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Sample records for late glacial terrestrial

  1. Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages

    USGS Publications Warehouse

    Thompson, W.B.; Griggs, C.B.; Miller, N.G.; Nelson, R.E.; Weddle, T.K.; Kilian, T.M.

    2011-01-01

    Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907??31 to 11,650??5014C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520+95/??20calyr BP. Ages of shells juxtaposed with the logs are 12,850??6514C yr BP (Mytilus edulis) and 12,800??5514C yr BP (Balanus sp.), indicating a marine reservoir age of about 1000yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England. ?? 2011 University of Washington.

  2. Paleoecology of late-glacial terrestrial deposits with in situ conifers from the submerged continental shelf of western canada

    NASA Astrophysics Data System (ADS)

    Lacourse, Terri; Mathewes, Rolf W.; Fedje, Daryl W.

    2003-09-01

    Extensive portions of the continental shelf off the coast of British Columbia were subaerially exposed during Late Wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m. Paleoecological analyses were conducted at two sites on the emergent continental shelf where terrestrial surfaces with in situ conifers are preserved. The woody plant remains confirm that, during the latest period of subaerial exposure, terrestrial vegetation was established on the continental shelf. Microscopic identification of fossil wood, and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive Pinus contorta-dominated communities with abundant Alnus crispa and ferns grew on the shelf adjacent to and on the Queen Charlotte Islands around 12,200 14C yr B.P. Dwarf shrubs including Salix and Empetrum, and herbaceous plants such as Heracleum lanatum and Hippuris vulgaris, were also important components of the shelf vegetation. Near northern Vancouver Island, mixed coniferous forests dominated by Pinus contorta with Picea, Tsuga spp., Alnus spp., and ferns occupied the shelf at 10,500 14C yr B.P.

  3. Climate, pCO2 and terrestrial carbon cycle linkages during late Palaeozoic glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Montañez, Isabel P.; McElwain, Jennifer C.; Poulsen, Christopher J.; White, Joseph D.; Dimichele, William A.; Wilson, Jonathan P.; Griggs, Galen; Hren, Michael T.

    2016-11-01

    Earth's last icehouse, 300 million years ago, is considered the longest-lived and most acute of the past half-billion years, characterized by expansive continental ice sheets and possibly tropical low-elevation glaciation. This atypical climate has long been attributed to anomalous radiative forcing promoted by a 3% lower incident solar luminosity and sustained low atmospheric pCO2 (<=300 ppm). Climate models, however, indicate a CO2 sensitivity of ice-sheet distribution and sea-level response that questions this long-standing climate paradigm by revealing major discrepancy between hypothesized ice distribution, pCO2, and geologic records of glacioeustasy. Here we present a high-resolution record of atmospheric pCO2 for 16 million years of the late Palaeozoic, developed using soil carbonate-based and fossil leaf-based proxies, that resolves the climate conundrum. Palaeo-fluctuations on the 105-yr scale occur within the CO2 range predicted for anthropogenic change and co-vary with substantial change in sea level and ice volume. We further document coincidence between pCO2 changes and repeated restructuring of Euramerican tropical forests that, in conjunction with modelled vegetation shifts, indicate a more dynamic carbon sequestration history than previously considered and a major role for terrestrial vegetation-CO2 feedbacks in driving eccentricity-scale climate cycles of the late Palaeozoic icehouse.

  4. Numerical modeling of late Glacial Laurentide advance of ice across Hudson Strait: Insights into terrestrial and marine geology, mass balance, and calving flux

    USGS Publications Warehouse

    Pfeffer, W.T.; Dyurgerov, M.; Kaplan, M.; Dwyer, J.; Sassolas, C.; Jennings, A.; Raup, B.; Manley, W.

