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1

Intensified deep Pacific inflow and ventilation in Pleistocene glacial times.  

PubMed

The production of cold, deep waters in the Southern Ocean is an important factor in the Earth's heat budget. The supply of deep water to the Pacific Ocean is presently dominated by a single source, the deep western boundary current east of New Zealand. Here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep-water properties and speed changes during the Pleistocene epoch. In physical and isotope proxies we find evidence for intensified deep Pacific Ocean inflow and ventilation during the glacial periods of the past 1.2 million years. The changes in throughflow may be directly related to an increased production of Antarctic Bottom Water during glacial times. Possible causes for such an increased bottom-water production include increasing wind strengths in the Southern Ocean or an increase in annual sea-ice formation, leaving dense water after brine rejection and thereby enhancing deep convection. We infer also that the global thermohaline circulation was perturbed significantly during the mid-Pleistocene climate transition between 0.86 and 0.45 million years ago. PMID:11518963

Hall, I R; McCave, I N; Shackleton, N J; Weedon, G P; Harris, S E

2001-08-23

2

Microfacies and diagenesis of older Pleistocene (pre-last glacial maximum) reef deposits, Great Barrier Reef,  

E-print Network

Expedition 325, 34 holes were drilled along five transects in front of the Great Barrier Reef of Australia, Great Barrier Reef Environmental Changes, Integrated Ocean Drilling Program, microfacies, PleistoceneMicrofacies and diagenesis of older Pleistocene (pre-last glacial maximum) reef deposits, Great

Schöne, Bernd R.

3

"Pleistocene Park" - A Glacial Ecosystem in a Warming World  

NASA Astrophysics Data System (ADS)

Most people if asked what association they have to the phrase - ice age, will answer - "Mammoth". But mammoths are not only big wooly elephants which went extinct in the beginning of Holocene. They were also part of a great ecosystem, the Northern Steppe or Mammoth Ecosystem, which was the world's largest ecosystem for hundreds thousand of years. This ecosystem, with extremely high rates of biocycling, could maintain animal densities which can be hardly found anywhere in the modern world. Northern steppe played an important role in shaping the glacial climate of the planet. High albedo grasslands reflected a much bigger portion of sun heat back to the atmosphere. Cold soils and permafrost served as sinks of carbon, helping to keep greenhouse gas concentration in the atmosphere at low levels. In the beginning of Holocene, simultaneously with wave of human expansion, an extinction wave took place. Tens of megafauna species became extinct at that time worldwide, while ones that resisted the extinction substantially dropped in numbers. The Northern Steppe ecosystem became imbalanced. Without large numbers of herbivores grazing and trampling the pasture, trees, shrubs and moss invaded grasslands. Within just a few hundreds years the mammoth ecosystem was gone, replaced by much lower productivity ecosystems. Already 14 thousand year ago, by simply increasing hunting pressure, humans managed to dramatically change Earth's appearance. We propose that by artificially maintaining a high animal density and diversity on a limited territory for extended period of time, it will be possible to reverse the shift, reestablishing the productive Northern Steppe ecosystem. Moss, shrubs and tree sprouts are not able to resist grazing pressure so they will be quickly replaced by grasses and herbs. Animals digesting all aboveground biomass would accelerate nutrition cycling and consequently increase bioproductivity. Higher bioproductivity would increase evapotranspiration, keeping soils dry and runoff low. This would further increase nutrient availability in the soil. Water limitation would force roots grow deeper to cold soil horizons where these roots (carbon) will be sequestered for a long period of time. After high productivity and high diversity of animals in the ecosystem is reached, this ecosystem will once again be able to compete and to expand. To test this hypothesis, we have started the experiment named "Pleistocene Park". For over 15 years we have brought different herbivore species to the fenced area in the Kolyma river lowland, keep them at high density and see the ecosystem transformation. Now Pleistocene Park is size of 20 km2 and home for 7 big herbivores species. It is a small version of how the Mammoth Steppe ecosystem looked in the past and may look in the future. Pleistocene Park is a place where scientists can conduct in situ research and see how restoration of the ice age ecosystem may help mitigate future climatic changes. Arctic is a weakly populated region with no possibilities for agriculture. Modern civilization treats bigger part of the Arctic as wastelands. So why don't turn this "wasteland" into something that can strongly benefit our civilization in the future?

Zimov, N.; Zimov, S. A.

2011-12-01

4

Geomorphological correlation of Late Pleistocene glacial complexes of Western and Eastern Beringia  

Microsoft Academic Search

Many fundamental problems exist in comparing the chronology and correlation of Late Pleistocene glaciations between Western and Eastern Beringia. However, geomorphological analysis, complemented by palynological studies and radiocarbon age estimates of glacial complexes found in the Ulakhan-Chistai, Bolshoi Annachag, and Pekulney ranges, northeastern Russia, and the Kigluaik Mountains and Brooks Range, Alaska, allow for broad comparisons. The data clearly confirm

O. Yu. Glushkova

2001-01-01

5

Glacial Southern Ocean freshening at the onset of the Middle Pleistocene Climate Transition  

E-print Network

Ocean has been proposed as one of the key regions of the global ocean in modulating pCO2 variationsLetters Glacial Southern Ocean freshening at the onset of the Middle Pleistocene Climate Transition of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT, UK a r t i c l e i n f o Article history

Gilli, Adrian

6

Paleoclimatic significance of Middle Pleistocene glacial deposits in the Kotzebue Sound region, northwest coastal Alaska  

SciTech Connect

During Middle Pleistocene time, glaciers extended from the western Brooks Range in NW Alaska to the coast at Kotzebue Sound, forming Baldwin Peninsula, a 120 km-long terminal moraine. Marine, glacigenic, and fluvial facies exposed along coastal bluffs surrounding Kotzebue Sound and Hotham Inlet indicate that at least the initial stages of the glacial advance occurred while sea level was high enough to cover the shallow Bering Shelf. Although it is presently uncertain if the ice actually reached tidewater before extensive middle-latitude ice-sheet formation, the marine and glacigenic facies clearly indicate that this advance must have occurred significantly out-of-phase with lower latitude glaciation. The authors believe an ice-free Bering Sea provided the moisture for glacier growth during the waning phases of a global interglacial climate. Although the magnitude of the Baldwin Peninsula advance was large compared to late Pleistocene advances, the timing with respect to sea level is consistent with observations by Miller and de Vernal that late Pleistocene polar glaciations also occurred near the end of interglacial periods, when global sea level was high, high-latitude oceans were relatively warm, and summer insolation was decreasing. An important implication of this out-of-phase glaciation hypothesis is that the critical transition point between climate states may be earlier in the interglacial-glacial cycle than previously thought. Because it appears that climate change is initiated in polar regions while the rest of Earth is experiencing an interglacial climate, many of their climate models must be revised. The glacial record at Baldwin Peninsula provides an opportunity to test, revise, and perhaps extend this out-of-phase glaciation hypothesis to the middle Pleistocene interval.

Roof, S.R.; Brigham-Grette, J. (Univ. of Massachusetts, Amherst, MA (United States))

1992-01-01

7

Glacially-influenced late Pleistocene stratigraphy of a passive margin: New Jersey's Record of the North American ice sheet  

USGS Publications Warehouse

Glacial isostasy and the sediment supply changes associated with the waxing and waning of ice sheets have dramatic effects on the stratigraphy of adjacent continental shelves. In ancient stratigraphic records, the glacial influences on such deposits could be difficult to recognize because of the removal of coeval terrestrial glacial deposits by erosion. This study illustrates the effects of the Laurentide Ice Sheet on a basin near its maximum limit, the New Jersey continental shelf. Analysis of 1600 km of Geopulse???, Uniboom???, Minisparker??? and airgun profiles reveals four depositional sequences that have a maximum thickness of ???75 m near the shelf edge. Sequences I and IV correspond to the major glacial-interglacial sea level changes at Marine Isotope Chron (MIC) 6/5e and 2/1, whereas sequences II and III reflect smaller-scale sea-level fluctuations during chrons 4/3c and 3b/3a, respectively. Sequences I and IV are characterized by relatively thick low stand to early transgressive deposits near the shelf edge formed during times of increased sediment supply, but are thin and discontinuous across much of the shelf. Reflection horizons in these units deepen northward in the northern half of the study area due to collapse of a peripheral bulge that formed at the margin of the Laurentide Ice Sheet. The Hudson River moved from a more southerly drainage pattern to the modern Hudson Shelf Valley position, possibly under the influence of the advancing peripheral bulge. Sequences II and III are largely preserved within a broad mid-shelf swale likely created by the migration of an ancestral Hudson River, and their thickness implies much higher sedimentation rates during chrons 4 and 3 than seen today. If the terrestrial glacial record was eroded, the increased rates of sedimentation during the Pleistocene, dominance of sediments derived from northern New England, and northward tilting of strata could be interpreted as a result of uplift of a northern source area. The unusually high frequency of the relative sea-level oscillations (20 kyr), the concentration of sediment supply during low stands and early transgressions, and the correspondence of sea-level change with climatic change could be used to infer their relationship to a nearby ice sheet. Geologists studying deposits formed during times of widespread continental glaciation should consider possible glacial influences on the stratigraphy of mid-latitude deposits, even in the absence of sediments directly deposited by ice. ?? 2005 Elsevier B.V. All rights reserved.

Carey, J.S.; Sheridan, R.E.; Ashley, G.M.; Uptegrove, J.

2005-01-01

8

Late-glacial pollen, macrofossils and fish remains in northeastern U.S.A. — The Younger Dryas oscillation. A contribution to the 'North Atlantic seaboard programme' of IGCP-253, 'Termination of the Pleistocene'  

NASA Astrophysics Data System (ADS)

The late-glacial environmental histories of Allamuchy Pond, New Jersey and Linsley Pond, Connecticut are reconstructed from pollen, macrofossil and fish scale remains. Accelerator mass spectrometry (AMS) 14C dating of seeds and needles indicates that the first organic deposition, evidenced by fossil Picea (spruce) needles, occurred approximately 12,400 BP. A major regional warming began in the northeastern United States at this time, correlative with the Bølling/Allerød warming of Europe and Greenland. The increase in Quercus (oak) pollen and presence of Pinus strobus (white pine) needles demonstrates the magnitude of warming reached at about 11,000 BP. The subsequent decline of thermophilous species and increase in boreal Picea, Abies (fir), Larix (larch), Betula papyrifera (paper birch) and Alnus (alder) from 10,800-10,000 BP was a regional vegetational reversal. Thus we find a North American expression of the Younger Dryas with a mean annual temperature depression of 3-4° C. The subsequent classical southern New England pine pollen zone 'B' and Pinus strobus macrofossils signalled a return to warmer conditions at approximately 10,000 BP, regionally, within approximately 50-100 years. A large increase in Quercus follows. This study is unique in documenting a continuous late-glacial record of fish remains from Allamuchy Pond, New Jersey sediments, indicating that members of the families Centrarchidae (sunfish), Salmonidae (trout), Percidae (perch) and Cyprinidae (minnow) were regionally present.

Peteet, D. M.; Daniels, R. A.; Heusser, L. E.; Vogel, J. S.; Southon, J. R.; Nelson, D. E.

9

Pleistocene-recent boundary and wisconsin glacial biostratigraphy in the northern Indian ocean.  

PubMed

Two faunal criteria define the Pleistocene-Recent boundary in the Andaman Sea and the Bay of Bengal: there is a marked decrease in the relative abundance of the Globigerina rubescens complex and a significant increase in the radiolarian number in sediments of the Recent epoch. The stratigraphic significance of the faunal criteria is supported by a carbon-14 date (8775 years before the present) obtained from foraminiferal tests in sediment at the faunal boundary, and previous publications on the stratigraphic significance of the radiolarian number in the eastern Pacific Ocean. The Globigerina rubescens complex, with greater relative abundances indicative of glacial substages, is an accurate indicator of cold and warm climatic intervals of the Wisconsin glacial stage. PMID:17773235

Frerichs, W E

1968-03-29

10

The glacial North Atlantic Oscillation Flavio Justino and W. Richard Peltier  

E-print Network

-called Atlantic Multidecadal Oscillation, AMO), this mode is predicted to be absent under LGM conditions. CitationThe glacial North Atlantic Oscillation Fla´vio Justino and W. Richard Peltier Department of Physics and glacial boundary conditions, we demonstrate that the glacial North Atlantic Oscillation was characterized

Peltier, W. Richard

11

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

SciTech Connect

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 {+-} 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.

Lewis, Claudia J [Los Alamos National Laboratory; Mcdonald, Eric [NON LANL; Sancho, Carlos [NON LANL; Pena, Jose- Luis [NON LANL

2008-01-01

12

Meltwater pathways and grain size transformation in a Pleistocene Mediterranean glacial-fluvial system  

NASA Astrophysics Data System (ADS)

The Pleistocene sedimentary records of Mount Orjen, western Montenegro, have been used to investigate changes in grain size characteristics of fine sediments transported from the glaciated mountains to the fluvial systems downstream. Understanding the particle size characteristics of the fine sediments transported by these cold stage river systems is important for several reasons. The braided rivers draining the glaciated mountains of the western Balkans may have been an important source of loess for example. It is also important to establish the grain size signature of suspended sediment delivered to the marine environment to aid land-marine correlations. The fine-grained component of the tills is dominated by glacially-comminuted limestone particles. Detailed particle size analysis of the fine sediment matrix component (<63 ?m) of glacial till and alluvial deposits has been undertaken using multiple samples at 12 sites surrounding the Orjen massif. This limestone karst terrain includes a range of meltwater pathways and depositional contexts, including: river valleys, alluvial fans, poljes, and ice marginal settings. 35 U-series ages and soil development indices have been used to develop a robust geochronology for the Pleistocene records Two dominant surface meltwater and sediment pathways have been identified around Mount Orjen. The particle size distributions reveal that these transportation routes can have distinctive sedimentological signatures. Type 1 pathways deliver meltwater and sediments downstream via bedrock gorges. In these settings, the fine grained alluvial matrix presents a largely bimodal particle size distribution (PSD). Type 2 pathways represent meltwater channels draining directly from the ice margin. Alluvial sediments within these environments more closely resemble the normally distributed PSD of the glacial tills. The transition to bimodal PSDs, downstream of Type 1 meltwater routes, suggests that the glacially-comminuted sediments are modified in the fluvial environment. Significantly, the carbonate component is preferentially depleted or removed from the fine silt size fraction. Non-carbonate sediments are instead concentrated into this particle size window. This is thought to be a product of physical and chemical weathering as well as the mechanical sorting of glacially-derived limestone sediments. This has important implications for our understanding of sediment transfer processes within glaciated catchments before these sediments are transported offshore.

Adamson, Kathryn; Woodward, Jamie; Hughes, Philip

2013-04-01

13

Cosmogenic nuclide depth profiles as a signal of Pleistocene glacial erosion  

NASA Astrophysics Data System (ADS)

Cosmogenic nuclide methods for measuring erosion rates of continuously exposed surfaces are well established, but cannot be applied to surfaces that were eroded while shielded by glacier ice. Instead, cosmogenic nuclide measurements on glaciated bedrock surfaces have been used to identify heavily eroded sites suitable for exposure dating, and to investigate the thermal regime of former glaciers and ice sheets. Because information from such surface samples is limited, we have developed an alternative method of measuring past glacial erosion using cosmogenic nuclide depth profiles. Owing to the penetration of cosmic ray muons, concentrations of cosmogenic nuclides produced deeper than 2-3 m below the rock surface during interglacial periods depend primarily on subsequent glacial erosion. Depth profiles thus accumulate information about the long-term erosion history, while near-surface nuclide concentrations contain information about erosion during the last few glaciations. Nuclide concentrations, concentration gradients and abundance ratios are all sensitive to the history of exposure to cosmic radiation and to erosion, and we can use inverse methods to recover long-term average erosion rates from these data. Exploratory calculations suggest that we will be able to estimate average erosion rates from near zero to greater than 100 m/Myr in favorable cases. The upper limit of measurable erosion is dependent on the fraction of time the surface was exposed. Timescales for erosion rate estimates are inversely related to erosion rate, but are typically on the order of 1 Myr. Published exposure age measurements from glaciated bedrock surfaces indicate that erosion rates within the measurable range are common, and that our method will be widely applicable to the study of mid- to late-Pleistocene erosion beneath glaciers and ice sheets. We demonstrate the use of this method to measure past erosion rates on glacially eroded surfaces in the northeastern United States using depth profiles of Be-10 and Al-26 in quartz collected from the walls of granite quarries in Maine.

Ploskey, Z. T.; Stone, J. O.

2012-12-01

14

Late Pleistocene and Holocene Glacial Evolution and Isotasy in the Antarctic Peninsula  

NASA Technical Reports Server (NTRS)

Employing a numerical model of Payne et al. that simulates the late-Pleistocene evolution of the former Antarctic Peninsula Ice Sheet (APIS) as a basis, we compute the present-day postglacial vertical isostasy of this region. The region may also experience significant mid-to late-Holocene glacial mass changes. Climate and oceanographic studies indicate that the ice mass imbalance of this region may be of larger magnitude that elsewhere in Antarctica. We compute the crustal response to these more recent ice mass changes and Holocene fluctuations with a simple gravitating Earth model consisting of an elastic lithosphere and a viscoelastic mantle (half-space). The calculations demonstrate that the present-day response could be significant, possibly at the level of about 4 - 11 mm/yr. Such significant crustal motion could be driven by glacial mass changes integrated over the last 1000 years if the regional mantle viscosity is below about 2 x 10(exp 20) Pa sec. In this lower viscosity range, present-day crustal motion has a significant phase-lagged character and the composite lithosphere/mantle viscoelastic response to late-Holocene events dominates over purely elastic (instantaneous) responses to present-day ice mass changes. For a higher mantle viscosity, greater than about 5 x 10(exp 20) Pa sec, the predicted present-day vertical isostasy is dominated by gravitational response to glacial unloading during the 18 - 6 kyr BP collapse of the APIS, and is analogous to that known to be occurring in the Gulf of Bothnia and Hudson Bay.

Ivins, E. R.; Raymond, Carol A.; Heflin, M. B.; James, T. S.

1989-01-01

15

Oscillators and relaxation phenomena in Pleistocene climate theory  

PubMed Central

Ice sheets appeared in the northern hemisphere around 3?Ma (million years) ago and glacial–interglacial cycles have paced Earth's climate since then. Superimposed on these long glacial cycles comes an intricate pattern of millennial and sub-millennial variability, including Dansgaard–Oeschger and Heinrich events. There are numerous theories about these oscillations. Here, we review a number of them in order to draw a parallel between climatic concepts and dynamical system concepts, including, in particular, the relaxation oscillator, excitability, slow–fast dynamics and homoclinic orbits. Namely, almost all theories of ice ages reviewed here feature a phenomenon of synchronization between internal climate dynamics and astronomical forcing. However, these theories differ in their bifurcation structure and this has an effect on the way the ice age phenomenon could grow 3 Ma ago. All theories on rapid events reviewed here rely on the concept of a limit cycle excited by changes in the surface freshwater balance of the ocean. The article also reviews basic effects of stochastic fluctuations on these models, including the phenomenon of phase dispersion, shortening of the limit cycle and stochastic resonance. It concludes with a more personal statement about the potential for inference with simple stochastic dynamical systems in palaeoclimate science. PMID:22291227

Crucifix, Michel

2012-01-01

16

Pleistocene coquinas of the glaciomarine Yakataga Formation, Alaska: implications for mixed glacial/carbonate sequences  

SciTech Connect

Of the several models available to students of mixed ancient glacial/carbonate rocks, most accommodate extreme climatic changes by fluctuations in either the Earth's orbital parameters, continental drift rates or the chemistry of early atmospheres and oceans. The Yakataga Formation, where it is exposed on Middleton Island, Alaska is dominated by thick sequences of massive muddy diamicts in which marine micro- and macrofaunas occur. The sequence records the influx onto the Gulf of Alaska continental shelf of large volumes of pelagic and ice-rafted debris from expanded temperate glaciers and ice shelves during the Early Pleistocene with deposition rates of 1m/1000 years. Diamicts contain multiple coquina bands up to 1m thick composed predominantly of cemented molluscan debris and traceable over several kilometers along strike. Analysis of foraminifera indicates that coquinas record episodic changes in relative sea level and non-deposition of mud when extensive communities of bottom dwelling molluscan faunas became established; ice-rafting continued during the formation and development of coquinas. Recent work stresses the accumulation of carbonates in clastic-starved polar glaciomarine environments; the Alaskan coquinas show that significant bioclastic carbonate accumulations also occur under more temperate glaciomarine conditions with higher sedimentation rates.

Kaye, B.G.; Eyles, N.; Lagoe, M.B.

1985-01-01

17

Polyploid evolution and Pleistocene glacial cycles: A case study from the alpine primrose Primula marginata (Primulaceae)  

PubMed Central

Background Recent studies highlighted the role of Pleistocene climatic cycles in polyploid speciation and of southern Alpine refugia as reservoirs of diversity during glacial maxima. The polyploid Primula marginata, endemic to the southwestern Alps, includes both hexaploid and dodecaploid cytotypes that show no ecological or morphological differences. We used flow cytometry to determine variation and geographic distribution of cytotypes within and between populations and analyses of chloroplast (cp) and nuclear ribosomal (nr) DNA sequences from the Internal Transcribed Spacer (ITS) region to infer the evolutionary history of the two cytotypes and the auto- vs. allopolyploid origin of dodecaploid populations. Results We did not detect any intermediate cytotypes or variation of ploidy levels within populations. Hexaploids occur in the western and dodecaploids in the eastern part of the distributional range, respectively. The cpDNA and nrDNA topologies are in conflict, for the former supports shared ancestry between P. marginata and P. latifolia, while the latter implies common origins between at least some ITS clones of P. marginata and P. allionii. Conclusions Our results suggest an initial episode of chloroplast capture involving ancestral lineages of P. latifolia and P. marginata, followed by polyploidization between P. marginata-like and P. allionii-like lineages in a southern refugium of the Maritime Alps. The higher proportion of ITS polymorphisms in dodecaploid than in hexaploid accessions of P. marginata and higher total nucleotide diversity of ITS clones in dodecaploid vs. hexaploid individuals sequences are congruent with the allopolyploid hypothesis of dodecaploid origin. PMID:22530870

2012-01-01

18

Interglacial and glacial climate oscillations in a marine shelf sequence from northern denmark — a multidisciplinary study  

Microsoft Academic Search

A 22.5m long marine shelf sequence in northern Denmark covers the climatic shifts from glacial environments, through interglacial and into early glacial conditions. The interglacial was interrupted by two cool intervals. Also the early glacial succession experienced oscillations of the climate, and a period with ameliorated temperature conditions has been separated as an interstadial. These results are based on a

P. Kristensen; K. L Knudsen; H. Lykkeandersen; E. Normark; J. D Peacock; A. Sinnott

1998-01-01

19

Late Pleistocene sedimentary history of multiple glacially dammed lake episodes along the Yarlung-Tsangpo river, southeast Tibet  

NASA Astrophysics Data System (ADS)

We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950-3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2.

Huang, Shao-Yi; Chen, Yue-Gau; Burr, George S.; Jaiswal, Manoj K.; Lin, Yunung Nina; Yin, Gongming; Liu, Jingwei; Zhao, Shujun; Cao, Zhongquan

2014-09-01

20

Quaternary Science Reviews 20 (2001) 405}417 Geomorphological correlation of Late Pleistocene glacial complexes  

E-print Network

glacial complexes of Western and Eastern Beringia O.Yu. Glushkova North-East Interdisciplinary Scientixc Beringia. However, geomorphological analysis, complemented by palynological studies and radiocarbon age

Ingólfsson, �lafur

21

On the Physical Significance of Statistically Significant Millennial Peaks in Late Pleistocene Glacial Intervals of Marine Sediment Cores.  

NASA Astrophysics Data System (ADS)

Multitaper and maximum entropy methods were used to determine the statistical significance and frequency, respectively, of millennial-band peaks in late Pleistocene glacial intervals of geochemical, petrological, and physical property time series generated from marine sediment cores, including ODP Site 980 and IODP Site U1308 (Reoccupied DSDP Site 609). A preliminary age model for Site U1308 was created by correlating the sediment lightness (L*) record to the Site 980 ?18O record. Marine Isotope Stages (MIS) 2-3 (Wisconsin glaciation), 6 (Penultimate glaciation), 8, 10, and 12 were analyzed as individual time series and interpolated to the average sampling resolution of each respective glacial interval. Results indicate the existence of many peaks statistically significant at a 95% or greater confidence interval within each individual glacial-interval time series. One may be tempted to accept each of these peaks as physically significant; however, the probability that a particular peak is significant by chance alone (i.e., 5% chance given a 95% confidence interval), must be considered. For example, Hyde and Crowley (2002) generated millennial-scale peaks significant at a 95% confidence interval in a 120 k.y. model run forced by white noise at a 100-year time step. Given these model results, we exercise caution in the interpretation of physical significance of peaks in the sediment core time series, placing physical significance only on peaks that consistently appear in most of the series.

Obrochta, S. P.; Crowley, T. J.

2005-12-01

22

Glacial geomorphology of the Pleistocene Lake Fagnano ice lobe, Tierra del Fuego, southern South America  

NASA Astrophysics Data System (ADS)

A regional geomorphological study is presented of the southern and eastern coast of Lake Fagnano, one of the most extensive glacial areas of Tierra del Fuego Island, at the southernmost tip of South America. A palaeoglacial reconstruction is made, based on the location of erosional and depositional glacial landforms. The outlet glacier flowing eastwards from the Darwin Cordillera (Fuegian Andes, Chile) had more than 50 tributary glaciers. An alpine-type landscape, including arêtes, cirques, truncated spurs and hanging valleys developed in the western region of the present lake, whereas a piedmont-type landscape including lateral moraines, glaciofluvial and glaciolacustrine terraces and an ice-disintegration landscape developed in the eastern region. The glacier spread over the low ranges and lowlands through three different lobes, and was drained by four main outwash basins, directly into the Atlantic Ocean. The ice-covered area is estimated at 4000 km 2; the maximum length of the main lobe at 132 km, and the general slope at 8°. Four terminal positions of the glacier were recognized and related to the Inútil Bay and Beagle Channel glacial areas, located to the north and south, respectively. 14C dates from basal peats show that most of the area, especially the easternmost part and the southern coast, were free of ice by 12,300 years B.P. Fossil peat contained in the lower basal till deposits yield 14C dates of 31,000-48,200 years B.P., indicating that a glacial advance occurred in the area prior to the Last Glacial Maximum (ca. 25,000-23,000 cal. years B.P.).

Coronato, A.; Seppälä, M.; Ponce, J. F.; Rabassa, J.

2009-11-01

23

Physiological and growth responses of C3 and C4 plants at the Pleistocene glacial maximum  

SciTech Connect

A C3 plant (Abutilon theophrasti) and a C4 plant (Amaranthus retroflexus) were grown from seed in the Duke University Phytotron under four CO2 concentrations (15 Pa, below the Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current), and 70 Pa (future) to examine photosynthetic, growth and reproduction responses of annual plants to historic and future levels of CO2. Net photosynthesis and growth were greatly inhibited at 15 Pa and greatly stimulated at 70 Pa. in the C3 Abutilon but only slightly affected in the C4 Amaranthus. Flower bud initiation was not affected by CO2 treatment in either species but all flower buds in 15 Pa CO2 aborted in the C3 within two days of appearance while no inhibition of reproduction was observed at low CO2 in the C4. Differences in physiology, growth and reproduction to the low levels of atmospheric CO2 of the Pleistocene suggest that competitive interactions of C3 and C4 annuals have changed through geologic time. A major question concerning the survival and evolution of obligate C3 annuals during the CO2 minima of the Pleistocene is raised by the results of this study.

Strain, B.R. [Duke Univ., Durham, NC (United States)

1995-06-01

24

The sequence and timing of large late Pleistocene floods from glacial Lake Missoula  

NASA Astrophysics Data System (ADS)

Glacial Lake Missoula formed when the Purcell Trench lobe of the Cordilleran ice sheet dammed Clark Fork River in Montana during the Fraser Glaciation (marine oxygen isotope stage 2). Over a period of several thousand years, the lake repeatedly filled and drained through its ice dam, and floodwaters coursed across the landscape in eastern Washington. In this paper, we describe the stratigraphy and sedimentology of a significant new section of fine-grained glacial Lake Missoula sediment and compare this section to a similar, previously described sequence of sediments at Ninemile Creek, 26 km to the northwest. The new exposure, which we informally term the rail line section, is located near Missoula, Montana, and exposes 29 units, each of which consists of many silt and clay couplets that we interpret to be varves. The deposits are similar to other fine-grained sediments attributed to glacial Lake Missoula. Similar varved sediments overlie gravelly flood deposits elsewhere in the glacial Lake Missoula basin. Each of the 29 units represents a period when the lake was deepening, and all units show evidence for substantial draining of glacial Lake Missoula that repeatedly exposed the lake floor. The evidence includes erosion and deformation of glaciolacustrine sediment that we interpret happened during draining of the lake, desiccation cracks that formed during exposure of the lake bottom, and fluvial sand deposited as the lake began to refill. The floods date to between approximately 21.4 and 13.4 cal ka ago based on regional chronological data. The total number of varves at the rail line and Ninemile sites are, respectively, 732 and 583. Depending on lake refilling times, each exposure probably records 1350-1500 years of time. We present three new optical ages from the rail line and Ninemile sites that further limit the age of the floods. These ages, in calendar years, are 15.1 ± 0.6 ka at the base of the Ninemile exposure, and 14.8 ± 0.7 and 12.6 ± 0.6 ka midway through the rail line exposure. The sediment at the two sections was deposited during later stages of glacial Lake Missoula, after the largest outburst events.

Hanson, Michelle A.; Lian, Olav B.; Clague, John J.

2012-01-01

25

Late Pleistocene debris-flow deposits in large glacial lakes in British Columbia and Alaska  

NASA Astrophysics Data System (ADS)

The movement of Late Wisconsin (<30,000 B.P.) ice-sheet lobes counter to the direction of regional drainage ponded large lakes (up to 5000 km 2) in both the Upper Fraser River Valley in British Columbia and the Cooper River Valley in Alaska. Along the Fraser River, near Quesnel, glaciolacustrine sediment gravity-flow complexes contain thick (up to 10 m) and laterally extensive (up to 3 km) diamict units containing large rafts of poorly lithified Tertiary rocks. Diamicts offlap and thin away from Tertiary bedrock highs and were emplaced by subaqueous debris flows. These flows probably evolved from slumps and slides associated with the downslope failure of unstable Tertiary bedrock slopes triggered by rising lake levels, a process akin to "first-filling" slope failures around the margins of man-made lakes. In Alaska, along the Copper River Valley, massive and stratified diamicts were also deposited by debris flows and are interbedded with thin-bedded turbidites, poorly sorted gravels and normally graded diamicts. Debris flow deposits show basal grooves, internal compressional structures and rafted clasts that protrude from bed tops. Flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins; an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock. Observations in both British Columbia and Alaska stress the significance of sediment gravity-flow processes acting to deposit "glacial" sedimentary successions in large ice-contact lake basins.

Eyles, Nicholas

1987-06-01

26

Climate oscillations and tephrochronology in eastern middle Sweden during the last glacial-interglacial transition  

Microsoft Academic Search

Two sequences spanning the last glacial-interglacial transition in southern Östergötland, eastern middle Sweden have been investigated for high-resolution vegetation change and tephrochronology. Organic carbon and pollen analysis indicates that the Younger Dryas-Preboreal climatic transition was characterised by at least one well-defined oscillation or possibly two shorter climatic oscillations. The Vedde Ash (ca. 12000 GRIP yr BP or ca. 10300 14C

Jonas Björck; Stefan Wastegård

1999-01-01

27

Size and shape stasis in late Pleistocene mammals and birds from Rancho La Brea during the Last Glacial-Interglacial cycle  

NASA Astrophysics Data System (ADS)

Conventional neo-Darwinian theory views organisms as infinitely sensitive and responsive to their environments, and considers them able to readily change size or shape when they adapt to selective pressures. Yet since 1863 it has been well known that Pleistocene animals and plants do not show much morphological change or speciation in response to the glacial-interglacial climate cycles. We tested this hypothesis with all of the common birds (condors, golden and bald eagles, turkeys, caracaras) and mammals (dire wolves, saber-toothed cats, giant lions, horses, camels, bison, and ground sloths) from Rancho La Brea tar pits in Los Angeles, California, which preserves large samples of many bones from many well-dated pits spanning the 35,000 years of the Last Glacial-Interglacial cycle. Pollen evidence showed the climate changed from chaparral/oaks 35,000 years ago to snowy piñon-juniper forests at the peak glacial 20,000 years ago, then back to the modern chaparral since the glacial-interglacial transition. Based on Bergmann's rule, we would expect peak glacial specimens to have larger body sizes, and based on Allen's rule, peak glacial samples should have shorter and more robust limbs. Yet statistical analysis (ANOVA for parametric samples; Kruskal-Wallis test for non-parametric samples) showed that none of the Pleistocene pit samples is statistically distinct from the rest, indicating complete stasis from 35 ka to 9 ka. The sole exception was the Pit 13 sample of dire wolves (16 ka), which was significantly smaller than the rest, but this did not occur in response to climate change. We also performed a time series analysis of the pit samples. None showed directional change; all were either static or showed a random walk. Thus, the data show that birds and mammals at Rancho La Brea show complete stasis and were unresponsive to the major climate change that occurred at 20 ka, consistent with other studies of Pleistocene animals and plants. Most explanations for such stasis (stabilizing selection, canalization) fail in this setting where climate is changing. One possible explanation is that most large birds and mammals are very broadly adapted and relatively insensitive to changes in their environments, although even the small mammals of the Pleistocene show stasis during climate change, too.

Prothero, Donald R.; Syverson, Valerie J.; Raymond, Kristina R.; Madan, Meena; Molina, Sarah; Fragomeni, Ashley; DeSantis, Sylvana; Sutyagina, Anastasiya; Gage, Gina L.

2012-11-01

28

Middle Pleistocene (?) buried glacial ice on Bylot Island, Canadian Arctic Archipleago  

NASA Astrophysics Data System (ADS)

Bylot Island is located north of Baffin Island (73°N, 80°W). More than the half of the island is covered by an ice cap and its outlet glaciers flowing towards the arctic lowland of the Lancaster formation. The study site comprises four main stratigraphic units. Overlying the shales (Tertiary) of the Lancaster Formation (500 m a.s.l.), a diamicton (unit 1) is covered by a “fossil forest-tundra” sequence (unit 2) containing abundant remains of trees and plants (Allard et al., submitted). Paleontological correlation of extinct species and reverse to normal palomagnetism polarities suggest a Late Pliocene to Early Pleistocene age for this unit. A sequence (unit 3) of ice-contact proximal to distal glacio-fluvial sediments overlies the organic beds. Paleomagnetic analysis showed that the upper glacio-fluvial sediments were likely deposited during the Brunhes polarity chron (younger than 0.73 Ma). The uppermost unit (unit 4) consists in a lodgement till containing clasts of Paleozoic limestone erratics. Based on amino acid ratios of shells fragments in the drift, Klassen (1993) suggested that this “foreign drift” was probably deposited during an "old" Quaternary glaciation named “Baffin glaciation” During July 2009 several active-layer detachment slides at the head of large gullies exposed large massive ice bodies located at the junction between units 3 and 4. A preliminary analysis of the ice facies and ice crystals revealed the presence of two distinct types of massive ice: 1) clear-ice bodies with very few sediments and no organic inclusions. The ice crystals were large (cm) and air bubbles were observed at the junction of crystals. These characteristics could potentially indicate an englacial origin for these clear ice bodies. In some places, the ice was stratified with undulating layers of sands and gravels. These micro-structures are very similar to basal ice facies we observed at the Matanuska Glacier in Alaska. The exposed massive ice sections were a few tens of meter wide and about 2 to 4 m deep but the real width and thickness of these ice masses are unknown. The upper part of the clear ice and stratified massive ice bodies were always in contact with various types of glacio-fluvial sediments which suggest that their preservation were likely related to rapid burial of the ice and refreezing of the overlying sediments following permafrost aggradation. 2) large, white to milky, epigenetic ice wedges with a typical sub-vertical foliated structure. The ice wedges were formed in unit 4 and, in some places, penetrated into the clear massive ice bodies described above which created a sharp visual contrast between the two types of ice. This also indicates that ice wedge development post-date the massive ice burial. Based on the chrono-stratigraphic context and on the similarities between 1) the clear ice masses and the contemporary englacial ice facies (e.g. on Bylot Island); and 2) the cryostructures of the stratified massive ice at the study site and the contemporary basal ice cryostructures observed at the Matanuska glaciers, we propose that the massive ice bodies exposed on Bylot Island are related to a Middle Pleistocene glaciation.

Fortier, D.; Godin, E.; Kanevskiy, M. Z.; Allard, M.

2009-12-01

29

Dansgaard-Oeschger oscillations predicted in a comprehensive model of glacial climate: A "kicked" salt oscillator in the Atlantic  

NASA Astrophysics Data System (ADS)

the period from 60,000 to 35,000 years ago, Summit-Greenland ice core records of the oxygen isotopic ratio 18O/16O exhibit intense millennium time scale oscillations. These Dansgaard-Oeschger oscillations have been interpreted to represent the variations in North Atlantic air temperature caused by correlative changes in the strength of North Atlantic Deep Water production. We apply a comprehensive model of glacial climate to unambiguously identify the mechanism responsible for this phenomenon. This is shown to involve a salt oscillation of relaxation oscillator form. This nonlinear oscillation does not require the existence of feedback due to freshwater release from grounded ice on the continents during the warm phase of the cycle.

Peltier, W. Richard; Vettoretti, Guido

2014-10-01

30

Climatic impact of glacial cycle polar motion: Coupled oscillations of ice sheet mass and rotation pole position  

USGS Publications Warehouse

Precessional motion of Earth's rotation axis relative to its orbit is a well-known source of long-period climatic variation. It is less well appreciated that growth and decay of polar ice sheets perturb the symmetry of the global mass distribution enough that the geographic location of the rotation axis will change by at least 15 km and possibly as much as 100 km during a single glacial cycle. This motion of the pole will change the seasonal and latitudinal pattern of temperatures. We present calculations, based on a diurnal average energy balance, which compare the summer and winter temperature anomalies due to a 1° decrease in obliquity with those due to a 1° motion of the rotation pole toward Hudson Bay. Both effects result in peak temperature perturbations of about 1° Celsius. The obliquity change primarily influences the amplitude of the seasonal cycle, while the polar motion primarily changes the annual mean temperatures. The polar motion induced temperature anomaly is such that it will act as a powerful negative feedback on ice sheet growth. We also explore the evolution of the coupled system composed of ice sheet mass and pole position. Oscillatory solutions result from the conflicting constraints of rotational and thermal stability. A positive mass anomaly on an otherwise featureless Earth is in rotational equilibrium only at the poles or the equator. The two polar equilibria are rotationally unstable, and the equatorial equilibrium, though rotationally stable, is thermally unstable. We find that with a plausible choice for the strength of coupling between the thermal and rotational systems, relatively modest external forcing can produce significant response at periods of 104–106 years, but it strongly attenuates polar motion at longer periods. We suggest that these coupled oscillations may contribute to the observed dominance of 100 kyr glacial cycles since the mid-Pleistocene and will tend to stabilize geographic patterns that are suitable to glaciations.

Bills, Bruce G.; James, Thomas S.; Mengel, John G.

1999-01-01

31

Glacially-influenced late Pleistocene stratigraphy of a passive margin: New Jersey's Record of the North American ice sheet  

Microsoft Academic Search

Glacial isostasy and the sediment supply changes associated with the waxing and waning of ice sheets have dramatic effects on the stratigraphy of adjacent continental shelves. In ancient stratigraphic records, the glacial influences on such deposits could be difficult to recognize because of the removal of coeval terrestrial glacial deposits by erosion. This study illustrates the effects of the Laurentide

John S. Carey; Robert E. Sheridan; Gail M. Ashley; Jane Uptegrove

2005-01-01

32

Late Pleistocene climate change and Paleolithic cultural evolution in northern China: Implications from the Last Glacial Maximum  

Microsoft Academic Search

Temporal and spatial patterns in archeological data from Pleistocene north China suggest strong correlations between climate change and culture change, but only in extreme cases. In these cases, climate has an immediate impact on human mobility, which is severely constrained during the pronounced cold\\/dry intervals of the Pleistocene. As high mobility becomes incompatible with the environmental limitations of extreme intervals,

Loukas Barton; P. Jeffrey Brantingham; Duxue Ji

2007-01-01

33

Effect of Pleistocene Climatic Oscillations on the Phylogeography and Demography of Red Knobby Newt (Tylototriton shanjing) from Southwestern China  

PubMed Central

Factors that determine the genetic structure of species in southwestern China remain largely unknown. In this study, phylogeography and demography of Tylototriton shanjing was investigated from a mitochondrial perspective to address the role of the Quaternary ice ages in shaping phylogeographic history and genetic diversity of Yunnan. A total of 146 individuals from 19 populations across the entire range of the species were collected. We detected four maternal phylogenetic lineages corresponding to four population groups, and found that major glaciation events during the Pleistocene have triggered the intra-specific divergence. Coalescent simulations indicated that the populations retreated to different refugia located in southern Yunnan, northwestern Yunnan, the border region of western Yunnan with Myanmar, and middle-western Yunnan, respectively, during previous glacial periods in the Pleistocene, and these four refugia were not retained during the Last Glacial Maximum. Population expansions occurred during the last inter-glaciation, during which ice core and pollen data indicated that the temperature and precipitation gradually increased, and declines of population sizes started after the beginning of the Last Glacial Maximum when the climate became cooler and dryer. The paleo-drainage system had no contribution to the current genetic structure and the rivers were not dispersal barriers for this salamander. PMID:23424644

Rao, Dingqi; Yang, Junxing

2013-01-01

34

Late-glacial environmental oscillations as recorded in the soil archives of Gasserplatz (Vorarlberg, Austria).  

NASA Astrophysics Data System (ADS)

Gasserplatz is a shallow basin in the rather flat, glacially eroded confluence area of the former Rhine glacier and the Ill glacier. It became ice-free during the Feldkirch stadium ( ? 15.500 calBP) and transferred in a tiny lake. During the Late-glacial lacustrine carbonate (calcareous gyttja) was deposited, in the Holocene peat accumulated. Gasserplatz deposits are valuable soil archives for palaeo-environmental research. The Late-glacial environmental fluctuations have been recorded in the gyttja deposits. The combined results of pollen, macro-remains and stable isotope analyses that have been put into an independent time frame demonstrate that these fluctuations are associated with large scale temperature oscillations as registered in Greenland ice cores. The results show also a slight delay in environmental response on temperature change. The isotope stratigraphy points to higher temperatures during the whole Bølling while Betula trees arrived in Gasserplatz area later. During the Allerød there are frequent short-lived oscillations in temperature, but the palynological expression of these changes resulted in not more than three Betula peaks. Comparison with the research results of similar Alpine lake deposits makes clear that the fluctuations in the Betula curve are not a local but a regional phenomenon.

van Mourik, Jan; Slotboom, Ruud; van der Plicht, Hans; Streurman, Harm Jan; Kuijper, Wim; Hoek, Wim; de Graaff, Leo

2013-04-01

35

The hierarchical structure of glacial climatic oscillations: Interactions between ice-sheet dynamics and climate  

SciTech Connect

Abrupt climatic oscillations around the North Atlantic have been identified recently in Greenland ice cores as well as in North Atlantic marine sediment cores. The good correlation between the {open_quote}Dansgaard Oeschger events{close_quote} in the ice and the {open_quote}Heinrich events{close_quote} in the ocean suggests climate, in the North Atlantic region, underwent several massive reorganizations in the last glacial period. A characteristic feature seems to be their hierarchical structure. Every 7 to 10-thousand years, when the temperature is close to its minimum, the ice-sheet undergoes a massive iceberg discharge. This Heinrich event is followed by an abrupt warming. then by other oscillations, each lasting between one and two thousand years. These secondary oscillations do not have a clear signature in marine sediments but constitute most of the{open_quote} Dansgaard-Oeschger events{close_quote} found in the ice. A simplified model coupling an ice-sheet and an ocean basin, to illustrate how the interactions between these two components can lead to such a hierarchical structure. The ice-sheet model exhibits internal oscillations composed of growing phases and basal ice melting phases that induce massive iceberg discharges. These fresh water inputs in the ocean stop for a moment the thermohaline circulation, enhancing the temperature contrast between low- and high-latitudes. Just after this event, the thermohaline circulation restarts and an abrupt warming of high-latitude regions is observed. For some parameter values, these warmer temperatures have some influence on the ice-sheet, inducing secondary oscillations similar to those found in paleoclimatic records. Although the mechanism presented here may be too grossly simplified. it nevertheless underlines the potential importance of the coupling between ice-sheet dynamics and oceanic thermohaline circulation on the structure of the climatic records during the last glacial period. 33 refs., 14 figs., 1 tab.

Paillard, D. [Centre d`Etudes de Saclay, Gif sur Yvette (France)] [Centre d`Etudes de Saclay, Gif sur Yvette (France)

1995-04-01

36

A salt oscillator in the glacial northern Atlantic? part II: A 'scale analysis' model  

NASA Astrophysics Data System (ADS)

A proposal has been made by Broecker et al. (1990) that rapid changes on a time scale of a thousand years or so, seen over much of the last major glacial in the Greenland ice core record, represent significant climate changes and are caused by a salt oscillator in the glacial Atlantic. This proposal is examined in terms of a rudimentary quantitative model. Scale analysis asserts that heat transported to the high-latitude atmosphere when the thermohaline circulation is turned on, is large enough to produce the melting rates found by Fairbanks (1989) for the time interval around that of the Younger Dryas event and that these melting rates are of the same order of magnitude as the mass flux associated with water vapor flux to the Pacific Ocean estimated by Broecker (1989). Scale analysis also suggests that the salinity fluxes associated with 1) the water vapor flux mechanism, 2) the rapid melting episodes of Fairbanks, 3) possibly ice sheet growth events, 4) net transport by the thermohaline circulation and 5) net transport by turbulent eddy mixing are roughly of the same order of magnitude and therefore may be important mechanisms for producing salinity oscillations on a time scale of a few thousands of years, (see Broecker, 1990). By integration of simple salt conservation equations, it is found that model oscillations with a period of a few thousand years occur over a significant range of salinity fluxes; estimated fluxes fall well within the range for which oscillations exist. The model also suggests that there may exist close coupling between the European-Scandinavian ice sheets and the bimodal response of the oscillator; that is, significant increases or decreases in continental ice volume may accompany each complete cycle of the oscillator. In addition, it appears that continental ice may be required for the salt oscillator to function. A crucial element, which cannot adequately be investigated with the present model, concerns the local effect of salinity source/sinks associated with melt water production. The proximity of these source regions on the neighboring ice sheets to the local regions where production of deep water occurs may play a critical role in the functioning of the proposed salt oscillator. In addition, further treatment of thermodynamics is needed to investigate the feasibility of a salinity driven oscillator.

Birchfield, G. Edward; Broecker, Wallace S.

1990-12-01

37

Phylogeographic analysis of the red seaweed Palmaria palmata reveals a Pleistocene marine glacial refugium in the English Channel  

Microsoft Academic Search

Phylogeography has provided a new approach to the analysis of the postglacial history of a wide range of taxa but, to date, little is known about the effect of glacial periods on the marine biota of Europe. We have utilized a combination of nuclear, plastid and mitochondrial genetic markers to study the biogeographic history of the red seaweed Palmaria palmata

JIM PROVAN; REMI A. W ATTIER; CHRISTINE A. M AGGS

38

Low but structured chloroplast diversity in Atherosperma moschatum (Atherospermataceae) suggests bottlenecks in response to the Pleistocene glacials  

PubMed Central

Background and Aims The cool temperate rainforests of Australia were much reduced in range during the cold and dry glacial periods, although genetic evidence indicates that two key rainforest species, Nothofagus cunninghamii and Tasmannia lanceolata, survived within multiple locations and underwent only local range expansions at the end of the Last Glacial. To better understand the glacial response of a co-occurring but wind-dispersed and less cold-tolerant rainforest tree species, Atherosperma moschatum, a chloroplast phylogeographic study was undertaken. Methods A total of 3294 bp of chloroplast DNA sequence was obtained for 155 samples collected from across the species' range. Key Results The distribution of six haplotypes observed in A. moschatum was geographically structured with an inferred ancestral haplotype restricted to Tasmania, while three non-overlapping and endemic haplotypes were found on the mainland of south-eastern Australia. Last glacial refugia for A. moschatum are likely to have occurred in at least one location in western Tasmania and in Victoria and within at least two locations in the Great Dividing Range of New South Wales. Nucleotide diversity of A. moschatum was lower (? = 0·00021) than either N. cunninghamii (0·00101) or T. lanceolata (0·00073), and was amongst the lowest recorded for any tree species. Conclusions This study provides evidence for past bottlenecks having impacted the chloroplast diversity of A. moschatum as a result of the species narrower climatic niche during glacials. This hypothesis is supported by the star-like haplotype network and similar estimated rates of chloroplast DNA substitution for A. moschatum and the two more cold tolerant and co-occurring species that have higher chloroplast diversity, N. cunninghamii and T. lanceolata. PMID:21856633

Worth, James R. P.; Marthick, James R.; Jordan, Gregory J.; Vaillancourt, René E.

2011-01-01

39

Reduced El Niño-Southern Oscillation during the Last Glacial Maximum.  

PubMed

El Niño-Southern Oscillation (ENSO) is a major source of global interannual variability, but its response to climate change is uncertain. Paleoclimate records from the Last Glacial Maximum (LGM) provide insight into ENSO behavior when global boundary conditions (ice sheet extent, atmospheric partial pressure of CO2) were different from those today. In this work, we reconstruct LGM temperature variability at equatorial Pacific sites using measurements of individual planktonic foraminifera shells. A deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue, resulting in reduced ENSO variability during the LGM compared to the Late Holocene. These results suggest that ENSO was not tied directly to the east-west temperature gradient, as previously suggested. Rather, the thermocline of the eastern equatorial Pacific played a decisive role in the ENSO response to LGM climate. PMID:25593181

Ford, Heather L; Ravelo, A Christina; Polissar, Pratigya J

2015-01-16

40

Influence of Pleistocene Glacial/Interglacial Cycles on the Genetic Structure of the Mistletoe Cactus Rhipsalis baccifera (Cactaceae) in Mesoamerica.  

PubMed

Phylogeographical work on cloud forest-adapted species provides inconsistent evidence on cloud forest dynamics during glacial cycles. A study of Rhipsalis baccifera (Cactaceae), a bird-dispersed epiphytic mistletoe cactus, was conducted to investigate genetic variation at sequence data from nuclear [internal transcribed spacer (ITS), 677 bp] and chloroplast (rpl32-trnL, 1092bp) DNA for 154 individuals across the species range in Mesoamerica to determine if such patterns are consistent with the expansion/contraction model of cloud forest during glacial cycles. We conducted population and spatial genetic analyses as well as gene flow and divergence time estimates between 24 populations comprising the distribution of R. baccifera in Mexico and Guatemala to gain insight of the evolutionary history of these populations, and a complementary species distribution modeling approach to frame information derived from the genetic analyses into an explicit paleoecological context. The results revealed a phylogeographical break at the Isthmus of Tehuantepec, and high levels of genetic diversity among populations and cloud forest areas. Despite the genetic differentiation of some R. baccifera populations, the widespread ITS ribotypes suggest effective nuclear gene flow via pollen and population differentiation shown by the rpl32-trnL suggests more restricted seed flow. Predictions of species distribution models under past last glacial maximum (LGM) climatic conditions and a significant signal of demographic expansion suggest that R. baccifera populations experienced a range expansion tracking the conditions of the cloud forest distribution and shifted to the lowlands with population connectivity during the LGM. PMID:25649131

Ornelas, Juan Francisco; Rodríguez-Gómez, Flor

2015-01-01

41

Lineage-specific late pleistocene expansion of an endemic subtropical gossamer-wing damselfly, Euphaea formosa , in Taiwan  

Microsoft Academic Search

Background  Pleistocene glacial oscillations have significantly affected the historical population dynamics of temperate taxa. However,\\u000a the general effects of recent climatic changes on the evolutionary history and genetic structure of extant subtropical species\\u000a remain poorly understood. In the present study, phylogeographic and historical demographic analyses based on mitochondrial\\u000a and nuclear DNA sequences were used. The aim was to investigate whether Pleistocene

Jen-Pan Huang; Chung-Ping Lin

2011-01-01

42

New data on the Late Pleistocene and Holocene glacial, climate and relative sea-level changes at Fildes Peninsula, King George Island (South Shetlands Islands, West Antarctica)  

NASA Astrophysics Data System (ADS)

New data on the Late Pleistocene and Holocene glacial, climate and relative sea-level changes at Fildes Peninsula, King George Island (South Shetlands Islands, West Antarctica) Verkulich S. R. (Arctic and Antarctic Research Institute, St. Petersburg, Russia) Pushina Z.V. (Arctic and Antarctic Research Institute, St. Petersburg, Russia) Tatur A. (Department of Antarctic Biology, Polish Academy of Sciences, Warsaw, Poland) During the 2008-2009 austral summer, co-operative Russian - Polish paleogeographical investigations allowed to refine the understanding of the past environmental events at Fildes Peninsula, King George Island. Old marine deposits (ca. 30000 yrs BP) with shells, whale bones and marine algae in situ were found in the western coastal and northern inland territories at the altitudes of 20-40 m a.s.l. that evidences the covering of considerable part of the peninsula by relatively warm sea waters before the Last Glacial Maximum. Quite good preservation of these deposits supposes relatively small thickness and weak erosional potential of ice masses overlying the area during the LGM. The early Holocene phase of the peninsula deglaciation was caused by both climate warming and marine transgression, which left the deposits with fossil flora and fauna at heights up to 15 m a.s.l. (maximum rise of the relative sea-level 7000-8000 yrs BP). During the middle Holocene, glacier contraction in the area continued (on the whole) due to mainly favorable climatic conditions. The presence of marine and terrestrial deposit blocks (with shells, algae, mosses) in moraine ridges on the surface of Collins Ice Cap signifies that this glacier could vanish from the peninsula during climate optimum (ca. 4000-3000 yrs BP). The processes of new formation and growth of the ice cap started probably ca. 2000 yrs BP; within the last 1000 years the limited advance of the glacier occurred (likely corresponding to the Little Ice Age), and was replaced then by modern process of its decay.

Verkulich, Sergey; Pushina, Zina; Tatur, Andrej

2010-05-01

43

Sedimentological evidence for a deforming bed in a late Pleistocene glacial sequence from ANDRILL AND-1B, Ross Sea, Antarctica  

NASA Astrophysics Data System (ADS)

A 1,284.87m-long sediment core (AND-1B) was drilled from beneath the McMurdo Ice Shelf sector of the Ross Ice Shelf as part of the Antarctic geological drilling program, ANDRILL. Snapshots of diamictite depositional processes and paleoenvironmental conditions have been interpreted from a nested set of samples collected at overlapping scales of observation. Data used for detailed sedimentological analyses include cm-scale core logging based on x-radiographs of the archive halves in addition to the original core description, bulk samples, and oriented 45 x 70mm thin sections of diamictites for micromorphology analysis. The 5.8m-thick interval studied contains a complete glacial advance-retreat sequence that is bracketed by glacial surfaces of erosion (GSE) at 41.9 and 47.7mbsf recording glacial advance over the core site. 4.6m of subglacial till is deposited above the lower GSE represented by a sequence of thin muddy conglomerate with diverse pebble lithologies, massive clast-rich muddy diamicite, and stratified diamictite with clast-rich and clast-free beds. The sand size fraction of bulk samples and thin sections from the till are dominated by aggregate grains, termed till pellets following terminology used by sedimentologists in the Ross Sea. The core of the pellet may be a lithic grain or stiff till with additional clay plastered on the outside forming rounded grains from angular ones. Till pellets are rounded, spherical to prolate in form and are associated with turbate structures and aligned grains in till thin sections - evidence of rotational deformation. The area beneath an ice shelf in front of a grounding line is recorded by a thin bed of granular particles that transitions to silty claystone stratified with granules. Granular layers are thought to be from periodic winnowing by strong currents focused near the grounding line. The sub-ice shelf transition from proximal grounding line to distal is recorded by a gradational contact between stratified silty claystone and massive silty claystone. The subglacial diamictites within this interval appear to have formed within a deforming bed. Clay content and high porewater pressures are key to development of till pellets because flow within the dilated till layer rounds intraclasts without crushing grains. Upon a drop in porewater pressure and draining of the till, accretion occurs as the grains solidify. Continuous deforming beds are likely to occur in ice-marginal locations where soft sediment is abundant and where subglacial water is spread diffusely rather than focused in channels.

Cowan, E. A.; Powell, R. D.

2009-12-01

44

Stochastic forcing of Pleistocene ice sheets: Implications for the origin of millennial-scale climate oscillations  

E-print Network

evidence now exists for high-frequency climate changes in the last ice age cycle (Dansgaard- Oeschger ages [Tarasov and Peltier, 1997; Hyde et al., 1999]. In this model ice flows subject to a temperatureStochastic forcing of Pleistocene ice sheets: Implications for the origin of millennial

45

Post-Last Glacial Maximum (Latest Pleistocene to Holocene) geology of the Santa Barbara shelf, southern California  

NASA Astrophysics Data System (ADS)

High-resolution bathymetric and seismic-reflection data collected for the California Seafloor Mapping Program (http://walrus.wr.usgs.gov/mapping/csmp/) provide new insights for understanding the post-Last Glacial Maximum (LGM) evolution of the Santa Barbara shelf, highlighting relationships between tectonics, eustasy, and sediment supply. The west-trending shelf extends offshore for 5 to 7 km and is bounded on the south by the deep Santa Barbara basin and on the north by a narrow coastal zone and the steep, rapidly uplifting Santa Ynez Mountains. The active, west-trending, north-dipping Ventura-Pitas Point-North Channel and Red Mountain fault systems form the structural boundary between two distinct shelf domains. The smooth, gently sloping, southern shelf is flooded by thick (35 to 40 m), prograding Santa Clara and Ventura River deltaic deposits. These thick strata drape the shelfbreak and fill the accommodation space created by rising sea level, largely masking the influence of active tectonics. In contrast, the northern shelf has complex bathymetry and a well-defined, sharp shelfbreak at ~90 m water depth. The northern shelf is relatively sediment starved (mean sediment thickness is 3 to 4 m), with thickest accumulations (up to ~18 m) forming shallow (< 30 m), discontinuous to laterally coalescing, inner-shelf bars that are best developed at the mouths of steep coastal watersheds. These watersheds also feed several distinct, coarse-grained sediment lobes (as large as ~1.5 km2, extending to 3 km offshore and depths of 70 m) that probably formed during massive flood events. The relative lack of offshore deposits on the northern shelf suggests sediment transport is dominated by easterly nearshore drift. Faulting and folding on the northern shelf are significant controls on sediment distribution and thickness, the occurrence of bedrock uplifts, and common hydrocarbon-associated seeps, pockmarks, and mounds. Bedrock, typically "soft" Neogene strata, is especially common on the mid- to-outer shelf, forming low-relief ribbed outcrops. Bedrock on the flat outer shelf contains nearshore clam (pholad) borings and is interpreted as the ~20 ka lowstand (Stage 2) wave-cut platform; its depth (< 90 m) indicates post-LGM uplift of about 40 m (rate of ~2 mm/yr) that is tied to slip on the underlying North Channel fault. Three or more(?) distinct submerged strandlines and wave-cut platforms occur within the northern shelf at shallower depths, and are inferred to record relative post-LGM stillstands associated with either pulses of slower sea-level rise or periods when sea level rise was matched by tectonic uplift.

Johnson, S. Y.; Ritchie, A. C.; Conrad, J. E.; Dartnell, P.; Phillips, E.; Sliter, R. W.

2011-12-01

46

Late Pleistocene evolution of the Rhine-Meuse system in the southern North Sea basin: imprints of climate change, sea-level oscillation and glacio-isostacy  

NASA Astrophysics Data System (ADS)

High-resolution continuous core material, geophysical measurements, and hundreds of archived core descriptions enabled to identify 13 Late Pleistocene Rhine-Meuse sedimentary units in the infill of the southern part of the North Sea basin (the Netherlands, northwestern Europe). This sediment record and a large set of Optical Stimulated Luminescence dates, 14C dates and biostratigraphical data, allowed to establish detailed relationships between climate change, sea-level oscillation, glaciation history and the sedimentary development of the Rhine fluvial system during the last glacial cycle (Marine Isotope Stages 5e-2, Eemian-Weichselian). A well-preserved Eemian sediment record was encountered as the infill of a Late Saalian (MIS6) subglacial basin. Part of this record reflects groundwater rise controlled (fine-grained) sedimentation as a result of postglacial (early) Eemian sea-level rise. It shows strong analogy to developments known from the Holocene Rhine-Meuse delta. Outside of the glacial depressions near coastal deposits are only fragmentarily preserved. The Early Glacial Rhine sediment record is dominated by organic debris and peat layers, marking landscape stability and low fluvial activity. Part of this record may have been formed under near coastal conditions. Significant amounts of reworked marine biomarkers in the lag-deposits of Early Pleniglacial (MIS4) fluvial systems indicate that this period is characterized by extensive reworking of older (MIS5) near-coastal sediments. Despite the marked Early Pleniglacial climatic cooling, input of new sediment from the drainage basin was relatively low, a feature that is related to the presence of regolith protective relic soil complexes in the basin. During the early Middle Pleniglacial, a major Rhine avulsion indicates the system was in an aggrading mode and that sediment supply into the lower reaches of the Rhine had strongly increased. This increase in sediment supply coincided with the timing of major climate cooling that occurred from ˜50 to 45 ka onwards. The increase in sediment supply is related to final breakup of the soil complexes in the drainage basin. After ˜24 ka, a strong input of coarse-grained gravelly sediments was observed which indicates a strong increase in physical weathering processes and periglacial-controlled supply of bedload sediment in the catchment. A time delay between climate change (˜30 ka) and channel belt aggradation (<24 ka), is explained as a result of transport path length between source and sink and/or effects of higher continental runoff rates after 22 ka. The Late Middle Pleniglacial, Late Pleniglacial and Lateglacial Rhine-Meuse record testifies for strong influence of glacio-isostatic-controlled differential upwarping of the study area. Glacio-isostatic-controlled forebulge upwarping and lateral valley tilting is shown to have deflected Rhine-Meuse channel belts after 35 ka. Glacio-isostatic upwarping is seen as the main cause for strong incision during the first phase of the Late Pleniglacial (30-24 ka). At later stage glacio-isostatic-controlled incision was overruled due to high climate-controlled sediment input from the catchment and probably initial glacio-isostatic subsidence. Migration of channel belts towards the direction of the former centre of glacio-isostatic uplift indicates that glacio-isostacy influenced Rhine-Meuse paleogeography until far into the Lateglacial.

