angeles and is a potential threat to communities in northern Mexico and southern California. We present a detailed Quaternary slip history for the ABF, including new quantitative constraints on geologic slip rates, slip-per-event, the timing of most recent earthquake, and the earthquake recurrence interval. Cosmogenic 10Be exposure dating of clasts from offset fluvial geomorphic surfaces at 2 sites located along the western, and most active, section of the ABF yield preliminary slip rate estimates of 2-4 mm/yr and 3 mm/yr since 20 ka and 2 ka, respectively. Fault zone geomorphology preserved at the younger site provides evidence for right-lateral surface displacements measuring 2.5 m in the past two ruptures. Luminescence dating of an offset alluvial fan at a third site is in progress, but is expected to yield a slip rate relevant to the past 10 kyr. Adjacent to this third site, we excavated 2 paleoseismic trenches across a sag pond formed by a right step in the fault. Preliminary radiocarbon dates indicate that the 4 surface ruptures identified in the trenches occurred in the past 6 kyr, although additional dating should clarify earthquake timing and the mid-Holocene to present earthquake recurrence interval, as well as the likely date of the most recent earthquake. Our new slip rate estimates are somewhat lower than, but comparable within error to, previous geologic estimates based on soil morphology and geodetic estimates from GPS, but the new record of surface ruptures exposed in the trenches is the most complete and comprehensively dated earthquake history yet determined for this fault. Together with new and existing mapping of tectonically generated geomorphology along the ABF, our constraints show that contrary to some theories of fault interaction and activity for this section of the San Andreas system, the Agua Blanca Fault has been active over the late Holocene, and should be considered as a potential source of seismic hazard.

High Resolution deglacial monsoon δ18O record from a new stalagmite from the Kailash Cave, Central India

NASA Astrophysics Data System (ADS)

Allu C, Narayana; Pawan K, Gautam; Shraddha, Band; Madhusudan G, Yadava; Rengaswamy, Ramesh; Shen, Chuan-Chou

2016-04-01

High resolution δ18O and δ13C data from absolutely dated stalagmites have been useful for reconstructing the Asian monsoon variability (e.g., Yadava et al., 2004; Laskar et al., 2013; Allu et al., 2014; Lone et al., 2014; Sinha et al., 2015). However, many studies lack high resolution spatial and temporal records leaving significant gaps which need to be filled for a vivid understanding of monsoonal variability. We report here the first high resolution stalagmite δ18O isotope results during the last deglacial obtained from the Kailash cave located from the core monsoon region. The length of stalagmite was 480 mm, with an average diameter of 120 mm. The sample was cut for continuous micro milling at 400μm intervals along the growth axis (using new wave research micro-mill-101288) for the analyses of stable oxygen and carbon isotopes using a Delta V plus IRMS at the Physical Research Laboratory, Ahmedabad. The physical appearance of the sample section reveals very fine, straight and clear laminations from the top to 310 mm from below, which have thick laminae. U-Th dates obtained from a Thermo Fisher NEPTUNE multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) at High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), National Taiwan University, Taiwan (Shen et al., 2012) showed the record spanned ~2400 years from ~14.6 ka to ~12.2 ka. Linear Age-Depth model constructed from dates suggests that the sample grew for ~2.400 years from ~14.6 ka to ~12.2 ka with varying resolutions from ~6 months to ~8 years. Hendy's test from 8 distinct layers shows poor correlation between δ18O and δ13C suggesting the isotopic equilibrium conditions at the time of crystallization. δ18O and δ13C results appear to be cyclic in nature varying in the range from +0.37‰ to -6.07‰ and -1.59‰ to -10.59‰ respectively. Enriched δ18O in top portion represents poor monsoon during the onset of Younger Drayas. Later, the δ18O signals corresponding to Bølling-Allerød Interstadial appear to be cyclic in nature. We performed time-series analyses on the δ18O record to investigate the periodicities to understand the influence of both solar and non-solar frequencies during last deglacial. REDFIT (Schulz & Mudelsee, 2002) with Monte Carlo simulation was used to calculate the red noises. Spectral analysis of the δ18O time series show statistically most significant periodicity (>95%) centered at 592 years. The other significant periodicities found are 42, 37, 19, 18, 16, and14.5 years.

Fossils reject climate change as the cause of extinction of Caribbean bats

PubMed Central

Soto-Centeno, J. Angel; Steadman, David W.

2015-01-01

We combined novel radiocarbon dates of bat fossils with time-scaled ecological niche models (ENM) to study bat extinctions in the Caribbean. Radiocarbon-dated fossils show that late Quaternary losses of bat populations took place during the late Holocene (<4 ka) rather than late Pleistocene (>10 ka). All bat radiocarbon dates from Abaco (Bahamas) that represent extirpated populations are younger than 4 ka. We include data on six bat species, three of which are Caribbean endemics, and include nectarivores as well as insectivores. Climate-based ENMs from the Last Glacial Maximum to the present reflect overall stability in distributions, with suitable climatic habitat being present over time. In the absence of radiocarbon dates, bat extinctions had been presumed to take place during the last glacial-interglacial transition (ca. 10 ka). Now we see that extirpation of bats on these tropical islands is more complex than previously thought and primarily postdates the major climate changes that took place during the late Pleistocene-Holocene transition. PMID:25610991

Fossils reject climate change as the cause of extinction of Caribbean bats.

PubMed

Soto-Centeno, J Angel; Steadman, David W

2015-01-22

We combined novel radiocarbon dates of bat fossils with time-scaled ecological niche models (ENM) to study bat extinctions in the Caribbean. Radiocarbon-dated fossils show that late Quaternary losses of bat populations took place during the late Holocene (<4 ka) rather than late Pleistocene (>10 ka). All bat radiocarbon dates from Abaco (Bahamas) that represent extirpated populations are younger than 4 ka. We include data on six bat species, three of which are Caribbean endemics, and include nectarivores as well as insectivores. Climate-based ENMs from the Last Glacial Maximum to the present reflect overall stability in distributions, with suitable climatic habitat being present over time. In the absence of radiocarbon dates, bat extinctions had been presumed to take place during the last glacial-interglacial transition (ca. 10 ka). Now we see that extirpation of bats on these tropical islands is more complex than previously thought and primarily postdates the major climate changes that took place during the late Pleistocene-Holocene transition.

The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination

NASA Astrophysics Data System (ADS)

Schaefer, Joerg M.; Putnam, Aaron E.; Denton, George H.; Kaplan, Michael R.; Birkel, Sean; Doughty, Alice M.; Kelley, Sam; Barrell, David J. A.; Finkel, Robert C.; Winckler, Gisela; Anderson, Robert F.; Ninneman, Ulysses S.; Barker, Stephen; Schwartz, Roseanne; Andersen, Bjorn G.; Schluechter, Christian

2015-04-01

Glacial maxima and their terminations provide key insights into inter-hemispheric climate dynamics and the coupling of atmosphere, surface and deep ocean, hydrology, and cryosphere, which is fundamental for evaluating the robustness of earth's climate in view of ongoing climate change. The Last Glacial Maximum (LGM, ∼26-19 ka ago) is widely seen as the global cold peak during the last glacial cycle, and its transition to the Holocene interglacial, dubbed 'Termination 1 (T1)', as the most dramatic climate reorganization during this interval. Climate records show that over the last 800 ka, ice ages peaked and terminated on average every 100 ka ('100 ka world'). However, the mechanisms pacing glacial-interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood. Here we show evidence for a full glacial maximum in the Southern Hemisphere 65.1 ± 2.7 ka ago and its 'Unfinished Termination'. Our 10Be chronology combined with a model simulation demonstrates that New Zealand's glaciers reached their maximum position of the last glacial cycle during Marine Isotope Stage-4 (MIS-4). Southern ocean and greenhouse gas records indicate coeval peak glacial conditions, making the case for the Southern Glacial Maximum about halfway through the last glacial cycle and only 15 ka after the last warm period (MIS-5a). We present the hypothesis that subsequently, driven by boreal summer insolation forcing, a termination began but remained unfinished, possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the North Atlantic through Heinrich Stadial 6 to drive a full termination. Yet the Unfinished Termination left behind substantial ice on the northern continents (about 50% of the full LGM ice volume) and after another 45 ka of cooling and ice sheet growth the earth was at inter-hemispheric Last Glacial Maximum configuration, when similar orbital forcing hit maximum-size northern ice sheets and ushered in T1 and thus the ongoing interglacial. This argument highlights the critical role of full glacial conditions in both hemispheres for terminations and implies that the Southern Hemisphere climate could transition from interglacial to full glacial conditions in about 15,000 years, while the Northern Hemisphere and its continental ice-sheets required half a glacial cycle.

Enhanced susceptibility of Prnp-deficient mice to kainate-induced seizures, neuronal apoptosis, and death: Role of AMPA/kainate receptors.

PubMed

Rangel, Alejandra; Burgaya, Ferran; Gavín, Rosalina; Soriano, Eduardo; Aguzzi, Adriano; Del Río, José A

2007-09-01

Normal physiologic functions of the cellular prion protein (PrPc) are still elusive. This GPI-anchored protein exerts many functions, including roles in neuron proliferation, neuroprotection or redox homeostasis. There are, however, conflicting data concerning its role in synaptic transmission. Although several studies report that PrPc participates in NMDA-mediated neurotransmission, parallel studies describe normal behavior of PrPc-mutant mice. Abnormal axon connections have been described in the dentate gyrus of the hippocampi of PrPc-deficient mice similar to those observed in epilepsy. A study indicates increased susceptibility to kainate (KA) in these mutant mice. We extend the observation of these studies by means of several histologic and biochemical analyses of KA-treated mice. PrPc-deficient mice showed increased sensitivity to KA-induced seizures in vivo and in vitro in organotypic slices. In addition, we show that this sensitivity is cell-specific because interference experiments to abolish PrPc expression increased susceptibility to KA in PrPc-expressing cells. We indicate a correlation of susceptibility to KA in cells lacking PrPc with the differential expression of GluR6 and GluR7 KA receptor subunits using real-time RT-PCR methods. These results indicate that PrPc exerts a neuroprotective role against KA-induced neurotoxicity, probably by regulating the expression of KA receptor subunits. (c) 2007 Wiley-Liss, Inc.

Last interglacial temperature seasonality reconstructed from tropical Atlantic corals

NASA Astrophysics Data System (ADS)

Brocas, William M.; Felis, Thomas; Obert, J. Christina; Gierz, Paul; Lohmann, Gerrit; Scholz, Denis; Kölling, Martin; Scheffers, Sander R.

2016-09-01

Reconstructions of last interglacial (LIG, MIS 5e, ∼127-117 ka) climate offer insights into the natural response and variability of the climate system during a period partially analogous to future climate change scenarios. We present well preserved fossil corals (Diploria strigosa) recovered from the southern Caribbean island of Bonaire (Caribbean Netherlands). These have been precisely dated by the 230Th/U-method to between 130 and 120 ka ago. Annual banding of the coral skeleton enabled construction of time windows of monthly resolved strontium/calcium (Sr/Ca) temperature proxy records. In conjunction with a previously published 118 ka coral record, our eight records of up to 37 years in length, cover a total of 105 years within the LIG period. From these, sea surface temperature (SST) seasonality and variability in the tropical North Atlantic Ocean is reconstructed. We detect similar to modern SST seasonality of ∼2.9 °C during the early (130 ka) and the late LIG (120-118 ka). However, within the mid-LIG, a significantly higher than modern SST seasonality of 4.9 °C (at 126 ka) and 4.1 °C (at 124 ka) is observed. These findings are supported by climate model simulations and are consistent with the evolving amplitude of orbitally induced changes in seasonality of insolation throughout the LIG, irrespective of wider climatic instabilities that characterised this period. The climate model simulations suggest that the SST seasonality changes documented in our LIG coral Sr/Ca records are representative of larger regions within the tropical North Atlantic. These simulations also suggest that the reconstructed SST seasonality increase during the mid-LIG is caused primarily by summer warming. A 124 ka old coral documents, for the first time, evidence of decadal SST variability in the tropical North Atlantic during the LIG, akin to that observed in modern instrumental records.

Late Pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at Crater Lake, Oregon

USGS Publications Warehouse

Bacon, C.R.; Lowenstern, J. B.

2005-01-01

Rhyodacite tephra and three lavas erupted ???27 ka, interpreted to be early leaks from the climactic magma chamber of Mount Mazama, contain ubiquitous resorbed crystals (antecrysts) that were recycled from young granodiorite and related plutonic rocks of the same magmatic system. The shallow composite pluton is represented by blocks ejected in the 7.7-ka climactic eruption that formed Crater Lake caldera. Plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented Fe-oxide needles exsolved at subsolidus conditions. At least 80% of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks. Other crystals in the rhyodacite, notably zircon, also were recycled. SIMS 238U- 230Th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between ???20 ka and ???300 ka with concentrations of analyses near 50-70, ???110, and ???200 ka that correspond to periods of dacitic volcanism dated by K- Ar. U-Th ages of zircon from a rhyodacite sample yield similar results. No analyzed zircons from the granodiorite or rhyodacite are pre-Quaternary. Zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton. Survival of zircon in zircon-undersaturated hydrous magma and of Fe-oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the ???27-ka eruption of the rhyodacite. The ???27-ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high-level magma chamber. In contrast, the voluminous 7.7-ka climactic rhyodacite pumice is virtually lacking in zircon, indicating dissolution of any granodioritic debris in the intervening period. Mineralogical evidence of assimilation may be destroyed in hot, vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of Mount Mazama. ?? 2005 Elsevier B.V. All rights reserved.

Timing of last deglaciation in the Cantabrian Mountains (Iberian Peninsula; North Atlantic Region) based on in situ-produced 10Be exposure dating

NASA Astrophysics Data System (ADS)

Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María José; Rinterknecht, Vincent; Pallàs, Raimon; Aumaître, Georges; Bourlès, Didier L.; Keddadouche, Karim; Aster Team

2017-09-01

The Last Glacial Termination led to major changes in ice sheet coverage that disrupted global patterns of atmosphere and ocean circulation. Paleoclimate records from Iberia suggest that westerly episodes played a key role in driving heterogeneous climate in the North Atlantic Region. We used 10Be Cosmic Ray Exposure (CRE) dating to explore the glacier response of small mountain glaciers (ca. 5 km2) that developed on the northern slope of the Cantabrian Mountains (Iberian Peninsula), an area directly under the influence of the Atlantic westerly winds. We analyzed twenty boulders from three moraines and one rock glacier arranged as a recessional sequence preserved between 1150 and 1540 m above sea level (a.s.l.) in the Monasterio valley (Redes Natural Park). Results complement previous chronologic data based on radiocarbon and optically stimulated luminescence from the Monasterio valley, which suggest a local Glacial Maximum (local GM) prior to 33 ka BP and a long-standing glacier advance at 24 ka coeval to the global Last Glacial Maximum (LGM). Resultant 10Be CRE ages suggest a progressive retreat and thinning of the Monasterio glacier over the time interval 18.1-16.7 ka. This response is coeval with the Heinrich Stadial 1, an extremely cold and dry climate episode initiated by a weakening of the Atlantic Meridional Overturning Circulation (AMOC). Glacier recession continued through the Bølling/Allerød period as indicate the minimum exposure ages obtained from a cirque moraine and a rock glacier nested within this moraine, which yielded ages of 14.0 and 13.0 ka, respectively. Together, they suggest that the Monasterio glacier experienced a gradual transition from glacier to rock glacier activity as the AMOC started to strengthen again. Glacial evidence ascribable to the Younger Dryas cooling was not dated in the Monasterio valley, but might have occurred at higher elevations than evidence dated in this work. The evolution of former glaciers documented in the Monasterio valley seems consistent with previous 10Be chronologies reported in other mountain ranges of the Iberian Peninsula, which have been recalculated according to a common production rate and scaling scheme. However, the re-evaluation of published 10Be chronologies has highlighted the fact that glacial evidence previously ascribed to the Younger Dryas might be more limited than previously thought and the need for additional studies to characterized the extent of glaciers during the Younger Dryas cooling.

Pollen-climate relationships in time (9 ka, 6 ka, 0 ka) and space (upland vs. lowland) in eastern continental Asia

NASA Astrophysics Data System (ADS)

Tian, Fang; Cao, Xianyong; Dallmeyer, Anne; Zhao, Yan; Ni, Jian; Herzschuh, Ulrike

2017-01-01

Temporal and spatial stability of the vegetation-climate relationship is a basic ecological assumption for pollen-based quantitative inferences of past climate change and for predicting future vegetation. We explore this assumption for the Holocene in eastern continental Asia (China, Mongolia). Boosted regression trees (BRT) between fossil pollen taxa percentages (Abies, Artemisia, Betula, Chenopodiaceae, Cyperaceae, Ephedra, Picea, Pinus, Poaceae and Quercus) and climate model outputs of mean annual precipitation (Pann) and mean temperature of the warmest month (Mtwa) for 9 and 6 ka (ka = thousand years before present) were set up and results compared to those obtained from relating modern pollen to modern climate. Overall, our results reveal only slight temporal differences in the pollen-climate relationships. Our analyses suggest that the importance of Pann compared with Mtwa for taxa distribution is higher today than it was at 6 ka and 9 ka. In particular, the relevance of Pann for Picea and Pinus increases and has become the main determinant. This change in the climate-tree pollen relationship parallels a widespread tree pollen decrease in north-central China and the eastern Tibetan Plateau. We assume that this is at least partly related to vegetation-climate disequilibrium originating from human impact. Increased atmospheric CO2 concentration may have permitted the expansion of moisture-loving herb taxa (Cyperaceae and Poaceae) during the late Holocene into arid/semi-arid areas. We furthermore find that the pollen-climate relationship between north-central China and the eastern Tibetan Plateau is generally similar, but that regional differences are larger than temporal differences. In summary, vegetation-climate relationships in China are generally stable in space and time, and pollen-based climate reconstructions can be applied to the Holocene. Regional differences imply the calibration-set should be restricted spatially.

Reproducibility of a Standardized Actigraphy Scoring Algorithm for Sleep in a US Hispanic/Latino Population

PubMed Central

Patel, Sanjay R.; Weng, Jia; Rueschman, Michael; Dudley, Katherine A.; Loredo, Jose S.; Mossavar-Rahmani, Yasmin; Ramirez, Maricelle; Ramos, Alberto R.; Reid, Kathryn; Seiger, Ashley N.; Sotres-Alvarez, Daniela; Zee, Phyllis C.; Wang, Rui

2015-01-01

Study Objectives: While actigraphy is considered objective, the process of setting rest intervals to calculate sleep variables is subjective. We sought to evaluate the reproducibility of actigraphy-derived measures of sleep using a standardized algorithm for setting rest intervals. Design: Observational study. Setting: Community-based. Participants: A random sample of 50 adults aged 18–64 years free of severe sleep apnea participating in the Sueño sleep ancillary study to the Hispanic Community Health Study/Study of Latinos. Interventions: N/A. Measurements and Results: Participants underwent 7 days of continuous wrist actigraphy and completed daily sleep diaries. Studies were scored twice by each of two scorers. Rest intervals were set using a standardized hierarchical approach based on event marker, diary, light, and activity data. Sleep/wake status was then determined for each 30-sec epoch using a validated algorithm, and this was used to generate 11 variables: mean nightly sleep duration, nap duration, 24-h sleep duration, sleep latency, sleep maintenance efficiency, sleep fragmentation index, sleep onset time, sleep offset time, sleep midpoint time, standard deviation of sleep duration, and standard deviation of sleep midpoint. Intra-scorer intraclass correlation coefficients (ICCs) were high, ranging from 0.911 to 0.995 across all 11 variables. Similarly, inter-scorer ICCs were high, also ranging from 0.911 to 0.995, and mean inter-scorer differences were small. Bland-Altman plots did not reveal any systematic disagreement in scoring. Conclusions: With use of a standardized algorithm to set rest intervals, scoring of actigraphy for the purpose of generating a wide array of sleep variables is highly reproducible. Citation: Patel SR, Weng J, Rueschman M, Dudley KA, Loredo JS, Mossavar-Rahmani Y, Ramirez M, Ramos AR, Reid K, Seiger AN, Sotres-Alvarez D, Zee PC, Wang R. Reproducibility of a standardized actigraphy scoring algorithm for sleep in a US Hispanic/Latino population. SLEEP 2015;38(9):1497–1503. PMID:25845697

The Seismic Stratigraphic Record of Quaternary Deformation Across the North Anatolian Fault System in Southern Marmara Sea, Turkey

NASA Astrophysics Data System (ADS)

Sorlien, C. C.; Seeber, L.; Diebold, J.; Shillington, D.; Steckler, M. S.; Gurcay, S.; Kucuk, H. M.; Akhun, S. D.; Timur, D.; Dondurur, D.; Kurt, H.; Perincek, E.; Ozer, P.; Imren, C.; Coskun, S.; Buyukasik, E.; Cevatoglu, M.; Cifci, G.; Demirbag, E.

2008-12-01

We collected high-resolution multichannel seismic reflection (MCS) and chirp seismic data across the North Anatolian Fault (NAF) system in the Marmara Sea aboard the R/V K. Piri Reis during July 2008. Three 1200+ m-deep bathymetric basins are arrayed along the North strand of the NAF. This strand passes closest to Istanbul and is considered to carry most of the current and late Holocene plate motion, but other strands to the south are active and may have been more important in the past. The transverse Central Marmara Ridge, formed by a contractional anticline, separates two of the basins. Filled sedimentary basins underlie the southern shelf, and, adjacent to that shelf, the partly-filled North Imrali basin underlies a 400 m-deep platform. Our chirp data image several strands of the southern fault system, 50 km south of the northern NAF on the inner (southern) shelf, that offset strata which postdate the ~12 ka marine transgression. Another W-striking fault that deforms post-12 ka strata cuts the mid-southern shelf. A WNW-striking segment of the Imrali fault system is associated with normal-separation, 300 m-high sea floor scarps that separate the shelf from the North Imrali basin. This basin is cut by numerous NW-striking normal-separation faults, some deforming the sea floor. At least 4 complexes of shelf edge deltas, whose tops were formed near sea level or lake level, are stacked between 500 and 900 m depth in this downthrown block of the Imrali fault. The originally sub- horizontal tops of each delta are now locally progressively tilted and folded near an ENE-striking branch of the Imrali fault (known as the Yalova fault). Lacking stratigraphic control, we infer that the deltas represent glacial intervals spaced at 100 ka during the late Pleistocene. Assuming a locally constant subsidence rate, with lowstands near -90 m, and the observed 130 m vertical spacing between the deltas, subsidence rates would be ~1.3 mm/yr, and the youngest well-preserved delta would be ~320 ka (MIS10). Alternatively, it corresponds to the pronounced 420 ka glacial (MIS12). Younger deltas did not form in this area, at least not with prograding geometries, because the water depth became too great. Possibly, outer shelf anticlinal growth may have diverted the river westward, where younger deltas are preserved on the shelf. The slope between the 400 m platform and the lower flank of the NE-trending Central Marmara Ridge is dominated by north-trending and northeast-trending 1 km-wavelength folds. These folds grew through the late Quaternary interval of deposition of the imaged deltas, and they deform the seafloor. They could be secondary shortening structures, forced folds above blind normal faults, or both. Farther east along the same slope, low-angle normal faults also grew through much of late Quaternary time. These faults root above unfaulted strata, and represent a slow collapse of the escarpment into the deep basin. NE-trending thrust- folds, NW-striking normal faults, WNW-striking transtensional faults, and ENE-striking transpressional faults are all consistent with the E-W right-lateral continental transform fault system.

Propolis ameliorates tumor nerosis factor-α, nitric oxide levels, caspase-3 and nitric oxide synthase activities in kainic acid mediated excitotoxicity in rat brain.

PubMed

Swamy, Mummedy; Suhaili, Dian; Sirajudeen, K N S; Mustapha, Zulkarnain; Govindasamy, Chandran

2014-01-01

Increased nitric oxide (NO), neuronal inflammation and apoptosis have been proposed to be involved in excitotoxicity plays a part in many neurodegenerative diseases. To understand the neuro-protective effects of propolis, activities of Nitric oxide synthase (NOS) and caspase-3 along with NO and tumor necrosis factor-α (TNF-α) levels were studied in cerebral cortex (CC), cerebellum (CB) and brain stem (BS) in rats supplemented with propolis prior to excitotoxic injury with kainic acid (KA). Male Sprague-Dawley rats were divided into four groups (n=6 rats per group) as Control, KA, Propolis and KA+Propolis. The control group and KA group have received vehicle and saline. Propolis group and propolis + KA group were orally administered with propolis (150 mg/kg body weight), five times every 12 hours. KA group and propolis +KA group were injected subcutaneously with kainic acid (15 mg/kg body weight) and were sacrificed after 2 hrs. CC, CB and BS were separated, homogenized and used for estimation of NOS, caspase-3, NO and TNF-α by commercial kits. Results were analyzed by one way ANOVA, reported as mean + SD (n=6 rats), and p<0.05 was considered statistically significant. The concentration of NO, TNF-α, NOS and caspase-3 activity were increased significantly (p<0.001) in all the three brain regions tested in KA group compared to the control. Propolis supplementation significantly (p<0.001) prevented the increase in NOS, NO, TNF-α and caspase-3 due to KA. Results of this study clearly demonstrated that the propolis supplementation attenuated the NOS, caspase-3 activities, NO, and TNF-α concentration and in KA mediated excitotoxicity. Hence propolis can be a possible potential protective agent against excitotoxicity and neurodegenerative disorders.

Reconstruction of precipitation variability in the Strait of Yucatan associated with latitudinal shifts in the position of the Intertropical Convergence Zone since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Staines-Urías, Francisca; Seidenkrantz, Marit-Solveig; Fischel, Andrea; Kuijpers, Antoon

2017-04-01

The elemental composition of sediments from gravity core HOLOVAR11-03 provides a ca. 40 ka record of past climate variability in the Strait of Yucatan, between the Caribbean Sea and the Gulf of Mexico, a region where precipitation variability is determined by the seasonal position of the Intertropical Convergence Zone (ITCZ). Within this region, sea level pressure decreases and rainfall increases as the ITCZ moves north of the equator in response to increased solar insolation in the Northern Hemisphere during boreal summer. In contrast, as the ITCZ retracts southward towards the equator during boreal winter, rainfall diminishes and the regional sea level pressure gradient strengthens. On interannual, multidecadal and millennial timescales, fluctuations in the average latitudinal position of the ITCZ in response to insolation forcing modulate the intensity and duration of the seasonal regimens, determining average regional precipitation and, ultimately, the elemental composition of the marine sedimentary record. Regionally, higher titanium and iron content in marine sediments reflect greater terrigenous input from inland runoff, indicating greater precipitation, hence a more northerly position of the ITCZ. Correspondingly, Ti and Fe concentration data were used to reconstruct regional rainfall variability since the Last Glacial Maxima (LGM ˜24 cal ka BP). HOLOVAR11-03 age model (based on 4 AMS 14C dates obtained from multi-specific samples of planktic foraminifera) shows stable sedimentation rates in the area throughout the cored period. Nonetheless, higher terrestrial mineral input is observed since the LGM and all through the last glacial termination (24 to 12 cal ka BP), indicating a period of increased precipitation. In contrast, lower Ti and Fe values are typical for the period between 12 and 8 cal ka BP, indicating reduced precipitation. A positive trend characterizes the following interval, showing a return to wetter conditions lasting until 5 cal ka BP. Notably, records of sea-surface temperature from the Caribbean indicate similar variability, with among others, colder than present conditions in the early Holocene indicating a more northerly mean ITCZ position, followed by warmer surface waters and a weaker tradewind associated with a southward displacement of the ITCZ, further illustrating the strong link between precipitation variability and oceanographic conditions in the region. After 5 cal ka BP, Ti and Fe values remain fairly stable at an intermediate level until shortly after 2 cal ka BP, when a sudden increase in Fe content is observed. At this time, a significant increase in precipitation has also been inferred from the δ18O signal of ostracods and gastropods in lake sediments from the Yucatan Peninsula and a stalagmite δ18O monsoon reconstruction from mainland Mexico. The drastic increment in Fe content also marks the beginning of a shift towards rapidly decreasing Ti and Fe values, suggesting an increasingly drier climate. Decrease inland runoff/precipitation during the late Holocene has also been observed in stalagmite and lacustrine δ18O signals from nearby locations, altogether indicating a southward displacement of the ITCZ.

Sea-level records at ~80 ka from tectonically stable platforms: Florida and Bermuda

USGS Publications Warehouse

Ludwig, K. R.; Muhs, D.R.; Simmons, K.R.; Halley, R.B.; Shinn, E.A.

1996-01-01

Studies from technically active coasts on New Guinea and Barbados have suggested that sea level at ???80 ka was significantly lower than present, whereas data from the Atlantic and Pacific coasts of North America indicate an ???80 ka sea level close to that of the present. We determined ages of corals from a shallow submerged reef off the Florida Keys and an emergent marine deposit on Bermuda. Both localities are on tectonically stable platforms distant from plate boundaries. Uranium-series ages show that corals at both localities grew during the ???80 ka sea-level highstand, and geologic data show that sea level at that time was no lower than 7-9 m below present (Florida) and may have been 1-2 m above present (Bermuda). The ice-volume discrepancy of the 80 ka sea-level estimates is greater than the volume of the Greenland or West Antarctic ice sheets. Comparison of our ages with high-latitude insolation values indicates that the sea-level stand near the present at ???80 ka could have been orbitally forced.

Early and mid-Holocene age for the Tempanos moraines, Laguna San Rafael, Patagonian Chile

NASA Astrophysics Data System (ADS)

Harrison, Stephan; Glasser, Neil F.; Duller, Geoff A. T.; Jansson, Krister N.

2012-01-01

Data about the nature and timing of Holocene events from the Southern Hemisphere, especially in southern South America, are required to provide insight into the extent and nature of past climate change in a region where land-based records are restricted. Here we present the first use of single grain Optically Stimulated Luminescence (OSL) dating of a moraine sequence recording glacial advance along the western side of the Patagonian Icefields. Dates from the Tempanos moraines at Laguna San Rafael (LSR) show that the San Rafael Glacier (SRG) advanced to maximum Holocene positions during the period 9.3 to 9.7 ka and at 5.7 ka. Outwash lying beneath the moraine in its northern portion, dated to 7.7 ka, indicates that the glacier front was also advanced at this time. Since these advances span both the regional early Holocene warm-dry phase (11.5 ka to 7.8 ka) and the subsequent cooling and rise in precipitation in the mid-late Holocene (since 6.6 ka) we infer that the advances of the SRG are not simply climate-driven, but that the glacier has also probably responded strongly to non-climatic stimuli such as internal ice dynamics and the transition between calving and non-calving. Many westwards-flowing glaciers in Patagonia were probably calving during much of the Late Pleistocene and Holocene, so we conclude that establishing robust glacial chronologies where climatic and non-climatic factors cannot be distinguished is likely to remain a challenge.

On the Performance of Adaptive Data Rate over Deep Space Ka-Bank Link: Case Study Using Kepler Data

NASA Technical Reports Server (NTRS)

Gao, Jay L.

2016-01-01

Future missions envisioned for both human and robotic exploration demand increasing communication capacity through the use of Ka-band communications. The Ka-band channel, being more sensitive to weather impairments, presents a unique trade-offs between data storage, latency, data volume and reliability. While there are many possible techniques for optimizing Ka-band operations such as adaptive modulation and coding and site-diversity, this study focus exclusively on the use of adaptive data rate (ADR) to achieve significant improvement in the data volume-availability tradeoff over a wide range of link distances for near Earth and Mars exploration. Four years of Kepler Ka-band downlink symbol signal-to-noise (SNR) data reported by the Deep Space Network were utilized to characterize the Ka-band channel statistics at each site and conduct various what-if performance analysis for different link distances. We model a notional closed-loop adaptive data rate system in which an algorithm predicts the channel condition two-way light time (TWLT) into the future using symbol SNR reported in near-real time by the ground receiver and determines the best data rate to use. Fixed and adaptive margins were used to mitigate errors in channel prediction. The performance of this closed-loop adaptive data rate approach is quantified in terms of data volume and availability and compared to the actual mission configuration and a hypothetical, optimized single rate configuration assuming full a priori channel knowledge.

A study pertaining to inertial energy storage machine designs for space applications

NASA Technical Reports Server (NTRS)

Zowarka, R. C.

1981-01-01

The preliminary design of a counterrotating fast discharge homopolar generator (HPG) and a counterrotating active rotary flux compressor (CARFC) for space application is reported. The HPG is a counterrotating spool-type homopolar with superconducting field coil excitation. It delivers a 20-ms, 145-kJ pulse to a magnetoplasmahydrodynamic thruster. The peak output current is 42.7 kA at 240 V. After 20 ms the current is 29.7 kA at 167 V. The CARFC delivers ten 50-kJ, 250 microsecond pulses at 50-ms interval to six Xenon flash lamps pumping an Nd glass laser. The flux compressor is counterrotating for torque compensation. Current is started in the machine with a 5-kV, 5-kJ pulse-charged capacitor. Both designs were based upon demonstrated technology. The sensitivity of the designs to technology that may be available in five to ten years was determined.

Migration of the Antarctic Polar Front through the mid-Pleistocene transition: evidence and climatic implications

NASA Astrophysics Data System (ADS)

Kemp, A. E. S.; Grigorov, I.; Pearce, R. B.; Naveira Garabato, A. C.

2010-08-01

The Antarctic Polar Front is an important biogeochemical divider in the Southern Ocean. Laminated diatom mat deposits record episodes of massive flux of the diatom Thalassiothrix antarctica beneath the Antarctic Polar Front and provide a marker for tracking the migration of the Front through time. Ocean Drilling Program Sites 1091, 1093 and 1094 are the only deep piston cored record hitherto sampled from the sediments of the circumpolar biogenic opal belt. Mapping of diatom mat deposits between these sites indicates a glacial-interglacial front migration of up to 6 degrees of latitude in the early/mid Pleistocene. The mid-Pleistocene transition marks a stepwise minimum 7° northward migration of the locus of the Polar Front sustained for about 450 kyr until an abrupt southward return to a locus similar to its modern position and further south than any mid-Pleistocene locus. This interval from a "900 ka event" that saw major cooling of the oceans and a δ 13C minimum through to the 424 ka Mid-Brunhes Event at Termination V is also seemingly characterised by 1) sustained decreased carbonate in the sub-tropical south Atlantic, 2) reduced strength of Antarctic deep meridional circulation, 3) lower interglacial temperatures and lower interglacial atmospheric CO 2 levels (by some 30 per mil) than those of the last 400 kyr, evidencing less complete deglaciation. This evidence is consistent with a prolonged period lasting 450 kyr of only partial ventilation of the deep ocean during interglacials and suggests that the mechanisms highlighted by recent hypotheses linking mid-latitude atmospheric conditions to the extent of deep ocean ventilation and carbon sequestration over glacial-interglacial cycles are likely in operation during the longer time scale characteristic of the mid-Pleistocene transition. The cooling that initiated the "900 ka event" may have been driven by minima in insolation amplitude related to eccentricity modulation of precession that also affected low latitude climates as marked by threshold changes in the African monsoon system. The major thresholds in earth system behaviour through the mid-Pleistocene transition were likely governed by an interplay of the 100 kyr and 400 kyr eccentricity modulation of precession.