    1997-01-01

    A time-dependent finite element model was used to reconstruct the advance of ice from a late Glacial dome on northern Quebec/Labrador across Hudson Strait to Meta Incognita Peninsula (Baffin Island) and subsequently to the 9.9-9.6 ka 14C Gold Cove position on Hall Peninsula. Terrestrial geological and geophysical information from Quebec and Labrador was used to constrain initial and boundary conditions, and the model results are compared with terrestrial geological information from Baffin Island and considered in the context of the marine event DC-0 and the Younger Dryas cooling. We conclude that advance across Hudson Strait from Ungava Bay to Baffin Island is possible using realistic glacier physics under a variety of reasonable boundary conditions. Production of ice flux from a dome centered on northeastern Quebec and Labrador sufficient to deliver geologically inferred ice thickness at Gold Cove (Hall Peninsula) appears to require extensive penetration of sliding south from Ungava Bay. The discharge of ice into the ocean associated with advance and retreat across Hudson Strait does not peak at a time coincident with the start of the Younger Dryas and is less than minimum values proposed to influence North Atlantic thermohaline circulation; nevertheless, a significant fraction of freshwater input to the North Atlantic may have been provided abruptly and at a critical time by this event.

  5. Late Glacial and Late Holocene Paleohydrology of Central Asia

    NASA Astrophysics Data System (ADS)

    Aichner, B.; Feakins, S. J.; Mischke, S.; Herzschuh, U.; Liu, X.; Rajabov, I.; Wang, Y.; Heinecke, L.

    2013-12-01

    The goal of this study is to deepen the understanding of past climatological, ecological and hydrological changes in Central Asia, by means of organic geochemical proxies and in close cooperation with other work groups providing biological and sedimentological data. We analysed an 8 m sediment core from Lake Karakuli, a small open freshwater lake situated at an altitude of 3,657 m between the massifs of Muztagh Ata (7,546 m) and Kongur Shan (7,719 m) in western China. Additional work is in progress on a 12 m core derived from Lake Karakul in Tajikistan, a large closed saline lake situated in a tectonic graben structure at an altitude of 3,928 m. The distance between the two lakes is 130 km and basal ages of the cores are ca. 4.7 ka BP (China) and ca. 27 ka BP (Tajikistan). The lake catchments may be classified as alpine steppe to alpine deserts with mean annual temperature of ca. 0 °C and mean annual precipitation of ca. 100 mm, respectively. Summer precipitation, associated with the Indian monsoon, accounts for <30% of the annual total, whereas most precipitation is supplied by mid-latitude Westerlies between March and May. In the small Chinese lake long-chain fatty acids (FAs) were mainly attributed to terrestrial sources by compound-specific carbon isotopic analyses. In contrast δ13C values up to -14‰ for abundant mid-chain FAs suggest aquatic origins in the large Lake Karakul. Hydrogen isotopic variability is ca. 15‰ in the mid-Holocene record and ca. 60‰ in the first data derived from the Late Glacial record. In the latter, the most pronounced change from higher to lower δD-values of aquatic biomarkers is tentatively interpreted as change from arid to more humid conditions at the Late Glacial to Holocene transition. Since in Central Asia isotopic variability of precipitation mainly correlates with temperature, we interpret high resolution δD data of terrestrial long-chain FAs in the younger core to mainly reflect mid-Holocene temperature variations

  6. Late glacial aridity in southern Rocky Mountains

    SciTech Connect

    Davis, O.K.; Pitblado, B.L.

    1995-09-01

    While the slopes of the present-day Colorado Rocky Mountains are characterized by large stands of subalpine and montane conifers, the Rockies of the late glacial looked dramatically different. Specifically, pollen records suggest that during the late glacial, Artemisia and Gramineae predominated throughout the mountains of Colorado. At some point between 11,000 and 10,000 B.P., however, both Artemisia and grasses underwent a dramatic decline, which can be identified in virtually every pollen diagram produced for Colorado mountain sites, including Como Lake (Sangre de Cristo Mountains), Copley Lake and Splains; Gulch (near Crested Butte), Molas Lake (San Juan Mountains), and Redrock Lake (Boulder County). Moreover, the same pattern seems to hold for pollen spectra derived for areas adjacent to Colorado, including at sites in the Chuska Mountains of New Mexico and in eastern Wyoming. The implications of this consistent finding are compelling. The closest modem analogues to the Artemisia- and Gramineae-dominated late-glacial Colorado Rockies are found in the relatively arid northern Great Basin, which suggests that annual precipitation was much lower in the late-glacial southern Rocky Mountains than it was throughout the Holocene.

  7. Glacial onset predated Late Ordovician climate cooling

    NASA Astrophysics Data System (ADS)

    Pohl, Alexandre; Donnadieu, Yannick; Le Hir, Guillaume; Ladant, Jean-Baptiste; Dumas, Christophe; Alvarez-Solas, Jorge; Vandenbroucke, Thijs R. A.