Busschers, F. S.; Kasse, C.; van Balen, R. T.; Vandenberghe, J.; Cohen, K. M.; Weerts, H. J. T.; Wallinga, J.; Johns, C.; Cleveringa, P.; Bunnik, F. P. M.

2007-12-01

47

Tempo of genetic diversification in southern African rodents: The role of Plio-Pleistocene climatic oscillations as drivers for speciation  

NASA Astrophysics Data System (ADS)

The evolution of the southern African faunal assemblages is thought to have been largely influenced by climatic oscillations of the Plio-Pleistocene. These fluctuations presumably had a major impact in the form of vicariant diversification of taxa by causing simultaneous speciation/cladogenetic events due to habitat fragmentation. We aimed to test this hypothesis by comparing the timing of diversification observed for several rodent lineages with three peaks of aridification described at approximately 2.8, 1.7 and 1.0 Mya. Our study included nine rodent taxa (Nannomys, Aethomys, Otomys, Myotomys, Rhabdomys and Mastomys for the Muridae, Saccostomus for the Nesomyidae, Cryptomys for the Bathyergidae, and Xerus for the Sciuridae) that showed intrageneric mitochondrial cytochrome b cladogenesis during the last 5 Ma. Phylogenetic analysis performed with maximum likelihood and Bayesian methods supported the monophyly of all subgenera and genera. Most diversifications are also well supported and in agreement with previously published studies. Divergence dates between lineages were estimated using a Bayesian relaxed molecular clock and the 7 Myr split between different Apodemus species as well as the divergence between Tatera and Gerbillurus at 6.3 Myr were used as calibration points. Our results did not provide any convincing evidence of a correspondence between rodent diversification events and peaks in aridity during the Plio-Pleistocene. The nearly perfect linear correlation between cladogenesis and time, during the last 5 Myr, strongly suggests that the diversification of southern African rodent lineages is driven by complex interactions between different factors, including life history, climatic changes, and topographic barriers.

Montgelard, Claudine; Matthee, Conrad A.

2012-07-01

48

Late Pleistocene ice margin fluctuations in the Nahanni National Park-UNESCO World Heritage Site and their impact on glacial lake formation and architecture of drainage systems across the Yukon-NWT continental divide  

NASA Astrophysics Data System (ADS)

In the late Pleistocene the southern Mackenzie region was glaciated by ice masses from a Cordilleran and continental source (Laurentide). Stratigraphic and geomorphologic evidence indicate that the two glaciers occupied this region at different times during the Late Pleistocene. The continental ice sheet advanced over the foothills and up major valleys reaching its maximum extent, ca. 30 ka. B. P. This took place when Cordilleran glaciers were in their initial stages of development. The Laurentide Ice Sheet blocked the drainage of the South Nahanni River near Virginia Falls, forming a glacial lake which inundated an area of approximately 900 km2 at its maximum stand, and had an outlet to the southwest, across the continental divide into the Yukon Territory and eventually into the Pacific Ocean. Lacustrine sediments at various sites reach thicknesses ranging from 110 to 120 metres, at an elevation of around 700 m. Cordilleran glaciers advanced eastward and approximately 5000 years later blocked this southwestward drainage, rerouting it to the east and north along the Mackenzie Mountain front. The drainage was confined between the mountains and continental ice margin where it incised major canyons into the limestone bedrock, and produced a spectacular karst landscape, which today forms part of the Nahanni National Park. During the retreat of the Laurentide and advance of Cordilleran glaciers, glacial Lake Nahanni cut an outlet to the east at First Canyon. This outlet drained into a continuous northbound network of marginal meltwater channels joining the north-flowing drainage that eventually reached the Arctic Ocean, and during further retreat of the ice sheet established the Mackenzie River in its modern location. The presence of Laurentide ice in this region is evidenced by large granite boulders carried from the Canadian Shield. Erratics are found up to 100 km west of the mountain front. Neotectonic activity in the area is interpreted from exposures such as those seen at Virginia Falls. Here glaciolacustrine sediments of Lake Nahanni are found both above and below the falls, but those above the falls are offset along the fault by approximately 30 meters, indicating that the falls most likely formed or were tectonically reactivated in postglacial time. Pre-late Pleistocene terraces of the South Nahanni River lie above the upstream terraces found near Virginia Falls, and slope to the west, further providing evidence of postglacial rebound and tectonics.

Duk-Rodkin, A.; Barendregt, R. W.

2009-12-01

49

Millennial and orbital variations of El Niño/Southern Oscillation and high-latitude climate in the last glacial period.  

PubMed

The El Niño/Southern Oscillation (ENSO) phenomenon is believed to have operated continuously over the last glacial-interglacial cycle. ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time, but the proposals disagree on whether increased frequency of El Niño events, the warm phase of ENSO, was linked to North Atlantic warm or cold periods. Here we present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges to grass, from northern Queensland, Australia, covering the past 45,000 yr. We observe millennial-scale dry periods, indicating periods of frequent El Niño events (summer precipitation declines in El Niño years in northeastern Australia). We find that these dry periods are correlated to the Dansgaard-Oeschger events--millennial-scale warm events in the North Atlantic climate record--although no direct atmospheric connection from the North Atlantic to our site can be invoked. Additionally, we find climatic cycles at a semiprecessional timescale (approximately 11,900 yr). We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales, which determined precipitation in northeastern Australia, also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections. PMID:15029193

Turney, Chris S M; Kershaw, A Peter; Clemens, Steven C; Branch, Nick; Moss, Patrick T; Fifield, L Keith

2004-03-18

50

Spatial and temporal variations of glacial erosion in the European Alps: numerical models and implications for slope stability (Invited)  

NASA Astrophysics Data System (ADS)

Glacial erosion in alpine landscapes can be highly variable in space and time and lead to significant morphologic modification and mass redistribution at virtually all scales. Because they affect the near-surface stress and strain distribution by producing cyclic variations of the surface load, removing and abrading rocks, storing/releasing sediments and affecting the surface and subsurface hydrology, glaciations have multiple effects on slope stability. Understanding how glacial erosion evolves in space and time is thus important for investigating potential feedbacks between glacial erosion and deep-seated gravitational slope deformation (DSGSD). The present-day topography of the European Alps shows evidence of intense glacial erosion. However, significant questions regarding Alpine landscape evolution during glaciations still persist. For example, large-scale topographic analyses suggest that glacial erosion is maximized at and above the glaciers' long-term Equilibrium Line Altitude. In contrast, measurements of long-term denudation rates from low-temperature thermochronology and reconstructions of the pre-glacial Alpine topography suggest high erosion towards low altitudes and formation of overdeepnenings, in turn indicating an increase of local relief in response to glacial processes. Based on sediment record, low-temperature thermochronology and burial cosmogenic nuclide dating, it has also been proposed that the mid-Pleistocene climatic transition from symmetric, 40kyr to asymmetric, 100kyr glacial/interglacial oscillations sets the onset of intense glacial erosion within the Alps. However, this climate threshold in glacial erosion has not been showed in other orogens, and positive feedbacks between climate periodicity and glacial erosion efficiency still remain to be proven. Numerical modeling provides estimates of the patterns and magnitudes of glacial erosion through time. Modeling results on an advanced reconstruction of the pre-glacial topography and the present-day landform suggest that glacial erosion propagates headward as the landscape evolves from a fluvial to a glacial state. This evolution of glacial erosion leads to an initial increase of the topographic relief, followed by subsequent erosion at high elevations, in turn reconciling previous, apparently discordant findings. Numerical predictions also suggest that the mid-Pleistocene climate transition may have produced an intensification of glacial erosion. However, other factors such as an increase of rock uplift and/or progressive climate cooling are required to explain enhanced valley carving at approximately 1Myr, as suggested from the Alpine record.

Sternai, P.; Herman, F.; Willett, S.; Champagnac, J.; Fox, M.; Valla, P.; Salcher, B.

2013-12-01

51

Carbon cycle instability as a cause of the late Pleistocene ice age oscillations - Modeling the asymmetric response  

NASA Technical Reports Server (NTRS)

A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model.

Saltzman, Barry; Maasch, Kirk A.

1988-01-01

52

Climatic Oscillations 10,000-155,000 yr B.P. at Owens Lake, California Reflected in Glacial Rock Flour Abundance and Lake Salinity in Core OL-92  

USGS Publications Warehouse

Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na2O, TiO2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to 36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO3 and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the ??18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation. ?? 1997 University of Washington.

Bischoff, J.L.; Menking, K.M.; Fitts, J.P.; Fitzpatrick, J.A.

1997-01-01

53

Synchronous, high-frequency oscillations in tropical sea surface temperatures and North Atlantic Deep Water production during the Last Glacial Cycle  

NASA Astrophysics Data System (ADS)

Stable isotopic measurements of G. sacculifer and C. wuellerstorfi in a core from the western equatorial Atlantic imply that there are parallel, suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3. Low values of G. sacculifer ?18O accompany high values of C. wuellerstorfi ?13C, linking warmer sea surface temperatures (SSTs) in the tropics with increased production of lower North Atlantic Deep Water (NADW). The amplitude of the ?18O oscillations is 0.6‰ (or 2°-3°C), which is superimposed on a glacial/interglacial amplitude of about 2.1‰. Using the G. sacculifer ?18O data, we calculate that surface waters were colder during stage 2 than calculated by CLIMAP [1976, 1981]. The longer-period (>2 kyr) oscillations in air temperature recorded in the Greenland and Antarctic ice cores appear to correlate with oscillations in sea surface temperature in the equatorial Atlantic. The magnitude of these oscillations in tropical SST is too large to have resulted from changes in meridional heat transport caused by the global conveyor alone. The apparent synchroneity of equatorial SST and polar air temperature changes, as well as the amplitude of the SST changes at the equator, are consistent with the climate effects expected from changes in the atmosphere's greenhouse gas content (H2Ovapor, CO2, and CH4).

Curry, W. B.; Oppo, D. W.

1997-01-01

54

Orbital forcing of the late Pleistocene boreal summer monsoon: Links to North Atlantic cold events and El Niño - Southern Oscillation  

Microsoft Academic Search

This thesis revolves about the timing of precession-related variations in the boreal summer monsoon and the impact of North Atlantic cold events and the El Niño Southern Oscillation on this timing. Transient climate modelling experiments indicate that the intensity of the Northern Hemisphere summer monsoon varies in-phase with peak summer insolation on orbital timescales. In contrast, marine proxy records suggest

M. Ziegler

2009-01-01

55

Glacial Isostatic Adjustment  

NSDL National Science Digital Library

To prepare for this activity students should be familiar with basic vocabulary associated with ice age glaciations. In the case of this course, they should have read the chapter on glaciation in Tarbuck & Lutgens, Earth, 8th edition. Their task begins with designing a hands-on lab to investigate the relationship between depressions in a surface caused by adding mass to a compressible medium such as a sponge. Students then use ArcGIS Explorer to investigate the Antarctic ice sheet and the Pleistocene ice sheet. The activity wraps up with students collecting data related to glacial isostatic adjustment in rebound centers around Canada over the past 6,000 years.

Awad, Aida

56

Glacial Landforms  

NSDL National Science Digital Library

The students have been lectured to about glacial processes, but the homework was given prior to a lecture about glacial landforms. A field trip surveying the glacial landforms of SE South Dakota was just completed. The students must draw upon their knowledge and utlize other sources to interpret the landforms they see in the imagery. Designed for a geomorphology course

Mark Sweeney

57

Guatemalan forest synthesis after Pleistocene aridity  

PubMed Central

Sediments from two lakes in the Peten Department, Guatemala, provide palynological evidence from Central America of late Pleistocene aridity and subsequent synthesis of mesic forests. Late Glacial vegetation consisted of marsh, savanna, and juniper scrub. An early Holocene temperate forest preceded a mesic tropical forest with Brosimum (ramon). Thus “primeval” rain forests of Guatemala are no older than 10,000 to 11,000 years and are considerably younger in the Peten due to Mayan disturbances. Among dated Neotropical sites, the Peten has the most mesic vegetation yet shown to have supplanted xeric vegetation present during the Pleistocene. The arid late Glacial-humid early Holocene transition appears to have been pantropical in the lowlands. The Peten was not a Pleistocene refugium for mesophytic taxa, as has been suggested. Thus genesis of extant rain forests in northern Central America and southern Mexico remains unexplained. Images PMID:16593498

Leyden, Barbara W.

1984-01-01

58

Miocene and Pliocene dominated diversification of the lichen-forming fungal genus Melanohalea (Parmeliaceae, Ascomycota) and Pleistocene population expansions  

PubMed Central

Background Factors promoting diversification in lichen symbioses remain largely unexplored. While Pleistocene events have been important for driving diversification and affecting distributions in many groups, recent estimates suggest that major radiations within some genera in the largest clade of macrolichens (Parmeliaceae, Ascomycota) vastly predate the Pleistocene. To better understand the temporal placement and sequence of diversification events in lichens, we estimated divergence times in a common lichen-forming fungal genus, Melanohalea, in the Northern Hemisphere. Divergence times were estimated using both concatenated gene tree and coalescent-based multilocus species tree approaches to assess the temporal context of major radiation events within Melanohalea. In order to complement our understanding of processes impacting genetic differentiation, we also evaluated the effects of Pleistocene glacial cycles on population demographics of distinct Melanohalea lineages, differing in reproductive strategies. Results We found that divergence estimates, from both concatenated gene tree and coalescent-based multilocus species tree approaches, suggest that diversification within Melanohalea occurred predominantly during the Miocene and Pliocene, although estimated of divergence times differed by up to 8.3 million years between the two methods. These results indicate that, in some cases, taxonomically diagnostic characters may be maintained among divergent lineages for millions of years. In other cases, similar phenotypic characters among non-sister taxa, including reproductive strategies, suggest the potential for convergent evolution due to similar selective pressures among distinct lineages. Our analyses provide evidence of population expansions predating the last glacial maximum in the sampled lineages. These results suggest that Pleistocene glaciations were not inherently unfavorable or restrictive for some Melanohalea species, albeit with apparently different demographic histories between sexually and vegetatively reproducing lineages. Conclusions Our results contribute to the understanding of how major changes during the Miocene and Pliocene have been important in promoting diversification within common lichen-forming fungi in the northern Hemisphere. Additionally, we provide evidence that glacial oscillations have influenced current population structure of broadly distributed lichenized fungal species throughout the Holarctic. PMID:22963132

2012-01-01

59

Middle to Late Pleistocene ice extents, tephrochronology and paleoenvironments of the White River area, southwest Yukon  

NASA Astrophysics Data System (ADS)

Sedimentary deposits from two Middle to Late Pleistocene glaciations and intervening non-glacial intervals exposed along the White River in southwest Yukon, Canada, provide a record of environmental change for much of the past 200 000 years. The study sites are beyond the Marine Isotope stage (MIS) 2 glacial limit, near the maximum regional extent of Pleistocene glaciation. Non-glacial deposits include up to 25 m of loess, peat and gravel with paleosols, pollen, plant and insect macrofossils, large mammal fossils and tephra beds. Finite and non-finite radiocarbon dates, and twelve different tephra beds constrain the chronology of these deposits. Tills correlated to MIS 4 and 6 represent the penultimate and maximum Pleistocene glacial limits, respectively. The proximity of these glacial limits to each other, compared to limits in central Yukon, suggests precipitation conditions were more consistent in southwest Yukon than in central Yukon during the Pleistocene. Conditions in MIS 5e and 5a are recorded by two boreal forest beds, separated by a shrub birch tundra, that indicate environments as warm or warmer than present. A dry, treeless steppe-tundra, dominated by Artemisia frigida, upland grasses and forbs existed during the transition from late MIS 3 to early MIS 2. These glacial and non-glacial deposits constrain the glacial limits and paleoenvironments during the Middle to Late Pleistocene in southwest Yukon.

Turner, Derek G.; Ward, Brent C.; Bond, Jeffrey D.; Jensen, Britta J. L.; Froese, Duane G.; Telka, Alice M.; Zazula, Grant D.; Bigelow, Nancy H.

2013-09-01

60

African climate change and faunal evolution during the Pliocene-Pleistocene  

NASA Astrophysics Data System (ADS)

Environmental theories of African faunal evolution state that important evolutionary changes during the Pliocene-Pleistocene interval (the last ca. 5.3 million years) were mediated by changes in African climate or shifts in climate variability. Marine sediment sequences demonstrate that subtropical African climate periodically oscillated between markedly wetter and drier conditions, paced by earth orbital variations, with evidence for step-like (±0.2 Ma) increases in African climate variability and aridity near 2.8 Ma, 1.7 Ma, and 1.0 Ma, coincident with the onset and intensification of high-latitude glacial cycles. Analysis of the best dated and most complete African mammal fossil databases indicates African faunal assemblage and, perhaps, speciation changes during the Pliocene-Pleistocene, suggesting more varied and open habitats at 2.9-2.4 Ma and after 1.8 Ma. These intervals correspond to key junctures in early hominid evolution, including the emergence of our genus Homo. Pliocene-Pleistocene shifts in African climate, vegetation, and faunal assemblages thus appear to be roughly contemporary, although detailed comparisons are hampered by sampling gaps, dating uncertainties, and preservational biases in the fossil record. Further study of possible relations between African faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries, emerging molecular biomarker methods for reconstructing African paleovegetation changes, tephra correlations between terrestrial and marine sequences, as well as continuing collaborations between the paleoclimatic and paleoanthropological communities.

deMenocal, Peter B.

2004-03-01

61

A high resolution history of the El Niño - Southern Oscillation and of the solar activity during the Late Glacial - Early Holocene in the subtropical Andean region.  

NASA Astrophysics Data System (ADS)

High-resolution laminated lacustrine sediments are excellent archives of the past hydrological changes and they provide valuable insights about the climatic processes that trigger these changes. The paleoclimatic records located in the Southern Hemisphere are fundamental for understanding the evolution of the El Niño - Southern Oscillation (ENSO) since this climatic phenomena is the main cause of droughts and floods in many areas of South America and other regions of the world, like Spain and Egypt. Available regional paleoclimate reconstructions show that modern climatic patterns in South America were established during the Late Holocene. The laminated sediments of Lago Chungará (18° 15' S - 69° 10' W, 4520 m a.s.l., Chilean altiplano) have allowed us to characterize the evolution of this climatic phenomena for the transition Late Glacial - Early Holocene (12,300 - 9,500 calendar years BP) as well as its relationship with other climate forcings, namely the solar activity. The studied sediments correspond to the lowermost 2.4 m of 8 m long Kullemberg cores recovered from this lake. These sediments are mainly made up of greenish and whitish laminae and thin layers constituted by diatomaceous oozes with carbonates and organic matter, arranged in rhythms and cycles. X-ray fluorescence (XRF) (Al, Si, S, K, Ca, Ti, Mn, Fe, Rb, Sr, Zn, Sb and Ba) analyses, total organic carbon (TOC), total carbon (TC), x-ray diffraction (XRD), biogenic silica, stable isotopes (delta18O and delta13C) on carbonates and on diatoms (delta18O) and magnetic susceptibility were determined in order to characterize the sediments of Lago Chungará. Previous statistical studies (cluster and Principal Component Analyses (PCA)) were used to disentangle the paleoclimatic signal from the other ones (volcanic and tectonic). The chronological model framework was built using 6 radiocarbon dates, allowing us to establish that laminated couplets were deposited on a pluriannual basis. These couplets are composed of a lower light lamina, progressively grading upwards to a dark lamina. Light laminae are composed by diatom valves of a single species (Cyclostephanos cf. andinus), accumulated during short-term extraordinary diatom blooms when water column mixing took place under abrupt and short-term climatic events. Dark laminae contain a complex diatom assemblage and are rich in organic matter representing the baseline limnological conditions during several years of deposition. Spectral analyses (Fast Fourier Transformation - FFT - and Time Frequency - TF - analyses) were performed on the isolated paleohydrological curve and on the gray color curve calculated for these laminated sediments. The FFT analyses of the paleohydrological signal obtained from the PCA highlights the record of 35-51 years cycles, that might correspond to the solar Bruckner cycle as well as to the inter-decadal changes in the variance of the ENSO phenomena. The results of the FFT analyses carried out on the gray curve reinforce the hypothesis of the solar control on the variations in the lake productivity: the 11-years Schwabe, 22-23-years Hale, 35-years Bruckner and the approx. 90-years Gleissberg cycles, as well as a strong to very strong ENSO phenomena (8.2 and 7.5-years cycles) are recorded. The TF analyses developed on the variations of the gray-colour curve reveal that all solar frequencies have modified intensities during the Late Glacial and Early Holocene. During the low activity periods of the 11-years Schwabe cycles, strong to very strong ENSO phenomena took place. These results show that ENSO-like variability was present during the late Glacial and early Holocene in the Altiplano.

Giralt, S.; Schimmel, M.; Hernández, A.; Bao, R.; Valero-Garcés, B. L.; Sáez, A.; Pueyo, J. J.

2009-04-01

62

Steppes, savannahs, forests and phytodiversity reservoirs during the Pleistocene in the Iberian Peninsula  

Microsoft Academic Search

A palaeobotanical analysis of the Pleistocene floras and vegetation in the Iberian Peninsula shows the existence of patched landscapes with Pinus woodlands, deciduous and mixed forests, parklands (savannah-like), shrublands, steppes and grasslands. Extinctions of Arctotertiary woody taxa are recorded during the Early and Middle Pleistocene, but glacial refugia facilitated the survival of a number of temperate, Mediterranean and Ibero-North African

Penélope González-Sampériz; Suzanne A. G. Leroy; José S. Carrión; Santiago Fernández; Mercedes García-Antón; María José Gil-García; Paloma Uzquiano; Blas Valero-Garcés; Isabel Figueiral

2010-01-01

63

Stability of North Atlantic water masses in face of pronounced climate variability during the Pleistocene  

Microsoft Academic Search

Geochemical profiles from the North Atlantic Ocean suggest that the vertical ?13C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. The most anomalous ?13C profiles are from the extreme interglaciations of the late Pleistocene.

M. E. Raymo; D. W. Oppo; B. P. Flower; D. A. Hodell; J. F. McManus; K. A. Venz; K. F. Kleiven; K. McIntyre

2004-01-01

64

Stability of North Atlantic water masses in face of pronounced climate variability during the Pleistocene  

Microsoft Academic Search

Geochemical profiles from the North Atlantic Ocean suggest that the vertical delta13C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. The most anomalous delta13C profiles are from the extreme interglaciations of the late Pleistocene.

M. E. Raymo; D. W. Oppo; B. P. Flower; D. A. Hodell; J. F. McManus; K. A. Venz; K. F. Kleiven; K. McIntyre

2004-01-01

65

Stability of North Atlantic Water Masses in Face of Pronounced Climate Variability During the Pleistocene  

Microsoft Academic Search

Geochemical profiles from the North Atlantic Ocean suggest that the vertical delta(13)C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. The most anomalous delta(13)C profiles are from the extreme interglaciations of the late Pleistocene.

M. E. Raymo; D. W. Oppo; Benjamin P. Flower; D. A. Hodell; J. F. McManus; K. A. Venz; K. F. Kleiven; K. McIntyre

2004-01-01

66

Pleistocene speciation in the genus Populus (salicaceae).  

PubMed

The macroevolutionary consequences of recent climate change remain controversial, and there is little paleobotanical or morphological evidence that Pleistocene (1.8-0.12 Ma) glacial cycles acted as drivers of speciation, especially among lineages with long generation times, such as trees. We combined genetic and ecogeographic data from 2 closely related North American tree species, Populus balsamifera and P. trichocarpa (Salicacaeae), to determine if their divergence coincided with and was possibly caused by Pleistocene climatic events. We analyzed 32 nuclear loci from individuals of P. balsamifera and P. trichocarpa to produce coalescent-based estimates of the divergence time between the 2 species. We coupled the coalescent analyses with paleodistribution models to assess the influence of climate change on species' range. Furthermore, measures of niche overlap were used to investigate patterns of ecological differentiation between species. We estimated the divergence date of P. balsamifera and P. trichocarpa at approximately 75 Ka, which corresponds closely with the onset of Marine Isotope Stage 4 (?76 Ka) and a rapid increase in global ice volume. Significance tests of niche overlap, in conjunction with genetic estimates of migration, suggested that speciation occurred in allopatry, possibly resulting from the environmental effects of Pleistocene glacial cycles. Our results indicate that the divergence of keystone tree species, which have shaped community diversity in northern North American ecosystems, was recent and may have been a consequence of Pleistocene-era glaciation and climate change. PMID:22213709

Levsen, Nicholas D; Tiffin, Peter; Olson, Matthew S

2012-05-01

67

Pleistocene Speciation in the Genus Populus (Salicaceae)  

PubMed Central

The macroevolutionary consequences of recent climate change remain controversial, and there is little paleobotanical or morphological evidence that Pleistocene (1.8–0.12 Ma) glacial cycles acted as drivers of speciation, especially among lineages with long generation times, such as trees. We combined genetic and ecogeographic data from 2 closely related North American tree species, Populus balsamifera and P. trichocarpa (Salicacaeae), to determine if their divergence coincided with and was possibly caused by Pleistocene climatic events. We analyzed 32 nuclear loci from individuals of P. balsamifera and P. trichocarpa to produce coalescent-based estimates of the divergence time between the 2 species. We coupled the coalescent analyses with paleodistribution models to assess the influence of climate change on species' range. Furthermore, measures of niche overlap were used to investigate patterns of ecological differentiation between species. We estimated the divergence date of P. balsamifera and P. trichocarpa at approximately 75 Ka, which corresponds closely with the onset of Marine Isotope Stage 4 (?76 Ka) and a rapid increase in global ice volume. Significance tests of niche overlap, in conjunction with genetic estimates of migration, suggested that speciation occurred in allopatry, possibly resulting from the environmental effects of Pleistocene glacial cycles. Our results indicate that the divergence of keystone tree species, which have shaped community diversity in northern North American ecosystems, was recent and may have been a consequence of Pleistocene-era glaciation and climate change. PMID:22213709

Levsen, Nicholas D.; Tiffin, Peter; Olson, Matthew S.

2012-01-01

68

Evolution of salt diapir and karst morphology during the last glacial cycle: Effects of sea-level oscillation, diapir and regional uplift, and erosion (Persian Gulf, Iran)  

NASA Astrophysics Data System (ADS)

Marine, fluvial and cave sediments, and karst phenomena were studied and dated by 14C, U-series, and OSL methods to determine the evolution of the Namakdan diapir and the world's longest salt cave (3N Cave) during the Holocene and the Last Glacial. Sea-level oscillations, the uplift rate of the diapir and its surroundings, and erosion are the main factors influencing the diapir morphology. Although the diapir uplift rate has been constant for the last 50 kyr (˜ 4 mm/yr at a distance 600 m from the diapir edge), the uplift rate decreases with the distance from the diapir center. Drag-induced host rock deformation extends for ˜ 300 m from the outside edge of the diapir, and host rocks in this zone have an uplift rate of 0.4-0.6 mm/yr, which is 2-3 times greater than the regional uplift rate. Based on known sea-level oscillations, radiometric dating, and geological evidence, the Namakdan diapir was repeatedly flooded by sea water between 130 and 80 kyr BP. Submarine residuum composed mainly of gypsum and dolomite formed cap rock on the diapir. After ˜ 80 kyr BP, surficial drainage network and karst development started. Blind valleys and their corresponding cave systems evolved continuously for ˜ 20-30 kyr. Between 9 and 6 cal kyr BP the rate of sea-level rise exceeded the Namakdan diapir uplift rate by the factor of 3. As a consequence upward incision of cave streams (paragenetic trend) occurred, and blind valleys near the seashore were filled with gravels. Cave passages now accessible on the Namakdan and Hormoz diapirs started to form 3-6 cal kyr BP when sea level stabilized and downward stream incision began. Older cave levels are still preserved but are filled with sediments and salt precipitates. A comparison of the Namakdan diapir evolution with data from the Hormoz and Larak diapirs shows that the evolution of diapir morphology is strongly affected by the differences in uplift rates and geological settings. The general scheme of the evolution of the Namakdan diapir is believed to be partly applicable to many other diapirs in coastal settings.

Bruthans, Ji?í; Filippi, Michal; Zare, Mohammad; Churá?ková, Zdenka; Asadi, Naser; Fuchs, Markus; Adamovi?, Ji?í

2010-09-01

69

Onset of major Pleistocene glaciations in the Alps  

NASA Astrophysics Data System (ADS)

Since alligators patrolled Greenland swamps in the Eocene, the Earth's climate underwent significant cooling, which culminated in the Pleistocene Ice Age with recurring glaciations in vast regions of the Alps, Eurasia and North America, and overgrowth of polar icecaps in Antarctica and Greenland. During main Pleistocene glacial penetrations, the Alpine icecap invaded the low gradients of the Central Europe uplands and Italian Po plain. Peri-glacial sedimentary basins such as the Po Basin are natural collectors of past biological and climatic changes involving the waxing and waning of major icecaps. We have found in a 200m-thick core from the central Po plain near Milan stratigraphic evidence for a major glacial pulsation of the nearby Alpine icecap, which occurred in correspondence of a seismically traceable unconformity of regional relevance, termed the "Red Unconformity" (RU) in Eni/Agip terminology. The RU is associated with a major reorganization of vegetation cover and Alpine drainage pattern. The age of the RU was constrained magnetostratigraphically to the the first major Pleistocene glacio-eustatic low-stand at 0.87Ma (Oxygen Isotope Stage 22). This corresponds to the end of the "Mid Pleistocene Revolution" (MPR), a marked reorganization of northern hemisphere glaciation pattern which took place in the late Early Pleistocene. We suggest that the MPR/MIS 22 was associated with the onset of the first major Pleistocene glaciation in the Alps. Noticing the similarity in number of major Pleistocene glacieustatic low-stands starting with MIS 22, and the four-fold Alpine glacial subdivision of Penck and Brückner (1909), we conclude that "Penck and Brückner in 1909 may not have been, after all, that wrong" (Kukla and Cilek, 1996).

Muttoni, G.; Carcano, C.; Garzanti, E.; Ghielmi, M.; Piccin, A.; Pini, R.; Rogledi, S.; Sciunnach, D.

2003-04-01

70

The case for an ice shelf in the pleistocene Arctic Ocean  

Microsoft Academic Search

During Pleistocene glacial maxima, including the last glacial maximum, a thick floating ice shelf covered all or most of the deep Arctic Ocean. This conclusion is based on a preponderance of results from field and modeling studies. Of special importance are recent discoveries in the Arctic Ocean: the deep ice plowmarks on the submarine Yermak Plateau and Chukchi Borderland, and

Mikhail G. Grosswald; Terence J. Hughes

2008-01-01

71

The End Pleistocene Extinction Event - What Caused It?  

Microsoft Academic Search

It is well established that the last catastrophic faunal extinction in the geologic past coincided with the end of the Pleistocene during the deglaciation between the last glacial episode and the present Holocene interglacial. The cause of this extinction has been debated for many years but remains highly controversial in part because of limitations of available data, but also because

L. Becker; R. Poreda; J. Kennett; W. Wolbach

2007-01-01

72

Pleistocene drainage incision in the upper Mississippi Valley Driftless Area  

Microsoft Academic Search

The deep dissection of the Wisconsin Driftless Area and topographically similar, but glaciated areas in adjacent states is generally acknowledged to have occurred during the Pleistocene, but the precise chronology has been poorly understood. The distribution of pre-Illinoian glacial outwash gravels on uplands and valley side benches near the Mississippi River, on the western margin of the Wisconsin Driftless Area,

Knox

1985-01-01

73

A Phylogeographic Study of the Tiger (Panthera tigris): Using Holocene Distribution Models to Assess Late Pleistocene Range Shifts   

E-print Network

Assessing tiger distributions through the Late Pleistocene can provide insight to the evolutionary histories of currently recognized tiger subspecies. If global tiger ranges have been continuous, and not sufficiently isolated through glacial...

Cooper, David Matthew

2013-11-28

74

The Role of Glacial Erosion in Limiting Ice Sheet Extents  

NASA Astrophysics Data System (ADS)

We aim to identify and quantify feedbacks between ice dynamics and glacial erosion. Whilst geological and geomorphological evidence indicates that ice sheets generally oscillate in time with orbital forcing, their extents are not necessarily a direct function of the amplitude of this forcing. Benthic ?18O records document glacial-interglacial fluctuations and indicate that maximum Pleistocene global ice volume occurs around 400 ka. However, geomorphological evidence in a number of regions is contradictory, with the most extensive ice masses often occurring 100's of kyrs prior to peaks in the ?18O record. For example, the glacial landforms of Patagonia preserve a record of just such behaviour with each successive glacial advance since 1.15 Ma covering an area less extensive than the previous expansion. This implies that other processes are modifying the linkages between ice sheets and climate. We ask: Could glacial erosion of bedrock have caused ice sheets to self-regulate their extents? Ground-breaking experiments by Oerlemans (1984) demonstrated that erosion induced margin retreat was indeed possible. He showed that retreat could be achieved but only where eroding ice streams were smaller in width than the wavelength of lithospheric response. In Patagonia however, the scales of retreat are much larger than this lithospheric wavelength - but could erosion still be an important factor? We use the GLIMMER 3-D thermomechanical ice sheet model (Payne, 1999) with an added erosion component to simulate long-term landscape evolution under theoretical ice sheets (Jamieson et al., 2007). We show that models of glacial erosion can generate feedbacks on a significant scale such that ice sheets can self-limit their extents over periods of 105 - 106 years regardless of the flexural response of the land surface. Erosion around the ELA enables increasingly efficient ice drainage, and the mass balance of the ice sheet thus shifts towards a more negative state. At the same time, the thermal regime of the ice alters and the drawdown and capture of warm ice into 'streams' causes more focussed selective erosion. The main control on the pattern of retreat is the pre-existing topography, which strongly controls erosion patterns. Ice streams retreat progressively in response to lowering valley floors and the impact of erosion induced self-limiting remains over successive glacial cycles. References: Jamieson, S.S.R., Hulton, N.R.J. and Hagdorn, M., 2007. Modelling landscape evolution under ice sheets. Geomorphology, doi:10.1016/j.geomorph.2007.02.047. Oerlemans, J., 1984. Numerical experiments on large-scale glacial erosion. Zeitschrift fur Gletscherkunde und Glazialgeologie, 20: 107-126. Payne, A.J., 1999. A thermomechanical model of ice flow in West Antarctica. Climate Dynamics, 15(2): 115-125.

Jamieson, S.; Hulton, N.

2007-12-01

75

A major change in North Atlantic deep water circulation during the Early Pleistocene transition 1.6 million years ago  

NASA Astrophysics Data System (ADS)

The global ocean-climate system has been highly sensitive to the formation and advection of deep water in the North Atlantic but its evolution over the Pliocene-Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters are not well constrained. Here we present new records of the bottom-water radiogenic neodymium isotope (ϵNd) variability obtained from three DSDP/ODP sites at water depths between 2100 and 5000 m in the Northeast Atlantic to reconstruct changes in deep water circulation over the past 4 million years. Prior to 1.6 million years ago (Ma), we find ϵNd values primarily oscillating between -9 and -11 at all sites, consistent with enhanced vertical mixing of water masses. At 1.6 Ma, the ϵNd signatures synchronously shifted to less radiogenic values around -12 at different water depths and water mass signatures gradually became more distinct. Since then values and amplitudes of "glacial/interglacial" ϵNd oscillations have been similar to the Late Quaternary at each site. This change 1.6 Ma reflects a major reorganization of deep water circulation in the Northeast Atlantic towards a more stratified water column with distinct water masses accompanying the enhanced response of climate to the Earth's obliquity forcing during the Early Pleistocene transition.

Khélifi, N.; Frank, M.

2013-12-01

76

Late Pleistocene dune activity in the central Great Plains, USA  

NASA Astrophysics Data System (ADS)

Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of cold, short growing seasons with relatively low precipitation and low atmospheric CO 2 that increased plant moisture stress, limiting the ability of vegetation to stabilize active dune sand. The apparent coexistence of large mobile dunes with boreal forest taxa suggests a Late Pleistocene environment with few modern analogs.

Mason, J. A.; Swinehart, J. B.; Hanson, P. R.; Loope, D. B.; Goble, R. J.; Miao, X.; Schmeisser, R. L.

2011-12-01

77

Viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern Cascadia subduction zone, British Columbia, Canada  

Microsoft Academic Search

Late glacial sea level curves located in the Cascadia subduction zone (CSZ) fore arc in southwestern British Columbia show that glacial isostatic adjustment (GIA) was rapid when the Cordilleran Ice Sheet collapsed in the late Pleistocene. GIA modeling with a linear Maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses, provided

Thomas S. James; Evan J. Gowan; Ikuko Wada; Kelin Wang

2009-01-01

78

Effects of extreme climate change on the erosion of non glaciated Alpine catchments during a glacial cycle  

Microsoft Academic Search

The European Alps were largely covered by ice during full glacial conditions of the Pleistocene. Nevertheless, large parts of the southwestern and eastern Alps remained unglaciated or covered only by small valley glaciers during glacials. The impact of a climatic decline of such a dimension on fluvially dominated catchments is not clear so far. Lake infillings may give precise information

Bernhard Salcher; Johanna Lomax; Florian Kober; Michael Wagreich

2010-01-01

79

Late Pleistocene loess-palaeosol sequences in the Vojvodina region, north Serbia  

Microsoft Academic Search

Late Pleistocene loess-palaeosol sequences are widespread in the Vojvodina region, with thicknesses reaching a maximum of about 20 m. Our investigations include more than 40 of these loess sections. Geochronology of the last glacial loess-palaeosol sequences, based on lumines- cence dating and amino acid racemisation, provides correlations between Upper Pleistocene loess-palaeosol sediments in Vojvodina and comparable deposits at other European

Slobodan B. Markovic; Mark P. Bokhorst; Jef Vandenberghe; William D. McCoy; Eric A. Oches; Urlich Hambach; Tivadar Gaudenyi; Mladjen Jovanovic; Ludwig Zöller; Thomas Stevens; Björn Machalett

2008-01-01

80

People of the ancient rainforest: Late Pleistocene foragers at the Batadomba-lena rockshelter, Sri Lanka  

Microsoft Academic Search

Batadomba-lena, a rockshelter in the rainforest of southwestern Sri Lanka, has yielded some of the earliest evidence of Homo sapiens in South Asia. H. sapiens foragers were present at Batadomba-lena from ca. 36,000 cal BP to the terminal Pleistocene and Holocene. Human occupation was sporadic before the global Last Glacial Maximum (LGM). Batadomba-lena’s Late Pleistocene inhabitants foraged for a broad spectrum of plant

Nimal Perera; Nikos Kourampas; Ian A. Simpson; Siran U. Deraniyagala; David Bulbeck; Johan Kamminga; Jude Perera; Dorian Q. Fuller; Katherine Szabó; Nuno V. Oliveira

2011-01-01

81

Antemortem trauma and survival in the late Middle Pleistocene human cranium from Maba, South China  

PubMed Central

Paleopathological assessment of the late Middle Pleistocene archaic human cranium from Maba, South China, has documented a right frontal squamous exocranially concave and ridged lesion with endocranial protrusion. Differential diagnosis indicates that it resulted from localized blunt force trauma, due to an accident or, more probably, interhuman aggression. As such it joins a small sample of pre-last glacial maximum Pleistocene human remains with probable evidence of humanly induced trauma. Its remodeled condition also indicates survival of a serious pathological condition, a circumstance that is increasingly documented for archaic and modern Homo through the Pleistocene. PMID:22106311

Wu, Xiu-Jie; Schepartz, Lynne A.; Liu, Wu; Trinkaus, Erik

2011-01-01

82

Pleistocene and Holocene Iberian flora: a complete picture and review  

NASA Astrophysics Data System (ADS)

A detailed analysis of the location and composition of Iberian vegetation types during the whole Pleistocene and Holocene periods shows a complex patched landscape with persistence of different types of ecosystems, even during glacial times. In addition, recent, high-resolution palaeoecological records are changing the traditional picture of post-glacial vegetation succession in the Iberian Peninsula. The main available charcoal and pollen sequences include, coniferous and deciduous forest, steppes, shrublands, savannahs and glacial refugia during the Pleistocene for Meso-thermophytes (phytodiversity reservoirs), in different proportions. This panorama suggests an environmental complexity that relates biotic responses to climate changes forced by Milankovitch cycles, suborbital forcings and by the latitudinal and physiographic particularities of the Iberian Peninsula. Thus, many factors are critical in the course of vegetational developments and strong regional differences are observed since the Early Pleistocene. Currently, the flora of Iberia is located in two biogeographical/climatic regions: the Eurosiberian and the Mediterranean. The first one includes northern and northwestern areas of the peninsula, where post-glacial responses of vegetation are very similar to Central Europe, although with some particularities due to its proximity to both the Atlantic Ocean and the Mediterranean region. The second one comprises the main territory of Iberia and shows more complex patterns and singularities, now and in the past. Steppe landscapes dominated extensive areas over all the territory during the cold spells of the Quaternary, especially during the Late Pleistocene up to the Last Glacial Maximum, but differences in composition of the dominant taxa (Compositae versus Artemisia) are observed since the Early Pleistocene, probably related to moisture regional gradients. Coastal shelves and intramountainous valleys, even in continental areas, are spots of floristic diversity and nuclei of population expansion during climatic ameliorations of the Pleistocene. The floristic composition, location and structure of glacial tree populations and communities may have been a primary control on these developments and on the origin and composition of Holocene scenarios. Refugial populations would have been a source, but not the only one, for the early Lateglacial oak expansions for example. From Middle to Late Holocene, inertial, resilient, and rapid responses of vegetation to climatic change are described, any time with regional and local differences. The role of fire, pastoralism, agriculture and other anthropogenic disturbances such as mining during the Copper, Bronze, Iberic, and Roman times must be also considered as an important factor of the current vegetation distribution. In fact, the Iberian Peninsula constitutes a territory where climatic, geological, biogeographical and historical conditions have converged to produce environmental heterogeneity, large biological diversity and ecosystem richness. A note of singularity: in comparison with other Mediterranean peninsulas, Iberia was, doubtless, particularly suitable for the survival and permanence of sclerophyllous elements of any kind (including Ibero-Maghrebian scrubs such as Maytenus, Periploca, Ziziphus,Withania, Lycium, and Calicotome), currently, during the Holocene, and even during glacial stages of the Pleistocene. However, no macro-remains of these taxa have been documented until Late Holocene chronologies, but the survival of other thermophilous species, such as Olea, reveals the existence of glacial refugia in the southernmost areas of Iberia. Over all, and dealing with plant species, the Iberian Peninsula is a land of survival.

González Sampériz, Penélope

2010-05-01

83

The glacial history of the Dinaric Alps, Montenegro  

NASA Astrophysics Data System (ADS)

Large areas of Montenegro were glaciated during the Pleistocene. This paper presents evidence from the massifs of central Montenegro, including Durmitor and Sinjajevina, Mora?ke Planine, Maganik, Prekornica and Vojnik. Glacial deposits have been subdivided on the basis of morphostratigraphy and soil weathering and 31 U-series ages from cemented tills provided a geochronological framework. The largest glaciation occurred before 350 ka when a series of conjoined ice caps over the massifs of central Montenegro covered a total area of nearly 1500 km 2. These formed during MIS 12 and correspond with the largest Skamnellian Stage glaciations in Greece to the south. Later Middle Pleistocene glaciations occurred during the penultimate glacial cycle correlating with the Vlasian Stage in Greece (MIS 6) when ice caps covered an area of 720 km 2 over central Montenegro. There is also geochronological evidence of glacial deposits dating from the interval between MIS 12 and MIS 6, before the interglacial complex of MIS 7. This glaciation appears to have been very similar in extent to that which occurred during MIS 6. The last glacial cycle in central Montenegro was characterised by valley and cirque glaciers covering a total area of 49 km 2. It is very likely that glaciers have been present in the mountains of central Montenegro during every glacial cycle since a small glacier still survives today. The smaller glaciers of the last glacial cycle are likely to have been associated with summer temperatures that were warmer than those of earlier cold stages. The striking contrast in the extent and thickness of ice cover during the cold stages of the Pleistocene has an important bearing on the geomorphological and biological evolution of the Balkans.

Hughes, P. D.; Woodward, J. C.; van Calsteren, P. C.; Thomas, L. E.

2011-11-01

84

Synchronous, high-frequency oscillations in tropical sea surface temperatures and North Atlantic Deep Water production during the Last Glacial Cycle  

Microsoft Academic Search

Stable isotopic measurements of G. sacculifer and C. wuellerstorfi in a core from the western equatorial Atlantic imply that there are parallel, suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3. Low values of G. sacculifer ?18O accompany high values of C. wuellerstorfi ?13C, linking warmer sea surface temperatures (SSTs) in

W. B. Curry; D. W. Oppo

1997-01-01

85

Synchronous, high-frequency oscillations in tropical sea surface temperatures and North Atlantic Deep Water production during the last glacial cycle  

Microsoft Academic Search

Stable isotopic measurements of G. sacculifer and C. wuellerstorfi in a core from the western equatorial Atlantic imply that there are parallel, suborbital oscillations in surface water hydrography and deep water circulation occurring during oxygen isotope stages 2 and 3. Low values of G. sacculifer delta18O accompany high values of C. wuellerstorfi delta13C, linking warmer sea surface temperatures (SSTs) in

W. B. Curry; D. W. Oppo

1997-01-01

86

Spawning sockeye salmon fossils in Pleistocene lake beds of Skokomish Valley, Washington  

Microsoft Academic Search

An assemblage of fossil sockeye salmon was discovered in Pleistocene lake sediments along the South Fork Skokomish River, Olympic Peninsula, Washington. The fossils were abundant near the head of a former glacial lake at 115 m elevation. Large adult salmon are concentrated in a sequence of death assemblages that include individuals with enlarged breeding teeth and worn caudal fins indicating migration,

Gerald R. Smith; David R. Montgomery; N. Phil Peterson; Bruce Crowley

2007-01-01

87

Late Pleistocene Variations in Oxygen Minimum Zone: Southern California Margin  

NASA Astrophysics Data System (ADS)

Oceanic carbon cycling is strongly influenced by the Oxygen Minimum Zone (OMZ). Studies of sediments from ODP Sites 893 (~595m) and 1017 (~955m) demonstrate that the strength of the OMZ off the Southern California margin (between ~500 and ~1000m) has fluctuated on orbital and millennial time scales during the late Pleistocene, affecting the preservation of organic carbon in marine sediments. Existing records do not adequately describe the history over the depth range of the OMZ. To augment the existing depth transect, we generated oxygen isotope and benthic foraminiferal assemblage records from core NBP0206 JPC1 (755m) located near the center of the OMZ. The chronology for this core was determined using radiocarbon analyses and oxygen isotope stratigraphy. The planktonic d18O record correlates well with the orbital and millennial- scale fluctuations recorded in nearby ODP Holes 893 and 1017. Benthic d18O data reflect orbital variations in upper intermediate waters, including a decrease of 1.6 ‰ across the last glacial termination, implying a temperature increase of 1-2 deg C (after ice volume correction). The millennial scale isotopic oscillations recorded in Hole 893 are absent here. Benthic foraminiferal assemblages are sensitive recorders of bottom water oxygenation. On orbital time scales, the fauna record an oxic Marine Isotope Stage 3 and Last Glacial Interval (LGI), and a dysoxic Holocene, supporting previous interpretations of orbital scale ventilation changes in intermediate water depths. The benthic assemblages record as low oxygen intervals 9 of the 13 interstadials of the last 50ka. An absence of associated changes in the benthic d18O on millennial scales implies that the low oxygen interstadials largely reflect changes in surface productivity, similar to those seen at Hole 1017. Millennial scale intermediate water ventilation changes, as interpreted in Hole 893, occurred above the depth of this core. During the LGI and the stadials of MIS 3, the OMZ appears to have entirely disappeared on the Southern California margin. This has major implications for the cycling of oceanic carbon.

Murphy, D. P.; Kennett, J. P.; Southon, J. R.

2006-12-01

88

Glaciers and rivers: Pleistocene uncoupling in a Mediterranean mountain karst  

NASA Astrophysics Data System (ADS)

Large-scale coupling between headwater catchments and downstream depocentres is a critical influence on long-term fluvial system behaviour and on the creation of the fluvial sedimentary record. However, it is often difficult to examine this control over multiple Quaternary glacial cycles and it has not been fully explored in karst basins. By investigating the Pleistocene glacial and fluvial records on and around Mount Orjen (1894 m) in Montenegro, we show how the changing connectivity between glaciated mountain headwater source zones and downstream alluvial basins is a key feature of long-term karst system behaviour - especially in relation to the creation and preservation of the surface sedimentary record. Middle and Late Pleistocene glacial deposits are well preserved on Mount Orjen. Uranium-series dating of 27 carbonate cements in fluvial sediments shows that many alluvial depocentres were completely filled with coarse glacial outwash before 350 ka during the largest recorded glaciation. This major glaciation is correlated with the Skamnellian Stage in Greece and Marine Isotope Stage 12 (MIS 12, c 480-420 ka). This was a period of profound landscape change in many glaciated catchments on the Balkan Peninsula. Later glaciations were much less extensive and sediment supply to fluvial systems was much diminished. The extreme base level falls of the Late Miocene produced the world's deepest karst networks around the Mediterranean. After MIS 12, the subterranean karst of Mount Orjen formed the dominant pathway for meltwater and sediment transfer so that the depositional basins below 1000 m became disconnected (uncoupled) from the glaciated headwaters. There is little evidence of post-MIS 12 aggradation or incision in these basins. This absence of later Pleistocene and Holocene fluvial activity means these basins contain some of the thickest and best-preserved outwash deposits in the Mediterranean.

Adamson, K. R.; Woodward, J. C.; Hughes, P. D.

2014-06-01

89

Palynology and age of the Tadmor Group (Late Miocene-Pliocene) and Porika Formation (early Pleistocene), South Island, New Zealand  

Microsoft Academic Search

The Porika Formation, type formation of the Porikan glacial stage, contains palynomorphs of early Pleistocene (Hautawan) age. The underlying Tadmor Group consists of the Moutere Gravel overlying the Glenhope Formation. Palynomorphs from the Moutere Gravel are assigned to the Waipipian-Hautawan (middle Pliocene-early Pleistocene) and from the Glenhope Formation are assigned to the ?Kapitean-Opoitian (Late Miocene-Early Pliocene), although basal beds may

D. C. Mildenhall; R. P. Suggate

1981-01-01

90

Late Pleistocene deposits at Wing, Rutland.  

PubMed

The context, lithostratigraphy and biostratigraphy of a series of Pleistocene deposits from Wing, Rutland, in the East Midlands of England are described. The sequence of till, lake clays, compressed wood and moss peats and peaty silts is shown to occupy a small, closed basin cut deeply into the Jurassic bedrock. The basin appears to have been excavated by ice responsible for the deposition of Chalky Jurassic Till in the area, and this till lines the floor and sides of the basin. Pollen and plant macrofossil analyses have provided a long and continuous record of vegetational and environmental history at the site and the deposits have been dated by pollen analysis to the Last (Ipswichian) Interglacial and early Devensian Glacial stages (pollen zones Ip IIb to e De). With certain reservations, the sequence is compared and correlated with other interglacial deposits in Britain. PMID:6104827

Hall, A R

1980-05-01

91

The integration of multiple independent data reveals an unusual response to Pleistocene climatic changes in the hard tick Ixodes ricinus.  

PubMed

In the last few years, improved analytical tools and the integration of genetic data with multiple sources of information have shown that temperate species exhibited more complex responses to ice ages than previously thought. In this study, we investigated how Pleistocene climatic changes affected the current distribution and genetic diversity of European populations of the tick Ixodes ricinus, an ectoparasite with high ecological plasticity. We first used mitochondrial and nuclear genetic markers to investigate the phylogeographic structure of the species and its Pleistocene history using coalescent-based methods; then we used species distribution modelling to infer the climatic niche of the species at last glacial maximum; finally, we reviewed the literature on the I. ricinus hosts to identify the locations of their glacial refugia. Our results support the scenario that during the last glacial phase, I. ricinus never experienced a prolonged allopatric divergence in separate glacial refugia, but persisted with interconnected populations across Southern and Central Europe. The generalist behaviour in host choice of I. ricinus would have played a major role in maintaining connections between its populations. Although most of the hosts persisted in separate refugia, from the point of view of I. ricinus, they represented a continuity of 'bridges' among populations. Our study highlights the importance of species-specific ecology in affecting responses to Pleistocene glacial-interglacial cycles. Together with other cases in Europe and elsewhere, it contributes to setting new hypotheses on how species with wide ecological plasticity coped with Pleistocene climatic changes. PMID:23398505

Porretta, Daniele; Mastrantonio, Valentina; Mona, Stefano; Epis, Sara; Montagna, Matteo; Sassera, Davide; Bandi, Claudio; Urbanelli, Sandra

2013-03-01

92

Damping of glacial-interglacial cycles from anthropogenic forcing  

E-print Network

Climate variability over the past million years shows a strong glacial-interglacial cycle of ~100,000 years as a combined result of Milankovitch orbital forcing and climatic resonance. It has been suggested that anthropogenic contributions to radiative forcing may extend the length of the present interglacial, but the effects of anthropogenic forcing on the periodicity of glacial-interglacial cycles has received little attention. Here I demonstrate that moderate anthropogenic forcing can act to damp this 100,000 year cycle and reduce climate variability from orbital forcing. Future changes in solar insolation alone will continue to drive a 100,000 year climate cycle over the next million years, but the presence of anthropogenic warming can force the climate into an ice-free state that only weakly responds to orbital forcing. Sufficiently strong anthropogenic forcing that eliminates the glacial-interglacial cycle may serve as an indication of an epoch transition from the Pleistocene to the Anthropocene.

Haqq-Misra, Jacob

2014-01-01

93

Late Pleistocene vegetation of Kings Canyon, Sierra Nevada, California  

NASA Astrophysics Data System (ADS)

Seven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers Juniperus occidentalis, Pinus cf. ponderosa, and P. monophylla. The pollen spectra of these Pleistocene middens are dominated by Pinus sp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), and Artemisia sp. Mesophytic conifers are represented by low macrofossil concentrations. Sequoiadendron giganteum is represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages. The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest that S. giganteum grew at lower elevations along the western side of the range and that P. monophylla was more widely distributed in cismontane California during the Pleistocene.

Cole, Kenneth

1983-01-01

94

Testing hypotheses of Pleistocene population history using coalescent simulations: phylogeography of the pygmy nuthatch (Sitta pygmaea)  

PubMed Central

In this paper, we use mitochondrial NADH dehydrogenase subunit 2 sequences to test Pleistocene refugial hypotheses for the pygmy nuthatch (Sitta pygmaea). Pygmy nuthatches are a common resident of long-needle pine forests in western North America and demonstrate a particular affinity with ponderosa pine (Pinus ponderosa). Palaeoecological and genetic data indicate that ponderosa pine was isolated in two Pleistocene refugia corresponding to areas in the southern Sierra Nevada in the west and southern Arizona and New Mexico in the east. We use coalescent simulations to test the hypothesis that pygmy nuthatches tracked the Pleistocene history of their preferred habitat and persisted in two refugia during the periods of glacial maxima. Coalescent simulation of population history does not support the hypothesis of two Pleistocene refugia for the pygmy nuthatch. Instead, our data are consistent with a single refuge model. Nucleotide diversity is greatest in the western populations of southern and coastal California. We suggest that the pygmy nuthatch expanded from a far western glacial refuge into its current distribution since the most recent glacial maximum. PMID:17015345

Spellman, Garth M; Klicka, John

2006-01-01

95

Testing hypotheses of Pleistocene population history using coalescent simulations: phylogeography of the pygmy nuthatch (Sitta pygmaea).  

PubMed

In this paper, we use mitochondrial NADH dehydrogenase subunit 2 sequences to test Pleistocene refugial hypotheses for the pygmy nuthatch (Sitta pygmaea). Pygmy nuthatches are a common resident of long-needle pine forests in western North America and demonstrate a particular affinity with ponderosa pine (Pinus ponderosa). Palaeoecological and genetic data indicate that ponderosa pine was isolated in two Pleistocene refugia corresponding to areas in the southern Sierra Nevada in the west and southern Arizona and New Mexico in the east. We use coalescent simulations to test the hypothesis that pygmy nuthatches tracked the Pleistocene history of their preferred habitat and persisted in two refugia during the periods of glacial maxima. Coalescent simulation of population history does not support the hypothesis of two Pleistocene refugia for the pygmy nuthatch. Instead, our data are consistent with a single refuge model. Nucleotide diversity is greatest in the western populations of southern and coastal California. We suggest that the pygmy nuthatch expanded from a far western glacial refuge into its current distribution since the most recent glacial maximum. PMID:17015345

Spellman, Garth M; Klicka, John

2006-12-22

96

Phylogeographic heterogeneity of the brown macroalga Sargassum horneri (Fucaceae) in the northwestern Pacific in relation to late Pleistocene glaciation and tectonic configurations.  

PubMed

Pleistocene glacial oscillations and associated tectonic processes are believed to have influenced the historical abundances and distribution of organisms in the Asia Northwest Pacific (ANP). Accumulating evidence indicates that factors shaping tempospatial population dynamics and distribution patterns of marine taxa vary with biogeographical latitude, pelagic behaviour and oceanographic regimes. To detect what kinds of historical and contemporary factors affected genetic connectivity, phylogeographic profiles of littoral macroalga Sargassum horneri in the ANP were analysed based on mitochondrial (Cox3) and chloroplast (rbcL) data sets. Five distinct clades were recovered. A strong signature of biogeographical structure was revealed (?(CT) = 0.487, P < 0.0001) derived from remarkable differentiation in clade distribution, as clade I is restricted to Chinese marginal seas (Yellow-Bohai Sea, East China Sea and South China Sea), whereas clades II-V are discontinuously scattered around the main Islands of Japan. Furthermore, two secondary contact regions were identified along the south Japan-Pacific coastline. This significant differentiation between the two basins may reflect historical glacial isolation in the northwestern Pacific, which is congruent with the estimates of clade divergence and demographic expansion during the late Quaternary low sea levels. Analysis of molecular variance and the population-pair statistic F(ST) also revealed significant genetic structural differences between Chinese marginal seas and the Japanese basin. This exceptional phylogeographic architecture in S. horneri, initially shaped by historical geographic isolation during the late Pleistocene ice age and physical biogeographical barriers, can be complicated by oceanographic regimes (ocean surface currents) and relocating behaviour such as oceanic drifting. PMID:21851438

Hu, Zi-Min; Uwai, Shinya; Yu, Shen-Hui; Komatsu, Teruhisa; Ajisaka, Tetsuro; Duan, De-Lin

2011-09-01

97

Terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the Himalayan orogen: Ladakh Range, northern India  

USGS Publications Warehouse

Terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the Ladakh Range of the Transhimalaya. The glacial stages that have been identified are: the Indus Valley glacial stage, dated at older than 430 ka; the Leh glacial stage occurring in the penultimate glacial cycle or older; the Karglacial stage, occurring during the early part of the last glacial cycle; the Bazgo glacial stage, at its maximum during the middle of the last glacial cycle; and the early Holocene Khalling glacial stage. The exposure ages of the Indus Valley moraines are the oldest observed to date throughout the Himalayan orogen. We observe a pattern of progressively more restricted glaciation during the last five glacial cycles, likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation. A possible explanation is that uplift of Himalayan ranges to the south and/or of the Karakoram Mountains to the west of the region may have effectively blocked moisture supply by the south Asian summer monsoon and mid-latitude westerlies, respectively. Alternatively, this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the Pleistocene. ?? 2006 Geological Society of America.

Owen, L.A.; Caffee, M.W.; Bovard, K.R.; Finkel, R.C.; Sharma, M.C.

2006-01-01

98

Deep-sea pleistocene biostratigraphy.  

PubMed

The first detailed paleontological analysis of a deep-sea pistoncore from the Caribbean Sea has been completed. The core, P6304-8, was raised from 3927 meters, east of Beata Ridge at 14 degrees 59'N, 69 degrees 20'W. Formerly, stratigraphic works in this area were based on studies of paleotemperature, measured by the oxygen isotope mass spectrometry method, or on micropaleontological analysis by means of rapid or cursory examinations. For core P6304-8, samples for foraminiferal analysis were taken at 10-centimeter intervals and split into smaller samples containing an average of 710 individuals (smallest sample, 517 individuals); all individuals were then identified and counted. By use of data derived from populations of this size, a statistical reliability was insured within a 5 percent limnit. Temperature oscillations, the best method of portraying Pleistocene stratigraphy, were shown by using ratios of the relative abundances of tropical and subtropical planktonic foraminifera to those found in temperate and cooler waters. These ratios correlate well with existing paleotemperature measurements for the same core, obtained by the oxygen isotope mass spectrometry method. PMID:17821563

Lidz, L

1966-12-16

99

The role of deep ocean circulation in setting glacial climates  

NASA Astrophysics Data System (ADS)

The glacial cycles of the Pleistocene involve changes in the circulation of the deep ocean in important ways. This review seeks to establish what were the robust patterns of deep-sea water mass changes and how they might have influenced important parts of the last glacial cycle. After a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses, I examine the data for biogeochemical, circulation rate, and conservative tracers during glacial climates. Some of the robust results from the literature of the last 30 years include: a shoaled version of northern source deep water in the Atlantic, expanded southern source water in the abyss and deep ocean, salt (rather than heat) stratification of the last glacial maximum (LGM) deep-sea, and several lines of evidence for slower overturning circulation in the southern deep cell. We combine these observations into a new idea for how the ocean-atmosphere system moves from interglacial to glacial periods across a single cycle. By virtue of its influence on the melting of land-based ice around Antarctica, cooling North Atlantic Deep Water (NADW) leads to a cold and salty version of Antarctic Bottom Water (AABW). This previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern, helping to lower atmospheric CO2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling.