Looking through the Zircon Kaleidoscope: Durations, Rates, and Fluxes in Silicic Magmatic System

NASA Astrophysics Data System (ADS)

Schaltegger, U.; Wotzlaw, J. F.

2014-12-01

The crystallization rate of zircon in a cooling magma depends on the cooling rate through the saturation interval in addition to compositional and kinetic factors. Repeated influx of hot magma over 10-20 ka leads to short-amplitude temperature oscillations, which are recorded by resorption/crystallization cycles of zircon. Plotting the number of dated zircons versus their high-precision U-Pb date results in curves that qualitatively relate to the evolution of magma temperature over time [1], [2]. The trace elemental, O and Hf isotopic composition of zircon gives indications about the degree of magma homogenization and thermal evolution. Zircons from systems with small volumes and magma fluxes record non-systematic chemical and Hf isotopic heterogeneity, suggesting crystallization in non-homogenized ephemeral magma batches. Such systems typically lead to small, mid-upper crustal plutons [3]. Zircons from large-volume crystal-poor rhyolites record initial heterogeneities and rapid amalgamation of smaller magma batches over 10 ka [4], while zircons from monotonous intermediates record magma evolution over several 100 ka with coherent fractionation trends suggesting homogenization and a coherent thermal evolution [2]. In both cases, volumes and flux rates were sufficient to produce large volumes of eruptible magma on very contrasting time scales. Zircon is therefore recording cyclic crystallization-rejuvenation processes during temperature fluctuations in intermediate to upper crustal magma reservoirs but may not relate to the physical pluton emplacement or eruption. We can quantify volumes, rates of magma influx, rates of cooling and crystallization, and the degree of convective homogenization from zircon data, and infer reservoir assembly and eruption trigger mechanisms. These parameters largely control the evolution of long-lived, low-flux silicic magmatic system typical for mid-to-upper crustal plutons, monotonous intermediates are characterized by intermediate durations and fluxes while short-lived, high-flux systems preferentially produce crystal-poor rhyolites. References: [1] Caricchi et al. (2014) Nature 511, 457-461; [2] Wotzlaw et al. (2013) Geology 41, 867-870; [3] Broderick (2013) PhD thesis, Univ. of Geneva; [3] Wotzlaw et al. (2014) Geology, doi:10.1130/G35979.1

Interrater Reliability of the Categorization of Late Radiographic Changes After Lung Stereotactic Body Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faruqi, Salman; Giuliani, Meredith E., E-mail: meredith.giuliani@rmp.uhn.on.ca; Raziee, Hamid

2014-08-01

Purpose: Radiographic changes after lung stereotactic body radiation therapy (SBRT) have been categorized into 4 groups: modified conventional pattern (A), mass-like fibrosis; (B), scar-like fibrosis (C), and no evidence of increased density (D). The purpose of this study was to assess the interrater reliability of this categorization system in patients with early-stage non-small cell lung cancer (NSCLC). Methods and Materials: Seventy-seven patients were included in this study, all treated with SBRT for early-stage (T1/2) NSCLC at a single institution, with a minimum follow-up of 6 months. Six experienced clinicians familiar with post-SBRT radiographic changes scored the serial posttreatment CT images independentlymore » in a blinded fashion. The proportion of patients categorized as A, B, C, or D at each interval was determined. Krippendorff's alpha (KA), Multirater kappa (M-kappa), and Gwet's AC1 (AC1) scores were used to establish interrater reliability. A leave-one-out analysis was performed to demonstrate the variability among raters. Interrater agreement of the first and last 20 patients scored was calculated to explore whether a training effect existed. Results: The number of ratings ranged from 450 at 6 months to 84 at 48 months of follow-up. The proportion of patients in each category was as follows: A, 45%; B, 16%; C, 13%; and D, 26%. KA and M-kappa ranged from 0.17 to 0.34. AC1 measure range was 0.22 to 0.48. KA increased from 0.24 to 0.36 at 12 months with training. The percent agreement for pattern A peaked at 12 month with a 54% chance of having >50% raters in agreement and decreased over time, whereas that for patterns B and C increased over time to a maximum of 20% and 22%, respectively. Conclusion: This post-SBRT radiographic change categorization system has modest interrater agreement, and there is a suggestion of a training effect. Patterns of fibrosis evolve after SBRT and alternative categorization systems should be evaluated.« less

Eruptive History and Chemical Evolution of the Precaldera and Postcaldera Basalt-Dacite Sequences, Long Valley, California: Implications for Magma Sources, Current Seismic Unrest, and Future Volcanism

USGS Publications Warehouse

Bailey, Roy A.

2004-01-01

The Long Valley Volcanic Field in east-central California straddles the East Sierran frontal fault zone, overlapping the Sierra Nevada and western Basin and Range Provinces. The volcanic field overlies a mature mid-Tertiary erosional surface that truncates a basement composed mainly of Mesozoic plutons and associated roof pendants of Mesozoic metavolcanic and Paleozoic metasedimentary rocks. Long Valley volcanism began about 4 Ma during Pliocene time and has continued intermittently through the Holocene. The volcanism is separable into two basalt-rhyolite episodes: (1) an earlier, precaldera episode related to Long Valley Caldera that climaxed with eruption of the Bishop Tuff and collapse of the caldera; and (2) a later, postcaldera episode structurally related to the north-south-trending Mono-Inyo Craters fissure system, which extends from the vicinity of Mammoth Mountain northward through the west moat of the caldera to Mono Lake. Eruption of the basalt-dacite sequence of the precaldera basalt-rhyolite episode peaked volumetrically between 3.8 and 2.5 Ma; few basalts were erupted during the following 1.8 m.y. (2.5?0.7 Ma). Volcanism during this interval was dominated by eruption of the voluminous rhyolites of Glass Mountain (2.2?0.8 Ma) and formation of the Bishop Tuff magma chamber. Catastrophic rupture of the roof of this magma chamber caused eruption of the Bishop Tuff and collapse of Long Valley Caldera (760 ka), after which rhyolite eruptions resumed on the subsided caldera floor. The earliest postcaldera rhyolite flows (700?500 ka) contain quenched globular basalt enclaves (mafic magmatic inclusions), indicating that basaltic magma had reentered shallow parts of the magmatic system after a 1.8-m.y. hiatus. Later, at about 400 ka, copious basalts, as well as dacites, began erupting from vents mainly in the west moat of the caldera. These later eruptions initiated the postcaldera basalt-rhyolite episode related to the Mono-Inyo Craters fissure system, which has been active through late Pleistocene and Holocene time.

Biomarkers in Lake Van sediments reveal dry conditions in eastern Anatolia during 110.000-10.000 years B.P.

NASA Astrophysics Data System (ADS)

Randlett, Marie-Eve; Bechtel, Achim; van der Meer, Marcel T. J.; Peterse, Francien; Litt, Thomas; Pickarski, Nadine; Kwiecien, Ola; Stockhecke, Mona; Wehrli, Bernhard; Schubert, Carsten J.

2017-02-01

Lipid biomarkers were analyzed in Lake Van sediments covering the last 600 ka, with a focus on the period between 110 and 10 ka, when a broad maximum in pore water salinity as a relict from the past suggests dry conditions. The occurrence and distribution of biomarkers indicative for terrestrial plants (long-chain n-alkane C29), haptophyte algae (methyl alkenones C37) and halophilic archaea (archaeol) all point toward a dry climate in Lake Van region during this time interval. The hydrogen isotopic composition of C29 n-alkanes (δDC29) and C37 alkenones (δDC37) is enriched between MIS 4 and MIS 2, which is interpreted as a decrease in the regional ratio of precipitation to evaporation. Similarly, the low abundance of the acyclic glycerol dialkyl glycerol tetraether GDGT-0 relative to archaeol, quantified by the Archaeol and Caldarchaeol Ecometric (ACE) is assumed to reflect the presence of halophilic euryarchaeota adapted to high salinity water. The climate around Lake Van appears in phase with the Yammouneh basin 800 km southwest and Lake Urmia 250 km southeast of Lake Van over the last two glacial periods. The results highlight the potential of combining ACE, δDC29, and δDC37 for reconstructing salinity changes and regional precipitation to evaporation ratio from lake sediments.

Millennial-scale climate variations recorded in Early Pliocene colour reflectance time series from the lacustrine Ptolemais Basin (NW Greece)

NASA Astrophysics Data System (ADS)

Steenbrink, J.; Kloosterboer-van Hoeve, M. L.; Hilgen, F. J.

2003-03-01

Quaternary climate proxy records show compelling evidence for climate variability on time scales of a few thousand years. The causes for these millennial-scale or sub-Milankovitch cycles are still poorly understood, not least due to the complex feedback mechanisms of large ice sheets during the Quaternary. We present evidence of millennial-scale climate variability in Early Pliocene lacustrine sediments from the intramontane Ptolemais Basin in northwestern Greece. The sediments are well exposed in a series of open-pit lignite mines and exhibit a distinct millennial-scale sedimentary cyclicity of alternating lignites and lacustrine marl beds that resulted from precession-induced variations in climate. The higher-frequency, millennial-scale cyclicity is particularly prominent within the grey-coloured marl segment of individual cycles. A stratigraphic interval of ˜115 ka, covering five precession-induced sedimentary cycles, was studied in nine parallel sections from two open-pit lignite mines located several km apart. High-resolution colour reflectance records were used to quantify the within-cycle variability and to determine its lateral continuity. Much of the within-cycle variability could be correlated between the parallel sections, even in fine detail, which suggests that these changes reflect basin-wide variations in environmental conditions related to (regional) climate fluctuations. Interbedded volcanic ash beds demonstrate the synchronicity of these fluctuations and spectral analysis of the reflectance time series shows a significant concentration of within-cycle variability at periods of ˜11, ˜5.5 and ˜2 ka. The occurrence of variability at such time scales at times before the intensification of the Northern Hemisphere glaciation suggests that they cannot solely have resulted from internal ice-sheet dynamics. Possible candidates include harmonics or combination tones of the main orbital cycles, variations in solar output or periodic motions of the Earth and Moon.

Proceedings of the Eleventh Advanced Communications Technology Satellite Propagation Studies Workshop (APSW 11)

NASA Technical Reports Server (NTRS)

Golshan, Nasser (Editor); Ho, Christian (Editor)

1998-01-01

The Advanced Communications Technology Satellite Propagation Studies Workshop (APSW) is convened each year to present the results of the Advanced Communications Technology Satellite (ACTS) Ka-band propagation campaign. Representatives from the space community including industry, academia, and government who are interested in radiowave propagation at Ka-band are invited to APSW for discussions and exchange of information. The ACTS Propagation campaign will complete five years of Ka-Band data collection at seven sites in North America by December 31, 1998. Through this effort, NASA is making a major contribution to the effective utilization of this band by providing timely propagation data and models for predicting the performance of Ka-band links between space and ground.

Laser-fusion 40Ar/39Ar Ages of Darwin Impact Glass

NASA Astrophysics Data System (ADS)

Lo, Ching-Hua; Howard, Kieren T.; Chung, Sun-Lin; Meffre, Sebastien

2002-11-01

Three samples of Darwin Glass, an impact glass found in Tasmania, Australia at the edge of the Australasian tektite strewn field were dated using the 40Ar/39Ar single-grain laser fusion technique, yielding isochron ages of 796-815 ka with an overall weighted mean of 816 ± 7 ka. These data are statistically indistinguishable from those recently reported for the Australasian tektites from Southeast Asia and Australia (761-816 ka; with a mean weighted age of 803 ± 3 ka). However, considering the compositional and textural differences and the disparity from the presumed impact crater area for Australasian tektites, Darwin Glass is more likely to have resulted from a distinct impact during the same period of time.

Robust 24 ± 6 ka 40Ar/39Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California

USGS Publications Warehouse

Turrin, Brent D.; Muffler, L. J. Patrick; Clynne, Michael A.; Champion, Duane E.

2007-01-01

40Ar/39Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K2O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield 40Ar/39Ar ages of 38 ± 7 ka (Cinder Butte; 1.65% K2O), 46 ± 7 ka (Sugarloaf Peak; 1.85% K2O), 67 ± 4 ka (Little Potato Butte; 1.42% K2O) and 77 ± 11 ka (Potato Butte; 1.62% K2O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K2O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26 ± 6 ka is seductively appealing. A second sample (0.17% K2O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26 ± 18, 30 ± 20 and 24 ± 6 ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24 ± 6 ka is preferred. As with all isotopically determined ages, confidence in the results is significantly enhanced when additional constraints imposed by other isotopic ages within a stratigraphic context are taken into account.

Perforating elastic fibers ('elastic fiber trapping') in the differentiation of keratoacanthoma, conventional squamous cell carcinoma and pseudocarcinomatous epithelial hyperplasia.

PubMed

Shah, Kabeer; Kazlouskaya, Viktoryia; Lal, Karan; Molina, David; Elston, Dirk M

2014-02-01

Keratoacanthoma (KA), an epithelial neoplasm occurring in sun-exposed skin of the elderly, is considered a well-differentiated form of conventional squamous cell carcinoma (SCC) that often follows a course of spontaneous regression. Distinguishing KA from conventional SCC or pseudocarcinomatous epithelial hyperplasia ensures proper diagnosis, treatment and management. For some time, perforating elastic fibers have been utilized in differentiating KA from SCC. This phenomenon may also occur in association with scars and hypertrophic lupus erythematosus (LE). To assess the diagnostic utility of perforating elastic fibers, we compared their incidence in KA, SCC, scars with overlying pseudocarcinomatous hyperplasia, hypertrophic LE, hypertrophic lichen planus (LP) and lichen simplex chronicus (LSC). A retrospective case search identified 359 lesions and the presence of perforating elastic fibers was evaluated using routinely stained sections. This phenomenon was documented in all studied groups except hypertrophic LP. The incidence was found to be 71% in KA, 37% in SCC, and was lowest in inflammatory conditions with associated pseudocarcinomatous hyperplasia (hypertrophic LP 0%, hypertrophic LE 5.9% and LSC 28.2%). The observed frequency in pseudocarcinomatous hyperplasia overlying scars (57.8%) vs. KA (71%) was not statistically different. Although elastic fiber trapping has potential value as a diagnostic criterion for KA, dermatopathologists should consider its limitations. Its diagnostic utility was greatest in distinguishing KA from hypertrophic LE and hypertrophic LP. Conversely, elastic trapping is not helpful differentiating pseudocarcinomatous hyperplasia from recurrent/persistent KA following surgery. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Global calibration/validation of 2 years of SARAL/AltiKa data

NASA Astrophysics Data System (ADS)

Scharroo, Remko; Lillibridge, John; Leuliette, Eric; Bonekamp, Hans

2015-04-01

The AltiKa altimeter flying onboard the French/Indian SARAL satellite provides the first opportunity to examine Ka-band measurements of sea surface height, significant wave height and ocean surface wind speed. In this presentation we provide the results from our global calibration/validation analysis of the AltiKa measurements, with an emphasis on near real-time applications of interest to both EUMETSAT and NOAA. Traditional along-track SSHA, and single as well as dual-satellite crossover assessments of the AltiKa performance are be provided. Unique aspects of the AltiKa mission such as improved along-track resolution, reduced ionospheric path delay corrections, mission-specific wind speed and sea state bias corrections, and sensitivity to liquid moisture and rain are also explored. In February 2014, a major update to the ground processing was introduced. "Patch-2" improved the way wind speed was derived from altimeter backscatter, as suggested by Lillibridge et al. (1). The backscatter attenuation is now derived from the radiometer measurements via neural network algorithms, which also determine the wet tropospheric correction. We emphasize these improvements in our analysis. After 2 years in flight, SARAL/AltiKa is already providing a significant contribution to the constellation of operational radar altimetry missions, demonstrating the large benefits of high-rate Ka-band altimetry. (1) Lillibridge, John, Remko Scharroo, Saleh Abdalla, Doug Vandemark, 2014: One- and Two-Dimensional Wind Speed Models for Ka-Band Altimetry. J. Atmos. Oceanic Technol., 31, 630-638. doi: http://dx.doi.org/10.1175/JTECH-D-13-00167.1

U-Th dating of calcite corals from the Gulf of Aqaba

NASA Astrophysics Data System (ADS)

Yehudai, Maayan; Lazar, Boaz; Bar, Neta; Kiro, Yael; Agnon, Amotz; Shaked, Yonathan; Stein, Mordechai

2017-02-01

Most of the fossil corals in the elevated reef terraces along the Gulf of Aqaba (GOA) were extensively altered to calcite. This observation indicates extensive interaction with freshwater, possibly when the terraces passed through a coastal aquifer that existed along the shores of the GOA, implying a wetter climate during the time of recrystallization from aragonite to calcite. Thus, dating of the recrystallization events should yield the timing of past wetter conditions in the current hyper-arid area of the GOA. In the present study, 18 aragonite and calcite corals were collected from several elevated coral reef terraces off the coast, south of the city of Aqaba. While aragonite corals were dated with the conventional closed system age equation (assuming zero initial Th), the dating of the calcite corals required the development of adequate equations to allow the calculation of both the initial formation age of the aragonite corals and the time of recrystallization to calcite. The two age calculations were based on the assumptions that each reef terrace went through a single and rapid recrystallization event and that the pristine aragonite corals were characterized by a rather uniform initial U concentration, typical for pristine modern corals. Two recrystallization events were identified at 104 ± 6 ka and 124 ± 8 ka. The ages coincide with the timing of sapropel events S4 and S5, respectively, when the African monsoon induced enhanced wetness in the desert area. Considering the age uncertainties, the times of formation of the two major reef terraces are estimated to be ∼124 ka (reef terrace R2) and ∼130 ka (reef terrace R3), matching the peaks in the global sea level during the last interglacial MIS 5e stage. Apparently, sea level of the GOA did not fluctuate a lot during the period between ∼130 ka and ∼104 ka and remained close to the Marine Isotopic stage (MIS) 5e highstand. The availability of freshwater (during the sapropel periods) and limited sea level fluctuations facilitated the recrystallization of the GOA reef corals to calcite.

Eolian depositional phases during the past 50 ka and inferred climate variability for the Pampean Sand Sea, western Pampas, Argentina

NASA Astrophysics Data System (ADS)

Tripaldi, Alfonsina; Forman, Steven L.

2016-05-01

The Pampean Sand Sea, which occurs from the Argentinian Pampas to the eastern Andean piedmont, hosts presently stabilized dune fields spanning the late Quaternary. This study integrates previous results and presents new geomorphic, stratigraphic, sedimentological, and chronologic data for nineteen >2 m-thick eolian successions for the San Luis paleo-dune field, western Pampas, to better constrain the depositional history. Six eolian depositional phases are identified spanning the past 50 ka, interposed with paleosols and/or bounded by erosive surfaces. Age control was from 61 OSL ages of small aliquots of quartz grains from eolian stratigraphic units. The inferred timing of eolian phases are at ca. 70 ± 10 yr, 190 ± 20 yr, 12 to 1 ka, 22 to 17 ka, 29 to 24 ka, and 40 to 32 ka. A maximum span for periods of pedogenesis at ca. 12 to 17 ka, 22 to 24 ka, and 29 to 32 ka was provided by bounding OSL ages, which broadly overlap with high stands of pluvial lakes and glacier advances in the central Andes. We infer that the added precipitation may reflect expansion of the Southern Hemisphere monsoon, associated with Northern Hemisphere Heinrich events, leading to episodes of significantly wetter conditions (>350 mm MAP) to at least 35° S. Most of the Holocene (12 ka to 0.8 ka) was characterized by sand sheet deposit under drier than present conditions (100-450 mm MAP), associated with Monte-type vegetation (shrub steppe). The latest two eolian depositional phases, occurred at ca. 190 and 70 yr ago, during the historic period with European settlement and are related to anthropogenic landscape disturbance, though the youngest phase was concomitant with 1930s drought. Wet conditions dominated since ca. AD 1970 with new lakes and rivers forming across this eolian terrain; an incongruous environmental response in reference to drier conditions for most of the Holocene.

Ka-Band, RF MEMS Switches on CMOS Grade Silicon with a Polyimide Interface Layer

NASA Technical Reports Server (NTRS)

Ponchak, George E.; Varaljay, Nicholas C.; Papapolymerou, John

2003-01-01

For the first time, RF MEMS switcbes on CMOS grade Si witb a polyimide interface layer are fabricated and characterized. At Ka-Band (36.6 GHz), an insertion loss of 0.52 dB and an isolation of 20 dB is obtained.

PIG2LIG-4FUTURE: a database

NASA Astrophysics Data System (ADS)

El Ouahabi, A.; Martrat, B.; Lopez, J. F.; Grimalt, J. O.

2012-04-01

The ability to simulate the rhythm of abrupt climate changes (ACCs) will depend on the availability of high quality palæoclimate databases with sufficient temporal resolution to make relevant inferences from a human perspective. This study presents the PIG2LIG-4FUTURE database (P2L-4F db). The philosophy behind is to facilitate access to data not only for the scientific community, but also for those outside this community and, in doing so, ensure that the data are as useful as possible to help in answering a challenging key question: What is the risk of ACCs in periods similar to the present one? The P2L-4F db identifies an intra- and inter-event stratigraphy. A breakdown of the events in the PIG (present interglacial, time period from which more information is available and it is reasonably well dated) is defined in order to (2) identify ACCs in the LIG (last interglacial, much less known and dated period) for (4) better evaluation of the likelihood of sudden shifts within warm climate behaviour (i.e. next centuries, FUTURE). For this db, both the PIG and the LIG include deglaciation and interglacial states and they are referred to by means of chronostratigraphy: (i) the PIG refers to the last 19 ka years, i.e. a precessional cycle should be complete within the next 5 ka years; (ii) the LIG is the time span between 133 ka and 109 ka years, i.e. a time slot of 24 ka years, roughly a precessional cycle. The db compiles comprehensive selected palæo-data retrieved from a variety of sources (http://www.ncdc.noaa.gov, http://www.pangaea.de and others) but also instrumental data, to validate reconstructions against observations (e.g. http://data.giss.nasa.gov, http://iridl.ldeo.columbia.edu, etc). The records included accomplish two simple criteria: they cover the time span of interest, specifically the PIG and the LIG periods, and have sufficient time resolution to distinguish between an ACC and a gradual event. The research has focussed on three main palæoarchives: (i) ice cores, because they have been the reference for ACCs for over half a century; (ii) stalagmites, because they are crucial for dating, particularly for the LIG; (iii) marine and continental sediments, because they have proven to be a powerful source of ACCs. The same response is not seen everywhere due to proxy and location effects (see-saws not only north-to-south between poles, but also tropics-to-poles and eastern-to-western gradients). However, by using global and regional stacks, PIG-like events have been located within the LIG period. The spatio-temporal pattern during several specific events will be discussed. For example, the results show that the PIG 8.2 ka-event was something akin to a dividing line, as it was a LIG event which occured at approximately 120 ka ago. Environment and climate were evidently very different before and after this type of events. Additionally, the 2.6 ka and 0.8 ka-events were more an exception than a rule, somewhat resembling a clear glacial inception initiated from 113 to 111 ka ago. However, ACCs within the PIG are not exactly the same as the ones for the LIG, either in intensity or rates of change. This fact is hardly surprising given that none of the triggers and sources of persistence were reproduced in an identical mode during both periods.

Swirls and Plumes or Application of Statistical Methods to Satellite-Derived Sea Surface Temperatures.

DTIC Science & Technology

1983-08-01

drift speed of about 10 ka /day, which places it at the circular drifter track on the release day (185). Note that all drifters south of Pt. Arena were...spatial resolu- tion of 4 ka . *.a Data Collection The NOAA satellites are polar-orbiting satellites which pass overhead twice per day. One pass is...then decreases so that the maximum signal-to-noise occurs for 10 km x 10 ka boxes. Thus at a 12-hour separation in time temperature features of 78 less

Pliocene environments

USGS Publications Warehouse

Poore, R.Z.

2007-01-01

The Pliocene spans the interval of Earth history from ca. 5.3 to 1.8 million years ago (Ma). Although details are still debated there is much evidence from continental and oceanic locations indicating that conditions from 5.3 to about 3.0 Ma were often warmer than in modern times in mid- and high latitudes and that climate variability was subdued compared to the Pleistocene. Millennial-scale early Pliocene climate records are dominated by 19–21 thousand years ago (ka) oscillations. Starting at about 3.0 Ma, a long-term trend toward climate cooling and the ice ages of the Pleistocene accelerated. Significant build-up of Northern Hemisphere ice sheets began around 2.9 Ma and climate variability as measured by the oxygen isotope record in deep-sea carbonate microfossils increased. Distinct glacial–interglacial cycles developed in the late Pliocene between 2.9 and 2.7 Ma.

Duration of mineralization and fluid-flow history of the Upper Mississippi Valley zinc-lead district

USGS Publications Warehouse

Rowan, E.L.; Goldhaber, M.B.

1995-01-01

Studies of fluid inclusions in sphalerite and biomarkers from the Upper Mississippi Valley zinc district show homogenization temperatures to be primarily between 90 and 150??C, yet show relatively low levels of thermal maturity. Numerical calculations are used to simulate fluid and heat flow through fracture-controlled ore zones and heat transfer to the adjacent rocks. Combining a best-fit path through fluid-inclusion data with measured thermal alteration of biomarkers, the time interval during which mineralizing fluids circulated through the Upper Mississippi Valley district was calculated to be on the order of 200 ka. Cambrian and Ordovician aquifers underlying the district, principally the St. Peter and Mt. Simon Sandstones, were the source of the mineralizing fluid. The duration of mineralization thus reflects the fluid-flow history of these regional aquifers. -from Authors

Rear-arc vs. arc-front volcanoes in the Katmai reach of the Alaska Peninsula: A critical appraisal of across-arc compositional variation

USGS Publications Warehouse

Hildreth, W.; Fierstein, J.; Siems, D.F.; Budahn, J.R.; Ruiz, J.

2004-01-01

Physical and compositional data and K-Ar ages are reported for 14 rear-arc volcanoes that lic 11-22 km behind the narrowly linear volcanic front defined by the Mount Katmai-to-Devils Desk chain on the Alaska Peninsula. One is a 30-km3 stratocone (Mount Griggs; 51-63% SiO2) active intermittently from 292 ka to Holocene. The others are monogenetic cones, domes, lava flows, plugs, and maars, of which 12 were previously unnamed and unstudied; they include seven basalts (48-52% SiO2), four mafic andesites (53-55% SiO2), and three andesite-dacite units. Six erupted in the interval 500-88 ka, one historically in 1977, and five in the interval 3-2 Ma. No migration of the volcanic front is discernible since the late Miocene, so even the older units erupted well behind the front. Discussion explores the significance of the volcanic front and the processes that influence compositional overlaps and differences among mafic products of the rear-arc volcanoes and of the several arc-front edifices nearby. The latter have together erupted a magma volume of about 200 km3, at least four times that of all rear-arc products combined. Correlation of Sr-isotope ratios with indices of fractionation indicates crustal contributions in volcanic-front magmas (0.7033-0.7038), but lack of such trends among the rear-arc units (0.70298-0.70356) suggests weaker and less systematic crustal influence. Slab contributions and mantle partial-melt fractions both appear to decline behind the front, but neither trend is crisp and unambiguous. No intraplate mantle contribution is recognized nor is any systematic across-arc difference in intrinsic mantle-wedge source fertility discerned. Both rear-arc and arc-front basalts apparently issued from fluxing of typically fertile NMORB-source mantle beneath the Peninsular terrane, which docked here in the Mesozoic. ?? Springer-Verlag 2004.

Surface faulting and paleoseismic history of the 1932 Cedar Mountain earthquake area, west-central Nevada, and implications for modern tectonics of the Walker Lane

USGS Publications Warehouse

Bell, J.W.; DePolo, C.M.; Ramelli, A.R.; Sarna-Wojcicki, A. M.; Meyer, C.E.

1999-01-01

The 1932 Cedar Mountain earthquake (Ms 7.2) was one of the largest historical events in the Walker Lane region of western Nevada, and it produced a complicated strike-slip rupture pattern on multiple Quaternary faults distributed through three valleys. Primary, right-lateral surface ruptures occurred on north-striking faults in Monte Cristo Valley; small-scale lateral and normal offsets occurred in Stewart Valley; and secondary, normal faulting occurred on north-northeast-striking faults in the Gabbs Valley epicentral region. A reexamination of the surface ruptures provides new displacement and fault-zone data: maximum cumulative offset is estimated to be 2.7 m, and newly recognized faults extend the maximum width and end-to-end length of the rupture zone to 17 and 75 km, respectively. A detailed Quaternary allostratigraphic chronology based on regional alluvialgeomorphic relationships, tephrochronology, and radiocarbon dating provides a framework for interpreting the paleoseismic history of the fault zone. A late Wisconsinan alluvial-fan and piedmont unit containing a 32-36 ka tephra layer is a key stratigraphic datum for paleoseismic measurements. Exploratory trenching and radiocarbon dating of tectonic stratigraphy provide the first estimates for timing of late Quaternary faulting along the Cedar Mountain fault zone. Three trenches display evidence for six faulting events, including that in 1932, during the past 32-36 ka. Radiocarbon dating of organic soils interstratified with tectonically ponded silts establishes best-fit ages of the pre-1932 events at 4, 5,12,15, and 18 ka, each with ??2 ka uncertainties. On the basis of an estimated cumulative net slip of 6-12 m for the six faulting events, minimum and maximum late Quaternary slip rates are 0.2 and 0.7 mm/yr, respectively, and the preferred rate is 0.4-0.5 mm/yr. The average recurrence (interseismic) interval is 3600 yr. The relatively uniform thickness of the ponded deposits suggests that similar-size, characteristic rupture events may characterize late Quaternary slip on the zone. A comparison of event timing with the average late Quaternary recurrence interval indicates that slip has been largely regular (periodic) rather than temporally clustered. To account for the spatial separation of the primary surface faulting in Monte Cristo Valley from the epicenter and for a factor-of-two-to-three disparity between the instrumentally and geologically determined seismic moments associated with the earthquake, we hypothesize two alternative tectonic models containing undetected subevents. Either model would adequately account for the observed faulting on the basis of wrench-fault kinematics that may be associated with the Walker Lane. The 1932 Cedar Mountain earthquake is considered an important modern analogue for seismotectonic modeling and estimating seismic hazard in the Walker Lane region. In contrast to most other historical events in the Basin and Range province, the 1932 event did not occur along a major range-bounding fault, and no single, throughgoing basement structure can account for the observed rupture pattern. The 1932 faulting supports the concept that major earthquakes in the Basin and Range province can exhibit complicated distributive rupture patterns and that slip rate may not be a reliable criterion for modeling seismic hazard.

Annual proxy data from Lago Grande di Monticchio (southern Italy) contributing to chronological constraints and abrupt climatic oscillations between 76 and 112 ka

NASA Astrophysics Data System (ADS)

Martin-Puertas, C.; Brauer, A.; Wulf, S.; Ott, F.; Lauterbach, S.; Dulski, P.

2014-06-01

We present annual sedimentological proxies and sub-annual element scanner data from the Lago Grande di Monticchio (MON) sediment record for the sequence 76-112 ka, which, combined with the decadal to centennial resolved pollen assemblage, allow a comprehensive reconstruction of six major abrupt cold and relatively humid spells (MON 1-6) in the central Mediterranean during early phase of the last glaciation. These climatic oscillations are defined by intervals of thicker varves and high Ti-counts and coincide with episodes of forest depletion interpreted as cold and wet oscillations. Based on the independent and slightly revised MON-2014 varve chronology (76-112 ka), a detailed comparison with the Greenland ice-core δ18O record (NGRIP) and northern Alps speleothem δ18O data (NALPS) is presented. Based on visual inspection of major changes in the proxy data, MON 2-6 are suggested to correlate with GS 25-20. MON 1 (Woillard event), the first and shortest cooling spell in the Mediterranean after a long phase of stable interglacial conditions, has no counterpart in the Greenland ice core, but coincides with the lowest isotope values at the end of the gradual decrease in δ18O in NGRIP during the second half of the GI 25. MON 3 is the least pronounced cold spell and shows gradual transitions, whereas its NGRIP counterpart GS 24 is characterized by sharp changes in the isotope records. MON 2 and MON 4 are the longest most pronounced oscillations in the MON sediments in good agreement with their counterparts in the ice and spelethem records. The length of MON 4 (correlating with GS 22) support the duration of this stadial proposed by the NALPS timescales and suggests ca. 500 yr longer duration than calculated by GICC05 and AICC2012, which would confirm a~possible underestimation in the ice-core. Absolute dating of the cold spells occurring from 112 to 100 ka (MON 1-3) in the MON-2014 chronology is in good agreement with the GICC05 and NALPS timescales but the younger oscillations (MON 4-6) are ca. 3500 yr younger in Monticchio suggesting a so far not recognized and explicable underestimation of varves within the interstadial interval between MON 3 and MON 4 (corresponding to GI 23-GI 22).

Alkenone-based reconstructions reveal four-phase Holocene temperature evolution for High Arctic Svalbard

NASA Astrophysics Data System (ADS)

van der Bilt, Willem G. M.; D'Andrea, William J.; Bakke, Jostein; Balascio, Nicholas L.; Werner, Johannes P.; Gjerde, Marthe; Bradley, Raymond S.

2018-03-01

Situated at the crossroads of major oceanic and atmospheric circulation patterns, the Arctic is a key component of Earth's climate system. Compounded by sea-ice feedbacks, even modest shifts in the region's heat budget drive large climate responses. This is highlighted by the observed amplified response of the Arctic to global warming. Assessing the imprint and signature of underlying forcing mechanisms require paleoclimate records, allowing us to expand our knowledge beyond the short instrumental period and contextualize ongoing warming. However, such datasets are scarce and sparse in the Arctic, limiting our ability to address these issues. Here, we present two quantitative Holocene-length paleotemperature records from the High Arctic Svalbard archipelago, situated in the climatically sensitive Arctic North Atlantic. Temperature estimates are based on U37K unsaturation ratios from sediment cores of two lakes. Our data reveal a dynamic Holocene temperature evolution, with reconstructed summer lake water temperatures spanning a range of ∼6-8 °C, and characterized by four phases. The Early Holocene was marked by an early onset (∼10.5 ka cal. BP) of insolation-driven Hypsithermal conditions, likely compounded by strengthening oceanic heat transport. This warm interval was interrupted by cooling between ∼10.5-8.3 ka cal. BP that we attribute to cooling effects from the melting Northern Hemisphere ice sheets. Temperatures declined throughout the Middle Holocene, following a gradual trend that was accentuated by two cooling steps between ∼7.8-7 ka cal. BP and around ∼4.4-4.3 ka cal. BP. These transitions coincide with a strengthening influence of Arctic water and sea-ice in the adjacent Fram Strait. During the Late Holocene (past 4 ka), temperature change decoupled from the still-declining insolation, and fluctuated around comparatively cold mean conditions. By showing that Holocene Svalbard temperatures were governed by an alternation of forcings, this study improves our understanding of Arctic climate dynamics.