    2016-06-01

    The Ordovician glaciation represents the acme of one of only three major icehouse periods in Earth's Phanerozoic history and is notorious for setting the scene for one of the "big five" mass extinction events. Nevertheless, the mechanisms that drove ice sheet growth remain poorly understood and the final extent of the ice sheet crudely constrained. Here using an Earth system model with an innovative coupling method between ocean, atmosphere, and land ice accounting for climate and ice sheet feedback processes, we report simulations portraying for the first time the detailed evolution of the Ordovician ice sheet. We show that the emergence of the ice sheet happened in two discrete phases. In a counterintuitive sequence of events, the continental ice sheet appeared suddenly in a warm climate. Only during the second act, and set against a background of decreasing atmospheric CO2, followed steeply dropping temperatures and extending sea ice. The comparison with abundant sedimentological, geochemical, and micropaleontological data suggests that glacial onset may have occurred as early as the Middle Ordovician Darriwilian, in agreement with recent studies reporting third-order glacioeustatic cycles during the same period. The second step in ice sheet growth, typified by a sudden drop in tropical sea surface temperatures by ˜8°C and the further extension of a single, continental-scale ice sheet over Gondwana, marked the onset of the Hirnantian glacial maximum. By suggesting the presence of an ice sheet over Gondwana throughout most of the Middle and Late Ordovician, our models embrace the emerging paradigm of an "early Paleozoic Ice Age."

  8. Rates of change and chronolgical problems during the late-glacial period

    SciTech Connect

    Lotter, A.F.; Sturm, M.; Ammann, B.

    1992-01-01

    Results of high-resolution AMS {sup 14}C dating of terrestrial plant macrofossils from late-glacial and early-Holocene lake deposits in Switzerland show three periods with constant radiocarbon ages. These plateaux of constant age occur at 12700, 10000, and 9500 y BP. A comparison of this radiocarbon chronology with a varve chronology documents discrepancies between the sidereal and the radiocarbon time-scale for the late-glacial period. The age-plateaux and the time-scale discrepancies have a significant impact on the estimation of rates of change during this period; estimates of rates of change can be very misleading if calculated on the basis of radiocarbon ages. This is illustrated by an example of estimated rates of late-glacial and early Holocene palynological change in Switzerland. 33 refs., 6 figs.

  9. Terrestrial glacial eskers: Analogs for Martian sinuous ridges

    NASA Technical Reports Server (NTRS)

    Kargel, Jeffrey S.; Strom, Roger G.

    1991-01-01

    A glacial model was introduced last year for the Argyre region, a concept which is now extended, and which was recently integrated with a Global Hydrologic Model incorporating many other aspects of Martian geology. Despite wide agreement that the Martian ridges strongly resemble glacial eskers, this hypothesis has been presented with great equivocation due to a perceived lack of other glacial landforms. Quite to the contrary, it is shown that the Martian ridges actually do occur in logical ordered sequences with many other types of characteristically glacial appearing landforms. Herein, the esker hypothesis is further supported in isolation from considerations of regional landform assemblages. It is concluded that Martian sinuous ridges are similar in every respect to terrestrial eskers: scale, morphology, planimetric pattern, and associations with other probable glaciogenic landforms. It is found that the esker hypothesis is well supported. Eskers are glaciofluvial structures, and owe their existence to large scale melting of stagnant temporate glaciers. Thus, eskers are indicators of an ameliorating climatic regime after a protracted episode of cold, humid conditions.

  10. Relative timing of last glacial maximum and late-glacial events in the central tropical Andes

    NASA Astrophysics Data System (ADS)

    Bromley, Gordon R. M.; Schaefer, Joerg M.; Winckler, Gisela; Hall, Brenda L.; Todd, Claire E.; Rademaker, Kurt M.