Adkins, Jess F.

2013-09-01

100

Glacial-interglacial modulation of eastern tropical North Pacific denitrification over the last 1.8-Myr  

NASA Astrophysics Data System (ADS)

A 1.8 Myr-long ?15N record from the California margin provides the first continuous record of denitrification in the Eastern Tropical North Pacific (ETNP) over the entire Pleistocene epoch. Comparison of the nitrogen isotopic time series with proxies for ice volume, sea surface temperature (SST), and biological productivity place variations in the intensity of the denitrification zone in the context of global and regional climatic changes. Throughout the Pleistocene, ETNP denitrification remained linked to glacial-interglacial climate cycles. The pacing of denitrification cycles switched from 41-kyr in the mid- to early Pleistocene to 100-kyr in the late Pleistocene, in tandem with the well-known frequency shift identified from ice volume records. It therefore appears that denitrification remained an integral component of the marine feedbacks to orbital forcing, and through its effect on the nitrate inventory of the ocean might have played a role in driving atmospheric CO2 cycles throughout the Pleistocene.

Liu, Zhonghui; Altabet, Mark A.; Herbert, Timothy D.

2005-12-01

101

Glacial Lake Hides Bacteria  

NSDL National Science Digital Library

This article highlights the published work of a geomicrobiology research team led by Eric Gaidos from the University of Hawaii and Brian Lanoil, from the University of California, Riverside. This group reports the identification of bacteria from an Icelandic sub-glacial lake, and how the collection and description of these microorganisms immured within glacial ice and sub-surface water serve as a model in the search for extra-terrestrial life.

Peplow, Mark

2010-03-01

102

Glacial lake hides bacteria  

NSDL National Science Digital Library

This article highlights the published work of a geomicrobiology research team led by Eric Gaidos from the University of Hawaii and Brian Lanoil, from the University of California, Riverside. This group reports the identification of bacteria from an Icelandic sub-glacial lake, and how the collection and description of these microorganisms immured within glacial ice and sub-surface water serve as a model in the search for extra-terrestrial life.

Peplow, Mark; Online, Bioed

103

Mid-Pleistocene Orbital and Millennial Scale Climate Change in a 200 ky lacustrine sediment core from SW North America  

NASA Astrophysics Data System (ADS)

How anthropogenic climate change will affect hydroclimate of the arid regions of SW North America over the next century is a concern. Model projections suggest permanent “dust bowl-like” conditions; however, any anthropogenic change will be superimposed on long-term natural climate variability. We use the paleoclimatic record from an 82-m deep lacustrine sediment core (VC-3) from the Valles Caldera, New Mexico to examine continental climate variations spanning two glacial cycles through the middle Pleistocene from MIS 14 to MIS 10 (552 ka to ~360 ka). Both orbital and millennial-scale variations are evident in multiple proxies, and a strong relationship occurs between the warmest temperatures in the record and periods of extended aridity. We suggest that these periods of aridity are characterized by decreased winter as well as summer precipitation amounts. A new group of organic geochemical proxies (MBT and CBT) allow us to reconstruct the annual mean air temperature (MAT) of the Valles Caldera watershed as well as the watershed soil pH down the length of the core. We compare these proxies to climatically sensitive pollen taxa and other core properties. The MAT record of VC-3 shows considerable glacial-interglacial variation and significant variability within individual glacial and interglacial periods. The warmest interglacial MATs (5 to 7°C) compare favorably with modern MATs of ~5°C in the Valle Grande. MIS 11 has three warm substages, based on MAT estimates (2°C warmer than the cool substages), warm (Juniperus, Quercus, Rosaceae) vs. cool (Abies, Picea, Artemisia) pollen taxa and variation in aquatic productivity proxies (TOC, Si:Ti). The three warm substages of MIS 11 appear to correspond to the three precessional peaks that occur during this interval. Glacial MATs range from -5 to +2°C, with multiple millennial-scale temperature oscillations evident. Several of the interstadials show a distinct pattern of relatively slower temperature increases and progressive declines in cold boreal taxa pollen percentages (Picea, Abies), while others are characterized by abrupt warmings and decreases in boreal taxa pollen. Maximum interstadial temperatures are followed by abrupt coolings of as much as 6 to 7°C, and rapid increases in Picea and Abies pollen. These results show that the continental climate of SW North America had a strong response to millennial-scale climate change as well as to orbital forcing, even during a time of muted precessional cycles (MIS 11).

Fawcett, P. J.; Werne, J. P.; Anderson, R. S.; Heikoop, J. M.; Brown, E. T.; Berke, M. A.; Smith, S.; Goff, F. E.; Hurley, L. L.; Cisneros Dozal, L. M.; Schouten, S.; Sinninghe Damsté, J. S.; Huang, Y.; Toney, J. L.; Fessenden, J. E.; Woldegabriel, G. W.; Geissman, J. W.; Allen, C. D.

2009-12-01

104

Pleistocene geomorphology and geochronology of eastern Grand Canyon: linkages of landscape components during climate changes  

Microsoft Academic Search

We report new mapping, soils, survey, and geochronologic (luminescence, U-series, and cosmogenic-nuclide) data from Pleistocene deposits in the arid setting of eastern Grand Canyon. The result is a stratigraphic framework of inset fill gravels and associated terraces that provide a record of the responses of hillslopes, tributary streams, and the Colorado River to the last ?400kyr of glacial–interglacial climate change.

Matt D. Anders; Joel L. Pederson; Tammy M. Rittenour; Warren D. Sharp; John C. Gosse; Karl E. Karlstrom; Laura J. Crossey; Ronald J. Goble; Lisa Stockli; Guang Yang

2005-01-01

105

Alaska PaleoGlacier Atlas: A Geospatial Compilation of Pleistocene Glacier Extents  

NSDL National Science Digital Library

The Alaska PaleoGlacier (APG) Atlas is a recently released, web-based summary of Pleistocene glaciation across Alaska. Students can access a gallery of maps depicting the extent of glaciers during the late Wisconsin glaciation in Alaska as well as the maximum extent reached during the last 3 million years by valley glaciers, ice caps, and the northwestern Cordilleran Ice Sheet. a set of links is also provided to sites on galcial geology and glacial geospatial data.

William Manley

106

Amazonian and neotropical plant communities on glacial time-scales: The failure of the aridity and refuge hypotheses  

Microsoft Academic Search

Plants respond to Pleistocene climatic change as species, not as associations or biomes. This has been demonstrated unequivocally by paleobotanical data for temperate latitudes. In the far richer vegetations of the tropics species populations also fluctuated independently in response to climatic forcing, from their longlasting glacial states to the patterns of brief interglacials like the present and back again. We

P. A. Colinvaux; P. E. De Oliveira; M. B. Bush

2000-01-01

107

Last Glacial and Holocene fluvial wetland sedimentary stratigraphy: Comparison between Soro-ri and Jangheung-ri archeological sites, Korea  

Microsoft Academic Search

Environmental changes in wetlands during the last glacial reflect the fluvial sedimentary sequences of South Korea. The stratigraphy of the latest Pleistocene sequences in several fluvial drainage basins includes organic mud layers, intercalated in fluvial deposits, particularly including those on the Soro-ri and Jangheung-ri sites of the Miho River and Nam River, respectively. Research methods included analyses of sedimentary facies,

Ju Yong Kim; Dong Yoon Yang; Wook Hyun Nahm; Sang Heon Yi; Jeong Chan Kim; Se-Sun Hong; Hyun-Su Yun; Jin Young Lee; Jin-Kwan Kim; Keun-Chang Oh; Don-Won Choi

2008-01-01

108

The bathymetric fabric flanking the East Pacific Rise carries the signature of glacial\\/interglacial changes in sea level (Invited)  

Microsoft Academic Search

We offer a test of the hypothesis that the changes in sea level associated with Pleistocene glaciations influence the magmatic production at mid-ocean ridges. The approximately 100 m variations in sea level associated with glacial\\/interglacial cycles is equivalent to suppressing 30 m of mantle upwelling, given the factor of three difference in density between water and mantle peridotite. If the

P. Huybers; C. H. Langmuir

2009-01-01

109

Glacial integrative modelling.  

PubMed

Understanding the mechanisms of past climate changes requires modelling of the complex interaction between all major components of the Earth system: atmosphere, ocean, cryosphere, lithosphere and biosphere. This paper reviews attempts at such an integrative approach to modelling climate changes during the glacial age. In particular, the roles of different factors in shaping glacial climate are compared based on the results of simulations with an Earth-system model of intermediate complexity, CLIMBER-2. It is shown that ice sheets, changes in atmospheric compositions, vegetation cover, and reorganization of the ocean thermohaline circulation play important roles in glacial climate changes. Another example of this approach is the modelling of two major types of abrupt glacial climate changes: Dansgaard-Oeschger and Heinrich events. Our results corroborate some of the early proposed mechanisms, which relate abrupt climate changes to the internal instability of the ocean thermohaline circulation and ice sheets. At the same time, it is shown that realistic representation of the temporal evolution of the palaeoclimatic background is crucial to simulate observed features of the glacial abrupt climate changes. PMID:14558899

Ganopolski, Andrey

2003-09-15

110

Stratigraphy of Late Pleistocene formations of the Mezen river valley  

NASA Astrophysics Data System (ADS)

Stratigraphy of Late Pleistocene formations of the Mezen river valley A.V. Maksimov, L.R. Semenova A.P. Karpinski All-Russian Geological Research Institute (VSEGEI), St.-Petersburg, Russia In recent years received extensive and contradictory evidence on the genesis, age and area of spreading of quaternary formations in NW Russia. The reason for this - the heterogeneity of investigated objects and methods of research. Within a valley of the river Mezen quaternary sediments are distributed everywhere. In outcrops opened sediments relating to the fifth and sixth stages of Middle Pleistocene, Upper Pleistocene and Holocene. Thickness of the quaternary sediments varies over a wide range, generally increasing from west to east. The authors have studied quaternary formations, opened in outcrops in valley of river Mezen (downstream) and its right tributary Peza, as well as in marine coastal cliffs. The aim of the study was to demonstrate specific features of the lithological composition of quaternary sediments from various (in age and origin) moraine complexes of the Russian NW and to reconstruction of paleogeographic sedimentary environments in the Late Pleistocene. Such attention to glacial sediments was dictated by the fact that they bear the most valuable information pertaining to the type and composition of provenances and to the geodynamic settings of feeding and sedimentation zones. To achieve these goals following tasks were set: 1. Lithostratigraphic subdivision of the section of Quaternary sediments. 2. Correlation of local stratigraphic units with stratigraphic scheme adjacent areas using the geochronological, paleontological and paleoclimatic data. 3. Reconstruction of the main geological events Late Pleistocene NW European part of Russia. First for glacial sediments in valley of the river Mezen applied lithological method, for determining the origin of formations. Was studied lithological composition of the sediments and were correlated geological sections. Also was conducted geochronological research. Based on these results, it was found that: - the glaciers of the Baltic Shield and the Czech lip penetrated into the valley of the river Mezen in Valdai time, forming moraines of different lithology; - sea waters penetrated to the valley of the river Mezen in Leningrad and Mikulino time. In Mikulino time the basin was deeper.

Maksimov, Anton; Semenova, Ljudmila

2014-05-01

111

Ecological structure of recent and last glacial mammalian faunas in northern Eurasia: the case of Altai-Sayan refugium.  

PubMed

Pleistocene mammalian communities display unique features which differ from present-day faunas. The paleocommunities were characterized by the extraordinarily large body size of herbivores and predators and by their unique structure consisting of species now inhabiting geographically and ecologically distinct natural zones. These features were probably the result of the unique environmental conditions of ice age ecosystems. To analyze the ecological structure of Last Glacial and Recent mammal communities we classified the species into biome and trophic-size categories, using Principal Component analysis. We found a marked similarity in ecological structure between Recent eastern Altai-Sayan mammalian assemblages and comparable Pleistocene faunas. The composition of Last Glacial and Recent eastern Altai-Sayan assemblages were characterized by the occurrence of large herbivore and predator species associated with steppe, desert and alpine biomes. These three modern biomes harbor most of the surviving Pleistocene mammals. None of the analyzed Palearctic Last Glacial faunas showed affinity to the temperate forest, taiga, or tundra biome. The Eastern part of the Altai-Sayan region could be considered a refugium of the Last Glacial-like mammalian assemblages. Glacial fauna seems to persist up to present in those areas where the forest belt does not separate alpine vegetation from the steppes and deserts. PMID:24454791

Pavelková ?i?ánková, V?ra; Robovský, Jan; Riegert, Jan

2014-01-01

112

Ecological Structure of Recent and Last Glacial Mammalian Faunas in Northern Eurasia: The Case of Altai-Sayan Refugium  

PubMed Central

Pleistocene mammalian communities display unique features which differ from present-day faunas. The paleocommunities were characterized by the extraordinarily large body size of herbivores and predators and by their unique structure consisting of species now inhabiting geographically and ecologically distinct natural zones. These features were probably the result of the unique environmental conditions of ice age ecosystems. To analyze the ecological structure of Last Glacial and Recent mammal communities we classified the species into biome and trophic-size categories, using Principal Component analysis. We found a marked similarity in ecological structure between Recent eastern Altai-Sayan mammalian assemblages and comparable Pleistocene faunas. The composition of Last Glacial and Recent eastern Altai-Sayan assemblages were characterized by the occurrence of large herbivore and predator species associated with steppe, desert and alpine biomes. These three modern biomes harbor most of the surviving Pleistocene mammals. None of the analyzed Palearctic Last Glacial faunas showed affinity to the temperate forest, taiga, or tundra biome. The Eastern part of the Altai-Sayan region could be considered a refugium of the Last Glacial-like mammalian assemblages. Glacial fauna seems to persist up to present in those areas where the forest belt does not separate alpine vegetation from the steppes and deserts. PMID:24454791

Pavelková ?i?ánková, V?ra; Robovský, Jan; Riegert, Jan

2014-01-01

113

Insights into the western tropical Pacific's role in late Pleistocene hydroclimate variability: 160ky Borneo stalagmite ?18O record (Invited)  

NASA Astrophysics Data System (ADS)

The presence of multiple physical mechanisms at play throughout the Late Pleistocene makes it difficult to confidently attribute climate variability to particular forcings. The tropical Pacific's role in past climate change is especially ambiguous because most tropical records lack the resolution, length, and chronological control to completely resolve rapid variability - including abrupt climate change events, ice age terminations, and sea level shifts - against a background of orbital-scale variations. Stalagmites from Gunung Mulu, located in northern Borneo, allow for the construction of reproducible centennial-scale records of hydrologic variability that are precisely-dated and continuous throughout most of the late Pleistocene. Comparison of such records to other regional and global paleorecords as well as relevant simulations from numerical climate models provide valuable insights into the mechanisms responsible for western tropical Pacific hydroclimate variability on centennial to multi-millennial scales. Here we present a large compilation of overlapping U/Th-dated Gunung Mulu stalagmite ?18O records spanning the last 160ky. The composite records demonstrate the complex response of northern Borneo convection to both high-latitude and low-latitude forcings and external insolation. The ice-volume-corrected Borneo ?18O records show little correspondence between regional convective activity and either global sea level shifts (e.g. 1) or Sunda Shelf areal exposure. This result stands in marked contrast to a recently published Last Glacial Maximum (LGM) data-model synthesis that implicates sea level as a dominant driver of tropical Indo-Pacific hydroclimate variability (2). Alternatively, when precessional signals are not muted, the composite Borneo ?18O record varies in phase with equatorial fall insolation, suggesting that precessional forcing is the dominant cause of tropical western Pacific hydroclimate variability on orbital timescales. This is best illustrated across Termination II, when the oscillation of equatorial fall insolation is large and out of phase with ice sheet decay (e.g. 3). During this transition, Borneo stalagmite ?18O begins a shift to more negative ?18O values at 128.8 × 0.9 kybp, almost directly overlapping the equatorial fall insolation cycle. The muted response of tropical western Pacific hydrology to global temperature change and sea level rise relative to precessional insolation represents an important observational constraint on the sequence of climate feedbacks responsible for glacial terminations. 1. M. Medina-Elizalde. Earth Planet. Sci. Lett. 362, 310 (Jan, 2013). 2. P. N. DiNezio, J. E. Tierney. Nature Geoscience 6, 485 (Jun, 2013). 3. A. L. Thomas et al. Science 324, 1186 (May, 2009).

Carolin, S. A.; Cobb, K.; Adkins, J. F.; Clark, B.; Lejau, S.; Lynch-Stieglitz, J.; Malang, J.; Tuen, A. A.

2013-12-01

114

11, 9791022, 2014 Glacial and  

E-print Network

in OS if available. On the glacial and inter-glacial thermohaline circulation and the associatedPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| Abstract The change of the thermohaline circulation (THC) between the Last Glacial Maximum (LGM, 21 kyrPaper|DiscussionPaper|DiscussionPaper|DiscussionPaper| 1 Introduction The thermohaline circulation (THC) is the large time- and spatial-scales ocean cir

Döös, Kristofer

115

A high-resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania)  

NASA Astrophysics Data System (ADS)

Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, ?13Ccalcite, ?18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, ?13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial-Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene-Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing ?18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring-summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.

Lacey, Jack H.; Francke, Alexander; Leng, Melanie J.; Vane, Christopher H.; Wagner, Bernd

2014-05-01

116

Late Pleistocene carbonate dissolution in the Venezuela Basin, Caribbean Sea  

SciTech Connect

Piston cores from water depths greater than 4000 m in the Venezuela Basin (Caribbean Sea) provide continuous late Pleistocene records of carbonate dissolution and accumulation. The authors examination of multiple dissolution indices indicate that, at least for the last 150,000 years, dissolution of carbonate in the Venezuela Basin has been more intense during interglacial than glacial periods, a pattern opposite to more general observations from the deep Atlantic and Gulf of Mexico. By virtue of its shallow sill depth (1815 m), the Venezuela Basin is relatively isolated from the mainstream of Atlantic thermohaline circulation, and presently is filled with homogeneous, relatively warm (3.8/sup 0/C) waters primarily derived from Upper North Atlantic Deep Water. During the last glacial, the enhanced preservation of carbonate in the Venezuela Basin suggests the presence of a less corrosive, more oxygenated water mass in the Atlantic near sill depth. However, this simple interpretations is potentially complicated by past changes in the rain of biogenic materials from surface waters to the deep basin in what must be an essentially closed system below sill depth. Their observations of increased interglacial dissolution may help to explain previously noted discrepancies in the local glacial to interglacial amplitude of delta/sup 18/O variations recorded by coccoliths and planktonic foraminifera.

Cofer-Shabica, N.B.; Peterson, L.C.

1985-01-01

117

Changes in deep Pacific temperature during the mid-Pleistocene transition and Quaternary  

NASA Astrophysics Data System (ADS)

An attempt is made to unravel the dual influences of seawater temperature and isotopic composition upon the oxygen-isotope records of benthic foraminifers from the deep Pacific ( ?18O b). Our approach is to estimate a non-linear transfer function between past sea level and ?18O b over the last two glacial cycles, with additional information from the mid-Pliocene. Combining this transfer function with the relationship between temperature and ?18O b permits a deconvolution of a ?18O b record from the deep Pacific into its temperature and sea-level constituents over the course of the Plio-Pleistocene. This deconvolution indicates that deep Pacific temperature is stable through much of the last glacial (MISs 4 through 2) and then increases by approximately 2 °C during the last deglaciation. This pattern of variability appears to generally be replicated every glacial cycle back to the mid-Pliocene, suggesting a pulse of warming in the deep Pacific on a ˜100 kyr time scale during the late Pleistocene. Thus, according to this partition, there is more ˜100 kyr variability in temperature than in ice variability. Spectral analysis reveals that this variability is likely the product of multiple obliquity cycles rather than a simple 100-kyr signal. The non-linear behaviour of deep ocean temperature, dominated by pulses at 100 kyr time scales, may identify it as a key player in governing the glacial cycles.

Siddall, Mark; Hönisch, Bärbel; Waelbroeck, Claire; Huybers, Peter

2010-01-01

118

Constraining Late Pleistocene Pluvial Lake Chronologies in Northeastern Nevada  

NASA Astrophysics Data System (ADS)

The presence of lakes in closed basins of the northern Great Basin during pluvial episodes of the Pleistocene has been recognized for over a century. Some of these lakes, such as Bonneville in western Utah and Lahontan in western Nevada, were large, and their histories are well constrained by field mapping, stratigraphic investigations, and geochronology. Dozens of other lakes with smaller dimensions are known to have existed, however with few exceptions their histories are virtually unknown. This situation is unfortunate because smaller, hydrologically closed lakes should be particularly sensitive to climatic changes that shifted the balance of precipitation and evaporation. Records of their fluctuations, therefore, could provide important information about atmospheric reorganization during the last glacial-interglacial transition. Ongoing work in northeastern Nevada is aimed at developing these records through detailed mapping, investigation of natural exposures and artificial excavations, and radiocarbon dating. Gastropod shells recovered from two sites along a beach ridge in the northeast Independence Valley indicate that Lake Clover reached its late Pleistocene highstand between 14,400 and 14,200 14C years BP (~17.5 cal. ka BP). Similarly, radiocarbon dating of gastropod shells from a beach ridge in the Ruby Valley indicates that Lake Franklin was near its late Pleistocene highstand at 13,400 14C years BP (~16.4 cal. ka BP). These ages are essentially synchronous with the highstands of Lakes Newark and Jakes ~150 km to the south, overlap with the hydrologic maximum of Lake Bonneville, and appear to predate the highstand of Lake Lahontan. Additional radiocarbon dating will refine these age relationships and attempt to constrain the timing of stillstands during the overall regression of these lakes in the latest Pleistocene.

Munroe, J. S.; Laabs, B. J.

2011-12-01

119

Glacial Geology of Wisconsin.  

ERIC Educational Resources Information Center

This publication is a teacher's resource and guidebook for the presentation of the three filmstrips in the "Glacial Geology of Wisconsin" series. The first filmstrip is subtitled, "Evidence of the Glaciers," the second "How the Glaciers Reshaped the Landscape," and the third "Fossils of the Ice Age." Included are a list of objectives, an outline…

Madison Public Schools, WI.

120

Glacial history of sub-Antarctic South Georgia based on the submarine geomorphology of its fjords  

NASA Astrophysics Data System (ADS)

We present multibeam swath bathymetric surveys of the major fjords surrounding the sub-Antarctic island of South Georgia to characterise the glacial geomorphology and to identify the relative timings and extent of past glacial advance and retreat. Bathymetry data revealed a range of glacial features including terminal, retreat and truncated moraines, deep (distal) outer and shallow (proximal) inner basins and cross shelf troughs. These provide evidence of glacial advance and retreat through several glacial cycles. A near consistent pattern of large scale submarine geomorphological features was observed in the different fjords suggesting a similar response of margins of the island ice cap to past climate forcing. A relative chronology based on the relationships between the submarine features with their radiocarbon and cosmogenic isotope dated terrestrial counterparts suggests that widely observed inner basin moraines date from the last major glacial advance or Last Glacial Maximum, while deep basin moraines may date from an earlier (pre-LGM) more extensive glaciation, which we speculate corresponds to MIS6. On the sides of the deep basins a series of truncated moraines show ice advance positions from preceding glacial periods. The cross shelf troughs, and mid-trough moraines are interpreted as the product of much more extensive glaciations that predate the fjord geomorphology mapped here, thus possibly older than MIS6. This hypothesis would suggest that South Georgia followed a glacial history similar to that of central Patagonia (46deg S)where a series of Pleistocene glaciations (of MIS 20 and younger) extended beyond LGM limits, with the most extensive glacial advance occurring at c. 1.1 Ma.

Hodgson, Dominic A.; Graham, Alastair G. C.; Griffiths, Huw J.; Roberts, Stephen J.; Cofaigh, Colm O.; Bentley, Michael J.; Evans, David J. A.

2014-05-01

121

Geochronology and paleoenvironments of the glacial-age Tahoka Formation, Texas and New Mexico High Plains  

Microsoft Academic Search

Radiocarbon ages on organic matter from the late Pleistocene Tahoka Formation at White Lake, Bailey County, Texas, provide a new chronology for playa lakes on the southern High Plains. Lacustrine muds at White Lake accumulated at least 20,000-17,000 14 C yrs B.P. during the last glacial maximum. The basin at White Lake also contained standing water ca 37,000 14 C

Salt Lake; Coyote Lake

2001-01-01

122

Is Gene Flow Promoting the Reversal of Pleistocene Divergence in the Mountain Chickadee (Poecile gambeli)?  

PubMed Central

The Pleistocene glacial cycles left a genetic legacy on taxa throughout the world; however, the persistence of genetic lineages that diverged during these cycles is dependent upon levels of gene flow and introgression. The consequences of secondary contact among taxa may reveal new insights into the history of the Pleistocene’s genetic legacy. Here, we use phylogeographic methods, using 20 nuclear loci from regional populations, to infer the consequences of secondary contact following divergence in the Mountain Chickadee (Poecile gambeli). Analysis of nuclear data identified two geographically-structured genetic groups, largely concordant with results from a previous mitochondrial DNA (mtDNA) study. Additionally, the estimated multilocus divergence times indicate a Pleistocene divergence, and are highly concordant with mtDNA. The previous mtDNA study showed a paucity of sympatry between clades, while nuclear patterns of gene flow show highly varied patterns between populations. The observed pattern of gene flow, from coalescent-based analyses, indicates southern populations in both clades exhibit little gene flow within or between clades, while northern populations are experiencing higher gene flow within and between clades. If this pattern were to persist, it is possible the historical legacy of Pleistocene divergence may be preserved in the southern populations only, and the northern populations would become a genetically diverse hybrid species. PMID:23152877

Manthey, Joseph D.; Klicka, John; Spellman, Garth M.

2012-01-01

123

Pleistocene Sea Surface Temperatures and Paleocirculation in the Japan Sea - Odp Site 798: a Multidisciplinary Study Involving Planktonic Foraminifers and Alkenones  

Microsoft Academic Search

The primary goal of this research was to reconstruct a record of variations in sea surface temperature (SST) in the Japan Sea during the late Pleistocene (0-700 ka) in order to contribute to understanding of glacial\\/interglacial climate and oceanography in this region. The principle research methods employed were (1) quantitative analysis of planktonic foraminifers and (2) variations in SST based

Tara Kheradyar

1995-01-01

124

Coalescent-based hypothesis testing supports multiple Pleistocene refugia in the Pacific Northwest for the Pacific giant salamander (Dicamptodon tenebrosus).  

PubMed

Phylogeographic patterns of many taxa are explained by Pleistocene glaciation. The temperate rainforests within the Pacific Northwest of North America provide an excellent example of this phenomenon, and competing phylogenetic hypotheses exist regarding the number of Pleistocene refugia influencing genetic variation of endemic organisms. One such endemic is the Pacific giant salamander, Dicamptodon tenebrosus. In this study, we estimate this species' phylogeny and use a coalescent modeling approach to test five hypotheses concerning the number, location and divergence times of purported Pleistocene refugia. Single refugium hypotheses include: a northern refugium in the Columbia River Valley and a southern refugium in the Klamath-Siskiyou Mountains. Dual refugia hypotheses include these same refugia but separated at varying times: last glacial maximum (20,000 years ago), mid-Pleistocene (800,000 years ago) and early Pleistocene (1.7 million years ago). Phylogenetic analyses and inferences from nested clade analysis reveal distinct northern and southern lineages expanding from the Columbia River Valley and the Klamath-Siskiyou Mountains, respectively. Results of coalescent simulations reject both single refugium hypotheses and the hypothesis of dual refugia with a separation date in the late Pleistocene but not hypotheses predicting dual refugia with separation in early or mid-Pleistocene. Estimates of time since divergence between northern and southern lineages also indicate separation since early to mid-Pleistocene. Tests for expanding populations using mismatch distributions and 'g' distributions reveal demographic growth in the northern and southern lineages. The combination of these results provides strong evidence that this species was restricted into, and subsequently expanded from, at least two Pleistocene refugia in the Pacific Northwest. PMID:16842421

Steele, Craig A; Storfer, Andrew

2006-08-01

125

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)

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 Du?e (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.

Helmens, Karin F.

2014-02-01

126

Geomorphic controls on Pleistocene knickpoint migration in Alpine valleys  

NASA Astrophysics Data System (ADS)

Recent insights into sub-glacial bedrock stress conditions suggest that the erosional efficiency of glaciers may reduce markedly following a major erosional cycle [Leith et al., 2013]. This implies that the formation of large glacial valleys within the Alps is likely to have occurred shortly after the onset of 100 ky glacial-interglacial cycles (at the mid-Pleistocene Revolution (MPR)). The majority of landscape change since this time may have therefore been driven by sub-aerial processes. This hypothesis is supported by observations of hillslope and channel morphology within Canton Valais (Switzerland), where major tributary valleys display a common morphology along their length, hinting at a shared geomorphic history. Glaciers currently occupy the headwaters of many catchments, while the upper reaches of rivers flow across extensive alluvial planes before abruptly transitioning to steep channels consisting of mixed bedrock and talus fan deposits. The rivers then converge to flow out over the alluvial plane of the Rhone Valley. Characteristically rough topographies within the region are suggested to mark the progressive transition from a glacial to fluvially-dominated landscape, and correlate well with steepened river channel sections determined from a 2.5 m resolution LiDAR DEM. We envisage a landscape in which ongoing tectonic uplift drives the emergence of Alpine bedrock through massive sedimentary valley infills (currently concentrated in the Rhone Valley), whose elevation is fixed by the consistent fluvial baselevel at Lake Geneva. As fluvial incision ceases at the onset of glaciation, continued uplift causes the formation of knickpoints at the former transition from bedrock to sedimentary infill. These knickpoints will then propagate upstream during subsequent interglacial periods. By investigating channel morphologies using an approach based on the steady-state form of the stream power equation, we can correlate steepened channel reaches (degraded knickpoints) across most major tributaries south of the Rhone River. The timing of apparent uplift events correlates well with that of cool Marine Isotope Stages derived from global oxygen isotope data up to the beginning of MIS 12. A weak correlation up to the beginning of MIS 18 suggests initial glacial incision may have occurred some time during MIS 14 - 20, and valley development has since been driven by fluvial processes. Leith, K., J. R. Moore, F. Amann, and S. Loew (2013), Sub-glacial extensional fracture development and implications for Alpine valley evolution, J. Geophys. Res. Earth Surf., doi:10.1002/2012JF002691.

Leith, Kerry; Fox, Matt; Moore, Jeffrey R.; Brosda, Julian; Krautblatter, Michael; Loew, Simon

2014-05-01

127

The consequences of pleistocene climate change on lowland neotropical vegetation  

SciTech Connect

Palynological reconstructions indicate that lowland tropical America was subject to intense cooling during the last ice-age. The descent of presently montane taxa into the lowlands of Amazonia and Minas Gerais indicate temperature depressions ranging from 5[degrees]C to 9[degrees]C cooler-than-present. The strengthened incursion of southerly airmasses caused a reassortment of vegetation throughout Amazonia. Presently allopatric species are found to have been sympatric as novel forest assemblages and formed and dissolved. Modest drying, perhaps a 20% reduction in precipitation, accounts for all the records that show a Pleistocene expansion of savanna. No evidence is found to support the fragmentation of Amazonian forests during glacial times, and the hypothesis of forest refuges as an explanation of tropical speciation is rejected on empirical grounds.

De Oliveira, P.E.; Colinvaux, P.A. (Smithsonian Tropical Research Institute, Panama City (Panama))

1994-06-01

128

The aftermath of megafaunal extinction: ecosystem transformation in Pleistocene Australia.  

PubMed

Giant vertebrates dominated many Pleistocene ecosystems. Many were herbivores, and their sudden extinction in prehistory could have had large ecological impacts. We used a high-resolution 130,000-year environmental record to help resolve the cause and reconstruct the ecological consequences of extinction of Australia's megafauna. Our results suggest that human arrival rather than climate caused megafaunal extinction, which then triggered replacement of mixed rainforest by sclerophyll vegetation through a combination of direct effects on vegetation of relaxed herbivore pressure and increased fire in the landscape. This ecosystem shift was as large as any effect of climate change over the last glacial cycle, and indicates the magnitude of changes that may have followed megafaunal extinction elsewhere in the world. PMID:22442481

Rule, Susan; Brook, Barry W; Haberle, Simon G; Turney, Chris S M; Kershaw, A Peter; Johnson, Christopher N

2012-03-23

129

Reduced ventilation and enhanced magnitude of the deep Pacific carbon pool during the last glacial period  

NASA Astrophysics Data System (ADS)

It has been proposed that the ventilation of the deep Pacific carbon pool was not significantly reduced during the last glacial period, posing a problem for canonical theories of glacial-interglacial CO2 change. However, using radiocarbon dates of marine tephra deposited off New Zealand, we show that deep- (> 2000 m) and shallow sub-surface ocean-atmosphere 14C age offsets (i.e. "reservoir-" or "ventilation" ages) in the southwest Pacific increased by ˜1089 and 337 yrs respectively, reaching ˜2689 and ˜1037 yrs during the late glacial. A comparison with other radiocarbon data from the southern high-latitudes suggests that broadly similar changes were experienced right across the Southern Ocean. If, like today, the Southern Ocean was the main source of water to the glacial ocean interior, these observations would imply a significant change in the global radiocarbon inventory during the last glacial period, possibly equivalent to an increase in the average radiocarbon age > 2 km of ˜ 700 yrs. Simple mass balance arguments and numerical model sensitivity tests suggest that such a change in the ocean's mean radiocarbon age would have had a major impact on the marine carbon inventory and atmospheric CO2, possibly accounting for nearly half of the glacial-interglacial CO2 change. If confirmed, these findings would underline the special role of high latitude shallow sub-surface mixing and air-sea gas exchange in regulating atmospheric CO2 during the late Pleistocene.

Skinner, L.; McCave, I. N.; Carter, L.; Fallon, S.; Scrivner, A. E.; Primeau, F.

2015-02-01

130

GEOLOGY | November 2012 | www.gsapubs.org 1023 North American terminal Pleistocene mammal extinctions are  

E-print Network

the Northern Hemisphere Bølling-Allerød oscillation preserved in Green- land ice cores and exhibited in the 18GEOLOGY | November 2012 | www.gsapubs.org 1023 ABSTRACT North American terminal Pleistocene mammal of 35 genera of mostly large mammals, 16 of which have last appearance dates occur- ring within a period

Lachniet, Matthew S.

131

Pleistocene marine ice sheets and ice shelves at the East Siberian continental margin  

NASA Astrophysics Data System (ADS)

RV "Polarstern" cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA03B (2012) investigated an area in the Arctic Ocean located between the Chukchi Borderland and the East Siberian Sea (between 165°W and 170°E). Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present evidence that the western Arctic Ocean had a glaciated continental margin during several glacial periods of the Pleistocene (Niessen et al. 2013). At the southern end of the Mendeleev Ridge and on the Chukchi and East Siberian continental slopes ice sheets and ice shelves grounded in up to 1200 m present water depth. We found mega-scale glacial lineations (MSGL) associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, capped with diamicton and draped by, in places, several metres of pelagic sediments. On the Arlis Plateau, a detailed bathymetric map exhibits several generations of MSGL, which we interpret as relicts of different Pleistocene glaciations. Traces of former grounding line positions suggest that an ice shelf of approximately 900 m in thickness has spread across the Southern Mendeleev Ridge in a north-easterly direction. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. A preliminary age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3 and clearly predates the Last Glacial Maximum. The oldest and deepest event predates MIS 6. The youngest grounding event on the Arlis Plateau is tentatively dated to have occurred during MIS 4. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for albedo, ocean-atmosphere heat exchange, moisture supply to and freshwater export from the Arctic Ocean and the formation of submarine permafrost on the East Siberian Shelf. Niessen, F., Hong, J. K. , Hegewald, A. , Matthiessen, J. , Stein, R. , Kim, H. , Kim, S. , Jensen, L. , Jokat, W. , Nam, S. I. and Kang, S. H. (2013) Repeated Pleistocene glaciation of the East Siberian continental margin, Nature Geoscience, 6 (10), pp. 842-846.

Niessen, Frank; Kuk Hong, Jong; Hegewald, Anne; Matthiessen, Jens; Stein, Rüdiger; Kim, Sookwan; Jensen, Laura; Jokat, Wilfried; Nam, Seung Il

2014-05-01

132

An outline of the Pleistocene stratigraphy of the kleszczów Graben, bec?hatów outcrop, central Poland  

NASA Astrophysics Data System (ADS)

The Pleistocene sequence of the Kleszczów Graben, central Poland, is located in a brown coal quarry 8 km long and 4 km wide. It contains ten separate organic horizons, in part, stacked one above another and, in part, correlated by reference to associated inorganic units using heavy minerals and gravel petrography. Three of the organic horizons represent interglacials: Ferdynandovian, Mazovian (Holsteinian) and Eemian. Others represent interstadial or periglacial deposits. The Tertiary/Quaternary boundary is recorded at the site by Reuverian C and prae-Tiglian biostratigraphy occurring in a single section. A major hiatus exists above the prae-Tiglian and Lower Pleistocene and Cromerian deposits are absent. Glacial deposits are represented by three Elsterian tills, five Saalian tills and glaciofluvial and glaciolacustrine deposits. The Czy?ów Formation lies between the Elsterian and Saalian deposits and contains at least two interglacials, the Ferdynandovian and Mazovian, and several interstadial units without glacial intervening deposits. The Lower Saalian (Odranian = Drenthe) deposits are separated from the Middle Saalian (Wartanian 1) by fluvial sands and organic deposits of the Pilica interstadial. The Middle (Wartanian 1) and Upper Saalian (Wartanian 2) also may be separated by an interstadial palaeosol. The evidence from the Kleszczów Graben, supported by other central European Quaternary sequences, suggest that only four glaciations occurred within the region during the Middle Pleistocene, and that these glaciations were separated by long periods with a complex climate ranging from temperate to periglacial.

Krzyszkowski, Dariusz

133

Ages and inferred causes of late Pleistocene glaciations on Mauna Kea, Hawai'i  

USGS Publications Warehouse

Glacial landforms on Mauna Kea, Hawai'i, show that the summit area of the volcano was covered intermittently by ice caps during the Late Pleistocene. Cosmogen 36Cl dating of terminal moraines and other glacial landforms indicates that the last two ice caps, called Older Makanaka and Younger Makanaka, retreated from their maximum positions approximately 23ka and 13ka, respectively. The margins and equilibrium line altitudes of these ice caps on the remote, tropical Pacific island were nearly identical, which would seem to imply the same mechanism for ice growth. But modelling of glacier mass balance, combined with palaeotemperature proxy data from the subtropical North Pacific, suggests that the causes of the two glacial expansions may have been different. Older Makanaka airatop Mauna Kea was likely wetter than today and cold, whereas Younger Makanaka times were slightly warmer but significantly wetter than the previous glaciation. The modelled increase in precipitation rates atop Mauna Kea during the Late Pleistocene is consistent with that near sea level inferred from pollen data, which suggests that the additional precipitation was due to more frequent and/ or intense tropical storms associated with eastward-moving cold fronts. These conditions were similar to modern La Ni??a (weak ENSO) conditions, but persisted for millennia rather than years. Increased precipitation rates and the resulting steeper temperature lapse rates created glacial conditions atop Mauna Kea in the absence of sufficient cooling at sea level, suggesting that if similar correlations existed elsewhere in the tropics, the precipitation-dependent lapse rates could reconcile the apparent difference between glacial-time cooling of the tropics at low and high altitudes. Copyright ?? 2008 John Wiley & Sons, Ltd.

Pigati, J.S.; Zreda, M.; Zweck, C.; Almasi, P.F.; Elmore, D.; Sharp, W.D.

2008-01-01

134

Pleistocene glaciation leaves deep signature on the freshwater crab Aegla alacalufi in Chilean Patagonia.  

PubMed

Quaternary glacial cycles have played an important role in shaping the biodiversity in temperate regions. This is well documented in Northern Hemisphere, but much less understood for Southern Hemisphere. We used mitochondrial DNA and nuclear elongation factor 1? intron sequences to examine the Pleistocene glacial impacts on the phylogeographical pattern of the freshwater crab Aegla alacalufi in Chilean Patagonia. Phylogenetic analyses, which separated the glaciated populations on eastern continent into a north group (seven populations) and a south group (one population), revealed a shallow phylogenetic structure in the north group but a deep one in the non-glaciated populations on western islands, indicating the significant influence of glaciation on these populations. Phylogenies also identified the Yaldad population on Chiloé Island as a potentially unrecognized new species. The non-glaciated populations showed higher among population genetic divergence than the glaciated ones, but lower population genetic diversity was not detected in the latter. The two glaciated groups, which diverged from the non-glaciated populations at ~96,800-29,500 years ago and ~104,200-73,800 years ago, respectively, seem to have different glacial refugia. Unexpectedly, the non-glaciated islands did not serve as refugia for them. Demographic expansion was detected in the glaciated north group, with a constant population increase after the last glacial maximum. Nested clade analyses suggest a possible colonization from western islands to eastern continent. After arriving on the continent and surviving the last glacial period there, populations likely have expanded from high to low altitude, following the flood of melting ice. Aegla alacalufi genetic diversity has been primarily affected by Pleistocene glaciation and minimally by drainage isolation. PMID:19207249

Xu, Jiawu; Pérez-Losada, Marcos; Jara, Carlos G; Crandall, Keith A

2009-03-01

135

Polymorphism in pleistocene land snails.  

PubMed

Under suitable conditions the colors and patterns of the shells of land snails may be preserved for thousands of years. In a late Pleistocene population of Limicolaria martensiana all the major color forms that occur in modern living snails may be distinguished, and the basic polymorphism is at least 8,000 to 10,000 year old. PMID:17830234

Owen, D F

1966-04-01

136

Somma-Vesuvius ground deformation over the last glacial cycle  

NASA Astrophysics Data System (ADS)

Vertical ground movements at Somma-Vesuvius during the last glacial cycle have been inferred from micropalaeontological and petrochemical analyses of rock samples from boreholes drilled at the archaeological sites of Herculaneum and Pompeii as well as on the apron of the volcano and the adjacent Sebeto and Sarno Valleys. Opposing movements occurred during the periods preceding and following the Last Glacial Maximum (LGM). The uplift began 20 ka ago with marine deposits rising several tens of metres up to 25 m a.s.l., recovering previous subsidence which occurred during the Late glacial period, suggesting a strict connection between volcano-tectonic and glacial cycles. Here we present the analysis of deposits predating the LGM, which confirms subsidence of the Campanian Plain where Mt. Somma-Vesuvius is located, shows variable surface loading effects and highlights the volcano-tectonic stages experienced by the volcano. The self-balancing mechanism of the volcanic system, evolving towards an explosive, subaerial activity 60 ka ago, is testified to by a large ground oscillation in phase with sea level change during the last glacial cycle.

Marturano, Aldo; Aiello, Giuseppe; Barra, Diana

2013-04-01

137

Glacial isostasy and plate motion  

Microsoft Academic Search

The influence of glacial-isostatic adjustment (GIA) on the motion of tectonic plates is usually neglected. Employing a recently developed numerical approach, we examine the effect of glacial loading on the motion of the Earth’s tectonic plates where we consider an elastic lithosphere of laterally variable strength and the plates losely connected by low viscous zones. The aim of this paper

Volker Klemann; Zdenek Martinec; Erik R. Ivins

2008-01-01

138

Is gene flow promoting the reversal of pleistocene divergence in the Mountain Chickadee (Poecile gambeli)?  

PubMed

The Pleistocene glacial cycles left a genetic legacy on taxa throughout the world; however, the persistence of genetic lineages that diverged during these cycles is dependent upon levels of gene flow and introgression. The consequences of secondary contact among taxa may reveal new insights into the history of the Pleistocene's genetic legacy. Here, we use phylogeographic methods, using 20 nuclear loci from regional populations, to infer the consequences of secondary contact following divergence in the Mountain Chickadee (Poecile gambeli). Analysis of nuclear data identified two geographically-structured genetic groups, largely concordant with results from a previous mitochondrial DNA (mtDNA) study. Additionally, the estimated multilocus divergence times indicate a Pleistocene divergence, and are highly concordant with mtDNA. The previous mtDNA study showed a paucity of sympatry between clades, while nuclear patterns of gene flow show highly varied patterns between populations. The observed pattern of gene flow, from coalescent-based analyses, indicates southern populations in both clades exhibit little gene flow within or between clades, while northern populations are experiencing higher gene flow within and between clades. If this pattern were to persist, it is possible the historical legacy of Pleistocene divergence may be preserved in the southern populations only, and the northern populations would become a genetically diverse hybrid species. PMID:23152877

Manthey, Joseph D; Klicka, John; Spellman, Garth M

2012-01-01

139

Exceptional record of mid-Pleistocene vertebrates helps differentiate climatic from anthropogenic ecosystem perturbations  

PubMed Central

Mid-Pleistocene vertebrates in North America are scarce but important for recognizing the ecological effects of climatic change in the absence of humans. We report on a uniquely rich mid-Pleistocene vertebrate sequence from Porcupine Cave, Colorado, which records at least 127 species and the earliest appearances of 30 mammals and birds. By analyzing >20,000 mammal fossils in relation to modern species and independent climatic proxies, we determined how mammal communities reacted to presumed glacial–interglacial transitions between 1,000,000 and 600,000 years ago. We conclude that climatic warming primarily affected mammals of lower trophic and size categories, in contrast to documented human impacts on higher trophic and size categories historically. Despite changes in species composition and minor changes in small-mammal species richness evident at times of climatic change, overall structural stability of mammal communities persisted >600,000 years before human impacts. PMID:15197254

Barnosky, Anthony D.; Bell, Christopher J.; Emslie, Steven D.; Goodwin, H. Thomas; Mead, Jim I.; Repenning, Charles A.; Scott, Eric; Shabel, Alan B.

2004-01-01

140

Glacial landscape evolution — Implications for glacial processes, patterns and reconstructions  

NASA Astrophysics Data System (ADS)

This special issue presents a collection of papers that address a wide range of important challenges and exciting advances in the field of glacial landscape evolution. Primarily, these papers reflect persistent uncertainty that surrounds the mechanisms and timescales of glacial landscape evolution. For example, estimates of the duration of glacial occupancy required for the evolution of characteristic glacial valley forms from previously fluvial landscapes range from 100 kyrs for landscapes beneath large ice sheets (Jamieson et al.) to ~ 400-600 kyrs for glaciated alpine terrains (Brook et al.). Further, the mechanisms of glacial erosion are debated through analyses of the importance of ice thickness (Brocklehurst et al.; van der Beek and Bourbon), ice surface steepness (Vieira) and, in the case of large ice sheets, the co-evolution of ice sheet thermal regime, dynamics, and subglacial topography (Kleman et al.; Swift et al.). Debate concerning the potential climatic impacts of landscape evolution in alpine terrains is represented by van der Beek and Bourbon, who infer a significant increase in relief as a direct result of glacial erosion, and by Brocklehurst et al. and Heimsath and McGlynn, who demonstrate respectively that glacial relief production can be surprisingly modest and that rates of glacial erosion may be lower than those for fluvial incision. Further confirmation that valleys beneath large ice sheets evolve through selective linear erosion comes from studies that have combined geomorphological evidence with cosmogenic nuclide (Briner et al.) and apatite (U-Th)/He thermochronometry (Swift et al.), and the resulting style of landscape evolution is demonstrated by the antiquity of fjords in East Greenland (Swift et al.) and of deep erosion zones and thick drift covered zones in Fennoscandia (Kleman et al.), although the location of areal scouring zones may be subject to major alteration during single glacial events (Kleman et al.). Another set of papers shows that analyses of glacial lineation systems continue to provide important data on the dynamics of glacial landscape evolution, whether the lineations are formed underneath ice streams (Bradwell et al.; Andreassen et al.) or not (Jansson and Glasser), and whether they indicate intricate patterns of landscape modification (Andreassen et al.) or preservation (Jansson and Glasser). The final three papers address rarely-reported issues relating to landscapes of glacial deposition, including moraine degradation (Putkonen et al.), proglacial hydrogeology (Robinson et al.), and the evolution of hummocky-till topography (Clayton et al.).

Stroeven, Arjen P.; Swift, Darrel A.

2008-05-01

141

Phylogeographic and demographic effects of Pleistocene climatic fluctuations in a montane salamander, Plethodon fourchensis.  

PubMed

Climatic changes associated with Pleistocene glacial cycles profoundly affected species distributions, patterns of interpopulation gene flow, and demography. In species restricted to montane habitats, ranges may expand and contract along an elevational gradients in response to environmental fluctuations and create high levels of genetic variation among populations on different mountains. The salamander Plethodon fourchensis is restricted to high-elevation, mesic forest on five montane isolates in the Ouachita Mountains. We used DNA sequence data along with ecological niche modelling and coalescent simulations to test several hypotheses related to the effects of Pleistocene climatic fluctuations on species in montane habitats. Our results revealed that P. fourchensis is composed of four well-supported, geographically structured lineages. Geographic breaks between lineages occurred in the vicinity of major valleys and a narrow high-elevation pass. Ecological niche modelling predicted that environmental conditions in valleys separating most mountains are suitable; however, interglacial periods like the present are predicted to be times of range expansion in P. fourchensis. Divergence dating and coalescent simulations indicated that lineage diversification occurred during the Middle Pleistocene via the fragmentation of a wide-ranging ancestor. Bayesian skyline plots showed gradual decreases in population size in three of four lineages over the most recent glacial period and a slight to moderate amount of population growth during the Holocene. Our results not only demonstrate that climatic changes during the Pleistocene had profound effects on species restricted to montane habitats, but comparison of our results for P. fourchensis with its parapatric, sister taxon, P. ouachitae, also emphasizes how responses can vary substantially even among closely related, similarly distributed taxa. PMID:19389165

Shepard, Donald B; Burbrink, Frank T

2009-05-01

142

What drives glacial cycles  

SciTech Connect

The Milankovitch theory advocates that the glacial cycles have three components: the tilt of the earth's spin axis; the shape of the earth's orbit; and the interaction between the tilt and the eccentricity effects. These three factors work together to vary the amount of sunshine reaching the high northern latitudes in summer and allow the great ice sheets to grow during intervals of cool summers and mild winters. Evidence is presented which indicates that the circulation pattern of the Atlantic ocean was shifted dramatically about 14,000 years ago, at the same time that glaciers in both hemispheres started to retreat. The authors believe that massive reorganizations of the ocean-atmosphere system are the key events that link cyclic changes in the earth's orbit to the advance and retreat of ice sheet.

Broecker, W.S.; Denton, G.H.

1990-01-01

143

Pleistocene glaciation in the blue ridge province, southern appalachian mountains, north Carolina.  

PubMed

Glacial polish, grooves, and striations discovered at an elevation of 1370 meters in the headwaters of Boone Fork on Grandfather Mountain, North Carolina, indicate the former, existence of alpine glaciation at a latitude of 36 degrees 07'N. The Boone Fork glacier was located 890 kilometers south of the previously recognized southern limit of alpine glaciation in the Appalachian Mountains, and 350 kilometers southeast of the nearest point on the Laurentide ice sheet. This find has significant implications for studies of Pleistocene geomorphology, paleobiology, and paleoclimatology in the eastern United States. PMID:17736977

Berkland, J O; Raymond, L A

1973-08-17

144

Pleistocene-Holocene transition in the central Mississippi River valley  

NASA Astrophysics Data System (ADS)

Within the northern Mississippi embayment the ancestral Mississippi River flowed south through the Western Lowlands and the ancestral Ohio River flowed through the Eastern Lowlands for most of the Pleistocene. Previous investigators have mapped and dated the terraces of their respective braid belts. This current research investigates the three-dimensional aspect of the Quaternary alluvium north of Memphis, Tennessee, through the interpretation of 3374 geologic well logs that are 91.4 m (300 ft) deep. The braid belts are capped by a thin silt/clay horizon (Pleistocene loess) that overlies gravelly sand, which in turn overlies sandy gravel. The base of the Pleistocene alluvium beneath the Ash Hill (27.3-24.6 ka), Melville Ridge (41.6-34.5 ka), and Dudley (63.5-50.1 ka) terraces of the Western Lowland slope southerly by 0.275 m/km and all have an average basal elevation of 38 m. Near Beedeville, Arkansas, the bases of these terraces descend 20 m across a northeast-striking down-to-the-southeast fault that coincides with the western margin of the Cambrian Reelfoot rift. The maximum depth of flow (lowest elevation of base of alluvium) occurred in the Eastern Lowlands and appears to have been the downstream continuation of the ancestral Ohio River Cache valley course in southern Illinois. In traversing from west to east in the Eastern Lowlands, the Sikeston braid belt (19.7-17.8 ka) has a basal elevation averaging 7 m, the Kennett braid belt (16.1-14.4 ka) averages 13 m, the Morehouse (12 ka) braid belt averages 24 m, and the Holocene (? 10 ka) Mississippi River floodplain has the highest average basal elevation at 37 m. Along this easterly traverse the base of the Quaternary alluvium rises and the age of alluvium decreases. The eastward thinning of the floodplain alluvium in the Eastern Lowlands appears to be caused by decreasing Mississippi River discharge as it transitioned from the Wisconsinan glacial maximum to the Holocene. The base of the Holocene Mississippi River floodplain averages 23 m higher in elevation than the Pleistocene floodplain bases in the Eastern Lowlands. This high suballuvial surface (platform) is bound by the tectonically uplifted Joiner ridge, Blytheville arch, Charleston uplift, and Bluff Line fault. The spatial relationship and similar histories of the platform and bounding structures suggest that Quaternary erosion and tectonics are related.

Van Arsdale, Roy B.; Cupples, William B.; Csontos, Ryan M.

2014-06-01

145

Thermohaline circulation crisis and impacts during the mid-Pleistocene transition.  

PubMed

The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41-thousand-year to 100-thousand-year cycles and developed higher-amplitude climate variability without substantial changes in the Milankovitch forcing. Here, we document, by using Nd isotopes, a major disruption of the ocean thermohaline circulation (THC) system during the MPT between marine isotope stages (MISs) 25 and 21 at ~950 to 860 thousand years ago, which effectively marks the first 100-thousand-year cycle, including an exceptional weakening through a critical interglacial (MIS 23) at ~900 thousand years ago. Its recovery into the post-MPT 100-thousand-year world is characterized by continued weak glacial THC. The MPT ocean circulation crisis facilitated the coeval drawdown of atmospheric CO2 and high-latitude ice sheet growth, generating the conditions that stabilized 100-thousand-year cycles. PMID:24968939

Pena, Leopoldo D; Goldstein, Steven L

2014-07-18

146

Could brown bears (Ursus arctos) have survived in Ireland during the Last Glacial Maximum?  

PubMed

Brown bears are recorded from Ireland during both the Late Pleistocene and early-mid Holocene. Although most of the Irish landmass was covered by an ice sheet during the Last Glacial Maximum (LGM), Irish brown bears are known to have hybridized with polar bears during the Late Pleistocene, and it is suggested that the Irish brown bear population did not become extinct but instead persisted in situ through the LGM in a southwestern ice-free refugium. We use historical population modelling to demonstrate that brown bears are highly unlikely to have survived through the LGM in Ireland under any combination of life-history parameters shown by living bear populations, but instead would have rapidly become extinct following advance of the British-Irish ice sheet, and probably recolonized Ireland during the end-Pleistocene Woodgrange Interstadial from a closely related nearby source population. The time available for brown bear-polar bear hybridization was therefore restricted to narrow periods at the beginning or end of the LGM. Brown bears would have been extremely vulnerable to extinction in Quaternary habitat refugia and required areas substantially larger than southwestern Ireland to survive adverse glacial conditions. PMID:23676655

Leonard, Saoirse A; Risley, Claire L; Turvey, Samuel T

2013-08-23

147

A Pleistocene coastal alluvial fan complex produced by Middle Pleistocene glacio-fluvial processes  

NASA Astrophysics Data System (ADS)

A coarse-grained alluvial fan sequence at Lipci, Kotor Bay, in western Montenegro, provides a sedimentary record of meltwater streams draining from the Orjen Massif (1,894 m a.s.l.) to the coastal zone. At Lipci sedimentary evidence and U-series ages have been used alongside offshore bathymetric imagery and seismic profiles to establish the size of the fan and constrain the nature and timing of its formation. Establishing the depositional history of such coastal fans is important for our understanding of cold stage sediment flux from glaciated uplands to the offshore zone, and for exploring the impact of sea level change on fan reworking. There is evidence of at least four phases of Pleistocene glaciation on the Orjen massif, which have been U-series dated and correlated to MIS 12, MIS 6, MIS 5d-2 and the Younger Dryas. A series of meltwater channels delivered large volumes of coarse- and fine-grained limestone sediment from the glaciated uplands into the Bay of Kotor. At the southern margin of the Orjen massif, a series of large (>700 m long) alluvial fans has developed. Some of these extend offshore for up to 600 m. Lipci fan lies downstream of end moraines in the valley immediately above, which were formed by an extensive outlet glacier of the Orjen ice cap during MIS 12. The terrestrial deposits are part of the fan apex (50 m a.s.l.) that lies at the foot of a steep bedrock channel, but the majority of the fan is now more than 25 m below sea level. The terrestrial fan sediments are strongly cemented by multiple generations of calcite precipitates: the oldest U-series ages are infinite indicating that the fan is >350 ka in age. These ages are in agreement with alluvial sedimentary evidence and U-series ages from other fluvial units on Mount Orjen. The terrestrial portion of the Lipci fan surface contains several channels. These are well preserved due to cementation with calcium carbonate. Submarine imagery indicates that the now submerged portion of the fan also contains deeply incised (up to 10 m) channels which are similar in morphology to those exposed onshore. It is likely that strong cementation of the fan sediments, and associated channel forms, has protected them from coastal erosion during several regression-transgression cycles. These records provide important opportunities to correlate the Pleistocene terrestrial glacial and fluvial records with the marine archive.

Adamson, Kathryn; Woodward, Jamie; Hughes, Philip; Giglio, Federico; Del Bianco, Fabrizio

2014-05-01

148

Sedimentary architecture of the Amundsen Sea Embayment shelf, West Antarctica, from pre-glacial to glacial processes  

NASA Astrophysics Data System (ADS)

Studies of the sedimentary architecture and characteristics of Antarctic shelves provide clues of past ice sheet advance-retreat cycles and help improve constraints for paleo-ice dynamic models since early glacial periods. A first seismostratigraphic analysis of the Amundsen Sea Embayment shelf and slope of West Antarctica reveals insights into the structural architecture of the continental margin and shows stages of sediment deposition, erosion and transport history from pre-glacial times to early glaciation and to the most recent glacial periods. The shelf geometry consists of a large pre- and syn-rift basin in the middle shelf region between outcropping basement of the inner shelf and basement ridges and highs beneath the outer shelf. A middle shelf sub-basin exists which may have formed as a result of motion along an early West Antarctic Rift System branch. At least 4 km of pre-glacial strata has been eroded from the present inner shelf and coastal hinterland by ice sheet advances since the onset of glaciation. Some of the eroded sediments were deposited as a progradational wedge extending the outer shelf by 25 to 65 km oceanward of the pre-glacial shelf-break. Comparing the observed seismic characteristics with those of other Antarctic shelf sequences, we assign an Early Cretaceous age for bottom sedimentary unit ASS-1, a Late Cretaceous to Oligocene age for unit ASS-2, an Early to Mid-Miocene age for unit ASS-3, a Mid-Miocene age for unit ASS-4, a Late Miocene to Early Pliocene age for unit ASS-5, and a Pliocene to Pleistocene age for the top unit ASS-6. The survival of buried grounding zone wedges in the upper part of unit ASS-5 of the outer shelf is consistent with the onset of a long warming phase and a retreated ice sheet in the early Pliocene as observed for the Ross Sea shelf and reconstructed from paleo-ice sheet models. Our data also reveal that the paleo-ice flow paths of the central Pine Island Trough system have remained stationary across the middle and outer shelf since early glacial advances. This study and its stratigraphic constraints will serve as a basis for future drilling operations required for an improved understanding of processes and mechanisms leading to West Antarctic Ice Sheet retreats, such as the rapid ice retreat presently observed in the Amundsen Sea Embayment.

Gohl, Karsten; Uenzelmann-Neben, Gabriele; Hillenbrand, Claus-Dieter; Larter, Robert; Nitsche, Frank

2013-04-01

149

Molecular analysis of the Pleistocene history of Saxifraga oppositifolia in the Alps.  

PubMed

A recent circumpolar survey of chloroplast DNA (cpDNA) haplotypes identified Pleistocene glacial refugia for the Arctic-Alpine Saxifraga oppositifolia in the Arctic and, potentially, at more southern latitudes. However, evidence for glacial refugia within the ice sheet covering northern Europe during the last glacial period was not detected either with cpDNA or in another study of S. oppositifolia that surveyed random amplified polymorphic DNA (RAPD) variation. If any genotypes survived in such refugia, they must have been swamped by massive postglacial immigration of periglacial genotypes. The present study tested whether it is possible to reconstruct the Pleistocene history of S. oppositifolia in the European Alps using molecular methods. Restriction fragment length polymorphism (RFLP) analysis of cpDNA of S. oppositifolia, partly sampled from potential nunatak areas, detected two common European haplotypes throughout the Alps, while three populations harboured two additional, rare haplotypes. RAPD analysis confirmed the results of former studies on S. oppositifolia; high within, but low among population genetic variation and no particular geographical patterning. Some Alpine populations were not perfectly nested in this common gene pool and contained private RAPD markers, high molecular variance or rare cpDNA haplotypes, indicating that the species could possibly have survived on ice-free mountain tops (nunataks) in some parts of the Alps during the last glaciation. However, the overall lack of a geographical genetic pattern suggests that there was massive immigration of cpDNA and RAPD genotypes by seed and pollen flow during postglacial times. Thus, the glacial history of S. oppositifolia in the Alps appears to resemble closely that suggested previously for the species in northern Europe. PMID:12144661

Holderegger, R; Stehlik, I; Abbott, R J

2002-08-01

150

Glacial terminations and the global water budget  

SciTech Connect

Evidence suggests that the last glacial period came to an abrupt close about 13,500 years ago. This evidence indicates: (1) that the melting of the North American ice sheet commenced abruptly at this time; (2) that surface temperatures in the northern Atlantic rose sharply at this time; (3) that surface water conditions in the Antarctic changed abruptly at this time; (4) that the salinity of the Red Sea dropped abruptly at this time; and (5) that accumulation rate of planktonic foraminifera in the South China Sea underwent an abrupt five-fold increase at this time. This project has been directed toward better developing and documenting our explanation for the abruptness of these changes. This project has supported investigation of several aspects of this hypothesis. We suggest that the Greenland climate changes are driven by oscillations in salt content which modulate the strength of the Atlantic's conveyor circulation.