Kv4 channels underlie A-currents with highly variable inactivation time courses but homogeneous other gating properties in the nucleus tractus solitarii.

PubMed

Strube, Caroline; Saliba, Layal; Moubarak, Estelle; Penalba, Virginie; Martin-Eauclaire, Marie-France; Tell, Fabien; Clerc, Nadine

2015-04-01

In the nucleus of the tractus solitarii (NTS), a large proportion of neurones express transient A-type potassium currents (I KA) having deep influence on the fidelity of the synaptic transmission of the visceral primary afferent inputs to second-order neurones. Up to now, the strong impact of I KA within the NTS was considered to result exclusively from its variation in amplitude, and its molecular correlate(s) remained unknown. In order to identify which Kv channels underlie I KA in NTS neurones, the gating properties and the pharmacology of this current were determined using whole cell patch clamp recordings in slices. Complementary information was brought by immunohistochemistry. Strikingly, two neurone subpopulations characterized by fast or slow inactivation time courses (respectively about 50 and 200 ms) were discriminated. Both characteristics matched those of the Kv4 channel subfamily. The other gating properties, also matching the Kv4 channel ones, were homogeneous through the NTS. The activation and inactivation occurred at membrane potentials around the threshold for generating action potentials, and the time course of recovery from inactivation was rapid. Pharmacologically, I KA in NTS neurones was found to be resistant to tetraethylammonium (TEA), sea anemone toxin blood-depressing substance (BDS) and dendrotoxin (DTX), whereas Androctonus mauretanicus mauretanicus toxin 3 (AmmTX3), a scorpion toxin of the α-KTX 15 family that has been shown to block all the members of the Kv4 family, inhibited 80 % of I KA irrespectively of its inactivation time course. Finally, immunohistochemistry data suggested that, among the Kv4 channel subfamily, Kv4.3 is the prevalent subunit expressed in the NTS.

Concentration-related response potentiometric titrations to study the interaction of small molecules with large biomolecules.

PubMed

Hamidi-Asl, Ezat; Daems, Devin; De Wael, Karolien; Van Camp, Guy; Nagels, Luc J

2014-12-16

In the present paper, the utility of a special potentiometric titration approach for recognition and calculation of biomolecule/small-molecule interactions is reported. This approach is fast, sensitive, reproducible, and inexpensive in comparison to the other methods for the determination of the association constant values (Ka) and the interaction energies (ΔG). The potentiometric titration measurement is based on the use of a classical polymeric membrane indicator electrode in a solution of the small-molecule ligand. The biomolecule is used as a titrant. The potential is measured versus a reference electrode and transformed into a concentration-related signal over the entire concentration interval, also at low concentrations, where the millivolt (y-axis) versus log canalyte (x-axis) potentiometric calibration curve is not linear. In the procedure, Ka is calculated for the interaction of cocaine with a cocaine binding aptamer and with an anticocaine antibody. To study the selectivity and cross-reactivity, other oligonucleotides and aptamers are tested, as well as other small ligand molecules such as tetrakis(4-chlorophenyl)borate, metergoline, lidocaine, and bromhexine. The calculated Ka compared favorably to the value reported in the literature using surface plasmon resonance. The potentiometric titration approach called "concentration-related response potentiometry" is used to study molecular interaction for seven macromolecular target molecules and four small-molecule ligands.

Onset and Evolution of Southern Annular Mode-Like Changes at Centennial Timescale.

PubMed

Moreno, P I; Vilanova, I; Villa-Martínez, R; Dunbar, R B; Mucciarone, D A; Kaplan, M R; Garreaud, R D; Rojas, M; Moy, C M; De Pol-Holz, R; Lambert, F

2018-02-22

The Southern Westerly Winds (SWW) are the surface expression of geostrophic winds that encircle the southern mid-latitudes. In conjunction with the Southern Ocean, they establish a coupled system that not only controls climate in the southern third of the world, but is also closely connected to the position of the Intertropical Convergence Zone and CO 2 degassing from the deep ocean. Paradoxically, little is known about their behavior since the last ice age and relationships with mid-latitude glacier history and tropical climate variability. Here we present a lake sediment record from Chilean Patagonia (51°S) that reveals fluctuations of the low-level SWW at mid-latitudes, including strong westerlies during the Antarctic Cold Reversal, anomalously low intensity during the early Holocene, which was unfavorable for glacier growth, and strong SWW since ~7.5 ka. We detect nine positive Southern Annular Mode-like events at centennial timescale since ~5.8 ka that alternate with cold/wet intervals favorable for glacier expansions (Neoglaciations) in southern Patagonia. The correspondence of key features of mid-latitude atmospheric circulation with shifts in tropical climate since ~10 ka suggests that coherent climatic shifts in these regions have driven climate change in vast sectors of the Southern Hemisphere at centennial and millennial timescales.

Experimental and analytical investigation on metal damage suffered from simulated lightning currents

NASA Astrophysics Data System (ADS)

Yakun, LIU; Zhengcai, FU; Quanzhen, LIU; Baoquan, LIU; Anirban, GUHA

2017-12-01

The damage of two typical metal materials, Al alloy 3003 and steel alloy Q235B, subjected to four representative lightning current components are investigated by laboratory and analytical studies to provide fundamental data for lightning protection. The four lightning components simulating the natural lightning consist of the first return stroke, the continuing current of interval stroke, the long continuing current, and the subsequent stroke, with amplitudes 200 kA, 8 kA, 400 A, and 100 kA, respectively. The damage depth and area suffered from different lightning components are measured by the ultrasonic scanning system. And the temperature rise is measured by the thermal imaging camera. The results show that, for both Al 3003 and steel Q235B, the first return stroke component results in the largest damage area with damage depth 0.02 mm uttermost. The long continuing current component leads to the deepest damage depth of 3.3 mm for Al 3003 and much higher temperature rise than other components. The correlation analysis between damage results and lightning parameters indicates that the damage depth has a positive correlation with charge transfer. The damage area is mainly determined by the current amplitude and the temperature rise increases linearly with the charge transfer larger.

A Record of Uranium-Series Transport in Fractured, Unsaturated Tuff at Nopal I, Sierra Peña Blanca, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Denton, J.; Goldstein, S. J.; Paviet, P.; Nunn, A. J.; Amato, R. S.; Hinrichs, K. A.

2015-12-01

In this study we utilize U-series disequilibria measurements to investigate mineral fluid interactions and the role fractures play in the geochemical evolution of an analogue for a high level nuclear waste repository, the Nopal I uranium ore deposit. Samples of fracture-fill materials have been collected from a vertical drill core and surface fractures. High uranium concentrations in these materials (12-7700 ppm) indicate U mobility and transport from the deposit in the past. U concentrations generally decrease with horizontal distance away from the ore deposit but show no trend with depth. Isotopic activity ratios indicate a complicated geochemical evolution in terms of the timing and extent of actinide mobility, possibly due to changing environmental (redox) conditions over the history of the deposit. 234U/238U activity ratios are generally distinct from secular equilibrium and indicate some degree of open system U behavior during the past 1.2 Ma. However, calculated closed system 238U-234U-230Th model ages are generally >313 ka and >183 ka for the surface fracture and drill core samples respectively, suggesting closed system behavior for U and Th over this most recent time period. Whole rock isochrons drawn for the drill core samples show that at two of three depths fractures have remained closed with respect to U and Th mobility for >200 ka. However, open system behavior for U in the last 350 ka is suggested at 67 m depth. 231Pa/235U activity ratios within error of unity suggest closed system behavior for U and Pa for at least the past 185 ka. 226Ra/230Th activity ratios are typically <1 (0.7-1.2), suggesting recent (<8 ka) radium loss and mobility due to ongoing fluid flow in the fractures. Overall, the mainly closed system behavior of U-Th-Pa over the past ~200 ka provides one indicator of the geochemical immobility of these actinides over long time-scales for potential nuclear waste repositories sited in fractured, unsaturated tuff.

LPJ-GUESS Simulated North America Vegetation for 21-0 ka Using the TraCE-21ka Climate Simulation

NASA Astrophysics Data System (ADS)

Shafer, S. L.; Bartlein, P. J.

2016-12-01

Transient climate simulations that span multiple millennia (e.g., TraCE-21ka) have become more common as computing power has increased, allowing climate models to complete long simulations in relatively short periods of time (i.e., months). These climate simulations provide information on the potential rate, variability, and spatial expression of past climate changes. They also can be used as input data for other environmental models to simulate transient changes for different components of paleoenvironmental systems, such as vegetation. Long, transient paleovegetation simulations can provide information on a range of ecological processes, describe the spatial and temporal patterns of changes in species distributions, and identify the potential locations of past species refugia. Paleovegetation simulations also can be used to fill in spatial and temporal gaps in observed paleovegetation data (e.g., pollen records from lake sediments) and to test hypotheses of past vegetation change. We used the TraCE-21ka transient climate simulation for 21-0 ka from CCSM3, a coupled atmosphere-ocean general circulation model. The TraCE-21ka simulated temperature, precipitation, and cloud data were regridded onto a 10-minute grid of North America. These regridded climate data, along with soil data and atmospheric carbon dioxide concentrations, were used as input to LPJ-GUESS, a general ecosystem model, to simulate North America vegetation from 21-0 ka. LPJ-GUESS simulates many of the processes controlling the distribution of vegetation (e.g., competition), although some important processes (e.g., dispersal) are not simulated. We evaluate the LPJ-GUESS-simulated vegetation (in the form of plant functional types and biomes) for key time periods and compare the simulated vegetation with observed paleovegetation data, such as data archived in the Neotoma Paleoecology Database. In general, vegetation simulated by LPJ-GUESS reproduces the major North America vegetation patterns (e.g., forest, grassland) with regional areas of disagreement between simulated and observed vegetation. We describe the regions and time periods with the greatest data-model agreement and disagreement, and discuss some of the strengths and weaknesses of both the simulated climate and simulated vegetation data.

On the Formation of Meridional Overturning Circulation in the Pacific Ocean during the MIS31 Interglacial

NASA Astrophysics Data System (ADS)

Justino, F. J.; Lindemann, D.; Kucharski, F.

2016-02-01

Earth climate history has been punctuated by cold (glacial) and warm (inter-glacial) intervals associated with modification of the planetary orbit and subsequently changes in paleotopography.During the Pleistocene epoch, the time interval between 1.8 million and 11,700 before present, remarkable episodes of warmer climates such as the Marine IsotopeStage (MIS) 1, 5e, 11c, and 31 which occurred at 9, 127, 409, and 1080 ka, lead to changes in air temperature in the polar regions and substantial melting of polar glaciers. Based on first ever multi-millennium coupled climate simulations of the Marine Isotope Stage 31 (MIS31), long-term oceanic conditions characteristic of this interval have been analyzed. Modeling experiments forced by modified West Antarctic Ice Sheet (WAIS) topography and astronomical configuration, demonstrated that substantial increase in the thermohaline flow and its associated northward heat transport in both Atlantic and Pacific oceans are predicted to occur during the MIS31. In the Atlantic these changes are driven by enhanced oceanic heat loss and increased water density. In the Pacific, anomalous atmospheric circulation leads to an overall increase of the water mass transport in the subtropical gyre, and drastically modified subtropical cell.Additional aspects related to the formation of the Pacific ocean MOC will be presented. This study is sponsored by the Brazilian Antarctic Program Grant CNPq 407681/2013-2.

Melt inclusion shapes: Timekeepers of short-lived giant magma bodies

DOE PAGES

Pamukcu, Ayla S.; Gualda, Guilherme A. R.; Bégué, Florence; ...

2015-09-24

The longevity of giant magma bodies in the Earth’s crust prior to eruption is poorly constrained, but recognition of short time scales by multiple methods suggests that the accumulation and eruption of these giant bodies may occur rapidly. We describe a new method that uses textures of quartz-hosted melt inclusions, determined using quantitative three-dimensional propagation phase-contrast X-ray tomography, to estimate quartz crystallization times and growth rates, and we compare the results to those from Ti diffusion profiles. We investigate three large-volume, high-silica rhyolite eruptions: the 240 ka Ohakuri-Mamaku and 26.5 ka Oruanui (Taupo Volcanic Zone, New Zealand), and the 760more » ka Bishop Tuff (California, USA). Our results show that (1) longevity estimates from melt inclusion textures and Ti diffusion profiles are comparable, (2) quartz growth rates average ∼10−12 m/s, and (3) quartz melt inclusions give decadal to centennial time scales, revealing that giant magma bodies can develop over notably short historical time scales.« less

Human predation contributed to the extinction of the Australian megafaunal bird Genyornis newtoni ∼47 ka

PubMed Central

Miller, Gifford; Magee, John; Smith, Mike; Spooner, Nigel; Baynes, Alexander; Lehman, Scott; Fogel, Marilyn; Johnston, Harvey; Williams, Doug; Clark, Peter; Florian, Christopher; Holst, Richard; DeVogel, Stephen

2016-01-01

Although the temporal overlap between human dispersal across Australia and the disappearance of its largest animals is well established, the lack of unambiguous evidence for human–megafauna interactions has led some to question a human role in megafaunal extinction. Here we show that diagnostic burn patterns on eggshell fragments of the megafaunal bird Genyornis newtoni, found at >200 sites across Australia, were created by humans discarding eggshell in and around transient fires, presumably made to cook the eggs. Dating by three methods restricts their occurrence to between 53.9 and 43.4 ka, and likely before 47 ka. Dromaius (emu) eggshell occur frequently in deposits from >100 ka to present; burnt Dromaius eggshell first appear in deposits the same age as those with burnt Genyornis eggshell, and then continually to modern time. Harvesting of their eggs by humans would have decreased Genyornis reproductive success, contributing to the bird's extinction by ∼47 ka. PMID:26823193

Late quaternary lake level changes of Taro Co and neighbouring lakes, southwestern Tibetan Plateau, based on OSL dating and ostracod analysis

NASA Astrophysics Data System (ADS)

Alivernini, Mauro; Lai, Zhongping; Frenzel, Peter; Fürstenberg, Sascha; Wang, Junbo; Guo, Yun; Peng, Ping; Haberzettl, Torsten; Börner, Nicole; Mischke, Steffen

2018-07-01

The Late Quaternary lake history of Taro Co and three neighbouring lakes was investigated to reconstruct local hydrological conditions and the regional moisture availability. Ostracod-based water depth and habitat reconstructions combined with OSL and radiocarbon dating are performed to better understand the Taro Co lake system evolution during the Late Quaternary. A high-stand is observed at 36.1 ka before present which represents the highest lake level since then related to a wet stage and resulting in a merging of Taro Co and its neighbouring lakes Zabuye and Lagkor Co this time. The lake level then decreased and reached its minimum around 30 ka. After c. 20 ka, the lake rose above the present day level. A minor low-stand, with colder and drier conditions, is documented at 12.5 cal. ka BP. Taro Co Zabuye and Lagkor Co formed one large lake with a corresponding high-stand during the early Holocene (11.2-9.7 cal. ka BP). After this Holocene lake level maximum, all three lakes shrank, probably related to drier conditions, and Lagkor Co became separated from the Taro Co-Zabuye system at c.7 ka. Subsequently, the lake levels decreased further about 30 m and Taro Co began to separate from Zabuye Lake at around 3.5 ka. The accelerating lake-level decrease of Taro Co was interrupted by a short-term lake level rise after 2 ka BP, probably related to minor variations of the monsoonal components. A last minor high-stand occurred at about 0.8 ka before today and subsequently the lake level of Taro Co registers a slight increase in recent years.

Equatorial Precession in the Control Software of the Ka-Band Object Observation and Monitoring Experiment

NASA Technical Reports Server (NTRS)

Jakeman, Hali L.

2013-01-01

The Ka-Band Object Observation and Monitoring, or KaBOOM, project is designed mainly to track and characterize near Earth objects. However, a smaller goal of the project would be to monitor pulsars and study their radio frequency signals for use as a clock in interstellar travel. The use of pulsars and their timing accuracy has been studied for decades, but never in the Ka-band of the radio frequency spectrum. In order to begin the use of KaBOOM for this research, the control systems need to be analyzed to ensure its capability. Flaws in the control documentation leave it unclear as to whether the control software processes coordinates from the J200 epoch. This experiment will examine the control software of the Intertronic 12m antennas used for the KaBOOM project and detail its capabilities in its "equatorial mode." The antennas will be pointed at 4 chosen points in the sky on several days while probing the virtual azimuth and elevation (horizon coordinate) registers. The input right ascension and declination coordinates will then be converted separately from the control software to horizontal coordinates and compared, thus determining the ability of the control software to process equatorial coordinates.

Classifying Types of Transitions of Past Environmental Change in East African Records

NASA Astrophysics Data System (ADS)

Trauth, M. H.

2016-12-01

The possible abruptness and internal variability of wet episodes in African climate and their consequences for humans is widely debated in the literature, in particular the last wet-dry transition in the Mid Holocene. We expect similar wet-dry and dry-wet transitions earlier in time, whose research is important for the discussion of the influence of climate change on early humans. Three examples of climate transitions, from wet to dry or from stable to unstable, are presented on three different time scales: (1) the Mid Holocene (MH) wet-dry transition in the Chew Bahir basin (Southern Ethiopian Rift; between 11 ka and 4 ka), (2) the MIS 5-4 transition in the Naivasha basin (Central Kenya Rift; between 160 ka and 50 ka), and (3) the Early Mid Pleistocene Transition (EMPT) in the Olorgesailie basin (Southern Kenya Rift; between 1.25 Ma and 0.4 Ma). A definition of abruptness, based on various statistical measures, used to classify characteristic types of transitions and the possible effect in the biosphere is presented.

A detailed 2,000-year late holocene pollen record from lower Pahranagat Lake, Southern Nevada, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hemphill, M L; Wigand, P E

Preliminary analysis of 128 pollen samples and seven radiocarbon dates from a 5-meter long, 10-cm diameter sediment core retrieved from Lower Pahranagat Lake (elevation - 975 in), Lincoln County, Nevada, gives us a rare, continuous, record of vegetation change at an interval of every 14 years over the last 2,000 years. During this period increasing Pinus (pine) pollen values with respect to Juniperus Ouniper pollen values reflect the increasing dominance of pinyon in southern Nevada woodlands during the last 2,000 years. Today Pinus pollen values indicate that pinyon pine is more frequent in the southern Great Basin since the endmore » of the Neoglacial 2,000 years ago. During the same time frame, a general decrease in Poaceae (grass) pollen values with respect to Artemisia (sagebrush) pollen values reflect the general trend of increasing dominance of steppe and desert scrub species with respect to grasses. Variations in these two species reflect not only the generally more xeric nature of climate during the last 2,000 years, but also periods of summer shifted rainfall - 1,500 years ago that encouraged both a period of grass and pinyon expansion. The ratio of aquatic to littoral pollen types indicates generally deeper water conditions 2 to 1 ka and more variable, but predominately more marshy, conditions at the site during most of the last 1 ka. Investigation of ostracodes from the same record being conducted by Dr. R. Forester at the USGS corroborate the pollen record by evidencing shifts between open and closed hydrologic systems including lake, marsh and even stream habitats. Analysis of an additional 10 meters of core recovered in the summer of 1994 with a basal date of 5.6 ka promises to provide the best record of middle through late Holocene vegetation and climate history for southern Nevada.« less

The movement of pre-adapted cool taxa in north-central Amazonia during the last glacial

NASA Astrophysics Data System (ADS)

D'Apolito, Carlos; Absy, Maria Lúcia; Latrubesse, Edgardo M.

2017-08-01

The effects of climate change on the lowland vegetation of Amazonia during the last glacial cycle are partially known for the middle and late Pleniglacial intervals (late MIS 3, 59-24 ka and MIS 2, 24-11 ka), but are still unclear for older stages of the last glacial and during the last interglacial. It is known that a more seasonal dry-wet climate caused marginal forest retraction and together with cooling rearranged forest composition to some extent. This is observed in pollen records across Amazonia depicting presence of taxa at glacial times in localities where they do not live presently. The understanding of taxa migration is hindered by the lack of continuous interglacial-glacial lowland records. We present new data from a known locality in NW Amazonia (Six Lakes Hill), showing a vegetation record that probably started during MIS 5 (130-71 ka) and lasted until the onset of the Holocene. The vegetation record unravels a novel pattern in tree taxa migration: (1) from the beginning of this cycle Podocarpus and Myrsine are recorded and (2) only later do Hedyosmum and Alnus appear. The latter group is largely restricted to montane biomes or more distant locations outside Amazonia, whereas the first is found in lowlands close to the study site on sandy soils. These findings imply that Podocarpus and Myrsine responded to environmental changes equally and this reflects their concomitant niche use in NW Amazonia. Temperature drop is not discarded as a trigger of internal forest composition change, but its effects are clearer later in the Pleniglacial rather than the Early Glacial. Therefore early climatic/environmental changes had a first order effect on vegetation that invoke alternative explanations. We claim last glacial climate-induced modifications on forest composition favoured the expansion of geomorphologic-soil related processes that initiated forest rearrangement.

History of late Holocene earthquakes at the Willow Creek site on the Nephi segment, Wasatch fault zone, Utah

USGS Publications Warehouse

Crone, Anthony J.; Personius, Stephen F.; Duross, Christopher; Machette, Michael N.; Mahan, Shannon

2014-01-01

This 43-page report presents new data from the Willow Creek site that provides well-defined and narrow bounds on the times of the three youngest earthquakes on the southern strand of the Nephi segment, Wasatch Fault zone, and refines the time of the youngest earthquake to about 200 years ago. This is the youngest surface rupture on the entire Wasatch fault zone, which occurred about a century or less before European settles arrived in Utah. Two trenches at the Willow Creek site exposed three scarp-derived colluvial wedges that are evidence of three paleoearthquakes. OxCal modeling of ages from Willow Creek indicate that paleoearthquake WC1 occurred at 0.2 ± 0.1 ka, WC2 occurred at 1.2 ± 0.1 ka, and WC3 occurred at 1.9 ± 0.6 ka. Stratigraphic constraints on the time of paleoearthquake WC4 are extremely poor, so OxCal modeling only yields a broadly constrained age of 4.7 ± 1.8 ka. Results from the Willow Creek site significantly refine the times of late Holocene earthquakes on the Southern strand of the Nephi segment, and this result, when combined with a reanalysis of the stratigraphic and chronologic information from previous investigations at North Creek and Red Canyon, yield a stronger basis of correlating individual earthquakes between all three sites.

The onset of the volcanism in the Ciomadul Volcanic Dome Complex (Eastern Carpathians): Eruption chronology and magma type variation

NASA Astrophysics Data System (ADS)

Molnár, Kata; Harangi, Szabolcs; Lukács, Réka; Dunkl, István; Schmitt, Axel K.; Kiss, Balázs; Garamhegyi, Tamás; Seghedi, Ioan

2018-04-01

Combined zircon U-Th-Pb and (U-Th)/He dating was applied to refine the eruption chronology of the last 2 Myr for the andesitic and dacitic Pilişca volcano and Ciomadul Volcanic Dome Complex (CVDC), the youngest volcanic area of the Carpathian-Pannonian region, located in the southernmost Harghita, eastern-central Europe. The proposed eruption ages, which are supported also by the youngest zircon crystallization ages, are much younger than the previously determined K/Ar ages. By dating every known eruption center in the CVDC, repose times between eruptive events were also accurately determined. Eruption of the andesite at Murgul Mare (1865 ± 87 ka) and dacite of the Pilişca volcanic complex (1640 ± 37 ka) terminated an earlier pulse of volcanic activity within the southernmost Harghita region, west of the Olt valley. This was followed by the onset of the volcanism in the CVDC, which occurred after several 100s kyr of eruptive quiescence. At ca. 1 Ma a significant change in the composition of erupted magma occurred from medium-K calc-alkaline compositions to high-K dacitic (Baba-Laposa dome at 942 ± 65 ka) and shoshonitic magmas (Malnaş and Bixad domes; 964 ± 46 ka and 907 ± 66 ka, respectively). Noteworthy, eruptions of magmas with distinct chemical compositions occurred within a restricted area, a few km from one another. These oldest lava domes of the CVDC form a NNE-SSW striking tectonic lineament along the Olt valley. Following a brief (ca. 100 kyr) hiatus, extrusion of high-K andesitic magma continued at Dealul Mare (842 ± 53 ka). After another ca. 200 kyr period of quiescence two high-K dacitic lava domes extruded (Puturosul: 642 ± 44 ka and Balvanyos: 583 ± 30 ka). The Turnul Apor lava extrusion occurred after a ca. 200 kyr repose time (at 344 ± 33 ka), whereas formation of the Haramul Mic lava dome (154 ± 16 ka) represents the onset of the development of the prominent Ciomadul volcano. The accurate determination of eruption dates shows that the volcanic eruptions were often separated by prolonged (ca. 100 to 200 kyr) quiescence periods. Demonstration of recurrence of volcanism even after such long dormancy has to be considered in assessing volcanic hazards, particularly in seemingly inactive volcanic areas, where no Holocene eruptions occurred. The term of 'volcanoes with Potentially Active Magma Storage' illustrates the potential of volcanic rejuvenation for such long-dormant volcanoes with the existence of melt-bearing crustal magma body.

The relationship between eruptive activity, flank collapse, and sea level at volcanic islands: A long-term (>1 Ma) record offshore Montserrat, Lesser Antilles

NASA Astrophysics Data System (ADS)

Coussens, Maya; Wall-Palmer, Deborah; Talling, Peter. J.; Watt, Sebastian. F. L.; Cassidy, Michael; Jutzeler, Martin; Clare, Michael A.; Hunt, James. E.; Manga, Michael; Gernon, Thomas. M.; Palmer, Martin. R.; Hatter, Stuart. J.; Boudon, Georges; Endo, Daisuke; Fujinawa, Akihiko; Hatfield, Robert; Hornbach, Matthew. J.; Ishizuka, Osamu; Kataoka, Kyoko; Le Friant, Anne; Maeno, Fukashi; McCanta, Molly; Stinton, Adam. J.

2016-07-01

Hole U1395B, drilled southeast of Montserrat during Integrated Ocean Drilling Program Expedition 340, provides a long (>1 Ma) and detailed record of eruptive and mass-wasting events (>130 discrete events). This record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano. Analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of Montserrat (˜930 to ˜900 ka, ˜810 to ˜760 ka, and ˜190 to ˜120 ka) that coincide with periods of increased volcano instability and mass-wasting. The youngest of these periods marks the peak in activity at the Soufrière Hills volcano. The largest flank collapse of this volcano (˜130 ka) occurred toward the end of this period, and two younger landslides also occurred during a period of relatively elevated volcanism. These three landslides represent the only large (>0.3 km3) flank collapses of the Soufrière Hills edifice, and their timing also coincides with periods of rapid sea level rise (>5 m/ka). Available age data from other island arc volcanoes suggest a general correlation between the timing of large landslides and periods of rapid sea level rise, but this is not observed for volcanoes in intraplate ocean settings. We thus infer that rapid sea level rise may modulate the timing of collapse at island arc volcanoes, but not in larger ocean-island settings.

Timing and Rate of Deglaciation of the MIS 2 Cordilleran Ice Sheet in Yukon Territory

NASA Astrophysics Data System (ADS)

Ward, B. C.; Bond, J. D.; Gosse, J. C.; Turner, D. G.

2015-12-01

The northern Cordilleran ice sheet (CIS) consisted of a series of quasi-independent ice lobes that coalesced during the last glacial maximum (LGM) to form a continuous carapace of precipitation limited ice over southern Yukon. Variations in effective precipitation to different source areas of these ice lobes have been used to explain disparities in glacier extents in marine oxygen isotope stages (MIS) 4 and 6. Deglaciation of the northern margin of the CIS and its rate of recession from the LGM are poorly understood. We use cosmogenic nuclide exposure dating (10Be and 36Cl) on groups of 3-4 glacial erratics to reconstruct the timing and rate of deglaciation. Our sampling concentrated on the St. Elias, Cassiar and Selwyn lobes, as well an independent glacier from the Ogilvie Mountains. Boulders sampled up-ice from terminal moraines show that the initiation of deglaciation varied regionally. 36Cl ages from the Ogilvie Mountains indicate that deglaciation initiated by 24.8 ka. Further south in the Selwyn Lobe, two sites separated by ~150 km returned ages of 15.2 and 16.1 ka. To the south-west, three boulders from the Cassiar Lobe are 13.6 ka. Rates of deglaciation are best constrained for the Cassiar Lobe with two transects along different flow lines. Multiple valley bottom samples in the mid-deglaciation setting at Whitehorse yielded ages of 12.0 ka, while one boulder from the adjacent ridge top 600 m above is 13.5 ka. In the accumulation zone, ice-free conditions occurred by 10.8 ka. The other transect has higher elevation samples in a mid-deglaciation setting in the Pelly Mountains that indicate deglaciation occurred by 13.0 ka. Samples taken from high elevation and valley bottom sites close to accumulation zones of the Cassiar Lobe yielded ages of 13.6 and 11.0 ka, respectively. These results provide a chronology for the style of deglaciation interpreted from regional mapping throughout Yukon: gradual initial retreat and thinning marked by moraines, followed by rapid downwasting and regional stagnation. Thinning of the ice to expose uplands in the Cassiar lobe was coincident with margin retreat. The increase in rates of deglaciation after 12 ka fits well with mapped evidence of regional stagnation. These ages correspond to evidence in the north Pacific of rapid warming immediately after the Younger Dryas in the pre-Boreal.

Climatic evolution of Marine Isotope Stage 5 and particularly the Eemian reconstructed from precisely dated speleothems from western Germany

NASA Astrophysics Data System (ADS)

Scholz, Denis; Hoffmann, Dirk L.; Spötl, Christoph; Hopcroft, Peter; Jochum, Klaus Peter; Richter, Detlev K.

2015-04-01

We present high-resolution δ18O, δ13C and trace element profiles for three stalagmites from western Germany, which grew during Marine Isotope Stage (MIS) 5. All stalagmites were precisely dated by MC-ICPMS 230Th/U-dating. Stalagmite HBSH-1 from Hüttenbläserschachthöhle grew between 130 and 80 ka and provides a climate record with decadal to centennial resolution. The other two stalagmites grew faster than HBSH 1, but their growth phases are shorter. Stalagmite HBSH 5 grew between 129 and 122 ka, whereas stalagmite BR 5 grew between 126 and 122 ka. The record of HBSH 1 shows four growth interruptions coinciding with Greenland Stadials (GS) 21, 22, 24, 25, and 26. This shows that stalagmite growth is a very sensitive proxy for cool and dry conditions in the northern hemisphere and enables us to precisely determine the timing and duration of the GS. We interpret stalagmite δ18O values as a proxy for supra-regional temperature changes in the North Atlantic realm, which is paticularly evident from their close resemblance with the δ18O values of the NGRIP and NEEM ice core records. Stalagmite δ13C values primarily reflect changes in hydrological balance and (local) vegetation and are, thus, a proxy for terrestrial climate change in central European. The δ13C record shows three pronounced negative peaks during MIS 5, and their timing is in agreement with MIS 5e, 5c and 5a. This suggests generally warm and humid climate in central Europe during these phases. The evolution of the δ18O and δ13C values during the Eemian is not parallel. The δ18O values progressively increase from 130 ka, peak at 125 ka and subsequently show a gradual decrease. The δ13C values, in contrast, start to decrease at 123 ka, show a negative peak at 120 ka and an aprupt increase at 114 ka. This suggests that the Eemian sensu strictu lasted from 124 to 114 ka, in agreement with a marine record from the Norwegian Sea and indicates and a strong influence on central European climate from high northern latitudes. We also compare our records with other MIS 5 climate records and climate modelling simulations performed with the general circulation model FAMOUS.

The intensification of deep-water mass changes in the deep Atlantic Ocean throughout the Mid-Pleistocene climate transition

NASA Astrophysics Data System (ADS)

Poirier, R. K.; Billups, K.

2012-12-01

We examine the deep-water hydrography at Ocean Drilling Project (ODP) Site 1063 (subtropical North Atlantic, ~4600 meter water depth) using high-resolution benthic stable isotope (δ18O, δ13C) and grain size (% coarse, % Sortable Silt - SS, SS mean diameter) analyses from ~490 to 740 ka. The benthic foraminiferal δ13C record from Site 1063 provides a proxy for changes in the relative flux of lower North Atlantic Deep Water (NADW) through time. This record will refine the timing of increases in the formation of the densest components of NADW on the orbital and millennial-scale. We explore whether or not grain size analyses provide a proxy for changes in the relative velocity of the deep current. The new stable isotope data from Site 1063, when combined with the records of Poli et al. (2000), Ferretti et al. (2005), and Billups et al. (2011), tuned to the global benthic isotope stack (LR05) of Liesicki and Raymo (2004), provides a complete deep water record spanning Marine Isotope Stage (MIS) 25 to MIS 8 (~1020 to ~240 ka). Compiling published records from 16 additional sites, we use the Ocean Data View (ODV) program (Schlitzer, 2012) to map deep-water mass distributions through time. Results reveal an increasing distribution and influence of the NADW in relation to the Antarctic Bottom Water mass within interglacial periods beginning at MIS 15 continuing though the end of the Site 1063 record within MIS 9. Preliminary grain size analyses over a short interval of time reveal regular high frequency variations on the millennial scale. We anticipate having complete, high-resolution stable isotope and grain size records to discuss the hydrographic changes within the MIS 16/15 glacial/interglacial transition, as well as throughout the Mid-Pleistocene transition (MPT).

Geomorphic origin of Merritt Island-Cape Canaveral, Florida, USA: A paleodelta of the reversed St. Johns River?

NASA Astrophysics Data System (ADS)

Adams, Peter N.