    2009-11-01

    Whether or not tropical climate fluctuated in synchrony with global events during the Late Pleistocene is a key problem in climate research. However, the timing of past climate changes in the tropics remains controversial, with a number of recent studies reporting that tropical ice age climate is out of phase with global events. Here, we present geomorphic evidence and an in-situ cosmogenic 3He surface-exposure chronology from Nevado Coropuna, southern Peru, showing that glaciers underwent at least two significant advances during the Late Pleistocene prior to Holocene warming. Comparison of our glacial-geomorphic map at Nevado Coropuna to mid-latitude reconstructions yields a striking similarity between Last Glacial Maximum (LGM) and Late-Glacial sequences in tropical and temperate regions. Exposure ages constraining the maximum and end of the older advance at Nevado Coropuna range between 24.5 and 25.3 ka, and between 16.7 and 21.1 ka, respectively, depending on the cosmogenic production rate scaling model used. Similarly, the mean age of the younger event ranges from 10 to 13 ka. This implies that (1) the LGM and the onset of deglaciation in southern Peru occurred no earlier than at higher latitudes and (2) that a significant Late-Glacial event occurred, most likely prior to the Holocene, coherent with the glacial record from mid and high latitudes. The time elapsed between the end of the LGM and the Late-Glacial event at Nevado Coropuna is independent of scaling model and matches the period between the LGM termination and Late-Glacial reversal in classic mid-latitude records, suggesting that these events in both tropical and temperate regions were in phase.

  11. Late-Glacial to Late-holocene Shifts in Global Precipitation Delta(sup 18)O

    NASA Technical Reports Server (NTRS)

    Jasechko, S.; Lechler, A.; Pausata, F.S.R.; Fawcett, P.J.; Gleeson, T.; Cendon, D.I.; Galewsky, J.; LeGrande, A. N.; Risi, C.; Sharp, Z. D.; Welker, J. M.; Werner, M.; Yoshimura, K.

    2015-01-01

    Reconstructions of Quaternary climate are often based on the isotopic content of paleo-precipitation preserved in proxy records. While many paleo-precipitation isotope records are available, few studies have synthesized these dispersed records to explore spatial patterns of late-glacial precipitation delta(sup 18)O. Here we present a synthesis of 86 globally distributed groundwater (n 59), cave calcite (n 15) and ice core (n 12) isotope records spanning the late-glacial (defined as 50,000 to 20,000 years ago) to the late-Holocene (within the past 5000 years). We show that precipitation delta(sup 18)O changes from the late-glacial to the late-Holocene range from -7.1% (delta(sup 18)O(late-Holocene) > delta(sup 18)O(late-glacial) to +1.7% (delta(sup 18)O(late-glacial) > delta(sup 18)O(late-Holocene), with the majority (77) of records having lower late-glacial delta(sup 18)O than late-Holocene delta(sup 18)O values. High-magnitude, negative precipitation delta(sup 18)O shifts are common at high latitudes, high altitudes and continental interiors.

  12. Late Glacial ice advances in southeast Tibet

    NASA Astrophysics Data System (ADS)

    Strasky, Stefan; Graf, Angela A.; Zhao, Zhizhong; Kubik, Peter W.; Baur, Heinrich; Schlüchter, Christian; Wieler, Rainer

    2009-03-01

    The sensitivity of Tibetan glacial systems to North Atlantic climate forcing is a major issue in palaeoclimatology. In this study, we present surface exposure ages of erratic boulders from a valley system in the Hengduan Mountains, southeastern Tibet, showing evidence of an ice advance during Heinrich event 1. Cosmogenic nuclide analyses ( 10Be and 21Ne) revealed consistent exposure ages, indicating no major periods of burial or pre-exposure. Erosion-corrected (3 mm/ka) 10Be exposure ages range from 13.4 to 16.3 ka. This is in agreement with recalculated exposure ages from the same valley system by [Tschudi, S., Schäfer, J.M., Zhao, Z., Wu, X., Ivy-Ochs, S., Kubik, P.W., Schlüchter, C., 2003. Glacial advances in Tibet during the Younger Dryas? Evidence from cosmogenic 10Be, 26Al, and 21Ne. Journal of Asian Earth Sciences 22, 301-306.]. Thus this indicates that local glaciers advanced in the investigated area as a response to Heinrich event 1 cooling and that periglacial surface adjustments during the Younger Dryas overprinted the glacial morphology, leading to deceptively young exposure ages of certain erratic boulders.

  13. Interhemispheric Correlation of Late Pleistocene Glacial Events

    NASA Astrophysics Data System (ADS)

    Lowell, T. V.; Heusser, C. J.; Andersen, B. G.; Moreno, P. I.; Hauser, A.; Heusser, L. E.; Schluchter, C.; Marchant, D. R.; Denton, G. H.