Broecker, W.S. (Columbia Univ., Palisades, NY (United States). Lamont-Doherty Geological Observatory)

1992-01-01

151

A low-order dynamical model of global climatic variability over the full Pleistocene  

SciTech Connect

A previously formulated dynamical model of the late Pleistocene ice ages (based on the hypothesis that the global CO{sub 2} system can provide the instability to drive a natural oscillation involving feedbacks between the cryosphere, atmosphere, and ocean) is extended to include (1) additive earth orbital forcing (summer insolation changes at 65{degree}N) and (2) tectonic forcing in the form of a postulated variation in the multiplicative parameters (rate constants) of the model system. The structural (e.g., bifurcation) properties of the model are examined in detail to reveal the regions of parameter space wherein the geologically inferred features of the full Pleistocene can be simulated, including the observed chronology, the phase relationships between ice, CO{sub 2}, and North Atlantic Deep Water formation, and the mid-Pleistocene transition.

Maasch, K.A.; Saltzman, B. (Yale Univ., New Haven, CT (United States))

1990-02-20

152

Shorelines of Glacial Lake Hitchcock  

NSDL National Science Digital Library

Bob Newton, Smith College Summary This activity uses GIS methods to subtract the isostatic rebound from a DEM in order to create a map of the shoreline of Glacial Lake Hitchcock. Students are then able to evaluate ...

Bob Newton

153

Sudbury Breccia and suevite as glacial indicators transported 800 km to Kentland Astrobleme, Indiana  

NASA Technical Reports Server (NTRS)

A glacial erratic whose place of origin is known by direct comparison with bedrock is known as an indicator. In 1971, while visiting the known astrobleme at Kentland, Indiana, Peredery recognized and sampled in the overlying glacial drift deposits a distinctive boulder of Sudbury suevite (black member, Onaping Formation) that normally occurs within the Sudbury Basin as an impact fall-back or wash-in deposit. The rock was sampled (but later mislaid) from a farmer's cairn next to a cleared field. Informal reports of this discovery prompted the other authors to recently reconnoiter the Kentland locality in an attempt to relocate the original boulder. Several breccia blocks were sampled but laboratory examination proved most of these probably to be diamictites from the Precambrian Gowganda Formation, which outcrops extensively in the southern Ontario. However, one sample was confirmed as typical Sudbury Breccia, which outcrops in the country rock surrounding the Sudbury Basin. Thus two glacial indicators were transported by Pleistocene continental glaciers about 820 km over a tightly proscribed path and, curiously, from one astrobleme to another. Brecciated boulders in the Illinois/Indiana till plain are usually ascribed to the Gowganda or Mississagi formations in Ontario. But impact-generated rocks need not be confused. The carbonaceous matrix of the suevite, for example, was sufficiently distinctive to assign it to the upper portion of the black Onaping. The unique and restricted source area of these indicators provide an accurate and reliable control for estimating Pleistocene ice movement.

Mchone, John F.; Dietz, Robert S.; Peredery, Walter V.

1992-01-01

154

Chronology for Fluctuations in Late Pleistocene Sierra Nevada Glaciers and Lakes  

Microsoft Academic Search

Mountain glaciers, because of their small size, are usually close to equilibrium with the local climate and thus should provide a test of whether temperature oscillations in Greenland late in the last glacial period are part of global-scale climate variability or are restricted to the North Atlantic region. Correlation of cosmogenic chlorine-36 dates on Sierra Nevada moraines with a continuous

Fred M. Phillips; Marek G. Zreda; Larry V. Benson; Mitchell A. Plummer; David Elmore; Pankaj Sharma

1996-01-01

155

Increased sensitivity of the Plio-Pleistocene northwest Pacific to obliquity forcing  

NASA Astrophysics Data System (ADS)

Insolation-driven changes in poleward heat transport and changes in greenhouse gas concentrations can explain aspects of the rise of obliquity-paced climate variability during the Pliocene-Pleistocene transition. Based on an alkenone-based sea surface temperature (SST) reconstruction of the Kuroshio Current Extension (KCE), we propose here that emergence of this region as the primary locus of ocean-atmosphere heat transfer in the Pacific Ocean promoted Northern Hemisphere Glaciation (NHG). Our record shows that with intensification of NHG at 2.7 Ma, the KCE cooled 2-4?°C during glacial intervals, likely in NH winter/spring. These high-amplitude 41-kyr SST cycles slightly lead ?O18 variations, ruling out global ice-volume changes as the primary cause. The lead of SST over ?O18 cycles matches the phasing between these two proxies observed in the tropics, supporting changes in CO2 concentrations as a unifying mechanism of ocean surface temperature change. However, the amplitude of the KCE SST cycle is twice that of the tropical records, pointing to an additional, regional process. We infer that cooling of the North Pacific sea surface by the East Asian winter monsoon and associated westerlies intensified during glacial intervals. This transfer of heat and moisture from the ocean to the atmosphere potentially furthered glacial formation by accelerating snow fall in North America. Therefore, these results might also support a role for tropical-extratropical heat balance in enhancing glacial growth via the obliquity pacing.

Venti, Nicholas L.; Billups, Katharina; Herbert, Timothy D.

2013-12-01

156

Glacial Features of North Dakota  

NSDL National Science Digital Library

The glacial landforms of North Dakota are revealed through photographs of an end moraine, glacial erratic, eskers, ice thrust masses, an ice-walled lake plain, a kame, kettle lakes, a meltwater channel, outwash, and till. Each image is accompanied by a brief description of the location, how the landform originated, and its composition. The descriptions point out that some features have commercial value as sources of sand and gravel.

157

Science Sampler: Glacial ice action  

NSDL National Science Digital Library

Current news reports discuss the loss of glacial ice in the Antarctic and Greenland as examples of the effects of global warming. But what are glaciers and how do they work? An understanding of the process that causes ice to melt is important in understanding the causes of global glacial loss. This article describes two inquiry-based activities that will help students to form a solid understanding of glaciers.

Bourdeau, Virginia

2008-10-01

158

New GEOPHYSICAL MAPPING of the CHUKCHI MARGIN reveals widespread GLACIAL EROSION  

NASA Astrophysics Data System (ADS)

Multibeam bathymetry, multi-channel, and chirp seismic data were acquired in a broad grid from R/V Marcus G. Langseth in September, 2011 over the outer Chukchi shelf, Chukchi Rise, Northwind Basin, and Northwind Ridge at water depths between 40 to 4,000 m. In the bathymetric data, iceberg scouring is dominant at depths less than 350 m, and multiple glacigenic bedforms are observed on the top and slopes (350-900 m) of Chukchi Rise and Borderland. The distribution mega-scale glacial lineations and ice-marginal moraines reveal a complex erosional history. The glacial lineations record two patterns of erosion which are likely formed by local and Laurentide sourced ice streams, recurrent over several glacial episodes. In the areas affected by glacial erosion, the chirp sub-bottom data reveal multiple sedimentary units including: well stratified post and inter-glacial deposits, transparent units interpreted as deformable tills, lenticular and fan shaped units interpreted as ice-marginal features and re-deposited sediments, and pre-glacial strata. A broadly observed buried erosional surface(s) exhibits high-frequency scouring and broad channelling also reveals multiple episodes of glacial erosion. A deeper erosional channel observed in the multi-channel seismic data is tunnel-valley like in form, and may be genetically linked to the large, buried erosional/drainage channels recently observed in the Bering Sea. The data obtained suggest that a Pleistocene ice sheet(s) existed on the northern Chukchi Shelf, and supports earlier conclusions of multiple erosions of the Borderland by SE-NW trending ice flows. The data greatly expand our knowledge on the Quaternary history of the Chukchi-Beringian region, and raise further questions about: the interaction of ice masses from the Laurentide, and potentially Chukchi and East-Siberian Shelf ice sheets, the glacio-isostatic history in the Bering region, and the implications for oceanic and atmospheric circulation, especially the Arctic-Pacific connection.

Dove, D.; Polyak, L. V.; Coakley, B.

2012-12-01

159

A fundamental Precambrian-Phanerozoic shift in earth's glacial style?  

NASA Astrophysics Data System (ADS)

It has recently been found that Neoproterozoic glaciogenic sediments were deposited mainly at low paleolatitudes, in marked qualitative contrast to their Pleistocene counterparts. Several competing models vie for explanation of this unusual paleoclimatic record, most notably the high-obliquity hypothesis and varying degrees of the snowball Earth scenario. The present study quantitatively compiles the global distributions of Miocene-Pleistocene glaciogenic deposits and paleomagnetically derived paleolatitudes for Late Devonian-Permian, Ordovician-Silurian, Neoproterozoic, and Paleoproterozoic glaciogenic rocks. Whereas high depositional latitudes dominate all Phanerozoic ice ages, exclusively low paleolatitudes characterize both of the major Precambrian glacial epochs. Transition between these modes occurred within a 100-My interval, precisely coeval with the Neoproterozoic-Cambrian "explosion" of metazoan diversity. Glaciation is much more common since 750 Ma than in the preceding sedimentary record, an observation that cannot be ascribed merely to preservation. These patterns suggest an overall cooling of Earth's longterm climate, superimposed by developing regulatory feedbacks involving an increasingly complex biosphere.

Evans, D. A. D.

2003-11-01

160

Variations in Glacial Erosion over Multiple Glacial-Interglacial Cycles  

NASA Astrophysics Data System (ADS)

Glacial erosion plays an important role in the construction and development of many mountain ranges. When modeling orogenic development, the choice of ice-flow physics can have an influence on developing topography, though many simple models can still produce the distinctive geomorphological features associated with glaciated topography. However, detailed comparisons at orogenic-time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. Within a modified version of the ICE-Cascade landscape evolution model, we present results from a comparison between two different numerical models of glacial flow. This orogenic model calculates not only glaciological processes but also hillslope and fluvial erosion, sediment transport, isostasy, and temporally and spatially variable orographic precipitation. Over single and multiple glaciations and in a variety of climate scenarios, glacial erosion rates and topographic evolution are analyzed. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3D Stokes-flow model calculated using COMSOL Multiphysics. The time-averaged erosion rates differ between the two models of ice physics. In addition, these results and the amount of variation between the models are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model leads to larger erosion rates, by almost an order of magnitude, also with more variance. Additionally, as the erosion, basal topography and the ice deformation are all interconnected through the glacial dynamics, comparisons of large-scale and glacier-wide properties can also be instructive. For these properties, particularly the ice thickness and extent, the higher-order glacial model can lead to variations between the ice flow models that are greater than 30%, again with larger differences for temperate ice. When compared after multiple glaciations and long-time scales, these results suggest that consideration of higher-order glacial physics may be necessary, particularly in regions with extensive temperate or polythermal glaciers.

Headley, R. M.; Ehlers, T. A.

2013-12-01

161

Molecular biogeography of Europe: Pleistocene cycles and postglacial trends  

PubMed Central

The climatic cycles with subsequent glacial and intergalcial periods have had a great impact on the distribution and evolution of species. Using genetic analytical tools considerably increased our understanding of these processes. In this review I therefore give an overview of the molecular biogeography of Europe. For means of simplification, I distinguish between three major biogeographical entities: (i) "Mediterranean" with Mediterranean differentiation and dispersal centres, (ii) "Continental" with extra-Mediterranean centres and (iii) "Alpine" and/or "Arctic" with recent alpine and/or arctic distribution patterns. These different molecular biogeographical patterns are presented using actual examples. Many "Mediterranean" species are differentiated into three major European genetic lineages, which are due to glacial isolation in the three major Mediterranean peninsulas. Postglacial expansion in this group of species is mostly influenced by the barriers of the Pyrenees and the Alps with four resulting main patterns of postglacial range expansions. However, some cases are known with less than one genetic lineage per Mediterranean peninsula on the one hand, and others with a considerable genetic substructure within each of the Mediterranean peninsulas, Asia Minor and the Maghreb. These structures within the Mediterranean sub-centres are often rather strong and in several cases even predate the Pleistocene. For the "Continental" species, it could be shown that the formerly supposed postglacial spread from eastern Palearctic expansion centres is mostly not applicable. Quite the contrary, most of these species apparently had extra-Mediterranean centres of survival in Europe with special importance of the perialpine regions, the Carpathian Basin and parts of the Balkan Peninsula. In the group of "Alpine" and/or "Arctic" species, several molecular biogeographical patterns have been found, which support and improve the postulates based on distribution patterns and pollen records. Thus, genetic studies support the strong linkage between southwestern Alps and Pyrenees, northeastern Alps and Carpathians as well as southeastern Alps and the Dinaric mountain systems, hereby allowing conclusions on the glacial distribution patterns of these species. Furthermore, genetic analyses of arctic-alpine disjunct species support their broad distribution in the periglacial areas at least during the last glacial period. The detailed understanding of the different phylogeographical structures is essential for the management of the different evolutionary significant units of species and the conservation of their entire genetic diversity. Furthermore, the distribution of genetic diversity due to biogeographical reasons helps understanding the differing regional vulnerabilities of extant populations. PMID:17439649

Schmitt, Thomas

2007-01-01

162

Pleistocene to Recent deep-coral growth on peri-Ionian escarpments, Mediterranean basin  

NASA Astrophysics Data System (ADS)

Significant growth of deep-sea cold-water coral build-ups is well documented in the Mediterranean basin since the late Pliocene at least. Early-Middle Pleistocene coral assemblages made up by the scleractinian triad Lophelia-Madrepora-Desmophyllum (LMD), crop out locally in areas subjected to considerable neotectonic uplift, i.e. Calabria, Sicily and Rhodes. Furthermore, submerged LMD build-ups, mostly dated to the latest Pleistocene, are common and widespread in the entire basin. LMD communities were severely impacted by post-glacial modifications of the Mediterranean oceanography that caused their general decline in this basin. As a result, the distribution of surviving LMD communities is today quite patchy in the Mediterranean Sea and this is especially true for the branching scleractinian Lophelia. The Ionian Sea is no exception and Pleistocene deep-coral thanatocoenoses are present on sediment-starved, rocky escarpments rimming this sub-basin. However, astonishingly healthy LMD banks dominated by living colonies of Lophelia prolifera, have been recently discovered on the eastern side of the Ionian Sea. The living coral banks are located on a gently dipping shelf offshore the Apulian coast at depths comprised between 300-1000 m. Side Scan Sonar, high-resolution seismic and direct sampling indicate that these Lophelia reefs colonize quasi-indurate Pleistocene sediment. By comparison with modern Eastern Atlantic and Pleistocene Mediterranean counterparts, these modern coral banks display a lesser-diversified associated invertebrate fauna. Finally, a direct link between the occurrence of these coral banks and seepage of hydrocarbons is not evident.

Taviani, M.; Corselli, C.; Freiwald, A.; Malinverno, E.; Mastrototaro, F.; Remia, A.; Savini, A.; Tursi, A.

2003-04-01

163

Coastal staircase sequences reflecting sea-level oscillations and tectonic uplift during the Quaternary and Neogene  

NASA Astrophysics Data System (ADS)

Many coasts feature sequences of Quaternary and Neogene shorelines that are shaped by a combination of sea-level oscillations and tectonics. We compiled a global synthesis of sea-level changes for the following highstands: MIS 1, MIS 3, MIS 5e and MIS 11. Also, we date the apparent onset of sequences of paleoshorelines either from published data or tentatively extrapolating an age for the uppermost, purported oldest shoreline in each sequence. Including the most documented MIS 5e benchmark, we identify 926 sequences out of which 185 also feature Holocene shorelines. Six areas are identified where elevations of the MIS 3 shorelines are known, and 31 feature elevation data for MIS 11 shorelines. Genetic relationships to regional geodynamics are further explored based on the elevations of the MIS 5e benchmark. Mean apparent uplift rates range from 0.01 ± 0.01 mm/yr (hotspots) to 1.47 ± 0.08 mm/yr (continental collision). Passive margins appear as ubiquitously uplifting, while tectonic segmentation is more important on active margins. From the literature and our extrapolations, we infer ages for the onset of formation for ~ 180 coastal sequences. Sea level fingerprinting on coastal sequences started at least during mid Miocene and locally as early as Eocene. Whether due to the changes in the bulk volume of seawater or to the temporal variations in the shape of ocean basins, estimates of eustasy fail to explain the magnitude of the apparent sea level drop. Thus, vertical ground motion is invoked, and we interpret the long-lasting development of those paleoshore sequences as the imprint of glacial cycles on globally uplifted margins in response to continental compression. The geomorphological expression of the sequences matches the amplitude and frequency of glacial cyclicity. From middle Pleistocene to present-day, moderately fast (100,000 yrs) oscillating sea levels favor the development of well identified strandlines that are distinct from one another. Pliocene and Lower Pleistocene strandlines associated with faster cyclicity (40,000 yrs) are more compact and easily merge into rasas, whereas older Cenozoic low-frequency eustatic changes generally led to widespread flat-lying coastal plains.

Pedoja, Kevin; Husson, Laurent; Johnson, Markes E.; Melnick, Daniel; Witt, Cesar; Pochat, Stéphane; Nexer, Maëlle; Delcaillau, Bernard; Pinegina, Tatiana; Poprawski, Yohann; Authemayou, Christine; Elliot, Mary; Regard, Vincent; Garestier, Franck

2014-05-01

164

Vegetation of the Central Beringian Lowlands: Evidence of a Glacial Refugium Found in IODP Expedition 323 Sediment  

NASA Astrophysics Data System (ADS)

The lowlands of central Beringia may have acted as a glacial refugium for boreal vegetation, which expanded into eastern and western Beringia as climate changed and glaciers retreated. Persistence of trees, shrubs and mesic-adapted vegetation in the vicinity of the modern Bering Strait and Bering Sea Shelf could have presented a barrier to migrating fauna during Pleistocene glacial stages. These hypotheses have been difficult to test, because sampling has been restricted to lacustrine sediment and peat deposits accessible in eastern and western Beringia. Pollen analysis of cores from IODP Expedition 323 (Bering Sea Expedition) sites U1339 and U1343, on the edge of the Bering Sea Shelf, permits reconstruction of the terrestrial vegetation of adjacent south-central Beringia. Palynological assemblages extracted from sediment that accumulated during Marine Isotope Stages 2 and 6 are dominated by grass (Poaceae ? 15%) and sedge (Cyperaceae ? 20%). Spruce (Picea ? 5%), birch (Betula ? 10%) and alder (Alnus ? 5%) are also consistently present throughout glacial/interglacial cycles, suggesting that small populations of trees and shrubs remained in central Beringia during glacial maxima. These results support the refugium hypothesis. Although it is possible that some of the boreal plant pollen deposited during glacial stages is derived from interglacial sediment reworked by rivers flowing across the emergent shelf, we postulate that such sources only contribute about 1-5% of the total sediment found at these Bering slope sites. Thus we consider the palynological assemblages from IODP Expedition 323 a robust proxy for the glacial vegetation of central Beringia.

Westbrook, R.; Fowell, S. J.; Bigelow, N. H.; VanLaningham, S.

2011-12-01

165

Glacial-interglacial organic carbon record from the Makassar Strait, Indonesia: Implications for regional changes in continental vegetation  

USGS Publications Warehouse

Recent studies convincingly show that climate in the Western Pacific Warm Pool and other equatorial/tropical regions was significantly colder (by ???3-4??C) during glacial periods, prompting a reexamination of the late Pleistocene paleoenvironments of these regions. This study examines changes in continental vegetation during the last two deglaciations (Terminations I and II) using a sediment core (MD9821-62) recovered from the Makassar Strait, Indonesia. Evidence based on the lignin phenol ratios suggests that vegetation on Borneo and other surrounding islands did not significantly change from tropical rainforest during the last two glacial periods relative to subsequent interglacial periods. This supports the hypothesis that the winter monsoon increased in strength during glacial periods, allowing Indonesia to maintain high rainfall despite the cooler conditions. ?? 2003 Elsevier Ltd. All rights reserved.

Visser, K.; Thunell, R.; Goni, M.A.

2004-01-01

166

The early rise and late demise of New Zealand's last glacial maximum.  

PubMed

Recent debate on records of southern midlatitude glaciation has focused on reconstructing glacier dynamics during the last glacial termination, with different results supporting both in-phase and out-of-phase correlations with Northern Hemisphere glacial signals. A continuing major weakness in this debate is the lack of robust data, particularly from the early and maximum phase of southern midlatitude glaciation (?30-20 ka), to verify the competing models. Here we present a suite of 58 cosmogenic exposure ages from 17 last-glacial ice limits in the Rangitata Valley of New Zealand, capturing an extensive record of glacial oscillations between 28-16 ka. The sequence shows that the local last glacial maximum in this region occurred shortly before 28 ka, followed by several successively less extensive ice readvances between 26-19 ka. The onset of Termination 1 and the ensuing glacial retreat is preserved in exceptional detail through numerous recessional moraines, indicating that ice retreat between 19-16 ka was very gradual. Extensive valley glaciers survived in the Rangitata catchment until at least 15.8 ka. These findings preclude the previously inferred rapid climate-driven ice retreat in the Southern Alps after the onset of Termination 1. Our record documents an early last glacial maximum, an overall trend of diminishing ice volume in New Zealand between 28-20 ka, and gradual deglaciation until at least 15 ka. PMID:25071171

Rother, Henrik; Fink, David; Shulmeister, James; Mifsud, Charles; Evans, Michael; Pugh, Jeremy

2014-08-12

167

Early Pleistocene origin of reefs around Lanai, Hawaii  

USGS Publications Warehouse

A sequence of submerged terraces (L1-L12) offshore Lanai was previously interpreted as reefal, and correlated with a similar series of reef terraces offshore Hawaii island, whose ages are known to be < 500 ka. We present bathymetric, observational, lithologic and 51 87Sr/86Sr isotopic measurements for the submerged Lanai terraces ranging from - 300 to - 1000 m (L3-L12) that indicate that these terraces are drowned reef systems that grew in shallow coral reef to intermediate and deeper fore-reef slope settings since the early Pleistocene. Age estimates based on 87Sr/86Sr isotopic measurements on corals, coralline algae, echinoids, and bulk sediments, although lacking the precision (??? ?? 0.23 Ma) to distinguish the age-depth relationship and drowning times of individual reefs, indicate that the L12-L3 reefs range in age from ??? 1.3-0.5 Ma and are therefore about 0.5-0.8 Ma older than the corresponding reefs around the flanks of Hawaii. These new age data, despite their lack of precision and the influence of later-stage submarine diagenesis on some analyzed corals, clearly revise the previous correlations between the reefs off Lanai and Hawaii. Soon after the end of major shield building (??? 1.3-1.2 Ma), the Lanai reefs initiated growth and went through a period of rapid subsidence and reef drowning associated with glacial/interglacial cycles similar to that experienced by the Hawaii reefs. However, their early Pleistocene initiation means they experienced a longer, more complex growth history than their Hawaii counterparts. ?? 2009 Elsevier B.V.

Webster, J.M.; Clague, D.A.; Faichney, I.D.E.; Fullagar, P.D.; Hein, J.R.; Moore, J.G.; Paull, C.K.

2010-01-01

168

Middle Pleistocene age of the Nome River glaciation, northwestern Alaska  

NASA Astrophysics Data System (ADS)

During the middle Pleistocene Nome River glaciation of northwestern Alaska, glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals. The age of the Nome River glaciation is constrained by laser-fusion {40Ar }/{39Ar} analyses of basaltic lava that overlies Nome River drift at Minnie Creek, central Seward Peninsula, that average 470,000 ± 190,000 yr (±1?). Milligram-size subsamples of the lava were dated to identify and eliminate extraneous 40Ar enrichments that rendered the mean of conventional K?Ar dates on larger bulk samples of the same flow too old (700,000 ± 570,000 yr). While the {40Ar }/{39Ar} analyses provide a minimum limiting age for the Nome River glaciation, maximum ages are provided by a provisional K?Ar date on a basaltic lava flow that underlies the Nome River drift at nearby Lave Creek, by paleomagnetic determinations of the drift itself at and near the type locality, and by amino acid epimerization analysis of molluscan fossils from nearshore sediments of the Anvilian marine transgression that underlie Nome River drift on the coastal plain at Nome. Taken together, the new age data indicate that the glaciation took place between 580,000 and 280,000 yr ago. The altitude of the Anvilian deposits suggests that eustatic sea level during the Anvilian transgression rose at least as high as and probably higher than during the last interglacial transgression; by correlation with the marine oxygen-isotope record, the transgression probably dates to stage 11 at 410,000 yr, and the Nome River glaciation is younger still. Analyses of floor altitudes of presumed Nome River cirques indicate that the Nome River regional snowline depression was at least twice that of the maximum late Wisconsin. The cause of the enhanced snowline lowering appears to be related to greater availability of moisture in northwestern Alaska during the middle Pleistocene.

Kaufman, Darrell S.; Walter, Robert C.; Brigham-Grette, Julie; Hopkins, David M.

1991-11-01

169

Paleoclimatic modeling and phylogeography of least killifish, Heterandria formosa: insights into Pleistocene expansion-contraction dynamics and evolutionary history of North American Coastal Plain freshwater biota  

PubMed Central

Background Climatic and sea-level fluctuations throughout the last Pleistocene glacial cycle (~130-0 ka) profoundly influenced present-day distributions and genetic diversity of Northern Hemisphere biotas by forcing range contractions in many species during the glacial advance and allowing expansion following glacial retreat ('expansion-contraction’ model). Evidence for such range dynamics and refugia in the unglaciated Gulf-Atlantic Coastal Plain stems largely from terrestrial species, and aquatic species Pleistocene responses remain relatively uninvestigated. Heterandria formosa, a wide-ranging regional endemic, presents an ideal system to test the expansion-contraction model within this biota. By integrating ecological niche modeling and phylogeography, we infer the Pleistocene history of this livebearing fish (Poeciliidae) and test for several predicted distributional and genetic effects of the last glaciation. Results Paleoclimatic models predicted range contraction to a single southwest Florida peninsula refugium during the Last Glacial Maximum, followed by northward expansion. We inferred spatial-population subdivision into four groups that reflect genetic barriers outside this refuge. Several other features of the genetic data were consistent with predictions derived from an expansion-contraction model: limited intraspecific divergence (e.g. mean mtDNA p-distance?=?0.66%); a pattern of mtDNA diversity (mean Hd?=?0.934; mean ??=?0.007) consistent with rapid, recent population expansion; a lack of mtDNA isolation-by-distance; and clinal variation in allozyme diversity with higher diversity at lower latitudes near the predicted refugium. Statistical tests of mismatch distributions and coalescent simulations of the gene tree lent greater support to a scenario of post-glacial expansion and diversification from a single refugium than to any other model examined (e.g. multiple-refugia scenarios). Conclusions Congruent results from diverse data indicate H. formosa fits the classic Pleistocene expansion-contraction model, even as the genetic data suggest additional ecological influences on population structure. While evidence for Plio-Pleistocene Gulf Coast vicariance is well described for many freshwater species presently codistributed with H. formosa, this species demography and diversification departs notably from this pattern. Species-specific expansion-contraction dynamics may therefore have figured more prominently in shaping Coastal Plain evolutionary history than previously thought. Our findings bolster growing appreciation for the complexity of phylogeographical structuring within North America’s southern refugia, including responses of Coastal Plain freshwater biota to Pleistocene climatic fluctuations. PMID:24107245

2013-01-01

170

Vicariance biogeography in the Pleistocene and speciation in North American wood warblers: a test of Mengel's model.  

PubMed Central

It is widely believed that habitat fragmentation during the Pleistocene initiated speciation events in many songbird genera. One such vicariance model for avian speciation in the Pleistocene was developed by R. M. Mengel for North American birds. This model suggests that the first Pleistocene glacial advance reduced the area of an extensive, eastern North American deciduous forest, forcing adaptation by some species to boreal forest. This, in turn, facilitated the development of transcontinental range expansions during interglacials. Subsequent glacial advances repeatedly fragmented the ranges of these species into eastern and western populations; western isolates speciated to form the multispecies groups observed among various North American birds. We used mtDNA restriction site data to reconstruct the phylogeny of the black-throated green warbler complex-the group that Mengel considered the best fit to his model. Contrary to Mengel's model, the phylogeny indicates that not all western endemics were derived from an eastern ancestor. Instead, our results imply a mix, wherein some western endemics were budded off an eastern source, as Mengel posits, while others probably resulted from intermontane isolations in the west. PMID:11607307

Bermingham, E; Rohwer, S; Freeman, S; Wood, C

1992-01-01

171

Gulf coastal plain evolution in West Louisiana: Heavy mineral provenance and Pleistocene alluvial chronology  

NASA Astrophysics Data System (ADS)

High Resolution Heavy Mineral Analysis (HRHMA) of late Pleistocene terrace samples, their Tertiary source rocks, and modern river sediments provided an effective tool for reconstructing sediment provenance and mapping heavy mineral provinces in southwest Louisiana. Each province, linked to a discrete source region, represents Pleistocene fluvial channel belts within which depositional activity was controlled by periods of climate, sediment supply, and sea level changes. Four coastal heavy mineral provinces have been identified. The Northern Province (NP), drained by the lower reaches of the Sabine and Calcasieu Rivers underlies level mid- and late Pleistocene coastal terrace surfaces and is distinguished by high-grade metamorphic assemblages (kyanite, staurolite, sillimanite) and abundant zircon, probably of Ouachita Mts. derivation. Transporting eroded Cretaceous, Tertiary, and Pleistocene coastal plain deposits, the modern Calcasieu and Sabine River sands in west-central and southwest Louisiana and east Texas, display identical heavy mineral composition to that of the NP. Level Late Pleistocene coastal terrace areas in the east represent the Red River Province (RRP) with dominant epidote, tourmaline, garnet, and zircon. Its mineralogy is influenced significantly by Paleozoic-Mesozoic sedimentary units that frame the drainage basin upstream. Modern Red River sands differ in their spectra both from Red River Pleistocene coastal terrace and valley terrace deposits, interpreted by temporal fluctuations in sediment supply initiating a variable contribution of detritus from different sources. Tributaries that drain formations with high concentrations of high-grade metamorphic minerals also affected Red River valley Pleistocene terrace deposits in west-central Louisiana, enriching them in kyanite and staurolite. The Mississippi Province (MP) occupies the eastern-southeastern area of the low, flat, gently seaward-sloping Prairie coastal terrace. Whereas modern Mississippi alluvium is dominated by hornblende, pyroxenes, and epidote, as the result of post-depositional dissolution, pyroxenes are rare in the MP. The Mixed Suite Province (MSP) reflects MP, RRP, and to a lesser degree, NP signatures and forms the Prairie fluvial coastal plain surface closer to the Texas state line. Raw data of the principal heavy minerals were used for statistical analysis. Statistical parameters proved consistent with mineralogy-derived reconstruction of sediment provenance and provinciality of heavy mineral suites, thus providing an independent and objective support to data interpretation. Optical and thermal luminescence dating at other Gulf locations [Otvos, E.G. (2005). Numerical chronology of Pleistocene coastal plain and valley development; extensive aggradation during glacial low sea levels. Quaternary Internat., 135 91-113.] supports the pre-Sangamon ages of the Intermediate Pleistocene terraces in the NP area. Sangamon (135-116 ka), Eowisconsin (114-76 ka), and Wisconsin (74-36 ka) dates characterize the four provinces in the low, level northern Gulf Prairie coastal plain. Refuting earlier assumptions that coastal plain aggradation occurred only during marine highstand phases, thermal and optical luminescence dates indicated that, despite the low Eowisconsin and Wisconsin eustatic sea levels of several preglacial and glacial stages and substages, coastal plain alluviation, paradoxically, recurred between 106 and 35 ka BP. An interesting outcome of our heavy mineral study is the recognition and dating of a previously undocumented, rare ash-fall event that originated in Caribbean andesitic volcanoes. It was identified by the presence of a volcanogenic heavy mineral suite, composed of pristine euhedral clinopyroxene, sphene, zircon, apatite, and hexagonal biotite. Unaffected by fluvial reworking, this suite was recovered from a MP sample, dated ca. 86 ka BP.

Mange, Maria A.; Otvos, Ervin G.

2005-12-01

172

Relationships of Palearctic and Nearctic 'glacial relict' Myoxocephalus sculpins from mitochondrial DNA data.  

PubMed

The relationships among Myoxocephalus quadricornis complex fish from Arctic coastal waters and from 'glacial relict' populations in Nearctic and Palearctic postglacial lakes were assessed using mtDNA sequence data (1978 bp). A principal phylogeographical split separated the North American continental deepwater sculpin (M. q. thompsonii) from a lineage of the Arctic marine and North European landlocked populations of the fourhorn sculpin (M. q. quadricornis). The North American continental invasion took place several glaciation cycles ago in the Early-to-Middle Pleistocene (0.9% sequence divergence); the divergence of the European and Arctic populations was somewhat later (0.5% divergence). The Nearctic-Palearctic freshwater vicariance in Myoxocephalus, however, appears clearly younger than in similarly distributed 'glacial relict' crustacean taxa; the phylogeographical structure is more similar to that in other northern Holarctic freshwater fish complexes. PMID:14629397

Kontula, Tytti; Väinölä, Risto

2003-11-01

173

Ocean circulation, ice sheet growth and interhemispheric coupling of millennial climate variability during the mid-Pleistocene (ca 800–400 ka)  

Microsoft Academic Search

Stable carbon and oxygen isotopes from benthic and planktic foraminifers, planktic foraminifer assemblages and ice rafted debris from the North Atlantic Site U1314 (Integrated Ocean Drilling Program Expedition 306) were examined to investigate orbital and millennial-scale climate variability in the North Atlantic and its impact on global circulation focusing on the development of glacial periods during the mid-Pleistocene (ca 800–400ka).

M. Alonso-Garcia; F. J. Sierro; M. Kucera; J. A. Flores; I. Cacho; N. Andersen

2011-01-01

174

Survival and long-term maintenance of tertiary trees in the Iberian Peninsula during the Pleistocene: first record of Aesculus L. (Hippocastanaceae) in Spain  

Microsoft Academic Search

The Italian and Balkan peninsulas have been places traditionally highlighted as Pleistocene glacial refuges. The Iberian Peninsula,\\u000a however, has been a focus of controversy between geobotanists and palaeobotanists as a result of its exclusion from this category\\u000a on different occasions. In the current paper, we synthesise geological, molecular, palaeobotanical and geobotanical data that\\u000a show the importance of the Iberian Peninsula

José María Postigo Mijarra; Fernando Gómez Manzaneque; Carlos Morla

2008-01-01

175

The Mid-Pleistocene Transition: Deep Sea Temperature And Global Ice Volume From Mg\\/Ca and delta18O In Benthic Foraminifera  

Microsoft Academic Search

The mid-Pleistocene transition (MPT), which occurred between ~1 to 0.7 Ma, is recorded in benthic foraminiferal oxygen isotope (delta18Ob) records as a shift in the periodicity of northern hemisphere glaciations from low amplitude 41-kyr to large amplitude 100-kyr glacial-interglacial cycles. The MPT has variably been attributed to either global cooling associated with a long-term decreasing trend in greenhouse gases, or

S. M. Sosdian; Y. Rosenthal; M. Raymo

2006-01-01

176

Surculichnus bifurcauda n. igen., n. isp., a trace fossil from Late Pleistocene glaciolacustrine varves of the Connecticut River Valley, USA, attributed to notostracan crustaceans based on neoichnological experimentation  

Microsoft Academic Search

New trace fossils found in the Late Pleistocene glaciolacustrine varves of the Connecticut River Valley, Vermont, USA represent the first known notostracan presence in glacial Lake Hitchcock. These unique trace fossils warrant a new ichnogenus and ichnospecies Surculichnus bifurcauda. The New England Varve Chronology (NEVC) constrains the initial presence of S. bifurcauda at ?13.3–13.2 kyr. The morphology of S. bifurcauda correlates

Richard J. Knecht; Jacob S. Benner; D. Christopher Rogers; John C. Ridge

2009-01-01

177

Chronology for fluctuations in late pleistocene Sierra Nevada glaciers and lakes  

SciTech Connect

Mountain glaciers, because of their small size, are usually close to equilibrium with the local climate and thus should provide a test of whether temperature oscillations in Greenland late in the last glacial period are part of global-scale climate variability or are restricted to the North Atlantic region. Correlation of cosmogenic chlorine-36 dates on Sierra Nevada moraines with a continuous radiocarbon-dated sediment record from nearby Owens Lake shows that Sierra Nevada glacial advances were associated with Heinrich events 5, 3, and 1. 27 refs., 2 figs., 1 tab.

Phillips, F.M.; Zreda, M.G.; Plummer, M.A. [New Mexico Institute of Mining and Technology, Socorro, NM (United States)] [and others] [New Mexico Institute of Mining and Technology, Socorro, NM (United States); and others

1996-11-01

178

Chronology for fluctuations in late Pleistocene Sierra Nevada glaciers and lakes  

USGS Publications Warehouse

Mountain glaciers, because of their small size, are usually close to equilibrium with the local climate and thus should provide a test of whether temperature oscillations in Greenland late in the last glacial period are part of global-scale climate variability or are restricted to the North Atlantic region. Correlation of cosmogenic chlorine-36 dates on Sierra Nevada moraines with a continuous radiocarbon-dated sediment record from nearby Owens Lake shows that Sierra Nevada glacial advances were associated with Heinrich events 5, 3, 2, and 1.

Phillips, F.M.; Zreda, M.G.; Benson, L.V.; Plummer, M.A.; Elmore, D.; Sharma, P.

1996-01-01

179

Magnetostratigraphy of continental glacial deposits in southernmost Patagonia  

NASA Astrophysics Data System (ADS)

Southernmost Patagonia has well preserved records of continental and alpine glaciations. It is the only region in the Southern Hemisphere outside Antarctica where large Pleistocene ice sheets developed, thus it offers a unique opportunity to enhance understanding of global climate variability. Previous research on the glacial history of Patagonia is largely based on geomorphology, with limited study of stratigraphy and relatively few absolute ages. Consequently, the number, ages, and geographic extent of individual glaciations are not well understood. Geomorphic evidence of multiple Quaternary glaciations is widespread in the region and includes moraines, erratics, drumlin fields, and outwash plains. Exposures of glacial sediments are common along the Atlantic coast, the Strait of Magellan, meltwater channels, and in gravel pits. Most of the glacial deposits are beyond the range of radiocarbon dating. K-Ar and Ar-Ar dating have been used to determine the ages of basalt flows interlayered with till and outwash in the southern Andes to the west and in the Rio Gallegos valley near the Atlantic coast. These absolute ages suggest that glaciation in Patagonia began in the late Miocene and that the Pleistocene Patagonian ice sheet may have decreased in size with each successive advance. We conducted a paleomagnetic study of glacial sediments to further constrain the timing of continental glaciations. The sediments are stably magnetized, providing clear directional data from which polarity can be determined. Most sediments in the area are normally magnetized, but some sediments near the outer limit of glaciation, within areas covered by the Patagonian ice sheet during the Great Patagonian Glaciation (GPG), are reversely magnetized. Recent field work indicates that drift of the GPG comprises deposits of several glaciations. Our paleomagnetic results suggest that the first continental glaciation(s) in the region occurred during the Matuyama Reversed Chron (2.6 - 0.78 Ma) and subsequent glaciations occurred during the Bruhnes Normal Chron (<0.78 Ma). Two interpretations of the data are possible. Our preferred interpretation is that reversely magnetized till(s) record the onset of the 100 ka Milankovitch cycles during the latest Matuyama Reversed Chron (MIS 22 - 20), and overlying normally magnetized tills were deposited during the Brunhes Normal Chron. An alternative interpretation is that glaciation in southernmost Patagonia was initiated during one of the cold periods preceding the Jaramillo normal subchron (MIS 36 - 32), depositing reversely magnetized till(s), and that one of the overlying normally magnetized tills from the most extensive glaciation was laid down during the Jaramillo subchron (MIS 30). The suite of normally magnetized tills must record more than one glaciation and thus could not have all been deposited within the relatively short time interval of the Jaramillo subcron (1.08 - 0.99 Ma). Rather, most of the younger tills and perhaps one or more of the GPG drift sheets, must date to glaciations within the Brunhes Chron. Both options indicate that the first continental glaciation(s) to affect the region occurred during the late Early Pleistocene, consistent with the magnetostratigraphy and chronologies reported for the Canadian Prairies, Northwestern Europe, and Russia.

Griffing, C. Y.; Barendregt, R. W.; Clague, J. J.; Roberts, N. J.; Corbella, H.; Ercolano, B.; Rabassa, J.

2012-12-01

180

Mapping Glacial Erratics with GPS and GIS  

NSDL National Science Digital Library

Katherine McCarville, Upper Iowa University Summary Students create a map of glacial erratics (in Northeast Iowa, although you could do this wherever you have glacial deposits). The activity uses local geology, ...

Katherine McCarville

181

A composite record of Late Pleistocene relative geomagnetic paleointensity from the Wilkes Land Basin (Antarctica)  

NASA Astrophysics Data System (ADS)

We report high-resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of the Wilkes Land Basin (WLB), East Antarctica, in the frame of the Italian/Australian Wilkes Land Glacial History (WEGA) project. The studied cores, with a length of ca. 4 m each, were collected from the gentle and steep sides of sedimentary ridges present in the lower part of the continental rise, and consist of very fine-grained sediments. Paleomagnetic measurements were carried out on u-channel samples. Apart from a low-coercivity magnetic overprint, removed after the first steps of alternating field demagnetization, each core is characterized by a well defined characteristic remanent magnetization. Paleomagnetic inclinations fluctuate around the expected value (of ca. -77°) for such high latitude sites and always indicate normal magnetic polarity. Short period oscillations to anomalously shallow paleomagnetic inclinations (up to -20°) were identified at different levels of the sampled sequences; positive (reverse) inclination values were however not observed. Specific rock magnetic measurements indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences. For each core we reconstructed curves of relative paleointensity (RPI, as computed by NRM 20 mT / ? and NRM 20 mT /ARM 20 mT ) variation of the geomagnetic field. An original age model was established by tuning the individual RPI curves with the available global and regional reference RPI stacks. Paleomagnetic results, supported by other limited bio- and chronostratigraphic constraints, establish that all the cores are Late Pleistocene in age: two provide an expanded record of the last ca. 30 ka (PC18 and PC19), three span the last ca. 100, 200 and 300 ka (respectively, PC25, PC27 and PC26), and one reaches back to ca. 780 ka (PC20), approaching the Brunhes-Matuyama transition. Thus, the WEGA paleomagnetic record provides the first experimental data documenting the dynamics and amplitude of the geomagnetic field variations at high southern latitudes during the Brunhes Chron. The individual normalized RPI records were merged in a WEGA RPI stacking curve spanning the last 300 kyr. The comparison of the WEGA RPI individual and stacked curves with the global references RPI stacks shows that geomagnetic paleointensity variations, with periods longer than a few to tens kyr depending on the sedimentation rate, can be safely recognized in this sector of the peri-Antarctic margins. Furthermore, the stacking of the individual ChRM inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations may be correlated to the main known geomagnetic excursions of the Brunhes Chron, supporting the validity of the age models. The reconstructed average sediment accumulation rates for the individual cores range from 0.6 to 19 cm/ka and are compatible with their position within the WLB, with the lowest rates found close to the ridge of the sedimentary drifts. Moreover, the high-resolution age models obtained in this study provide original constraints to assess chronology, rates and amplitudes of the climatic and environmental processes affecting this key area of the peri-Antarctic margins during the Late Pleistocene.

Macrì, Patrizia; Sagnotti, Leonardo; Dinarès-Turell, Jaume; Caburlotto, Andrea

2005-08-01

182

Pleistocene landscapes in central Iberia inferred from pollen analysis of hyena coprolites  

NASA Astrophysics Data System (ADS)

New pollen data from hyena coprolites from central Spain are presented. The fossil faecal material has been recovered from two karstic systems in different localities, Villacastín and Los Torrejones, which are both around 1000 m a.s.l. The combined findings of bone remains and coprolites in both locations suggest the following chronology: late Middle Pleistocene for Villacastín and early Upper Pleistocene for Los Torrejones. The environments inferred from pollen are broadly in keeping with evidence from associated vertebrate fossil remains, and include a shifting mosaic of open and wooded habitats with abundant pine and juniper species, steppe-grassland areas with composites and chenopods, and enclaves with mixed oak forests. However, Los Torrejones appears to have been less forested than Villacastín. The abundance of oaks in Villacastín may imply the presence of refugia within an interconnected network of several enclaves during the glacial stages in the Upper Pleistocene. A possible explanation for the patchiness of the landscape may be in the role of herbivores, although the long distances and variety of habitats that hyenas had to roam through could be another explanation for the heterogeneous pollen contents in their dung. Copyright

Carrión, J. S.; Scott, L.; Arribas, A.; Fuentes, N.; Gil-Romera, G.; Montoya, E.

2007-02-01

183

Persistent 400,000-year variability of Antarctic ice volume and the carbon cycle is revealed throughout the Plio-Pleistocene.  

PubMed

Marine sediment records from the Oligocene and Miocene reveal clear 400,000-year climate cycles related to variations in orbital eccentricity. These cycles are also observed in the Plio-Pleistocene records of the global carbon cycle. However, they are absent from the Late Pleistocene ice-age record over the past 1.5 million years. Here we present a simulation of global ice volume over the past 5 million years with a coupled system of four three-dimensional ice-sheet models. Our simulation shows that the 400,000-year long eccentricity cycles of Antarctica vary coherently with ?(13)C data during the Pleistocene, suggesting that they drove the long-term carbon cycle changes throughout the past 35 million years. The 400,000-year response of Antarctica was eventually suppressed by the dominant 100,000-year glacial cycles of the large ice sheets in the Northern Hemisphere. PMID:24385005

de Boer, B; Lourens, Lucas J; van de Wal, Roderik S W

2014-01-01

184

Gulf coastal Pleistocene units and time stratigraphy; reevaluation and problems of Atlantic correlation  

SciTech Connect

Outdated glacial subdivisions and misinterpretations of alluvial interfluve ridges as marine terraces hampered advances in coastal stratigraphy. One problem involves C.W. Cooke's extension of his Atlantic shorelines along the NE Gulf into the Mississippi Embayment. The mirage of an inter-Wisconsinan interglacial gave way to beliefs in high glacial Wisconsinan sea levels that were assumed to have resulted in barriers and intensive alluvial aggradation on the TX-LA coastal plain. Without vertical definitions, Fisk assigned formation status to alluvial and brackish-marine sediments that directly underlie four coastwise Pleistocene terraces in SW Louisiana. The youngest (Prairie) and associated formations were recently (re)defined and correlated with other coastal areas. Brackish and marine deposits in the subsurface have been correlated with Fisk's second youngest coastwise surface. Detailed facies analyses of cores from hundreds of drillholes indicated that, in sharp contrast with Plio-Pleistocene barriers on the Atlantic coast, only a single, Sangamonian (Sg) barrier shore complex remains on the NE Gulf coastal plain after intensive uplift/erosion. Few isolated remnants of pre-Sg Pleistocene alluvial units occur, including flora elements in peat lenses at one location. An early, low Sg sea level stand near Apalachicola is marked by transgressive deposits at c. [minus]37.5m. Thin NE Gulf Sg sequence includes the fine-grained, open marine-to-estuarine Biloxi, the regressive, shallow subtidal-to-supratidal, mainland Gulfport barrier and the alluvial Prairie Formations. These are correlatable Gulfwide. Contrary to widespread assumption, the Gulfport-Ingleside barriers were not islands but mainland strandplains. The Sg complex correlates with oxygen isotope Stage 5 units of the Mid/South Atlantic coastal plain and shelf. Thick LA-TX shelf/slope intervals display about ten fourth-order cycles within 4 primary ones.

Otvos, E.G. (Gulf Coast Research Lab., Ocean Springs, MS (United States). Geology Section)

1993-03-01

185

Evidence for a Younger Dryas glacial advance in the Andes of northwestern Venezuela  

NASA Astrophysics Data System (ADS)

Deposits of push moraine, outwash and glaciolacustrine sediments, recovered from two areas in the northwestern Venezuelan Andes document the latest Pleistocene advance of Mérida ice. Underlying peats provide maximum ages on till and outwash evidently emplaced during the Younger Dryas (YD) climatic event. One example recovered from the Humboldt Massif, where the farthest extent of YD ice buried peat in the surface of Late Glacial till, provides a within-glacier advance age of 12.4 ka cal BP. The peat lies on moraine deposited during a stillstand event when the Humboldt Glacier retreated to the area of Lago Verde at ˜ 4000 m a.s.l. Approximately 0.5 km upvalley, toward Lago Suero, YD till buries peat deposited in glaciolacustrine sediments of presumed Late Glacial age. Farther north, in the Mucuñuque-Mucubají Catchment of the eastern cordillera, a push moraine of possible YD age buries older till of Late Glacial age; ˜ 0.2 km upvalley, outwash of YD age buries glaciolacustrine peat and organic-rich alluvial sediment dated to 13.7 and 13.3 ka cal BP. The latest Mérida advance documented here is approximately synchronous with the YD cold event of Europe and the North Atlantic Region (ca. 11.6-12.7 ka cal BP). The YD event in both areas of the northwestern Venezuelan Andes nearly reestablished earlier Late Glacial ice positions, and termination appears to have been abrupt; the valleys in both areas were evacuated of YD ice without emplacement of recessional moraines as during the main deglaciation. At the Humboldt site, equilibrium line altitudes (ELA's) for the Late Glacial were about 50 m lower than during the inferred YD; in the Mucuñuque-Mucubají catchment, ELA's for the Late Glacial (~ 3900 m a.s.l.) are difficult to establish given the absence of lateral moraines.

Mahaney, William C.; Milner, M. W.; Kalm, Volli; Dirszowsky, Randy W.; Hancock, R. G. V.; Beukens, Roelf P.

2008-04-01

186

The distinct roles of the Antarctic and Subantarctic Zones in ocean productivity and atmospheric CO2 across the Mid-Pleistocene transition  

NASA Astrophysics Data System (ADS)

The emergence of low frequency, high-amplitude, quasi-periodic (100-kyr) glacial variability during the middle Pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system. The mid-Pleistocene transition (MPT), which occurred between 1.2 and 0.7 Myr, has variably been attributed to either global cooling possibly associated with a long-term decrease in greenhouse gas concentrations or changes in internal ice-sheet dynamics independent of changes in atmospheric pCO2. The available low-resolution pCO2 estimates indicate that atmospheric CO2 concentrations were 30 ppm higher during glacial stages before the MPT, but also that interglacial values were similar to those of the late Pleistocene. This resulted in no significant change in the atmospheric CO2 trend. However, the higher atmospheric CO2 concentrations during glacial stages resulted in an increase in glacial temperatures in the tropics, and a 30% decrease in glacial/interglacial amplitude before 450 kyr. During this period Southern Ocean dust fluxes doubled and reached values that are comparable to those of the LGM. Thus, an increase in Fe availability may have potentially contributed, in combination with other mechanisms to explain part of the 30 ppm decrease in glacial atmospheric CO2 observed across the MPT. This observation is coherent with a progressive increase in glacial carbon sequestration due to Fe fertilization in the Southern Ocean as Northern Hemisphere glaciations intensify. Here, we investigate how the combined changes in Fe supply and in the strength of vertical convection have affected the sequestration of remineralized carbon in the ocean interior over the last 1.6 Myrs. We will show highly-resolved, continuous records from two South Atlantic ODP sedimentary archives located on either side of the Antarctic polar front highlighting the existence of a strong positive feedback mechanism between ice volume, Southern Ocean dust deposition and export production that has gradually strengthened through the Pliocene-Pleistocene.

Jaccard, S.; Martinez-Garcia, A.; Hasenfratz, A.; Sigman, D. M.; Haug, G. H.

2012-12-01

187

Arsenic Geochemistry and Hydrostratigraphy in Midwestern U.S. Glacial Deposits  

USGS Publications Warehouse

Arsenic concentrations exceeding the U.S. EPA's 10 ??g/L standard are common in glacial aquifers in the midwestern United States. Previous studies have indicated that arsenic occurs naturally in these aquifers in association with metal-(hydr)oxides and is released to groundwater under reducing conditions generated by microbial oxidation of organic matter. Despite this delineation of the arsenic source and mechanism of arsenic mobilization, identification of arsenic-impacted aquifers is hindered by the heterogeneous and discontinuous nature of glacial sediments. In much of the Midwest, the hydrostratigraphy of glacial deposits is not sufficiently characterized to predict where elevated arsenic concentrations are likely to occur. This case study from southeast Wisconsin presents a detailed characterization of local stratigraphy, hydrostratigraphy, and geochemistry of the Pleistocene glacial deposits and underlying Silurian dolomite. Analyses of a single core, water chemistry data, and well construction reports enabled identification of two aquifers separated by an organic-rich aquitard. The upper, unconfined aquifer provides potable water, whereas arsenic generally exceeds 10 ??g/L in the deeper aquifer. Although coring and detailed hydrostratigraphic characterization are often considered impractical, our results demonstrate that a single core improved interpretation of the complex lithology and hydrostratigraphy. This detailed characterization of hydrostratigraphy facilitated development of well construction guidelines and lays the ground work for further studies of the complex interactions among aquifer sediments, hydrogeology, water chemistry, and microbiology that lead to elevated arsenic in groundwater. Copyright ?? 2009 The Author(s). Journal compilation ?? 2009 National Ground Water Association.

Root, T.L.; Gotkowitz, M.B.; Bahr, J.M.; Attig, J.W.

2010-01-01

188

Periglacial fires and trees in a continental setting of Central Canada, Upper Pleistocene.  

PubMed

Fire is a key factor controlling global vegetation patterns and carbon cycling. It mostly occurs under warm periods during which fuel builds up with sufficient moisture, whereas such conditions stimulate fire ignition and spread. Biomass burning increased globally with warming periods since the last glacial era. Data confirming periglacial fires during glacial periods are very sparse because such climates are likely too cold to favour fires. Here, tree occurrence and fires during the Upper Pleistocene glacial periods in Central Canada are inferred from botanical identification and calibrated radiocarbon dates of charcoal fragments. Charcoal fragments were archived in sandy dunes of central Saskatchewan and were dated >50000-26600 cal BP. Fragments were mostly gymnosperms. Parallels between radiocarbon dates and GISP2-?¹?O records deciphered relationships between fire and climate. Fires occurred either hundreds to thousands of years after Dansgaard-Oeschger (DO) interstadial warming events (i.e., the time needed to build enough fuel for fire ignition and spread) or at the onset of the DO event. The chronological uncertainties result from the dated material not precisely matching the fires and from the low residual ¹?C associated with old sample material. Dominance of high-pressure systems and low effective moisture during post-DO coolings likely triggered flammable periglacial ecosystems, while lower moisture and the relative abundance of fuel overshadowed lower temperatures for fire spread. Laurentide ice sheet (LIS) limits during DO events are difficult to assess in Central Canada due to sparse radiocarbon dates. Our radiocarbon data set constrains the extent of LIS. Central Saskatchewan was not covered by LIS throughout the Upper Pleistocene and was not a continental desert. Instead, our results suggest long-lasting periods where fluctuations of the northern tree limits and fires after interstadials occurred persistently. PMID:24405713

Bélanger, N; Carcaillet, C; Padbury, G A; Harvey-Schafer, A N; Van Rees, K J C

2014-03-01

189

Environmental Influences on Pleistocene Hominid Dental Evolution  

ERIC Educational Resources Information Center

Considers natural and cultural environmental factors likely to have been responsible for reduction in size of hominid teeth and simplification of their morphology during the Pleistocene. Cites fossil evidence and postulates selective mechanisms. (EB)

Greene, David L.

1970-01-01

190

Last Glacial Maximum  

NSDL National Science Digital Library

Short lecture on CLIMAP project (see PowerPoint) 20 minutes Powerpoint (PowerPoint 444kB Nov7 10) Group activity - Reading for CLIMAP study assumptions, 20 minutes to read, 20 minutes for discussion Student Handout (Microsoft Word 50kB Nov7 10) Students break into groups (4 per group is good division of work) with 2 students per paper. Split the assumptions between students. Each group skims the CLIMAP papers for the assumptions (modern and/or LGM) used in the CLIMAP model-based reconstruction of the LGM. In the groups, students compare the assumptions between papers. Resources: CLIMAP (1976), The surface of the ice-age earth, Science, 191(4232), 1131-1137 and CLIMAP (1984), The last interglacial ocean, Quaternary Research, 21(2), 123. Class Discussion - Summarize assumptions used in CLIMAP studies. Group activity Exploring CLIMAP LGM Reconstructions, 40 minutes for model data, 20 minutes for discussion (Could be modified with as a "jigsaw" activity with a larger class). Learn more about the jigsaw teaching method. Students work on this activity in pairs; one person will create LGM maps, the other modern. Students should sit together with their computer monitors close together to compare. The students will use the IRI/LDEO Climate Data Library to access the CLIMAP reconstruction and produce maps using the tools available on this web site. In a web browser, go to http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/ This is the main page for the CLIMAP Model output for the LGM 18,000 BP. In the middle of the page is the label "Datasets and variables" with two data sets below http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/.LGM/ and http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/.MOD/. Each student clicks on the link they are assigned to. There are several data sets listed for each period and the students will examine each data set and compare the LGM and Modern. As a class, go through each data set allowing pairs to compare the maps then summarize the results as a class. The worksheet has a table for the students and the PowerPoint has table for summarizing. Class Discussion - Summarize differences between modern and LGM in the CLIMAP model output. Discuss how the assumptions of the CLIMAP model studies may have influenced the results. Extra activities The students can explore the data further using the data selection and filters in the IRI/LDEO Climate Data Library. For the two SST data sets, click on "Data Selection" and narrow the data to the just the tropics (23.5º N-S). Click on "Filters" then select XY next to "Average over." The next window gives you the average over the tropics close to the top of the page. In the next class, the students repeat the Readings exercise by reading the COHMAP and MARGO papers to see how the scientific knowledge has progressed since the original CLIMAP studies. COHMAP Members, (1988), Climatic Changes of the Last 18,000 Years: Observations and Model Simulations, Science, 241(4869), 1043-1052. MARGO (2009), Constraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum, Nature Geoscience, 2(2), 127-132.

Kristine DeLong

191

Predicting Pleistocene climate from vegetation  

NASA Astrophysics Data System (ADS)

Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder than those produced by climate simulations. Biogeographic evidence also argues against these inferred cold climates. The recolonization of glaciated zones in eastern North America following the last ice age produced distinct biogeographic patterns. It has been assumed that a wide zone south of the ice was tundra or boreal parkland (Boreal-Parkland Zone or BPZ), which would have been recolonized from southern refugia as the ice melted, but the patterns in this zone differ from those in the glaciated zone, which creates a major biogeographic anomaly. In the glacial zone, there are few endemics but in the BPZ there are many across multiple taxa. In the glacial zone, there are the expected gradients of genetic diversity with distance from the ice-free zone, but no evidence of this is found in the BPZ. Many races and related species exist in the BPZ which would have merged or hybridized if confined to the same refugia. Evidence for distinct southern refugia for most temperate species is lacking. Extinctions of temperate flora were rare. The interpretation of spruce as a boreal climate indicator may be mistaken over much of the region if the spruce was actually an extinct temperate species. All of these anomalies call into question the concept that climates in the zone south of the ice were very cold or that temperate species had to migrate far to the south. Similar anomalies exist in Europe and on tropical mountains. An alternate hypothesis is that low CO2 levels gave an advantage to pine and spruce, which are the dominant trees in the BPZ, and to herbaceous species over trees, which also fits the observed pattern. Most temperate species could have survived across their current ranges at lower abundance by retreating to moist microsites. These would be microrefugia not easily detected by pollen records, especially if most species became rare. These results mean that climate reconstruction based on terrestrial plant indicators will not be valid for periods with markedly different CO2 levels.

Loehle, C.

2006-10-01

192

Constraints on the Pleistocene chronology of sediments from the Lomonosov Ridge  

USGS Publications Warehouse

Despite its importance in the global climate system, age-calibrated marine geologic records reflecting the evolultion of glacial cycles through the Pleistocene are largely absent from the central Arctic Ocean. This is especially true for sediments older than 200 ka. Three sites cored during the Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), provide a 27 m continuous sedimentary section from the Lomonosov Ridge in the central Arctic Ocean. Two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the Cobb Mountain subchron (1215 ka). Beyond 1215 ka, two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change. Within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted Milankovitch frequencies. These cyclic variations record "glacial" and "interglacial" modes of sediment deposition on the Lomonosov Ridge as evident in studies of ice-rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model. Potential errors, which largely arise from uncertainties in the nature of downhole paleomagnetic variability, and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions. Copyright 2008 by the American Geophysical Union.

O'Regan, M.; King, J.; Backman, J.; Jakobsson, M.; Palike, H.; Moran, K.; Heil, C.; Sakamoto, T.; Cronin, T. M.; Jordan, R.W.