2018-04-01

The Merritt Island-Cape Canaveral (MICCSC) sedimentary complex consists of a series of adjacent, non-conformable, beach ridge sets that suggest a multi-phase constructional history, but the feature's geomorphic and sedimentary origins are not well-understood. In spite of its notable sedimentary volume (surface area = 1200 km2), the MICCSC lacks a clear sediment source, or supply mechanism, to explain its presence today. Previously published U/Th, radiocarbon and OSL dates indicate that beach ridge deposition was active during MIS 5 (130-80 ka) on Merritt Island, but has occurred over a shorter, younger time interval on Cape Canaveral proper (6 ka to present). In this paper, it is proposed that the MICCSC is an abandoned paleodelta whose fluvial source provided a sediment supply sufficient for coastal progradation. Although the MICCSC, today, does not receive an appreciable sediment supply, the nearly 23,000 km2 drainage basin of the St. Johns River may well have provided such a sediment supply during MIS 5 times. This low-gradient fluvial system currently empties to the Atlantic Ocean some 200 km north of the MICCSC (near Jacksonville, Florida) but may have flowed southward during the time of MICCSC sedimentary construction, then experienced flow reversal since MIS 5 times. Three possible uplift mechanisms are proposed to explain the northward down-tilting that may have reversed the flow direction of the St. Johns, abandoning deltaic construction of the MICCSC: (1) karst-driven, flexural isostatic uplift in response to carbonate rock dissolution in central Florida, (2) glacio-hydro-isostatic tilting/back-tilting cycles during loading and unloading of the Laurentide ice sheet during the Pleistocene, and (3) mantle convection-driven dynamic topography operating within southeastern North America since the Pliocene. This example testifies to the sensitivity of low-gradient, low-relief landscapes to various sources of uplift, be they isostatic or otherwise.

Sea surface temperatures in the North Atlantic Ocean from 30ka to 10ka

NASA Astrophysics Data System (ADS)

Barrack, Kerr; Greenop, Rosanna; Burke, Andrea; Barker, Stephen; Chalk, Thomas; Crocker, Anya

2016-04-01

Some of the most striking features of the Late Pleistocene interval are the rapid changes in climate between warmer interstadial and cold stadial periods which, when coupled, are termed Dansgaard-Oeschger (D-O) events. This shift between warm and cold climates has been interpreted to result from changes in the thermohaline circulation (Broecker et al., 1985) triggered by, for instance, freshwater input from the collapse of the Laurentide ice sheet (Zahn et al., 1997). However, a recent study suggests that major ice rafting events cannot be the 'trigger' for the centennial to millennial scale cooling events identified over the past 500kyr (Barker at al., 2015). Polar planktic foraminiferal and lithogenic/terrigenous grain counts reveal that the southward migration of the polar front occurs before the deposition of ice rafted debris and therefore the rafting of ice during stadial periods. Based upon this evidence, Barker et al. suggest that the transition to a stadial state is a non-linear response to gradual cooling in the region. In order to test this hypothesis, our study reconstructs sea surface temperature across D-O events and the deglaciation in the North Atlantic between 30ka and 10ka using Mg/ Ca paleothermometry in Globigerina bulloides at ODP Sites 980 and 983 (the same sites as used in Barker et al., 2015) with an average sampling resolution of 300 years. With our new record we evaluate the timing of surface ocean temperature change, frontal shift movement, and ice rafting to investigate variations in the temperature gradient across the polar front over D-O events. References: Barker, S., Chen, J., Gong, X., Jonkers, L., Knorr, G., Thornalley, D., 2015. Icebergs not the trigger for North Atlantic cold events. Nature, 520(7547), pp.333-336. Broecker, W.S., Peteer, D.M., Rind, D., 1985. Does the ocean-atmosphere system have more than one stable mode of operation? Nature, 315 (6014), pp.21-26. Zahn, R., Schönfeld, J., Kudrass, H.-R., Park, M.-H., Erlenkeuser, H., Grootes, P, 1997. Thermohaline instability in the North Atlantic during meltwater events: Stable isotope and ice-rafted detritus records from Core SO75-26KL, Portuguese Margin. Paleoceanography, 12(5), pp.696-710.

Holocene earthquakes of magnitude 7 during westward escape of the Olympic Mountains, Washington

USGS Publications Warehouse

Nelson, Alan R.; Personius, Stephen; Wells, Ray; Schermer, Elizabeth R.; Bradley, Lee-Ann; Buck, Jason; Reitman, Nadine G.

2017-01-01

The Lake Creek–Boundary Creek fault, previously mapped in Miocene bedrock as an oblique thrust on the north flank of the Olympic Mountains, poses a significant earthquake hazard. Mapping using 2015 light detection and ranging (lidar) confirms 2004 lidar mapping of postglacial (<13  ka"><13  ka) and Holocene fault scarps along the 22‐km‐long eastern section of the fault and documents Holocene scarps that extend ≥14  km">≥14  km along a splay fault, the Sadie Creek fault, west of Lake Crescent. Scarp morphology suggests repeated earthquake ruptures along the eastern section of the Lake Creek–Boundary Creek fault and the Sadie Creek fault since ∼13  ka">∼13  ka. Right‐lateral (∼11–28  m">∼11–28  m) and vertical (1–2 m) cumulative fault offsets suggest slip rates of ∼1–2  mm/yr">∼1–2  mm/yr Stratigraphic and age‐model data from five trenches perpendicular to scarps at four sites on the eastern section of the fault show evidence of 3–5 surface‐rupturing earthquakes. Near‐vertical fault dips and upward‐branching fault patterns in trenches, abrupt changes in the thickness of stratigraphic units across faults, and variations in vertical displacement of successive stratigraphic units along fault traces also suggest a large lateral component of slip. Age models suggest two earthquakes date from 1.3±0.8">1.3±0.8 and 2.9±0.6  ka">2.9±0.6  ka; evidence and ages for 2–3 earlier earthquakes are less certain. Assuming 3–5 postglacial earthquakes, lateral and vertical cumulative fault offsets yield average slip per earthquake of ∼4.6  m">∼4.6  m, a lateral‐to‐vertical slip ratio of ∼10:1">∼10:1, and a recurrence interval of 3.5±1.0  ka">3.5±1.0  ka. Empirical relations yield moment magnitude estimates of M 7.2–7.5 (slip per earthquake) and 7.1–7.3 (56 km maximum rupture length). An apparent left‐lateral Miocene to right‐lateral Holocene slip reversal on the faults is probably related to overprinting of east‐directed, accretion‐dominated deformation in the eastern core of the Olympic Mountains by north‐directed, margin‐parallel shortening and westward escape of the mountains.

10-Be Constraints on the Timing of the Last Glacial Maximum and Deglaciation in the Northern Peruvian Andes

NASA Astrophysics Data System (ADS)

Shakun, J. D.; Clark, P. U.; Marcott, S. A.; Brook, E. J.; Caffee, M. W.

2007-12-01

Eighteen 10Be ages were determined on quartzite boulders from two latest Pleistocene moraines in the northern Peruvian Andes at 7°S. Pleistocene moraines in this area are only a few hundred meters below the highest summits and represent small glaciers sensitive to climate change. A moraine corresponding to the local Last Glacial Maximum (LGM) yields a mean age of 19.2 +/- 1.1 10Be ka using the scaling of Lal (1991) and the production rate of Stone (2000). This age agrees fairly well with the onset of deglaciation inferred from other records in the tropical Andes including 10Be dating of moraines in the Cordillera Blanca, glaciogenic sediment input into Lakes Junin and Titicaca, and Huascaran d18O, as well as the initiation of warming seen in many marine records throughout the tropics at ~19 ka. These data do not seem to support an early local LGM in the tropical Andes, although ongoing cosmogenic work at our field site seeks to better clarify this issue. A deglacial moraine in an adjacent valley has a mean age of 15.8 +/- 1.4 10Be ka and best represents the timing of ice withdrawal from this region. Numerous other moraines throughout Peru and northern Bolivia have also been dated to ~15 10Be ka (Farber et al, 2005; Smith et al, 2005). Other records from the southern tropics indicate drying at this time, perhaps in response to a northward shift of the intertropical convergence zone associated with a resumption of thermohaline circulation, which may explain this deglacial event. While Schaefer et al. (2006) found a near-synchronous termination of the LGM in the mid-latitudes of both the Northern and Southern Hemispheres at ~17 10Be ka, the ~15 10Be ka age of moraines from the tropical Andes may indicate an asynchronous onset of the last deglaciation between the low and mid-latitudes.

Authigenic 10Be/9Be Ratio Signatures of the Cosmogenic Nuclide Production Linked to Geomagnetic Dipole Moment Variation During and Since the Brunhes/Matuyama Boundary

NASA Astrophysics Data System (ADS)

Simon, Q.; Thouveny, N.; Bourles, D. L.; Ménabréaz, L.; Valet, J. P.; Valery, G.; Choy, S.

2015-12-01

The atmospheric production rate of cosmogenic nuclides is linked to the geomagnetic dipole moment (GDM) by a non-linear inverse relationship. Large amplitude GDM variations associated with reversals and excursions can potentially be reconstructed using time variation of the cosmogenic beryllium-10 (10Be) production recorded in ocean sediments. Downcore profiles of authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) in oceanic cores provide independent and additional records of the evolution of the geomagnetic intensity and complete previous information derived from relative paleointensity (RPI). Here are presented new authigenic 10Be/9Be results obtained from cores MD05-2920 and from the top of core MD05-2930 collected in the West Equatorial Pacific Ocean. Completing data of Ménabréaz et al. (2012, 2014), these results provide the first continuous 10Be production rate sedimentary record covering the last 800 ka. Along these cores, authigenic 10Be/9Be ratio peaks are recorded - within methodological errors - at the stratigraphic level of RPI lows. High-resolution chronologies (δ18O-derived) lead to interpret these peaks as successive global 10Be overproduction events triggered by geomagnetic dipole lows present in the PISO-1500 and Sint-2000 stacks. The largest amplitude 10Be production enhancement is synchronous to the very large decrease of the dipole field associated with the last polarity reversal (772 ka). It is consistent in shape and duration with the peak recorded in core MD90-0961 from the Maldive area (Indian Ocean) (Valet et al. 2014). Two significant 10Be production enhancements are coeval with the Laschamp (41 ka) and Icelandic basin (190 ka) excursions, while 10Be production peaks of lower amplitude correlate to other recognized excursions such as the Blake (120 ka), Pringle-Falls (215 ka), Portuguese Margin (290 ka), Big Lost (540 ka) among others. This study provides new data on the amplitude and timing of dipole field variations, helping to understand the difference between paleosecular variation, excursions, aborted reversals and reversals regimes.

Paleoseismology of the Southern Section of the Black Mountains and Southern Death Valley Fault Zones, Death Valley, United States

USGS Publications Warehouse

Sohn, Marsha S.; Knott, Jeffrey R.; Mahan, Shannon

2014-01-01

The Death Valley Fault System (DVFS) is part of the southern Walker Lane–eastern California shear zone. The normal Black Mountains Fault Zone (BMFZ) and the right-lateral Southern Death Valley Fault Zone (SDVFZ) are two components of the DVFS. Estimates of late Pleistocene-Holocene slip rates and recurrence intervals for these two fault zones are uncertain owing to poor relative age control. The BMFZ southernmost section (Section 1W) steps basinward and preserves multiple scarps in the Quaternary alluvial fans. We present optically stimulated luminescence (OSL) dates ranging from 27 to 4 ka of fluvial and eolian sand lenses interbedded with alluvial-fan deposits offset by the BMFZ. By cross-cutting relations, we infer that there were three separate ground-rupturing earthquakes on BMFZ Section 1W with vertical displacement between 5.5 m and 2.75 m. The slip-rate estimate is ∼0.2 to 1.8 mm/yr, with an earthquake recurrence interval of 4,500 to 2,000 years. Slip-per-event measurements indicate Mw 7.0 to 7.2 earthquakes. The 27–4-ka OSL-dated alluvial fans also overlie the putative Cinder Hill tephra layer. Cinder Hill is offset ∼213 m by SDVFZ, which yields a tentative slip rate of 1 to 8 mm/yr for the SDVFZ.

Tephrostratigraphy of the late Quaternary record from Lake Chalco, central México

NASA Astrophysics Data System (ADS)

Ortega-Guerrero, Beatriz; Caballero García, Lizeth; Linares-López, Carlos

2018-01-01

Lacustrine sequences in active volcanic settings preserve the record of fall-out products (tephras) from explosive volcanic activity from both proximal and distal sources. Sediments of Lake Chalco, located in the western part of the Trans Mexican Volcanic Belt, offer the opportunity to develop a detailed tephrostratigraphy of proximal and distal sources, and to provide stratigraphic marker horizons for the correlation of paleoclimate records. Here, we present major oxide glass and pumice data from 18 tephra layers interbedded in the lacustrine sediments of Chalco, from 11.5 to 31.3 cal ka BP. Tephra glass compositions range from basaltic trachyandesitic to rhyolitic. Two tephras were successfully correlated with the Tutti Frutti Plinian Eruption of Popocatépetl volcano; and two tephra layers from the Nevado de Toluca Plinian activity: the Upper Toluca Pumice and the Lower Toluca Pumice. Although the source of most of the tephras analyzed is unknown, their geochemical characterization, coupled with a robust chronology, contributes to establish a detailed tephrostratigraphy for the region. This tephra record also contributes to improving the estimated frequency of explosive volcanic activity for future hazards in the Basin of México and surrounding areas, where more than 29 million people live. Our findings estimate a recurrence interval of volcanic activity of ca. 1100 years in the interval between ca. 32 and 11.5 cal ka BP, shorter than previously estimated.

The pace of Holocene vegetation change - testing for synchronous developments

NASA Astrophysics Data System (ADS)

Giesecke, Thomas; Bennett, K. D.; Birks, H. John B.; Bjune, Anne E.; Bozilova, Elisaveta; Feurdean, Angelica; Finsinger, Walter; Froyd, Cynthia; Pokorný, Petr; Rösch, Manfred; Seppä, Heikki; Tonkov, Spasimir; Valsecchi, Verushka; Wolters, Steffen

2011-09-01

Mid to high latitude forest ecosystems have undergone several major compositional changes during the Holocene. The temporal and spatial patterns of these vegetation changes hold potential information to their causes and triggers. Here we test the hypothesis that the timing of vegetation change was synchronous on a sub-continental scale, which implies a common trigger or a step-like change in climate parameters. Pollen diagrams from selected European regions were statistically divided into assemblage zones and the temporal pattern of the zone boundaries analysed. The results show that the temporal pattern of vegetation change was significantly different from random. Times of change cluster around 8.2, 4.8, 3.7, and 1.2 ka, while times of higher than average stability were found around 2.1 and 5.1 ka. Compositional changes linked to the expansion of Corylus avellana and Alnus glutinosa centre around 10.6 and 9.5 ka, respectively. A climatic trigger initiating these changes may have occurred 0.5 to 1 ka earlier, respectively. The synchronous expansion of C. avellana and A. glutinosa exemplify that dispersal is not necessarily followed by population expansion. The partly synchronous, partly random expansion of A. glutinosa in adjacent European regions exemplifies that sudden synchronous population expansions are not species specific traits but vary regionally.

Holocene fluctuations of Quelccaya Ice Cap, Peru based on lacustrine and surficial geologic archives

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.

2013-12-01

Peru's Quelccaya Ice Cap (QIC; 13.9°S, 70.8°W, ~5200-5670 m asl) is an important site for understanding tropical paleoclimate, mainly because of annually layered ice cores that provide an ~1800 year long record of tropical paleoclimatic conditions (e.g., Thompson et al., 2013). Here, we present a detailed record of QIC fluctuations using surficial deposits and lake sediments that extend back to late glacial time. We compare the late Holocene records of QIC 10Be-dated moraines and ice core data with lake sediments from a nearby glacially fed lake to establish the framework we use to interpret a Holocene long sediment record from a glacially fed lake. We also examine sediments from a nearby non-glacial lake to constrain non-glacial clastic input. We collected two ~5 m-long sediment cores, one from Laguna Challpacocha, which is currently fed by QIC meltwater, and one from the Laguna Yanacocha, which has not received QIC meltwater since ~12.3 ka. Changes in magnetic susceptibility, loss on ignition, bulk density and X-ray fluorescence chemistry combined with 14C and 210Pb chronologies provide information about sediment transported to the lakes. Retreat from the late Holocene extent defined by the 10Be-dated moraine record (~0.52 ka) is contemporaneous with a sharp transition from organic to clastic sedimentation in the Challpacocha core at ~ 0.52 ka. This implies that glacially-sourced clastic sedimentation, as tracked by loss on ignition, Ti counts and bulk density, increased during ice cap recession. Based on these same proxy data, we suggest the following Holocene history of QIC: QIC receded from the Challpacocha basin by ~10.6 ka. Increased clastic sedimentation at 8.2 - 4.1, 3.6 - 2.7 ka and from 0.55 ka - present are interpreted as times of ice cap recession. The increased clastic sedimentation at ~8.2 - 4.1 ka is consistent with surficial deposits near the present-day ice margin that indicate that at ~7.0 - 4.6 ka QIC was smaller than at present (Buffen et al., 2009). Clastic sedimentation may reflect the glacier thermal regime. Relic plants now being uncovered by the receding QIC (Thompson et al., 2006, 2013) suggest advance of cold-based ice that did not produce significant meltwater or rock flour. Striations, also present on the landscape, indicate warm-based ice conditions, which would produce meltwater and rock flour. We suggest that these striations were likely produced during ice cap retreat. A small QIC during early and middle Holocene time and large QIC during late Holocene time is similar to the Holocene extents of many Northern Hemisphere glaciers and apparently follows the pattern of Northern Hemisphere summer insolation.

High resolution dating of moraines on Kodiak Island, Alaska links Atlantic and North Pacific climatic changes during the late glacial

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mann, D.H.

1992-01-01

Much less is known about the paleoclimate and paleoceanography of the North Pacific than the North Atlantic despite the North Pacific's important role in the global ocean-climate system. Kodiak Island lies in the northwestern Gulf of Alaska astride the eastern end of the Aleutian Low. On southwestern Kodiak Island, coastal bluffs section a series of moraines, kettle ponds, and bogs formed between 15 and 9 ka BP. Distinctive tephras from volcanoes on the Alaska Peninsula provide time-lines within the stratigraphy. Deformation events recorded in sediment stacks from basins within glaciotectonic landforms allows precise dating of glacial events. An ice capmore » occupied the Kodiak archipelago during the last glaciation. Three glacial advances of the southwestern margin of this ice cap occurred after 15 ka BP. At 13.4 ka, piedmont ice lobes formed large push moraines extending into Shelikof Strait during the Low Cape Advance. The less-extensive Tundra Advance culminated between 12 and 11.7 ka BP followed by glacier retreat then readvance to form the prominent Olga Moraine system between 11 and 10 ka BP. The timing of the Tundra and Olga Advances correlates closely with that of the Older and Younger Dryas cold episodes in northwestern Europe suggesting that these climatic oscillations were synchronous throughout the northern hemisphere.« less

The shaping of human diversity: filters, boundaries and transitions

PubMed Central

Mirazón Lahr, Marta

2016-01-01

The evolution of modern humans was a complex process, involving major changes in levels of diversity through time. The fossils and stone tools that record the spatial distribution of our species in the past form the backbone of our evolutionary history, and one that allows us to explore the different processes—cultural and biological—that acted to shape the evolution of different populations in the face of major climate change. Those processes created a complex palimpsest of similarities and differences, with outcomes that were at times accelerated by sharp demographic and geographical fluctuations. The result is that the population ancestral to all modern humans did not look or behave like people alive today. This has generated questions regarding the evolution of human universal characters, as well as the nature and timing of major evolutionary events in the history of Homo sapiens. The paucity of African fossils remains a serious stumbling block for exploring some of these issues. However, fossil and archaeological discoveries increasingly clarify important aspects of our past, while breakthroughs from genomics and palaeogenomics have revealed aspects of the demography of Late Quaternary Eurasian hominin groups and their interactions, as well as those between foragers and farmers. This paper explores the nature and timing of key moments in the evolution of human diversity, moments in which population collapse followed by differential expansion of groups set the conditions for transitional periods. Five transitions are identified (i) at the origins of the species, 240–200 ka; (ii) at the time of the first major expansions, 130–100 ka; (iii) during a period of dispersals, 70–50 ka; (iv) across a phase of local/regional structuring of diversity, 45–25 ka; and (v) during a phase of significant extinction of hunter–gatherer diversity and expansion of particular groups, such as farmers and later societies (the Holocene Filter), 15–0 ka. This article is part of the themed issue ‘Major transitions in human evolution’. PMID:27298471

Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition.

PubMed

Dong, Yajie; Wu, Naiqin; Li, Fengjiang; Huang, Linpei; Wen, Wenwen

2015-01-01

The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45-63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL) samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3-4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast.

Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition

PubMed Central

Dong, Yajie; Wu, Naiqin; Li, Fengjiang; Huang, Linpei; Wen, Wenwen

2015-01-01

The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45–63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL) samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3–4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast. PMID:26186443

Anterior thalamic nuclei deep brain stimulation reduces disruption of the blood-brain barrier, albumin extravasation, inflammation and apoptosis in kainic acid-induced epileptic rats.

PubMed

Chen, Ying-Chuan; Zhu, Guan-Yu; Wang, Xiu; Shi, Lin; Du, Ting-Ting; Liu, De-Feng; Liu, Yu-Ye; Jiang, Yin; Zhang, Xin; Zhang, Jian-Guo

2017-12-01

Objective The therapeutic efficacy of anterior thalamic nuclei deep brain stimulation (ATN-DBS) against seizures has been largely accepted; however, the effects of ATN-DBS on disruption of the blood-brain barrier (BBB), albumin extravasation, inflammation and apoptosis still remain unclear. Methods Rats were distributed into four treatment groups: physiological saline (PS, N = 12), kainic acid (KA, N = 12), KA-sham-DBS (N = 12) and KA-DBS (N = 12). Seizures were monitored using video-electroencephalogram (EEG). One day after surgery, all rats were sacrificed. Then, samples were prepared for quantitative real-time PCR (qPCR), western blot, immunofluorescence (IF) staining, and transmission electron microscopy to evaluate the disruption of the BBB, albumin extravasation, inflammation, and apoptosis. Result Because of the KA injection, the disruption of the BBB, albumin extravasation, inflammation and apoptosis were more severe in the KA and the KA-sham-DBS groups compared to the PS group (all Ps < 0.05 or < 0.01). The ideal outcomes were observed in the KA-DBS group. ATN-DBS produced a 46.3% reduction in seizure frequency and alleviated the disruption of the BBB, albumin extravasation, inflammatory reaction and apoptosis in comparison to the KA-sham-DBS group (all Ps < 0.05 or < 0.01). Conclusion (1) Seizures can be reduced using ATN-DBS in the epileptogenic stage. (2) ATN-DBS can reduce the disruption of the BBB and albumin extravasation. (3) ATN-DBS has an anti-inflammatory effect in epileptic models.

Late Quaternary stream piracy and strath terrace formation along the Belle Fourche and lower Cheyenne Rivers, South Dakota and Wyoming

USGS Publications Warehouse

Stamm, John F.; Hendricks, Robert R.; Sawyer, J. Foster; Mahan, Shannon; Zaprowski, Brent J.; Geibel, Nicholas M.; Azzolini, David C.

2013-01-01

Stream piracy substantially affected the geomorphic evolution of the Missouri River watershed and drainages within, including the Little Missouri, Cheyenne, Belle Fourche, Bad, and White Rivers. The ancestral Cheyenne River eroded headward in an annular pattern around the eastern and southern Black Hills and pirated the headwaters of the ancestral Bad and White Rivers after ~ 660 ka. The headwaters of the ancestral Little Missouri River were pirated by the ancestral Belle Fourche River, a tributary to the Cheyenne River that currently drains much of the northern Black Hills. Optically stimulated luminescence (OSL) dating techniques were used to estimate the timing of this piracy event at ~ 22–21 ka. The geomorphic evolution of the Cheyenne and Belle Fourche Rivers is also expressed by regionally recognized strath terraces that include (from oldest to youngest) the Sturgis, Bear Butte, and Farmingdale terraces. Radiocarbon and OSL dates from fluvial deposits on these terraces indicate incision to the level of the Bear Butte terrace by ~ 63 ka, incision to the level of the Farmingdale terrace at ~ 40 ka, and incision to the level of the modern channel after ~ 12–9 ka. Similar dates of terrace incision have been reported for the Laramie and Wind River Ranges. Hypothesized causes of incision are the onset of colder climate during the middle Wisconsinan and the transition to the full-glacial climate of the late-Wisconsinan/Pinedale glaciation. Incision during the Holocene of the lower Cheyenne River is as much as ~ 80 m and is 3 to 4 times the magnitude of incision at ~ 63 ka and ~ 40 ka. The magnitude of incision during the Holocene might be due to a combined effect of three geomorphic processes acting in concert: glacial isostatic rebound in lower reaches (~ 40 m), a change from glacial to interglacial climate, and adjustments to increased watershed area resulting from piracy of the ancestral headwaters of the Little Missouri River.

Late Quaternary stream piracy and strath terrace formation along the Belle Fourche and lower Cheyenne Rivers, South Dakota and Wyoming

NASA Astrophysics Data System (ADS)

Stamm, John F.; Hendricks, Robert R.; Sawyer, J. Foster; Mahan, Shannon A.; Zaprowski, Brent J.; Geibel, Nicholas M.; Azzolini, David C.

2013-09-01

Stream piracy substantially affected the geomorphic evolution of the Missouri River watershed and drainages within, including the Little Missouri, Cheyenne, Belle Fourche, Bad, and White Rivers. The ancestral Cheyenne River eroded headward in an annular pattern around the eastern and southern Black Hills and pirated the headwaters of the ancestral Bad and White Rivers after ~ 660 ka. The headwaters of the ancestral Little Missouri River were pirated by the ancestral Belle Fourche River, a tributary to the Cheyenne River that currently drains much of the northern Black Hills. Optically stimulated luminescence (OSL) dating techniques were used to estimate the timing of this piracy event at ~ 22-21 ka. The geomorphic evolution of the Cheyenne and Belle Fourche Rivers is also expressed by regionally recognized strath terraces that include (from oldest to youngest) the Sturgis, Bear Butte, and Farmingdale terraces. Radiocarbon and OSL dates from fluvial deposits on these terraces indicate incision to the level of the Bear Butte terrace by ~ 63 ka, incision to the level of the Farmingdale terrace at ~ 40 ka, and incision to the level of the modern channel after ~ 12-9 ka. Similar dates of terrace incision have been reported for the Laramie and Wind River Ranges. Hypothesized causes of incision are the onset of colder climate during the middle Wisconsinan and the transition to the full-glacial climate of the late-Wisconsinan/Pinedale glaciation. Incision during the Holocene of the lower Cheyenne River is as much as ~ 80 m and is 3 to 4 times the magnitude of incision at ~ 63 ka and ~ 40 ka. The magnitude of incision during the Holocene might be due to a combined effect of three geomorphic processes acting in concert: glacial isostatic rebound in lower reaches (~ 40 m), a change from glacial to interglacial climate, and adjustments to increased watershed area resulting from piracy of the ancestral headwaters of the Little Missouri River.

Geology and preliminary dating of the hominid-bearing sedimentary fill of the Sima de los Huesos Chamber, Cueva Mayor of the Sierra de Atapuerca, Burgos, Spain.

PubMed

Bischoff, J L; Fitzpatrick, J A; León, L; Arsuagà, J L; Falgueres, C; Bahain, J J; Bullen, T

1997-01-01

Sediments of the Sima de los Huesos vary greatly over distances of a few meters. This is typical of interior cave facies, and caused by cycles of cut and fill. Mud breccias containing human bones, grading upwards to mud containing bear bones, fill an irregular surface cut into basal marks and sands. The lack of Bedding and the chaotic abundance of fragile speleothem clasts in the fossiliferous muds suggests that the deposit was originally a subterranean pond facies, and that after emplacement of the human remains, underwent vigorous post-depositional rotation and collapse and brecciation, caused by underlying bedrock dissolution and undermining. The fossiliferous deposits are capped by flowstone and guano-bearing muds which lack large-mammal fossils. U-series and radiocarbon dating indicates the capping flowstones formed from about 68 ka to about 25 ka. U-series analyses of speleothem clasts among the human fossils indicate that all are at, or close to, isotopic equilibrium (> 350 ka). The distribution of U-series dates for 25 bear bones (154 +/- 66 ka) and for 16 human bones (148 +/- 34 ka) is similar and rather broad. Because the human bones seem to be stratigraphically older than chose of the bears, the results would indicate that most of the bones have been accumulating uranium irregularly with time. Electron spin resonance (ESR) analyses of six selected bear bones indicates dates of 189 +/- 28 ka, for which each is cordant with their corresponding U-series date (181 +/- 41 ka). Combined ESR and U-series dates for these samples yielded 200 +/- 4 ka. Such agreement is highly suggestive that uranium uptake in these bones was close to the early-uptake (EU) model, and the dates are essentially correct. Another three selected samples yielded combined ESR U-series dates of 320 +/- 4 ka with a modeled intermediate-mode of uranium uptake. The dating results, therefore, seem to provide a firm minimum age of about 200 ka for the human entry: and suggestive evidence of entry before 320 ka.

Multiple constraints on the age of a Pleistocene lava dam across the Little Colorado River at Grand Falls, Arizona

USGS Publications Warehouse

Duffield, W.; Riggs, N.; Kaufman, D.; Champion, D.; Fenton, C.; Forman, S.; McIntosh, W.; Hereford, R.; Plescia, J.; Ort, M.

2006-01-01

The Grand Falls basalt lava flow in northern Arizona was emplaced in late Pleistocene time. It flowed 10 km from its vent area to the Little Colorado River, where it cascaded into and filled a 65-m-deep canyon to form the Grand Falls lava dam. Lava continued ???25 km downstream and ???1 km onto the far rim beyond where the canyon was filled. Subsequent fluvial sedimentation filled the reservoir behind the dam, and eventually the river established a channel along the margin of the lava flow to the site where water falls back into the pre-eruption canyon. The ca. 150 ka age of the Grand Falls flow provided by whole-rock K-Ar analysis in the 1970s is inconsistent with the preservation of centimeter-scale flow-top features on the surface of the flow and the near absence of physical and chemical weathering on the flow downstream of the falls. The buried Little Colorado River channel and the present-day channel are at nearly the same elevation, indicating that very little, if any, regional downcutting has occurred since emplacement of the flow. Newly applied dating techniques better define the age of the lava dam. Infrared-stimulated luminescence dating of silty mudstone baked by the lava yielded an age of 19.6 ?? 1.2 ka. Samples from three noneroded or slightly eroded outcrops at the top of the lava flow yielded 3He cosmogenic ages of 16 ?? 1 ka, 17 ?? 1 ka, and 20 ?? 1 ka. A mean age of 8 ?? 19 ka was obtained from averaging four samples using the 40Ar/39Ar step-heating method. Finally, paleomagnetic directions in lava samples from two sites at Grand Falls and one at the vent area are nearly identical and match the curve of magnetic secular variation at ca. 15 ka, 19 ka, 23 ka, and 28 ka. We conclude that the Grand Falls flow was emplaced at ca. 20 ka. ?? 2006 Geological Society of America.

Geology and preliminary dating of the hominid-bearing sedimentary fill of the Sima de los Huesos Chamber, Cueva Mayor of the Sierra de Atapuerca, Burgos, Spain

USGS Publications Warehouse

Bischoff, J.L.; Fitzpatrick, J.A.; Leon, L.; Arsuaga, J.L.; Falgueres, Christophe; Bahain, J.-J.; Bullen, T.

1997-01-01

Sediments of the Sima de los Huesos vary greatly over distances of a few meters. This is typical of interior cave facies, and caused by cycles of cut and fill. Mud breccias containing human bones, grading upwards to mud containing bear bones, fill an irregular surface cut into basal marls and sands. The lack of bedding and the chaotic abundance of fragile speleothem clasts in the fossiliferous muds suggests that the deposit was originally a subterranean pond facies, and that after emplacement of the human remains, underwent vigorous post-depositional rotation and collapse and brecciation, caused by underlying bedrock dissolution and undermining. The fossiliferous deposits are capped by flowstone and guano-bearing muds which lack large-mammal fossils. U-series and radiocarbon dating indicates the capping flowstones formed from about 68 ka to about 25 ka. U-series analyses of speleothem clasts among the human fossils indicate that all are at, or close to, isotopic equilibrium (>350 ka). The distribution of U-series dates for 25 bear bones (154??66ka) and for 16 human bones (148??34 ka) is similar and rather broad. Because the human bones seem to be stratigraphically older than those of the bears, the results would indicate that most of the bones have been accumulating uranium irregularly with time. Electron spin resonance (ESR) analyses of six selected bear bones indicates dates of 189??28 ka, for which each is concordant with their corresponding U-series date (181??41 ka). Combined ESR and U-series dates for these samples yielded 200??4 ka. Such agreement is highly suggestive that uranium uptake in these bones was close to the early-uptake (EU) model, and the dates are essentially correct. Another three selected samples yielded combined ESR-U-series dates of 320??4 ka with a modeled intermediate-mode of uranium uptake. The dating results, therefore, seem to provide a firm minimum age of about 200 ka for the human entry; and suggestive evidence of entry before 320 ka. ?? 1997 Academic Press Limited.

Groundwater flowpaths and residence times inferred by 14C, 36Cl and 4He isotopes in the Continental Intercalaire aquifer (North-Western Africa)

NASA Astrophysics Data System (ADS)

Petersen, J. O.; Deschamps, P.; Hamelin, B.; Fourré, E.; Gonçalvès, J.; Zouari, K.; Guendouz, A.; Michelot, J.-L.; Massault, M.; Dapoigny, A.; ASTER Team

2018-05-01

In a semi-arid to arid climate context, dependency on groundwater resources may lead to overexploitation and deterioration of water quality. The Continental Intercalaire (CI) aquifer is one such continental-scale aquifer (more than a million of km2), which is mainly confined, poorly recharged but intensely abstracted. To date, the management of this resource relies on hydrogeological modelling and key parameters such as recharge/discharge rate and groundwater dynamics. We use a combination of residence time indicators (14C, 36Cl, 4He) and stable isotopes of water (2H and 18O) to give greater constraint on the groundwater residence time in the CI. In previous studies, 14C measurements and steady state modelling indicate a residence time of less than 100 ka whereas in others, 36Cl measurements and transient scenarios modelling suggest a longer residence time (>500 ka). In this study, most of the 14C measurements are below the limit of detection, establishing residence times greater than 40 ka and confirming the necessity of strict sampling protocols to exclude all air and AMS measurements when low 14C concentrations are expected. In the Tunisian recharge area, detectable 14C indicate sporadic recharge episodes (3-7 ka and 29-43 ka), whereas 4He and 36Cl concentrations in central areas suggest very old (<2 Ma) groundwaters. In these central areas, chlorine concentration can reach more than 2 g/l. Since 36Cl concentrations are up to 4 time less than the initial input, we are confident there is no excessive deep 36Cl production. We characterise five distinct flowpaths reaching the Tunisian discharge area using their isotopic signatures. According to our mixing model, the average contribution from the main recharge area, the Algerian Atlas Mountains, is around 88%. This value is close to hydrogeological models. Conversely, the contribution from the Dahar Mountains is lower than in the hydrogeological modelling (2% against 10%) whereas the Tinhert shows a greater contribution (10% against 1%). Increase of abstraction from the CI can potentially activate the circulation of old brackish groundwaters and dramatically decrease the water quality in the whole system.

Switching for electric rail guns

NASA Astrophysics Data System (ADS)

Barber, J. P.; Bauer, D. P.