    1995-09-01

    A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and >=33,500 carbon-14 years before present (14C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000 14C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720 14C yr B.P., and at the beginning of the Younger Dryas at 11,050 14C yr B.P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges.

  14. Interhemispheric correlation of late pleistocene glacial events

    SciTech Connect

    Lowell, T.V.; Heusser, C.J.; Andersen, B.G.

    1995-09-15

    A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and {ge}33,500 carbon-14 years before present ({sup 14}C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000 {sup 14}C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720 {sup 14}C yr B.P., and at the beginning of the Younger Dryas at 11,050 {sup 14}C yr B.P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges. 51 refs., 3 figs., 1 tab.

  15. Obliquity pacing of the late Pleistocene glacial terminations.

    PubMed

    Huybers, Peter; Wunsch, Carl

    2005-03-24

    The 100,000-year timescale in the glacial/interglacial cycles of the late Pleistocene epoch (the past approximately 700,000 years) is commonly attributed to control by variations in the Earth's orbit. This hypothesis has inspired models that depend on the Earth's obliquity (approximately 40,000 yr; approximately 40 kyr), orbital eccentricity (approximately 100 kyr) and precessional (approximately 20 kyr) fluctuations, with the emphasis usually on eccentricity and precessional forcing. According to a contrasting hypothesis, the glacial cycles arise primarily because of random internal climate variability. Taking these two perspectives together, there are currently more than thirty different models of the seven late-Pleistocene glacial cycles. Here we present a statistical test of the orbital forcing hypothesis, focusing on the rapid deglaciation events known as terminations. According to our analysis, the null hypothesis that glacial terminations are independent of obliquity can be rejected at the 5% significance level, whereas the corresponding null hypotheses for eccentricity and precession cannot be rejected. The simplest inference consistent with the test results is that the ice sheets terminated every second or third obliquity cycle at times of high obliquity, similar to the original proposal by Milankovitch. We also present simple stochastic and deterministic models that describe the timing of the late-Pleistocene glacial terminations purely in terms of obliquity forcing.

  16. Tropical ocean-atmospheric forcing of Late Glacial and Holocene glacier fluctuations in the Cordillera Blanca, Peru

    NASA Astrophysics Data System (ADS)

    Stansell, Nathan D.; Licciardi, Joseph M.; Rodbell, Donald T.; Mark, Bryan G.

    2017-05-01

    Evaluating the timing and style of past glacier fluctuations in the tropical Andes is important for our scientific understanding of global environmental change. Terrestrial cosmogenic nuclide ages on moraine boulders combined with 14C-dated clastic sediment records from alpine lakes document glacial variability in the Cordillera Blanca of Peru during the last 16 ka. Late Glacial ice extents culminated at the start of the Antarctic Cold Reversal and began retracting prior to the Younger Dryas. Multiple moraine crests dating to the early Holocene mark brief readvances or stillstands that punctuated overall retreat of the Queshque Valley glacier terminus during this interval. Glaciers were less extensive during the middle Holocene before readvancing during the latest Holocene. These records suggest that tropical Atlantic and Pacific ocean-atmospheric processes exerted temporally variable forcing of Late Glacial and Holocene glacial changes in the Peruvian Andes.

  17. Late Pleistocene glacial fluctuations in Cordillera Oriental, subtropical Andes

    NASA Astrophysics Data System (ADS)

    Martini, Mateo A.; Kaplan, Michael R.; Strelin, Jorge A.; Astini, Ricardo A.; Schaefer, Joerg M.; Caffee, Marc W.; Schwartz, Roseanne