2008-01-01

193

MtDNA markers reveal the existence of allopatric evolutionary lineages in the threatened lampreys Lampetra fluviatilis (L.) and Lampetra planeri (Bloch) in the Iberian glacial refugium  

Microsoft Academic Search

The Iberian Peninsula has been identified as an important glacial refugium during the Pliocene and Pleistocene epochs for\\u000a the genus Lampetra, providing intermittent refuge and postglacial opportunities for colonization and expansion. We used mitochondrial DNA markers\\u000a to investigate the processes that have shaped present-day genetic constitution of the genus Lampetra within the Iberian Peninsula. We surveyed 1,173 bp of the cytochrome

C. S. Mateus; P. R. Almeida; B. R. Quintella; M. J. Alves

2011-01-01

194

Architecture of Late Ordovician glacial valleys in the Tassili N'Ajjer area (Algeria)  

NASA Astrophysics Data System (ADS)

The architecture of three Late Ordovician glacial valleys was studied in detail in the Tassili N'Ajjer (SE Algeria) outcrops. The valleys are oriented south-north, 2 to 5 km wide, and up to 250 m deep. The valley-fills revealed a very complex sedimentary architecture with significant lateral facies changes. Several glacial cycles induced the formation of Glacial Erosion Surfaces (GES) at the base and within the glacial valleys. The first type of GES shows a sharp and steep-angled contact without striations or associated syn-sedimentary deformation, suggesting that subglacial meltwater was the dominant erosive agent. A second type associated with the deformation of pre-glacial and syn-glacial sediment, suggests that ice was in contact with the valley floor. Four facies associations are proposed: FA1: subglacial tillite; FA2: Sub-to pro-glacial ice contact fans; FA3: Proglacial sub-aqueous gravity flows; and FA4: outwash fans. The stratigraphic architecture of three of the main valleys reveals a complex polyphase infill. At least two main cycles of ice-sheet advance and retreat can be interpreted from the sedimentary succession of each valley. Minor glacial cycles by ice oscillations also occur locally. GES morphology and the facies sequence suggest that the Iherir valleys were initiated by meltwater erosion in subglacial channels, whereas the Dider and Ouarsissen valleys were part of a large ice stream pathway. Above the valley-fill and the interfluves, a sand-rich unit of stacked lobes and channels is interpreted as submarine outwash fans deposited during final ice retreat. A glacial sequence found between two GES comprises fluvio-glacial or ice-contact fan deposits, fluvio-glacial eskers and tills. These sediments were deposited subglacially or at the glacier front during the ice maximum phase and/or the early ice retreat phase. During the ice retreat, interbedded subaqueous gravity flow deposits and diamictites filled the glacially cut topography as the sea invaded the valleys. Maximum ice retreat was associated with high water fluxes and sediment discharge, causing a sand-dominated outwash fan to prograde out over the valleys and interfluves. This outwash fan was supplied mainly by flood activity at the ice front, involving high-density sustained flows. The dominant facies consists of giant aggrading climbing dunes filling channels or constructing sandy lobes downstream.

Deschamps, Rémy; Eschard, Rémi; Roussé, Stéphane

2013-05-01

195

Phylogeographical analysis of mtDNA data indicates postglacial expansion from multiple glacial refugia in woodland caribou (Rangifer tarandus caribou).  

PubMed

Glacial refugia considerably shaped the phylogeographical structure of species and may influence intra-specific morphological, genetic, and adaptive differentiation. However, the impact of the Quaternary ice ages on the phylogeographical structure of North American temperate mammalian species is not well-studied. Here, we surveyed ~1600 individuals of the widely distributed woodland caribou (Rangifer tarandus caribou) using mtDNA control region sequences to investigate if glacial refugia contributed to the phylogeographical structure in this subspecies. Phylogenetic tree reconstruction, a median-joining network, and mismatch distributions supported postglacial expansions of woodland caribou from three glacial refugia dating back to 13544-22005 years. These three lineages consisted almost exclusively of woodland caribou mtDNA haplotypes, indicating that phylogeographical structure was mainly shaped by postglacial expansions. The putative centres of these lineages are geographically separated; indicating disconnected glacial refugia in the Rocky Mountains, east of the Mississippi, and the Appalachian Mountains. This is in congruence with the fossil record that caribou were distributed in these areas during the Pleistocene. Our results suggest that the last glacial maximum substantially shaped the phylogeographical structure of this large mammalian North American species that will be affected by climatic change. Therefore, the presented results will be essential for future conservation planning in woodland caribou. PMID:23285137

Klütsch, Cornelya F C; Manseau, Micheline; Wilson, Paul J

2012-01-01

196

Phylogeographical Analysis of mtDNA Data Indicates Postglacial Expansion from Multiple Glacial Refugia in Woodland Caribou (Rangifer tarandus caribou)  

PubMed Central

Glacial refugia considerably shaped the phylogeographical structure of species and may influence intra-specific morphological, genetic, and adaptive differentiation. However, the impact of the Quaternary ice ages on the phylogeographical structure of North American temperate mammalian species is not well-studied. Here, we surveyed ?1600 individuals of the widely distributed woodland caribou (Rangifer tarandus caribou) using mtDNA control region sequences to investigate if glacial refugia contributed to the phylogeographical structure in this subspecies. Phylogenetic tree reconstruction, a median-joining network, and mismatch distributions supported postglacial expansions of woodland caribou from three glacial refugia dating back to 13544–22005 years. These three lineages consisted almost exclusively of woodland caribou mtDNA haplotypes, indicating that phylogeographical structure was mainly shaped by postglacial expansions. The putative centres of these lineages are geographically separated; indicating disconnected glacial refugia in the Rocky Mountains, east of the Mississippi, and the Appalachian Mountains. This is in congruence with the fossil record that caribou were distributed in these areas during the Pleistocene. Our results suggest that the last glacial maximum substantially shaped the phylogeographical structure of this large mammalian North American species that will be affected by climatic change. Therefore, the presented results will be essential for future conservation planning in woodland caribou. PMID:23285137

Klütsch, Cornelya F. C.; Manseau, Micheline; Wilson, Paul J.

2012-01-01

197

Dynamics of the late Plio-Pleistocene West Antarctic Ice Sheet documented in subglacial diamictites, AND-1B drill core  

NASA Astrophysics Data System (ADS)

Geologic studies of sediment deposited by glaciers can provide crucial insights into the subglacial environment. We studied muddy diamictites in the ANtarctic geological DRILLing (ANDRILL) AND-1B drill core, acquired from beneath the Ross Ice Shelf in McMurdo Sound, with the aim of identifying paleo-ice stream activity in the Plio-Pleistocene. Glacial advances were identified from glacial surfaces of erosion (GSEs) and subglacial diamictites within three complete sequences were investigated using lithofacies associations, micromorphology, and quartz sand grain microtextures. Whereas conditions in the Late Pliocene resemble the modern Greenland Ice Sheet where fast flowing glaciers lubricated by surface meltwater terminate directly in the sea (interval 201-212 mbsl) conditions in the Late Pleistocene are similar to modern West Antarctic Ice Sheet (WAIS) ice streams (38-49 mbsl). We identify the latter from ductile deformation and high pore-water pressure, which resulted in pervasive rotation and formation of till pellets and low relief, rounded sand grains dominated by abrasion. In the transitional period during the Mid-Pleistocene (55-68 mbsf), a slow moving inland ice sheet deposited tills with brittle deformation, producing lineations and bi-masepic and unistrial plasma fabric, along with high relief, conchoidally fractured quartz grains. Changes in the provenance of gravel to cobble-size clasts support a distant source area of Byrd Glacier for fast-flowing paleo-ice streams and a proximal area between Darwin and Skelton Glaciers for the slow-moving inland ice sheet. This difference in till provenance documents a shift in direction of glacial flow at the core site, which indirectly reflects changes in the size and thickness of the WAIS. Hence, we found that fast ice streaming motion is a consequence of a thicker WAIS pushing flow lines to the west and introducing clasts from the Byrd Glacier source area to the drill site. The detailed analysis of diamictites in AND-1B demonstrates that Pliocene glacial intervals were warmer than in the Pleistocene when polar ice sheets grew from local inland ice to regional ice streams.

Cowan, Ellen A.; Christoffersen, Poul; Powell, Ross D.; Talarico, Franco M.

2014-08-01

198

First ancient DNA sequences from the Late Pleistocene red deer (Cervus elaphus) in the Crimea, Ukraine  

NASA Astrophysics Data System (ADS)

The Late Pleistocene has been a period of significant population and species turnover and extinctions among the large mammal fauna. Massive climatic and environmental changes during Pleistocene significantly influenced the distribution and also genetic diversity of plants and animals. The model of glacial refugia and habitat contraction to southern peninsulas in Europe as areas for the survival of temperate animal species during unfavourable Pleistocene glaciations is at present widely accepted. However, both molecular data and the fossil record indicate the presence of northern and perhaps north-eastern refugia in Europe. In recent years, much new palaeontological data have been obtained in the Crimean Peninsula, Ukraine, following extensive investigations. The red deer (Cervus elaphus) samples for aDNA studies were collected in Emine-Bair-Khosar Cave, situated on the north edge of Lower Plateau of the Chatyrdag Massif (Crimean Mountains). The cave is a vertical shaft, which functioned as a huge mega-trap over a long period of time (probably most of the Pleistocene). The bone assemblages provided about 5000 bones belonging to more than 40 species. The C. elaphus bones were collected from three different stratigraphical levels, radiocarbon dated by accelerator mass spectrometry (AMS) method. The bone fragments of four specimens of red deer were used for the DNA isolation and analysis. The mtDNA (Cytochome b) was successfully isolated from three bone fragments and the cytochrome b sequences were amplified by multiplex PCR. The sequences obtained so far allowed for the reconstruction of only preliminary phylogenetic trees. A fragment of metatarsus from level dated to ca. 48,500±2,000 years BP, yielded a sequence of 513 bp, allowing to locate the specimen on the phylogenetic tree within modern C. elaphus specimens from southern and middle Europe. The second bone fragment, a fragment of mandible, collected from level dated approximately to ca. 33,500±400 years BP, yielded a sequence (696 bp) locating this specimen much closer to the modern C. elaphus specimens from China and Far East. From the third bone fragment (metatarsus), dated between ca. 12,000 years BP and 30,000 years BP, the sequence of only 346 bp has been obtained. It locates this specimen between European and Asiatic haplogroups. The preliminary results of analysis of the DNA from Crimean C. elaphus fossils reveal the great genetic heterogeneity and a complex phylogeographical pattern of the material studied. The obtained results support the opinion that Crimean Peninsula was the most north-eastern refugium in Europe during Late Pleistocene playing a major role in recolonization and dispersal processes of temperate species during and after the Late Pleistocene in this part of the Euro-Asian continent.

Stankovi?, Ana; Nadachowski, Adam; Doan, Karolina; Stefaniak, Krzysztof; Baca, Mateusz; Socha, Pawe?; Wegle?ski, Piotr; Ridush, Bogdan

2010-05-01

199

Climate change and evolving human diversity in Europe during the last glacial.  

PubMed Central

A link between climate change and human evolution during the Pleistocene has often been assumed but rarely tested. At the macro-evolutionary level Foley showed for hominids that extinction, rather than speciation, correlates with environmental change as recorded in the deep sea record. Our aim is to examine this finding at a smaller scale and with high-resolution environmental and archaeological archives. Our interest is in changing patterns of human dispersal under shifting Pleistocene climates during the last glacial period in Europe. Selecting this time frame and region allows us to observe how two hominid taxa, Neanderthals and Crô-Magnons, adapted to climatic conditions during oxygen isotope stage 3. These taxa are representative of two hominid adaptive radiations, termed terrestrial and aquatic, which exhibited different habitat preferences but similar tolerances to climatic factors. Their response to changing ecological conditions was predicated upon their ability to extend their societies in space and time. We examine this difference further using a database of all available radiocarbon determinations from western Europe in the late glacial. These data act as proxies for population history, and in particular the expansion and contraction of regional populations as climate changed rapidly. Independent assessment of these processes is obtained from the genetic history of Europeans. The results indicate that climate affects population contraction rather than expansion. We discuss the consequences for genetic and cultural diversity which led to the legacy of the Ice Age: a single hominid species, globally distributed. PMID:15101580

Gamble, Clive; Davies, William; Pettitt, Paul; Richards, Martin

2004-01-01

200

Last Glacial mammals in South America: a new scenario from the Tarija Basin (Bolivia).  

PubMed

The chronology, sedimentary history, and paleoecology of the Tarija Basin (Bolivia), one of the richest Pleistocene mammalian sites in South America, are revised here based on a multidisciplinary study, including stratigraphy, sedimentology, geomorphology, paleontology, isotope geochemistry, and (14)C geochronology. Previous studies have indicated a Middle Pleistocene age for this classic locality. We have been able to obtain a series of (14)C dates encompassing all the fossil-bearing sequences previously studied in the Tarija Basin. The dated layers range in age from about 44,000 to 21,000 radiocarbon years before present (BP), indicating that the Tarija fauna is much younger than previously thought. Glacial advances correlated to marine isotopic stages (MIS) 4 and 2 (ca. 62 and 20 ka BP, respectively) are also documented at the base and at the very top of the Tarija-Padcaya succession, respectively, indicating that the Bolivian Altiplano was not dry but sustained an ice cap during the Last Glacial Maximum. The results of this multidisciplinary study enable us to redefine the chronological limits of the Tarija sequence and of its faunal assemblage and to shift this paleontological, paleoclimatological, and paleoecological framework to the time interval from MIS 4 to MIS 2. PMID:17180614

Coltorti, M; Abbazzi, L; Ferretti, M P; Iacumin, P; Rios, F Paredes; Pellegrini, M; Pieruccini, P; Rustioni, M; Tito, G; Rook, L

2007-04-01

201

Push moraines in the upper valley of Santa Cruz river, southwest Argentina. Structural analysis and relationship with Late Pleistocene paleoclimate  

NASA Astrophysics Data System (ADS)

The upper cliff of the Santa Cruz River was used to assess the proglacial environments of the Argentino Glacier outlet of Late Pleistocene age. These cliffs show glaciolacustrine, fluvioglacial and till deposits, where only the first one are deformed. Glacial landforms in the area and these structures suggest that the ice mass advanced, topographically controlled, towards the east from the Patagonian Ice Sheet pushing up the proglacial sediments. The spatial arrangement of thrusts and overturned folds, the drumlins-flutes moraine directions and the end moraines shape, allow inferring the dynamic and the Argentino glacier profile. Detailed analyses of the glaciotectonic structures indicate that these have two origins: load in the north with stress transfer to the southeast, and push from the west. Through the analysis of deformed sediments, their thickness and their sedimentary and structural features, three zones of deformations were recognized. Each of these zones was associated to glacial advances because of changes of the regional climate conditions.

Goyanes, Gabriel; Massabie, Armando

2015-01-01

202

Late Glacial-Holocene climatic transition record at the Argentinian Andean piedmont between 33 and 34° S  

NASA Astrophysics Data System (ADS)

The Arroyo La Estacada (~ 33°28' S, 69°02' W), eastern Andean piedmont of Argentina, cuts through an extensive piedmont aggradational unit composed of a dominant Late Pleistocene-early Holocene (LP-EH) alluvial sequence that includes several paleosols. One of these paleosols developed affecting the topmost part of likely Late Glacial aeolian deposits aggraded into a floodplain environment by the end of the Late Pleistocene. The paleosol shows variable grade of development along the arroyo outcrops. Organic matter humification, carbonate accumulation and redox processes were the dominant processes associated with paleosol formation. By the early Holocene, when the formation of the paleosol ended, renewed alluvial aggradation and high magnitude flooding events affected the arroyo's floodplain environment. Accordignly, a period of relative landscape stability in the Arroyo La Estacada basin is inferred from the paleosol developed by the LP-EH transition in response to the climatic conditions in the Andes cordillera piedmont after the Late Glacial arid conditions. The analyzed Late Glacial-Holocene alluvial record of the Andean piedmont constitutes a suitable record of the LP-EH climatic transition in the extra-Andean region of Argentina. It is in agreement with regional paleoclimatic evidence along the southern tip of the South American continent, where other pedosedimentary sequences record similar late Quaternary paleoenvironmental changes over both fluvial and interfluvial areas.

Mehl, A. E.; Zárate, M. A.

2014-04-01

203

Strong and deep Atlantic meridional overturning circulation during the last glacial cycle  

NASA Astrophysics Data System (ADS)

Extreme, abrupt Northern Hemisphere climate oscillations during the last glacial cycle (140,000 years ago to present) were modulated by changes in ocean circulation and atmospheric forcing. However, the variability of the Atlantic meridional overturning circulation (AMOC), which has a role in controlling heat transport from low to high latitudes and in ocean CO2 storage, is still poorly constrained beyond the Last Glacial Maximum. Here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima. Our results are based on a reconstruction of both the strength and the direction of the AMOC during the last glacial cycle from a highly resolved marine sedimentary record in the deep western North Atlantic. Parallel measurements of two independent chemical water tracers (the isotope ratios of 231Pa/230Th and 143Nd/144Nd), which are not directly affected by changes in the global cycle, reveal consistent responses of the AMOC during the last two glacial terminations. Any significant deviations from this configuration, resulting in slowdowns of the AMOC, were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials. Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage, probably as a result of increased fresh-water input. In contrast, the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states, and an active AMOC prevailed during Dansgaard-Oeschger interstadials (Greenland warm periods).

Böhm, E.; Lippold, J.; Gutjahr, M.; Frank, M.; Blaser, P.; Antz, B.; Fohlmeister, J.; Frank, N.; Andersen, M. B.; Deininger, M.

2015-01-01

204

Strong and deep Atlantic meridional overturning circulation during the last glacial cycle.  

PubMed

Extreme, abrupt Northern Hemisphere climate oscillations during the last glacial cycle (140,000 years ago to present) were modulated by changes in ocean circulation and atmospheric forcing. However, the variability of the Atlantic meridional overturning circulation (AMOC), which has a role in controlling heat transport from low to high latitudes and in ocean CO2 storage, is still poorly constrained beyond the Last Glacial Maximum. Here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima. Our results are based on a reconstruction of both the strength and the direction of the AMOC during the last glacial cycle from a highly resolved marine sedimentary record in the deep western North Atlantic. Parallel measurements of two independent chemical water tracers (the isotope ratios of (231)Pa/(230)Th and (143)Nd/(144)Nd), which are not directly affected by changes in the global cycle, reveal consistent responses of the AMOC during the last two glacial terminations. Any significant deviations from this configuration, resulting in slowdowns of the AMOC, were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials. Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage, probably as a result of increased fresh-water input. In contrast, the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states, and an active AMOC prevailed during Dansgaard-Oeschger interstadials (Greenland warm periods). PMID:25517093

Böhm, E; Lippold, J; Gutjahr, M; Frank, M; Blaser, P; Antz, B; Fohlmeister, J; Frank, N; Andersen, M B; Deininger, M

2015-01-01

205

Late Pleistocene Crocuta crocuta spelaea (Goldfuss 1823) populations from the Emscher River terrace open air hyena den near Bottrop and other sites in NW Germany: Their bone accumulations along rivers in lowland mammoth steppe environments and scavenging activities on woolly rhinoceros  

Microsoft Academic Search

Crocuta crocuta spelaea (Goldfuss, 1823) remains (NISP = 50) are present in the early to middle Upper Pleistocene Emscher River terrace open air den site along the Rhine–Herne Canal near Bottrop (Westphalia, NW Germany). The population includes bones from cubs and bones with pathological features from old animals but is predominantly made up of adult hyenas (NISP = 3820) found within the glacial mammoth

Cajus G. Diedrich

206

Glacial-interglacial variations of microbial communities in permafrost and lake deposits in the Siberian Arctic  

NASA Astrophysics Data System (ADS)

The Artic regions are expected to be very sensitive to the currently observed climate change. When permafrost is thawing, the stored carbon becomes available again for microbial degradation, forming a potential source for the generation of carbon dioxide and methane with their positive feedback effect on the climate warming. For the prediction of future climate evolution it is, therefore, important to improve our knowledge about the microbial-driven greenhouse gas dynamics in the Siberian Arctic and their response to glacial-interglacial changes in the past. Sample material was drilled on Kurungnahk Island (Russian-German LENA expedition) located in the southern part of the Lena delta and in lake El'gygytgyn (ICDP-project) in the eastern part of Siberia. The Kurungnahk samples comprise Late Pleistocene to Holocene deposits, whereas the lake El'gygytgyn samples cover Middle to Late Pleistocene sediments. Samples were investigated applying a combined biogeochemical and microbiological approach. The methane profile of the Kurungnahk core reveals highest methane contents in the warm and wet Holocene and Late Pleistocene (LP) deposits and correlates largly to the organic carbon (TOC) contents. Archaeol concentrations, being a biomarker for past methanogenic archaea, are also high during the warm and wet Holocene and LP intervals and low during the cold and dry LP periods. This indicates that part of the methane might be produced and trapped in the past. However, biomarkers for living microorganisms (bacteria and archaea) and microbial activity measurements of methanogens point, especially, for the Holocene to a viable archaeal community, indicating a possible in-situ methane production. Furthermore, warm/wet-cold/dry climate cycles are recorded in the archaeal diversity as revealed by genetic fingerprint analysis. Although the overlying lake water buffers the temperature effect on the lake sediments, which never became permafrost, the bacterial and archaeal biomarker profiles from lake El'gygytgyn deposits reveal also a glacial-interglacial variability. A reason for this seems to be higher TOC contents during the interglacials forming the carbon and energy source for the indigenous microbial communities. Algae blooms during the interglacials are indicated by the biogenic silica profile. The variety of methanogenic archaea is higher during the interglacials and methane production experiments reveal a high potential for methane production during these periods. Thus, overall the data indicate production and subsequent release of methane from the lake during interglacial periods. However, occasionally higher biomarker contents for methanogens accompanied by significant methane production potentials during glacial periods suggest that lakes might also produce and release methane during glacial periods.

Mangelsdorf, Kai; Bischoff, Juliane; Gattinger, Andreas; Wagner, Dirk

2013-04-01

207

The Pleistocene glacial cycles shaped the historical demography and phylogeography of a pine fungal endophyte  

Microsoft Academic Search

The fungal endophyte Lophodermium nitens is an obligate symbiont of soft pines inhabiting only two pine species in Mexico with a broad distribution of geographically\\u000a isolated populations. A previous study for the hosts indicated a main east–west subdivision with recurrent gene flow within\\u000a these regions and demographic expansion of populations. We took these patterns as null hypotheses to test for

Rodolfo Salas-Lizana; Nadia S. Santini; Adán Miranda-Pérez; Daniel I. Piñero

208

Ar Chronology of Late Pliocene and Early Pleistocene Geomagnetic and Glacial Events in Southern Argentina  

E-print Network

in Southern Argentina Brad S. Singer1 , Laurie L. Brown2 , Jorge O. Rabassa3 , Hervé Guillou4 the core and lowermost mantle [Gubbins, 1999; Glatzmaeir et al., 1999; Singer et al., 2002; Hoffman disputed [Kidane et al., 1999; Baksi and Hoffman 2000; Baksi, 2001; Lanphere et al., 2002]. This reflects

Singer, Bradley S.

209

Glacially conditioned specific stream powers in low-relief river catchments of the southern Laurentian Great Lakes  

NASA Astrophysics Data System (ADS)

Fluvial systems of the southern Laurentian Great Lakes region are carved into a complex glacial landscape shaped by continental ice and meltwater of the late Pleistocene. These glacially conditioned river catchments are typically small with drainage areas < 104 km2. A 10-m digital elevation model (DEM) is used to map the spatial distribution of stream gradient for 22 major river catchments of peninsular southern Ontario, which drain to base levels in the lower Great Lakes (Huron, St. Clair, Erie, and Ontario). Raw data from the DEM show stream gradients that exhibit multiscale variance from real and from artifact sources. Based on a vertical slice and multiple-pass moving-window averaging approach, slope data are generalised to the river reach scale (1-2 km) as a representative spatial scale for fluvial processes operating over Holocene timescales. Models of specific stream power are then compared with glacial landform and surface geology mapping. Inherited glacial signatures in river slope appear as deviations in a stream length-gradient index (SL/K index), where river reaches are frequently oversteepened or understeepened. Based on a slope-area analysis, and complementary to theories of channel pattern discrimination, constant stream power curves (with power-law exponent of - 0.4) provide a first-order approach to stratify river reaches in terms of glacial conditioning and expected planform morphologies. However, multiple-channel planform types are rare and localised in southern Ontario, indicating that oversteepened reaches with high stream powers may often be moderated by (1) sediment calibre, with cobble-beds from inherited glacial sediments; and/or (2) relative bank strength, with limited channel widening particularly in gravel and sand-bed channels. Further discrimination of glacially conditioned fluvial process domains will ultimately require consideration of alluvial floodplain characteristics in addition to general observations of river morphology and channel pattern.

Phillips, R. T. J.; Desloges, J. R.

2014-02-01

210

Caribbean Salinity Variation During the Last Glacial Cycle  

NASA Astrophysics Data System (ADS)

Evaporation exceeds precipitation in the tropical Atlantic, resulting in a net freshwater removal across the Central American Isthmus. Because most of the north Atlantic's subtropical gyre water circulates through the Caribbean before flowing north to sub-polar regions via the Gulf Stream, changes in tropical atmospheric circulation have the potential to affect the salinity and density structure of the entire north Atlantic, thereby influencing glacial-interglacial oscillations in North Atlantic Deep Water (NADW) formation. Here, we combine Mg/Ca measurements (a proxy for the temperature of calcification) and ? 18O analyses of shells from the surface-dwelling foraminifera Globigerinoides ruber s.s. (white var.) from the western Caribbean Colombian Basin at ODP Site 999A (2827m; 4cm/ka sed. rate) and VM28-122 (3623m; 4-10cm/ka sed. rate) to produce the first continuous record of western tropical Atlantic ? 18OSEAWATER (? 18OSW) during the last 130ka. In order to generate a record for sea surface salinity (SSS) due to regional hydrological change, we removed the ? 18OSW signal due to glacial ice volume variation and normalized the residual to the modern ? 18OSW value for the Colombian Basin (0.8‰ ). The resulting ice volume-free (? ? 18OIVF-SW) record shows that Caribbean ? ? 18OIVF-SW increased by ˜0.5‰ during the Last Glacial Maximum and Marine Isotope Stage 4. Using a modern western Caribbean ? 18OSW:SSS relationship, these enriched ? 18OSW values suggest glacial Caribbean salinities were 2.3 - 2.8‰ higher than modern after removing the influence of ice-volume. Our data supports the hypothesis that the tropics might have been in a state more similar to the modern El Nino mode, characterized by a more southerly position of the ITCZ, during cold phases of the last glacial cycle. Within the resolution of our ? ? 18OIVF-SW record from VM28-122, elevated glacial Caribbean salinity decreased to modern levels at the onset of the Bolling-Allerod (B/A) interstadial event (14.6 cal ka) as NADW formation reinitiated and the ITCZ migrated northward. We hypothesize that the transport of salty tropical waters into the North Atlantic during the early deglaciation, in combination with a reorganization of ocean circulation, may have served to increase subpolar surface water density and amplify the overturning circulation that produced the warm B/A. The B/A salinity reduction occurs simultaneously with previous evidence for wetter conditions in the Cariaco Basin, suggesting a northward shift in the ITCZ to a wetter, more La Nina-like state in the tropics.

Schmidt, M. W.; Spero, H. J.; Lea, D. W.

2003-12-01

211

Hørbyebreen polythermal glacial landsystem, Svalbard  

Microsoft Academic Search

A contoured surficial geology and geomorphology map of the forelands of the Hørbyebreen, Svenbreen and Ferdinandbreen valley glaciers in Petuniabukta, Svalbard was compiled from an orthophotograph based upon aerial photographs taken in 2009. The map reveals typical polythermal glacial landsystems, comprising ice-cored latero-frontal moraine arcs grading up valley into fluted till surfaces draped by supraglacially-derived longitudinal debris stripes. The additional

David J. A. Evans; Mateusz Strzelecki; David G. Milledge; Chris Orton

2012-01-01

212

Extraterrestrial accretion and glacial cycles  

NASA Technical Reports Server (NTRS)

We propose that the approx. 100-k.y. cycle seen in terrestrial glaciation is due to changes in meteor flux that come from changes in the Earth's orbit. This model can explain a 70-k.y. 'anomalous' period in climate data and the apparent discrepancy between present extraterrestrial fluxes and those in oceanic sediments. It can be tested by measuring Ir densities in sediments and ice during glacials and interglacials.

Muller, R. A.

1994-01-01

213

Glacial climate in the tropics  

SciTech Connect

New findings have caused ideas about the Earth`s climate during the Pleistocene glaciation to change. A consensus seems to be forming that during times of glaciation, climatic conditions in the tropics were quite different from those today. However still to be explained is why strontium-calcium measurements on corals and moble gas measurements of ground water suggest a tropical cooling of 4-6 C while foraminiferal speciation, oxygen isotope, and alkenone results suggest a cooling of no more than 3 C. This article discusses different aspects of the debate. 9 refs., 1 fig.

Broecker, W. [Columbia Univ., Palisades, NY (United States)

1996-06-28

214

Glacitectonic rafting and associated deformation of mid-Pleistocene glacigenic sediments, near Central Graben, central North Sea; results of a 2D High-Resolution Geophysical Survey  

NASA Astrophysics Data System (ADS)

Glacitectonic rafts are defined as dislocated slabs of bedrock or unconsolidated sediments, transported from their original position by glacial action. These relatively thin, slab-like bodies feature transport distances ranging from tens of meters to hundreds of kilometers. They occur as either single rafts, or multiple stacked bodies associated with a variety of ice-pushed landforms. Internally, rafts frequently appear undeformed although at a larger scale, they may be folded or cut by shear zones and brittle faults. However, the processes leading to the detachment, transport and subsequent emplacement of the rafts remain uncertain. This work describes the results of a geophysical 2D seismic survey of thrust-bound glacitectonic rafts and associated deformation structures, occurring within mid-Pleistocene glacigenic sediments of the Central Graben, central North Sea. The total shortened length of the rafted section is 2.4km, comprising a series of nine discrete rafts which individually range from 235m to 1018m in length. The principle basal detachment occurs at the erosive contact between Aberdeen Ground Formation and overlying Ling Bank Formation. The ice-proximal (northern) limit of rafting is defined by the presence of a large-scale palaeo-channel oriented perpendicular to the direction of rafting, composed of sediments of the Ling Bank Formation and the Forth Formation. The observed deformation structures infer a mean tectonic direction of 178°, indicating that they are associated with an active glacial advance from the north. The resulting deformation creates a minimum lateral shortening throughout the observed sequence of 35%, typifying a strongly compressional regieme associated with rafting. Throughout the surveyed area, structurally younger rafts are found to be emplaced towards the south, compared to the structurally older rafts which are emplaced towards the south-east. This distinction is suggested to be caused by early rafts creating an obstacle to transport for later stages of deformation, resulting in strike-slip basal detachment being associated with the later rafts. Localised distributions of high amplitude surfaces located adjacent to the primary detachment surface are identified through amplitude extraction techniques. These are indicative of migration and collection of gas along the inclined lower surfaces of rafted blocks. They represent a gas risk for drilling operations and demonstrate the significance and possible hazards of glacitectonic deformation to the exploration industry. A model for raft detachment and emplacement is proposed whereby; i) saturated sediments within the palaeo-channel are subject to pressurisation associated with overburden caused by over-riding ice, ii) elevated pore-water pressure develops along the principle detachment surface of the rafts, iii) early stages of deformation consist of ice-distal (southern) blocks becoming emplaced at relatively low angles of inclination, iv) with more proximal blocks accumulating as an imbricate thrust-stack sequence at relatively high angles of elevation. This interpretation suggests a significant subglacial hydrological control upon raft detachment and transport, with fluctuations between an extensional and compressive deformation regime caused by a switch from actively advancing glacial conditions to an oscillating ice-margin at this location. Tectono-stratigraphic evidence indicates that rafting occurring throughout the site is likely to be associated with a glacial advance of the Anglian (MIS 12).

Vaughan-Hirsch, David

2013-04-01

215

Synchronous extinction of North America's Pleistocene mammals  

PubMed Central

The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago (?13,800–11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000–10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant. PMID:19934040

Faith, J. Tyler; Surovell, Todd A.

2009-01-01

216

Global sensitivity analysis of the Indian monsoon during the Pleistocene  

NASA Astrophysics Data System (ADS)

The sensitivity of the Indian monsoon to the full spectrum of climatic conditions experienced during the Pleistocene is estimated using the climate model HadCM3. The methodology follows a global sensitivity analysis based on the emulator approach of Oakley and O'Hagan (2004) implemented following a three-step strategy: (1) development of an experiment plan, designed to efficiently sample a five-dimensional input space spanning Pleistocene astronomical configurations (three parameters), CO2 concentration and a Northern Hemisphere glaciation index; (2) development, calibration and validation of an emulator of HadCM3 in order to estimate the response of the Indian monsoon over the full input space spanned by the experiment design; and (3) estimation and interpreting of sensitivity diagnostics, including sensitivity measures, in order to synthesise the relative importance of input factors on monsoon dynamics, estimate the phase of the monsoon intensity response with respect to that of insolation, and detect potential non-linear phenomena. By focusing on surface temperature, precipitation, mixed-layer depth and sea-surface temperature over the monsoon region during the summer season (June-July-August-September), we show that precession controls the response of four variables: continental temperature in phase with June to July insolation, high glaciation favouring a late-phase response, sea-surface temperature in phase with May insolation, continental precipitation in phase with July insolation, and mixed-layer depth in antiphase with the latter. CO2 variations control temperature variance with an amplitude similar to that of precession. The effect of glaciation is dominated by the albedo forcing, and its effect on precipitation competes with that of precession. Obliquity is a secondary effect, negligible on most variables except sea-surface temperature. It is also shown that orography forcing reduces the glacial cooling, and even has a positive effect on precipitation. As regards the general methodology, it is shown that the emulator provides a powerful approach, not only to express model sensitivity but also to estimate internal variability and detect anomalous simulations.

Araya-Melo, P. A.; Crucifix, M.; Bounceur, N.

2015-01-01

217

Remote identification of a gravel laden Pleistocene river bed  

NASA Technical Reports Server (NTRS)

The abundance of gravel deposits is well known in certain areas across the Gulf of Mexico coastal plain, including lands within several National Forests. These Pleistocene gravels were deposited following periods of glacial buildup when ocean levels were down and the main river channels had cut deep gorges, leaving the subsidiary streams with increased gradients to reach the main channels. During the warm interglacial periods that followed each glaciation, melting ice brought heavy rainfall and torrents of runoff carrying huge sediment loads that separated into gravel banks below these steeper reaches where abraiding streams, developed. As the oceans rose again, filling in the main channels, these abraiding areas were gradually flattened and covered over by progressively finer material. Older terraces were uplifted by tectonic movements associated with the Gulf Coastal Plain, and the subsequent erosional processes gradually brought the gravels closer to the surface. The study area is located on the Kisatchie National Forest, in central Louisiana, near Alexandria. Details of the full study have been discussed elsewhere. The nearest source of chert is in the Ouachita Mountains located to the northeast. The Ouachita River flows south, out of these mountains, and in Pleistocene times probably carried these chert gravels into the vicinity of the present day Little River Basin which lies along the eastern boundary of the National Forest. Current day drainages cross the National Forest from west to east, emptying into the Little River on the east side. However, a north-south oriented ridge of hills along the west side of the Forest appears to be a recent uplift associated with the hinge line of the Mississippi River depositional basin further to the east, and 800,000 years ago, when these gravels were first deposited during the Williana interglacial period, the streams probably flowed east to west, from the Little River basin to the Red River basin on the west side of the Forest. Within the National Forest and north of Alexandria, along Fish Creek, and east and west of an area known as Breezy Hill, exist several small, worked out gravel pits on privately owned blocks of land, formerly used by the state and county road departments. The pattern presented by these pits gives the impression of a series of north-south drainages lacing through the Forest, probable tributaries to Fish Creek which flows south of east from the west side of the Forest to empty into the Little River. Because of this predominant north-south pattern, no consideration was given to areas between these drainages during early gravel exploration efforts.

Scholen, Douglas E.

1993-01-01

218

Thermohaline Circulation Crisis and Changes Through the Mid-Pleistocene Transition  

NASA Astrophysics Data System (ADS)

The Mid-Pleistocene Transition (MPT) marked a fundamental change in glacial-interglacial periodicity, transitioning from ~41,000 to 100,000 year cycles, accompanied by higher amplitude climate variability. It occurred without a significant change in orbital forcing, and thus its causes are poorly understood. We report major changes in the pre- and post-MPT mode of the ocean thermohaline circulation (THC), and a THC crisis during the MPT, from Nd isotopes in ODP Sites 1088 (~42S, 2082m) and 1090 (~43S, 3702m). The core locations are at the transition between the South Atlantic and the Southern oceans, a major gateway for the exchange of northern- and southern-sourced water masses. The new data show that in the ';40-kyr world' prior to the MPT, NADW export was strong during both interglacials and glacials. At ~900 ka the THC system underwent a major crisis, with an unprecedented weakening in NADW export during Marine Isotope Stages (MIS) 22-24. The recovery of the THC system in the post-MPT ';100-kyr world' is characterized by strong THC during interglacials, similar to pre-MPT interglacials, but much weaker THC during glacials. The ';THC crisis' interval includes MIS 23, which is unique as an interglacial where the THC operated in the same weak mode as post-MPT glacials. The MIS 22-24 interval has been recognized as a time of abrupt atmospheric pCO2 drawdown (Hoenisch et al. 2009) and significant cooling of ocean deep water, and Antarctic ice sheet expansion (Elderfield et al. Science 2012). Our data indicate that THC changes played an important role as a primary driving force, and helped to generate a series of positive feedbacks. This drastic change in deep-ocean circulation had important implications for the coeval drawdown of atmospheric pCO2, and the absence of a strong THC system through a glacial-to-interglacial-to-glacial cycle had a major impact on high latitude ice sheet growth. We suggest that the weak NADW export during MIS 24-22 resulted in reduced vertical exchange between Antarctic surface and deep waters, which helped to induce the drop in atmospheric pCO2, and in turn generated significant cooling which facilitated ice sheet expansion. These impacts were amplified by anomalously low Southern Hemisphere summer insolation during MIS 23, which resulted in suppressed ice sheet melting. Increased sea-ice coverage around the Antarctic continent during this time period may have generated increased AABW formation, which would have further drawn down CO2 from the atmosphere.

Goldstein, S. L.; Pena, L.

2013-12-01

219

Development of a glacially dominated shelf-slope-fan system in tectonically active southeast Alaska: Results of IODP Expedition 341 core-log-seismic integrated studies at glacial cycle resolution  

NASA Astrophysics Data System (ADS)

Collision of the Yakutat microplate with North American formed the St. Elias Mountains in coastal Gulf of Alaska. While the tectonic driver for orogenesis has been ongoing since the Miocene, results from the Integrated Ocean Drilling Program Expedition 341 suggests that direct climatic perturbation of active orogenesis through glacial erosion is non-linear. Geophysical studies of the glaciated continental margin, slope, and adjacent deep-sea Surveyor Fan allow examination of the glaciated orogen from source to sink. Using high-resolution and crustal-scale seismic data and through comparison with other glaciated margins, we can identify key diagnostic seismic morphologies and facies indicative of glacial proximity and sediment routing. Expedition drilling results calibrated these images suggesting a timeline for initial advances of the Cordilleran ice sheet related glacial systems onto the shelf and a further timeline for the development of ice streams that reach the shelf edge. Comparisons can be made within this single margin between evolution of the tectonic-glacial system where erosion and sediment transport are occurring within a fold and thrust belt versus on a more stable shelf region. Onshore the Bering-Bagley glacial system in the west flows across the Yakataga fold and thrust belt, allowing examination of whether glacial erosion can cause tectonic feedbacks, whereas offshore the Bering-Bagley system interacts with the Pamplona Zone thrusts in a region of significant sediment accommodation. Results from Expedition 341 imply that timing of glacial advance to the shelf edge in this region may be driven by the necessity of filling up the accommodation through aggradation followed by progradation and thus is autogenic. In contrast the Malaspina-Hubbard glacial system to the east encountered significantly less accommodation and more directly responded to climatic forcing including showing outer shelf glacial occupation since the mid-Pleistocene transition-MPT to 100 kyr glacial-interglacial cycles. Examination of the sink for both of these systems, which includes the Surveyor Fan and Aleutian Trench wedge, demonstrates a clear climatic driver for sediment flux to the deep sea. The first appearance of ice-rafted debris at our distal drill site closely approximates the start of the Pleistocene and a doubling of sediment accumulation accompanies the MPT. Converting sediment volumes just within the deep-sea sinks back to erosion rates in the orogen and correlating with changes in exhumation rates from thermochronology demonstrates a lack of accelerated tectonic response to the intensification of Northern Hemisphere glaciations at the start of the Pleistocene but increased shortening and exhumation of sediments at the MPT. The form of tectonic response differs between out-of-sequence thrusting or antiformal stacking within the fold and thrust belt to the west and a near vertical advection of material in a tectonic aneurysm in the core of the orogen to the east.

Gulick, Sean; Jaeger, John; Mix, Alan; Swartz, John; Worthington, Lindsay; Reece, Robert

2014-05-01

220

Glacial-interglacial variation in denudation rates from interior Texas, USA, established with cosmogenic nuclides  

NASA Astrophysics Data System (ADS)

The Brazos, Colorado, and Trinity rivers of Texas drain a tectonically quiescent, non-glaciated, and low-relief landscape inland from the Gulf of Mexico, where long-term [103-105 a] changes in denudation rates are probably driven largely by climate change. Here, we use cosmogenic 10Be to obtain spatially averaged denudation rates for these river catchments, primarily from terrace deposits associated with glacial or interglacial intervals over the past half million years. The denudation rates are ?30-35% higher during interglacial periods than during glacial periods, and correlate broadly with temperature. The results are consistent with predictions from the BQART sediment flux model, and support the hypothesis that increased weathering rates associated with warmer climates will accelerate landscape erosion. Furthermore, by analyzing 26Al/10Be in these deposits, we can estimate the bed load sourced from up-catchment surfaces. The stored coastal plain fraction varies from ?10% to 30%, and is greater during times of relatively lower sea level. The results indicate that although sediment flux is moderated by coastal-plain storage, increased up-catchment flux during warmer interglacial periods outpaces evacuation of stored sediment during glacial periods, resulting in a net increase in sediment flux to the ocean during warm intervals. If this temperature-sediment flux relationship is valid beyond the Plio-Pleistocene transition, then global sediment flux to the ocean from passive, non-glaciated, and low-relief landscapes would have been greater during the Pliocene than in the cooler Quaternary.

Hidy, Alan J.; Gosse, John C.; Blum, Michael D.; Gibling, Martin R.

2014-03-01

221

The dispersion of fibrous amphiboles by glacial processes in the area surrounding Libby, Montana, USA  

USGS Publications Warehouse

Mining operations began at a world-class vermiculite deposit at Vermiculite Mountain near Libby, Montana, circa 1920 and ended in 1990. Fibrous and asbestiform amphiboles intergrown with vermiculite ore are suspected to be a causative factor in an abnormally high number of cases of respiratory diseases in former mine and mill workers, and in residents of Libby. The question addressed in this report is whether some of the amphibole from Vermiculite Mountain could have been dispersed by Pleistocene glacial processes rather than by human activity after vermiculite mining began. The history of Pinedale glaciation in the Libby area provides a framework for estimating the presence and distribution of asbestiform amphiboles derived from Vermiculite Mountain and found in naturally occurring sediments of Glacial Lake Kootenai that underlie the Libby Valley area. There were two situations where sediments derived from Vermiculite Mountain were deposited into Glacial Lake Kootenai: (1) as lake-bottom sediments derived from meltwater flowing down Rainy Creek when the valley south of Vermiculite Mountain was free of ice but active ice still covered Vermiculite Mountain; and (2) as lake-bottom sediments eroded from the Rainy Creek outwash and re-deposited during a re-advance of the Purcell Trench Glacier lobe near Moyie Springs, Idaho.

Langer, William H.; Van Gosen, Bradley S.; Meeker, Gregory P.; Adams, David T.; Hoefen, Todd M.

2011-01-01

222

{13C }/{12C } ratios of pleistocene mummified remains from beringia  

NASA Astrophysics Data System (ADS)

During the Quaternary glacial episodes, when sea level was considerably lower, Asia and North America were linked by large extensions of circumarctic land (Beringia), which remained unglaciated. This land mass served not only as a biogeographical bridge for plants, animals, and humans, but also supported a biome very different from present tundra or boreal coniferous forests, which was dominated by steppes and a rich mammalian megafauna. Carbon stable isotope ratios of Beringian late Pleistocene mummified remains of bison, equids, mammoth, caribou, musk-ox, moose, woolly rhino, and other undetermined species, found preserved in permafrost, indicate that these megaherbivores fed exclusively on C 3 plants, and that C 4 grasses were not differentially ingested by bison, as previously suggested. Paleoclimatic constraints probably prevented the formation of a warm-season (C 4) guild during the later part of the growing season in the steppes of Beringia during the last glaciation.

Bombin, Miguel; Muehlenbachs, Karlis

1985-01-01

223

The Pleistocene climate-controlled fluvial sedimentary record in the Be?chatów mine (central Poland)  

NASA Astrophysics Data System (ADS)

Sedimentological analyses of fluvial formations in the Be?chatów mine have yielded results that have more than regional significance. They concern the reaction of rivers to climatic changes in the Pleistocene. Changes in river geometry and their depositional records are examined from two fluvial formations. These formations represent different times, but show similar palaeoenvironmental changes. Cool temperate climate conditions resulted in meandering (or anastomosing) river sedimentation, which was controlled by equalized precipitation and by a well-developed vegetation cover. Cold periglacial climate conditions resulted in braided river sedimentation immediately before the Glacial Maximum, with high discharges and a high sediment load. The palaeoclimatic and palaeohydrologic analyses of the Weichselian fluvial deposits in Be?chatów provide additional information to that from similar studies in Germany and the Netherlands, thus jointly resulting in a consistent palaeogeographic model of western-middle Europe.

Zieli?ski, Tomasz

2007-01-01

224

Pliocene to Pleistocene climate and environmental history of Lake El'gygytgyn, Far East Russian Arctic, based on high-resolution inorganic geochemistry data  

NASA Astrophysics Data System (ADS)

The 3.6 Ma sediment record of Lake El'gygytgyn/NE Russia, Far East Russian Arctic, represents the longest continuous climate archive of the terrestrial Arctic. Its elemental composition as determined by X-ray fluorescence scanning exhibits significant changes since the mid-Pliocene caused by climate-driven variations in primary production, postdepositional diagenetic processes, and lake circulation as well as weathering processes in its catchment. During the mid- to late Pliocene, warmer and wetter climatic conditions are reflected by elevated Si / Ti ratios, indicating enhanced diatom production in the lake. Prior to 3.3 Ma, this signal is overprinted by intensified detrital input from the catchment, visible in maxima of clastic-related proxies, such as K. In addition, calcite formation in the early lake history points to enhanced Ca flux into the lake caused by intensified weathering in the catchment. A lack of calcite deposition after ca. 3.3 Ma is linked to the development of permafrost in the region triggered by cooling in the mid-Pliocene. After ca. 3.0 Ma the elemental data suggest a gradual transition to Pleistocene-style glacial-interglacial cyclicity. In the early Pleistocene, the cyclicity was first dominated by variations on the 41 kyr obliquity band but experienced a change to a 100 kyr eccentricity dominance during the middle Pleistocene transition (MPT) at ca. 1.2-0.6 Ma. This clearly demonstrates the sensitivity of the Lake El'gygytgyn record to orbital forcing. A successive decrease of the baseline levels of the redox-sensitive Mn / Fe ratio and magnetic susceptibility between 2.3 and 1.8 Ma reflects an overall change in the bottom-water oxygenation due to an intensified occurrence of pervasive glacial episodes in the early Pleistocene. The coincidence with major changes in the North Pacific and Bering Sea paleoceanography at ca. 1.8 Ma implies that the change in lake hydrology was caused by a regional cooling in the North Pacific and the western Beringian landmass and/or changes in the continentality. Further increases in total organic carbon and total nitrogen content after ca. 1.6 Ma are attributed to reduced organic matter decay in the sediment during prolonged anoxic periods. This points to more extensive periods of perennial ice coverage, and thus, to a progressive shifts towards more intense peak glacial periods. In the course of the Pleistocene glacial-interglacial sequence eight so-called "super-interglacials" occur. Their exceptionally warm conditions are reflected by extreme Si / Ti peaks accompanied by lows in Ti, K, and Fe, thus indicating extraordinary high lake productivity.

Wennrich, V.; Minyuk, P. S.; Borkhodoev, V.; Francke, A.; Ritter, B.; Nowaczyk, N. R.; Sauerbrey, M. A.; Brigham-Grette, J.; Melles, M.

2014-07-01

225

Using Climate Models to Evaluate Mechanisms of Glacial Inception  

NASA Technical Reports Server (NTRS)

The initiation and subsequent growth of an ice sheet or large glacier is based on two primary factors: 1. Most fundamentally, a region must exist with a positive net snow accumulation, that is, cold season snowfall exceeds warm season snowmelt. Because snow can melt very rapidly, in a practical sense this probably means that little or no snow melt should occur in the warm season (mountain glaciers being one possible exception). 2. When sufficient ice builds in a region with a positive net snow accumulation, the ice will flow into adjoining regions with a negative mass balance. Feedbacks can also then arise between the emerging ice sheet and the overall climate, which, among other effects, may cause the mass balance in that region to turn positive. A key question is the relative importance of these two factors. In particular, is it possible for a large lowland region to experience a positive mass balance, such that the ice sheet can arise largely 'in-situ'? Or instead are uplands necessary, such that essentially mountain glaciers form first, and then, under the right conditions, grow and coalesce, eventually spreading out into the lowlands? This is probably the single most fundamental question to be addressed in the modeling of glacial inception. Other key questions then focus on how the (upland or low-land) positive mass balance is obtained at some times, but not others (the ice sheets are not continuously present). For Northern Hemisphere ice sheets in particular, what climatic conditions can lead to abundant winter snowfall in the Canadian Arctic and northern Labrador in conjunction with cool summertime conditions? Are both required, or will cool summer conditions alone suffice? Conversely, are a few years of abnormally heavy snowfall all that is required to trigger glacial inception? A major need at present is for carefully constructed climate model studies aimed at addressing these questions. A successful strategy will almost certainly require more than just a global model; while the global climate model might be necessary to properly simulate large-scale forcing, such models have insufficient spatial resolution to adequately address the roles of topography and the nature of the land surface. Necessary also is the use of a high-resolution regional climate model (in conjunction with a global model). Possible forcing mechanisms of Pleistocene ice ages are well known (e.g., orbital forcing; CO2 fluctuations) but we must understand and be able to successfully model the actual processes involved in glacial inception before we can fully understand the true roles played by these forcing mechanisms.

Oglesby, Robert J.; Arnold, James E. (Technical Monitor)

2001-01-01

226

Spatial and temporal patterns of Pleistocene biogenic sediment accumulation in the Gulf of Alaska  

NASA Astrophysics Data System (ADS)

Reconstructing the timing and nature of past changes in aquatic productivity in the Gulf of Alaska (GoA) can shed light on the primary processes driving biogeochemical cycling over geologic timescales. Today, Fe is an important micronutrient that limits primary productivity in surface waters beyond the continental shelf in much of the GoA. However, we have a relatively poor understanding of how Fe-delivery processes, combined with changing climate, environmental, and oceanographic conditions, interact to influence primary production over glacial-interglacial timescales. An important first step is to identify the spatial and temporal patterns of increased productivity in the sediment record. Here, we present sedimentologic and physical property data from IODP Expedition 341 and identify intervals where diatom ooze and diatom-rich mud lithofacies are prevalent during the Pleistocene. Among the Expedition 341 recovered cores, were high-recovery intervals in the outer (Site U1417) and inner (U1418) Surveyor Fan, and from a small slope basin at the edge of the continental shelf (Site U1419). In general, greenish gray diatomaceous ooze (containing >50 % diatoms in smear slides) and diatom-rich mud (>25% diatoms) is found in beds ranging in thickness from 20 to 150 cm, interbedded with gray mud that commonly contains lonestones. Ooze is occasionally found immediately overlying volcanic ash. Compared to non-biogenic mud, diatomaceous sediments are generally characterized by lower magnetic susceptibility, natural gamma ray, bulk density, and higher b* color reflectance. At Site U1417, we observe a frequent occurrence of diatomaceous ooze during the middle Pleistocene relative to the early and late Pleistocene. At Site U1418, intervals containing diatom ooze are less common than at U1417 and biogenic sediments are mainly observed within the late Pleistocene portion of the record. However, higher sedimentation rates at U1418 relative to U1417, and the co-occurrence of sand and interbedded mud and silt indicate that clastic sediment dilution may obscure biogenic sediment contribution. At Site U1419, two prominent ~5 m thick intervals of diatomaceous ooze are found (within the uppermost 5 m and between 80 and 90 m composite depth, respectively). Between these intervals are numerous 20 cm thick intervals of biogenic sediment that were likely deposited during the middle or late Pleistocene based on preliminary shipboard age models. Biogenic intervals observed at Expedition 341 sites may be related to increased productivity driven by a combination of the aforementioned processes, but additional chronological and geochemical constraints are needed from all sites to rule out the role that changing sedimentation rates and/or silica dissolution plays in controlling the distribution of ooze in these records.

Moy, C. M.; Bahlburg, H.; Childress, L. B.; Cowan, E. A.; Forwick, M.; Müller, J.; Ribeiro, F.; Ridgway, K. D.; Mix, A. C.

2013-12-01

227

Phylogeography of the large white-bellied rat Niviventer excelsior suggests the influence of Pleistocene glaciations in the Hengduan mountains.  

PubMed

The Hengduan Mountains, situated in the southeastern Tibetan Plateau, have undergone dramatic geological and climatic changes over the Pleistocene epoch. Several studies have revealed that the mountains served as a refugium during the ice age. The large white-bellied rat Niviventer excelsior is a rodent endemic to the Hengduan Mountains, which makes it an appropriate species for investigating the influence of glacial movements on the genetic structure of mammals. In this study, we sequenced the partial mitochondrial DNA control region from 72 N. excelsior specimens collected from 20 localities. The results revealed very high levels of haplotype diversity (h = 0.947) and nucleotide diversity (pi = 0.101) in this species. No common haplotype was found to be shared in samples from all geographic regions. Demographic analyses suggested that N. excelsior populations had not been subject to either expansion or bottleneck. The phylogenetic relationships among the haplotypes have no correlation with their geographical origins, while topology revealed two major clades. We speculate that the populations of N. excelsior may have been restricted to two separate refugia during the Last Glacial Maximum (0.60-0.17 Mya), with one west and one east of the Shaluli Mountains. Between the two major refugia, there existed a more widely distributed network subrefugia, which conserved genetic variations in N. excelsior. These results indicated that complex topographic configuration in the Hengduan Mountains provided a network of refugia to maintain the high level of genetic diversity in Pleistocene glaciations. PMID:20528155

Chen, Weicai; Liu, Shaoying; Liu, Yang; Hao, Haibang; Zeng, Bo; Chen, Shunde; Peng, Hongyuan; Yue, Bisong; Zhang, Xiuyue

2010-06-01

228

Connecting Soils and Glacial Geology  

NSDL National Science Digital Library

The goal of this activity is to provide students an opportunity to connect soil science to surficial geology by using a Soil Surveys. By the end of the activity, students should be able to use a Soil Survey to identify and interpret landforms and surficial features. This activity can be adapted to variety of process (ex. eolian deposits, glacial deposits, bedrock weathering, etc.). County-level soil surveys are available in both paper and online formats for the majority of the United States. Designed for a geomorphology course Has minimal/no quantitative component

Holly Dolliver

229

The intensification of northern component deepwater formation during the mid-Pleistocene climate transition  

NASA Astrophysics Data System (ADS)

reconstruct mid-Pleistocene (marine isotope stages (MISs) 13-18) deepwater hydrography at Ocean Drilling Program Site 1063 (4583 m water depth, subtropical North Atlantic) using benthic foraminiferal stable isotope records. These new records complete an ~900 kyr long stratigraphy spanning MISs 8-29 (~250-1030 Ka) when combined with previously published records from Site 1063. The results indicate a change in the circulation regime of the abyssal subtropical North Atlantic during MIS 17. Prior to MIS 17, no significant glacial or interglacial ?13C gradients are evident between Site 1063 and the deep South Atlantic. After MIS 17, interglacial intervals at Site 1063 are characterized by ?13C values that consistently approach those recorded in the deep North Atlantic. Comparing Site 1063 ?13C values to 26 additional published records throughout the entire Atlantic basin supports the idea that this ?13C increase is unique to the deep North Atlantic. After MIS 17, the basin-wide influence of higher ?13C values suggests an increased relative flux of northern sourced bottom waters during interglacial periods. The timing of northern sourced water influence at Site 1063 is consistent with the timing of a shift in the orientation of the Arctic Front. Thus, this shift may signify a link between the northward penetration of relatively warm, saline surface waters into the Norwegian-Greenland Seas stimulating deep convection. Our findings fit well with the model of Imbrie et al. (1993) for the importance of the Nordic heat pump in establishing strong 100 kyr cyclicity in late Pleistocene glacial cycles.

Poirier, Robert K.; Billups, Katharina

2014-11-01

230

American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change.  

PubMed

Existing radiocarbon ((14)C) dates on American mastodon (Mammut americanum) fossils from eastern Beringia (Alaska and Yukon) have been interpreted as evidence they inhabited the Arctic and Subarctic during Pleistocene full-glacial times (?18,000 (14)C years B.P.). However, this chronology is inconsistent with inferred habitat preferences of mastodons and correlative paleoecological evidence. To establish a last appearance date (LAD) for M. americanum regionally, we obtained 53 new (14)C dates on 36 fossils, including specimens with previously published dates. Using collagen ultrafiltration and single amino acid (hydroxyproline) methods, these specimens consistently date to beyond or near the ?50,000 y B.P. limit of (14)C dating. Some erroneously "young" (14)C dates are due to contamination by exogenous carbon from natural sources and conservation treatments used in museums. We suggest mastodons inhabited the high latitudes only during warm intervals, particularly the Last Interglacial [Marine Isotope Stage (MIS) 5] when boreal forests existed regionally. Our (14)C dataset suggests that mastodons were extirpated from eastern Beringia during the MIS 4 glacial interval (?75,000 y ago), following the ecological shift from boreal forest to steppe tundra. Mastodons thereafter became restricted to areas south of the continental ice sheets, where they suffered complete extinction ?10,000 (14)C years B.P. Mastodons were already absent from eastern Beringia several tens of millennia before the first humans crossed the Bering Isthmus or the onset of climate changes during the terminal Pleistocene. Local extirpations of mastodons and other megafaunal populations in eastern Beringia were asynchrononous and independent of their final extinction south of the continental ice sheets. PMID:25453065

Zazula, Grant D; MacPhee, Ross D E; Metcalfe, Jessica Z; Reyes, Alberto V; Brock, Fiona; Druckenmiller, Patrick S; Groves, Pamela; Harington, C Richard; Hodgins, Gregory W L; Kunz, Michael L; Longstaffe, Fred J; Mann, Daniel H; McDonald, H Gregory; Nalawade-Chavan, Shweta; Southon, John R

2014-12-30

231

Phylogeography and Pleistocene refugia of the adder (Vipera berus) as inferred from mitochondrial DNA sequence data.  

PubMed

In order to contribute to the debate about southern glacial refugia used by temperate species and more northern refugia used by boreal or cold-temperate species, we examined the phylogeography of a widespread snake species (Vipera berus) inhabiting Europe up to the Arctic Circle. The analysis of the mitochondrial DNA (mtDNA) sequence variation in 1043 bp of the cytochrome b gene and in 918 bp of the noncoding control region was performed with phylogenetic approaches. Our results suggest that both the duplicated control region and cytochrome b evolve at a similar rate in this species. Phylogenetic analysis showed that V. berus is divided into three major mitochondrial lineages, probably resulting from an Italian, a Balkan and a Northern (from France to Russia) refugial area in Eastern Europe, near the Carpathian Mountains. In addition, the Northern clade presents an important substructure, suggesting two sequential colonization events in Europe. First, the continent was colonized from the three main refugial areas mentioned above during the Lower-Mid Pleistocene. Second, recolonization of most of Europe most likely originated from several refugia located outside of the Mediterranean peninsulas (Carpathian region, east of the Carpathians, France and possibly Hungary) during the Mid-Late Pleistocene, while populations within the Italian and Balkan Peninsulas fluctuated only slightly in distribution range, with larger lowland populations during glacial times and with refugial mountain populations during interglacials, as in the present time. The phylogeographical structure revealed in our study suggests complex recolonization dynamics of the European continent by V. berus, characterized by latitudinal as well as altitudinal range shifts, driven by both climatic changes and competition with related species. PMID:16968280

Ursenbacher, S; Carlsson, M; Helfer, V; Tegelström, H; Fumagalli, L

2006-10-01

232

Phylogeographic and population genetic analyses reveal Pleistocene isolation followed by high gene flow in a wide ranging, but endangered, freshwater mussel.  

PubMed

Freshwater organisms of North America have had their contemporary genetic structure shaped by vicariant events, especially Pleistocene glaciations. Life history traits promoting dispersal and gene flow continue to shape population genetic structure. Cumberlandia monodonta, a widespread but imperiled (IUCN listed as endangered) freshwater mussel, was examined to determine genetic diversity and population genetic structure throughout its range. Mitochondrial DNA sequences and microsatellite loci were used to measure genetic diversity and simulate demographic events during the Pleistocene using approximate Bayesian computation (ABC) to test explicit hypotheses explaining the evolutionary history of current populations. A phylogeny and molecular clock suggested past isolation created two mtDNA lineages during the Pleistocene that are now widespread. Two distinct groups were also detected with microsatellites. ABC simulations indicated the presence of two glacial refugia and post-glacial admixture of them followed by simultaneous dispersal throughout the current range of the species. The Ouachita population is distinct from others and has the lowest genetic diversity, indicating that this is a peripheral population of the species. Gene flow within this species has maintained high levels of genetic diversity in most populations; however, all populations have experienced fragmentation. Extirpation from the center of its range likely has isolated remaining populations due to the geographic distances among them. PMID:24149656

Inoue, K; Monroe, E M; Elderkin, C L; Berg, D J

2014-03-01

233

Glacial biogeography of North American coho salmon (Oncorhynchus kisutch).  