1984-03-01

The switching requirements of single-stage electric railguns powered by inductive energy stores are analyzed, and the design of a 500-kA commutation switch is shown. The closed, commutation, and off states of the switch and the reclosure function at the end of the projectile acceleration are discussed in general terms, and the specific requirements of the railgun facility at Australian National University are listed. The switch designed is essentially a railgun mounted perpendicular to the breech of the electric railgun, with the armature accelerating down copper rails at closing speeds from 50 m/sec at 100 kA to 300 m/sec at 500 kA to commutate current to the railgun. Commutation time and maximum voltage during 200 shots at 400 kA were found to be 50 microsec and 100 V; commutation inductance was 18-20 nH.

Flip or Flop: Are Math Teachers Using Khan Academy as Envisioned by Sal Khan?

ERIC Educational Resources Information Center

Cargile, Lori A.; Harkness, Shelly Sheats

2014-01-01

Khan Academy (KA) is a free web-based intelligent tutor, which has been featured in countless media outlets for its potential to change mathematics instruction. The founder and executive director, Salman Khan, recommends that KA be used to personalize instruction, freeing up class time for engaging high yield activities like student discourse and…

Mars Global Surveyor Ka-Band Frequency Data Analysis

NASA Astrophysics Data System (ADS)

Morabito, D.; Butman, S.; Shambayati, S.

2000-01-01

The Mars Global Surveyor (MGS) spacecraft, launched on November 7, 1996, carries an experimental space-to-ground telecommunications link at Ka-band (32 GHz) along with the primary X-band (8.4 GHz) downlink. The signals are simultaneously transmitted from a 1.5-in diameter parabolic high gain antenna (HGA) on MGS and received by a beam-waveguide (BWG) R&D 34-meter antenna located in NASA's Goldstone Deep Space Network (DSN) complex near Barstow, California. The projected 5-dB link advantage of Ka-band relative to X-band was confirmed in previous reports using measurements of MGS signal strength data acquired during the first two years of the link experiment from December 1996 to December 1998. Analysis of X-band and Ka-band frequency data and difference frequency (fx-fka)/3.8 data will be presented here. On board the spacecraft, a low-power sample of the X-band downlink from the transponder is upconverted to 32 GHz, the Ka-band frequency, amplified to I-W using a Solid State Power Amplifier, and radiated from the dual X/Ka HGA. The X-band signal is amplified by one of two 25 W TWTAs. An upconverter first downconverts the 8.42 GHz X-band signal to 8 GHz and then multiplies using a X4 multiplier producing the 32 GHz Ka-band frequency. The frequency source selection is performed by an RF switch which can be commanded to select a VCO (Voltage Controlled Oscillator) or USO (Ultra-Stable Oscillator) reference. The Ka-band frequency can be either coherent with the X-band downlink reference or a hybrid combination of the USO and VCO derived frequencies. The data in this study were chosen such that the Ka-band signal is purely coherent with the X-band signal, that is the downconverter is driven by the same frequency source as the X-band downlink). The ground station used to acquire the data is DSS-13, a 34-meter BWG antenna which incorporates a series of mirrors inside beam waveguide tubes which guide the energy to a subterranean pedestal room, providing a stable environment for the feed and electronics equipment. A dichroic plate is used to reflect the X-band energy and pass the Ka-band energy to another mirror. The RF energy for each band is then focused onto a feed horn and low-noise amplifier package. After amplification and RF/IF downconversion, the IF signals are sent to the Experimental Tone Tracker (ETT), a digital phase-lock-loop receiver, which simultaneously tracks both X-band and Ka-band carrier signals. Once a signal is detected, the ETT outputs estimates of the SNR in a I -Hz bandwidth (Pc/No), baseband phase and frequency of the signals every I -sec. Between December 1996 and December 1998, the Ka-band and X-band signals from MGS were tracked on a regular basis using the ETT. The Ka-band downlink frequencies described here were referenced to the spacecraft's on-board USO which was also the X-band frequency reference (fka= 3.8 fx). The ETT estimates of baseband phase at I -second sampled time tags were converted to sky frequency estimates. Frequency residuals were then generated for each band by removing a model frequency from each observable frequency at each time tag. The model included Doppler and other effects derived from spacecraft trajectory files obtained from the MGS Navigation Team. A simple troposphere correction was applied to the data. In addition to residuals, the USO frequencies emitted by the spacecraft were estimated. For several passes, the USO frequencies were determined from X-band data and from Ka-band data (referred to X-band by dividing by 3.8) and were found to be in good agreement. In addition, X-band USO frequency estimates from MGS Radio Science data acquired from operational DSN stations were available for comparison and were found to agree within the I Hz level. The remaining sub-Hertz differences were attributed to the different models and software algorithms used by MGS Radio Science and KaBLE-11. A summary of the results of a linear fit of the USO frequency versus time (day of year) is presented in Table I for an initial segment of passes.

Patient radiation doses in interventional cardiology in the U.S.: Advisory data sets and possible initial values for U.S. reference levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Donald L.; Hilohi, C. Michael; Spelic, David C.

2012-10-15

Purpose: To determine patient radiation doses from interventional cardiology procedures in the U.S and to suggest possible initial values for U.S. benchmarks for patient radiation dose from selected interventional cardiology procedures [fluoroscopically guided diagnostic cardiac catheterization and percutaneous coronary intervention (PCI)]. Methods: Patient radiation dose metrics were derived from analysis of data from the 2008 to 2009 Nationwide Evaluation of X-ray Trends (NEXT) survey of cardiac catheterization. This analysis used deidentified data and did not require review by an IRB. Data from 171 facilities in 30 states were analyzed. The distributions (percentiles) of radiation dose metrics were determined for diagnosticmore » cardiac catheterizations, PCI, and combined diagnostic and PCI procedures. Confidence intervals for these dose distributions were determined using bootstrap resampling. Results: Percentile distributions (advisory data sets) and possible preliminary U.S. reference levels (based on the 75th percentile of the dose distributions) are provided for cumulative air kerma at the reference point (K{sub a,r}), cumulative air kerma-area product (P{sub KA}), fluoroscopy time, and number of cine runs. Dose distributions are sufficiently detailed to permit dose audits as described in National Council on Radiation Protection and Measurements Report No. 168. Fluoroscopy times are consistent with those observed in European studies, but P{sub KA} is higher in the U.S. Conclusions: Sufficient data exist to suggest possible initial benchmarks for patient radiation dose for certain interventional cardiology procedures in the U.S. Our data suggest that patient radiation dose in these procedures is not optimized in U.S. practice.« less

Atmospheric moisture transport to western North America during the Last Glacial Maximum and deglaciation

NASA Astrophysics Data System (ADS)

Lora, J. M.; Mitchell, J.; Risi, C.; Tripati, A.

2016-12-01

Proxy reconstructions of the paleoclimate of western North America indicate that the southwest was considerably wetter during the Last Glacial Maximum (LGM; 21 ka) than in the present, while the Pacific Northwest received substantially less rainfall. Pluvial paleolake systems existed in regions that today are arid, from the Great Basin down to the modern Mojave Desert. Many lakes grew to highstands during the early deglaciation, before quickly falling to near-modern levels of dryness around 15 ka, around the same time when moisture in the northwest increased. The timing and distribution of these shifts observed in hydroclimate proxies have been hypothesized to reflect changes in the position of the polar jet stream or the seasonality of precipitation, but the source and delivery processes of the water feeding these regions are debated. Using results from a range of climate models and reanalyses, we explore the role of atmospheric rivers in delivering water to western North America during the glacial, as well as the evolution of water delivery during the deglaciation. Due to the presence of continental ice sheets, deepened Aleutian Low and weakened North Pacific High pressure systems concentrated water transport in atmospheric rivers into California relative to the present, enhancing moisture and precipitation in the southwest and shifting it away from the northwest. As the ice sheets receded, a rapid reorganization of the atmospheric circulation, accompanied by abrupt changes of the semi-permanent pressure systems, precipitated drying and moistening of southwestern and northwestern North America, respectively. We find that during this interval, changes in the water budget of western North America are attributable to the intensity of moisture transport into the continent, and not to the position of the jet stream.

Non-linear regime shifts in Holocene Asian monsoon variability: potential impacts on cultural change and migratory patterns

NASA Astrophysics Data System (ADS)

Donges, J. F.; Donner, R. V.; Marwan, N.; Breitenbach, S. F. M.; Rehfeld, K.; Kurths, J.

2015-05-01

The Asian monsoon system is an important tipping element in Earth's climate with a large impact on human societies in the past and present. In light of the potentially severe impacts of present and future anthropogenic climate change on Asian hydrology, it is vital to understand the forcing mechanisms of past climatic regime shifts in the Asian monsoon domain. Here we use novel recurrence network analysis techniques for detecting episodes with pronounced non-linear changes in Holocene Asian monsoon dynamics recorded in speleothems from caves distributed throughout the major branches of the Asian monsoon system. A newly developed multi-proxy methodology explicitly considers dating uncertainties with the COPRA (COnstructing Proxy Records from Age models) approach and allows for detection of continental-scale regime shifts in the complexity of monsoon dynamics. Several epochs are characterised by non-linear regime shifts in Asian monsoon variability, including the periods around 8.5-7.9, 5.7-5.0, 4.1-3.7, and 3.0-2.4 ka BP. The timing of these regime shifts is consistent with known episodes of Holocene rapid climate change (RCC) and high-latitude Bond events. Additionally, we observe a previously rarely reported non-linear regime shift around 7.3 ka BP, a timing that matches the typical 1.0-1.5 ky return intervals of Bond events. A detailed review of previously suggested links between Holocene climatic changes in the Asian monsoon domain and the archaeological record indicates that, in addition to previously considered longer-term changes in mean monsoon intensity and other climatic parameters, regime shifts in monsoon complexity might have played an important role as drivers of migration, pronounced cultural changes, and the collapse of ancient human societies.

Metal Deposition Along the Peru Margin Since the Last Glacial Maximum: Evidence For Regime Change at \\sim 6ka

NASA Astrophysics Data System (ADS)

Tierney, J.; Cleaveland, L.; Herbert, T.; Altabet, M.

2004-12-01

The Peru Margin upwelling zone plays a key role in regulating marine biogeochemical cycles, particularly the fate of nitrate. High biological productivity and low oxygen waters fed into the oxygen minimum zone result in intense denitrification in the modern system, the consequences of which are global in nature. It has been very difficult, however, to study the paleoclimatic history of this region because of the poor preservation of carbonate in Peru Margin sediments. Here we present records of trace metal accumulation from two cores located in the heart of the suboxic zone off the central Peru coast. Chronology comes from multiple AMS 14C dates on the alkenone fraction of the sediment, as well as correlation using major features of the \\delta 15N record in each core. ODP Site 1228 provides a high resolution, continuous sediment record from the Recent to about 14ka, while gravity core W7706-41k extends the record to the Last Glacial Maximum. Both cores were sampled at a 100 yr resolution, then analyzed for % N, \\delta 15N, alkenones, and trace metal concentration. Analysis of redox-sensitive metals (Mo and V) alongside metals associated with changes in productivity (Ni and Zn) provides perspective on the evolution of the upwelling system and distinguishes the two major factors controlling the intensity of the oxygen minimum zone. The trace metal record exhibits a notable increase in the intensity and variability of low oxygen waters and productivity beginning around 6ka and extending to the present. Within this most recent 6ka interval, the data suggest fluctuations in oxygenation and productivity occur on 1000 yr timescales. Our core records, therefore, suggest that the Peru Margin upwelling system strengthened significantly during the mid to late Holocene.

High-resolution record of the Laschamp geomagnetic excursion at the Blake-Bahama Outer Ridge

NASA Astrophysics Data System (ADS)

Bourne, Mark D.; Mac Niocaill, Conall; Thomas, Alex L.; Henderson, Gideon M.

2013-12-01

Geomagnetic excursions are brief deviations of the geomagnetic field from behaviour expected during `normal secular' variation. The Laschamp excursion at ˜41 ka was one such deviation. Previously published records suggest rapid changes in field direction and a concurrent substantial decrease in field intensity associated with this excursion. Accurate dating of excursions, and determination of their durations from multiple locations, is vital to our understanding of global field behaviour during these deviations. We present here high-resolution palaeomagnetic records of the Laschamp excursion obtained from two Ocean Drilling Program (ODP) Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge (ODP Leg 172). High sedimentation rates (˜30-40 cm kyr-1) at these locations allow determination of transitional field behaviour during the excursion. Palaeomagnetic measurements of discrete samples from four cores reveal a single excursional feature, across an interval of 30 cm, associated with a broader palaeointensity low. We determine the age and duration of the Laschamp excursion using a stratigraphy linked to the δ18O record from the Greenland ice cores. This chronology dates the Laschamp excursion at the Blake Ridge to 41.3 ka. The excursion is characterized by rapid transitions (less than 200 yr) between stable normal polarity and a partially reversed polarity state. The palaeointensity record is in good agreement between the two sites, revealing two prominent minima. The first minimum is associated with the Laschamp excursion at 41 ka and the second corresponds to the Mono Lake excursion at ˜35.5 ka. We determine that the directional excursion during the Laschamp at this location was no longer than ˜400 yr, occurring within a palaeointensity minimum that lasted 2000 yr. The Laschamp excursion at this location is much shorter in duration than the Blake and Iceland Basin excursions.

Trace Metal Variations Detected by Using Continuous XRF Core Scanning: Preliminary Results on Redox-sensitive Elements in East Sea, Korea

NASA Astrophysics Data System (ADS)

Cho, J. H.; Shin, D. H.; Kim, J. K.; Hyun, S.; Jang, S.; Kum, B. C.; Yoo, K. C.; Moh, T. J.

2017-12-01

The cruise of R/V ISABU focused on the detailed geological, geochemical and paleoceanographical investigations in the East Sea. The purpose of this cruise was the use of technically sophisticated Giant Piston Corer (GPC, OSIL) as well as the recovery of the longest piston core (20.7 m, ISA-16ESUB-2B) ever recorded in KIOST with a high resolution of stratigraphic sedimentary layer. The Late Pleistocene to the Holocene sediments in the Ulleung Basin are characterized by several volcanic tephra layers with alternations of fine light and dark clayey layers, reflecting variability in the paleoenvironment. Based on the previous researches and AMS results, we determine the ages of sedimentary layers from three tephra layers, 1.86 mbsf (U-Oki, 10.7 ka), 3.31 mbsf (AT, 29.4 ka), 11.67 mbsf (Aso-4, 88.0 ka) and 17.09 mbsf (Aso-3, 133.0 ka) respectively. Sediment textures are identified as hemipelagic mud, bioturbated mud and laminated mud with tephra layers. The sedimentation rates of each intervals are 0.174 m/kyr (present to U-Oki), 0.078 m/kyr (U-Oki to AT), 0.143 m/kyr (AT to Aso-4) and 0.120 m/kyr (Aso-4 to Aso-3) respectively. Sensitivity of XRF core scanner was obtained by establishing equivalences between peak areas. Element concentrations are analyzed by traditional techniques such as ICP-MS, ICP-OES. The Ca/Fe ratio reflects carbonate content and ISA-16ESUB-2B core shows strong correlation to sedimentary horizons. Sr/Ca ratio has good correlation with sedimentary units. Enhanced Sr contents indicates strong surface ocean production. Br/Cl ratio are high peak during MIS 5.5. Br content implies generally high organic rich sediments.

Ka-Band Site Characterization of the NASA Near Earth Network in Svalbard, Norway

NASA Technical Reports Server (NTRS)

Acosta, R.; Morse, J.; Nessel, J.; Zemba, M.; Tuttle, K.; Caroglanian, A.; Younes, B.; Pedersen, Sten-Chirstian

2011-01-01

Critical to NASA s rapid migration toward Ka-Band is the comprehensive characterization of the communication channels at NASA's ground sites to determine the effects of the atmosphere on signal propagation and the network's ability to support various classes of users in different orbits. Accordingly, NASA has initiated a number of studies involving the ground sites of its Near Earth and Deep Space Networks. Recently, NASA concluded a memorandum of agreement (MOA) with the Norwegian Space Centre of the Kingdom of Norway and began a joint site characterization study to determine the atmospheric effects on Ka-Band links at the Svalbard Satellite Station in Norway, which remains a critical component of NASA s Near Earth Communication Network (NEN). System planning and design for Ka-band links at the Svalbard site cannot be optimally achieved unless measured attenuation statistics (e.g. cumulative distribution functions (CDF)) are obtained. In general, the CDF will determine the necessary system margin and overall system availability due to the atmospheric effects. To statistically characterize the attenuation statistics at the Svalbard site, NASA has constructed a ground-based monitoring station consisting of a multi-channel total power radiometer (25.5 - 26.5 GHz) and a weather monitoring station to continuously measure (at 1 second intervals) attenuation and excess noise (brightness temperature). These instruments have been tested in a laboratory environment as well as in an analogous outdoor climate (i.e. winter in Northeast Ohio), and the station was deployed in Svalbard, Norway in May 2011. The measurement campaign is planned to last a minimum of 3 years but not exceeding a maximum of 5 years.

Latest Quaternary paleoseismology and evidence of distributed dextral shear along the Mohawk Valley fault zone, northern Walker Lane, California

USGS Publications Warehouse

Gold, Ryan D.; Briggs, Richard; Personius, Stephen; Crone, Anthony J.; Mahan, Shannon; Angster, Stephen

2014-01-01

The dextral-slip Mohawk Valley fault zone (MVFZ) strikes northwestward along the eastern margin of the Sierra Nevada in the northern Walker Lane. Geodetic block modeling indicates that the MVFZ may accommodate ~3 mm/yr of regional dextral strain, implying that it is the highest slip-rate strike-slip fault in the region; however, only limited geologic data are available to constrain the system’s slip rate and earthquake history. We mapped the MVFZ using airborne lidar data and field observations and identified a site near Sulphur Creek for paleoseismic investigation. At this site, oblique dextral-normal faulting on the steep valley margin has created a closed depression that floods annually during spring snowmelt to form an ephemeral pond. We excavated three fault-perpendicular trenches at the site and exposed pond sediment that interfingers with multiple colluvial packages eroded from the scarp that bounds the eastern side of the pond. We documented evidence for four surface-rupturing earthquakes on this strand of the MVFZ. OxCal modeling of radiocarbon and luminescence ages indicates that these earthquakes occurred at 14.0 ka, 12.8 ka, 5.7 ka, and 1.9 ka. The mean ~4 kyr recurrence interval is inconsistent with slip rates of ~3 mm/yr; these rates imply surface ruptures of more than 10 m per event, which is geologically implausible for the subdued geomorphic expression and 60 km length of the MVFZ. We propose that unidentified structures not yet incorporated into geodetic models may accommodate significant dextral shear across the northern Walker Lane, highlighting the role of distributed deformation in this region.

The latest explosive eruptions of Ciomadul (Csomád) volcano, East Carpathians - A tephrostratigraphic approach for the 51-29 ka BP time interval

NASA Astrophysics Data System (ADS)

Karátson, D.; Wulf, S.; Veres, D.; Magyari, E. K.; Gertisser, R.; Timar-Gabor, A.; Novothny, Á.; Telbisz, T.; Szalai, Z.; Anechitei-Deacu, V.; Appelt, O.; Bormann, M.; Jánosi, Cs.; Hubay, K.; Schäbitz, F.

2016-06-01

The most recent, mainly explosive eruptions of Ciomadul, the youngest volcano in the Carpatho-Pannonian Region, have been constrained by detailed field volcanological studies, major element pumice glass geochemistry, luminescence and radiocarbon dating, and a critical evaluation of available geochronological data. These investigations were complemented by the first tephrostratigraphic studies of the lacustrine infill of Ciomadul's twin craters (St. Ana and Mohoş) that received tephra deposition during the last eruptions of the volcano. Our analysis shows that significant explosive activity, collectively called EPPA (Early Phreatomagmatic and Plinian Activity), started at Ciomadul in or around the present-day Mohoş, the older crater, at ≥ 51 ka BP. These eruptions resulted in a thick succession of pyroclastic-fall deposits found in both proximal and medial/distal localities around the volcano, characterized by highly silicic (rhyolitic) glass chemical compositions (ca. 75.2-79.8 wt.% SiO2). The EPPA stage was terminated by a subplinian/plinian eruption at ≥ 43 ka BP, producing pumiceous pyroclastic-fall and -flow deposits of similar glass composition, probably from a "Proto-St. Ana" vent located at or around the younger crater hosting the present-day Lake St. Ana. After a quiescent period with a proposed lava dome growth in the St. Ana crater, a new explosive stage began, defined as MPA (Middle Plinian Activity). In particular, a significant two-phase eruption occurred at 31.5 ka BP, producing pyroclastic flows from vulcanian explosions disrupting the preexisting lava dome of Sf. Ana, and followed by pumiceous fallout from a plinian eruption column. Related pyroclastic deposits show a characteristic, less evolved rhyolitic glass composition (ca. 70.2-74.5 wt.% SiO2) and occur both in proximal and medial/distal localities up to 21 km from source. The MPA eruptions, that may have pre-shaped a crater similar to, but possibly smaller than, the present-day St. Ana crater, was followed by a so far unknown, but likewise violent last eruptive stage from the same vent, creating the final morphology of the crater. This stage, referred to as LSPA (Latest St. Ana Phreatomagmatic Activity), produced pyroclastic-fall deposits of more evolved rhyolitic glass composition (ca. 72.8-78.8 wt.% SiO2) compared to that of the previous MPA stage. According to radiocarbon age constraints on bulk sediment, charcoal and organic matter from lacustrine sediments recovered from both craters, the last of these phreatomagmatic eruptions - that draped the landscape toward the east and southeast of the volcano - occurred at 29.6 ka BP, some 2000 years later than the previously suggested last eruption of Ciomadul.

Holocene paleosecular variation from dated lava flows on Maui (Hawaii)

NASA Astrophysics Data System (ADS)

Herrero-Bervera, Emilio; Valet, Jean-Pierre

2007-05-01

Low inclination and low secular variation seem to be present for at least the past 5 Myear in central Pacific. The period covering the past 10 kyear is crucial to the study of the field variability and to fill the gap between historical field measurements and long-term paleomagnetic records. We have conducted a paleomagnetic study of 13 sites of basaltic lava flows from Maui island with 14C ages between 10.3 and 0.2 ka. Two other sites dated at 45 and 730 ka were also sampled. Eight to 10 samples from each site were demagnetized using thermal treatment and companion specimens from the same samples were demagnetized by alternating fields (af). Thermomagnetic and hysteresis measurements indicated that magnetite (575 °C) in fine grains was the dominant magnetic carrier, although in many cases we also observed a low-temperature phase which is likely carried by titanomagnetite with low titanium content. The existence of relatively high coercivities associated with these two mineralogical phases generated overlapping components which could not be properly isolated using af demagnetization. Successful results were obtained after thermal demagnetization for 13 sites with a mean inclination of 36.9 ± 4°. The mean inclination (inc. = 36.3°) of the eleven sites younger than 10.5 ka is also very close to the value (37°) of the geocentric axial dipole (GAD) at the site latitude, but the angular dispersion of the virtual geomagnetic poles (VGPs) about the spin axis (9° with N = 13 and 6.7° with N = 11) is significantly lower than the predictions of the models of paleosecular variation at this latitude. The inclination variations for the past 10 kyear are in excellent agreement with the very detailed dataset which has previously been obtained from the big island of Hawaii. The mean inclination of all volcanic records ( N = 132) is 1.8° lower than expected, but this is likely caused by the lack of records between 5 and 7 ka B.P. We note also that the inclinations from Lake Waiau sediments (big island) are shallower than those of the volcanic records (Mauna Kea, Hawaii) and were thus probably affected by compaction. We infer that there is no striking evidence for an inclination anomaly under Hawaii during this period, being aware of the need for additional records covering at least the 5-7 ka B.P. time interval. The absence of a systematic deviation going beyond the dispersion of the inclinations obtained for the past millions of years neither pleads for a significant long-term persistent anomaly. However, all studies report a low dispersion of the VGPs which must reflect low secular variation.

The active submarine NW termination of the South Aegean Active Volcanic Arc: The Submarine Pausanias Volcanic Field

NASA Astrophysics Data System (ADS)

Foutrakis, Panagiotis M.; Anastasakis, George

2018-05-01

Methana peninsula shows the longest recorded volcanic history at the western end of the South Aegean Active Volcanic Arc, including volcanic products from the Upper Pliocene to recent times. The volcanic rocks comprise widespread dacite domes and andesite lava flows from several small volcanic centers and are only imprecisely dated. In this paper, the integrated analysis of swath bathymetry, side scan sonar data, and high resolution seismic reflection profiles correlated with core samples, has allowed detailed mapping, characterization and precise chronological identification of the Pausanias submarine volcanic field activity offshore northern Methana. Six volcanic cones or domes are recognized, typically 1-3 km in diameter, some elongated NE-SW and some with a small central crater. On their flanks, the acoustically reflective volcanic rocks pass laterally into incoherent transparent seismic facies interpreted as volcaniclastic deposits, possibly including hyaloclastites, that interfinger with the regional basin sediments. A sea-bottom hummocky field, is interpreted as volcanic avalanche and appears to be the submarine continuation of the volcaniclastic apron of northern Methana peninsula. A robust chronostratigraphic framework has been established, based on the recognition of shoreline progradational units and their connection with Quaternary eustatic sea level cycles. Relative dating of the different phases of submarine volcanic activity during the Upper Quaternary has been achieved by correlating the imaged volcaniclastic flows, interlayered within the chronostratigraphically dated sediments. Dating by stratigraphic position, relative to 2D imaged eustatic sea level clinoform wedges appears to be more precise than radiometric methods on land. Three main submarine Volcanic Events (VE) are recognized: VE3 at 450 ka, a less precisely dated interval at 200-130 ka (VE2), and VE1 at 14 ka. Based on chronostratigraphic constraints, subsidence rates of 0.16 (±0.008) m/ka in-between Marine Isotopic Stages 6 and 12 and 0.19 (±0.009) m/ka in-between Marine Isotopic Stages 12 and 16 were estimated for the marine basin north of Methana. The morphological similarity to the onshore volcanoes of Methana Peninsula implies that magmatic constructive processes were dominant, regardless of whether in air or in water. The Upper Quaternary submarine volcanic rocks of Methana differ from those known from stratovolcanoes elsewhere in the Mediterranean, (e.g. Kos-Nisyros, Stromboli) and in other volcanic arcs (e.g., Montserrat, St Vincent), in the submarine development of domes or small cones, the paucity of volcano flank failure deposits and the lack of explosive events. Pausanias volcanic products date the onset of NE-SW faulting as well as the following tectonic phase of E-W striking faults, possibly related to basin inversion, caused by a major rifting phase that also affected most of the South Aegean Arc and the adjacent Gulfs of Corinth and Argolikos.

Reconstructing the geomorphic history of Liang Bua, Flores, Indonesia: a stratigraphic interpretation of the occupational environment.

PubMed

Westaway, K E; Sutikna, T; Saptomo, W E; Jatmiko; Morwood, M J; Roberts, R G; Hobbs, D R

2009-11-01

Liang Bua, in Flores, Indonesia, was formed as a subterranean chamber over 600ka. From this time to the present, a series of geomorphic events influenced the structure of the cave and cave deposits, creating a complex stratigraphy. Within these deposits, nine main sedimentary units have been identified. The stratigraphic relationships between these units provide the evidence needed to reconstruct the geomorphic history of the cave. This history was dominated by water action, including slope wash processes, channel formation, pooling of water, and flowstone precipitation, which created waterfalls, cut-and-fill stratigraphy, large pools of water, and extensive flowstone cappings. The reconstructed sequence of events over the last 190k.yr. has been summarized by a series of time slices that demonstrate the nature of the occupational environment in Liang Bua. The earliest artifacts at the site, dated to approximately 190ka, testify to hominin presence in the area, but the reconstructions suggest that occupation of the cave itself may not have been possible until after approximately 100ka. At approximately 95ka, channel erosion of a basal unit, which displays evidence of deposition in a pond environment, created a greater relief on the cave floor, and formed remanent areas of higher ground that later became a focus for hominin occupation from 74-61ka by the west wall and in the center of the cave, and from approximately 18-17ka by the east wall. These zones have been identified according to the sloping nature of the stratigraphy and the distribution of artifacts, and their locations have implications for the archaeological interpretation of the site.

Middle Holocene thermal maximum in eastern Beringia

NASA Astrophysics Data System (ADS)

Kaufman, D. S.; Bartlein, P. J.

2015-12-01

A new systematic review of diverse Holocene paleoenvironmental records (Kaufman et al., Quat. Sci. Rev., in revision) has clarified the primary multi-centennial- to millennial-scale trends across eastern Beringia (Alaska, westernmost Canada and adjacent seas). Composite time series from midges, pollen, and biogeochemical indicators are compared with new summaries of mountain-glacier and lake-level fluctuations, terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies. The paleo observations are also compared with recently published simulations (Bartlein et al., Clim. Past Discuss., 2015) that used a regional climate model to simulate the effects of global and regional-scale forcings at 11 and 6 ka. During the early Holocene (11.5-8 ka), rather than a prominent thermal maximum as suggested previously, the newly compiled paleo evidence (mostly sensitive to summer conditions) indicates that temperatures were highly variable, at times both higher and lower than present, although the overall lowest average temperatures occurred during the earliest Holocene. During the middle Holocene (8-4 ka), glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka, as reflected in most proxy types. The paleo evidence for low and variable temperatures during the early Holocene contrasts with more uniformly high temperatures during the middle Holocene and agrees with the climate simulations, which show that temperature in eastern Beringia was on average lower at 11 ka and higher at 6 ka than at present (pre-industrial). Low temperatures during the early Holocene can be attributed in part to the summer chilling caused by flooding the continental shelves, whereas the mid-Holocene thermal maximum was likely driven by the loss of the Laurentide ice sheet, rise in greenhouse gases, higher-than-present summer insolation, and expansion of forest over tundra.

Preconditioned wire array Z-pinches driven by a double pulse current generator

NASA Astrophysics Data System (ADS)

Wu, Jian; Lu, Yihan; Sun, Fengju; Li, Xingwen; Jiang, Xiaofeng; Wang, Zhiguo; Zhang, Daoyuan; Qiu, Aici; Lebedev, Sergey

2018-07-01

Suppression of the core-corona structure and wire ablation in wire array Z-pinches is investigated using a novel double pulse current generator ‘Qin-1’ facility. The ‘Qin-1’ facility allows coupling a ∼10 kA 20 ns prepulse generator with a ∼0.8 MA 160 ns main current generator. The tailored prepulse current preheats wires to a gaseous state and the time interval between the prepulse and the main current pulse allows formation of a more uniform mass distribution for the implosion. The implosion of a gasified two aluminum-wire array showed no ablation phase and allowed all array mass to participate in the implosion. The initial perturbations formed from the inhomogeneous ablation were suppressed, however, the magneto Rayleigh–Taylor (MRT) instability during the implosion was still significant and further researches on the generation and development of the MRT instabilities of this gasified wire array are needed.

Tropical ocean-atmospheric forcing of Late Glacial and Holocene glacier fluctuations in the Cordillera Blanca, Peru

NASA Astrophysics Data System (ADS)

Stansell, Nathan D.; Licciardi, Joseph M.; Rodbell, Donald T.; Mark, Bryan G.

2017-05-01

Evaluating the timing and style of past glacier fluctuations in the tropical Andes is important for our scientific understanding of global environmental change. Terrestrial cosmogenic nuclide ages on moraine boulders combined with 14C-dated clastic sediment records from alpine lakes document glacial variability in the Cordillera Blanca of Peru during the last 16 ka. Late Glacial ice extents culminated at the start of the Antarctic Cold Reversal and began retracting prior to the Younger Dryas. Multiple moraine crests dating to the early Holocene mark brief readvances or stillstands that punctuated overall retreat of the Queshque Valley glacier terminus during this interval. Glaciers were less extensive during the middle Holocene before readvancing during the latest Holocene. These records suggest that tropical Atlantic and Pacific ocean-atmospheric processes exerted temporally variable forcing of Late Glacial and Holocene glacial changes in the Peruvian Andes.

Increase in flood frequency during extreme aridity in the Eastern Mediterranean at the last interglacial

NASA Astrophysics Data System (ADS)

Kiro, Yael; Goldstein, Steven L.; Kushnir, Yochanan; Lazr, Boaz; Stein, Mordechai

2017-04-01

The Levant region of the Eastern Mediterranean is expected to suffer greatly from climate change. It is a drought-sensitive area, where warming climate may have already affected political stability in the region. Climate models and observations show a recent drying trend around the entire Mediterranean during winter, the wet season, that has been attributed to a combination of natural variability and increased greenhouse gas concentrations. Together with the drying trend, the region has also experienced more intense rainfall events. Thick halite sequences revealed by the Dead Sea Deep Drilling project (DSDDP) cores show that extremely arid conditions prevailed in the Levant during Marine Isotope Stage (MIS) 5e. This time interval was relatively warm and characterized by an average precipitation rate of 50% compared to the present (based on water and salt budgets). It also exhibited strong fluctuations between wet periods similar to the present-day lasting a few thousands of years, and dry periods with precipitation as low as 20% of the present-day over intervals lasting a few hundreds of years. At the same time, the climate was characterized by scarce but intense rainfall events in the southern Levant and increased flash flood frequency. The increase in precipitation in the south is indicated by changes in 234U/238U activity ratios in authigenic minerals in the cores, which is a good proxy for identifying changes in water sources. The synoptic configuration, of overall increased aridity together with an increase in southern precipitation and flash floods, is known from the present climate but is less dominant than the normal conditions whereby winter precipitation is fed by a Mediterranean moisture source. Climate models suggest that an increase in both summer and winter precipitation occurred during the peak insolation at 125 ka, with both the Mediterranean and the tropics as possible moisture sources. At 120 ka, climate model runs using the NCAR CCM3, show a decrease in precipitation, which coincides with the thick sequence of halite in the DSDDP core. Despite the decrease in total annual precipitation, the 120 ka simulation shows an increase in autumn precipitation that seems to be the result of intensification of the African Monsoon. This autumn intensification coincides with a drift in the positive summer insolation anomaly toward the fall season, and highlights the significance of the orbital forcing of mid-latitude climate. These results have a direct relationship to modern climate and possibly its expected future changes. Today, a manifestation of the African Monsoon in the Levant is the active Red Sea Trough (RST), which is responsible for major flooding in the Levant and the Middle East during the autumn. Modern observations show that the current increase in aridity is associated with a decrease in the major Mediterranean source (the Cyprus Low) contributor to Levant precipitation and an increase in RST frequency.