    2017-09-01

    The behavior of subtropical glaciers during Middle to Late Pleistocene global glacial maxima and abrupt climate change events, specifically in Earth's most arid low-latitude regions, remains an outstanding problem in paleoclimatology. The present-day climate of Cordillera Oriental, in arid northwestern Argentina, is influenced by shifts in subtropical climate systems, including the South American Summer Monsoon. To understand better past glacier-subtropical climates during the global Last Glacial Maximum (LGM, 26.5-19 ka) and other time periods, we combined geomorphic features with forty-two precise 10Be ages on moraine boulders and reconstructed paleo-equilibrium line altitudes (ELA) at Nevado de Chañi (24°S) in the arid subtropical Andes. We found a major glacial expansion at ∼23 ± 1.6 ka, that is, during the global LGM. Additional glacial expansions are observed before the global LGM (at ∼52-39 ka), and after, at 15 ± 0.5 and 12 ± 0.6 ka. The ∼15 ka glacial event was found on both sides of Chañi and the ∼12 ka event is only recorded on the east side. Reconstructed ELAs of the former glaciers exhibit a rise from east to west that resembles the present subtropical climate trajectory from the Atlantic side of the continent; hence, we infer that this climate pattern must have been present in the past. Based on comparison with other low-latitude paleoclimate records, such as those from lakes and caves, we infer that both temperature and precipitation influenced past glacial occurrence in this sector of the arid Andes. Our findings also imply that abrupt deglacial climate events associated with the North Atlantic, specifically curtailed meridional overturning circulation and regional cooling, may have had attendant impacts on low subtropical Southern Hemisphere latitudes, including the climate systems that affect glacial activity around Nevado de Chañi.

  18. Late glacial and holocene landscapes of central Beringia

    NASA Astrophysics Data System (ADS)

    Lozhkin, Anatoly V.; Anderson, Patricia; Eisner, Wendy R.; Solomatkina, Tatiana B.

    2011-11-01

    New palynological and sedimentological data from St. Lawrence Island present a rare view into late-glacial and Holocene environments of the central Bering Land Bridge. The late glaciation was a time of dynamic landscape changes in south-central Beringia, with active thermokarst processes, including the formation and drainage of thaw lakes. The presence of such a wet, unstable substrate, if widespread, probably would have had an adverse impact on food sources and mobility for many of the large mammal populations. The establishment of Betula shrub tundra on the island suggests late-glacial summers that were warmer than present, consistent with regional paleoclimatic interpretations. However, the increasing proximity to the Bering Sea, as postglacial sea levels rose, modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of Beringia at this time. The mid- to late Holocene is marked by more stable land surfaces and development of Sphagnum and Cyperaceae peat deposits. The accumulation of organic deposits, decline of shrub Betula, and decrease in thermokarst disturbance suggest that conditions were cooler than the previous. A recent decline in peat accumulation at the study sites may relate to local geomorphology, but similar decreases have been noted for other arctic regions.

  19. Re-assessment of the mid to late Quaternary glacial and environmental history of the Boco Plain, western Tasmania.

    NASA Astrophysics Data System (ADS)

    Augustinus, Paul; Fink, David; Fletcher, Michael-Shawn; Thomas, Ian

    2017-03-01

    The glacial geomorphology and drill core-based stratigraphy of the Boco Plain, western Tasmania, reveal a complex sequence of Quaternary glacial and non-glacial episodes. The upper part of the southern Boco Plain stratigraphy was previously dated by 14C and U-series on interbedded organics of MIS 1 to MIS 5 affinity. U-series dating of ferricretes associated with glacial diamictons from Boco Plain cores suggested that there were glacial advances broadly correlative with MIS 6, 8 and ≥10. However, terrestrial cosmogenic nuclide (10Be and 26Al) exposure ages for the moraine sequence preserved on the wider Boco Plain area indicate that moraines previously attributed to MIS 6 and 8 advances were deposited during MIS 10 or earlier cold stages. There is no evidence for MIS 2, 4 or 6 affinity glacial advances onto the Boco Plain with ice of this age restricted to the West Coast Range. New palynological records from the Boco Plain core 6690 confirmed the late Quaternary ages of the upper part of the sequence, whilst extinct palynomorphs indicate a pre-Quaternary age for the glacial diamictons at the base of core Boco 4 and 10. Consequently, the mid-Pleistocene glacial sequence preserved in the Boco Plain is significantly older than previously envisaged, with the post MIS 10 to 12 geomorphology of the plain dominated by fluvial deltaic, swamp peat and lacustrine environments.

  20. Late veneer and late accretion to the terrestrial planets

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Mojzsis, S. J.; Werner, S. C.; Matsumura, S.; Ida, S.