PubMed

To study the glacial biogeography of coho we examined 20 microsatellite loci and mitochondrial DNA D-loop sequence in samples from Alaska to California. Microsatellite data divided our samples among five biogeographic regions: (1) Alaska and northern coastal British Columbia; (2) the Queen Charlotte Islands; (3) the mainland coast of British Columbia and northern Washington State; (4) the Thompson River; and (5) Oregon and California. The D-loop sequence data suggested three geographical regions: (1) Oregon and California; (2) the Thompson River; and (3) all the other sites north of the southern ice margin. Microsatellite data revealed no difference in the number of alleles in different regions, but mitochondrial DNA data revealed a cline of decreasing diversity from south to north. We suggest that the two signals presented by these different marker types illuminate two time frames in the history of this species. Endemic microsatellite diversity in Alaska and on the Queen Charlotte Islands provides evidence in favour of Fraser Glaciation refugia in these regions. The loss of mitochondrial variation from south to north suggests that one of the earlier, more extensive, Pleistocene glaciations eliminated coho from its northern range. PMID:11903891

Smith, C T; Nelson, R J; Wood, C C; Koop, B F

2001-12-01

234

Sea-level variability over five glacial cycles  

NASA Astrophysics Data System (ADS)

Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum ‘natural’ (pre-anthropogenic forcing) sea-level rise rates below 2?m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2?kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records.

Grant, K. M.; Rohling, E. J.; Ramsey, C. Bronk; Cheng, H.; Edwards, R. L.; Florindo, F.; Heslop, D.; Marra, F.; Roberts, A. P.; Tamisiea, M. E.; Williams, F.

2014-09-01

235

Sea-level variability over five glacial cycles.  

PubMed

Research on global ice-volume changes during Pleistocene glacial cycles is hindered by a lack of detailed sea-level records for time intervals older than the last interglacial. Here we present the first robustly dated, continuous and highly resolved records of Red Sea sea level and rates of sea-level change over the last 500,000 years, based on tight synchronization to an Asian monsoon record. We observe maximum 'natural' (pre-anthropogenic forcing) sea-level rise rates below 2?m per century following periods with up to twice present-day ice volumes, and substantially higher rise rates for greater ice volumes. We also find that maximum sea-level rise rates were attained within 2?kyr of the onset of deglaciations, for 85% of such events. Finally, multivariate regressions of orbital parameters, sea-level and monsoon records suggest that major meltwater pulses account for millennial-scale variability and insolation-lagged responses in Asian monsoon records. PMID:25254503

Grant, K M; Rohling, E J; Ramsey, C Bronk; Cheng, H; Edwards, R L; Florindo, F; Heslop, D; Marra, F; Roberts, A P; Tamisiea, M E; Williams, F

2014-01-01

236

Seismic characterization of glacial sediments in central Illinois  

NASA Astrophysics Data System (ADS)

The vertical distribution of compressional wave velocity (Vp) and shear wave velocity (Vs) acquired from fifteen boreholes in central Illinois using the standard surface-source downhole-receiver method was studied. The velocity logs were compared with lithologic logs and gamma-ray logs acquired from the same boreholes to: 1) better understand the Vp and Vs ranges and variations within glacial sediments, 2) determine whether characteristic seismic velocities could be resolved to distinguish among the three major Pleistocene glaciations of Wisconsin (WI), Illinois (IL), and pre-Illinois (PIL), and 3) examine velocity variations corresponding to heterogeneities in the sediments composing these three major units. Results showed that deposits composing these units had highly variable Vp and Vs values. Only the contact between deposits of the WI and IL episodes could be delineated by a corresponding slight decrease in Vp. Other than that, neither Vp nor Vs logs showed significant contrasts at the contacts between these units. Some individual sediment packages, or intraunits, exhibited distinctive velocity patterns in the study area and were identified more clearly from Vs than from Vp logs. These intraunits are Wisconsin tills (T), Vandalia till (GV) and Mahomet sand (BM).

Ismail, Ahmed; Stumpf, Andrew; Bauer, Robert

2014-02-01

237

Episodic glacially derived thrusts: a case study from the central North Sea Basin  

NASA Astrophysics Data System (ADS)

An extensive survey of 2D seismic in the central North Sea has revealed a series of thrusts within glacial sediments on the western flank of the Dogger Bank. The tectonic movement is evidenced by both imbricated thrust faults and 'pop-up' structures suggesting lateral compression of the sediment sequence. The closely spaced (100m) sparker profiles provide an opportunity to examine a glacial process whose geometry is normally difficult to assess from surface exposures. Initial studies suggest the thrusts extending to near seabed indicate eastward movement from one of two decollement surfaces located up to 200m below seabed. The structures affect sediments deposited since the Last Glacial Maximum (e.g. Bolders Bank Formation). However, the lower decollement surface is located with pre-glacial deltaic deposits and it is considered that hydrogeological controls have determined the surfaces upon which the movement occurs. The thrust structures are mapped over 100km2 with thrust planes 200-500m apart. Individual thrust planes have a width of up to 6km and may extend 2km upwards from the decollement surface to the seabed. They can be mapped in groups with slightly different alignments suggesting that the process causing these features to form was repeated several times, possibly at an oscillating ice-margin. The direction of movement is from the west, with ice belonging to the British and Irish Ice Sheet. The thrusting may have been caused by sub-glacial, ice marginal or pro-glacial processes, or a combination of these at a fluctuating ice-margin. Although the thrusts extend upwards to near seabed there is no apparent seabed morphological expression, suggesting that the expected topography of broad ridges aligned along the thrust surfaces has been eroded by later glacial or periglacial erosion or the subsequent Holocene marine transgression.

Cotterill, C.; Ruiter, A.; Dove, D.; Long, D.; James, L.; Forsberg, C.

2013-12-01

238

Glacial Earthquakes in Greenland and Antarctica  

E-print Network

, but they exhibit several characteristics similar to glacial earthquakes in Greenland. 467 Annu.Rev.EarthPlanetGlacial Earthquakes in Greenland and Antarctica Meredith Nettles and G¨oran Ekstr¨om Lamont@ldeo.columbia.edu Annu. Rev. Earth Planet. Sci. 2010. 38:467­91 First published online as a Review in Advance on February

Jellinek, Mark

239

Temporal labyrinths of eastern Eurasian Pleistocene humans  

PubMed Central

One of the morphological features that has been identified as uniquely derived for the western Eurasian Neandertals concerns the relative sizes and positions of their semicircular canals. In particular, they exhibit a relatively small anterior canal, a relatively larger lateral one, and a more inferior position of the posterior one relative to the lateral one. These discussions have not included full paleontological data on eastern Eurasian Pleistocene human temporal labyrinths, which have the potential to provide a broader context for assessing Pleistocene Homo trait polarities. We present the temporal labyrinths of four eastern Eurasian Pleistocene Homo, one each of Early (Lantian 1), Middle (Hexian 1), and Late (Xujiayao 15) Pleistocene archaic humans and one early modern human (Liujiang 1). The labyrinths of the two earlier specimens and the most recent one conform to the proportions seen among western early and recent modern humans, reinforcing the modern human pattern as generally ancestral for the genus Homo. The labyrinth of Xujiayao 15 is in the middle of the Neandertal variation and separate from the other samples. This eastern Eurasian labyrinthine dichotomy occurs in the context of none of the distinctive Neandertal external temporal or other cranial features. As such, it raises questions regarding possible cranial and postcranial morphological correlates of Homo labyrinthine variation, the use of individual “Neandertal” features for documenting population affinities, and the nature of late archaic human variation across Eurasia. PMID:25002467

Wu, Xiu-Jie; Crevecoeur, Isabelle; Liu, Wu; Xing, Song; Trinkaus, Erik

2014-01-01

240

Temporal labyrinths of eastern Eurasian Pleistocene humans.  

PubMed

One of the morphological features that has been identified as uniquely derived for the western Eurasian Neandertals concerns the relative sizes and positions of their semicircular canals. In particular, they exhibit a relatively small anterior canal, a relatively larger lateral one, and a more inferior position of the posterior one relative to the lateral one. These discussions have not included full paleontological data on eastern Eurasian Pleistocene human temporal labyrinths, which have the potential to provide a broader context for assessing Pleistocene Homo trait polarities. We present the temporal labyrinths of four eastern Eurasian Pleistocene Homo, one each of Early (Lantian 1), Middle (Hexian 1), and Late (Xujiayao 15) Pleistocene archaic humans and one early modern human (Liujiang 1). The labyrinths of the two earlier specimens and the most recent one conform to the proportions seen among western early and recent modern humans, reinforcing the modern human pattern as generally ancestral for the genus Homo. The labyrinth of Xujiayao 15 is in the middle of the Neandertal variation and separate from the other samples. This eastern Eurasian labyrinthine dichotomy occurs in the context of none of the distinctive Neandertal external temporal or other cranial features. As such, it raises questions regarding possible cranial and postcranial morphological correlates of Homo labyrinthine variation, the use of individual "Neandertal" features for documenting population affinities, and the nature of late archaic human variation across Eurasia. PMID:25002467

Wu, Xiu-Jie; Crevecoeur, Isabelle; Liu, Wu; Xing, Song; Trinkaus, Erik

2014-07-22

241

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa  

PubMed Central

Extremely arid conditions in tropical Africa occurred in several discrete episodes between 135 and 90 ka, as demonstrated by lake core and seismic records from multiple basins [Scholz CA, Johnson TC, Cohen AS, King JW, Peck J, Overpeck JT, Talbot MR, Brown ET, Kalindekafe L, Amoako PYO, et al. (2007) Proc Natl Acad Sci USA 104:16416–16421]. This resulted in extraordinarily low lake levels, even in Africa's deepest lakes. On the basis of well dated paleoecological records from Lake Malawi, which reflect both local and regional conditions, we show that this aridity had severe consequences for terrestrial and aquatic ecosystems. During the most arid phase, there was extremely low pollen production and limited charred-particle deposition, indicating insufficient vegetation to maintain substantial fires, and the Lake Malawi watershed experienced cool, semidesert conditions (<400 mm/yr precipitation). Fossil and sedimentological data show that Lake Malawi itself, currently 706 m deep, was reduced to an ?125 m deep saline, alkaline, well mixed lake. This episode of aridity was far more extreme than any experienced in the Afrotropics during the Last Glacial Maximum (?35–15 ka). Aridity diminished after 95 ka, lake levels rose erratically, and salinity/alkalinity declined, reaching near-modern conditions after 60 ka. This record of lake levels and changing limnological conditions provides a framework for interpreting the evolution of the Lake Malawi fish and invertebrate species flocks. Moreover, this record, coupled with other regional records of early Late Pleistocene aridity, places new constraints on models of Afrotropical biogeographic refugia and early modern human population expansion into and out of tropical Africa. PMID:17925446

Cohen, Andrew S.; Stone, Jeffery R.; Beuning, Kristina R. M.; Park, Lisa E.; Reinthal, Peter N.; Dettman, David; Scholz, Christopher A.; Johnson, Thomas C.; King, John W.; Talbot, Michael R.; Brown, Erik T.; Ivory, Sarah J.

2007-01-01

242

Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska  

NASA Astrophysics Data System (ADS)

The Canyon Creek vertebrate-fossil locality is an extensive road cut near Fairbanks that exposes sediments that range in age from early Wisconsin to late Holocene. Tanana River gravel at the base of the section evidently formed during the Delta Glaciation of the north-central Alaska Range. Younger layers and lenses of fluvial sand are interbedded with arkosic gravel from Canyon Creek that contains tephra as well as fossil bones of an interstadial fauna about 40,000 years old. Solifluction deposits containing ventifacts, wedge casts, and rodent burrows formed during a subsequent period of periglacial activity that took place during the maximum phase of Donnelly Glaciation about 25,000-17,000 years ago. Overlying sheets of eolian sand are separated by a 9500-year-old paleosol that may correlate with a phase of early Holocene spruce expansion through central Alaska. The Pleistocene fauna from Canyon Creek consists of rodents (indicated by burrows), Mammuthus primigenius (woolly mammoth), Equus lambei (Yukon wild ass), Camelops hesternus (western camel), Bison sp. cf. B. crassicornis (large-horned bison), Ovis sp. cf. O. dalli (mountain sheep), Canis sp. cf. C. lupus (wolf), Lepus sp. cf. L. othus or L. arcticus (tundra hare), and Rangifer sp. (caribou). This assemblage suggests an open landscape in which trees and tall shrubs were either absent or confined to sheltered and moist sites. Camelops evidently was present in eastern Beringia during the middle Wisconsin interstadial interval but may have disappeared during the following glacial episode. The stratigraphic section at Canyon Creek appears to demonstrate that the Delta Glaciation of the north-central Alaska Range is at least in part of early Wisconsin age and was separated from the succeeding Donnelly Glaciation by an interstadial rather than interglacial episode.

Weber, Florence R.; Hamilton, Thomas D.; Hopkins, David M.; Repenning, Charles A.; Haas, Herbert

1981-09-01

243

Late Pleistocene environments of the western Noatak basin, northwestern Alaska  

USGS Publications Warehouse

Glacial Lake Noatak formed repeatedly during middle and late Pleistocene time as expanding glaciers from the DeLong Mountains blocked the Noatak River valley. Downcutting by the Noatak River has exposed thick sediment successions in bluffs up to 86 m high. Two river bluffs, Nk-26 and Nk-29A, contain correlative organic-rich flood-plain deposits that were formed during and after deposition of the Old Crow tephra at about the transition between oxygen isotope stage 6 and oxygen isotope stage 5, at the beginning of the last interglaciation. Both bluffs also contain older interglacial or interstadial flood-plain deposits of uncertain age. Pollen and beetle remains were recovered from the older and younger flood-plain deposits at each bluff. Pollen from the younger flood-plain deposits suggests tundra vegetation with local dominance of sedge. Juniperus abundances were locally high, especially around the time of Old Crow tephra deposition. Mutual climatic range (MCR) estimates from the insect fossil assemblages suggest that mean summer temperatures (Tmax) near the time of Old Crow tephra deposition were about 2 ??C colder than modern; mean winter temperatures were very similar to those of today. A younger sample from the same interglacial deposit yielded a Tmax estimate of 2 ??C warmer than modern, signaling interglacial warming. Pollen from the older interglacial deposit at Nk-29A suggests mesic tundra, with boreal forest more distant than it is today. MCR analysis of a possibly correlative older interglacial deposit at Nk-26 suggests a Tmax about 2 ??C below present.

Elias, S.A.; Hamilton, T.D.; Edwards, M.E.; Beget, J.E.; Krumhardt, A.P.; Lavoie, C.

1999-01-01

244

Late Pleistocene voles (Arvicolinae, Rodentia) from the Baranica Cave (Serbia)  

NASA Astrophysics Data System (ADS)

Baranica is a cave system situated in the south-eastern part of Serbia, four kilometers south to Knjaževac, on the right bank of the Trgovi\\vski Timok. The investigations in Baranica were conducted from 1994 to 1997 by the Faculty of Philosophy from Belgrade and the National Museum of Knjaževac. Four geological layers of Quaternary age were recovered. The abundance of remains of both large and small mammals was noticed in the early phase of the research. In this paper, the remains of eight vole species are described: Arvicola terrestris (Linnaeus, 1758), Chionomys nivalis (Martins, 1842), Microtus (Microtus) arvalis (Pallas, 1778) and Microtus (Microtus) agrestis (Linnaeus, 1761), Microtus (Stenocranius) gregalis (Pallas, 1779), Microtus (Terricola) subterraneus (de Sélys-Longchamps, 1836), Clethrionomys glareolus (Schreber, 1780) and Lagurus lagurus (Pallas, 1773). Among them, steppe and open area inhabitants prevail. Based on the evolutionary level and dimensions of the Arvicola terrestris molars, as well as the overall characteristics of the fauna, it was concluded that the deposits were formed in the last glacial period of the Late Pleistocene. These conclusions are rather consistent with the absolute dating of large mammal bones (23.520 ± 110 B.P. for Layer 2 and 35.780 ± 320 B.P. for Layer 4).

Bogi?evi?, Katarina; Nenadi?, Draženko; Mihailovi?, Dušan

2012-02-01

245

Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska  

USGS Publications Warehouse

The Canyon Creek vertebrate-fossil locality is an extensive road cut near Fairbanks that exposes sediments that range in age from early Wisconsin to late Holocene. Tanana River gravel at the base of the section evidently formed during the Delta Glaciation of the north-central Alaska Range. Younger layers and lenses of fluvial sand are interbedded with arkosic gravel from Canyon Creek that contains tephra as well as fossil bones of an interstadial fauna about 40,000 years old. Solifluction deposits containing ventifacts, wedge casts, and rodent burrows formed during a subsequent period of periglacial activity that took place during the maximum phase of Donnelly Glaciation about 25,000-17,000 years ago. Overlying sheets of eolian sand are separated by a 9500-year-old paleosol that may correlate with a phase of early Holocene spruce expansion through central Alaska. The Pleistocene fauna from Canyon Creek consists of rodents (indicated by burrows), Mammuthus primigenius (woolly mammoth), Equus lambei (Yukon wild ass), Camelops hesternus (western camel), Bison sp. cf. B. crassicornis (large-horned bison), Ovis sp. cf. O. dalli (mountain sheep), Canis sp. cf. C. lupus (wolf), Lepus sp. cf. L. othus or L. arcticus (tundra hare), and Rangifer sp. (caribou). This assemblage suggests an open landscape in which trees and tall shrubs were either absent or confined to sheltered and moist sites. Camelops evidently was present in eastern Beringia during the middle Wisconsin interstadial interval but may have disappeared during the following glacial episode. The stratigraphic section at Canyon Creek appears to demonstrate that the Delta Glaciation of the north-central Alaska Range is at least in part of early Wisconsin age and was separated from the succeeding Donnelly Glaciation by an interstadial rather than interglacial episode. ?? 1981.

Weber, F.R.; Hamilton, T.D.; Hopkins, D.M.; Repenning, C.A.; Haas, H.

1981-01-01

246

Millennial-scale climate variability during the mid-Pleistocene transition period in the northern South China Sea  

NASA Astrophysics Data System (ADS)

Stable isotopes of foraminiferal multispecies (surface dwelling Globigerinoides ruber, thermocline dwelling Pulleniatina obliquiloculata, and benthic Uvigerina peregrina) and Mg/Ca ratios of G. ruber shells were analyzed with an average time resolution of ˜370 yr for reconstructing the orbital- and millennial-scale changes in the East Asian monsoon and associated upper water structure during the mid-Pleistocene period of 800-1060 ka at ODP Site 1144 in the northern South China Sea (SCS). It has been found that generally the sea surface temperature (SST) were lower and the depth of thermocline (DOT) was deeper during glacial stages and vice versa during interglacial stages, indicating a strengthened winter monsoon and weakened summer monsoon during glacial stages. The sea surface salinity (SSS) was relatively lower during glacials, induced by the greatly reduced distance of this site to the shore during times of low sea level. Further, spectral analyses have revealed significant semi-precessional and/or precessional cycles in the planktic ?18O, SST and the proxies of SSS and DOT, showing the typical characteristics of tropical climate change. This means that during the mid-Pleistocene climate transition (MPT) period the East Asian monsoon evolution and associated changes of upper water column structure in the northern SCS were probably driven partly by tropical forcing, like in the southern SCS, and should not be related only to the high latitude ice sheet changes. Particularly, millennial-scale climate fluctuations (mainly ˜1.4 kyr cycle) were found to exist throughout the glacial and interglacial stages during the MPT period in the northern SCS, but slightly different from the sawtooth-like D/O events recorded in late Quaternary Greenland ice cores. During the mid-Pleistocene terminations, the SST warming was synchronous with the northern ice sheet retreat, indicated by benthic ?18O, in the northern SCS, which is consistent to the previous findings in the late Quaternary SCS and apparently different from that in the western equatorial Pacific Ocean, providing new insights into the studies of East Asian monsoon evolution and rapid climate change.

Jin, Haiyan; Jian, Zhimin

2013-06-01

247

Timing and dynamics of Late Pleistocene mammal extinctions in southwestern Australia.  

PubMed

Explaining the Late Pleistocene demise of many of the world's larger terrestrial vertebrates is arguably the most enduring and debated topic in Quaternary science. Australia lost >90% of its larger species by around 40 thousand years (ka) ago, but the relative importance of human impacts and increased aridity remains unclear. Resolving the debate has been hampered by a lack of sites spanning the last glacial cycle. Here we report on an exceptional faunal succession from Tight Entrance Cave, southwestern Australia, which shows persistence of a diverse mammal community for at least 100 ka leading up to the earliest regional evidence of humans at 49 ka. Within 10 millennia, all larger mammals except the gray kangaroo and thylacine are lost from the regional record. Stable-isotope, charcoal, and small-mammal records reveal evidence of environmental change from 70 ka, but the extinctions occurred well in advance of the most extreme climatic phase. We conclude that the arrival of humans was probably decisive in the southwestern Australian extinctions, but that changes in climate and fire activity may have played facilitating roles. One-factor explanations for the Pleistocene extinctions in Australia are likely oversimplistic. PMID:21127262

Prideaux, Gavin J; Gully, Grant A; Couzens, Aidan M C; Ayliffe, Linda K; Jankowski, Nathan R; Jacobs, Zenobia; Roberts, Richard G; Hellstrom, John C; Gagan, Michael K; Hatcher, Lindsay M

2010-12-21

248

A late Pleistocene steppe bison ( Bison priscus) partial carcass from Tsiigehtchic, Northwest Territories, Canada  

NASA Astrophysics Data System (ADS)

A partial steppe bison ( Bison priscus) carcass was recovered at Tsiigehtchic, near the confluence of the Arctic Red and Mackenzie Rivers, Northwest Territories, Canada in September of 2007. The carcass includes a complete cranium with horn cores and sheaths, several complete post-cranial elements (many of which have some mummified soft tissue), intestines and a large piece of hide. A piece of metacarpal bone was subsampled and yielded an AMS radiocarbon age of 11,830 ± 45 14C yr BP (OxA-18549). Mitochondrial DNA sequenced from a hair sample confirms that Tsiigehtchic steppe bison ( Bison priscus) did not belong to the lineage that eventually gave rise to modern bison ( Bison bison). This is the first radiocarbon dated Bison priscus in the Mackenzie River valley, and to our knowledge, the first reported Pleistocene mammal soft tissue remains from the glaciated regions of northern Canada. Investigation of the recovery site indicates that the steppe bison was released from the permafrost during a landslide within unconsolidated glacial outwash gravel. These data indicate that the lower Mackenzie River valley was ice free and inhabited by steppe bison by ˜11,800 14C years ago. This date is important for the deglacial chronology of the Laurentide Ice Sheet and the opening of the northern portal to the Ice Free Corridor. The presence of steppe bison raises further potential for the discovery of more late Pleistocene fauna, and possibly archaeological evidence, in the region.

Zazula, Grant D.; MacKay, Glen; Andrews, Thomas D.; Shapiro, Beth; Letts, Brandon; Brock, Fiona

2009-12-01

249

The role of Pleistocene refugia and rivers in shaping gorilla genetic diversity in central Africa  

PubMed Central

The role of Pleistocene forest refugia and rivers in the evolutionary diversification of tropical biota has been the subject of considerable debate. A range-wide analysis of gorilla mitochondrial and nuclear variation was used to test the potential role of both refugia and rivers in shaping genetic diversity in current populations. Results reveal strong patterns of regional differentiation that are consistent with refugial hypotheses for central Africa. Four major mitochondrial haplogroups are evident with the greatest divergence between eastern (A, B) and western (C, D) gorillas. Coalescent simulations reject a model of recent east–west separation during the last glacial maximum but are consistent with a divergence time within the Pleistocene. Microsatellite data also support a similar regional pattern of population genetic structure. Signatures of demographic expansion were detected in eastern lowland (B) and Gabon/Congo (D3) mitochondrial haplogroups and are consistent with a history of postglacial expansion from formerly isolated refugia. Although most mitochondrial haplogroups are regionally defined, limited admixture is evident between neighboring haplogroups. Mantel tests reveal a significant isolation-by-distance effect among western lowland gorilla populations. However, mitochondrial genetic distances also correlate with the distance required to circumnavigate intervening rivers, indicating a possible role for rivers in partitioning gorilla genetic diversity. Comparative data are needed to evaluate the importance of both mechanisms of vicariance in other African rainforest taxa. PMID:18077351

Anthony, Nicola M.; Johnson-Bawe, Mireille; Jeffery, Kathryn; Clifford, Stephen L.; Abernethy, Kate A.; Tutin, Caroline E.; Lahm, Sally A.; White, Lee J. T.; Utley, John F.; Wickings, E. Jean; Bruford, Michael W.

2007-01-01

250

Late-glacial and Holocene vegetation and climate change at the Palü glacier, Bernina Pass, Grisons Canton, Switzerland  

Microsoft Academic Search

Pollen and macrofossil data from Alpe PAlü, south-eastern Switzerland, are presented. On the basis of these data and the geomorphological evidence for local glacier movement, Holocene climatic oscillations and vegetation change at this upland site (1940 m asl), are reconstructed. The morainic deposits and glacial clays, as well as the pollen data from the base of the pollen profile, clearly

Heinrich Zoller; Nikolaos Athanasiadis; Annekäthi Heitz-Weniger

1998-01-01

251

JGR -Atmospheres Apr 2001 (in press) Effects of Glacial Meltwater in the GISS Coupled Atmosphere-Ocean  

E-print Network

-Ocean Model: Part I: North Atlantic Deep Water Response David Rind, 1 P. Demenocal, 2 Gary L. Russell, 1-ocean model. The results show a generally linear response in percentage North Atlantic Deep Water (NADW evidence exists that North Atlantic Deep Water (NADW) production has oscil- lated during the glacial age

252

Prospects for Complete Middle Pleistocene Loess Records in Interior Alaska: A Role for Tephrochronology  

NASA Astrophysics Data System (ADS)

Loess records in unglaciated Yukon and Alaska (eastern Beringia) are exceptional repositories for paleoenvironmental studies. The volcanic ash (tephra) beds found within the loess provide a means to date and correlate these deposits across this region. However, the middle Pleistocene (~780-130 ka) is poorly represented and/or has not been fully recognized at most previously examined sites. This is problematic because important events took place in the middle Pleistocene, including the transition from 40 to 100 ka interglacial-glacial cycles, the evolution and dispersion of steppe fauna, and interglacials that are thought to have been longer and warmer than the Holocene. However, studies at several sites in the interior of Alaska in recent years demonstrate that middle Pleistocene loess deposits are widespread across the interior of Alaska, some of which are relatively continuous. Here we focus on loess and tephra exposures at Gold Hill (<70 ka to ~3 Ma) near Fairbanks, the Palisades (<125 ka to >2 Ma) in west-central Alaska, and Birch Creek (<125 to >220 ka) and Chester Bluff (~70 to 780 ka) in east-central Alaska. Multiple tephra beds are present in these sections, and allow correlation of sites to one another, strengthening their respective chronologies. The tephra beds also highlight unconformities, which are common in loess deposits but often difficult to identify by lithostratigraphy alone. The improved chronologic control will allow more robust interpretation of high-resolution paleoenvironmental proxy records from these sites, including a 5-cm-resolution magnetic susceptibility profile through ~30 m of Gold Hill loess, from the ~1 Ma old AT tephra to several metres above the ~80 ka VT tephra. Dated tephra beds present in this sequence, such as GI (~560 ka), HP (~610 ka) and SP (~870 ka), provide critical chronostratigraphic control for this magnetic susceptibility record.

Jensen, B. J.; Reyes, A.; Froese, D. G.

2009-12-01

253

Geographic and temporal trends in proboscidean and human radiocarbon histories during the late Pleistocene  

NASA Astrophysics Data System (ADS)

The causes of large animal extinctions at the end of the Pleistocene remain a hotly debated topic focused primarily on the effects of human over hunting and climate change. Here we examine multiple, large radiocarbon data sets for humans and extinct proboscideans and explore how variation in their temporal and geographic distributions were related prior to proboscidean extinction. These data include 4532 archaeological determinations from Europe and Siberia and 1177 mammoth and mastodont determinations from Europe, Siberia, and North America. All span the period from 45,000 to 12,000 calendar years BP. We show that while the geographic ranges of dated human occupations and proboscidean remains overlap across the terminal Pleistocene of the Old World, the two groups remain largely segregated and increases in the frequency of human occupations do not coincide with declines in proboscidean remains. Prior to the Last Glacial Maximum (LGM; ca 21,000 years BP), archaeological 14C determinations increase slightly in frequency worldwide while the frequency of dated proboscidean remains varies depending on taxon and location. After the LGM, both sympatric and allopatric groups of humans and proboscideans increase sharply as climatic conditions ameliorate. Post-LGM radiocarbon frequencies among proboscideans peak at different times, also depending upon taxon and location. Woolly mammoths in Beringia reach a maximum and then decline beginning between 16,000 and 15,500 years BP, woolly mammoths in Europe and Siberia ca 14,500 and 13,500 BP, and Columbian mammoth and American mastodont only after 13,000 BP. Declines among woolly mammoths appear to coincide with the restructuring of biotic communities following the Pleistocene-Holocene transition.

Ugan, Andrew; Byers, David

2007-12-01

254

Pliocene-Pleistocene diatom biostratigraphy of nearshore Antarctica from the AND-1B drillcore, McMurdo Sound  

NASA Astrophysics Data System (ADS)

The near-shore open-marine diatom record recovered in the ANtarctic geological DRILLing (ANDRILL) McMurdo Ice Shelf Project (MIS) AND-1B drillcore, McMurdo Sound, Antarctica, advances our understanding of the marine conditions present in the southern Ross Sea during the Pliocene and early Pleistocene. This diatom history is recorded within alternating diamictite and diatomite that reflect alternating glacial activity and high marine primary productivity. The diatomite units were deposited in a continental shelf open-marine setting during periods of reduced ice cover in West Antarctica. A new diatom biostratigraphic scheme spanning the last ca. 5 Ma is proposed for the Antarctic near-shore area, based on prior work from high latitude drillcores. Four new zones are proposed for the Pliocene/Pleistocene, with eight in total for the new zonal scheme, utilizing Actinocylus fasciculatus, Actinocyclus maccollumii, Fragilariopsis bohatyii, Rouxia antarctica, and Thalassiosira fasciculata as new zonal markers. The early Pliocene shares the most assemblage commonality with that of the Southern Ocean with greater numbers of endemic species observed in the late Pliocene and early Pleistocene; a group of related Fragilaripsis species characterizes much of this later part of the time column. Two new species are proposed, Fragilariopsis tigris sp. nov. Riesselman and Thalassiosira teres sp. nov. Winter; a formal name is also proposed for another species, Rhizosolenia harwoodii sp. nov. Winter. The new zonation is tied to a robust chronology utilizing diatom biostratigraphy, volcanic 40Ar/39Ar ages and magnetostratigraphy.

Winter, D.; Sjunneskog, C.; Scherer, R.; Maffioli, P.; Riesselman, C.; Harwood, D.

2012-10-01

255

Pliocene-Pleistocene continental deposits in western Kentucky: A new look at regional stratigraphy and depositional history  

SciTech Connect

Pliocene and Pleistocene age sediments of the northernmost Mississippi Embayment consist of a thick sequence of continental deposits which rest unconformably on Cretaceous through Eocene strata. The continental deposits have been tentatively correlated to the Pliocene Mounds Gravel and Pleistocene Henry and Equality Formations of southern Illinois. These sediments have previously been interpreted as representing alluvial fan and fluvial deposits. The continental deposits are generally divided into three lithofacies: (1) silt/clay dominated; (2) sand dominated, and (3) gravel dominated. A subsurface study utilizing approximately 300 soil borings has shown that (1) the continental deposits, particularly the gravel facies, exhibit significant local changes in thickness, (2) the upper portion of the sequence consists predominantly of finer-grained silt/clay lithofacies, and (3) sand and gravel lithofacies within the upper sequence often occur at predictable horizons. These observations indicate a paleovalley fill with distinct depositional episodes. As a result of Pleistocene base level fluctuations, stream systems became deeply entrenched in the Pliocene alluvial fan and older sediments. Fan deposits were initially transported and redeposited in a braided fluvial system. As valley alluviation continued and gradients decreased, the braided fluvial system evolved into a meandering system. During Woodfordian time, slackwater lakes created by glacial outwash dams produced extensive lacustrine deposits. At least two major episodes of lacustrine sedimentation are apparent. Significant fluctuations of lake level are recognized in the subsurface by local erosional surfaces overlain by coarser-grained sediments deposited in basinward-migrating channel and shoreline facies.

Phillips, B.E. (Martin Marietta Energy Systems, Inc., Paducah, KY (United States))

1992-01-01

256

Rapid thinning of the late Pleistocene Patagonian Ice Sheet followed migration of the Southern Westerlies  

PubMed Central

Here we present the first reconstruction of vertical ice-sheet profile changes from any of the Southern Hemisphere's mid-latitude Pleistocene ice sheets. We use cosmogenic radio-nuclide (CRN) exposure analysis to record the decay of the former Patagonian Ice Sheet (PIS) from the Last Glacial Maximum (LGM) and into the late glacial. Our samples, from mountains along an east-west transect to the east of the present North Patagonian Icefield (NPI), serve as ‘dipsticks' that allow us to reconstruct past changes in ice-sheet thickness, and demonstrates that the former PIS remained extensive and close to its LGM extent in this region until ~19.0?ka. After this time rapid ice-sheet thinning, initiated at ~18.1?ka, saw ice at or near its present dimension by 15.5?ka. We argue this rapid thinning was triggered by a combination of the rapid southward migration of the precipitation bearing Southern Hemisphere (SH) westerlies and regional warming. PMID:23817136

Boex, J.; Fogwill, C.; Harrison, S.; Glasser, N. F.; Hein, A.; Schnabel, C.; Xu, S.

2013-01-01

257

Isotopic composition of old ground water from Lake Agassiz: Implications for late Pleistocene climate  

SciTech Connect

A uniform oxygen isotope value of -25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial Lake Agassiz basin. The lake occupied parts of North Dakota and southern Manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of Canada. Ground water from thick late Pleistocene-age clay deposits elsewhere, a till in southern Saskatchewan, and a glaciolacustrine deposit in northern Ontario show the same value at similar depths. These sites are at about 50[degrees]N latitude, span a distance of 2000 kilometers, and like the Lake Agassiz sites, have a ground-water velocity of less than a few millimeters per year. The value of -25 per mil is characteristic of meltwater impounded in the southern basin of Lake Agassiz. This value corresponds to an estimated air temperature of -16[degrees]C, compared with the modern temperature of 0[degrees]C for this area. 15 refs., 5 figs.

Remenda, V.H.; Cherry, J.A.; Edwards, T.W.D. (Univ. of Waterloo, Ontario (Canada))

1994-12-23

258

Spawning sockeye salmon fossils in Pleistocene lake beds of Skokomish Valley, Washington  

NASA Astrophysics Data System (ADS)

An assemblage of fossil sockeye salmon was discovered in Pleistocene lake sediments along the South Fork Skokomish River, Olympic Peninsula, Washington. The fossils were abundant near the head of a former glacial lake at 115 m elevation. Large adult salmon are concentrated in a sequence of death assemblages that include individuals with enlarged breeding teeth and worn caudal fins indicating migration, nest digging, and spawning prior to death. The specimens were 4 yr old and 45-70 cm in total length, similar in size to modern sockeye salmon, not landlocked kokanee. The fossils possess most of the characteristics of sockeye salmon, Oncorhynchus nerka, but with several minor traits suggestive of pink salmon, O. gorbuscha. This suggests the degree of divergence of these species at about 1 million yr ago, when geological evidence indicates the salmon were deposited at the head of a proglacial lake impounded by the Salmon Springs advance of the Puget lobe ice sheet. Surficial geology and topography record a complicated history of glacial damming and river diversion that implies incision of the modern gorge of the South Fork Skokomish River after deposition of the fossil-bearing sediments.

Smith, Gerald R.; Montgomery, David R.; Peterson, N. Phil; Crowley, Bruce

2007-09-01

259

Late Pleistocene alluvial plain sedimentation in Lower Narmada Valley, Western India: Palaeoenvironmental implications  

NASA Astrophysics Data System (ADS)

Late Pleistocene fluvial sediments that were deposited in a slowly sinking basin are now exposed as 30-50 m high incised vertical cliffs all along the Lower Narmada Valley in western India. The exposed fluvial deposits have been classified into two sediment packages, alluvial fan sediments overlain by alluvial plain sediments. The alluvial plain sequence has not been studied previously. It consists mainly of sands and silts and is dominated by overbank deposits. Occurrence of large scale bedforms in the alluvial plain sequence points to the existence of a large sand bed river in an alluvial plain setting. The major sedimentary facies in stratigraphic order include large channel fills, giant epsilon cross bedded strata, overbank fines occurring in horizontal, massive and undulatory stratified forms associated with crevasse splay and backswamp deposits, and a reddish brown palaeosol overlain by thinly stratified sands and silts at the top of the exposed sediment succession. Large sized channel fills occur at two stratigraphic levels, which are morphologically similar and are indicative of high rates of deposition and avulsion. The large channel fill structures and the giant epsilon cross bedded strata indicate a large single channel river that was consistently 10-15 m deep and about 70-80 m wide even during the dry seasons. These dimensions are larger than those of the present day Narmada River at low discharge levels. The overbank sediments indicate rapid deposition through frequent overbank floods and floodplain aggradation by a laterally shifting river. Available chronologic data suggests that the reddish brown palaeosol correlates with a regional phase of pedogenesis in the alluvial plain of Gujarat prior to the Last Glacial Maximum (LGM). The thinly stratified sands and silts overlying the palaeosol were deposited by a considerably depleted but perennial river during the arid phase of the Last Glacial Maximum. Overall, the alluvial plain sediments of the Lower Narmada valley, particularly those below the palaeosol, have been attributed to a hyper-avulsive large river with low sinuosity whose high discharge levels were determined primarily by a large catchment area further to the east and not by the semiarid climate prevailing in the Gujarat alluvial plain during the upper part of the Late Pleistocene. The study concludes that the Narmada River has maintained a large catchment at least since the last 100 ka, however, the river was characterised by a much bigger channel during much of the Late Pleistocene with discharge levels higher than the present day.

Bhandari, S.; Maurya, D. M.; Chamyal, L. S.

2005-01-01

260

Middle Pleistocene palaeoenvironmental changes of the eastern Canary Islands - revealed by the Mála dune-palaeosol-sequence at Lanzarote (Canary Islands)  

NASA Astrophysics Data System (ADS)

The Canary Islands are located at the transition between the Mediterranean and the Saharan climate off NW-Africa. Thus, they are a key area for the investigation of palaeoenvironmental changes. Several terrestrial studies investigated the palaeoenvironmental development of that region during the later part of the last glacial cycle. However, apart from recent investigations of "vega" sediments on Lanzarote Island (Suchodoletz et al. 2010) the palaeoenvironmental evolution during the Middle Pleistocene is hardly studied yet, basically due to the lack of reliable geochronological data. The Mála dune-palaeosol-sequence is located in the north of Lanzarote. It consists of marine shell detritus originally blown out from the insular shelf during periods of low global sea level, and to a small part of Saharan dust and fine quartz sand. The aeolian layers are intercalated with up to eight silty-clayey palaeosol horizons. Unlike the dune sands, the soils indicate stable landscape conditions with trapping of Saharan dust. Using a combination of ESR and luminescence dating techniques, we are able to place this sequence into the Middle Pleistocene, in contrast to former investigations based on 14C datings postulating a Late Pleistocene age (Ortiz et al. 2006). As a consequence, clayey-silty palaeosols represent periods of stable landscape conditions in the Canarian region during the Middle Pleistocene, which we compare with marine palaeoclimatic studies from the area.

von Suchodoletz, H.; Zöller, L.; Hilgers, A.; Radtke, U.; Faust, D.

2012-04-01

261

Obsidian hydration dates glacial loading?  

PubMed

Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming. The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow. PMID:17806883

Friedman, I; Pierce, K L; Obradovich, J D; Long, W D

1973-05-18

262

Obsidian hydration dates glacial loading?  

USGS Publications Warehouse

Three different groups of hydration rinds have been measured on thin sections of obsidian from Obsidian Cliff, Yellowstone National Park, Wyoming . The average thickness of the thickest (oldest) group of hydration rinds is 16.3 micrometers and can be related to the original emplacement of the flow 176,000 years ago (potassium-argon age). In addition to these original surfaces, most thin sections show cracks and surfaces which have average hydration rind thicknesses of 14.5 and 7.9 micrometers. These later two hydration rinds compare closely in thickness with those on obsidian pebbles in the Bull Lake and Pinedale terminal moraines in the West Yellowstone Basin, which are 14 to 15 and 7 to 8 micrometers thick, respectively. The later cracks are thought to have been formed by glacial loading during the Bull Lake and Pinedale glaciations, when an estimated 800 meters of ice covered the Obsidian Cliff flow.

Friedman, I.; Pierce, K.L.; Obradovich, J.D.; Long, W.D.

1973-01-01

263

Late Pleistocene glaciation of the Mt Giluwe volcano, Papua New Guinea  

USGS Publications Warehouse

The Mt Giluwe shield volcano was the largest area glaciated in Papua New Guinea during the Pleistocene. Despite minimal cooling of the sea surface during the last glacial maximum, glaciers reached elevations as low as 3200 m. To investigate changes in the extent of ice through time we have re-mapped evidence for glaciation on the southwest flank of Mt Giluwe. We find that an ice cap has formed on the flanks of the mountain on at least three, and probably four, separate occasions. To constrain the ages of these glaciations we present 39 new cosmogenic 36Cl exposure ages complemented by new radiocarbon dates. Direct dating of the moraines identifies that the maximum extent of glaciation on the mountain was not during the last glacial maximum as previously thought. In conjunction with existing potassium/argon and radiocarbon dating, we recognise four distinct glacial periods between 293-306 ka (Gogon Glaciation), 136-158 ka (Mengane Glaciation), centred at 62 ka (Komia Glaciation) and from >20.3-11.5 ka (Tongo Glaciation). The temperature difference relative to the present during the Tongo Glaciation is likely to be of the order of at least 5 ??C which is a minimum difference for the previous glaciations. During the Tongo Glaciation, ice was briefly at its maximum for less than 1000 years, but stayed near maximum levels for nearly 4000 years, until about 15.4 ka. Over the next 4000 years there was more rapid retreat with ice free conditions by the early Holocene. ?? 2011 Elsevier Ltd.

Barrows, T.T.; Hope, G.S.; Prentice, M.L.; Fifield, L.K.; Tims, S.G.

2011-01-01

264

Young glacially-induced tectonic activity of the Osning Thrust in Central Europe  

NASA Astrophysics Data System (ADS)

A series of complex metre-scale faults and related fold structures are developed within the Upper Pleistocene alluvial-aeolian complex of the Upper Senne in northern Germany. They are exposed in a pit 1 km away from the Osning Thrust. Growth strata indicate a two-fold evolution of the structures. The faults began as normal faults and were later transformed into reverse faults, which resulted in the formation of small-scale inversion structures with a typical harpoon shape (Brandes et al., in review). OSL ages imply that the sedimentary succession was deposited during the Late Pleniglacial to Late Glacial between 29.3 ± 3.2 ka and 13.1 ± 1.5 ka (Roskosch et al., accept.). We postulate that these structures were caused by activity on the Osning Thrust, during the generation of the forebulge of the Late Pleistocene ice sheet. This led to normal faulting as a consequence of extension in the forebulge area. The OSL ages for the normal fault-related growth strata are in a range of 16-13 ka. Reverse movements occurred later during deglaciation, due to the N-S directed compressional stress field in N Germany. Numerical simulations of the deglaciation seismicity point to seismic events with a thrust mechanism in the study area between 15.5-12.3 ka, although normal faulting is also possible in this time period. In addition various soft-sediment deformation structures occur in the sand pits, including sand blows, clastic dykes and sills, dish-, flame-, and ball and pillow structures. The main driving mechanism for these structures were seismic shock waves. This implies that movement on the Osning Thrust caused earthquakes of a significant magnitude. The soft-sediment deformation varies along strike of the Osning Thrust. In the NW the above-mentioned soft-sediment structures were generated, whereas in a pit 5.5 km to the SE only minor diffuse flower- to antler-like dewatering structures occur. This might indicate that the epicentre of the Late Glacial seismic activity was closer to the NW (Brandes & Winsemann, in review). In the autumn of 1612, an earthquake took place in this area. It is very likely that this event is related to background seismicity on the fault, although the influence of the ongoing glacial rebound in Fennoscandia is also possible. The repeated occurrence of seismicity in the Late Pleniglacial/Late Glacial and in the 17th century indicates ongoing crustal movements along the Osning Thrust and sheds new light on the seismic activity of northern Germany.

Brandes, C.; Winsemann, J.; Roskosch, J.; Meinsen, J.; Tanner, D.; Frechen, M.; Steffen, H.; Wu, P.

2012-04-01

265

Age of Pre-late-Wisconsin Glacial-Estuarine Sedimentation, Bristol Bay, Alaska  

NASA Astrophysics Data System (ADS)

Pleistocene glacial-estuarine sediment deposited in an intertidal environment of northeastern Bristol Bay, southwestern Alaska, was dated using a variety of approaches, including infrared stimulated and thermoluminescence (IRSL and TL) techniques. Analysis of modern and 14C-dated Holocene tide-flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation, thereby lending confidence to ages obtained from similar Pleistocene deposits by luminescence techniques. IRSL seems to be especially well suited for dating, with resolution on time scales of <10,000 yr. The ages of tide-flat mud of the Nushagak Formation, derived from the Ahklun Mountains to the northwest of Bristol Bay, and of Halfmoon Bay drift, derived from the Alaska Peninsula to the southeast, suggest contemporaneous glacial-estuarine deposition related to independent glacial source areas about 75,000-80,000 yr ago. This age is consistent with other geochronological data that indicate a pre-late-Wisconsin and post-substage-5e age, including nonfinite 14C ages, a lack of interglacial indicators, and Old Crow tephra (˜140,000 yr) atop the drift, normal paleomagnetic inclinations, and amino acid (isoleucine) epimerization ratios (aIle/Ile). AIle/Ile ratios in Portlandia arctica(0.052 ± 0.003) from a marine-lag horizon at South Naknek beach, which separates Halfmoon Bay drift above from older glacial-estuarine drift below, are only slightly higher than in Mya truncata(0.041 ± 0.007) from last-interglacial Pelukian deposits at Nome. As laboratory heating experiments show that the two genera epimerize at similar rates, these data imply correlation of the marine lag at South Naknek beach with Pelukian deposits. Hence, glaciers on the Alaska Peninsula experienced major pre-late-Wisconsin advances both before and after the last interglaciation. Shells reworked into Halfmoon Bay drift yield aIle/Ile ratios of 0.028 ± 0.005 for Portlandiaat Second Point and 0.027 ± 0.001 for Hiatella arcticaat Etolin Point. Together with assumptions about the postdepositional temperature history, these ratios indicate that the shells are at least 55,000 yr, and probably closer to ˜90,000 yr, although the uncertainty in this age estimate is broad. The amino acid and luminescence data converge on an age between about 75,000, and 90,000 yr, late during oxygen-isotope stage 5, for a major ice advance far beyond late-Wisconsin limits.

Kaufman, Darrell S.; Forman, Steven L.; Lea, Peter D.; Wobus, Cameron W.

1996-01-01

266

Pleistocene calcrete deposits from southern Spain as indicators of climatic conditions and tectonic activity  

NASA Astrophysics Data System (ADS)

Quaternary calcrete horizons are common weathering products in arid and semi-arid regions of southern Spain. We have analysed a calcrete profile developed within poorly sorted gravels of an alluvial fan. These deposits were sourced from the Carrascoy Range, a fault generated mountain front located in the Internal Zones of the Betic Cordillera (South Spain). During the Pleistocene the climate in southern Spain was dry, either in the form of semi-arid/arid conditions or as seasonal moisture deficits. Alluvial channel incision trends appeared to be disrupted by episodes of alluvial aggradation produced during cold and dry glacial periods. At the top of the aggradational phases, pedogenic processes operated profusely, and, as a result, several calcretes (stage V mature calcrete profiles) were formed. We have analysed one of these calcrete profiles that appears subvertical within the forelimb of a regional fold in relation to the Carrascoy Fault activity. The calcrete consist of a densely cemented hardpan horizon (20 to 40 cm thick) overlain by a thin, 2-cm thick laminar crust. Below the hardpan horizon, carbonate concentrations gradually decrease to clast-coating textures. Calcretes form progressively and a wide range of carbonate phases occur within a single horizon, being the laminar crust the final stage of evolution within a mature pedogenic calcrete deposit, and, therefore, the carbonate within it postdates all the cement phases within the profile. The location of the latest cement phase of the calcrete deposit has been estimated by microscopic observations (to establish their suitability for dating) together with a detailed sedimentological analysis of the calcrete profile in the field. The laminar crust consists of less than 1 mm thick laminae characterized by the alternation of layers of micrite and layers of micrite with ooids, detrital grains and clays indicating environmental conditions in which sedimentation rates were low and episodic. By using radiometric 232Th/238U dating methods we obtain an age of formation of the laminar crust of ~209 Ka (upper part of the Middle Pleistocene). This age corresponds to the warm stage 7c within the glacial Riss period. As pointed out before, the studied calcrete appears subvertical as a result of the activity of the Carrascoy Fault, and, therefore, the fault was active only after the calcrete was formed. Our study permits, as well, to reliably asses the timing of changes in alluvial processes, to characterized this part of the stratigraphic succession as corresponding to an arid to semi-arid environment, and to conclude that this particular calcrete was developed during a relative European warm period within a glacial stage.

Herrero, Maria J.; Insua-Arevalo, Juan M.; Garcia-Mayordomo, Julian; Martin-Banda, Raquel

2014-05-01

267

Simulated variations of eolian dust from inner Asian deserts at the mid-Pliocene, last glacial maximum, and present day: contributions from the regional tectonic uplift and global climate change  

Microsoft Academic Search

Northern Tibetan Plateau uplift and global climate change are regarded as two important factors responsible for a remarkable\\u000a increase in dust concentration originating from inner Asian deserts during the Pliocene–Pleistocene period. Dust cycles during\\u000a the mid-Pliocene, last glacial maximum (LGM), and present day are simulated with a global climate model, based on reconstructed\\u000a dust source scenarios, to evaluate the relative

Zhengguo Shi; Xiaodong Liu; Zhisheng An; Bingqi Yi; Ping Yang; Natalie Mahowald

268

The Idea of Marine Exogenic Processes in Glacial and Contemporary Periods  

NASA Astrophysics Data System (ADS)

Ideas of exogenic processes on continental margin and in the open ocean of polar and moderate latitudes are based on the leading role of quaternary glaciation. Vast primary bottom relief and quaternary sediments' data, accumulated by the Russian marine research institutes, provided a possibility to have a new view on geomorphology formation of the North Atlantic, Norwegian - Greenland basins, West Arctic shelves and inland seas [Matishov, 1980, 1984; Matishov and Pavlova, 1990]. Analysis of bottom morphosculpture, including cartographic, geomorphologic, morpholithologic, seismoacoustic, and other methods, grounds our researches. As a result, previously held views on the forms' sculpturing and types have been reconsidered, as well as new theoretic principles of exogenic morphogenesis and vast continental glacial covers, spread onto the shelves and conditioning oceanic periglacial in deepwater parts of the ocean, have been developed. Glaciers of continental type repeatedly covered the continental shelves of Europe and North America in the period of quaternary glaciations [Markov et al., 1965; Matishov, 1980, 1986]. Reconstructing the genetic picture of bottom pre-glacier landscapes, large thawing waters' runoff valleys, sandr plains have been indicated, thus letting propose the idea of «periglacial shelves». There are no structures of analogous dimensions on land. Glacial morphogenesis, in many aspects, was determined by pre-quaternary structure-geomorphologic plan. Various glacial troughs, moraine ranges, water-glacier formations, now located at the depths from 50-200 to 400 m, are mapped on the glacial shelves in details [Matishov, 1984, 1987]. Capacities, substance composition, texture of moraine, fluvioglacial and glacial-marine sediments, composing the forms of glacial morphosculpture, have been ascertained. Most discussable is the problem of the Barents-Kara Sea shelf glaciation. Complex, but rather orderly Barents Sea shelf glacier morphosculpture, probably, was formed in the process of active spread of periphery parts of Scandinavian, Novaya Zemlya, Spitzbergen glacier covers from mainland to shelf. The fact is proved by detailed bathymetric maps, bottom relief regularities, lithology of subsurface moraines. Especially convincing are the newest radiocarbon dating of ancient coastlines of the Franz Josef Land, Novaya Zemlya, Kola Peninsula [Forman et al., 2004]. Cognition of marine and terrestrial ecosystems' evolution in contemporary and former periglacial zones requires quaternary geology and biology basic researches, reconstruction of Pleistocene and Holocene paleogeographic and paleoecological situations. Reconstruction of paleoclimate and paleobiogeocenoses (for instance, ancient soils) will let forecast dynamics of contemporary marine and terrestrial ecosystems in periglacial regions.

Matishov, G. G.

2009-04-01

269

Palaeoenvironmental and cultural dynamics of the coast of Málaga (Andalusia, Spain) during the Upper Pleistocene and early Holocene  

NASA Astrophysics Data System (ADS)

The impact of late Upper Pleistocene climate change in the western Mediterranean region has been mainly documented through marine records. Archaeological and geomorphological continental records now available for the coast of Málaga complement these records for the second part of the last major glacial episode and the early stages of the Holocene. This paper provides an overview of the archaeological, chronological and palaeoenvironmental data from the end of the Middle Palaeolithic period to the Epipalaeolithic. Sequences from the two major sites, Nerja and Bajondillo, indicate a mosaic-type response of ecosystems to the rapidly shifting conditions of the Last Glacial episode. Terrestrial mammals, for example, show no major variations from present-day communities. Plant remains in contrast, demonstrates the existence of localised refuge areas for species that would not otherwise have survived in the more widely prevailing climatic conditions of the time, whereas remains of fish and, secondarily, birds demonstrate the existence of communities without any present-day analogues combining Mediterranean and Boreal (i.e., northern Atlantic) taxa. From an archaeological standpoint, the major cultural shift is the onset of marine fishing, beginning in the Solutrean. This coincided with the end of the Last Glacial Maximum (LGM) episode. The faunal record also testifies to the rising importance of marine resources more generally. Although the data have not been used systematically to test the validity of the Broad Spectrum Revolution (BSR) hypothesis, the hints for it in the area seem compelling from the start of the Solutrean onwards.

Cortés-Sánchez, Miguel; Morales-Muñiz, Arturo; Simón-Vallejo, María D.; Bergadà-Zapata, M. Mercè; Delgado-Huertas, Antonio; López-García, Pilar; López-Sáez, José A.; Lozano-Francisco, M. Carmen; Riquelme-Cantal, José A.; Roselló-Izquierdo, Eufrasia; Sánchez-Marco, Antonio; Vera-Peláez, José L.

2008-11-01

270

A multilocus evaluation of ermine (Mustela erminea) across the Holarctic, testing hypotheses of Pleistocene diversification in response to climate change  

USGS Publications Warehouse

Aim: We examined data for ermine (Mustela erminea) to test two sets of diversification hypotheses concerning the number and location of late Pleistocene refugia, the timing and mode of diversification, and the evolutionary influence of insularization. Location: Temperate and sub-Arctic Northern Hemisphere. Methods: We used up to two mitochondrial and four nuclear loci from 237 specimens for statistical phylogeographical and demographic analyses. Coalescent species-tree estimation used a Bayesian approach for clade divergence based on external mutation rate calibrations. Approximate Bayesian methods were used to assess population size, timing of divergence and gene flow. Results: Limited structure coupled with evidence of population growth across broad regions, including previously ice-covered areas, indicated expansion from multiple centres of differentiation, but high endemism along the North Pacific coast (NPC). A bifurcating model of diversification with recent growth spanning three glacial cycles best explained the empirical data. Main conclusions: A newly identified clade in North America indicated a fourth refugial area for ermine. The shallow coalescence of all extant ermine reflects a recent history of diversification overlying a deeper fossil record. Post-glacial colonization has led to potential contact zones for multiple lineages in north-western North America. A model of diversification of ermine accompanied by recent gene flow was marginally less well supported than a model of divergence of major clades in response to the most recent glacial cycles.

Dawson, Natalie G.; Hope, Andrew G.; Talbot, Sandra L.; Cook, Joseph A.

2013-01-01

271

Glacial erosion and expected permafrost thickness of Fennoscandia and adjacent regions  

NASA Astrophysics Data System (ADS)

Linked geological, geomorphological and tectonic features of Fennoscandia with adjacent regions of East-European plain and Barents-Kara shelf indirectly influenced the history of glacial grows and decays. The first-order bedrock landscape elements (often created or exhumed during pre-glacial Cenozoic stages) were the major factors that could partly control centers of ice nucleation and basal velocities, serve natural barriers shaping ice sheet margin during some time intervals, etc. On the hand, many landforms were powerfully modified by glacial and periglacial processes, in particular by strong glacial erosion with lithological and structural control. Quantitative estimation of Plio-Pleistocene erosion and deposition was performed combining regional geological-geomorphological analysis (GA) and modeling with rate-based time-scale reconstructions (RR), and mass-balance control. Of special GA importance was to compare and extract changes of preserved elements of pre-glacial Neogene topography from areas that underwent different duration of glacial activity, in comparison with bordering non-glaciated ones. More distinct radial glacial erosion pattern and larger basal ice velocities seem likely at the beginning of the early ice-age stage, with partial widening of pre-glacial drainage elements. Few wide lowlands with meandering rivers in permafrost condition could provoke early stage onset of topographic ice-streams. Over time, further complication of the pattern from radial to "spider web" is expected due to developing of topographic ice-streams. Worth to mention is progressive exhumation of resistant formations, additional complications of the pattern by fluvioglacial activity and glacial sedimentation, "pendulum" principle, with increasing amount of glacial and interglacial sedimentation in eroded material. Approximated variable permafrost distribution seems to be additional weighty aspect, changing erosion rates at some time intervals. To estimate mean annual temperatures and solve the Stefan's problem several known climate reconstructions were involved, but with account of possible ice-sheet related temperature depressions. In time-slices they were reinterpolated in agreement with changing the outlines of the ice sheets. Models of the basal sub-ice temperature based on relevant models for Greenland (Huybrechts P., 1996) and Antarctic ice sheets (Pattyn F., 2010) were accounted to estimate possible zonation and variability of warming effects of ice sheets. Expected lower permafrost thickness (first hundreds meters) and extent in the Barents region could be caused by unfavorable conditions and relatively high heat flow. Lowlands bearing major topographic ice streams were likely represented by taliks not affected by continuous permafrost or - depending on scenarios and parameters - were shortly affected by reduced permafrost with thick active layer. The same is expected for the Novaya Zemlya trench of the Kara Sea, while bordering shallow shelf parts were possibly characterized by thick permafrost, especially growing in time of eustatic ocean lowering. Permafrost in Fennoscandia and adjacent regions could be strongly variable but shortly relatively thick (hundreds meters) over large areas, including higher landscape on sedimentary cover west of Baltic - White Sea lowland. Linear taliks of discontinous permafrost zone on terrigenous sediments could contribute tunnel valley formation.

Amantov, Aleksey

2013-04-01

272

Post-glacial recolonization of the Great Lakes region by the common gartersnake (Thamnophis sirtalis) inferred from mtDNA sequences.  

PubMed

Pleistocene events played an important role in the differentiation of North American vertebrate populations. Michigan, in particular, and the Great Lakes region, in general, were greatly influenced by the last glaciation. While several hypotheses regarding the recolonization of this region have been advanced, none have been strongly supported. We generated 148 complete ND2 mitochondrial DNA (mtDNA) sequences from common gartersnake (Thamnophis sirtalis) populations throughout the Great Lakes region to evaluate phylogeographic patterns and population structure and to determine whether the distribution of haplotypic variants is related to the post-Pleistocene retreat of the Wisconsinan glacier. The common gartersnake was utilized, as it is believed to have been one of the primary vertebrate invaders of the Great Lakes region following the most recent period of glacial retreat and because it has been a model species for a variety of evolutionary, ecological, behavioral, and physiological studies. Several genetically distinct evolutionary lineages were supported by both genealogical and molecular population genetic analyses, although to different degrees. The geographic distribution of the majority of these lineages is interpreted as reflecting post-glacial recolonization dynamics during the late Pleistocene. These findings generally support previous hypotheses of range expansion in this region. PMID:17174111

Placyk, John S; Burghardt, Gordon M; Small, Randall L; King, Richard B; Casper, Gary S; Robinson, Jace W

2007-05-01

273

Pre-Late-Wisconsin glacial history, coastal Ahklun Mountains, southwestern Alaska - new amino acid, thermoluminescence, and 40Ar/ 39Ar results  

NASA Astrophysics Data System (ADS)

New stratigraphic and geochronologic data from the Togiak Bay area of southwestern Alaska indicate that glaciers advanced from the southern Ahklun Mountains at least three and as many as six times prior to the late Wisconsin. The oldest glaciations are represented by glacial-marine sediment in coastal exposures on Hagemeister Island. The extent of amino acid (isoleucine) epimerization in fossil molluscs indicates that at least one, and possibly four, older middle Pleistocene glacial intervals are represented, with age estimates spanning ˜500-280 ka and averaging ˜400±100 ka. The youngest glacial-marine drift on Hagemeister Island may correlate with the eruption of the Togiak tuya. A new 40Ar/ 39Ar age on basalt that overlies pillow lava indicates that the volcano erupted through glacial ice at least 300 m thick 263±22 ka. The youngest drift in the region overlies the Old Crow tephra (140±10 ka) and a 70±10 ka basaltic lava flow dated by thermoluminescence analysis of underlying baked sediment. The drift delimits flat piedmont lobes that spread out onto the continental shelf and terminated >100 km from their source areas during the early Wisconsin (sensu lato). The glacial-geologic evidence suggests that major expansions of glaciers were out of phase with global ice volume.