Ku/Ka band observations over polar ice sheets

NASA Astrophysics Data System (ADS)

Thibaut, Pierre; Lasne, Yannick; Guillot, Amandine; Picot, Nicolas; Rémy, Frédérique

2015-04-01

For the first time, comparisons between Ku and Ka altimeter measurements are possible thanks to the new AltiKa instrument embarked onboard the Saral mission launched on February 25, 2013. This comparison is of particular interest when dealing with ice sheet observations because both frequencies have different penetration characteristics. We propose in this paper to revisit the estimation of the ice sheet topography (and other related parameters) with altimeter systems and to present illustrations of the differences observed in Ku and Ka bands using AltiKa, Envisat/RA-2 but also Cryosat-2 measurements. Working on AltiKa waveforms in the frame of the PEACHI project has allowed us to better understand the impact of the penetration depth on the echo shape, to improve the estimation algorithm and to compare its output with historical results obtained on Envisat and ERS missions. In particular, analyses at cross-overs of the Cryosat-2 and Saral data will be presented. Sentinel-3 mission should be launch during 2015. Operating in Ku band and in delay/doppler mode, it will be crucial to account for penetration effects in order to accurately derive the ice sheet heights and trends. The results of the work presented here, will benefit to the Sentinel-3 mission.

Holocene depocenter migration and sediment accumulation in Delaware Bay: A submerging marginal marine sedimentary basin

USGS Publications Warehouse

Fletcher, C. H.; Knebel, H.J.; Kraft, J.C.

1992-01-01

The Holocene transgression of the Delaware Bay estuary and adjacent Atlantic coast results from the combined effect of regional crustal subsidence and eustasy. Together, the estuary and ocean coast constitute a small sedimentary basin whose principal depocenter has migrated with the transgression. A millenial time series of isopach and paleogeographic reconstructions for the migrating depocenter outlines the basin-wide pattern of sediment distribution and accumulation. Upland sediments entering the basin through the estuarine turbidity maximum accumulate in tidal wetland or open water sedimentary environments. Wind-wave activity at the edge of the tidal wetlands erodes the aggraded Holocene section and builds migrating washover barriers. Along the Atlantic and estuary coasts of Delaware, the area of the upland environment decreases from 2.0 billion m2 to 730 million m2 during the transgression. The area of the tidal wetland environment increases from 140 million to 270 million m2, and due to the widening of the estuary the area of open water increases from 190 million to 1.21 billion m2. Gross uncorrected rates of sediment accumulation for the tidal wetlands decrease from 0.64 mm/yr at 6 ka to 0.48 mm/yr at 1 ka. In the open water environments uncorrected rates decrease from 0.50 mm/yr to 0.04 mm/yr over the same period. We also present data on total sediment volumes within the tidal wetland and open water environments at specific intervals during the Holocene. 

Strong Paleoearthquakes along the Aksuu Border Fault according to the Results of Dating the Offset Terrace Complex of the Chon-Aksuu River, Northern Tien Shan

NASA Astrophysics Data System (ADS)

Korzhenkov, A. M.; Arrowsmith, J. R.; Crosby, C. J.; Guralnik, B.; Rogozhin, E. A.; Sorokin, A. A.; Abdieva, S. V.; Fortuna, A. B.; Yudakhin, A. S.; Agatova, A. R.; Deev, E. V.; Mazeika, J. V.; Rodkin, M. V.; Shen, J.

2018-03-01

The study and radiocarbon dating of the low alluvial terraces of the Chon-Aksuu River, in the Northern Issyk-Kul region, which were broken by the Kebin (Kemin) earthquake of 1911 (Ms = 8.2, Io = 10 to 11), are carried out. The obtained radiocarbon dated ages refer to the second half of the Holocene. Since that time, at least eight strong earthquakes took place along this (Chon-Aksuu) segment of the Aksuu border fault. Three seismic events, including the earthquake of 1911 occurred in the second millennium A.D. This outburst of seismic energy was preceded by two millennia of seismic quiescence, which set in after another pulse of seismic activation. The latter lasted for 1.5 millennia and included five strong earthquakes. The recurrence period of seismic events during the activations is 300-600 years. Hence, the seismic regime along the Chon-Aksuu segment of the Aksuu border fault in the second half of the Holocene was a succession of two seismic activations, each with a duration of 1.0-1.5 ka, which were separated by a 2-ka interval of seismic quiescence. Therefore, the absolute datings of the river terraces of different ages which have been broken by a seismogenic rupture can serve as a reliable source of information about the age of the strong earthquakes that occurred along the seismogenic fault.

Vegetation and Water Level Changes for the Northeast U.S. During the "8.2 ka Event"

NASA Astrophysics Data System (ADS)

Newby, P. E.; Donnelly, J. P.; Shuman, B.; MacDonald, D.

2006-12-01

Cool conditions, known as the "8.2 ka event", occurred between 8400 and 7900 cal yr B.P. in Greenland, Europe and elsewhere in the North Atlantic. The impact of this brief cool interval on local forests is recorded in radiocarbon-dated, high-resolution pollen stratigraphies for New Long Pond (41^{0}50'N, 70^{0}42'W) and Davis Pond (42^{0}30'N, 73^{0}19'W), Massachusetts. The vegetation response to the event is recorded differently for regions with contrasting soil types. At New Long Pond, the sandy outwash derived soils are associated with changes in jack/red, white and pitch pine populations, whereas the dominant changes in vegetation for the clay-rich, proglacial lake derived soils around Davis Pond are among oak, hemlock, and beech. At both sites, pollen evidence for the "8.2 ka event" may be easily overlooked within the more dominant regional pattern for the Northeast, which shows a shift from dry to moist conditions in conjunction with changes from predominantly white pine to oak with more mesic plant taxa between 9000 and 8000 cal yr B.P. At New Long Pond, the "8.2 ka event" is brief, preceded by a low-stand in water-level during the early Holocene and dominated by white pine pollen. After 9000 cal yr B.P., pitch pine with beech, maple, hop/hornbeam, elm and ash pollen indicate a mixed mesophytic forest. A radiocarbon-dated decrease in loss-on-ignition values at 8400 cal yr B.P., likely related to a drawdown in lake level, distinguishes the "8.2 event" and helps highlight subtle shifts in vegetation that favor colder and drier conditions than before the event. Following this brief episode, the pollen data indicate a return to warm and moist conditions until about 5600 years ago. At Davis Pond, increased oak and decreased hemlock pollen abundances, followed by an increase in beech pollen abundance is evident and show what may be the dominant regional pollen signature for the "8.2 ka event" in the Northest. This pattern is also recorded at nearby Berry and North Ponds in western Massachusetts. The appearance of ragweed pollen at both Davis and New Long Pond may indicate perturbations to the vegetation that also relate to the "8.2 ka event".

Mammoth Mountain and its mafic periphery—A late Quaternary volcanic field in eastern California

USGS Publications Warehouse

Hildreth, Wes; Fierstein, Judith; Champion, Duane E.; Calvert, Andrew T.

2014-01-01

The trachydacite complex of Mammoth Mountain and an array of contemporaneous mafic volcanoes in its periphery together form a discrete late Pleistocene magmatic system that is thermally and compositionally independent of the adjacent subalkaline Long Valley system (California, USA). The Mammoth system first erupted ca. 230 ka, last erupted ca. 8 ka, and remains restless and potentially active. Magmas of the Mammoth system extruded through Mesozoic plutonic rocks of the Sierra Nevada batholith and extensive remnants of its prebatholith wall rocks. All of the many mafic and silicic vents of the Mammoth system are west or southwest of the structural boundary of Long Valley caldera; none is inboard of the caldera’s buried ring-fault zone, and only one Mammoth-related vent is within the zone. Mammoth Mountain has sometimes been called part of the Inyo volcanic chain, an ascription we regard inappropriate and misleading. The scattered vent array of the Mammoth system, 10 × 20 km wide, is unrelated to the range-front fault zone, and its broad nonlinear footprint ignores both Long Valley caldera and the younger Mono-Inyo range-front vent alignment. Moreover, the Mammoth Mountain dome complex (63%–71% SiO2; 8.0%–10.5% alkalies) ended its period of eruptive activity (100–50 ka) long before Holocene inception of Inyo volcanism. Here we describe 25 silicic eruptive units that built Mammoth Mountain and 37 peripheral units, which include 13 basalts, 15 mafic andesites, 6 andesites, and 3 dacites. Chemical data are appended for nearly 900 samples, as are paleomagnetic data for ∼150 sites drilled. The 40Ar/39Ar dates (230–16 ka) are given for most units, and all exposed units are younger than ca. 190 ka. Nearly all are mildly alkaline, in contrast to the voluminous subalkaline rhyolites of the contiguous long-lived Long Valley magma system. Glaciated remnants of Neogene mafic and trachydacitic lavas (9.1–2.6 Ma) are scattered near Mammoth Mountain, but Quaternary equivalents older than ca. 230 ka are absent. The wide area of late Quaternary Mammoth magmatism remained amagmatic during the long interval (2.2–0.3 Ma) of nearby Long Valley rhyolitic eruptions.

Holocene climate variability, vegetation dynamics and fire regime in the central Pyrenees: the Basa de la Mora sequence (NE Spain)

NASA Astrophysics Data System (ADS)

Pérez-Sanz, A.; González-Sampériz, P.; Moreno, A.; Valero-Garcés, B.; Gil-Romera, G.; Rieradevall, M.; Tarrats, P.; Lasheras-Álvarez, L.; Morellón, M.; Belmonte, A.; Sancho, C.; Sevilla-Callejo, M.; Navas, A.

2013-08-01

High resolution multiproxy data (pollen, sedimentology, geochemistry, chironomids and charcoal) from the Basa de la Mora (BSM) lake sequence (42° 32' N, 0° 19' E, 1914 m a.s.l.) show marked climate variability in the central southern Pyrenees throughout the Holocene. A robust age model based on 15 AMS radiocarbon dates underpins the first precise reconstruction of rapid climate changes during the Holocene from this area. During the Early Holocene, increased winter snowpack and high snowmelt during summer, as a consequence of high seasonality, led to higher lake levels, a chironomid community dominated by non-lacustrine taxa (Orthocladiinae) related to higher inlet streams, and a forested landscape with intense run-off processes in the watershed. From 9.8 to 8.1 cal ka BP, climate instability is inferred from rapid and intense forest shifts and high fluctuation in surface run-off. Shifts among conifers and mesophytes reveal at least four short-lived dry events at 9.7, 9.3, 8.8 and 8.3 cal ka BP. Between 8.1 and 5.7 cal ka BP a stable climate with higher precipitation favoured highest lake levels and forest expansion, with spread of mesophytes, withdrawal of conifers and intensification of fires, coinciding with the Holocene Climate Optimum. At 5.7 cal ka BP a major change leading to drier conditions contributed to a regional decline in mesophytes, expansion of pines and junipers, and a significant lake level drop. Despite drier conditions, fire activity dropped as consequence of biomass reduction. Two arid intervals occurred between 2.9 and 2.4 cal ka BP and at 1.2-0.7 cal ka BP (800-1300 AD). The latter coincides with the Medieval Climate Anomaly and is one of the most arid phases of the Holocene in BSM sequence. Anthropogenic disturbances were small until 700 AD, when human pressure over landscape intensified, with Olea cultivation in the lowlands and significant deforestation in highlands. Colder and unfavourable weather conditions during the second part of the Little Ice Age caused a temporary cease of high-land management. The most intense anthropogenic disturbances occurred during the second half of 19th century. Last decades are characterized by recovery of the vegetation cover as a result of land abandonment, and lowered lake levels, probably due to higher temperatures.

Global Electric Circuit Diurnal Variation Derived from Storm Overflight and Satellite Optical Lightning Datasets

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Blakeslee, R. J.; Bateman, M. J.; Bailey, J. C.

2011-01-01

We have combined analyses of over 1000 high altitude aircraft observations of electrified clouds with diurnal lightning statistics from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) to produce an estimate of the diurnal variation in the global electric circuit. Using basic assumptions about the mean storm currents as a function of flash rate and location, and the global electric circuit, our estimate of the current in the global electric circuit matches the Carnegie curve diurnal variation to within 4% for all but two short periods of time. The agreement with the Carnegie curve was obtained without any tuning or adjustment of the satellite or aircraft data. Mean contributions to the global electric circuit from land and ocean thunderstorms are 1.1 kA (land) and 0.7 kA (ocean). Contributions to the global electric circuit from ESCs are 0.22 kA for ocean storms and 0.04 kA for land storms. Using our analysis, the mean total conduction current for the global electric circuit is 2.0 kA.

Geochronology and eruptive history of the Katmai volcanic cluster, Alaska Peninsula

USGS Publications Warehouse

Hildreth, Wes; Lanphere, Marvin A.; Fierstein, Judy

2003-01-01

In the Katmai district of the Alaska Peninsula, K–Ar and 40Ar/39Ar ages have been determined for a dozen andesite–dacite stratocones on the arc front and for 11 rear-arc volcanoes, 10 of which are monogenetic. Tied to mapping and stratigraphic studies, our dating emphasized proximal basal lavas that rest on basement rocks, in order to estimate ages of inception of each polygenetic cone. Oldest among arc-front cones is Alagogshak Volcano (690–43 ka), succeeded in the Holocene by the active Mount Martin cone. Mount Mageik consists of four overlapping subedifices, basal lavas of which give ages of 93, 71, and 59 ka, and Holocene. The three small prehistoric cones of Trident Volcano yield ages of 143, 101–58, and 44 ka. Falling Mountain and Mount Cerberus, dacite domes near the 1912 Novarupta vent, are related compositionally to the Trident group and give ages of 70 ka and 114 ka. Mount Katmai, which underwent caldera collapse in 1912, consists of two subedifices that overlapped in space and time, and is the only arc-front center here to include basalt and rhyolite; one cone began by 90 ka, the other by 47 ka. Snowy Mountain also consists of two contiguous cones, which started around 200 and 171 ka, respectively, the younger remaining active into the Holocene. Devils Desk, the only mafic cone on the arc front, was short-lived at about 245 ka. In the rear-arc, (1) Mount Griggs produced mafic-to-silicic andesite in several episodes between 292 ka and the Holocene; (2) the Savonoski River cluster includes a Pliocene dacite dome and five small mafic cones (390–88 ka); (3) Gertrude Creek cone (49.8% SiO2) yields an age of 500 ka; and (4) the Saddlehorn Creek cluster includes five Pliocene basalt-to-andesite remnants. Eruptive volumes were reconstructed, permitting estimates of average eruption rates for edifice lifetimes. Since the mid Pleistocene, total volume erupted along the arc front here is 210±47 km3 and in the rear-arc 39±6 km3, of which Mount Griggs alone accounts for 35±5 km3. Most productive has been Mount Katmai at 70±18 km3, yielding a rate of ∼1 km3/kyr, followed by Mount Mageik (0.33 km3/kyr) and Mount Griggs (0.3 km3/kyr since 50 ka).  

A 13,500 Year Record of Holocene Climate, Fire and Vegetation from Swan Lake, Idaho, USA

NASA Astrophysics Data System (ADS)

Wahl, D.; Anderson, L.; Miller, D. M.; Rosario, J. J.; Starratt, S.; McGeehin, J. P.; Bright, J. E.

2015-12-01

Modern climate dynamics in the western US are largely determined by a combination of two factors: 1) the strength and position of midlatitude pressure systems, which, in turn, are responsible for the generation and trajectory of winter storms, and 2) the strength of the North America Monsoon (NAM) which brings summer precipitation northward in response to northern hemisphere warming. Paleoclimate records from the Great Basin of the western US suggest some coherence in the timing of major climatic shifts during the Holocene. However, knowledge of the timing and magnitude of these changes at local scales, which can help explain the relative contribution of midlatitude winter storms vs. NAM, is lacking in many places. Here we present new data that constrain the timing and magnitude of late glacial and Holocene climate variability in the northeastern Great Basin, provide insight into past spatial variability of precipitation patterns in the western US, and improve our understanding of regional scale influences on Great Basin climate. In 2011, a 7.65 m sediment core was raised from Swan Lake, a small wetland located in southeastern Idaho that was formed in the spillway channel created by the catastrophic flooding of Lake Bonneville ~18 ka BP. Pollen, charcoal, clumped isotope, diatom, ostracod, and sedimentological data are used to reconstruct vegetation, fire history, and lake level/groundwater flux over the last 13,500 years. Age control is provided by 19 AMS radiocarbon determinations, which are reported as thousands of calibrated years before present (ka BP). This effort builds on earlier work by Bright (1966) who reported on pollen, macrofossils, and sediment type from Swan Lake. Our data suggest cool and wet conditions prevailed until around 12.3 ka BP, after which a drying trend begins. The early Holocene was marked by a warmer, drier climate, which persisted until around 6.2 ka BP. Moister conditions after 6.2 ka BP likely resulted from a combination of enhanced NAM and increased winter storm activity. The period from 4.6-1.1 ka BP is characterized by increased variability, although it appears to have been relatively dry compared to the preceding two millennia. Data suggest that climate in the area was relatively wet from 1.1 ka BP to the present.

Timing and warmth of the Last Interglacial period: New U-series evidence from Hawaii and Bermuda and a new fossil compilation for North America

USGS Publications Warehouse

Muhs, D.R.; Simmons, K.R.; Steinke, B.

2002-01-01

The timing and duration of the Last Interglacial period have been controversial, with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing. New, high-precison thermal ionization mass spectrometric (TIMS) U-series ages of Last Interglacial corals from Hawaii and Bermuda test these competing hypotheses. Waimanalo Formation corals from slowly uplifting Oahu, Hawaii range in age from ???134 to ???113 ka, with most ages between ???125 and ???115 ka. Combined with published U-series ages from nearby Lanai, the data suggest a long Last Interglacial period that may have occurred from ???136 to at least 115 ka. The results indicate that orbital forcing may not have been the only control on ice sheet growth and decay, because sea level would have been high at times of relatively low Northern Hemisphere summer insolation. On tectonically stable Bermuda, deposits from the ???200 ka (penultimate interglacial period), ???120 ka (peak Last Interglacial period) and ???80 ka (late Last Interglacial period) high sea stands have been newly dated. Fossil corals on Bermuda are derived from patch reefs that likely were "catch-up" responses to sea level rise. It is expected that U-series ages of Last-Interglacial corals on Bermuda should overlap with, but not be as old as the range of corals on Oahu. Last-Interglacial corals on Bermuda give a range of ???125-113 ka, which supports this hypothesis. A large number of emergent marine deposits on Hawaii, Bermuda and along coastal North America have now been dated to the Last Interglacial period. Both Oahu and Bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks, suggesting warmer-than-present waters during the Last Interglacial period. Warmer waters are also suggested for Last-Interglacial localities around most of North America, from Florida to Canada and Greenland and Baja California to Alaska. These observations are consistent with similar warm-water faunas of Last-Interglacial age reported from Japan, the Mediterranean basin and Western Australia. It is likely that significant changes in ocean currents took place during the Last Interglacial period, with a movement of relatively warm waters to higher latitudes than is the case today. ?? 2002 Elsevier Science Ltd. All rights reserved.

Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka

PubMed Central

An, Zhisheng; Colman, Steven M.; Zhou, Weijian; Li, Xiaoqiang; Brown, Eric T.; Jull, A. J. Timothy; Cai, Yanjun; Huang, Yongsong; Lu, Xuefeng; Chang, Hong; Song, Yougui; Sun, Youbin; Xu, Hai; Liu, Weiguo; Jin, Zhangdong; Liu, Xiaodong; Cheng, Peng; Liu, Yu; Ai, Li; Li, Xiangzhong; Liu, Xiuju; Yan, Libin; Shi, Zhengguo; Wang, Xulong; Wu, Feng; Qiang, Xiaoke; Dong, Jibao; Lu, Fengyan; Xu, Xinwen

2012-01-01

Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely records the variability of both the Westerlies and the ASM since 32 ka, reflecting the interplay of these two systems. These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales. During the last glaciation, the influence of the Westerlies dominated; prominent dust-rich intervals, correlated with Heinrich events, reflect intensified Westerlies linked to northern high-latitude climate. During the Holocene, the dominant ASM circulation, punctuated by weak events, indicates linkages of the ASM to orbital forcing, North Atlantic abrupt events, and perhaps solar activity changes. PMID:22943005

New data for Late Pleistocene Pinedale alpine glaciation from southwestern Colorado

USGS Publications Warehouse

Benson, L.; Madole, R.; Landis, G.; Gosse, J.

2005-01-01

New cosmogenic surface-exposure ages of moraine-crest boulders from southwestern Colorado are compared with published surface-exposure ages of boulders from moraine complexes in north-central Colorado and in west-central (Fremont Lake basin) Wyoming. 10Be data sets from the three areas were scaled to a single 10Be production rate of 5.4 at/g/yr at sea level and high latitude (SLHL), which represents the average 10Be production rate for two high-altitude, mid-latitude sites in the western United States (US) and Austria. Multiple nuclide ages on single boulders indicate that this 10Be production rate yields ages comparable to those calculated with a commonly used 36Cl production scheme. The average age and age range of moraine-crest boulders on terminal moraines at the southwestern Colorado and Wyoming sites are similar, indicating a retreat from their positions ???16.8 36Cl ka (Cosmogenic ages in this paper are labeled 10Be or 36Cl ka or just ka when both 10Be or 36Cl ages are being discussed; radiocarbon ages are labeled 14C ka, calibrated radiocarbon are labeled cal ka, and calendar ages are labeled calendar ka. Errors (??1??) associated with ages are shown in tables. Radiocarbon ages were calibrated using the data of Hughen et al. (Science 303 (2004) 202). This suggests a near-synchronous retreat of Pinedale glaciers across a 470-km latitudinal range in the Middle and Southern Rocky Mountains. Hypothetical corrections for snow shielding and rock-surface erosion shifts the time of retreat to between 17.2 and 17.5 10Be ka at Pinedale, Wyoming, and between 16.3 and 17.3 36Cl ka at Hogback Mountain, Colorado. ?? 2004 Elsevier Ltd. All rights reserved.

Everolimus is better than rapamycin in attenuating neuroinflammation in kainic acid-induced seizures.

PubMed

Yang, Ming-Tao; Lin, Yi-Chin; Ho, Whae-Hong; Liu, Chao-Lin; Lee, Wang-Tso

2017-01-21

Microglia is responsible for neuroinflammation, which may aggravate brain injury in diseases like epilepsy. Mammalian target of rapamycin (mTOR) kinase is related to microglial activation with subsequent neuroinflammation. In the present study, rapamycin and everolimus, both as mTOR inhibitors, were investigated in models of kainic acid (KA)-induced seizure and lipopolysaccharide (LPS)-induced neuroinflammation. In vitro, we treated BV2 cells with KA and LPS. In vivo, KA was used to induce seizures on postnatal day 25 in B6.129P-Cx3cr1 tm1Litt /J mice. Rapamycin and everolimus were evaluated in their modulation of neuroinflammation detected by real-time PCR, Western blotting, and immunostaining. Everolimus was significantly more effective than rapamycin in inhibiting iNOS and mTOR signaling pathways in both models of neuroinflammation (LPS) and seizure (KA). Everolimus significantly attenuated the mRNA expression of iNOS by LPS and nitrite production by KA and LPS than that by rapamycin. Only everolimus attenuated the mRNA expression of mTOR by LPS and KA treatment. In the present study, we also found that the modulation of mTOR under LPS and KA treatment was not mediated by Akt pathway but was primarily mediated by ERK phosphorylation, which was more significantly attenuated by everolimus. This inhibition of ERK phosphorylation and microglial activation in the hippocampus by everolimus was also confirmed in KA-treated mice. Rapamycin and everolimus can block the activation of inflammation-related molecules and attenuated the microglial activation. Everolimus had better efficacy than rapamycin, possibly mediated by the inhibition of ERK phosphorylation. Taken together, mTOR inhibitor can be a potential pharmacological target of anti-inflammation and seizure treatment.

Ebw Assisted Plasma Current Startup in Mast

NASA Astrophysics Data System (ADS)

Shevchenko, Vladimir; Saveliev, Alexander

2009-04-01

EBW current drive assisted plasma current start-up has been demonstrated for the first time in a tokamak. It was shown that plasma currents up to 17 kA can be generated non-inductively by 100 kW of RF power injected. With optimized vertical field ramps, plasma currents up to 33 kA have been achieved without the use of solenoid flux. With limited solenoid assist (0.2 V × 20 ms, less than 0.5% of total solenoid flux), plasma currents up to 55 kA have been generated and sustained further non-inductively. Experimentally obtained plasma currents are consistent with Fokker-Planck modelling.

Postglacial eruptive history of the Askja region, North Iceland

NASA Astrophysics Data System (ADS)

Hartley, Margaret E.; Thordarson, Thorvaldur; de Joux, Alexandra

2016-04-01

Temporal variations in magma discharge rates on Iceland's neovolcanic rift zones have been associated with deglaciation. We have used tephrochronological and stratigraphic dating of 175 separate eruptive units to estimate volumetric output and reconstruct eruption rates in the Askja region over the postglacial period. We have identified 14 tephra layers that can be used as time marker horizons in the near vicinity of Askja, including the Vatnaöldur (871 ± 2 AD) tephra which has not previously been reported in surface cover profiles in this region. Our improved tephrochronological resolution indicates that, over the past c. 1,500 years, Askja has been significantly more active than has previously been recognised. A minimum of 39 km3 of basaltic magma has been erupted at Askja since the area became ice-free at around 10.3 ka. The absence of the 7.2 ka Hekla 5 tephra from the Askja region suggests that all postglacial lavas now exposed at the surface are younger than 7.2 ka. Time-averaged magma discharge rates at Askja were highest between 7.2 and 4.3 ka. However, the available tephrochronological resolution is not sufficient to resolve any peak in volcanic activity following deglaciation.

The Antarctic ice core chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years

NASA Astrophysics Data System (ADS)

Veres, D.; Bazin, L.; Landais, A.; Toyé Mahamadou Kele, H.; Lemieux-Dudon, B.; Parrenin, F.; Martinerie, P.; Blayo, E.; Blunier, T.; Capron, E.; Chappellaz, J.; Rasmussen, S. O.; Severi, M.; Svensson, A.; Vinther, B.; Wolff, E. W.

2013-08-01

The deep polar ice cores provide reference records commonly employed in global correlation of past climate events. However, temporal divergences reaching up to several thousand years (ka) exist between ice cores over the last climatic cycle. In this context, we are hereby introducing the Antarctic Ice Core Chronology 2012 (AICC2012), a new and coherent timescale developed for four Antarctic ice cores, namely Vostok, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML) and Talos Dome (TALDICE), alongside the Greenlandic NGRIP record. The AICC2012 timescale has been constructed using the Bayesian tool Datice (Lemieux-Dudon et al., 2010) that combines glaciological inputs and data constraints, including a wide range of relative and absolute gas and ice stratigraphic markers. We focus here on the last 120 ka, whereas the companion paper by Bazin et al. (2013) focuses on the interval 120-800 ka. Compared to previous timescales, AICC2012 presents an improved timing for the last glacial inception, respecting the glaciological constraints of all analyzed records. Moreover, with the addition of numerous new stratigraphic markers and improved calculation of the lock-in depth (LID) based on δ15N data employed as the Datice background scenario, the AICC2012 presents a slightly improved timing for the bipolar sequence of events over Marine Isotope Stage 3 associated with the seesaw mechanism, with maximum differences of about 600 yr with respect to the previous Datice-derived chronology of Lemieux-Dudon et al. (2010), hereafter denoted LD2010. Our improved scenario confirms the regional differences for the millennial scale variability over the last glacial period: while the EDC isotopic record (events of triangular shape) displays peaks roughly at the same time as the NGRIP abrupt isotopic increases, the EDML isotopic record (events characterized by broader peaks or even extended periods of high isotope values) reached the isotopic maximum several centuries before. It is expected that the future contribution of both other long ice core records and other types of chronological constraints to the Datice tool will lead to further refinements in the ice core chronologies beyond the AICC2012 chronology. For the time being however, we recommend that AICC2012 be used as the preferred chronology for the Vostok, EDC, EDML and TALDICE ice core records, both over the last glacial cycle (this study), and beyond (following Bazin et al., 2013). The ages for NGRIP in AICC2012 are virtually identical to those of GICC05 for the last 60.2 ka, whereas the ages beyond are independent of those in GICC05modelext (as in the construction of AICC2012, the GICC05modelext was included only via the background scenarios and not as age markers). As such, where issues of phasing between Antarctic records included in AICC2012 and NGRIP are involved, the NGRIP ages in AICC2012 should therefore be taken to avoid introducing false offsets. However for issues involving only Greenland ice cores, there is not yet a strong basis to recommend superseding GICC05modelext as the recommended age scale for Greenland ice cores.

Terminal Pleistocene to early Holocene volcanic eruptions at Zuni Salt Lake, west-central New Mexico, USA

NASA Astrophysics Data System (ADS)

Onken, Jill; Forman, Steven

2017-01-01

Zuni Salt Lake (ZSL) is a large maar in the Red Hill-Quemado volcanic field located in west-central New Mexico in the southwestern USA. Stratigraphic analysis of sections in and around the maar, coupled with optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C dating, indicate that ZSL volcanic activity occurred between ˜13.4 and 9.9 ka and was most likely confined to a ≤500-year interval sometime between ˜12.3 and 11.0 ka. The basal volcanic unit consists of locally widespread basaltic ash fallout interpreted to represent a violent or wind-aided strombolian eruption tentatively attributed to Cerro Pomo, a scoria cone ˜10 km south of ZSL. Subsequent eruptions emanated from vents near or within the present-day ZSL maar crater. Strombolian eruptions of multiple spatter and scoria cones produced basaltic lava and scoria lapilli fallout. Next, a phreatomagmatic eruption created the maar crater and surrounding tephra rim and apron. ZSL eruptions ended with strombolian eruptions that formed three scoria cones on the crater floor. The revised age range of ZSL is younger and more precise than the 190-24 ka 2-sigma age range derived from previous argon dating. This implies that other morphologically youthful, argon-dated volcanoes on the southern margin of the Colorado Plateau might be substantially younger than previously reported.

Extraterrestrial 3He in Paleocene sediments from Shatsky Rise: Constraints on sedimentation rate variability

NASA Astrophysics Data System (ADS)

Marcantonio, Franco; Thomas, Deborah J.; Woodard, Stella; McGee, David; Winckler, Gisela

2009-09-01

We attempt to constrain the variability of the flux of extraterrestrial 3He in the Paleocene by studying sediments from Shatsky Rise (Ocean Drilling Program, ODP Leg 198) that have tight orbital age control. 3He concentrations in Shatsky Rise sediments vary periodically at high frequency by about a factor of 6 over the 800-ka record analyzed. Virtually all of the sedimentary 3He (> 99.98%) is of extraterrestrial origin. The total helium in the sediments can be explained as a binary mixture of terrestrial and extraterrestrial components. We calculate an average 3He/ 4He ratio for the extraterrestrial endmember of 2.41 ± 0.29 × 10 - 4 , which is, remarkably, equal to that measured in present-day interplanetary dust particles. We determine a constant extraterrestrial 3He flux of 5.9 ± 0.9 × 10 - 13 cm 3STP .cm - 2 ka - 1 for our 800-ka Paleocene record at ~ 58 Ma. This value is identical within error to those for the late Paleocene in sediments from the northern Pacific and the Weddell Sea. Bulk sediment MARs (derived using a constant extraterrestrial 3He flux) respond to climate-forced carbonate preservation cycles and changes in eolian flux over the late Paleocene. This is the first direct evidence for significant changes in dust accumulation in response to eccentricity forcing during a greenhouse climate interval.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deino, A.; Potts, R.

Single-crystal laser fusion {sup 40}Ar/{sup 39}Ar analyses and several conventional bulk fusion {sup 40}K- {sup 40}Ar dates have been used to determine the age of volcaniclastic strata within the Olorgesailie Formation and of associated volcanic and sedimentary units of the southern Kenya rift. In the principal exposures along the southern edge of the Legemunge Plain, the formation spans the interval from approximately 500 to 1,000 ka. Deposition continued to the east along the Ol Keju Nyiro river where a tuff near the top of the formation has been dated at 215 ka. In these exposures, the formation is unconformably overlainmore » by sediments dated at 49 ka. A possible source for the Olorgesailie tephra, the Ol Doinyo Nyokie volcanic complex, contains as ash flow dated at {approximately} 1 Ma, extending the known age range of this complex to encompass that of virtually the entire Olorgesailie Formation in the Legemunge Plain. These geologic examples illustrate the importance of the single-crystal {sup 40}Ar/{sup 39}Ar dating technique whereby contaminant, altered, or otherwise aberrant grains can be identified and eliminated from the determination of eruptive ages for reworked or altered pyroclastic deposits. The authors have presented a computer-modeling procedure based on an inverse-isochron analysis that promotes a more objective approach to trimming {sup 40}Ar/{sup 39}Ar isotope data sets of this type.« less

Validation of SARAL/AltiKa data in the Amazon basin

NASA Astrophysics Data System (ADS)

Santos da Silva, Joecila; Calmant, Stephane; Medeiros Moreira, Daniel; Oliveira, Robson; Conchy, Taina; Gennero, Marie-Claude; Seyler, Frederique

2015-04-01

SARAL/AltiKa is a link between past missions (since it flies on the ERS-ENVISAT orbit with Ku band nadir altimeters in LRM) and future missions such as SWOT's Ka band interferometry swaths. In the present study, we compare the capability of its altimeter AltiKa to that of previous missions working in the Ku band such as ENVISAT and Jason-2 in retrieving water levels over the Amazon basin. Same as for the aforementioned preceding missions, the best results were obtained with the ICE-1 retracking algorithm. We qualitatively analyze the impact of rainfalls in the loss of measurements. Since making long -multi mission- time series is of major importance either for hydro-climatic studies or for basin management, we also present an estimate of the altimeter bias in order that the SARAL series of water level can be appended to those of these previous missions.

Abrupt lake-level changes in the Rocky Mountains and surrounding regions since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Shuman, B. N.; Serravezza, M.

2016-12-01

The paleohydrologic record of western North America since the last glacial maximum reveals a wide range of hydroclimatic variability and distinctive patterns associated with abrupt climate changes. To evaluate the sequence of abrupt hydroclimatic shifts and centennial-to-millennial hydrologic variability in western North America over the past 17 ka, we reconstruct lake-level histories from two high-elevation lakes in the Beartooth and Bighorn Mountains. The lakes represent the headwaters of the Missouri River drainage in northern Wyoming, but also have the potential to capture regional hydroclimate variability that links the northern Rocky Mountains to the mid-continent, Pacific Northwest, and the Great Basin. We first discuss the stratigraphic record of lake-level changes in small mid-latitude lakes and then use ground-penetrating radar (GPR) and sediment cores to track the elevations of shoreline sediments within the lakes through time. We compare the stratigraphies to the records from four other lakes in Wyoming and Colorado, and find widespread evidence for a Terminal Pleistocene Drought from 15-11 ka, an early Holocene humid period from 11-8 ka, and a period of severe mid-Holocene aridity from 8-5.7 ka. The northern Wyoming lakes also provide evidence of high levels before ca. 15 ka, including rapid hydroclimatic changes at ca. 16.8 ka during Heinrich Event 1. We place the changes in a broad context by summarizing and mapping water-level changes from 107 additional, previously studied lakes. Important patterns include 1) extensive drying across the western U.S. after 15 ka; 2) coherent sub-regional differences during the Younger Dryas and Pleistocene-Holocene transition; 3) a north-south contrast from 9-6 ka consistent with a northward shift in storm tracks as the influence of the Laurentide Ice Sheet diminished; and 4) rapid increases in effective moisture across much of western North America from 6-4 ka.