    2016-12-01

    It is generally accepted that silicate-metal ('rocky') planet formation relies on coagulation from a mixture of sub-Mars sized planetary embryos and (smaller) planetesimals that dynamically emerge from the evolving circum-solar disc in the first few million years of our Solar System. Once the planets have, for the most part, assembled after a giant impact phase, they continue to be bombarded by a multitude of planetesimals left over from accretion. Here we place limits on the mass and evolution of these planetesimals based on constraints from the highly siderophile element (HSE) budget of the Moon. Outcomes from a combination of N-body and Monte Carlo simulations of planet formation lead us to four key conclusions about the nature of this early epoch. First, matching the terrestrial to lunar HSE ratio requires either that the late veneer on Earth consisted of a single lunar-size impactor striking the Earth before 4.45 Ga, or that it originated from the impact that created the Moon. An added complication is that analysis of lunar samples indicates the Moon does not preserve convincing evidence for a late veneer like Earth. Second, the expected chondritic veneer component on Mars is 0.06 weight percent. Third, the flux of terrestrial impactors must have been low (≲10-6 M⊕ Myr-1) to avoid wholesale melting of Earth's crust after 4.4 Ga, and to simultaneously match the number of observed lunar basins. This conclusion leads to an Hadean eon which is more clement than assumed previously. Last, after the terrestrial planets had fully formed, the mass in remnant planetesimals was ∼10-3 M⊕, lower by at least an order of magnitude than most previous models suggest. Our dynamically and geochemically self-consistent scenario requires that future N-body simulations of rocky planet formation either directly incorporate collisional grinding or rely on pebble accretion.

  1. Reconstruction of Hydrologic Variability at Lake Elsinore, California, During the Late-Glacial to Holocene Transition

    NASA Astrophysics Data System (ADS)

    Fantozzi, J. M.; Bonuso, N.; Kirby, M. E.; Zimmerman, S. R.; Hiner, C.

    2011-12-01

    A multi-proxy sedimentological study was completed on a section of a sediment core from Lake Elsinore, California, that spans the late-Glacial to Holocene transition (17,619-9,587 calendar years before present [cy BP]). The results of the study provide the first high resolution terrestrial climate record from Southern California that spans this interesting interval in Earth's climate history. The sedimentological observations and proxy results indicate that the depositional and climatic environments of Lake Elsinore changed significantly across the late-Glacial to Holocene transition. Interpretation of the results suggests that the lake was relatively deep during the last glacial period, but then became relatively shallow and less stable near the beginning of the Holocene interglacial. Interpretation of the results also suggests that the Lake Elsinore deglaciation sequence was characterized by two step-wise decreases in precipitation. Here, this two step drying trend is explained by changes in the extent of the North American ice sheet and variations in the intensity of the Atlantic Meridional Overturning Circulation. Together, the latter two forcings acted to modulate the average position of the circumpolar jet stream, the mean latitude of the Intertropical Convergence Zone, and their combined impacts on the Northern Hemisphere winter storm tracks, which determine the annual hydrologic budget of Southern California. A comparison of the Lake Elsinore deglaciation sequence with other regional paleoclimate records shows strong evidence for synchronous hydrologic change between study sites throughout southwestern North America. Additionally, a comparison of the Lake Elsinore record with the Greenland ice core record provides evidence for a coupling between changes in climate over the North Atlantic and Southern California during the late-Glacial to Holocene transition.

  2. Climatic Instability and Regional Glacial Advances in the Late Ediacaran

    NASA Astrophysics Data System (ADS)

    Hannah, J. L.; Stein, H. J.; Marolf, N.; Bingen, B.

    2014-12-01

    The Ediacaran Period closed out the environmentally raucous Neoproterozoic Era with the last of multiple glacial events and the first ephemeral glimmer of multicellular life. As such, evolution of Earth's biosphere and the marine environments that nurtured this nascent biota are of particular interest. Because the Ediacaran biota appear in the stratigraphic record just above tillites in many localities, inferences are naturally drawn to link glaciation to bioevolution. Here we review known controls on the timing and extent of the late Ediacaran Gaskier and Varanger glacial events, bolstered by new constraints on the Moelv tillite of South Norway. The elusive mid-Ediacaran glacial strata are poorly dated, patchy in distribution, and relatively limited in thickness. The type Gaskier glaciogenic units in Newfoundland are 582 to 584 Ma, based on U-Pb zircon ages from intercalated ash beds [1]. The Varanger glaciogenic deposits in northern Norway, in contrast, remain only roughly constrained to ca. 630 to 560 Ma. Post-Gaskier negative carbon isotope excursions (CIEs) have been reported from multiple localities in both China and SW United States, suggesting climatic instability in the late Ediacaran. Although most localities lack solid geochronology, paleontologic constraints place the Hongtiegou glacial diamictite and accompanying CIE in the Chaidam Basin, NW China, in the latest Ediacaran, ca. 555 Ma [2]. We previously suggested that the Moelv tillite in south Norway was roughly equivalent to the Gaskier, based on an imprecise Re-Os age of ~560 Ma [3] for the underlying Biri shale. Reanalysis of these data shows that the upper part of the shale section was disturbed by a redox front during the Caledonian orogeny. The undisturbed lower part of the section yields a more precise Model 1 isochron age of 559.5 ± 6.2 Ma, clearly post-dating the Gaskier event well outside analytical uncertainty. These new results bolster arguments that the Gaskier glaciation was not a global