Kaufman, Darrell S.; Manley, William F.; Forman, Steve L.; Layer, Paul W.

2001-01-01

274

Timing and depositional environments of a Middle Pleistocene glaciation of northeast England: New evidence from Warren House Gill, County Durham  

NASA Astrophysics Data System (ADS)

At various times during the Quaternary, north-eastern England was a zone of confluence between dynamic ice lobes sourced from the Pennines, northern Scotland, the Cheviots, and Scandinavia. The region thus has some of the most complex exposures of Middle to Late Pleistocene sediments in Britain, with both interglacial and glacial sediments deposited in terrestrial and marine settings. We investigated sedimentary sequences exposed on the coastline of County Durham at Warren House Gill, and present a new model of British and Fennoscandian Ice Sheet interaction in the North Sea Basin during the Middle Pleistocene. The stratigraphy at Warren House Gill consists of a lower diamicton and upper estuarine sediments, both part of the Warren House Formation. They are separated from the overlying Weichselian Blackhall and Horden tills by a substantial unconformity. The lower diamicton of the Warren House Formation is re-interpreted here as an MIS 8 to 12 glaciomarine deposit containing ice-rafted lithics from north-eastern Scotland and the northeast North Sea, and is renamed the 'Ash Gill Member'. It is dated by lithological comparison to the Easington Raised Beach, Middle Pleistocene Amino Acid Racemisation values, and indirectly by optically stimulated luminescence. The overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity. They are named the 'Whitesides Member', and form the uppermost member of the Warren House Formation. During glaciation, ice-rafted material was deposited in a marine embayment. There is no evidence of a grounded, onshore Scandinavian ice sheet in County Durham during MIS 6, which has long been held as the accepted stratigraphy. This has major implications for the currently accepted British Quaternary Stratigraphy. Combined with recent work on the Middle Pleistocene North Sea Drift from Norfolk, which is now suggested to have been deposited by a Scottish ice sheet, the presence of a Scandinavian ice sheet in eastern England at any time during the Quaternary is becoming increasingly doubtful.

Davies, B. J.; Roberts, D. H.; Bridgland, D. R.; Ó Cofaigh, C.; Riding, J. B.; Demarchi, B.; Penkman, K. E. H.; Pawley, S. M.

2012-06-01

275

Late Pleistocene stalagmite growth in Wolkberg Cave, South Africa  

NASA Astrophysics Data System (ADS)

Little is known about the sequence of climate and environmental change in southern Africa during the last glacial period, in spite of the intimations from records, such as Antarctic ice cores and archaeological sites, that very marked changes took place which would have had profound effects on vegetation and animal distributions across the sub-continent. High-resolution, (semi-) continuous climate and environmental records can be extracted from suitable cave speleothems. Speleothems are reasonably abundant in southern Africa, but their occurrence is patchy in time and space and the records can be difficult to interpret. Here we report our assessment of the stalagmite W5 from Wolkberg Cave in the northeastern part of South Africa, as an archive for glacial-period climatic and environmental shifts. The cave is located at 1450 m asl, in the dolomitic limestones of the Transvaal System in an area currently dominated by C 4 grass vegetation. Nine U/Th dates show growth from 58 to 46 ka, and a second brief phase ca. 40 ka, indicating that the available moisture was sufficient to allow speleothems to form. The ?18O and ?13C values along the growth axis show variability in the order of 2‰ for the former, while variability in the latter is characterized by a shift from values near - 2‰ in the older section to + 2‰ or more in the younger part. These high ?13C values are probably the combined result of CO 2 degassing of the percolating soil water prior to the carbonate precipitation in the cave chamber, the increasing dominance of C 4 over C 3 vegetation, and the high percentage of aragonite towards the stalagmite's top. The retrieved data point towards increasingly drier and colder conditions during the growth period of the stalagmite. Furthermore, the high-frequency variations of ?18O values indicate the presence of short term climate oscillations that are probably linked to shifts of the Intertropical Convergence Zone.

Holzkämper, Steffen; Holmgren, Karin; Lee-Thorp, Julia; Talma, Siep; Mangini, Augusto; Partridge, Tim

2009-05-01

276

3D seismic interpretations of the Pliocene-Pleistocene stratigraphy and tunnel valleys of the North Sea Plateau-Fladen area, northern North Sea  

NASA Astrophysics Data System (ADS)

The increasing coverage of 3D seismic data across the North Sea has allowed the detailed investigation of depositional environments extending beyond the most recent glacial advance into the basin. There are several generations of channels and incisions interpreted as tunnel valleys of varying size at varying stratigraphic depths throughout the Pliocene-Pleistocene units in the North Sea. Many of these features appear to have been reactivated on more than one occasion. The acoustic character of sediments infilling these features is also variable even within the same channel and their significance in relation to palaeo-ice sheet dynamics is still debated. We suggest that some of the observed incisions/valleys, particularly those formed around the Pliocene-Pleistocene boundary, may in fact be fluvial features rather than subglacially formed (based on size and flow path). Many of the smaller, straighter more recent generations of channels probably formed subglacially. If some of the older channels are fluvial, this has significant implications for the marine limit during this late Pliocene early Pleistocene period in the northern North Sea. Palaeo-iceberg scours are also found at certain stratigraphic horizons and these can be compared to those horizons with valleys/channels. Interpretations of the acoustic units/features will also be based on information from well and shallow core data allowing their depositional history and chronology to be investigated. Several physical properties have been measured on a number of cores from the investigated area. To be able to refine the chronology of the Pleistocene sediments for this part of the North Sea we plan to carry out new analyses and dating (strontium, radiocarbon and amino acid) on shallow cores/well material from the region. This will allow us to better constrain the times at which channels were being formed in this area and relate this to known glacial cycles in the North Sea.

Reinardy, Benedict; Hjelstuen, Berit; Petter Sejrup, Hans; Stoddart, Daniel

2014-05-01

277

Genetic signals of demographic expansion in Downy Woodpecker (Picoides pubescens) after the last North American glacial maximum.  

PubMed

The glacial cycles of the Pleistocene have been recognized as important, large-scale historical processes that strongly influenced the demographic patterns and genetic structure of many species. Here we present evidence of a postglacial expansion for the Downy Woodpecker (Picoides pubescens), a common member of the forest bird communities in North America with a continental distribution. DNA sequences from the mitochondrial tRNA-Lys, and ATPase 6 and 8 genes, and microsatellite data from seven variable loci were combined with a species distribution model (SDM) to infer possible historical scenarios for this species after the last glacial maximum. Analyses of Downy Woodpeckers from 23 geographic areas suggested little differentiation, shallow genealogical relationships, and limited population structure across the species' range. Microsatellites, which have higher resolution and are able to detect recent differences, revealed two geographic groups where populations along the eastern edge of the Rocky Mountains (Montana, Utah, Colorado, and southern Alberta) were genetically isolated from the rest of the sampled populations. Mitochondrial DNA, an important marker to detect historical patterns, recovered only one group. However, populations in Idaho and southeast BC contained high haplotype diversity and, in general were characterized by the absence of the most common mtDNA haplotype. The SDM suggested several areas in the southern US as containing suitable Downy Woodpecker habitat during the LGM. The lack of considerable geographic structure and the starburst haplotype network, combined with several population genetic tests, suggest a scenario of demographic expansion during the last part of Pleistocene and early Holocene. PMID:22792306

Pulgarín-R, Paulo C; Burg, Theresa M

2012-01-01

278

Late pleistocene passerine birds from Sonora, Mexico  

Microsoft Academic Search

Songbirds (Passeriformes) have a very limited fossil record in spite of making up more than one-half of the world's 10,000 living species of birds. From the late Pleistocene fossil site of Térapa in east-central Sonora, Mexico, the identifiable fossils of songbirds consist exclusively of species of Icteridae. The seven extant species (Red-winged Blackbird Agelaius phoeniceus, Yellow-headed Blackbird Xanthocephalus xanthocephalus, Brewer's

Jessica A. Oswald; David W. Steadman

2011-01-01

279

Pleistocene vertebrates of the Yukon Territory  

NASA Astrophysics Data System (ADS)

Unglaciated parts of the Yukon constitute one of the most important areas in North America for yielding Pleistocene vertebrate fossils. Nearly 30 vertebrate faunal localities are reviewed spanning a period of about 1.6 Ma (million years ago) to the close of the Pleistocene some 10 000 BP (radiocarbon years before present, taken as 1950). The vertebrate fossils represent at least 8 species of fishes, 1 amphibian, 41 species of birds and 83 species of mammals. Dominant among the large mammals are: steppe bison ( Bison priscus), horse ( Equus sp.), woolly mammoth ( Mammuthus primigenius), and caribou ( Rangifer tarandus) - signature species of the Mammoth Steppe fauna ( Fig. 1), which was widespread from the British Isles, through northern Europe, and Siberia to Alaska, Yukon and adjacent Northwest Territories. The Yukon faunas extend from Herschel Island in the north to Revenue Creek in the south and from the Alaskan border in the west to Ketza River in the east. The Yukon holds evidence of the earliest-known people in North America. Artifacts made from bison, mammoth and caribou bones from Bluefish Caves, Old Crow Basin and Dawson City areas show that people had a substantial knowledge of making and using bone tools at least by 25 000 BP, and possibly as early as 40 000 BP. A suggested chronological sequence of Yukon Pleistocene vertebrates ( Table 1) facilitates comparison of selected faunas and indicates the known duration of various taxa.

Harington, C. R.

2011-08-01

280

Pleistocene glaciations of Central Asia: results from 10Be surface exposure ages of erratic boulders from the Pamir (Tajikistan), and the Alay–Turkestan range (Kyrgyzstan)  

Microsoft Academic Search

We have determined the timing of glaciations in the Pamir (Tajikistan) and the Alay–Turkestan Range (Kyrgyzstan) using 10Be surface exposure dating. Glacial advances in the area have occurred >93–136, ?60–80, (40–55), ?27–25, ?22–20, ?19–17, ?16–15, ?15–13, and 11–9calka BP. All Late Pleistocene glaciers in the Pamir, and the Alay–Turkestan Ranges have been valley glaciers except for the most extended glaciers

U. Abramowski; A. Bergau; D. Seebach; R. Zech; B. Glaser; P. Sosin; P. W. Kubik; W. Zech

2006-01-01

281

Modeling of supraglacial debris and glacial stagnation  

NASA Astrophysics Data System (ADS)

We model the role of supraglacial debris in stagnation of terminal regions of glaciers, as part of an ongoing effort to use the character of glacial deposits to learn the size and rate of the warming that caused retreat. We conduct numerical modeling experiments, using a glacier model, coupled with a dynamic layer of sediment on the ice surface. The supraglacial debris is assumed to reduce glacier melting exponentially proportional to the debris thickness. Our experiments indicate that supraglacial debris is a key factor in the onset of glacial stagnation events. We model a variety of sources for supraglacial debris, including rock avalanche (from above the ice), melt out of englacial material, and spreading of lateral moraines on to the ice. Glacial stagnation occurs regardless of the source of debris. We conclude that the presence of supraglacial debris is very important in the onset of glacial stagnation events.

Vacco, D.; Alley, R.; Pollard, D.

2012-04-01

282

Combined use of relative and numerical dating techniques for detecting signals of Alpine landscape evolution during the late Pleistocene and early Holocene in Val di Rabbi (Trentino, northern Italy)  

NASA Astrophysics Data System (ADS)

A combined use of relative and absolute dating techniques was applied on nine soil profiles in order to reconstruct late Pleistocene and early Holocene landscape evolution in an Alpine environment located in Val di Rabbi (Trentino, northern Italy). The degree of podzolisation, clay mineral evolution and element mass balances of each site were investigated. Furthermore, the stable fraction of the soil organic matter (SOM) was extracted from selected horizons with 10% H2O2 and 14C-dated. The ages of the organic residues were compared with the ages of charcoal fragments found in one of the studied soils and with the ages of rock boulders obtained by the surface exposure dating (SED) method with cosmogenic 10Be. The combination of 14C dating of SOM and SED indicated that deglaciation processes in Val di Rabbi were very much advanced around 14000 cal BP and that glacier oscillations have affected the highest part of the region until about 9000 cal BP. The development of clay mineral reflects weathering intensity. We found a close link between secondary clay minerals like smectite and vermiculite and soil age as obtained by H2O2. The degree of podzolisation is time dependent and was used as an evidence of surface stability. The amount of Fe and Al forms that migrated and accumulated in the illuvial horizon correlated well with the time of soil development. Element mass balance calculations strongly correlated with the ages derived from 14C measurements. Old soils have lost a major part of base cations (up to 75%), Fe and Al. Chemical and mineralogical analyses were in good agreement with numerical dating techniques, showing the dynamics of an Alpine landscape within a relatively small area and enabling a relative and absolute differentiation of landscape elements. The combination of relative and numerical dating techniques is a promising tool to understand landscape evolution and to provide absolute chronologies of the Late glacial in high-elevation Alpine areas with siliceous parent material.

Favilli, F.; Egli, M.; Brandova, D.; Ivy-Ochs, S.; Kubik, P.; Cherubini, P.; Mirabella, A.; Sartori, G.; Giaccai, D.; Haeberli, W.

2009-04-01

283

What Controls the Pacing of 100-ky Glacial Cycles?  

NASA Astrophysics Data System (ADS)

Climate variations over the last ~700,000 years are characterized by orbital periodicities of 100, 41 and 23 ky. While 23- and 41-ky components are understood as linear climatic responses to forcing by precession (modulated by eccentricity) and obliquity, respectively, the 100-ky cycle cannot be explained as a linear response to eccentricity. Rather, it has been suggested that the 100-ky cycle is caused by skipping of higher frequency beats which results in the bundling of either 4 or 5 precession cycles (Raymo, Paleoceanography, 1997), or 2 or 3 obliquity cycles (Huybers and Wunsch, Nature, 2005), each grouping resulting in an average 100 ky periodicity. However, verification of these competing hypotheses has not been possible because of the lack of accurately dated climate proxies. Here, using statistical tests of newly established chronologies of Antarctic climate (Kawamura et al., AGU 2006 fall meeting) and sea level high stands (Thompson, in preparation), we show that precession pacing is statistically more significant than obliquity pacing for the last five glacial terminations. We used the timings of Antarctic warmings at terminations from the Dome Fuji ice core for termination I to III, and from the Vostok core for termination IV. The timing of termination V was estimated by shifting the Dome C (EDC2) timescale to match the timing of peak MIS 11.3 with the Vostok record. The time of onset for the sea level high stands of the last four interglacial periods were estimated by correcting radiometric fossil coral ages with open-system age equations (Thompson et al., 2003, EPSL). Our results show that the null hypothesis for precession pacing can be rejected at the 3% significance level for the last five terminations from ice cores and for four terminations from sea level high stands, whereas the null hypothesis for obliquity pacing can be rejected only at >10% significance level. The statistical power of test for obliquity is high (>95% at the 10% significance level) owing to the high accuracy of the chronologies. Our results are consistent with the hypothesis that high northern latitude summer insolation is the primary pacemaker of the late Pleistocene glacial cycles.

Raymo, M. E.; Kawamura, K.; Lisiecki, L.; Thompson, W. G.; Severinghaus, J. P.

2006-12-01

284

The impact of Pleistocene climate change on an ancient arctic–alpine plant: multiple lineages of disparate history in Oxyria digyna  

PubMed Central

The ranges of arctic–alpine species have shifted extensively with Pleistocene climate changes and glaciations. Using sequence data from the trnH-psbA and trnT-trnL chloroplast DNA spacer regions, we investigated the phylogeography of the widespread, ancient (>3 million years) arctic–alpine plant Oxyria digyna (Polygonaceae). We identified 45 haplotypes and six highly divergent major lineages; estimated ages of these lineages (time to most recent common ancestor, TMRCA) ranged from ?0.5 to 2.5 million years. One lineage is widespread in the arctic, a second is restricted to the southern Rocky Mountains of the western United States, and a third was found only in the Himalayan and Altai regions of Asia. Three other lineages are widespread in western North America, where they overlap extensively. The high genetic diversity and the presence of divergent major cpDNA lineages within Oxyria digyna reflect its age and suggest that it was widespread during much of its history. The distributions of individual lineages indicate repeated spread of Oxyria digyna through North America over multiple glacial cycles. During the Last Glacial Maximum it persisted in multiple refugia in western North America, including Beringia, south of the continental ice, and within the northern limits of the Cordilleran ice sheet. Our data contribute to a growing body of evidence that arctic–alpine species have migrated from different source regions over multiple glacial cycles and that cryptic refugia contributed to persistence through the Last Glacial Maximum. PMID:22822441

Allen, Geraldine A; Marr, Kendrick L; McCormick, Laurie J; Hebda, Richard J

2012-01-01

285

The impact of Pleistocene climate change on an ancient arctic-alpine plant: multiple lineages of disparate history in Oxyria digyna.  

PubMed

The ranges of arctic-alpine species have shifted extensively with Pleistocene climate changes and glaciations. Using sequence data from the trnH-psbA and trnT-trnL chloroplast DNA spacer regions, we investigated the phylogeography of the widespread, ancient (>3 million years) arctic-alpine plant Oxyria digyna (Polygonaceae). We identified 45 haplotypes and six highly divergent major lineages; estimated ages of these lineages (time to most recent common ancestor, T(MRCA)) ranged from ?0.5 to 2.5 million years. One lineage is widespread in the arctic, a second is restricted to the southern Rocky Mountains of the western United States, and a third was found only in the Himalayan and Altai regions of Asia. Three other lineages are widespread in western North America, where they overlap extensively. The high genetic diversity and the presence of divergent major cpDNA lineages within Oxyria digyna reflect its age and suggest that it was widespread during much of its history. The distributions of individual lineages indicate repeated spread of Oxyria digyna through North America over multiple glacial cycles. During the Last Glacial Maximum it persisted in multiple refugia in western North America, including Beringia, south of the continental ice, and within the northern limits of the Cordilleran ice sheet. Our data contribute to a growing body of evidence that arctic-alpine species have migrated from different source regions over multiple glacial cycles and that cryptic refugia contributed to persistence through the Last Glacial Maximum. PMID:22822441

Allen, Geraldine A; Marr, Kendrick L; McCormick, Laurie J; Hebda, Richard J

2012-03-01

286

Glacially generated overpressure on the New England continental shelf: Integration of full-waveform inversion and overpressure modeling  

NASA Astrophysics Data System (ADS)

zones of high-amplitude, discontinuous seismic reflections 100 km off the coast of Massachusetts, USA, have P wave velocities up to 190 m/s lower than those of adjacent sediments of equal depth (250 m below the sea floor). To investigate the origin of these low-velocity zones, we compare the detailed velocity structure across high-amplitude regions to adjacent, undisturbed regions through full-waveform inversion. We relate the full-waveform inversion velocities to effective stress and overpressure with a power law model. This model predicts localized overpressures up to 2.2 MPa associated with the high-amplitude reflections. To help understand the overpressure source, we model overpressure due to erosion, glacial loading, and sedimentation in one dimension. The modeling results show that ice loading from a late Pleistocene glaciation, ice loading from the Last Glacial Maximum, and rapid sedimentation contributed to the overpressure. Localized overpressure, however, is likely the result of focused fluid flow through a high-permeability layer below the region characterized by the high-amplitude reflections. These high overpressures may have also caused localized sediment deformation. Our forward models predict maximum overpressure during the Last Glacial Maximum due to loading by glaciers and rapid sedimentation, but these overpressures are dissipating in the modern, low sedimentation rate environment. This has important implications for our understanding continental shelf morphology, fluid flow, and submarine groundwater discharge off Massachusetts, as we show a mechanism related to Pleistocene ice sheets that may have created regions of anomalously high overpressure.

Siegel, Jacob; Lizarralde, Daniel; Dugan, Brandon; Person, Mark

2014-04-01

287

Glacial lakes in the Indian Himalayas --From an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes  

E-print Network

Glacial lakes in the Indian Himalayas -- From an area-wide glacial lake inventory to on-site and modeling based risk assessment of critical glacial lakes Raphael Worni a,b, , Christian Huggel a,c , Markus-8057 Zurich, Switzerland H I G H L I G H T S We present the first comprehensive glacier lake inventory

Butler, David R. - Department of Geography, Texas State University

288

Interplay between climatic and tectonic processes in the St. Elias foreland, southern Alaska: Evolution of a glaciated convergent margin since the mid-Pleistocene  

NASA Astrophysics Data System (ADS)

The offshore St. Elias fold-thrust belt records the complex interaction between collisional tectonics and glacial climate variability, providing insight for models of orogenesis and the evolution of glacial depocenters. Ongoing collision of the Yakutat (YAK) microplate with North America (NA) has driven orogenesis of the St. Elias Mountains and the advance of the offshore deformation front to the southeast. Glacial erosion and deposition have provided sediment that constructed the upper continental shelf, much of which has been reincorporated into the orogenic wedge through offshore faulting and folding. We integrate core and downhole logging data from IODP Expedition 341 (Sites U1420 and U1421) drilled on the Yakutat shelf and slope with high-resolution and regional seismic profiles to investigate the coupled structural and stratigraphic evolution of the St. Elias margin. Site U1420 lies on the Yakutat shelf within the Bering Trough, a shelf-crossing trough that is within primary depocenter for Bering Glacier sediments. The sub-seafloor architecture of the Bering Trough region is defined by a regional unconformity that marks the first glacial advance to the shelf edge. Below the unconformity, the shelf is constructed by multiple aggradational packages that are likely a series of pro-glacial outer shelf/slope fans. Two faults underlie the glacial packages and have been rendered inactive as the depositional environment has evolved, while faulting elsewhere on the shelf has initiated. Site U1421 lies on the current continental slope, within the backlimb of an active thrust that forms part of the modern YAK-NA deformation front. At each of these sites, we recovered glacigenic diamict (at depths up to ~1015 m at Site U1420), all of which is younger than 0.781 Ma. Preliminary age models for the Bering Trough region indicate that the entire outer shelf and shelf edge environment have been built since the Mid-Pleistocene Transition (MPT), and is possibly even younger. In stark contrast to previous interpretations, the shelf environment, in addition to the proximal deep-sea fan system, appears to be a primary glacial depocenter since the MPT, with an average accumulation rate >1.3 mm/yr. Additionally, initiation of active deformation away from the Bering Trough depocenter likely occurred since ~1 Ma. These observations suggest that possible tectonic reorganization due to mass redistribution by glacial processes occurs at time scales on the order of 100kyr-1Myr. It follows that the St. Elias orogenic system may be more sensitive to glacial-interglacial cycles than previously recognized.

Worthington, L. L.; Gulick, S. P.; Ridgway, K. R.; Jaeger, J. M.; Cowan, E. A.; Slagle, A. L.; Forwick, M.

2013-12-01

289

Relationship between peat bed formation and climate changes during the last glacial in the Venice area  

NASA Astrophysics Data System (ADS)

Core and seismic data from the Venice lagoon area, located in the foreland region between the northern Apennines and the southern Alps (northern Italy), allow a detailed investigation of the Late Pleistocene fully continental succession accumulated during the last glacial phase. These deposits consist of an aggrading alluvial plain, some tens of meters thick, which is locally incised by river channels, while both patchy and continuous peat layers complete the succession. In particular, a very continuous peat layer up to 1 m thick (P1), sandwiched within alluvial plain sediments, is well recognizable in the whole lagoon area in both cores and seismic lines. 14C datings of P1 reveal an age ranging between 22 and 24 cal ka B.P., confirming its lateral continuity. All these elements suggest that P1 developed after an episode of marked moisture and large scale cut-off of terrigenous sediment, leading to the establishment of generalized paludal conditions probably during the Laugerie interstadial. As at these latitudes interstadial phases were commonly typified by enhanced arboreal vegetation cover preventing significant terrigenous supply, swamp areas characterized by peat accumulation developed. The present evidence is helpful to recognize stadial-interstadial cycles during the last glacial phase, and may integrate the current knowledge to establish a correlation between cycles recorded in fully continental deposits and those recognizable in ice cores and marine successions.

Zecchin, Massimo; Caffau, Mauro; Tosi, Luigi

2011-06-01

290

Continuity of brown bear maternal lineages in northern England through the Last-glacial period  

NASA Astrophysics Data System (ADS)

Brown bears recolonised Europe rapidly after the Last Glacial Maximum (LGM), but there has been debate about whether bear populations were confined to separate glacial refugia in southern Europe, or if there was continuous gene flow among groups. To look in more detail at recolonisation routes into the British Isles after the LGM, 16 brown bear (Ursus arctos) samples from Lateglacial Yorkshire were analysed for mitochondrial DNA survival. The resulting data were compared with earlier work on Late Pleistocene and Holocene bears from Ireland (Edwards et al., 2011), as well as with both modern and ancient bears from across continental Europe. The results highlight the temporal and spatial continuity of brown bear maternal lineages through the Lateglacial period in northern England. While this region was not a refugial area in the LGM for the Irish Clade 2 brown bears, our data suggest that populations of brown bear in England did act as refugial sources for the later colonisation of Ireland, by Clade 1-i bears, during the Holocene. Our results contribute to a wider understanding of the phylogenetic relationships of brown bears through the Late Quaternary, and lend a valuable perspective on bear migration into peripheral Europe.

Edwards, Ceiridwen J.; Ho, Simon Y. W.; Barnett, Ross; Coxon, Peter; Bradley, Daniel G.; Lord, Tom C.; O'Connor, Terry

2014-07-01

291

Ancient DNA supports southern survival of Richardson's collared lemming (Dicrostonyx richardsoni) during the last glacial maximum.  

PubMed

Collared lemmings (genus Dicrostonyx) are circumpolar Arctic arvicoline rodents associated with tundra. However, during the last glacial maximum (LGM), Dicrostonyx lived along the southern ice margin of the Laurentide ice sheet in communities comprising both temperate and boreal species. To better understand these communities and the fate of these southern individuals, we compare mitochondrial cytochrome b sequence data from three LGM-age Dicrostonyx fossils from south of the Laurentide ice sheet to sequences from modern Dicrostonyx sampled from across their present-day range. We test whether the Dicrostonyx populations from LGM-age continental USA became extinct at the Pleistocene-Holocene transition ~11000 years ago or, alternatively, if they belong to an extant species whose habitat preferences can be used to infer the palaeoclimate along the glacial margin. Our results indicate that LGM-age Dicrostonyx from Iowa and South Dakota belong to Dicrostonyx richardsoni, which currently lives in a temperate tundra environment west of Hudson Bay, Canada. This suggests a palaeoclimate south of the Laurentide ice sheet that contains elements similar to the more temperate shrub tundra characteristic of extant D. richardsoni habitat, rather than the very cold, dry tundra of the Northern Arctic. While more data are required to determine whether or not the LGM southern population is ancestral to extant D. richardsoni, it seems most probable that the species survived the LGM in a southern refugium. PMID:23495672

Fulton, Tara L; Norris, Ryan W; Graham, Russell W; Semken, Holmes A; Shapiro, Beth

2013-05-01

292

Late Cenozoic oscillations of Antarctic ice sheets revealed by provenance of basement clasts and grain detrital modes in ANDRILL core AND-1B  

NASA Astrophysics Data System (ADS)

Petrological investigations of the sand fraction and of granule- to cobble-sized clasts in the Plio-Pleistocene sedimentary cycles of the AND-1B drill core at the NW edge of the Ross Ice Shelf (McMurdo Sound) highlight significant down-core modal and compositional variations. These variations provide: (i) direct information about potential source regions during both glacial maxima and minima; and (ii) evidence of an evolving provenance, documented by long-term shifts in compositional patterns that can be interpreted as reflecting variations in ice volume and ice sheet thermal regimes and changes in paleogeography related to the emergence of several volcanic centres during the deposition of the drill core over the past ca. 3.5 Ma. The most significant change in diamictite provenance (identified at 82.7 metre below the sea floor, mbsf), coincides with a change in sedimentary cycle architecture from sequences that are dominated by diamictites (Mid-Late Pleistocene, above 82.7 mbsf) to sequences characterised by cycles of diamictite (subglacial) and diatomite (open-marine) deposition (Pliocene, below 82.7 mbsf). In the Mid-Late Pleistocene glacial/interglacial cycles diamictites show high amounts of Skelton-Mulock sourced clasts, supplied from both basement and overlying Beacon and Ferrar supergroups, and they also include a variable contribution from reworking of glacial sediments that were deposited during earlier glacial activity. In the Pliocene to early Pleistocene diatomite-diamictite cycles basement clast compositions indicate the same provenance (Mulock-Skelton) but the main debris load was picked up from volcanic centres in the McMurdo Sound area. Similarly, associated glacial minima sediments (i.e., diatomite intervals) are dominated by volcanic clasts suggesting calving of glaciers from Ross Island or the Koettlitz Glacier region during interglacials. In agreement with previous glaciological reconstructions and numerical ice sheet models, the provenance of glacially transported material is firmly identified in the region between Ross Island and the Skelton-Mulock glacier area (South Victoria Land). The reconstructed ice directions and ice dynamic model are comparable to the configurations proposed for the grounded ice expansion within the McMurdo Sound during the Last Glacial Maximum, and they are also consistent with ice-flow patterns previously reconstructed for Pliocene and Pleistocene glacial settings in the region.

Talarico, F. M.; McKay, R. M.; Powell, R. D.; Sandroni, S.; Naish, T.

2012-10-01

293

Authigenic carbonate mineral formation in a latest Pleistocene palaeolake, Greece  

NASA Astrophysics Data System (ADS)

The Pagassitikos Gulf in Greece, is a semi-enclosed bay with maximum depth 102 m. According to the present-day bathymetric configuration and the sea level during the latest Pleistocene, the gulf would have been isolated from the open sea, forming a palaeolake since ~32 cal. ka B.P.. Initial visual inspection of sediment core B-4 (length, 258 cm), recovered from the deepest sector of the Pagassitikos Gulf, revealed evidence of a totally different depositional environment in the lowest part of the core: this contained light grey-coloured sediments, contrasting strongly with the overlain olive grey muds of the upper part. Multi-proxy analyses (mineralogy, geochemistry and scanning electron microscopy) showed the predominance of carbonate minerals (aragonite, dolomite and calcite) together with gypsum in the lowest part of the core. Additional evidence (?18O and ?13C isotopes, and AMS 14C datings) suggest that carbonate mineral deposition can be attributed to autochthonous precipitation that took place in a saline palaeolake during the last glacial-early deglacial period. High ?18O values recorded in the lowest part of the core were associated with hypersaline and evaporative depositional environment. The most plausible explanation for the formation of the observed carbonate minerals directs to dolomite precipitation from hypersaline evaporating water bodies at low precipitation rates. Under varying weather conditions the precipitation of aragonite is favoured. Alternatively, high evaporation rates and gypsum formation, favouring an increase in Mg/Ca ratio, is proposed as a possible mechanism supporting authigenic dolomite precipitation. The lowest core sample to be AMS 14C dated provided an age of 19.53 cal. ka B.P. The palaeolake was presumably reconnected to the open sea at ~13.2 cal. ka B.P. during the last sea-level rise, marking the commencement of marine sedimentation characterised by the predominance of terrigenous aluminosilicates and fairly homogeneous depositional conditions lasting up to the present day. Fig. 1 Core B-4 (0-258 cm): a lithological log showing the sedimentological units defined in this study; b age model based on six AMS 14C ages (triangles); c-d down-core profiles in c aragonite, calcite and dolomite, d ?13C and ?18O.; Figure. 1 Core B-4 (0-258 cm): a lithological log; b age model based on six AMS 14C ages (triangles); c down-core profiles of aragonite, calcite and dolomite; and d down-core profiles of ?13C and ?18O.

Karageorgis, A. P.; Kanellopoulos, T. D.; Mavromatis, V.; Anagnostou, C. L.; Koutsopoulou, E.; Schmidt, M.; Pavlopoulos, K.; Tripsanas, E. K.; Hallberg, R. O.

2012-12-01

294

Late Pleistocene dune activity in the central Great Plains, USA  

Microsoft Academic Search

Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated

J. A. Mason; J. B. Swinehart; P. R. Hanson; D. B. Loope; R. J. Goble; X. Miao; R. L. Schmeisser

295

Multiple glacial culminations from the Lateglacial to the late Holocene in central and southern Peru (Invited)  

NASA Astrophysics Data System (ADS)

Fluctuations in small tropical mountain glaciers serve as sensitive indicators of variations in past and present-day climate. Most of the world's modern tropical glaciers reside in the Peruvian Andes, where a growing number of well-dated glacial records have recently been developed. As additional records are documented, regional patterns of late Pleistocene to Holocene glacial activity have begun to emerge. Here we present a compilation of new and previously obtained 10Be surface exposure ages from boulders on well-preserved moraine successions in two glaciated Andean ranges: the Cordillera Vilcabamba of southern Peru (13°20'S, 72°32'W) and the Huaguruncho massif (10°32'S, 75°56'W), located in central Peru ~450 km northwest of the Vilcabamba. A high-resolution composite chronology that merges >100 10Be measurements on moraine sequences in five glaciated drainages of the Cordillera Vilcabamba reveals the occurrence of at least five discrete glacial culminations from the Lateglacial to the late Holocene. At the Huaguruncho massif, >20 10Be exposure ages obtained from moraine sequences in a south-facing cirque indicate at least three major glacial stages spanning the Lateglacial to the Little Ice Age. The moraine ages at Huaguruncho are broadly correlative with the Vilcabamba moraine chronologies, with some dated moraine belts exhibiting geomorphic expressions that closely resemble those of their coeval counterparts in the Vilcabamba. A recurring finding in both field areas is a mismatch between basal radiocarbon ages from bog and lake sediments and 10Be exposure ages on outboard moraines, which enclose the depositional basins. These age discrepancies suggest that cosmogenic 10Be production rates scaled to high altitudes in the tropics are substantially lower than previous estimates. While we anticipate that future refinements to scaled isotope production rates may significantly affect correlation of 10Be exposure ages in the high Andes with ages derived from other dating methods, the revised production rates should have a negligible impact on 10Be age comparisons between the Vilcabamba and Huaguruncho moraines, which lie at similar elevations. The correspondence in age between moraine sequences in these two widely separated ranges suggests regional-scale coherency of multiple glacial fluctuations across the central to southern Peruvian Andes from the Lateglacial to the late Holocene, implying spatially uniform climate drivers along this transect.

Licciardi, J. M.; Schaefer, J. M.; Rodbell, D. T.; Stansell, N.; Schweinsberg, A.; Finkel, R. C.; Zimmerman, S. R.

2013-12-01

296

Weak oceanic heat transport as a cause of the instability of glacial climates  

NASA Astrophysics Data System (ADS)

The stability of the thermohaline circulation of modern and glacial climates is compared with the help of a two dimensional ocean—atmosphere—sea ice coupled model. It turns out to be more unstable as less freshwater forcing is required to induce a polar halocline catastrophy in glacial climates. The large insulation of the ocean by the extensive sea ice cover changes the temperature boundary condition and the deepwater formation regions moves much further South. The nature of the instability is of oceanic origin, identical to that found in ocean models under mixed boundary conditions. With similar strengths of the oceanic circulation and rates of deep water formation for warm and cold climates, the loss of stability of the cold climate is due to the weak thermal stratification caused by the cooling of surface waters, the deep water temperatures being regulated by the temperature of freezing. Weaker stratification with similar overturning leads to a weakening of the meridional oceanic heat transport which is the major negative feedback stabilizing the oceanic circulation. Within the unstable regime periodic millennial oscillations occur spontaneously. The climate oscillates between a strong convective thermally driven oceanic state and a weak one driven by large salinity gradients. Both states are unstable. The atmosphere of low thermal inertia is carried along by the oceanic overturning while the variation of sea ice is out of phase with the oceanic heat content. During the abrupt warming events that punctuate the course of a millennial oscillation, sea ice variations are shown respectively to damp (amplify) the amplitude of the oceanic (atmospheric) response. This sensitivity of the oceanic circulation to a reduced concentration of greenhouse gases and to freshwater forcing adds support to the hypothesis that the millennial oscillations of the last glacial period, the so called Dansgaard—Oeschger events, may be internal instabilities of the climate system.

Colin de Verdière, Alain; Te Raa, L.

2010-12-01

297

Plio-Pleistocene Bering Sea - North Pacific Ocean Circulation Dynamics Inferred from Sediment Source Changes at the Meiji Drift, Northwest Pacific Ocean  

NASA Astrophysics Data System (ADS)

The Pliocene is an interesting time in Earth’s history because it was warmer than today and could serve as an analog for how Earth might behave in response to future warming. It also precedes the onset of Northern Hemisphere glaciation that started ~3 million years ago. Yet it remains an open question whether closing of the Isthmus of Panama and opening of the Bering Strait impacted ocean circulation and climate 4-5 Ma. A large drift deposit in the northwest Pacific known as the Meiji Drift may hold clues about the possible impact of the Bering gateway on Pliocene climate dynamics in the Northern Hemisphere. It was previously demonstrated that the Meiji Drift is sensitive to changes at the Bering Strait, at least over the last 150 ka. This work investigates Plio-Pleistocene changes at the Meiji Drift using mineralogical and bulk sediment Nd isotopic techniques applied to the terrigenous fraction. Quantitative mineralogy of Meiji Drift sediment shows significant changes in quartz, plagioclase, K-feldspar, and amphibole at 5 Ma as well as around 1.5-2 Ma. Nd isotopic data show a transition from epsilon Nd values of +8 at 5 Ma to +1 by 3 Ma. These data suggest that circum-Pacific arc rocks were the dominant source of terrigenous sediment to the Meiji Drift around 5 Ma. From 5 to 3 Ma the sediment became progressively mixed with more continental-like source rocks. It is likely that increased flow from the Bering Sea (dominated by detritus from the Yukon River) to the North Pacific occurred ~5 Ma. This coincides with when the Bering Strait likely first opened with southward flow. But after the onset of Northern Hemisphere glaciation the sediment sources to the Meiji Drift likely began to oscillate at higher frequency with the opening and closing of the Bering gateway on glacial-interglacial timescales. Higher resolution work on the detrital fraction of the Meiji Drift will better constrain the timing, magnitude, and direction of ocean circulation changes in the Bering Sea and North Pacific region.

Vanlaningham, S.; Haley, B.; Hillier, S.; Alizai, A. H.

2010-12-01

298

A late-glacial transition from Picea glauca to Picea mariana in southern New England  

NASA Astrophysics Data System (ADS)

Picea is an important taxon in late-glacial pollen records from eastern North America, but little is known about which species of Picea were present. We apply a recently developed palynological method for discriminating the three Picea species in eastern North America to three records from New England. Picea glauca was dominant at ˜ 14,500-14,000 cal yr BP, followed by a transition to Picea mariana between ˜ 14,000 and 13,500 cal yr BP. Comparison of the pollen data with hydrogen isotope data shows clearly that this transition began before the beginning of the Younger Dryas Chronozone. The ecological changes of the late-glacial interval were not a simple oscillation in the position of a single species' range, but rather major changes in vegetation structure and composition occurring during an interval of variations in several environmental factors, including climate, edaphic conditions, and atmospheric CO 2 levels.

Lindbladh, Matts; Oswald, W. Wyatt; Foster, David R.; Faison, Edward K.; Hou, Juzhi; Huang, Yongsong

2007-05-01

299

Iceberg discharges of the last glacial period driven by oceanic circulation changes  

PubMed Central

Proxy data reveal the existence of episodes of increased deposition of ice-rafted detritus in the North Atlantic Ocean during the last glacial period interpreted as massive iceberg discharges from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence of the crucial role that the ocean plays both for past and future behavior of the cryosphere suggests a climatic control of these ice surges. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet–ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. The model generates a time series of iceberg discharge that closely agrees with ice-rafted debris records over the past 80 ka, indicating that oceanic circulation variations were responsible for the enigmatic ice purges of the last ice age. PMID:24062437

Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa; Ritz, Catherine

2013-01-01

300

Glacial influence on caldera-forming eruptions Adelina Geyer a,  

E-print Network

glacial time represent the most dynamic time in a multi-caldera volcano life (as compared to more quiet with the morphologically preserved calderas, correspond in time with "maximum glacial" conditions for the past several

Bindeman, Ilya N.

301

Middle-Late Pleistocene polycyclic evolution of a stable coastal area (southern Apulia, Italy)  

NASA Astrophysics Data System (ADS)

The Otranto-Leuca coastal tract is marked by the presence of numerous sea caves placed close to present sea level. They are located generally at the back of a shore platform covered by a sequence of breccia deposits, marine sediments and speleothems. At Grotta di Masseria dell'Orte, marine cemented sands rest on a narrow shore platform at about 6.2 m above mean sea level and are covered by speleothems older than 185 ka. At Grotta del Diavolo, which is mostly filled by breccia deposits, three beach levels have been detected at about 3.0, 3.5 and 5.9 m above msl. They are either covered by or overlie speleothems that yield an U/Th age of 340, 78 ka and between 170.3 and 146.5, respectively. Geomorphological evidence and radiometric ages indicate that the area after a period of uplift has been tectonically stable since the last part of the Middle Pleistocene so that marine landforms close to the present shoreline underwent a polycyclic evolution. The sedimentary fills of sea caves formed during Middle-Late Pleistocene glacial stages, when arid or semiarid conditions promoted the removal of regolith and the development of thick breccia deposits. During Marine Isotope Stages (MIS) 9.3, 5.5 and 5.1, cave sediments were partially eroded whereas beach layers and related speleothems developed. These are, in fact, the only marine isotope stages marked by a sea level position which in this Mediterranean region was either close to, or slightly higher than, the present one.

Mastronuzzi, Giuseppe; Quinif, Yves; Sansò, Paolo; Selleri, Gianluca

2007-05-01

302

Climatic variability and plant food distribution in Pleistocene Europe: Implications for Neanderthal diet and subsistence  

NASA Astrophysics Data System (ADS)

Contrary to their cold-adapted image, Neanderthals inhabited Pleistocene Europe during a time of great climatic fluctuation with temperatures ranging from as warm as present-day during the last interglacial to as cold as those of the last glacial maximum. Cold-adapted Neanderthals are similarly most often associated with the exploitation of large mammals who are themselves cold-adapted (mammoth, bison, reindeer, etc.). Cold, high-latitude environments are typically seen as lacking in plants generally and in plant foods in particular. Plant foods are therefore usually ignored and Neanderthals are increasingly being viewed as top carnivores who derived the vast majority of their diet from meat. Support for this hypothesis comes largely from stable isotope analysis which tracks only the protein portion of the diet. Diets high in lean meat largely fulfill micronutrient needs but can pose a problem at the macronutrient level. Lean meat can compose no more than 35% of dietary energy before a protein ceiling is reached. Exceeding the protein ceiling can have detrimental physiological effects on the individual. Neanderthals would have needed energy from alternative sources, particularly when animals are fat-depleted and lean meat intake is high. Underground storage organs (USOs) of plants offer one such source, concentrating carbohydrates and energy. USOs could also provide an important seasonal energy source since they are at their maximum energy storage in late fall/winter. Although Paleolithic sites are increasingly yielding plant remains, their presence is rare and they are often given only passing mention in Neanderthal dietary reconstructions. The complexity and number of potential wild plant foods, however, defies easy discussion. Native European wild edible plants with starchy USOs would have been potentially available throughout the Neanderthal range, even during the coldest periods of the Late Pleistocene.

Hardy, Bruce L.

2010-03-01

303

Pleistocene climate change promoted rapid diversification of aquatic invertebrates in Southeast Australia  

PubMed Central

Background The Pleistocene Ice Ages were the most recent geohistorical event of major global impact, but their consequences for most parts of the Southern hemisphere remain poorly known. We investigate a radiation of ten species of Sternopriscus, the most species-rich genus of epigean Australian diving beetles. These species are distinct based on genital morphology but cannot be distinguished readily by mtDNA and nDNA because of genotype sharing caused by incomplete lineage sorting. Their genetic similarity suggests a Pleistocene origin. Results We use a dataset of 3858 bp of mitochondrial and nuclear DNA to reconstruct a phylogeny of Sternopriscus using gene and species trees. Diversification analyses support the finding of a recent rapid speciation event with estimated speciation rates of up to 2.40 species per MY, which is considerably higher than the proposed average rate of 0.16 species per MY for insects. Additionally, we use ecological niche modeling and analyze data on habitat preferences to test for niche divergence between species of the recent Sternopriscus radiation. These analyses show that the species can be characterized by a set of ecological variables referring to habitat, climate and altitude. Conclusions Our results suggest that the repeated isolation of populations in glacial refugia might have led to divergent ecological adaptations and the fixation of morphological traits supporting reproductive isolation and therefore may have promoted speciation. The recent Sternopriscus radiation fulfills many characteristics of a species flock and would be the first described example of an aquatic insect species flock. We argue that the species of this group may represent a stage in speciation past the species flock condition because of their mostly broad and often non-overlapping ranges and preferences for different habitat types. PMID:22873814

2012-01-01

304

Late Pleistocene and Holocene environmental history of the Iguala Valley, Central Balsas Watershed of Mexico  

PubMed Central

The origin of agriculture was a signal development in human affairs and as such has occupied the attention of scholars from the natural and social sciences for well over a century. Historical studies of climate and vegetation are closely associated with crop plant evolution because they can reveal the ecological contexts of plant domestication together with the antiquity and effects of agricultural practices on the environment. In this article, we present paleoecological evidence from three lakes and a swamp located in the Central Balsas watershed of tropical southwestern Mexico that date from 14,000 B.P. to the modern era. [Dates expressed in B.P. years are radiocarbon ages. Calibrated (calendar) ages, expressed as cal B.P., are provided for dates in the text.] Previous molecular studies suggest that maize (Zea mays L.) and other important crops such as squashes (Cucurbita spp.) were domesticated in the region. Our combined pollen, phytolith, charcoal, and sedimentary studies indicate that during the late glacial period (14,000–10,000 B.P.), lake beds were dry, the climate was cooler and drier, and open vegetational communities were more widespread than after the Pleistocene ended. Zea was a continuous part of the vegetation since at least the terminal Pleistocene. During the Holocene, lakes became important foci of human activity, and cultural interference with a species-diverse tropical forest is indicated. Maize and squash were grown at lake edges starting between 10,000 and 5,000 B.P., most likely sometime during the first half of that period. Significant episodes of climatic drying evidenced between 1,800 B.P. and 900 B.P. appear to be coeval with those documented in the Classic Maya region and elsewhere, showing widespread instability in the late Holocene climate. PMID:17537917

Piperno, D. R.; Moreno, J. E.; Iriarte, J.; Holst, I.; Lachniet, M.; Jones, J. G.; Ranere, A. J.; Castanzo, R.

2007-01-01

305

The ancient tropical rainforest tree Symphonia globulifera L. f. (Clusiaceae) was not restricted to postulated Pleistocene refugia in Atlantic Equatorial Africa  

PubMed Central

Understanding the history of forests and their species' demographic responses to past disturbances is important for predicting impacts of future environmental changes. Tropical rainforests of the Guineo-Congolian region in Central Africa are believed to have survived the Pleistocene glacial periods in a few major refugia, essentially centred on mountainous regions close to the Atlantic Ocean. We tested this hypothesis by investigating the phylogeographic structure of a widespread, ancient rainforest tree species, Symphonia globulifera L. f. (Clusiaceae), using plastid DNA sequences (chloroplast DNA [cpDNA], psbA-trnH intergenic spacer) and nuclear microsatellites (simple sequence repeats, SSRs). SSRs identified four gene pools located in Benin, West Cameroon, South Cameroon and Gabon, and São Tomé. This structure was also apparent at cpDNA. Approximate Bayesian Computation detected recent bottlenecks approximately dated to the last glacial maximum in Benin, West Cameroon and São Tomé, and an older bottleneck in South Cameroon and Gabon, suggesting a genetic effect of Pleistocene cycles of forest contraction. CpDNA haplotype distribution indicated wide-ranging long-term persistence of S. globulifera both inside and outside of postulated forest refugia. Pollen flow was four times greater than that of seed in South Cameroon and Gabon, which probably enabled rapid population recovery after bottlenecks. Furthermore, our study suggested ecotypic differentiation—coastal or swamp vs terra firme—in S. globulifera. Comparison with other tree phylogeographic studies in Central Africa highlighted the relevance of species-specific responses to environmental change in forest trees. PMID:23572126

Budde, K B; González-Martínez, S C; Hardy, O J; Heuertz, M

2013-01-01

306

Impacts of post-glacial lake drainage events and revised chronology of the Champlain Sea episode 13-9??ka  

USGS Publications Warehouse

Lithologic, CHIRP (Compressed High Intensity Radar Pulse) sonar, paleomagnetic, stable isotopic and micropaleontological analyses of sediment cores from Lake Champlain (New York, Vermont) were used to determine the age of the post-glacial Champlain Sea marine episode, the timing of salinity changes and their relationship to freshwater discharge from mid-continent glacial lakes. Calibrated radiocarbon ages on plant material provide an improved post-glacial chronology overcoming problems from shell ages caused by carbon reservoir effects up to 1500??yr. The final drainage of glacial Lake Vermont and the inception of marine conditions occurred ??? 13.1-12.8??ka (kiloannum, calendar years) and a sharp decrease in Champlain Sea salinity from ??? 25 to 7-8??psu (practical salinity units) occurred approximately 11.4-11.2??ka. Reduced salinity was most likely caused by rapid freshwater inflow eastward from glacial Lake Algonquin into the Champlain Basin. The timing of inferred freshwater event coincides with the widespread climatic cooling called the Preboreal Oscillation.

Cronin, T. M.; Manley, P.L.; Brachfeld, S.; Manley, T.O.; Willard, D.A.; Guilbault, J.-P.; Rayburn, J.A.; Thunell, R.; Berke, M.

2008-01-01

307

Comparative phylogeography of five avian species: implications for Pleistocene evolutionary history in the Qinghai-Tibetan plateau.  

PubMed

Pleistocene climate fluctuations have shaped the patterns of genetic diversity observed in extant species. In contrast to Europe and North America where the effects of recent glacial cycles on genetic diversity have been well studied, the genetic legacy of the Pleistocene for the Qinghai-Tibetan (Tibetan) plateau, a region where glaciation was not synchronous with the North Hemisphere ice sheet maxima, remains poorly understood. Here, we compared the phylogeographical patterns of five avian species on the Qinghai-Tibetan plateau by three mitochondrial DNA fragments: the Tibetan snow finch (Montifringilla adamsi), the Blanford's snow finch (Pyrgilauda blanfordi), the horned lark (Eremophila alpestris), the twite (Carduelis flavirostris) and the black redstart (Phoenicurus ochruros). Our results revealed the three species mostly distributed on the platform region of the plateau that experienced population expansion following the retreat of the extensive glaciation period (0.5-0.175 Ma). These results are at odds with the results from avian species of Europe and North America, where population expansions occurred after Last Glacial Maximum (LGM, 0.023-0.018 Ma). A single refugium was identified in a restricted semi-continuous area around the eastern margin of the plateau, instead of multiple independent refugia for European and North American species. For the other two species distributed on the edges of the plateau (the twite and black redstart), populations were maintained at stable levels. Edge areas are located on the eastern margin, which might have had little or no ice cover during the glaciation period. Thus, milder climate may have mitigated demographic stresses for edge species relative to the extremes experienced by platform counterparts, the present-day ranges of which were heavily ice covered during the glaciation period. Finally, various behavioural and ecological characteristics, including dispersal capacities, habitat preference and altitude specificity along with evolutionary history might have helped to shape different phylogeographical structures appearing in these five species. PMID:20002586

Qu, Y; Lei, F; Zhang, R; Lu, X

2010-01-01

308

Exploring hypsometry in glacial and fluvial environments  

NSDL National Science Digital Library

This laboratory exercise explores the topographic signature of fluvial and glacial landscapes in different tectonic environments. Students develop a list of mountain ranges around the world to explore, then extract topographic data from 90-meter SRTM DEMs, and develop a series of hypsometric curves for each range. Each student works on a single range, but as a class we build up a database of 10-15 ranges around the world. The hypsometric curves are compared with each other and with published curves to look for signals of fluvial incision vs. glacial erosion in the landscapes.

Gran, Karen

309

The Puelche volcanic field: Extensive Pleistocene rhyolite lava flows in the Andes of central Chile  

USGS Publications Warehouse

A remote volcanic field in the rugged headwaters of the Rio Puelche and Rio Invernada (35.8??S) constitutes the largest cluster of Quaternary rhyolite lava flows yet identified in the Andean Southern Volcanic Zone. The Puelche Volcanic Field belongs to an intra-arc belt of silicic magmatic centers that extends, at least, 140 km north-south and lies well east of the volcanic front but nonetheless considerably west of the intraplate extensional fields of basaltic and alkaline centers of pampean Argentina. The authors' mapping has distinguished one shallow intrusive mass of early Pleistocene biotite rhyodacite (70.5% SiO2), 11 eruptive units of mid-Pleistocene high-K biotite-rhyolite lava (71.3-75.6% SiO2), and 4 eruptive units of basaltic andesite (53.95-4.9% SiO2), the conduits of which cut some of the rhyolites. Basal contacts of the rhyolite lava flows (and subjacent pyroclastic precursors) are generally scree covered, but glacial erosion has exposed internal flow structures and lithologic zonation superbly. Thicknesses of individual rhyolite lava flows range from 75 m to 400 m. Feeders for several units are well exposed. Cliff-draping unconformities and intracanyon relationships among the 11 rhyolite units show that the eruptive sequence spanned at least one glacial episode that accentuated the local relief. Lack of ice-contact features suggests, however, that all or most eruptions took place during non-glacial intervals probably between 400 ka and 100 ka. Post-eruptive glacial erosion reduced the rhyolites to several non-contiguous remnants that altogether cover 83 km2 and represent a surviving volume of about 21 km3. Consideration of slopes, lava thicknesses, and paleotopography suggest that the original area and volume were each about three times greater. Phenocryst content of the rhyolites ranges from 1 to 12%, with plagioclase>>biotite>FeTi oxides in all units and amphibole conspicuous in the least silicic. The chemically varied basaltic andesites range from phenocryst-poor to phenocryst-rich, exhibiting large differences in proportions of clinopyroxene, olivine, plagioclase, and xenocrystic quartz. Compositional bimodality of the volcanic field is striking, there being no Quaternary eruptive units having SiO2 contents between 55 and 70%. Major and trace element compositions of the mafic and silicic rocks are nonetheless typical of continental-margin arc suites, not of intracontinental suites. The lack of intermediate eruptive units and the differences between the mafic and rhyolitic lavas in Sr-isotope composition suggest that the rhyolites fractionated from a hybrid parent rather than continuously from basaltic magma. The rhyolites may contain larger contributions of upper-crustal partial melts than do silicic products of the volcanic-front centers 30 km to the west.

Hildreth, W.; Fierstein, J.; Godoy, E.; Drake, R.E.; Singer, B.

1999-01-01

310

Style and timing of glacial and paraglacial sedimentation in a monsoon-influenced high Himalayan environment, the upper Bhagirathi Valley, Garhwal Himalaya  

Microsoft Academic Search

The Gangotri Glacier, at the source of the Ganges River, has fluctuated greatly throughout the late Quaternary in response to climatic oscillations. This has resulted in impressive moraines, paraglacial debris flow fans and terraces along the upper stretches of the Bhagirathi Valley. Cosmogenic radionuclide (CRN) dating of glacial and paraglacial landforms shows that fans, terraces and associated moraines formed approximately

Patrick L. Barnard; Lewis A. Owen; Robert C. Finkel

2004-01-01

311

Neurodynamic oscillators  

NASA Technical Reports Server (NTRS)

Oscillation of electrical activity has been found in many nervous systems, from invertebrates to vertebrates including man. There exists experimental evidence of very simple circuits with the capability of oscillation. Neurons with intrinsic oscillation have been found and also neural circuits where oscillation is a property of the network. These two types of oscillations coexist in many instances. It is nowadays hypothesized that behind synchronization and oscillation there is a system of coupled oscillators responsible for activities that range from locomotion and feature binding in vision to control of sleep and circadian rhythms. The huge knowledge that has been acquired on oscillators from the times of Lord Rayleigh has made the simulation of neural oscillators a very active endeavor. This has been enhanced with more recent physiological findings about small neural circuits by means of intracellular and extracellular recordings as well as imaging methods. The future of this interdisciplinary field looks very promising; some researchers are going into quantum mechanics with the idea of trying to provide a quantum description of the brain. In this work we describe some simulations using neuron models by means of which we form simple neural networks that have the capability of oscillation. We analyze the oscillatory activity with root locus method, cross-correlation histograms, and phase planes. In the more complicated neural network models there is the possibility of chaotic oscillatory activity and we study that by means of Lyapunov exponents. The companion paper shows an example of that kind.

Espinosa, Ismael; Gonzalez, Hortensia; Quiza, Jorge; Gonazalez, J. Jesus; Arroyo, Ruben; Lara, Ritaluz

1995-01-01

312

Plio-Pleistocene climate change in Asian: Evidence from terrestrial lipids at ODP Site 1143 in the South China Sea  

NASA Astrophysics Data System (ADS)

A homologous series of n-alkanes (C24-C35) were detected at the ODP site 1143 (9°21.72'N, 113°17.11'E) in southern South China Sea and were used to reconstruct the paleoclimate change in the eastern Asian over the past 5Ma. Strong odd-carbon number predominance with a maximum at C29 or C31 in these n-alkanes indicated their origins of terrestrial higher plant waxes, which are transported to the deep sea mainly by rivers. In general, the profile of ?Alkanes (sum of C24-C35) can be subdivided into two time intervals: Before 2.7 Ma, the ?Alkanes fluctuated between 100 and 500 ng/g, averaging at 250 ng/g, which was lower than that in late Pleistocene but higher than that in early Pleistocene. Highland sea level during this period might have caused the deposition of the ?Alkanes, which reflected the riverine discharge and rainfall intensity . After 2.7Ma, ?Alkanes varied between 80-750 ng/g, with big fluctuations in the late Pleistocene. Alkane abundances depict a robust positive relationship with ?18OG. ruber but inverse relationship with temperature with maximum concentrations corresponding to heavier ?18OG. rube and lower temperature during glacial periods. This related to the changes in flux of the materials transported by the river, which, in turn, would have been influenced by sea level and/or precipitation. During glacial low stands of sea-levels, especially in the late Pleistocene, the emergence of the huge continental platforms in the south of the SCS led to the development of numerous drainage systems that significantly increased the input of terrestrial material and thus n-alkanes contents. Besides ?Alkanes, the alkane indices, i.e. the ratio of n-C31 /n-C27 and average carbon chain lengths (ACLs) of odd carbon-number, also recorded the palaeoenvironment and palaeoclimate changes. Although studies show that plants tend to synthesize longer chain length n-alkanes in response to elevated temperature and/or aridity, the higher n-C31 /n-C27 and ACLs in the late Pleistocene than Pliocene (a warm periods than present), suggested the alkane indices in the studied region mainly correspond to the humidity other than temperature. Alkane indices over the past 5 Ma indicate relative humid climate during the Pliocene, especially in the early Pliocene, which is the most humid climate in the 5 Ma period of time. But since the onset of northern hemisphere glaciation, the climate became progressively arid until 1.5-1.2 Ma; after that time the climate changed to a huge alternation of dry and humid climates. The uplift of the Tibetan Plateau, the closure of the Panamanian Seaway, the formation of east -west equatorial temperature gradient may exert a complex and profound effect upon atmospheric circulation and environmental changes of Eastern Asia over the Plio-Pleistocene periods.

Li, L.; Wang, H.; Wang, P.

2010-12-01

313

Impact of glacial erosion on 10 Be concentrations in fluvial  

E-print Network

Impact of glacial erosion on 10 Be concentrations in fluvial sediments of the Marsyandi catchment] Several processes contribute to denudation in high-mountain environments. Of these, glacial erosion significant variations in glacial erosion, both in space and magnitude, within the Marsyandi catchment

Bookhagen, Bodo

314

Pleistocene trends in interglacial climate development: The case of Stage 9  

NASA Astrophysics Data System (ADS)

Ice core records (carbondioxide, methane, temperature) from Antarctica clearly indicate an intensification of interglacial warmth since the end of glacial stage 12, rendering all the preceding interglacial periods as times with lower temperatures. Such a general trend is in accordance with the hypothesis of the development of more pronounced glacial-interglacial contrasts during the mid-Pleistocene evolution due to a distinct change in orbitally forced parameters. For past analogue-studies with the Holocene climate development, much attention has been given to stages 5e and 11 because they share some typical similarities with respect to enhanced contents of atmospheric carbondioxide, methane and temperature. However, considerably less is known about stage 9, although this interval shows by far the highest values in all of these atmospheric proxies. In this study, we therefore concentrated on a high resolution, multiproxy approach using a core from the mid-latitudes of the North Atlantic. The data allow a clear insight into the millennial-scale variability of the deep and surface water structure across stage 9. Comparing the orbital forcing as well as the interglacial trends in the atmospheric data across stages 5e and 9 from the southern hemisphere with our marine dataset indicate that both of these stages developed in a rather similar fashion. Both also reveal a very distinct ';overshoot' during their earlier developing phases. A good comparability with our marine records leads us to conclude that the interglacial inception of stage 9 and 5e might have been strongly forced by early changes in the southern hemisphere which then propagated northward some time later.

Bauch, H. A.; Kandiano, E.

2013-12-01

315

A lacustrine record from Lop Nur, Xinjiang, China: Implications for paleoclimate change during Late Pleistocene  

USGS Publications Warehouse

Climate variability during the Late Pleistocene is studied from the proxies in core CK-2 drilled from the Luobei Depression (91??03???E, 40??47???N), Lop Nur in the eastern Tarim Basin, Xinjiang, China. Geophysical and geochemical properties, including magnetic susceptibility, granularity, chroma, carbonate content, loss on ignition and trace elements, have been determined to reconstruct the environmental evolution of the area during 32-9 ka BP. The chronology is established by uranium-thorium disequilibrium dating techniques. Our data suggest four paleoclimate stages, indicating glacial variations between cold-humid and warm-arid environments. A period of extreme humidity occurred during 31,900-19,200 yr BP is attributed the last glacial maximum (LGM). The period was followed by a warm-arid episode during 19,200-13,500 yr BP. Then a cold-humid interval during 13,500-12,700 yr BP may correspond to another cooling phases at high latitudes of the Northern Hemisphere. The last stage from 12,700 to 9000 yr BP has a trend that the climate turned warm and arid. The Lop Nur region is characterized by particularly humid stadials and arid interstadials. The climate variability in Lop Nur was constrained by global climate change because it is correlated with Dansgaard-Oeschger and Heinrich events, which were observed at the northern high latitudes. The synchroneity of the palaeoclimatic events suggested that cold air activity at the northern high latitudes was the most important factor that influenced the climate evolution in the Lop Nur region. A probable mechanism that involves the migration of westerly winds is proposed to interpret this synchroneity. ?? 2008 Elsevier Ltd.