Holocene coastal dune fields used as indicators of net littoral transport: West Coast, USA

USGS Publications Warehouse

Peterson, C.D.; Stock, E.; Hart, R.; Percy, D.; Hostetler, S.W.; Knott, J.R.

2010-01-01

Between Point Grenville, Washington, and Point Conception, California (1500 km distance) 21 dune fields record longshore transport in 20 littoral cells during the late Holocene. The direction of predominant littoral transport is established by relative positions of dune fields (north, central, or south) in 17 representative littoral cells. Dune field position is north of cell midpoints in northernmost Oregon and Washington, but is south of cell midpoints in southern Oregon and California. Downdrift sand trapping occurs at significant changes in shoreline angle and/or at bounding headlands that project at least 2.5 km seaward from the general coastal trend. Sand bypassing occurs around small headlands of less than 0.5 km in projection distance. A northward shift of the winter low-pressure center in the northeast Pacific Ocean is modeled from 11 ka to 0 ka. Nearshore current forcing in southern Oregon and northern California switched from northward in earliest Holocene time to southward in late Holocene time. The late Holocene (5-0 ka) is generally characterized by net northward littoral drift in northernmost Oregon and Washington and by net southward littoral drift in southernmost Oregon and California. A regional divergence of net transport direction in central Oregon, i.e. no net drift, is consistent with modeled wind and wave forcing at the present time (0 ka). ?? 2009 Elsevier B.V.

Dating the last Neanderthals in Central Iberia - New evidence from Abrigo del Molino, Segovia, Spain

NASA Astrophysics Data System (ADS)

Kehl, Martin; Álvarez-Alonso, David; de Andrés-Herrero, María; Díez-Herrero, Andrés; Klasen, Nicole; Rojo-Hernández, Julio; Weniger, Gerd-Christian

2017-04-01

The timing of Neanderthal disappearance in the Iberian Peninsula is a hotly debated subject in Palaeolithic archaeology. Several studies suggested a late survival in South and Central Iberia until about 32,000 year ago (ka), but were probably subject to significant age underestimation due to contamination of dating samples and/or lack of stratigraphic integrity. More recently, Late Neanderthal presence was dated to no later than 38 ka. In Central Iberia, few archaeological sites contain Mousterian levels attesting occupation by Neanderthals. The newly discovered rock shelter of Abrigo del Molino contains chronologically well-constraint Mousterian levels, which, according to radiocarbon dating on bone, place the latest Neanderthal occupation to around 42-44 ka and within Greenland interstadial 11. Accumulation of these levels took place after deposition of fluvial and slope sediments, dated to around 46 ± 3.5 ka using luminescence techniques, and probably correlating with Greenland stadial 13 including Heinrich event 5. Micromorphological evidence of banded sediment fabrics suggests frost dynamics pointing to cold climate conditions during that time in Central Spain. Abrigo del Molino thus provides a detailed and chronologically well-constrained record on Late Neanderthal presence and morphodynamic change in Central Iberia during times of millennial-scale climate changes. The site gives further evidence for an early rather than late disappearance of Neanderthals in Iberia.

Luminescence chronology of cave sediments at the Atapuerca paleoanthropological site, Spain.

PubMed

Berger, G W; Pérez-González, A; Carbonell, E; Arsuaga, J L; Bermúdez de Castro, J-M; Ku, T-L

2008-08-01

Ascertaining the timing of the peopling of Europe, after the first out-of-Africa demographic expansion at the end of the Pliocene, is of great interest to paleoanthropologists. One of the earliest direct evidences for fossil hominins in western Europe comes from an infilled karstic cave site called Gran Dolina at Atapuerca, in a stratum approximately 1.5m below the Brunhes-Matuyama (B-M) geomagnetic boundary (780ka) within lithostratigraphic unit TD6. However, most of the meters of fossil- and tool-bearing strata at Gran Dolina have been difficult to date. Therefore, we applied both thermoluminescence (TL) and infrared-stimulated-luminescence (IRSL) multi-aliquot dating methods to fine-silt fractions from sediment samples within Gran Dolina and the nearby Galería cave site. We also applied these methods to samples from the present-day surface soils on the surrounding limestone hill slopes to test the luminescence-clock-zeroing-by-daylight assumption. Within the uppermost 4m of the cave deposits at Gran Dolina, TL and paired TL and IRSL ages range stratigraphically from 198+/-19ka to 244+/-26ka. Throughout Gran Dolina, all luminescence results are stratigraphically self-consistent and, excepting results from two stratigraphic units, are consistent with prior ESR-U-series ages from progressively deeper strata. Thermoluminescence ages culminate at 960+/-120ka approximately 1m below the 780ka B-M boundary. At Galería, with one exception, TL and IRSL ages range stratigraphically downward from 185+/-26ka to 503+/-95ka at the base of the lowermost surface-inwash facies. These results indicate that TL and (sometimes) IRSL are useful dating tools for karstic inwash sediments older than ca. 100ka, and that a more accurate chronostratigraphic correlation is now possible among the main Atapuerca sites (Gran Dolina, Galería, Sima de los Huesos). Furthermore, the oldest TL age of ca. 960ka from Gran Dolina, consistent with biostratigraphic and paleomagnetic evidence, implies a probable numeric age of 900-950ka for the oldest hominin remains ( approximately 0.8m below the TL sample). This age window suggests a correspondence to Marine Isotope Stage (MIS) 25, a relatively warm and humid interglaciation.

Geochronologic evidence for a possible MIS-11 emergent barrier/beach-ridge in southeastern Georgia, USA

USGS Publications Warehouse

Markewich, H.W.; Pavich, M.J.; Schultz, A.P.; Mahan, S.A.; Aleman-Gonzalez, W. B.; Bierman, P.R.

2013-01-01

Predominantly clastic, off-lapping, transgressive, near-shore marine sediment packages that are morphologically expressed as subparallel NE-trending barriers, beach ridges, and associated back-barrier areas, characterize the near-surface stratigraphic section between the Savannah and the Ogeechee Rivers in Effingham County, southeastern Georgia. Each barrier/back-barrier (shoreline) complex is lower than and cut into a higher/older complex. Each barrier or shoreline complex overlies Miocene strata. No direct age data are available for these deposits. Previous researchers have disagreed on their age and provenance. Using luminescence and meteoric beryllium-10 (10Be) inventory analyses, we estimated a minimum age for the largest, westernmost, morphologically identifiable, and topographically-highest, barrier/beach-ridge (the Wicomico shoreline barrier) and constrained the age of a suite of younger barrier/beach-ridges that lie adjacent and seaward of the Wicomico shoreline barrier. At the study site, the near-shore marine/estuarine deposits underlying the Wicomico shoreline barrier are overlain by eolian sand and an intervening zone-of-mixing. Optically stimulated luminescence (OSL) data indicate ages of ≤43 ka for the eolian sand and 116 ka for the zone-of-mixing. Meteoric 10Be and pedostratigraphic data indicate minimum residence times of 33.4 ka for the eolian sand, 80.6 ka for the zone-of-mixing, and 247 ka for the paleosol. The combined OSL and 10Be age data indicate that, at this locality, the barrier/beach ridge has a minimum age of about 360 ka. This age for the Wicomico shoreline-barrier deposit is the first for any Pleistocene near-shore marine/estuarine deposit in southeast Georgia that is conclusively older than 80 ka. The 360-ka minimum age is in agreement with other geochronologic data for near-coastline deposits in Georgia and South Carolina. The geomorphic position of this barrier/beach-ridge is similar to deposits in South Carolina considered to be ~450 ka to >1 Ma. The age and geomorphic data for Georgia and South Carolina possibly suggest the presence of MIS-11 (~420−360 ka) shoreline deposits between 15 m and 28 m above present sea level in the Southeastern Atlantic Coastal Plain.

Refining the timing of the MIS 5e signal, West Caicos, Bristish West Indies:implications for paleoclimatic interpretation of the stratigraphic record

NASA Astrophysics Data System (ADS)

Kerans, C.; Zahm, C.; Bachtel, S.; Hearty, P.; Cheng, H.

2017-12-01

The progressive refinement of the Last Interglacial (LIG) tropical carbonate record has focused attention on the dramatically abrupt and episodic nature of this critical approximate 12 ka time window. From initial carbonate platform flooding at 133 ka to rapid sea level fall and exposure at 118 ka, the majority of present-day Bahamian and Caribbean strata were produced in a remarkably similar pattern extending from Bermuda and the Bahamas through the Cayman Islands, Yucatan, and south to the Dominican Republic. The position of coral reefs and oolitic sands of the LIG to a first order fit the global insolation-driven climate warming signal. Less well accepted/resolved is the existence of two distinct SL peaks with an intervening sea level fall implying a non-orbitally forced climate shift during this broader highstand. West Caicos, a 10 x 5 km leeward island on the Caicos Platform is an excellent example of LIG carbonate stratigraphic complexity. We collected sub-meter-resolution whole-island airborn LIDAR and decimeter-resolution UAV-constructed DEM's of the western and southern coastal outcrops to serve as a base for decimeter-scale mapping of the MIS 11, 7?, 5e, and Holocene units of the island, with particular focus on the continuous 8.4 km west coast outcrop of the MIS 5e. Seventy-five AAR relative age assignments from ooid separates, pinned by 16 U/Th dates from corals coming from MIS stage 11, lower MIS 5e, and upper MIS 5e reefs helped establish the age model for the Pleistocene-Holocene stratigraphy. The lower MIS 5e reef system averages 128 ka with an onset age of 133 ka. Upper MIS 5e corals ranges from 123 ka to 116 ka, bracketing the intra-MIS 5e sea-level fall between to approximately 125 ka. The intra-MIS 5e fall is a distinct erosional unconformity across 5 km of continuous outcrop, truncating the upper 2.5 m of lower 5e reef. The complexity of MIS 5e record on West Caicos and in the Northern Atlantic and Caribbean platforms regionally provides important insights for those using the Pleistocene as a model for older stratigraphic successions and their linked paleoclimatic records.

Time constraints for post-LGM landscape response to deglaciation in Val Viola, Central Italian Alps

NASA Astrophysics Data System (ADS)

Scotti, Riccardo; Brardinoni, Francesco; Crosta, Giovanni Battista; Cola, Giuseppe; Mair, Volkmar

2017-12-01

Across the northern European Alps, a long tradition of Quaternary studies has constrained post-LGM (Last Glacial Maximum) landscape history. The same picture remains largely unknown for the southern portion of the orogen. In this work, starting from existing 10Be exposure dating of three boulders in Val Viola, Central Italian Alps, we present the first detailed, post-LGM reconstruction of landscape (i.e., glacial, periglacial and paraglacial) response south of the Alpine divide. We pursue this task through Schmidt-hammer exposure-age dating (SHD) at 34 sites including moraines, rock glaciers, protalus ramparts, rock avalanche deposits and talus cones. In addition, based on the mapping of preserved moraines and on the numerical SHD ages, we reconstruct the glacier extent of four different stadials, including Egesen I (13.1 ± 1.1 ka), Egesen II (12.3 ± 0.6 ka), Kartell (11.0 ± 1.4 ka) and Kromer (9.7 ± 1.4 ka), whose chronologies agree with available counterparts from north of the Alpine divide. Results show that Equilibrium Line Altitude depressions (ΔELAs) associated to Younger Dryas and Early Holocene stadials are smaller than documented at most available sites in the northern Alps. These findings not only support the hypothesis of a dominant north westerly atmospheric circulation during the Younger Dryas, but also suggest that this pattern could have lasted until the Early Holocene. SHD ages on rock glaciers and protalus ramparts indicate that favourable conditions to periglacial landform development occurred during the Younger Dryas (12.7 ± 1.1 ka), on the valley slopes above the glacier, as well as in newly de-glaciated areas, during the Early Holocene (10.7 ± 1.3 and 8.8 ± 1.8 ka). The currently active rock glacier started to develop before 3.7 ± 0.8 ka and can be associated to the Löbben oscillation. Four of the five rock avalanches dated in Val Viola cluster within the Early Holocene, in correspondence of an atmospheric warming phase. By contrast, the timing of the main Val Viola rock avalanche, 7.7 ± 0.3 ka during the Holocene Thermal Optimum, suggests a possible causal linkage to permafrost degradation. Overall, Schmidt-hammer proved to be an effective, inexpensive and versatile tool for improving the spatial resolution of Val Viola post-LGM landscape history, starting from existing numerical age constrains.

Inferring LGM sedimentary and climatic changes in the southern Eastern Alps foreland through the analysis of a 14C ages database (Brenta megafan, Italy)

NASA Astrophysics Data System (ADS)

Rossato, Sandro; Mozzi, Paolo

2016-09-01

The analysis of a database of radiocarbon ages is proposed as a tool for investigating major glaciofluvial systems of the Last Glacial Maximum (LGM) in the Alpine foreland, and their relations with glacier dynamics and climatic fluctuations. Our research concerns the Brenta megafan (NE Italy), where 110 radiocarbon dates integrate a robust regional stratigraphic and palaeoclimatic framework. Age-depth models allowed us to calculate sedimentation rates, while the time distribution of peat layers, which recurrently formed in this region during the LGM, were estimated through meta-analysis. The reliability of statistical results was carefully evaluated using Pearson and Spearman coefficients. Sedimentation rates in the Brenta megafan markedly fluctuated during LGM: ≈1.8 m/ka between 40 and 26.7 ka cal BP; ≈3 m/ka between 26.7 and 23.8 ka cal BP and ≈1.4 m/ka from 23.8 to 17.5 ka cal BP, when the distributary system deactivated due to fan-head trenching. This is evidence that sediment input and routing in the glaciofluvial distributary system was particularly efficient during the central part of LGM, when glaciers were stable at their outermost position. Meta-analysis indicates an increase in peat formation in correspondence with global (Heinrich Event 3 and/or the Greenland Interstadial 5.1 and 4 for the 30.5, 29.6 and 28.8 ka cal BP peaks) and regional (23.5 ka cal BP) wet events. Other peaks at 22.2, 21.8, 20.2 and 19 ka cal BP correlate with fluctuations of south-eastern Alpine glaciers. Significant peat formation continued until ≈18 ka cal BP, when the last peak occurred. A marked decrease in peat formation is recorded concomitantly with the onset of Heinrich Event 2 (i.e. the 26 ka cal BP trough). The good correspondence of sedimentary events in the Brenta glaciofluvial system with the dynamics of glaciers and glaciofluvial and lacustrine systems in the southern Eastern Alps suggests a common climatic forcing on the whole region during the LGM. Peat layer formation in the floodplain fens increased significantly in correspondence with glacier withdrawals and/or wetter climatic episodes, constituting a good proxy for climatic fluctuations during glacial periods. It also allows correlations across different continental environments and regions in the northern hemisphere.

Composite δ13C and petrographic 195-355 ka record from Frasassi cave (central Italy) stalagmites: investigating drivers of speleothem calcite carbon isotope signals.

NASA Astrophysics Data System (ADS)

Vanghi, V.; Borsato, A.; Frisia, S.; Drysdale, R.; Hellstrom, J. C.; Bajo, P.; Montanari, A.

2016-12-01

Carbon isotope ratio of speleothem calcite is known to be a proxy for climate-dependent soil CO2 production. One of the paradigms is that, ideally, C stable isotope incorporation occurred in equilibrium. Yet, the process of degassing in the cave commonly results in δ13C values more positive than theoretically expected for speleothems formed in temperate-humid settings. Fabrics then provide the benchmark to unravel local, regional and global significance of speleothem δ13C. The δ13C time-series from two precisely U-Th dated Frasassi stalagmites covering the interval from 195 ka to 355 ka (Marine Isotope Stages 7 - 10) were interpreted on the basis of the sequence of fabrics. Columnar fabrics indicated deposition under constant kinetic fractionation, whereby δ13C shifts through time reflected a combination of atmospheric CO2 concentration changes and soil efficiency variability, controlled by regional mean annual temperature. Given that the δ13C values are constantly more-positive-than-expected because of the effect of degassing, shifts to more positive δ13C values above a baseline of -7 permil during glacials are here interpreted as driven by low soil efficiency and higher contribution of atmospheric CO2 (Breecker et al. 2012, Borsato et al. 2015). The comparison of high resolution δ13C curves with atmospheric pCO2 and benthic δ18O records further suggests that hemispheric temperature changes driven by insolation modulated the δ13C shifts above or below the baseline. Thus, a -3‰ shift from glacial to interglacial at terminations IV and III is here ascribed to changes in atmospheric pCO2 (Schubert and Jahren 2012). More open fabrics mark warmer conditions and increased soil productivity and are associated with more negative δ13C. In conclusion, only by coupling petrography and geochemical properties the global and local drivers of δ13C anomalies in stalagmites from this deep cave could be distinguished. Borsato et al. (2015), Earth Surface Processes and Landforms 40 (9), 1158-1170. Breecker et al. (2012), Geochimica et Cosmochimica Acta 96 (1), 230-246. Schubert and Jahren (2012), Geochimica et Cosmochimica Acta 96, 29-43.

The Last Interglacial-Glacial cycle (MIS 5-2) re-examined based on long proxy records from central and northern Europe

NASA Astrophysics Data System (ADS)

Helmens, Karin F.

2014-02-01

Current multi-proxy studies on a long sediment sequence preserved at Sokli (N Finland), i.e. in the central area of Fennoscandian glaciations, are drastically changing classic ideas of glaciations, vegetation and climate in northern Europe during the Late Pleistocene. The sediments in the Sokli basin have escaped major glacial erosion due to non-typical bedrock conditions. In this review, the Sokli record is compared in great detail with other long proxy records from central, temperate and northern, boreal Europe. These comprise the classic records of La Grande Pile (E France) and Oerel (N Germany) and more recently obtained records from Horoszki Duże (E Poland) and Lake Yamozero (NW Russia). The focus of the review is on pollen, lithology and macrofossil- and insect-based temperature inferences. The long records are further compared with recent proxy data from nearby terrestrial sites as well as with the rapidly accumulating high-resolution proxy data from the ocean realm. The comparison allows a re-examination of the environmental history and climate evolution of the Last Interglacial-Glacial (LI-G) cycle (MIS 5-2). It shows that environmental and climate conditions during MIS 5 (ca 130-70 ka BP) were distinctly different from those during MIS 4-2 (ca 70-15 ka BP). MIS 5 is characterized by three long forested intervals (broadly corresponding to MIS 5e, 5c, 5a), both in temperate and northern boreal Europe. These mild periods were interrupted by two short, relatively cold and dry intervals (MIS 5d and 5b) with mountain-centered glaciation in Fennoscandia. Millennial scale climate events were superimposed upon these longer lasting climate fluctuations. The time interval encompassing MIS 4-2 shows open vegetation. It is characterized by two glacial maxima (MIS 4 and 2) with sub-continental scale glaciation over northern Europe and dry conditions in strongly continental eastern European settings. High amplitude climate oscillations of millennial duration characterized the climate variability of MIS 3. Mild climate conditions in early MIS 3 caused large-scale deglaciation of the Fennoscandian Ice Sheet, and ice-free conditions with Betula-dominated vegetation (including tree birch) persisted over large parts of Fennoscandia, possibly interrupted by glaciation, during major part of MIS 3 till ca 35 ka BP. Overall, MIS 5 was mostly mild with warmest or peak interglacial conditions at the very start during MIS 5e. MIS 4-2 was mostly cold with most extreme or peak glacial conditions in the closing phase during MIS 2. This points to a subdivision of the last climate cycle into an early, overall mild interglacial half and a late, overall cold glacial half, each with duration of ca 50 ka. This review also shows that the climate variability in central and northern Europe during the LI-G cycle was mostly in degrees of continentality with major shifts in winter temperature and precipitation values; summer temperatures, on the other hand, remained largely unchanged. It points to the waxing and waning of sea-ice over the North Atlantic Ocean as a possible characteristic feature of the Late Pleistocene. The present compilation, based on long terrestrial sequences, high-resolution multi-proxy data from the oceans, and quantified paleo-climate data, strongly favors a definition of entire Marine Oxygen Isotope Stage 5 as the Last Interglacial similar as in the original marine stratigraphy and the stratigraphy at La Grande Pile in France. The proxy-based climate data places the start of the Last Glacial at the base of MIS 4 and the northwest European Pleniglacial. It shows that the division between the Eemian (MIS 5e) and the Early Weichselian (MIS 5d-a) is not useful, as not relevant from a climate point of view.

Palaeocirculation across New Zealand during the last glacial maximum at ˜21 ka

NASA Astrophysics Data System (ADS)

Lorrey, Andrew M.; Vandergoes, Marcus; Almond, Peter; Renwick, James; Stephens, Tom; Bostock, Helen; Mackintosh, Andrew; Newnham, Rewi; Williams, Paul W.; Ackerley, Duncan; Neil, Helen; Fowler, Anthony M.

2012-03-01

What circulation pattern drove Southern Alps glacial advances at ˜21 ka? Late 20th century glacial advances in New Zealand are commonly attributed to a dual precipitation increase and cooler than normal temperatures associated with enhanced westerly flow that occur under synoptic pressure patterns termed 'zonal' regimes (Kidson, 2000). But was the circulation pattern that supported major Southern Alps glacial advances during the global LGM similar to the modern analog? Here, a Regional Climate Regime Classification (RCRC) time slice was used to infer past circulation for New Zealand during the LGM at ˜21 ka. Palaeoclimate information that supported the construction of the ˜21 ka time slice was derived from the NZ-INTIMATE Climate Event Stratigraphy (CES), one new Auckland maar proxy record, and additional low-resolution data sourced from the literature. The terrestrial evidence at ˜21 ka implicates several possibilities for past circulation, depending on how interpretations for some proxies are made. The interpretation considered most tenable for the LGM, based on the agreement between terrestrial evidence, marine reconstructions and palaeoclimate model results is an 'anticyclonic/zonal' circulation regime characterized by increased influences from blocking 'highs' over the South Island during winter and an increase in zonal and trough synoptic types (with southerly to westerly quarter wind flow) during summer. These seasonal circulation traits would have generated lower mean annual temperatures, cooler than normal summer temperatures, and overall lower mean annual precipitation for New Zealand (particularly in the western South Island) at ˜21 ka. The anticyclonic/zonal time slice reconstruction presented in this study has different spatial traits than the late 20th Century and the early Little Ice Age signatures, suggesting more than one type of regional circulation pattern can drive Southern Alps glacial activity. This finding lends support to the hypothesis that temperature over precipitation change is more important as the primary modulator of Southern Alps ice advances. The RCRC approach also demonstrates some subtle advantages of integrating multi-proxy data within a palaeocirculation context for New Zealand, notably because this reconstruction technique enables direct comparisons to coarsely resolved palaeoclimate model outputs that do not have downscaled information.

Timing of lake-level changes for a deep last-glacial Lake Missoula: optical dating of the Garden Gulch area, Montana, USA

NASA Astrophysics Data System (ADS)

Smith, Larry N.; Sohbati, Reza; Buylaert, Jan-Pieter; Lian, Olav B.; Murray, Andrew; Jain, Mayank

2018-03-01

Glaciolacustrine sediments in the Clark Fork River valley at Garden Gulch, near Drummond, Montana, USA record highstand positions of the ice-dammed glacial Lake Missoula and repeated subaerial exposure. During these highstands the lake was at greater than 65% of its recognized maximum capacity. The initial lake transgression deposited a basal sand unit. Subsequent cycles of lake-level fluctuations are recorded by sequences of laminated and cross laminated silt, sand, and clay deformed by periglacial processes during intervening periods of lower lake levels. Optically stimulated luminescence (OSL) dating of quartz sand grains, using single-aliquot regenerative-dose procedures, was carried out on 17 samples. Comparison of infrared stimulated luminescence (IRSL) from K-rich feldspar to OSL from quartz for all the samples suggests that they were well bleached prior to deposition and burial. Ages for the basal sand and overlying glaciolacustrine exposure surfaces are indistinguishable within one standard deviation, and give a weighted mean age of 20.9 ± 1.3 ka (n = 11). Based on sedimentological and stratigraphic analysis we infer that the initial transgression, and at least six cycles of lake-level fluctuation, occurred over time scales of decades to ∼2 ka. Bioturbated sandy slopewash dated at 10.6 ± 0.9 ka and 11.9 ± 1.2 ka unconformably overlies the upper glaciolacustrine deposits. The uppermost sediments, above the glaciolacustrine section, are younger than the Glacier Peak tephra (13.7-13.4 cal ka B.P.), which was deposited across parts of the drained lake basin, but has not been found at Garden Gulch. Our study indicates that glacial Lake Missoula reached >65 percent of maximum capacity by about 20.9 ± 1.3 ka and either partially or completely drained twelve times from this position. Rapid lowering from the lake's highstand position due to ice-dam failure likely led to scour in the downstream portions of the glacial Lake Missoula basin and megafloods in the Channeled Scabland.

The biogeophysical climatic impacts of anthropogenic land use change during the Holocene

NASA Astrophysics Data System (ADS)

Smith, M. C.; Singarayer, J. S.; Valdes, P. J.; Kaplan, J. O.; Branch, N. P.

2015-10-01

The first agricultural societies were established around 10 ka BP and had spread across much of Europe and southern Asia by 5.5 ka BP with resultant anthropogenic deforestation for crop and pasture land. Various studies have attempted to assess the biogeochemical implications for Holocene climate in terms of increased carbon dioxide and methane emissions. However, less work has been done to examine the biogeophysical impacts of this early land use change. In this study, global climate model simulations with HadCM3 were used to examine the biogeophysical effects of Holocene land cover change on climate, both globally and regionally, from the early Holocene (8 ka BP) to the early industrial era (1850 CE). Two experiments were performed with alternative descriptions of past vegetation: (i) potential natural vegetation simulated by TRIFFID but no land-use changes, and (ii) where the anthropogenic land use model, KK10 (Kaplan et al., 2009, 2011) has been used to set the HadCM3 crop regions. Snapshot simulations have been run at 1000 year intervals to examine when the first signature of anthropogenic climate change can be detected both regionally, in the areas of land use change, and globally. Results indicate that in regions of early land disturbance such as Europe and S.E. Asia detectable temperature changes, outside the normal range of variability, are encountered in the model as early as 7 ka BP in the June/July/August (JJA) season and throughout the entire annual cycle by 2-3 ka BP. Areas outside the regions of land disturbance are also affected, with virtually the whole globe experiencing significant temperature changes (predominantly cooling) by the early industrial period. Large-scale precipitation features such as the Indian monsoon, the intertropical convergence zone (ITCZ), and the North Atlantic storm track are also impacted by local land use and remote teleconnections. We investigated how advection by surface winds, mean sea level pressure (MSLP) anomalies, and tropospheric stationary wave train disturbances in the mid- to high-latitudes led to remote teleconnections.

Multistage late Cenozoic evolution of the Amargosa River drainage, southwestern Nevada and eastern California Society of America. All rights reserved

USGS Publications Warehouse

Menges, C.M.

2008-01-01

Stratigraphic and geomorphic analyses reveal that the regional drainage basin of the modern Amargosa River formed via multistage linkage of formerly isolated basins in a diachronous series of integration events between late Miocene and latest Pleistocene-Holocene time. The 275-km-long Amargosa River system drains generally southward across a large (15,540 km ²) watershed in southwestern Nevada and eastern California to its terminus in central Death Valley. This drainage basin is divided into four major subbasins along the main channel and several minor subbasins on tributaries; these subbasins contain features, including central valley lowlands surrounded by highlands that form external divides or internal paleodivides, which suggest relict individual physiographic-hydrologic basins. From north to south, the main subbasins along the main channel are: (1) an upper headwaters subbasin, which is deeply incised into mostly Tertiary sediments and volcanic rocks; (2) an unincised low-gradient section within the Amargosa Desert; (3) a mostly incised section centered on Tecopa Valley and tributary drainages; and (4) a west- to northwest-oriented mostly aggrading lower section along the axis of southern Death Valley. Adjoining subbasins are hydro-logically linked by interconnecting narrows or canyon reaches that are variably incised into formerly continuous paleodivides. The most important linkages along the main channel include: (1) the Beatty narrows, which developed across a Tertiary bedrock paleodivide between the upper and Amargosa Desert subbasins during a latest Miocene-early Pliocene to middle Pleistocene interval (ca. 4-0.5 Ma); (2) the Eagle Mountain narrows, which cut into a mostly alluvial paleodivide between the Amar-gosa Desert and Tecopa subbasins in middle to late Pleistocene (ca. 150-100 ka) time; and (3) the Amargosa Canyon, which formed in late middle Pleistocene (ca. 200140 ka) time through a breached, actively uplifting paleodivide between the Tecopa and southern Death Valley subbasins. Collectively, the interconnecting reaches represent discrete integration events that incrementally produced the modern drainage basin starting near Beatty sometime after 4 Ma and ending in the Salt Creek tributary in the latest Pleistocene to Holocene (post-30 ka). Potential mechanisms for drainage integration across paleodivides include basin overtopping from sedimentary infilling above paleodivide elevations, paleolake spillover, groundwater sapping, and (or) headward erosion of dissecting channels in lower-altitude subbasins. These processes are complexly influenced by fluvial responses to factors such as climatic change, local base-level differences across divides, and (or) tectonic activity (the latter only recognized in Amargosa Canyon). ?? 2008 The Geological Society of America.

Early Wisconsinan (MIS 4) Arctic ground squirrel middens and a squirrel-eye-view of the mammoth-steppe

NASA Astrophysics Data System (ADS)

Zazula, Grant D.; Froese, Duane G.; Elias, Scott A.; Kuzmina, Svetlana; Mathewes, Rolf W.

2011-08-01

Fossil arctic ground squirrel ( Spermophilus parryii) middens were recovered from ice-rich loess sediments in association with Sheep Creek-Klondike and Dominion Creek tephras (ca 80 ka) exposed in west-central Yukon. These middens provide plant and insect macrofossil evidence for a steppe-tundra ecosystem during the Early Wisconsinan (MIS 4) glacial interval. Midden plant and insect macrofossil data are compared with those previously published for Late Wisconsinan middens dating to ˜25-29 14C ka BP (MIS 3/2) from the region. Although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils, the co-occurrence of steppe-tundra plants and insects (e.g., Elymus trachycaulus, Kobresia myosuroides, Artemisia frigida, Phlox hoodii, Connatichela artemisiae) provides evidence for successive reestablishment of the zonal steppe-tundra habitats during cold stages of the Late Pleistocene. Arctic ground squirrels were well adapted to the cold, arid climates, steppe-tundra vegetation and well-drained loessal soils that characterize cold stages of Late Pleistocene Beringia. These glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of Alaska and Yukon, including the Klondike, where they are absent today. Arctic ground squirrels have endured numerous Quaternary climate oscillations by retracting populations to disjunct "interglacial refugia" during warm interglacial periods (e.g., south-facing steppe slopes, well-drained arctic and alpine tundra areas) and expanding their distribution across the mammoth-steppe biome during cold, arid glacial intervals.

Deep Space Ka-band Link Management and the MRO Demonstration: Long-term Weather Statistics Versus Forecasting

NASA Technical Reports Server (NTRS)

Davarian, Faramaz; Shambayati, Shervin; Slobin, Stephen

2004-01-01

During the last 40 years, deep space radio communication systems have experienced a move toward shorter wavelengths. In the 1960s a transition from L- to S-band occurred which was followed by a transition from S- to X-band in the 1970s. Both these transitions provided deep space links with wider bandwidths and improved radio metrics capability. Now, in the 2000s, a new change is taking place, namely a move to the Ka-band region of the radio frequency spectrum. Ka-band will soon replace X-band as the frequency of choice for deep space communications providing ample spectrum for the high data rate requirements of future missions. The low-noise receivers of deep space networks have a great need for link management techniques that can mitigate weather effects. In this paper, three approaches for managing Ka-band Earth-space links are investigated. The first approach uses aggregate annual statistics, the second one uses monthly statistics, and the third is based on the short-term forecasting of the local weather. An example of weather forecasting for Ka-band link performance prediction is presented. Furthermore, spacecraft commanding schemes suitable for Ka-band link management are investigated. Theses schemes will be demonstrated using NASA's Mars Reconnaissance Orbiter (MRO) spacecraft in the 2007 to 2008 time period, and the demonstration findings will be reported in a future publication.

10Be exposure age chronology of the last glaciation in the Krkonoše Mountains, Central Europe

NASA Astrophysics Data System (ADS)

Engel, Zbyněk; Braucher, Régis; Traczyk, Andrzej; Laetitia, Léanni; AsterTeam

2014-02-01

A new chronology of the last glaciation is established for the Krkonoše (Giant) Mountains, Central Europe, based on in-situ produced 10Be in moraine boulders. Exposure ages and Schmidt Hammer rebound values obtained for terminal moraines on the northern and southern flank of the mountains suggest that the oldest preserved moraines represent early phases of the Last Glacial Maximum (LGM). Large moraines at the outlet of the Snowy Cirques (Śnieżne Kotły) and in the middle part of the Úpa (Obří důl) trough were deposited around 21 ka while a series of smaller moraines above the LGM deposits represent readvances that occurred no later than 18.1 ± 0.6 ka, 15.7 ± 0.5 ka, 13.5 ± 0.5 ka and 12.9 ± 0.7 ka. An exposure age of 13.8 ± 0.4 ka obtained for protalus ramparts at the foot of the Úpská jáma Cirque headwall indicates that glaciers advanced only in north- to east-facing cirques during the Lateglacial. The last glacier fluctuation was synchronous with the Younger Dryas cold event. The timing of local glacier advances during the last glacial episode correlates with the late Weichselian glacier phases in the Alps and in the Bavarian/Bohemian Forest.