Chao, L.; Zicheng, P.; Dong, Y.; Weiguo, L.; Zhaofeng, Z.; Jianfeng, H.; Chenlin, C.

2009-01-01

316

Multi-proxy evidence for Late Pleistocene-Holocene climatic and environmental changes in Lop-Nur, Xinjiang, Northwest China  

USGS Publications Warehouse

A 10.35-m-long sediment core from the Luobei depression in Lop-Nur, Xinjiang, Northwest China, provides detailed information about environmental changes during the Late Pleistocene. The samples taken every 5 cm of the core were analyzed for 10 environmental proxies, including magnetic susceptibility, granularity, chroma, carbonate and loss on ignition (LOI), and pH value. The chronology data are provided by the uranium/thorium disequilibrium dates. The sediments of the section were deposited during the last 32000 years. The results of analysis of 10 proxies were examined using multivariate statistical analysis, and the principal components were calculated. According to the results, the Late Pleistocene sequence contains four climatic and environmental stages appearing in the cycles of cold-wet and warm-dry changes. During 10-9 ka BP, it was the earliest warm episode in the Holocene. Environmental changes in this district were restricted by global change, as suggested by the analysis of glacial-interglacial cycles. But it was different from the mutative trend of a monsoon region in East China because of its own characteristics, which was the situation of cold-wet and warm-dry climate-environment change. The candidate reason may be the uplift of the Tibet Plateau and the westerly wind circulation. ?? Science Press, Institute of Geochemistry, CAS and Springer-Verlag GmbH 2008.

Luo, C.; Yang, D.; Peng, Z.; Zhang, Z.; Weiguo, L.; He, J.; Zhou, C.

2008-01-01

317

Evidence for survival of Pleistocene climatic changes in Northern refugia by the land snail Trochoidea geyeri (Soós 1926) (Helicellinae, Stylommatophora)  

PubMed Central

Background The study of organisms with restricted dispersal abilities and presence in the fossil record is particularly adequate to understand the impact of climate changes on the distribution and genetic structure of species. Trochoidea geyeri (Soós 1926) is a land snail restricted to a patchy, insular distribution in Germany and France. Fossil evidence suggests that current populations of T. geyeri are relicts of a much more widespread distribution during more favourable climatic periods in the Pleistocene. Results Phylogeographic analysis of the mitochondrial 16S rDNA and nuclear ITS-1 sequence variation was used to infer the history of the remnant populations of T. geyeri. Nested clade analysis for both loci suggested that the origin of the species is in the Provence from where it expanded its range first to Southwest France and subsequently from there to Germany. Estimated divergence times predating the last glacial maximum between 25–17 ka implied that the colonization of the northern part of the current species range occurred during the Pleistocene. Conclusion We conclude that T. geyeri could quite successfully persist in cryptic refugia during major climatic changes in the past, despite of a restricted capacity of individuals to actively avoid unfavourable conditions. PMID:12720575

Pfenninger, Markus; Posada, David; Magnin, Frédéric

2003-01-01

318

Hydrogeology of Palm Valley, central Australia; a Pleistocene flora refuge?  

NASA Astrophysics Data System (ADS)

The Palm Valley Oasis (Finke Gorge National Park) in arid central Australia is characterised by large stands of red cabbage palm trees ( Livistona mariae). How these unique plants, over 1000 km away from nearest relatives in the tropical parts of northern Australia persist, has long fascinated visitors. The hydrogeology of this area helps explain this phenomenon. Stable isotope (? 2H, ? 8O) analyses shows groundwater to have a uniform composition that plots on or near a local meteoric water line. Carbon-14 results are observed to vary throughout this aquifer from effectively dead (<4%) to 87% modern carbon. Ratios of chlorine-36 to chloride range from 130 to 290×10 -1536Cl/Cl. In this region atmospheric 36Cl/Cl ratio is around 300×10 -15. Thus an age range of around 300 ka is indicated if, as is apparent radioactive decay is the only significant cause of 36Cl/Cl variation within the aquifer. The classic homogenous aquifer with varying surface topography flow model is the simplest conceptual model that need be invoked to explain these data. Complexities, associated with local topography flow cells superimposed on the regional gradient, may mean groundwater with markedly different flow path lengths has been sampled. This potential flow path complexity, which is also evidenced by slight variation in groundwater cation ratios, can account for the distribution of isotope age data throughout the aquifer. Given the likely very slow travel times indicated by this aquifer's hydraulic properties, age differences of the magnitude indicated from chlorine-36 data are feasible. The likely slow travel times (>100 ka) along some flow paths indicate groundwater discharge would endure through arid phases associated with Quaternary climate oscillations. Such a flow system can explain the persistence of this population of Palms and also highlight the possibility that Palm Valley has acted as a flora refuge since at least the mid Pleistocene.

Wischusen, John D. H.; Fifield, L. Keith; Cresswell, Richard G.

2004-06-01

319

Loess record of the Pleistocene-Holocene transition on the northern and central Great Plains, USA  

USGS Publications Warehouse

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.

Mason, J.A.; Miao, X.; Hanson, P.R.; Johnson, W.C.; Jacobs, P.M.; Goble, R.J.

2008-01-01

320

Ocean circulation in the southern Benguela region from the Pliocene to the Pleistocene: tracking Agulhas leakage into the SE Atlantic  

NASA Astrophysics Data System (ADS)

The transition from the warmth of the middle Pliocene to the large amplitude, 100 kyr glacial-interglacial cycles of the late Pleistocene provides a way to understand the forcings and impacts of regional and global climate change. Here, we investigate changes in ocean circulation over the period from 3.5 Ma to present using a marine sediment core, ODP Site 1087 (31o28'S, 15o19'E, 1374m water depth). ODP 1087 is located in the South-east Atlantic Ocean, outside the Benguela upwelling region. Its location allows investigation of the history of the heat and salt transfer to the Atlantic Ocean from the Indian Ocean ("Agulhas leakage"), which plays an important part in the global thermohaline circulation. It is not known how this transfer reacted to generally warmer global temperatures during the mid-Pliocene, nor to the transition to a globally cooler climate in the early Pleistocene. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the history of ODP 1087. These include the U37K' index to reconstruct sea surface temperatures, pigment analysis for understanding productivity changes, and foraminifera assemblage analysis to detect the presence of different water masses at the site. We have identified changes in SSTs and biological productivity that we argue to reflect shifts in the position of the Benguela upwelling cells, and a changing influence of Agulhas leakage. Our new data reveal a different organization in the Southeast Atlantic. It shows that during the Pliocene ODP 1087 was dominated by Benguela upwelling which had shifted south. We find no evidence for Agulhas leakage during the mid Pliocene, which could mean that Agulhas Leakage was severely reduced during the mid Pliocene. The implications of these results for understanding Plio-Pleistocene climate changes will be explored here.

Petrick, Benjamin; McClymont, Erin; Felder, Sojna; Leng, Melanie

2013-04-01

321

Analysis of modern and Pleistocene hydrologic exchange between Saginaw Bay (Lake Huron) and the Saginaw Lowlands area  

USGS Publications Warehouse

Two numerical models, one simulating present groundwater flow conditions and one simulating ice-induced hydraulic loading from the Port Huron ice advance, were used to characterize both modern and Pleistocene groundwater exchange between the Michigan Basin and near-surface water systems of Saginaw Bay (Lake Huron) and the surrounding Saginaw Lowlands area. These models were further used to constrain the origin of saline, isotopically light groundwater, and porewater from the study area. Output from the groundwater-flow model indicates that, at present conditions, head in the Marshall aquifer beneath Saginaw Bay exceeds the modern lake elevation by as much as 21 m. Despite this potential for flow, simulated groundwater discharge through the Saginaw Bay floor constitutes only 0.028 m3 s-1 (???1 cfs). Bedrock lithology appears to regulate the rate of groundwater discharge, as the portion of the Saginaw Bay floor underlain by the Michigan confining unit exhibits an order of magnitude lower flux than the portion underlain by the Saginaw aquifer. The calculated shoreline discharge of groundwater to Saginaw Bay is also relatively small (1.13 m3 s-1 or ???40 cfs) because of low gradients across the Saginaw Lowlands area and the low hydraulic conductivities of lodgement tills and glacial-lake clays surrounding the bay. In contrast to the present groundwater flow conditions, the Port Huron ice-induced hydraulic-loading model generates a groundwater-flow reversal that is localized to the region of a Pleistocene ice sheet and proglacial lake. This area of reversed vertical gradient is largely commensurate with the distribution of isotopically light groundwater presently found in the study area. Mixing scenarios, constrained by chloride concentrations and ??18O values in porewater samples, demonstrate that a mixing event involving subglacial recharge could have produced the groundwater chemistry currently observed in the Saginaw Lowlands area. The combination of models and mixing scenarios indicates that structural control is a major influence on both the present and Pleistocene flow systems.

Hoaglund, J. R., III; Kolak, J.J.; Long, D.T.; Larson, G.J.

2004-01-01

322

Were the Late Pleistocene climatic changes responsible for the disappearance of the European spotted hyena populations? Hindcasting a species geographic distribution across time  

NASA Astrophysics Data System (ADS)

This article examines the role of the Late Pleistocene climatic changes in the disappearance of the European populations of spotted hyenas. A species distribution model was built using both current and past environmental requirements of the species. Model projections were made with climatic scenarios provided by the GENESIS 2.0 General Circulation Model (126 ka, 42 ka, 30 ka and 21 ka). Those projections indicate (1) that during the Late Pleistocene warm scenarios spotted hyenas should have been widespread in Europe, and (2) that during the last glacial maximum their potential climatically suitable geographic distribution diminished in size. The decrease in the potential climatic distribution was strictly restricted to Northern Europe. Climatic conditions in Southern Europe during the Late Pleistocene remained within the spotted hyena climatic tolerance. Hence, climate changes could have directly affected the Northern distribution of the species during the last glaciations. However, climate change alone is not sufficient to have caused the disappearance of the spotted hyena populations in Southern Europe. That is, other factors, such as prey abundance or human ecological impacts, in addition to climatic change, are needed to completely account for extinction of the European spotted hyena.

Varela, Sara; Lobo, Jorge M.; Rodríguez, Jesús; Batra, Persaram

2010-08-01

323

Pleistocene Speciation in North American Lichenized Fungi and the Impact of Alternative Species Circumscriptions and Rates of Molecular Evolution on Divergence Estimates  

PubMed Central

Pleistocene climatic fluctuations influenced patterns of genetic variation and promoted speciation across a wide range of species groups. Lichens are commonly found in habitats that were directly impacted by glacial cycles; however, the role of Pleistocene climate in driving speciation in most lichen symbionts remains unclear. This uncertainty is due in part to limitations in our ability to accurately recognize independently evolving lichen-forming fungal lineages and a lack of relevant fossil calibrations. Using a coalescent-based species tree approach, we estimated divergence times for two sister clades in the genus Xanthoparmelia (Parmeliaceae) restricted to western North America. We assessed the influence of two different species circumscription scenarios and various locus-specific rates of molecular evolution on divergence estimates. Species circumscriptions were validated using the program BP&P. although speciation was generally supported in both scenarios, divergence times differed between traditional species circumscriptions and those based on genetic data, with more recent estimates resulting from the former. Similarly, rates of evolution for different loci resulted in variable divergence time estimates. However, our results unambiguously indicate that diversification in the sampled Xanthoparmelia clades occurred during the Pleistocene. Our study highlights the potential impact of ambiguous species circumscriptions and uncertain rates of molecular evolution on estimating divergence times within a multilocus species tree framework. PMID:24386465

Leavitt, Steven D.; Lumbsch, H. Thorsten; Stenroos, Soili; Clair, Larry L. St.

2013-01-01

324

Pleistocene surface water temperatures in the Benguela upwelling area  

NASA Astrophysics Data System (ADS)

Analysis of carbonate microfossils (planktonic foraminifers and nannoplankton) in the DSDP Hole 362 Quaternary section made it possible to specify its zonal subdivision (almost all zones of Gartner's high-resolution nannofossil scale are recognized), establish depositional environments, and restore past surface water temperatures. The latter appeared to be several degrees lower than their present-day values, which is evident from the anomalously high share of the subpolar species Neogloboquadrina pachyderma sin. that constitutes 97% of the fossil assemblage in Lower Pleistocene sediments. It is shown that the Benguela upwelling existed throughout the entire Pleistocene, being less intense in the Late Pleistocene and Holocene.

Os'kina, N. S.; Dmitrenko, O. B.

2011-08-01

325

Cosmogenic exposure dating in arctic glacial landscapes: implications for the glacial history of northeastern Baffin Island, Arctic Canada  

Microsoft Academic Search

Cosmogenic exposure dating and detailed glacial-terrain mapping from the Clyde Foreland, Baffin Island, Arctic Canada, reveal new information about the extent and dynamics of the northeastern sector of the Laurentide Ice Sheet (LIS) during the last glacial maximum (LGM). The Clyde Foreland is composed of two distinct landscape zones: (1) glacially scoured terrain proximal to the major sources of Laurentide

Jason P. Briner; Gifford H. Miller; P. Thompson Davis; Robert C. Finkel

2005-01-01

326

Glacial-marine and glacial-lacustrine sedimentation in Sebago Lake, Maine: Locating the marine limit  

SciTech Connect

The marine limit in Maine marks a sea-level highstand at approximately 13 ka. It was inferred to cross Sebago Lake near Frye Island by Thompson and Borns (1985) on the Surficial Geological Map of Maine, dividing the lake into a northern glacial-lacustrine basin and a southern glacial-marine basin. This study examined the accuracy of the mapped marine limit in the lake and the nature of glacial-lacustrine and glacial-marine facies in Maine. Recognition of the marine limit is usually based on mapped shorelines, glacial-marine deltas, and contacts with glacial-marine sediments. This study, in Maine's second largest lake, collected 100 kilometers of side-scan sonar images, 100 kilometers of seismic reflection profiles, and one core. Side-scan sonar records show coarse sand and gravel and extensive boulder fields at an inferred grounding-line position near Frye Island, where the marine limit was drawn. ORE Geopulse seismic reflection profiles reveal a basal draping unit similar to glacial-marine units identified offshore. Later channels cut more than 30 m into the basal stratified unit. In addition, till and a possible glacial-tectonic grounding-line feature were identified. Slumps and possible spring disruptions are found in several locations. The top unit is an onlapping ponded Holocene lacustrine unit. Total sediment is much thicker in the southern basin; the northern basin, >97 m deep, north of the marine limit appears to have been occupied by an ice block. Retrieved sediments include 12 meters of rhythmites. Microfossil identifications and dating will resolve the environments and time of deposition in this core.

Johnston, R.A.; Kelley, J.T. (Maine Geological Survey, Augusta, ME (United States)); Belknap, D. (Univ. of Maine, Orono, ME (United States). Dept. of Geological Sciences)

1993-03-01

327

Glacial Retreat The Great Lakes are Born  

E-print Network

1 Glacial Retreat The Great Lakes are Born Retreat of the Ice Margin Main lines of evidence for process come from the end moraines left behind The Saginaw lobe was thinner than the Lake Michigan streams could not carry, was laid down as outwash, in broad, flat outwash plains Ice-marginal lakes (or

Cochran-Stafira, D. Liane

328

Glacial geography and native North American languages  

NASA Astrophysics Data System (ADS)

This study tests the hypothesis that the number and distribution of some native American languages may be related to ice-margin changes of the Wisconsin glaciation. The analysis indicated that the number of languages per unit area is much greater in unglaciated areas of the last glacial maximum than in glaciated areas. The pattern of languge overlap between land areas sequentially exposed during deglaciation appears to indicate the direction of movement of populations from the periphery toward the core of the area once covered by the Wisconsin Ice Sheet. The data strongly indicate that North America was inhabited prior to the Wisconsin glacial maximum, because glacial maximum conditions apparently influenced linguistic distributions. Evidence suggests that ancestral Eskimo-Aleut and Na-Dene speakers occupied the northwestern edge of the continental ice mass, and that ancestral Algonquian speakers were south of the ice mass during the Wisconsin glacial maximum (approximately 18,000 yr ago). These three linguistic groups were the principal ones to spreas into areas exposed by the recession of the Wisconsin ice.

Rogers, Richard A.

1985-01-01

329

Illustrated Glossary of Alpine Glacial Landforms  

NSDL National Science Digital Library

Although there are not a lot of images here, the ones included are succinctly described and have accompanying topographic map examples, allowing students to see the correlation between photo and map. Images are divided into three sections: divided into "Erosional Landforms," "Depositional Landforms," and "Ice Features." Nine short exercises test student knowledge of both glacial landform images and the topographic expression of the landforms.

Karen A Lemke

330

Sub-glacial processes interpreted from 3D and high-resolution 2D seismic data from the Central North Sea  

NASA Astrophysics Data System (ADS)

A near complete record of Quaternary deposition, comprising more than 1000m of sediments, is preserved within the Central North Sea (CNS). This study presents evidence interpreted from seismic data of sub-glacial processes at a variety of scales for several Pleistocene glacial events. The study area has been the subject of hydrocarbon exploration since the mid 1960s and is covered by 3D seismic datasets up to 1000km2 as well as high-resolution 2D (HR2D) seismic datasets covering areas of 1-25km2. These data have been examined using a variety of techniques and attributes, including time-slicing, horizon slicing, topographic mapping and attribute analysis, to map erosion surfaces, depositional bodies, sedimentary textures and deformation events. An Early Pleistocene seismic event has been identified on 3D data, at 800-1000m MSL, within the southern part of the CNS, which marks the first appearance of iceberg ploughmarks. This event has been traced into the northern part of the study area, where iceberg ploughmarks are absent, but a set of mega-scale lineations at 700-800ms TWT are interpreted as ice-stream scour marks. A series of complex seismic events overlying the ice-scoured surface are interpreted as glacial deposits, at the top of which a network of channels, interpreted to be the result of glacial meltwaters, is associated with features interpreted as over-bank sand bodies. Higher in the sequence, timeslice images of Early to Middle Pleistocene deposits show trains of sub-parallel, curvi-linear, events, several km in length and 50-300m in width. Analysis of these events on HR2D data reveals them to consist of series of short, imbricated, dipping reflectors, terminated by complex, mounded structures. Individual sheets display up to 60ms TWT (55m) vertical displacement over horizontal distances of 200-250m. Two deformed packages are evident on HR2D data. A lower sequence, consisting of discrete thrust sheets lies above an erosion or dislocation surface (MP1). Top of the lower sequence is marked by a reflection termed MP2, above which is an upper sequence displaying lower reflection amplitudes, smaller scale deformation structures, but a more comprehensively deformed fabric. To the south of these tectonised intervals, deposits are completely undeformed and this lateral transtion is interpreted to mark an ice limit or lift-off point. Within a Middle to Late Pleistocene sequence a series of glacial and glacio-marine depositional units are bounded by surfaces characterised by tunnel valley development, recording at least three glacial advances and subsequent retreats. The uppermost surface displays various features indicative of an ice-moulded surface; the largest exhibit asymmetric long profiles and complex internal structures and are interpreted as drumlin-like structures, one of which extends into a long, broad ridge, approximately 800m across and 15m high extending for several km. Two or three smaller ridges, approximately 3-5m high and 30-40m across and interpreted as flute-like structures are traceable for more than 5km over several datasets. All of these features are oriented on a constant bearing of 316° , recording ice-flow orientation at the time of their formation. The bedforms are cut by a coeval or slightly later sub-glacial tunnel valley on a similar orientation.

Buckley, Francis

2013-04-01

331

The disappearance of glaciers in the Tien Shan Mountains in Central Asia at the end of Pleistocene  

NASA Astrophysics Data System (ADS)

Glaciers in Central Asia are among the largest ice masses in the Eurasian continent and have supplied vital water to local inhabitants for thousands of years. The glaciers in this region are generally believed to be remnants of the last deglaciation, however, glacier variability in the central Asian mountains since the Last Glacial Maximum (LGM) has not been well documented. Here, we report an 86.87 m-deep ice core record drilled on an ice cap in the Tien Shan Mountains of Central Asia. Radiocarbon dating of organic soil from the bottom of the ice-core borehole showed that the age of the soil was 12,656 - 12,434 cal years before present, coincident with the beginning of the Younger Dryas cold period (YD). This result indicates that the ice cap did not exist in the Bølling-Allerød period (BA), which was the warm period before the YD, and that the BA climate was significantly warmer than at present. It also indicates that the ice cap has never entirely disappeared in any warm periods throughout the Holocene. We estimated that during the BA its extent was 43% or less of the present glacier coverage in the mountains. Our results suggest that this region at the end of Pleistocene was considerably warmer than at present, and that most of the present glaciers in this region are not relics of the Last Glacial period, but are composed of ice formed during the YD and Holocene.

Takeuchi, Nozomu; Fujita, Koji; Aizen, Vladimir B.; Narama, Chiyuki; Yokoyama, Yusuke; Okamoto, Sachiko; Naoki, Kazuhiro; Kubota, Jumpei

2014-11-01

332

Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene  

NASA Astrophysics Data System (ADS)

Changes in the Sr to Ca ratio of sea water have important implications for the interpretation of past climate. It has proven difficult to interpret Sr/Ca of foraminiferal calcite as a measure of seawater Sr/Ca or as reflecting the influence of deep water carbonate ion saturation (?[CO32-]) on the incorporation of Sr into benthic foraminiferal carbonate. Here, we address this issue by measurements of paired benthic foraminiferal Sr/Ca and B/Ca (a proxy for deep water ?[CO32-]) for core-tops from the global ocean and three down cores at different settings during the Last Glacial-interglacial cycle. These new data suggest a significant control of deep water ?[CO32-] on benthic foraminiferal Sr/Ca, and that down-core shell Sr/Ca variations can be largely accounted for by past deep water ?[CO32-] changes. We conclude that seawater Sr/Ca has likely remained near-constant on glacial-interglacial timescales during the late Pleistocene, in agreement with model results. With due caution, benthic Sr/Ca may be used as an auxiliary proxy for deep water ?[CO32-] if seawater Sr/Ca is constant.

Yu, Jimin; Elderfield, Henry; Jin, Zhangdong; Tomascak, Paul; Rohling, Eelco J.

2014-08-01

333

Aeolian dust dynamics in Central Asia during the Pleistocene: driven by alternating atmospheric circulation patterns and/or the seasonal shift of the Asiatic polar front  

NASA Astrophysics Data System (ADS)

Loess-palaeosol sequences preserve detailed archives of climate change, reflecting the dynamics of aeolian dust sedimentation and the palaeo-dust content of the atmosphere. The detailed investigation of particle size distributions of windblown sediments is an increasingly used approach to assess the palaeorecord of aeolian dust dynamics. The Central Asian loess belt offers the potential to carry out granulometric studies and to reconstruct Pleistocene atmospheric circulation patterns in Eurasia. In this study we present the aeolian dust record of the loess sequence at Remisowka (Almaty, SE Kazakhstan), which reflects a detailed signal of glacial-interglacial dynamics in Central Asia. Based on radiocarbon and amino acid geochronologic data, long-term semi- continuous trends in the aeolian dust record of the Last Glacial Cycle are measured in order to interpret their palaeoclimate signal. In consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in Central Asia, it is likely that the observed trends reflect a long term signal of seasonality, triggered by changes in duration and permanency of the seasonal shift of the Asiatic polar front during the middle to late Pleistocene. Previously published models, which focused on the glacial-interglacial reciprocity of the zonal Westerlies and Asiatic high in Central Asia, were overly simplified and should be modified to include the influence of the Asiatic polar front. As the position of the high level planetary frontal zone mainly affects the development and seasonal shift of the Asiatic polar front, it is likely that an inter-hemispheric mechanism exists, that links dust deposition between Europe and Central Asia.

Machalett, B.; Oches, E. A.; Frechen, M.; Zoeller, L.; Mavlyanova, N.; Markovic, S. B.; Hambach, U.; Endlicher, W.

2007-12-01

334

The granite tors of Dartmoor, Southwest England: rapid and recent emergence revealed by Late Pleistocene cosmogenic apparent exposure ages  

NASA Astrophysics Data System (ADS)

Dartmoor, in SW England, is a classic periglaciated granite upland adorned with a population of over 150 tors. The origin of the tors has been controversial, but their emergence by differentiation after stripping of regolith during Pleistocene cold phases is accepted. However, their actual age has been unknown, with possible scenarios ranging from preservation since the early Middle Pleistocene to relatively short-lived landforms in a maritime climate with high denudation rates. The latter is now supported by 32 cosmogenic surface exposure dates from 28 tors across the whole upland. The distribution of apparent 10Be ages peaks strongly in the Middle Devensian (36-50 ka), which with corrections for weathering and limited ice shielding could be interpreted as Early Devensian. These ages are much younger than those found for three glacially unmodified Cairngorms tors, and somewhat younger even than glacially modified Cairngorms tors. The dates show little spatial variation. Although an ice cap has now been modelled in the heart of northern Dartmoor, tors here are of median age, suggesting that ice cover sufficient to shield tors from incoming radiation was of short duration. The few younger tor ages support the idea of continuing landform instability across the landscape, with weathering flakes redeveloping soon after inferred loss of top pillows by gelifraction or gravitational toppling. The few older tor ages have no systematic explanation, and may indicate inheritance from an earlier cycle of bedrock near-exposure. Since most tors are modest in height (typically 2-5 m), volumetrically insignificant, and often in advanced stages of disintegration, the general impression is that they are evanescent features, which emerge and quickly disappear during every Pleistocene climatic downturn. Tor populations may thus flicker across the landscape rather randomly over the Quaternary. The remarkably consistent age of the present tor population could be associated with a stripping event at the start of the Devensian, but fuller analysis must await closer controls on tor denudation rates in different climatic phases, and on ice cover extent and duration. These results only date extant tor surfaces, not the landscape, but as the best available erosion pins they have evident value in exploring theories of the evolution of Dartmoor during the Quaternary.

Gunnell, Yanni; Jarman, David; Braucher, Régis; Calvet, Marc; Delmas, Magali; Leanni, Laetitia; Bourlès, Didier; Arnold, Maurice; Aumaître, Georges; Keddaouche, Karim

2013-02-01

335

Late Pleistocene and Holocene hydrological change in central Indonesia from Lake Towuti, Sulawesi  

NASA Astrophysics Data System (ADS)

The tropical Pacific plays a fundamentally important role in global climate change due to the interaction between the El Niño Southern Oscillation (ENSO), the Intertropical Convergence Zone (ITCZ), and the Asian monsoons. Indonesia sits at the heart of the tropical western Pacific, yet we have very few terrestrial paleoclimate records from Indonesia to evaluate hydrological changes in the tropical western Pacific during the last 21,000 years. Here we present new sediment piston core and seismic reflection data from Lake Towuti, a large tectonic lake in central Sulawesi, that document the region’s late Pleistocene to Holocene climate evolution. Lithologic and magnetic susceptibility variations in ten piston cores from the lake can be clearly correlated to acoustic reflectors in our seismic stratigraphy and document substantial, basin-wide variations in precipitation and surface runoff through time. Our provisional age model suggests wetter conditions than present in central Indonesia during the latest Pleistocene and early to mid-Holocene. This behavior is generally in phase with the northern hemisphere tropics, despite the near-equatorial (2.7 degrees South) location of our site, suggesting that early Holocene intensification of the Asian monsoon and northward migration of the tropical rain belt did not result in drier conditions at the equator. Multiproxy analyses of our new cores, including compound-specific stable isotope data, will further elucidate centennial- to millennial-scale climate variations in the region.

Russell, J. M.; Bijaksana, S.; Wattrus, N. J.; Noren, A. J.; Konecky, B.; Wicaksono, S. A.

2010-12-01

336

Phylogenetic relationships among Palearctic and Nearctic burbot (Lota lota): Pleistocene extinctions and recolonization.  

PubMed

The burbot (Lota lota Linnaeus, 1758) is the only freshwater species from the cod family. Various taxonomic hypotheses were tested against molecular data by sequencing the mitochondrial cytochrome b locus of 120 burbot from 41 populations together with the related species Molva molva (ling) and Brosme brosme (tusk), which represented the other Lotinae genera. Within the genus Lota two distinct phylogroups were observed: one in North America south of the Great Slave Lakes (Lota lota maculosa) and one in Eurasia and the remainder of the Nearctic region (Lota lota lota). The burbot lineage separated 10 Myr BP from the other Lotinae, while the genetic variation within burbot appeared to be approximately 1 Myr old. However, fossil evidence suggested that burbot already existed in the Early Pliocene in Europe, from were it probably colonized North America in the Early Pleistocene. While Nearctic burbot survived climatic oscillations and diverged in several refugia, the Eurasian form became extinct or was reduced to a very small population. In the Late Pleistocene the species recolonized the Palearctic region to establish its present distribution range. PMID:14615196

Van Houdt, J K; Hellemans, B; Volckaert, F A M

2003-12-01

337

Assessing the strength of the monsoon during the late Pleistocene in southwestern United States  

NASA Astrophysics Data System (ADS)

Improved predictions of drought require an understanding of natural and human-induced climate variability. Long-term records across glacial-interglacial cycles provide the natural component of variability, however few such records exist for the southwestern United States (US) and quantitative or semi-quantitative records of precipitation are absent. Here we use the hydrogen isotope (?D) value of C28n-alkanoic acid in lacustrine sediments of Pleistocene age to reconstruct ?D values of precipitation in northern New Mexico over two glacial-interglacial cycles (?550,000-360,000 years before present) and obtain a record of monsoon strength. Overall, reconstructed ?D values range from -53.8‰ to -94.4‰, with a mean value of -77.5 ± 8‰. Remarkably, this variation falls within the measured present-day summer monsoonal and winter weighted means (-50.3 ± 3‰ and -106.4 ± 20‰ respectively), suggesting that processes similar to those of present time also controlled precipitation during Marine Isotope Stage (MIS) 13 to 10. Using the ?D summer monsoonal and winter mean values as end-members, we interpret our reconstructed ?D record of precipitation as a direct, and semi-quantitative, indicator of monsoon strength during MIS 13 to 10. Interglacial periods were characterized by greater monsoon strength but also greater variability compared to glacial periods. Pronounced cycles in the strength of the monsoon occurred during interglacial periods and in general were positively correlated with maximum mean annual temperatures. Our estimates of monsoon strength are supported by independent proxies of ecosystem productivity, namely, TOC, ?13C of TOC and Si/Ti ratio and warm pollen taxa Juniperus and Quercus. Interglacial variability in the strength of the monsoon resembles a response to the land-sea surface temperature contrast (LSTC) except for the early part of MIS 11. During this period, LSTC would have remained relatively strong while monsoonal strength decreased to a minimum. This minimum occurred following the warmest interval of MIS 11, suggesting a more complex driving of monsoon strength during warm periods. In addition, this period of monsoon minimum coincided with a core section of mud-cracked sediments that suggest low monsoonal precipitation was an important factor in the onset of drought. Our estimates of monsoon strength represent a record of natural variability in the region that is relevant to present time, in particular the variability during interglacial MIS 11, which is considered an analog for the current interglacial. Our results suggest that natural variability can cause significant reductions in monsoonal precipitation with the implication of a potentially adverse effect from sustained warming.

Cisneros-Dozal, Luz M.; Huang, Yongsong; Heikoop, Jeffrey M.; Fawcett, Peter J.; Fessenden, Julianna; Anderson, R. Scott; Meyers, Philip A.; Larson, Toti; Perkins, George; Toney, Jaime; Werne, Josef P.; Goff, Fraser; WoldeGabriel, Giday; Allen, Craig D.; Berke, Melissa A.

2014-11-01

338

Stratigraphy of the Upper Pleistocene Miami Limestone of Florida  

Microsoft Academic Search

The upper Pleistocene Miami Limestone is probably the most stratigraphically-complex formation in the Cenozoic of Florida. The Miami overlies and vertically\\/laterally grades into the upper Pleistocene Ft. Thompson Formation to the west in southeast Palm Beach County (west of I-95); to the west in Broward County (west of the Turnpike); and to the north in south Broward County (along U.S.

Johnson

1993-01-01

339

Coral associations of the Pleistocene Ironshore Formation, Grand Cayman  

NASA Astrophysics Data System (ADS)

The 125-ka sea level, which was approximately 6 m above present-day sea level, led to the partial flooding of many Caribbean islands. On Grand. Cayman, this event led to the formation of the large Ironshore Lagoon that covered most of the western half of the island and numerous, small embayments along the south, east, and north coasts. At that time, at least 33 coral species grew in waters around Grand Cayman. This fauna, like the modern coral fauna of Grand Cayman, was dominated by Montastrea annularis, Porites porites, Acropora polmata, and A. cervicornis. Scolymia cubensis and Mycetophyllia ferox, not previously identified from the Late Pleistocene, are found in the Pleistocene patch reefs. Madracis mirabilis, Colpophyllia breviserialis, Agaricia tenuifolia, A. lamarcki, A. undata, Millepora spp., Mycetophyllia reesi, M. aliciae, and M. danaana, found on modern reefs, have not been identified from the Late Pleistocene reefs. Conversely, Pocillopora sp. cf. P. palmata, which is found in Late Pleistocene reefs, is absent on the modern reefs around Grand Cayman. The corals in the Ironshore Formation of Grand Cayman have been divided into 10 associations according to their dominant species, overall composition, and faunal diversity. Many of these associations are similar to the modern associations around Grand Cayman. Each of the Pleistocene coral associations, which can be accurately located on the known Late Pleistocene paleogeography of Grand Cayman, developed in distinct environmental settings. Overall trends identified in the modern settings are also apparent in the Late Pleistocene faunas. Thus, the diversity of the coral faunas increased from the interior of the Ironshore Lagoon to the reef crest. Similarly, the coral diversity in the Pleistocene patch reefs was related to the size of the reefs and their position relative to breaks in the barrier reef. The barrier reef included corals that are incapable of sediment rejection; whereas the patch reefs lacked such corals.

Hunter, I. G.; Jones, B.

1996-11-01

340

Upper Pleistocene interstratal piping-cave speleogenesis: The Seso Cave System (Central Pyrenees, Northern Spain)  

NASA Astrophysics Data System (ADS)

The Seso Cave System (SCS, South Central Pyrenees, Northeastern Spain) develops in poorly soluble marly interstratum between limestone beds of Eocene age. We propose an innovative and singular pseudokarstic speleogenetic model under vadose conditions based on cave morphological evidence, physicochemical and mineralogical characteristics of the Eocene marly host rock, U-Th dating of cave deposits, and local geological and geomorphological information. Eocene marls are shown to be sensitive to dispersion processes supported by their high clay content and the high concentration of sodium and low electrical conductivity in the seepage water. Runoff inside the cave results from water that infiltrates through joints and seepage water in cave walls. Thereby piping processes become very active, triggering mechanical scouring and outwashing mechanisms. The hydraulic gradient required to develop piping activity is determined by regional fluvial incision. The base level controlling water discharge during opening of the SCS coincides with a terrace of the Ara River dated at 65 ka BP. Considering this age, as well as the U-Th age of the oldest speleothems dated in the cave at 38 ka BP, the timing of the SCS interstratal piping-cave speleogenesis is constrained to the Upper Pleistocene; very likely at the end of Marine Isotope Stage 4 during a period characterized by high water availability following glacial retreat in northern Iberian mountains.

Bartolomé, M.; Sancho, C.; Moreno, A.; Oliva-Urcia, B.; Belmonte, Á.; Bastida, J.; Cheng, H.; Edwards, R. L.

2015-01-01

341

Phylogeography of the widespread African puff adder (Bitis arietans) reveals multiple Pleistocene refugia in southern Africa.  

PubMed

Evidence from numerous Pan-African savannah mammals indicates that open-habitat refugia existed in Africa during the Pleistocene, isolated by expanding tropical forests during warm and humid interglacial periods. However, comparative data from other taxonomic groups are currently lacking. We present a phylogeographic investigation of the African puff adder (Bitis arietans), a snake that occurs in open-habitat formations throughout sub-Saharan Africa. Multiple parapatric mitochondrial clades occur across the current distribution of B. arietans, including a widespread southern African clade that is subdivided into four separate clades. We investigated the historical processes responsible for generating these phylogeographic patterns in southern Africa using species distribution modelling and genetic approaches. Our results show that interior regions of South Africa became largely inhospitable for B. arietans during glacial maxima, whereas coastal and more northerly areas remained habitable. This corresponds well with the locations of refugia inferred from mitochondrial data using a continuous phylogeographic diffusion model. Analysis of data from five anonymous nuclear loci revealed broadly similar patterns to mtDNA. Secondary admixture was detected between previously isolated refugial populations. In some cases, this is limited to individuals occurring near mitochondrial clade contact zones, but in other cases, more extensive admixture is evident. Overall, our study reveals a complex history of refugial isolation and secondary expansion for puff adders and a mosaic of isolated refugia in southern Africa. We also identify key differences between the processes that drove isolation in B. arietans and those hypothesized for sympatric savannah mammals. PMID:23286376

Barlow, Axel; Baker, Karis; Hendry, Catriona R; Peppin, Lindsay; Phelps, Tony; Tolley, Krystal A; Wüster, Catharine E; Wüster, Wolfgang

2013-02-01

342

Late Pleistocene human occupation of the hyperarid core in the Atacama Desert, northern Chile  

NASA Astrophysics Data System (ADS)

Few archeological sites in South America contain uncontroversial evidence for when the first peopling of the continent occurred. Largely ignored in this debate, extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability. Here, we report on a rare 12-13 ka human occupation from Quebrada Maní (site QM12), a plantless, near rainless landscape (1240 m asl and 85 km from the Pacific Ocean) located in the hyperarid core of the Atacama Desert. This location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central Andes during the latest Pleistocene. Excavations at QM12 yielded a diverse cultural assemblage of lithics, burned and cut bones, marine gastropods, pigments, plant fibers, and wooden artifacts alongside a prepared fireplace. Sixteen radiocarbon dates from site QM12 on charcoal, marine shells, animal dung, plant remains and wood reveal that the occupation took place between 12.8 and 11.7 ka. These results demonstrate that the Atacama Desert was not a barrier to early American settlement and dispersal, and provide new clues for understanding the cultural complexity and diversity of the peopling of South America during the Last Glacial-interglacial transition.

Latorre, Claudio; Santoro, Calogero M.; Ugalde, Paula C.; Gayo, Eugenia M.; Osorio, Daniela; Salas-Egaña, Carolina; De Pol-Holz, Ricardo; Joly, Delphine; Rech, Jason A.

2013-10-01

343

Dating Early and Middle (Reid) Pleistocene Glaciations in Central Yukon by Tephrochronology  

NASA Astrophysics Data System (ADS)

The late Cenozoic deposits of central Yukon contain numerous distal tephra beds, derived from vents in the Wrangell Mountains and Aleutian arc-Alaska Peninsula region. We use a few of these tephra beds to gain a better understanding on the timing of extensive Pleistocene glaciations that affected this area. Exposures at Fort Selkirk show that the Cordilleran Ice Sheet advanced close to the outer limit of glaciation about 1.5 myr ago. At the Midnight Dome Terrace, near Dawson City, exposed outwash gravel, aeolian sand, and loess, related to valley glaciers in the adjacent Ogilvie Mountains, are of the same age. Reid glacial deposits at Ash Bend on the Stewart River are older than oxygen isotope stage (OIS) 6 and likely of OIS 8 age, that is, about 250,000 yr B.P. Supporting evidence for this chronology comes from major peaks in the rates of terrigeneous sediment input into the Gulf of Alaska at 1.5 and 0.25 myr B.P.

Westgate, John A.; Preece, Shari J.; Froese, Duane G.; Walter, Robert C.; Sandhu, Amanjit S.; Schweger, Charles E.

2001-11-01

344

A link between global climate variability in the Pleistocene and variations in the Earth's orbital parameters  

NASA Astrophysics Data System (ADS)

The study demonstrates that the orbital climatic diagram (OCD) built on the basis of the simplified and general concepts of mechanisms for climatic response to orbital forcing can be a reasonable alternative to Milankovitch's and his followers' discrete insolation curves, which are widely used in paleoclimate interpretations. Comparison of the OCD and the oxygen isotope record LR04 indicates a fairly good match (considering the simplicity of the OCD construction and interpretation) in 0-1240 ka. The study discusses some discrepancies in the chronology and structure of the LR04 and OCD. It was shown that climate response may differ from that predicted by orbital insolation forcing on the basis of the generally accepted mechanisms causing transformation of orbital signals. It was shown that a shift from a dominant glacial periodicity of 41 to 100 k.y. (Middle Pleistocene transition) took place at ˜1240 ka. Since then, the 100-k.y. eccentricity cycle has not been interrupted. Therefore, strictly speaking, the revised numbering of marine isotope stages (MIS) should be adopted for the interval of 1240-900 ka to reflect realistic 100-k.y. cycles instead of 41-k.y. cycles, similar to the interval of 900-100 ka.

Bol'shakov, V. A.

2014-09-01

345

3D hydro-mechanically coupled groundwater flow modelling of Pleistocene glaciation effects  

NASA Astrophysics Data System (ADS)

Pleistocene glaciation led to temporal and spatial variations of sub-surface pore fluid pressure. In basins covered by ice sheets, fluid flow and recharge rates are strongly elevated during glaciations as compared to inter-glacial periods. Present-day hydrogeological conditions across formerly glaciated areas are likely to still reflect the impact of glaciations that ended locally more than 10 thousand years before present. 3D hydro-mechanical coupled modelling of glaciation can help to improve the management of groundwater resources in formerly glaciated basins. An open source numerical code for solving linear elasticity, which is based on the finite element method (FEM) in 3D, has been developed. By coupling this code with existing 3D flow codes it is possible to enable hydro-mechanical coupled modelling. Results of two benchmark simulations are compared to existing analytical solutions to demonstrate the performance of the newly developed code. While the result for a fluid-structure coupled case is in reasonable agreement with the analytical model, the result for a classical structure-fluid coupled benchmark showed that the analytical solution only matches the numerical result when the relevant coupling parameter (loading efficiency) is known in advance. This indicates that the applicability of widely applied approaches using an extra term in the groundwater flow equation for vertical stress to simulate hydro-mechanical coupling might have to be re-evaluated. A case study with the commercial groundwater simulator FEFLOW demonstrates the newly developed solution.

Rühaak, Wolfram; Bense, Victor F.; Sass, Ingo

2014-06-01

346

The nature of the Pleistocene-Holocene palaeosols in the Gaza Strip, Palestine  

NASA Astrophysics Data System (ADS)

The Pleistocene to Holocene succession in the Gaza Strip, Palestine, consists of an alternation of calcareous sandstones and reddish fine-grained deposits (palaeosols). The palaeosols can be subdivided into two main groups based on the sand-sized versus clay- to silt-sized grains: (1) the sandy hamra palaeosols, and (2) the loess and loess-derived palaeosols. The hamra palaeosols can, in turn, also be subdivided into two main types according to their colour and grain size: (1) light brown loamy to sandy hamra palaeosols, and (2) dark brown sandy clay hamra palaeosols. The hamra palaeosols are polygenetic and originated in humid environments. Their red colour results from ferric oxides coating the sand grains, but also by illuviation. The various pedogenitic units and their gradual transition to loess palaeosols are due to different phases of dust accretion. Both groups of palaeosols developed during the last glacial. They are considered to represent different climate environments: hamra palaeosols represent humid climates, whereas the loess and loess-derived palaeosols represent dry and semi-dry climates.

Ubeid, Khalid F.

2011-09-01

347

The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe.  

PubMed

Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before--and possibly after--the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities. PMID:23658198

Yeakel, Justin D; Guimarães, Paulo R; Bocherens, Hervé; Koch, Paul L

2013-07-01

348

Hot spots of genetic diversity descended from multiple Pleistocene refugia in an alpine ungulate.  

PubMed

Species that inhabit naturally fragmented environments are expected to be spatially structured and exhibit reduced genetic diversity at the periphery of their range. Patterns of differentiation may also reflect historical processes such as recolonization from glacial refugia. We examined the relative importance of these factors in shaping the spatial patterns of genetic differentiation across the range of an alpine specialist, the North American mountain goat (Oreamnos americanus). Contrary to fossil evidence that suggests a single southern refugium, we detected evidence for additional refugia in northern British Columbia and the Alaskan coast using both mitochondrial and microsatellite DNA. A core area of elevated genetic diversity characterized both regions, and molecular dating suggested a recent Pleistocene split was followed by demographic expansion. Across their range, mountain goats were highly genetically structured and displayed the expected pattern of declining diversity toward the periphery. Gene flow was high within contiguous mountain ranges, but cross-assignments paradoxically suggest that long-distance contemporary dispersal movements are not uncommon. These results improve our understanding of how historical vicariance and contemporary fragmentation influence population differentiation, and have implications for conserving the adaptive potential of alpine populations and habitat. PMID:20731714

Shafer, Aaron B A; Côté, Steeve D; Coltman, David W

2011-01-01

349

Coupled Warming and Drought in the American Southwest During Long mid-Pleistocene Interglacials (MIS 11 and 13)  

NASA Astrophysics Data System (ADS)

An 82-m deep lacustrine sediment core from the Valles Caldera, northern New Mexico reveals details of climate change over two glacial cycles in the middle Pleistocene. Core VC-3, taken from the Valle Grande, has a basal 40Ar/39Ar date of 552 kyr from a tephra associated with the eruption of the South Mountain rhyolite which formed the lake. A variety of proxies including core sedimentology, organic carbon and carbon isotopic ratios, pollen, scanning XRF analysis and a new paleotemperature proxy, MBT (methylated branched tetraether) content of soil bacteria reveal two major warm periods above the basal tephra which we correlate with interglacials MIS 13 and MIS 11. This chronology is corroborated by the identification of two geomagnetic field "events" which are correlated with globally recognized events (14? and 11?). The lacustrine record terminates at ~350 ka when the lake filled its available accommodation space behind the dam of rhyolite lava. MBT temperature estimates show average glacial temperatures in core VC-3 of ~ -4°C, and average interglacial temperatures of ~ +4°C, and the general trends are well corroborated by multiple proxies including pollen and lacustrine organic productivity estimates. A temperature increase of ~9°C occurs during Termination V, the largest glacial termination in the Pleistocene. Multiple proxies from VC-3 show significant structure during the two interglacials present in the core (MIS 13 and 11). Three warm substages (~ 2°C warmer) are recognized within MIS 11 based on organic productivity (Corg, Si/Ti ratios), pollen taxa, elevated charcoal from fires, and the MBT temperature estimates. These warm substages appear to be a strong response to precessional forcing in the SW continental interior even though the amplitude of eccentricity-modulated precession was at a minimum during MIS 11. These results suggest that future climate change in the SW may be characterized by similar natural temperature variability on precessional timescales, superimposed on future anthropogenic warming. Intervals of mudcrack facies representing significant drought conditions occur during or just after the warmest phases of the two interglacials. This past coupling between warm temperatures and extended drought in the SW as a natural feature of long interglacials is consistent with recent predictions of extended Dust-Bowl-like conditions in the SW as a response to global warming.

Fawcett, P. J.; Werne, J.; Anderson, R.; Heikoop, J.; Brown, E.; Hurley, L.; Smith, S.; Berke, M.; Soltow, H.; Goff, F.; Geissman, J.; Woldegabriel, G.; Fessenden, J.; Cisneros-Dozal, M.; Allen, C. D.

2008-12-01

350

Variations in Glacial Erosion over Multiple Glacial-Interglacial Cycles: A Numerical Modelling Approach  

NASA Astrophysics Data System (ADS)

Mountain topography is constructed through a variety of interacting processes. As one of these processes, glacial erosion plays an important role in the development of landscapes by the formation of distinctive topographic features. Glacial landscape evolution models reproduce many observed features at the orogen scale. Detailed comparisons at the scale of individual valleys holds potential for quantifying the influence of glacial physics in glacial erosion models. Over long timescales (>10,000 yr), glacial erosion has typically been simulated using a modified shallow ice approximation (SIA) approach. In this study, we compare the strengths and weaknesses of shallow ice and high-order, Stokes-flow glacial landscape evolution models. Our emphasis is placed on the patterns and rates of glacial erosion over multiple glacial-interglacial cycles. We present a comparison of two different numerical models for glacial erosion. For both approaches, a modified version of the ICE Cascade model is used to develop and evolve topography. This model calculates hillslope and fluvial erosion and sediment transport, isostasy, temporally variable orographic precipitation, and a range of glaciological processes: glacial mass balance, snow avalanching, basal ice superfreezing, and basal water buoyancy feedback in large overdeepenings. Within this framework, we compare the predicted ice-flow field and erosion patterns using a modified SIA as well as predictions from a nested, thermally-coupled, Stokes-flow model calculated using COMSOL Multiphysics. Simulations are conducted for a range of amplitudes and periodicity in surface temperature change between glacial and interglacial periods. We investigate these simulations, as well as the effects of each model for various initial topographies and with a temperature-dependent ice rheology. In general, both models predict visually similar patterns in sliding velocity, and resulting erosion rates, assuming the erosion rate scales with the sliding velocity; however, within different climate scenarios, a few key differences stand out. For one, these results are sensitive to the climate and the ice temperature. In general, for colder climates, the effects of the higher-order model on the erosion rate are less. For warmer climates with more sliding, the higher-order model has a larger impact on the erosion rate and basal shear stress. The instantaneous velocity, and the corresponding erosion rate, can vary by over 50% between the high-order physics model and the modified SIA model. This variation is not independent of the variations in ice covered area and ice thickness, however. As the sliding velocity affects the full flow column of the ice, the ice thickness and extent are also influenced. The higher-order glacial model can lead to variations in total ice-covered area averaging around 5-10%, again with larger differences for warmer ice. Extrapolated over geologic time scales and multiple glaciations these results suggest that consideration of higher-order glacial physics may be necessary, particularly in regions with extensive temperate or polythermal glaciers, when comparing model predictions to observed chronologies of glacial erosion.

Headley, Rachel M.; Ehlers, Todd A.

2013-04-01

351

Post-glacial expansion into the Paleozoic Plateau: evidence of an Ozarkian refugium for the Ozark minnow Notropis nubilus (Teleostei: Cypriniformes).  

PubMed

Genetic variation was examined within the Ozark minnow Notropis nubilus using complete mtDNA cytochrome b gene sequences from 160 individuals representing 30 localities to test hypotheses on the origin of the distribution. Phylogenetic analyses revealed three strongly supported clades of haplotypes consistent with geographic distributions: a clade from the Western Ozarks, a clade from the Southern Ozarks and a clade from the Northern Ozarks and upper Mississippi River basin. The estimated mean ages of these clades indicated that they diverged during pre-Illinoian glacial cycles extending from the late Pliocene into the early Pleistocene. Results of demographic analyses based on coalescent approaches supported the hypothesis that the Paleozoic Plateau was not a refugium for N. nubilus during periodic glacial advances. There is evidence of a genetic signature of northern expansion into the Paleozoic Plateau from a Southern Ozarkian refugium. Populations expanded out of drainages in the Northern Ozarks into the Paleozoic Plateau during the late Pleistocene. Subsequently, the two regions were isolated due to the recent extirpation of intervening populations caused by the loss of suitable habitat. PMID:21039494

Berendzen, P B; Dugan, J F; Gamble, T

2010-10-01

352

Multiple glacial refugia in the North American Arctic: inference from phylogeography of the collared lemming (Dicrostonyx groenlandicus).  

PubMed Central

Cryptic northern refugia beyond the ice limit of the Pleistocene glaciations may have had significant influence on the current pattern of biodiversity in Arctic regions. In order to evaluate whether northern glacial refugia existed in the Canadian Arctic, we examined mitochondrial DNA phylogeography in the northernmost species of rodents, the collared lemming (Dicrostonyx groenlandicus) sampled across its range of distribution in the North American Arctic and Greenland. The division of the collared lemming into the Canadian Arctic and eastern Beringia phylogroups does not support postglacial colonization of the North American Arctic from a single eastern Beringia refugium. Rather, the phylogeographical structure and sparse fossil records indicate that, during the last glaciation, some biologically significant refugia and important sources of postglacial colonization were located to the northwest of the main ice sheet in the Canadian Arctic. PMID:12396480

Fedorov, Vadim B; Stenseth, Nils Chr

2002-01-01

353

Ice flow models and glacial erosion over multiple glacial-interglacial cycles  

NASA Astrophysics Data System (ADS)

Mountain topography is constructed through a variety of interacting processes. Over glaciological time scales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes-flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model has a larger impact on the erosion rate, with variations of almost an order of magnitude. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered that are greater than 30%, again with larger differences for temperate ice. Over multiple glaciations and long-time scales, these results suggest that consideration of higher-order glacial physics may be necessary, particularly in temperate, mountainous settings.

Headley, R. M.; Ehlers, T. A.

2014-06-01

354

New Tooth Enamel Isotopic Data from the West Coast of South Africa and a Comparison of Terrestrial and Marine Records of Plio-Pleistocene Climate Change  

NASA Astrophysics Data System (ADS)

The Plio-Pleistocene transition marks a change in the Earth's climate from relative global warmth to colder temperatures with the initiation of glacial-interglacial cycles. Proxy records from marine cores off SW Africa archive changes in ocean upwelling and terrestrial vegetation that suggest increased aridity across the Plio-Pleistocene transition. Today, the SW African coast has a Winter Rainfall Zone (WRZ) and is dominated by C3 vegetation, which results from the regional high-pressure system and upwelling in the Benguela Current. While marine records provide an integrated perspective on regional responses to global climate change, terrestrial paleoclimate records are needed to assess the effects of these changes in a heterogeneous environment like southern Africa. Archeological and paleontological sites can provide useful proxies of paleoclimate, but many southern African sites are poorly dated or postdate the Plio-Pleistocene transition. Langebaanweg (LBW, ~5 Ma) and Elandsfontein (EFT, ~1.0-0.6 Ma) are sites on the SW coast of South Africa that are rich in fossil mammals and represent landscapes where surface water was more prevalent than it is in today's dry coastal environment. Fossil teeth of large herbivores (e.g. hippopotamids, giraffids, bovids, rhinocerotids, suids and equids) are preserved at both sites and enable isotopic studies of vegetation and climate across the Plio-Pleistocene transition. In this study, carbon and oxygen isotopic data are reported for 100 fossil teeth (11 herbivore taxa) at EFT and are compared to published isotopic data from early Pliocene teeth from LBW for many of the same genera. ?13C values of the EFT tooth enamel range from 13 to 8‰ (VPDB) and ?18O values range from -2 to +3‰ (VPDB). Among the EFT data, there are consistent differences in the distribution of both ?13C and ?18O values among the sampled taxa. When the EFT and LBW isotopic results are compared, ?13C values from the two sites are similar within each taxonomic group. However, ?18O values of the EFT teeth are more than 2‰ higher than ?18O values of LBW teeth for each herbivore family that was sampled. Enamel ?13C values from LBW and EFT indicate herbivore diets that were dominated by C3 vegetation during the Pliocene and Pleistocene. Mesowear studies of teeth suggest that the West Coast of South Africa was a forested environment with seasonal grasses during the Pliocene but that it supported trees, fynbos and grasses in the mid-Pleistocene. The isotopic indications of C3 diets among grazers from both sites suggest that a WRZ must have existed across the Plio-Pleistocene transition. The positive shift in ?18O values of fossil tooth enamel between the early Pliocene and the mid-Pleistocene on the West Coast of South Africa might suggest a change in the oxygen isotopic composition of rainfall and a decrease in the amount of rainfall across the Plio-Pleistocene transition. Excluding diagenesis, these conclusions are consistent with marine records. This study indicates the potential for using the stable isotope records from fossil teeth from the West Coast of South Africa to evaluate how the intensification of the Benguela Upwelling System, which is well documented in the marine records, affected terrestrial ecosystems across the Plio-Pleistocene transition.

Lehmann, S. B.; Levin, N. E.; Stynder, D. D.; Bishop, L. C.; Forrest, F.; Braun, D. R.

2012-12-01

355

Pleistocene seismic sequences may result from eustatic change but can they be used for global correlations? New Insights from the Canterbury Basin, New Zealand  

NASA Astrophysics Data System (ADS)

To understand the influence of eustasy on continental margin sedimentation and test the concepts of sequence stratigraphy, Integrated Ocean Drilling Program Expedition 317 drilled four sites on the continental shelf and upper slope of the Canterbury Basin, eastern South Island, New Zealand. We present results from upper slope Site U1352 (320 m water depth). A high-resolution multiproxy approach involving geochemical elemental analyses, lithostratigraphy and biostratigraphy, calibrated to an oxygen isotope scale, was applied to understand sedimentation over the past ~1.8 million years. Multichannel seismic data (EW00-01 survey) provided a seismic sequence stratigraphic framework against which to interpret the data. Seismic sequence boundaries are represented by a unique geochemical signature and arrangement of overlying sedimentary facies. However, several such geochemical-lithologic units are commonly contained within each seismic sequence. These higher frequency, intrasequence geochemical units generally correlate with100 ky glacial-interglacial Milankovic variability in the late Pleistocene, revealing that it took several glacio-eustatic cycles to build each seismic sequence. These findings support prior results obtained from Pleistocene sediments recovered by Ocean Drilling Program Leg 174A that drilled on the New Jersey margin with similar objectives to those of Expedition 317. In both northern and southern hemisphere siliciclastic settings there is a strong correlation between seismic sequences and glacio-eustasy, but the correlation between isotopic cycles and sequence boundaries is not one-to-one: only a subset of the glacioeustatic cycles result in a preserved seismic sequence boundary. Furthermore, late Pleistocene sequence boundaries on the two margins are not synchronous. Local conditions cause different isotopic peaks to be preferentially preserved as sequence boundaries in each location and preserved seismic sequences contain different groupings of marine isotope stages. Therefore, high-frequency Pleistocene seismic sequences may not correlate globally even though they are driven by glacio-eustasy.

McHugh, C. M.; Fulthorpe, C.; Hoyanagi, K.; Blum, P.

2013-12-01

356

Late Glacial-Holocene climatic transition record at the Argentinian Andean piedmont between 33-34° S  

NASA Astrophysics Data System (ADS)

The Arroyo La Estacada (~33°28' S, 69°02' W), eastern Andean piedmont of Argentina, cuts through an extensive piedmont aggradational unit composed of a dominant late Pleistocene-early Holocene (LP-EH) alluvial sequence including several paleosols. The arroyo sedimentary record exhibits a paleosol developed affecting the topmost part of likely Lateglacial aeolian deposits aggraded into a floodplain environment by the end of the late Pleistocene. The paleosol shows variable grade of development in the outcrops along the arroyo probably in relation to fluvial valley paleotopography. Organic matter humification, carbonate accumulation and redox processes were the dominant processes associated with paleosol formation. By the early Holocene, when the formation of the paleosol ended, alluvial aggradation renewed and a higher frequency of flooding events could have affected the arroyo's floodplain environment. A period of relative landscape stability in the Arroyo La Estacada basin is inferred from the paleosol developed by the LP-EH transition in response to a climatic amelioration in the Andes cordillera piedmont after the Late Glacial arid conditions. The renewal of early Holocene alluvial aggradation was probably influenced by the South American Monsoon and resulted in a change in the sedimentary dynamics of the arroyo. The analyzed Late Glacial-Holocene alluvial record of the Andean piedmont constitutes a suitable record of the LP-EH climatic transition at the extra Andean region of Argentina. It is in agreement with regional paleoclimatic evidence along the southern tip of the South American continent, where other sedimentary sequences record similar late Quaternary paleoenvironmental changes over both fluvial and interfluvial areas.

Mehl, A. E.; Zárate, M. A.

2013-10-01

357

Palaeoflood estimates of Pleistocene coarse grained river terrace landforms (Río Almanzora, SE Spain)  

NASA Astrophysics Data System (ADS)

A series of palaeoflood estimation techniques are applied to an inset sequence of Middle to Late Pleistocene river terrace landforms associated with the Río Almanzora, SE Spain. The study area is a 7 km-long transverse reach, where 4 terrace levels (Level 1 = highest and oldest, Level 4 = lowest and youngest) document some 200 m of incision across an uplifted basement block during the Pleistocene. For the broader region, river terrace aggradation is attributed to increased sediment supply during glacial to interglacial transitions (Level 1 = Marine oxygen isotope stages [MOIS] 12/11, L2 = 10/9, L3 = 8/7 and L4 = 6/5). Within the transverse reach, terrace Levels 2, 3 and 4 are characterised by coarse boulder-rich gravels (Dmax = 2.5 m) organised into 3-5 m-high cross-beds. Level 4 is characterised by a series of km-scale abandoned meander loops, with Levels 2 and 3 showing evidence for similar degraded high sinuosity forms. The fluvial setting is interpreted as a braided river environment, with lateral and longitudinal gravel barforms. Using field-derived sedimentary (boulder size etc) and morphological (width, slope etc) features, flow competence- and regime-based methods were applied. Palaeoflood estimates varied from 40 to 2859 m3/s, with mean maximum discharges showing an increase through time (L2 = 278, L3 = 413, L4 = 1361 m3/s). Palaeoflood estimates were compared to flood events associated with the ephemeral modern Río Almanzora (catchment = 2500 km2) to establish whether palaeoflood values were reasonable estimations. A 46-year (1963-2009) modern flood gauge record shows infrequent flood events with discharges typically < 40 m3/s. A rare flood event in 1973 (5680 m3/s) provides an upper value for comparison with the palaeoflood estimates. Although estimates appear reasonable they should be considered as minimum values due to 1) some disparities between flow depths derived from the palaeoflood equations (0.7-4 m) and field-based evidence (3-5 m-high cross-beds); 2) issues related to field sampling of boulders from sections, and 3) uncerta