Cosmogenic exposure age constraints on deglaciation and flow behaviour of a marine-based ice stream in western Scotland, 21-16 ka

NASA Astrophysics Data System (ADS)

Small, David; Benetti, Sara; Dove, Dayton; Ballantyne, Colin K.; Fabel, Derek; Clark, Chris D.; Gheorghiu, Delia M.; Newall, Jennifer; Xu, Sheng

2017-07-01

Understanding how marine-based ice streams operated during episodes of deglaciation requires geochronological data that constrain both timing of deglaciation and changes in their flow behaviour, such as that from unconstrained ice streaming to topographically restricted flow. We present seventeen new 10Be exposure ages from glacial boulders and bedrock at sites in western Scotland within the area drained by the Hebrides Ice Stream, a marine-based ice stream that drained a large proportion of the former British-Irish Ice Sheet. Exposure ages from Tiree constrain deglaciation of a topographic high within the central zone of the ice stream, from which convergent flowsets were produced during ice streaming. These ages thus constrain thinning of the Hebrides Ice Stream, which, on the basis of supporting information, we infer to represent cessation of ice streaming at 20.6 ± 1.2 ka, 3-4 ka earlier than previously inferred. A period of more topographically restricted flow produced flow indicators superimposed on those relating to full ice stream conditions, and exposure ages from up-stream of these constrain deglaciation to 17.5 ± 1.0 ka. Complete deglaciation of the marine sector of the Hebrides Ice Stream occurred by 17-16 ka at which time the ice margin was located near the present coastline. Exposure ages from the southernmost Outer Hebrides (Mingulay and Barra) indicate deglaciation at 18.9 ± 1.0 and 17.1 ± 1.0 ka respectively, demonstrating that an independent ice cap persisted on the southern Outer Hebrides for 3-4 ka after initial ice stream deglaciation. This suggests that deglaciation of the Hebrides Ice Stream was focused along major submarine troughs. Collectively, our data constrain initial deglaciation and changes in flow regime of the Hebrides Ice Stream, final deglaciation of its marine sector, and deglaciation of the southern portion of the independent Outer Hebrides Ice Cap, providing chronological constraints on future numerical reconstructions of this key sector of the former British-Irish Ice Sheet.

Terminal Pleistocene Alaskan genome reveals first founding population of Native Americans.

PubMed

Moreno-Mayar, J Víctor; Potter, Ben A; Vinner, Lasse; Steinrücken, Matthias; Rasmussen, Simon; Terhorst, Jonathan; Kamm, John A; Albrechtsen, Anders; Malaspinas, Anna-Sapfo; Sikora, Martin; Reuther, Joshua D; Irish, Joel D; Malhi, Ripan S; Orlando, Ludovic; Song, Yun S; Nielsen, Rasmus; Meltzer, David J; Willerslev, Eske

2018-01-11

Despite broad agreement that the Americas were initially populated via Beringia, the land bridge that connected far northeast Asia with northwestern North America during the Pleistocene epoch, when and how the peopling of the Americas occurred remains unresolved. Analyses of human remains from Late Pleistocene Alaska are important to resolving the timing and dispersal of these populations. The remains of two infants were recovered at Upward Sun River (USR), and have been dated to around 11.5 thousand years ago (ka). Here, by sequencing the USR1 genome to an average coverage of approximately 17 times, we show that USR1 is most closely related to Native Americans, but falls basal to all previously sequenced contemporary and ancient Native Americans. As such, USR1 represents a distinct Ancient Beringian population. Using demographic modelling, we infer that the Ancient Beringian population and ancestors of other Native Americans descended from a single founding population that initially split from East Asians around 36 ± 1.5 ka, with gene flow persisting until around 25 ± 1.1 ka. Gene flow from ancient north Eurasians into all Native Americans took place 25-20 ka, with Ancient Beringians branching off around 22-18.1 ka. Our findings support a long-term genetic structure in ancestral Native Americans, consistent with the Beringian 'standstill model'. We show that the basal northern and southern Native American branches, to which all other Native Americans belong, diverged around 17.5-14.6 ka, and that this probably occurred south of the North American ice sheets. We also show that after 11.5 ka, some of the northern Native American populations received gene flow from a Siberian population most closely related to Koryaks, but not Palaeo-Eskimos, Inuits or Kets, and that Native American gene flow into Inuits was through northern and not southern Native American groups. Our findings further suggest that the far-northern North American presence of northern Native Americans is from a back migration that replaced or absorbed the initial founding population of Ancient Beringians.

First Toba supereruption revival

NASA Astrophysics Data System (ADS)

Lee, Meng-Yang; Chen, Chang-Hwa; Wei, Kuo-Yen; Iizuka, Yoshiyuki; Carey, Steven

2004-01-01

Little has been known about the earliest Toba eruptive episodes that created the largest-known caldera complex of Quaternary age. Here we report evidence for the eastward dispersal of the oldest Toba tuff in South China Sea sediments to 2500 km away from the source. The tephra deposits occur below the Brunhes-Matuyama geomagnetic boundary (778 ka) and slightly above the Australasian microtektite layer (793 ka). Calibrated by astronomically tuned oxygen isotope stratigraphy, the middle Pleistocene Toba eruption occurred during the deglaciation at 788 ± 2.2 ka, according to the tephra occurrence between marine isotope stages 20 and 19. This refined age is in good agreement with the 40Ar/39Ar date of 800 ± 20 ka for the Toba tephra (layer D) from Ocean Drilling Program (ODP) Site 758, but significantly younger than the commonly cited Ar/Ar age of 840 ± 30 ka. The eruption expelled at least 800 1000 km3 dense-rock-equivalent of rhyolitic magma on the basis of the widespread tephra-fall deposit in the basins of the Indian Ocean and the South China Sea. In spite of its exceptional magnitude, the timing of this major eruption does not indicate a causal linkage between this event and a long-term global climatic deterioration.

The Rurrand Fault, Germany: A Holocene surface rupture and new slip rate estimates

NASA Astrophysics Data System (ADS)

Grützner, Christoph; Fischer, Peter; Reicherter, Klaus

2016-04-01

Very low deformation rates in continental interiors are a challenge for research on active tectonics and seismic hazard. Faults tend to have very long earthquake recurrence intervals and morphological evidence of surface faulting is often obliterated by erosion and sedimentation. The Lower Rhine Graben in Central Europe is characterized by slow active faults with individual slip rates of well less than 0.1 mm/a. As a consequence, most geodetic techniques fail to record tectonic motions and the morphological expression of the faults is subtle. Although damaging events are known from this region, e.g. the 1755/56 Düren earthquakes series, there is no account for surface rupturing events in instrumental and historical records. Owing to the short temporal coverage with respect to the fault recurrence intervals, these records probably fail to depict the maximum possible magnitudes. In this study we used morphological evidence from a 1 m airborne LiDAR survey, near surface geophysics, and paleoseismological trenching to identify surface rupturing earthquakes at the Rurrand Fault between Cologne and Aachen in W Germany. LiDAR data allowed identifying a young fault strand parallel to the already known main fault with the subtle morphological expression of recent surface faulting. In the paleoseismological trenches we found evidence for two surface rupturing earthquakes. The most recent event occurred in the Holocene, and a previous earthquake probably happened in the last 150 ka. Geophysical data allowed us to estimate a minimum slip rate of 0.03 mm/a from an offset gravel horizon. We estimate paleomagnitudes of MW5.9-6.8 based on the observed offsets in the trench (<0.5 m per event) and fault scaling relationships. Our data imply that the Rurrand Fault did not creep during the last 150 ka, but rather failed in large earthquakes. These events were much stronger than those known from historical sources. We are able to show that the Rurrand Fault did not rupture the surface during the Düren 1755/56 seismic crisis and conclude that these events likely occurred on another nearby fault system or did not rupture the surface at all. The very long recurrence interval of 25-65 ka for surface rupturing events illustrates the problems of assessing earthquake hazard in such slowly deforming regions. We emphasize that geological data must be included in seismic hazard and surface rupture hazard assessments in order to obtain a complete picture of a region's seismic potential.

Laurentide Ice Sheet meltwater and the Atlantic meridional overturning circulation since the last glacial maximum: A view from the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Flower, B. P.; Williams, C.; Brown, E. A.; Hastings, D. W.; Hendricks, J.; Goddard, E. A.

2010-12-01

The influence of ice sheet meltwater on the Atlantic meridional overturning circulation (AMOC) since the last glacial maximum represents an important issue in abrupt climate change. Comparison of Greenland and Antarctic ice core records has revealed a complex interhemispheric linkage and led to different models of ocean circulation including the “bipolar seesaw.” Meltwater input from the Laurentide Ice Sheet has been invoked as a cause of proximal sea-surface temperature (SST) and salinity change in the North Atlantic, and of regional to global climate change via its influence on the AMOC. We present published and new Mg/Ca, Ba/Ca, and δ18O data on the planktic foraminifer Globigerinoides ruber from northern Gulf of Mexico sediment cores that provide detailed records of SST, δ18O of seawater (δ18Osw), and inferred salinity for the 20-8 ka interval. Age control for Orca Basin core MD02-2550 is based on >40 AMS 14C dates on Globigerinoides ruber and documents continuous sedimentation at rates >35 cm/kyr. Early meltwater input is inferred from δ18Osw and Ba/Ca data prior to and during the Mystery Interval, consistent with a high sensitivity to solar insolation and greenhouse forcing. New bulk sediment δ18O data show major spikes reaching -5.5‰ ca. 14.6 and 12.6 ka. We speculate that these excursions represent fine carbonate sediment from Canadian Paleozoic marine carbonates, analogous to detrital carbonate in the North Atlantic which has a δ18O value of -5‰. Partial support for our hypothesis comes from SEM photomicrographs of bulk sediment from this section, which show no coccoliths or foraminifera in contrast to other intervals. The biogenic carbonate flux seems to have been greatly reduced by fine sediment input. Inferred peak meltwater flow appears to have been associated with the Bolling warming and meltwater pulse 1a. Finally, meltwater reduction at the start of the Younger Dryas supports models for a diversion to North Atlantic outlets and AMOC reduction ca. 12.9 ka, but alternatively could represent diminished ice melting. Overall, the relations between Gulf of Mexico meltwater input, Heinrich events, Antarctic warm events, and AMOC variability suggest bipolar warming and enhanced seasonality during meltwater episodes. We formulate a “meltwater capacitor” hypothesis for understanding enhanced seasonality in the North Atlantic region during abrupt climate change.

Resilient terrestrial ecosystems at the Paleocene-Eocene Thermal Maximum (Invited)

NASA Astrophysics Data System (ADS)

Wing, S.

2010-12-01

The Paleocene-Eocene Thermal Maximum (PETM) was an interval of global warming lasting ~200 ka that began ~56 Ma. Global temperature rose 5-8 °C in association with the emission of thousands of Pg of carbon into the ocean-atmosphere system. PETM rocks and fossils are extensively exposed in the SE Bighorn Basin of Wyoming, where the event is represented by ~40 m of fluvial rocks. Fossil plants demonstrate a rapid and nearly complete turnover in floral composition that also suggests a change in the structure of vegetation. Floras collected from the last ~50 ka of the Paleocene are composed of Platanaceae (sycamores), Betulaceae (birches), Fagaceae (oaks), Lauraceae (laurels), Juglandaceae (walnuts), Cercidiphyllaceae (katsura), Taxodiaceae (dawn redwood), and Arecaceae (palms), among others. Many of these families are most diverse and abundant today in temperate to subtropical, mid-latitude forests. During the body of the carbon isotope excursion (CIE) associated with the PETM fossil floras have a completely different composition. All of the latest Paleocene plant types are absent, except for palms, and instead the floras are dominated by Fabaceae (bean family). Other taxa include Sapindaceae (soapberry), Annonaceae (paw-paw), and Hernandiaceae. Where living relatives are known, they live in dry tropical forests of Central and South America. This floral composition is maintained through the ~30 m of section representing the ~110 ka-long body of the CIE, the same interval characterized by dwarfed mammalian faunas. During the recovery phase of the CIE most of the latest Paleocene plants returned to the area of study, although some new taxa appeared, apparently coming in from Europe or Asia. The distinctive PETM floral types are not seen after the recovery phase of the CIE. Change in floral composition during the PETM apparently represents regional extirpations of populations of plants that preferred warm, mesic conditions, and northward range extensions of plants that preferred dry tropical climates. This process was reversed at the end of the PETM. Although characteristics of PETM vegetation cannot be assessed directly, the distribution of living relatives is consistent with the idea that PETM vegetation was more water-stressed and more open than pre- and post-PETM vegetation. This is also matches inference from paleosol features. The radical change in composition and probable structure of vegetation across the PETM is particularly notable in light of the low extinction rates at this time. Although there is strong evidence of rapid range change and rapid evolution, the increase in temperature and decrease in precipitation do not appear to have exceeded the capacity of lineages to respond, even though the PETM is cited as an example of geologically rapid environmental change.

Reconstruction of the Late Quaternary Glaciation of the Macha Khola valley (Gorkha Himal, Nepal) using relative and absolute ( 14C, 10Be, dendrochronology) dating techniques

NASA Astrophysics Data System (ADS)

Zech, W.; Glaser, B.; Abramowski, U.; Dittmar, C.; Kubik, P. W.

2003-11-01

Late Quaternary glacier fluctuations in the Macha Khola valley (Gorkha Himal, Nepal) were reconstructed using relative and absolute dating techniques. Our results indicate that younger moraine complexes were left by Late Holocene (<1.7 cal. ka BP), mid-Holocene (ca 3 cal. ka BP), and Lateglacial (ca 13 cal. ka BP) ice advances. Older Late Quaternary glacier advances occurred during Marine Oxygen Isotope Stages (MIS) 2 and 3-4. No relics of Middle or Early Pleistocene glaciations could be found. During MIS 3-4, glaciers advanced down to an altitude of at least 2150 m a.s.l., corresponding to an ELA depression of approximately 1300 m. At about 3500 m a.s.l., the MIS 2 Macha Khola glacier reached almost the thickness of the former MIS 3-4 glacier and retreated some time before 17.9 cal. ka BP. The Lateglacial glacier advanced again several times to altitudes between 2450 and 3400 m a.s.l. The mid-Holocene glaciers extended much farther down-valley than the Late Holocene ones. Dendrochronological data of Abies spectabilis suggested several periods of unfavourable growth conditions especially at the beginning of the 19th (1820) and 20th (1905) centuries.

Earth's magnetic field is probably not reversing.

PubMed

Brown, Maxwell; Korte, Monika; Holme, Richard; Wardinski, Ingo; Gunnarson, Sydney

2018-05-15

The geomagnetic field has been decaying at a rate of ∼5% per century from at least 1840, with indirect observations suggesting a decay since 1600 or even earlier. This has led to the assertion that the geomagnetic field may be undergoing a reversal or an excursion. We have derived a model of the geomagnetic field spanning 30-50 ka, constructed to study the behavior of the two most recent excursions: the Laschamp and Mono Lake, centered at 41 and 34 ka, respectively. Here, we show that neither excursion demonstrates field evolution similar to current changes in the geomagnetic field. At earlier times, centered at 49 and 46 ka, the field is comparable to today's field, with an intensity structure similar to today's South Atlantic Anomaly (SAA); however, neither of these SAA-like fields develop into an excursion or reversal. This suggests that the current weakened field will also recover without an extreme event such as an excursion or reversal. The SAA-like field structure at 46 ka appears to be coeval with published increases in geomagnetically modulated beryllium and chlorine nuclide production, despite the global dipole field not weakening significantly in our model during this time. This agreement suggests a greater complexity in the relationship between cosmogenic nuclide production and the geomagnetic field than is commonly assumed.

Modelling of crater formation on anode surface by high-current vacuum arcs

NASA Astrophysics Data System (ADS)

Tian, Yunbo; Wang, Zhenxing; Jiang, Yanjun; Ma, Hui; Liu, Zhiyuan; Geng, Yingsan; Wang, Jianhua; Nordlund, Kai; Djurabekova, Flyura

2016-11-01

Anode melting and crater formation significantly affect interruption of high-current vacuum arcs. The primary objective of this paper is to theoretically investigate the mechanism of anode surface crater formation, caused by the combined effect of surface heating during the vacuum arc and pressure exerted on the molten surface by ions and electrons from the arc plasma. A model of fluid flow and heat transfer in the arc anode is developed and combined with a magnetohydrodynamics model of the vacuum arc plasma. Crater formation is observed in simulation for a peak arcing current higher than 15 kA on 40 mm diam. Cu electrodes spaced 10 mm apart. The flow of liquid metal starts after 4 or 5 ms of arcing, and the maximum velocities are 0.95 m/s and 1.39 m/s for 20 kA and 25 kA arcs, respectively. This flow redistributes thermal energy, and the maximum temperature of the anode surface does not remain in the center. Moreover, the condition for the liquid droplet formation on the anode surfaces is developed. The solidification process after current zero is also analyzed. The solidification time has been found to be more than 3 ms after 25 kA arcing. The long solidification time and sharp features on crater rims induce Taylor cone formation.

Correlation of the KHS Tuff of the Kibish Formation to volcanic ash layers at other sites, and the age of early Homo sapiens (Omo I and Omo II).

PubMed

Brown, Francis H; McDougall, Ian; Fleagle, John G

2012-10-01

Hominin specimens Omo I and Omo II from Member I of the Kibish Formation, Ethiopia are attributed to early Homo sapiens, and an age near 196 ka has been suggested for them. The KHS Tuff, within Member II of the Kibish Formation has not been directly dated at the site, but it is believed to have been deposited at or near the time of formation of sapropel S6 in the Mediterranean Sea. Electron microprobe analyses suggest that the KHS Tuff correlates with the WAVT (Waidedo Vitric Tuff) at Herto, Gona, and Konso (sample TA-55), and with Unit D at Kulkuletti in the Ethiopian Rift Valley. Konso sample TA-55 is older than 154 ka, and Unit D at Kulkuletti is dated at 183 ka. These correlations and ages provide strong support for the age originally suggested for the hominin remains Omo I and Omo II, and for correlation of times of deposition in the Kibish region with formation of sapropels in the Mediterranean Sea. The Aliyo Tuff in Member III of the Kibish Formation is dated at 104 ka, and correlates with Gademotta Unit 15 in the Ethiopian Rift Valley. Copyright © 2012 Elsevier Ltd. All rights reserved.

Post-glacial inflation-deflation cycles, tilting, and faulting in the Yellowstone Caldera based on Yellowstone Lake shorelines

USGS Publications Warehouse

Pierce, Kenneth L.; Cannon, Kenneth P.; Meyer, Grant A.; Trebesch, Matthew J.; Watts, Raymond D.

2002-01-01

The Yellowstone caldera, like many other later Quaternary calderas of the world, exhibits dramatic unrest. Between 1923 and 1985, the center of the Yellowstone caldera rose nearly one meter along an axis between its two resurgent domes (Pelton and Smith, 1979, Dzurisin and Yamashita, 1987). From 1985 until 1995-6, it subsided at about two cm/yr (Dzurisin and others, 1990). More recent radar interferometry studies show renewed inflation of the northeastern resurgent dome between 1995 and 1996; this inflation migrated to the southwestern resurgent dome from 1996 to 1997 (Wicks and others, 1998). We extend this record back in time using dated geomorphic evidence of postglacial Yellowstone Lake shorelines around the northern shore, and Yellowstone River levels in the outlet area. We date these shorelines using carbon isotopic and archeological methods. Following Meyer and Locke (1986) and Locke and Meyer (1994), we identify the modern shoreline as S1 (1.9 ? 0.3 m above the lake gage datum), map paleoshoreline terraces S2 to S6, and infer that the prominent shorelines were cut during intracaldera uplift episodes that produced rising water levels. Doming along the caldera axis reduces the gradient of the Yellowstone River from Le Hardys Rapids to the Yellowstone Lake outlet and ultimately causes an increase in lake level. The 1923-1985 doming is part of a longer uplift episode that has reduced the Yellowstone River gradient to a ?pool? with a drop of only 0.25 m over most of this 5 km reach. We also present new evidence that doming has caused submergence of some Holocene lake and river levels. Shoreline S5 is about 14 m above datum and estimated to be ~12.6 ka, because it post-dates a large hydrothermal explosion deposit from the Mary Bay area (MB-II) that occurred ~13 ka. S4 formed about 8 m above datum ~10.7 ka as dated by archeology and 14C, and was accompanied by offset on the Fishing Bridge fault. About 9.7 ka, the Yellowstone River eroded the ?S-meander?, followed by a ~5 m rise in lake level to S2. The lowest generally recognizable shoreline is S2. It is ~5 m above datum (3 m above S1) and is ~8 ka, as dated on both sides of the outlet. Yellowstone Lake and the river near Fishing Bridge were 5-6 m below their present level about 3-4 ka, as indicated by 14C ages from submerged beach deposits, drowned valleys, and submerged Yellowstone River gravels. Thus, the lake in the outlet region has been below or near its present level for about half the time since a 1 km-thick icecap melted from the Yellowstone Lake basin about 16 ka. The amplitude of two rises in lake and river level can be estimated based on the altitude of Le Hardys Rapids, indicators of former lake and river levels, and reconstruction of the river gradient from the outlet to Le Hardys Rapids. Both between ~9.5 ka and ~8.5 ka, and after ~3 ka, Le Hardys Rapids (LHR) was uplifted about 8 meters above the outlet, suggesting a cyclic deformation process. Older possible rises in lake level are suggested by locations where the ~10.7 ka S4 truncates older shorelines, and valleys truncated by the ~12.6 ka S5 shoreline. Using these controls, a plot of lake level through time shows 5-7 millennial-scale oscillations since 14.5 ka. Major cycles of inflation and deflation are thousands of years long. Le Hardys Rapids has twice been uplifted ~8 m relative to the lake outlet. These two locations span only the central 25% of the historic caldera doming, so that if we use historic doming as a model, total projected uplift would be ~32 m. This ?heavy breathing? of the central part of the Yellowstone caldera may reflect a combination of several possible processes: magmatic inflation, tectonic stretching and deflation, and hydrothermal fluid sealing and inflation followed by cracking of the seal, pressure release, and deflation. Over the entire postglacial period, subsidence has balanced or slightly exceeded uplift as shown by older shorelines that descend towards the caldera axis. We

Multi-proxy dating of Holocene maar lakes and Pleistocene dry maar sediments in the Eifel, Germany

NASA Astrophysics Data System (ADS)

Sirocko, Frank; Dietrich, Stephan; Veres, Daniel; Grootes, Pieter M.; Schaber-Mohr, Katja; Seelos, Klemens; Nadeau, Marie-Josée; Kromer, Bernd; Rothacker, Leo; Röhner, Marieke; Krbetschek, Matthias; Appleby, Peter; Hambach, Ulrich; Rolf, Christian; Sudo, Masafumi; Grim, Stephanie

2013-02-01

During the last twelve years the ELSA Project (Eifel Laminated Sediment Archive) at Mainz University has drilled a total of about 52 cores from 27 maar lakes and filled-in maar basins in the Eifel/Germany. Dating has been completed for the Holocene cores using 6 different methods (210Pb and 137Cs activities, palynostratigraphy, event markers, varve counting, 14C). In general, the different methods consistently complement one another within error margins. Event correlation was used for relating typical lithological changes with historically known events such as the two major Holocene flood events at 1342 AD and ca 800 BC. Dating of MIS2-MIS3 core sections is based on greyscale tuning, radiocarbon and OSL dating, magnetostratigraphy and tephrochronology. The lithological changes in the sediment cores demonstrate a sequence of events similar to the North Atlantic rapid climate variability of the Last Glacial Cycle. The warmest of the MIS3 interstadials was GI14, when a forest with abundant spruce covered the Eifel area from 55 to 48 ka BP, i.e. during a time when also other climate archives in Europe suggested very warm conditions. The forest of this "Early Stage 3 warm phase" developed subsequently into a steppe with scattered birch and pine, and finally into a glacial desert at around 25 ka BP. Evidence for Mono Lake and Laschamp geomagnetic excursions is found in two long cores. Several large eruptions during Middle and Late Pleistocene (Ulmener Maar - 11,000 varve years BP, Laacher See - 12,900 varve years BP, Mosenberg volcanoes/Meerfelder Maar 41-45 cal ka BP, Dümpel Maar 116 ka BP, Glees Maar - 151 ka BP) produced distinct ash-layers crucial for inter-core and inter-site correlations. The oldest investigated maar of the Eifel is 40Ar/39Ar dated to the time older than 520 ka BP.

Localized rejuvenation of a crystal mush recorded in zircon temporal and compositional variation at the Lassen Volcanic Center, northern California

USGS Publications Warehouse

Klemetti, Erik W.; Clynne, Michael A.

2014-01-01

Zircon ages and trace element compositions from recent silicic eruptions in the Lassen Volcanic Center (LVC) allow for an evaluation of the timing and conditions of rejuvenation (reheating and mobilization of crystals) within the LVC magmatic system. The LVC is the southernmost active Cascade volcano and, prior to the 1980 eruption of Mount St. Helens, was the site of the only eruption in the Cascade arc during the last century. The three most recent silicic eruptions from the LVC were very small to moderate-sized lava flows and domes of dacite (1915 and 27 ka eruptions of Lassen Peak) and rhyodacite (1.1 ka eruption of Chaos Crags). These eruptions produced mixed and mingled lavas that contain a diverse crystal cargo, including zircon. 238U-230Th model ages from interior and surface analyses of zircon reveal ages from ~17 ka to secular equilibrium (>350 ka), with most zircon crystallizing during a period between ~60–200 ka. These data support a model for localized rejuvenation of crystal mush beneath the LVC. This crystal mush evidently is the remnant of magmatism that ended ~190 ka. Most zircon are thought to have been captured from “cold storage” in the crystal mush (670–725°C, Hf >10,000 ppm, Eu/Eu* 0.25–0.4) locally remobilized by intrusion of mafic magma. A smaller population of zircon (>730°C, Hf <10,000 ppm, Eu/Eu* >0.4) grew in, and are captured from, rejuvenation zones. These data suggest the dominant method to produce eruptible melt within the LVC is small-scale, local rejuvenation of the crystal mush accompanied by magma mixing and mingling. Based on zircon stability, the time required to heat, erupt and then cool to background conditions is relatively short, lasting a maximum of 10 s–1000 s years. Rejuvenation events in the LVC are ephemeral and permit eruption within an otherwise waning and cooling magmatic body.

Late Pleistocene and Holocene Geology and Hazards at Glacier Peak Volcano, Washington

NASA Astrophysics Data System (ADS)

Vallance, J. W.; Van Eaton, A. R.; Ramsey, D. W.

2015-12-01

Recent fieldwork, improved radiocarbon dating, and mapping on recently acquired LiDAR base have better delineated timing, frequency, and style of volcanism at Glacier Peak. The work shows that, after Mount St. Helens, Glacier Peak is one of the most frequently active Cascade volcanoes. The volcano has erupted multiple times 13-14 ka, 5­-7 ka, 1-2.5 ka, and perhaps as recently as a few hundred years ago. The plinian eruptions of ~13.5 ka were much more voluminous than those of Mount St. Helens in 1980 and show that Glacier Peak is among the most explosive of Cascade volcanoes. These eruptions dispersed ash fallout hundreds of kilometers downwind in Idaho, Montana and Wyoming; produced a partly welded ignimbrite and a small debris avalanche; and caused lahars and flooding far across Puget Sound lowland. Numerous more recent eruptions during the periods 5-7 ka and 1-2.5 ka extruded lava domes whose hot rock avalanched across snow and ice to produce pyroclastic flows and lahars. These eruptions dispersed ash tens of to a hundred or more kilometers downwind. Resulting lahars and floods inundated as far as Puget Sound lowland. Glacier Peak is remote and hidden from most areas of the densely populated Puget Sound lowland; hence, it gets less attention than other prominent Cascade volcanoes like Mounts Rainier, Baker, and St. Helens. Despite its remote location, Glacier Peak poses substantial hazard because even small eruptions on ice-clad volcanoes can have devastating consequences. Distal threats include hazard to air traffic owing to ash plumes. Lahars and potential long-term sedimentation and flooding downstream pose threats to communities near rivers along Skagit and Stillaguamish River drainages. Farther downstream, sedimentation is likely to decrease channel capacity, increasing likelihood of floods. Lava flows, pyroclastic flows, and debris avalanches will threaten hikers in the wilderness near Glacier Peak.

Risk Assessment of Mineral Groundwater Near Rogaška Slatina

NASA Astrophysics Data System (ADS)

Trcek, Branka; Leis, Albrecht

2017-10-01

Groundwater resources of mineral and thermo-mineral water are invaluable for planning a sustainable spatial and economic development of the Rogaška Slatina area, which requires a protection of this natural heritage. Numerous previous investigations of Rogaška groundwaters were subjects to balneology and to demands for larger exploitation quantities, that is why information are missing that are essential for definition of the Rogaška fractured aquifer system with mineral and thermo-mineral water and for its protection. The isotopic investigations of groundwaters stored in the Rogaška Slatina fractured aquifer system were performed aiming at answering open questions on the groundwater recharge and dynamics, on connections between different types of aquifers and on solute transport. Environmental isotopes 2H, 18O, 3H, 13C of dissolved inorganic carbon and 14C were analysed in mineral, thermo-mineral and spring waters. Results indicated the source and mechanism of groundwater recharge, its renewability, a transit time distribution, hydraulic interrelationships, the groundwater origin and its evolution due to effects of water-rock interaction. The mean residence time estimates of mineral and thermo- mineral water in the aquifer are between 3400 and 14000 years. On the other hand, the mixing processes between younger and older waters or mineral and spring waters are reflected as well as waters that infiltrated predominantly after the 1960s. These suggest the vulnerability of the research systems to man-made impacts. The presented results coupled with available information on a physical hydrogeology and water chemistry asses the optimal balance between the environmental protection and economic use of mineral water resources in the study area. They are essential for the protection strategy development of mineral and thermo-mineral water in the Rogaška Slatina area bringing together the state administration and local authorities and stakeholders.

Reaching and abandoning the furthest ice extent during the Last Glacial Maximum in the Alps

NASA Astrophysics Data System (ADS)

Ivy-Ochs, Susan; Wirsig, Christian; Zasadni, Jerzy; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

2016-04-01

During the Last Glacial Maximum (LGM) in the European Alps (late Würm) local ice caps and extensive ice fields in the high Alps fed huge outlet glaciers that occupied the main valleys and extended onto the forelands as piedmont lobes. Records from numerous sites suggest advance of glaciers beyond the mountain front by around 30 ka (Ivy-Ochs 2015 and references therein). Reaching of the maximum extent occurred by about 27-26 ka, as exemplified by dates from the Rhein glacier area (Keller and Krayss, 2005). Abandonment of the outermost moraines at sites north and south of the Alps was underway by about 24 ka. In the high Alps, systems of transection glaciers with transfluences over many of the Alpine passes dominated, for example, at Grimsel Pass in the Central Alps (Switzerland). 10Be exposure ages of 23 ± 1 ka for glacially sculpted bedrock located just a few meters below the LGM trimline in the Haslital near Grimsel Pass suggest a pulse of ice surface lowering at about the same time that the foreland moraines were being abandoned (Wirsig et al., 2016). Widespread ice surface lowering in the high Alps was underway by no later than 18 ka. Thereafter, glaciers oscillated at stillstand and minor re-advance positions on the northern forelands for several thousand years forming the LGM stadial moraines. Final recession back within the mountain front took place by 19-18 ka. Recalculation to a common basis of all published 10Be exposure dates for boulders situated on LGM moraines suggests a strong degree of synchrony for the timing of onset of ice decay both north and south of the Alps. Ivy-Ochs, S., 2015, Cuadernos de investigación geográfica 41: 295-315. Keller, O., Krayss, E., 2005, Vierteljahrschr. Naturforsch. Gesell. Zürich 150: 69-85. Wirsig, C. et al., 2016, J. Quat. Sci. 31: 46-59.

Localized rejuvenation of a crystal mush recorded in zircon temporal and compositional variation at the Lassen Volcanic Center, northern California.

PubMed

Klemetti, Erik W; Clynne, Michael A

2014-01-01

Zircon ages and trace element compositions from recent silicic eruptions in the Lassen Volcanic Center (LVC) allow for an evaluation of the timing and conditions of rejuvenation (reheating and mobilization of crystals) within the LVC magmatic system. The LVC is the southernmost active Cascade volcano and, prior to the 1980 eruption of Mount St. Helens, was the site of the only eruption in the Cascade arc during the last century. The three most recent silicic eruptions from the LVC were very small to moderate-sized lava flows and domes of dacite (1915 and 27 ka eruptions of Lassen Peak) and rhyodacite (1.1 ka eruption of Chaos Crags). These eruptions produced mixed and mingled lavas that contain a diverse crystal cargo, including zircon. 238U-230Th model ages from interior and surface analyses of zircon reveal ages from ∼17 ka to secular equilibrium (>350 ka), with most zircon crystallizing during a period between ∼60-200 ka. These data support a model for localized rejuvenation of crystal mush beneath the LVC. This crystal mush evidently is the remnant of magmatism that ended ∼190 ka. Most zircon are thought to have been captured from "cold storage" in the crystal mush (670-725°C, Hf >10,000 ppm, Eu/Eu* 0.25-0.4) locally remobilized by intrusion of mafic magma. A smaller population of zircon (>730°C, Hf <10,000 ppm, Eu/Eu* >0.4) grew in, and are captured from, rejuvenation zones. These data suggest the dominant method to produce eruptible melt within the LVC is small-scale, local rejuvenation of the crystal mush accompanied by magma mixing and mingling. Based on zircon stability, the time required to heat, erupt and then cool to background conditions is relatively short, lasting a maximum of 10 s-1000 s years. Rejuvenation events in the LVC are ephemeral and permit eruption within an otherwise waning and cooling magmatic body.

Timing and nature of alluvial fan development along the Chajnantor Plateau, northern Chile

NASA Astrophysics Data System (ADS)

Cesta, Jason M.; Ward, Dylan J.

2016-11-01

Alluvial systems in the Atacama Desert provide a unique opportunity to elucidate the sedimentary response to climate variability, particularly changes in precipitation, in hyperarid environments. Alluvial fans along the eastern margin of the Salar de Atacama, adjacent to the Chajnantor Plateau in the Atacama Desert of northern Chile, provide an archive of climate-modulated sediment transfer and erosion at an extreme of Earth's climate. Three regional alluvial fan surfaces (Qf1 [oldest] to Qf3 [youngest]) were mapped along the western flank of the Chajnantor Plateau. The alluvial fans were examined with geomorphic and terrestrial cosmogenic 36Cl surface exposure dating methods to define the timing of alluvial fan formation and to determine the role of climatic processes on fan development in a hyperarid environment. Alluvial fans in the study area are comprised of hyperconcentrated flow and boulder-rich debris flow deposits that reflect deposition transitioning between cohesive and noncohesive regimes. Alluvial fan surfaces yield exposure ages that range from 49.6 ± 4.4 to 194 ± 12 ka, while debris flow boulders yield exposure ages ranging from 12.4 ± 2.1 to 229 ± 53 ka. Cosmogenic 36Cl exposure ages indicate that abandonment of alluvial fan surfaces Qf1, Qf2, and Qf3 date to 175 ± 22.6 ka (MIS 6), 134.5 ± 9.18 ka (MIS 6), and 20.07 ± 6.26 ka (MIS 2), respectively. A 36Cl concentration-depth profile through alluvial fan Qf1 suggests a simple depositional history with minimal nuclide inheritance implying relatively rapid aggradation (6 m in ca. 25 kyr) followed by surface abandonment ca. 180-200 ka. Our data support a strong climatic control on alluvial fan evolution in the region, and we propose that the alluvial fans along the margins of the Salar de Atacama form according to the humid model of fan formation.