  3. Late-glacial and Holocene fluctuations at Monte Fitz Roy (49°S), Southern Patagonia

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Former glacier fluctuations provide a crucial terrestrial record of paleoclimate in alpine regions. However, uneven coverage of paleoglacier chronologies has hindered efforts to decipher the nature of regional and interhemispheric climate relationships, without which mechanisms driving past climate variability cannot be adequately evaluated. We present a preliminary chronology of fluctuations of the Torre glacier (49.3°S), adjacent to the Southern Patagonian Ice Field, as determined using geomorphic mapping and 10Be cosmogenic surface exposure dating of former glacier limits. The record spans the last glacial-interglacial transition to the latest Holocene, and no fewer than seven progressively less-extensive glacier advances are observed during this time period. The late-glacial record parallels the Antarctic pattern of deglacial temperature fluctuations, with glacier maxima at c. 18 and 13 ka corresponding to the onset of the termination and the Antarctic Cold Reversal, respectively. The Holocene record's relationship to the Antarctic is less clear; the stepwise pattern of declining glacier extent most closely parallels that of New Zealand. Taken together, fluctuations of the Torre glacier indicate changing modes of control on regional glaciation, dependent upon the glacial versus interglacial state of global climate.

  4. Patagonian Glacier Response During the Late Glacial Holocene Transition

    NASA Astrophysics Data System (ADS)

    Ackert, Robert P.; Becker, Richard A.; Singer, Brad S.; Kurz, Mark D.; Caffee, Marc W.; Mickelson, David M.

    2008-07-01

    Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (50°S), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 ± 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49°S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation—reflecting changes in the Southern Westerly circulation—rather than regional cooling.

  5. Patagonian glacier response during the late glacial-Holocene transition.

    PubMed

    Ackert, Robert P; Becker, Richard A; Singer, Brad S; Kurz, Mark D; Caffee, Marc W; Mickelson, David M

    2008-07-18

    Whether cooling occurred in the Southern Hemisphere during the Younger Dryas (YD) is key to understanding mechanisms of millennial climate change. Although Southern Hemisphere records do not reveal a distinct climate reversal during the late glacial period, many mountain glaciers readvanced. We show that the Puerto Bandera moraine (50 degrees S), which records a readvance of the Southern Patagonian Icefield (SPI), formed at, or shortly after, the end of the YD. The exposure age (10.8 +/- 0.5 thousand years ago) is contemporaneous with the highest shoreline of Lago Cardiel (49 degrees S), which records peak precipitation east of the Andes since 13 thousand years ago. Absent similar moraines west of the Andes, these data indicate an SPI response to increased amounts of easterly-sourced precipitation-reflecting changes in the Southern Westerly circulation-rather than regional cooling.

  6. Fast Vegetational Responses to Late-Glacial Climate Change

    NASA Astrophysics Data System (ADS)

    Williams, J. W.; Post, D. M.; Cwynar, L. C.; Lotter, A. F.; Levesque, A. J.

    2001-12-01

    How rapidly can natural ecosystems respond to rapid climate change? This question can be addressed by studying paired paleoecological and paleoclimatological records spanning the last deglaciation. Between 16 and 10 ka, abrupt climatic oscillations (e.g. Younger Dryas, Gerzensee/Killarney Oscillations) interrupted the general warming trend. Rates of climate change during these events were as fast or faster than projected rates of change for this century. We compiled a dozen high-resolution lacustrine records in North America and Europe with a pollen record and independent climatic proxy, a clear Younger Dryas signal, and good age control. Cross-correlation analysis suggests that vegetation responded rapidly to late-glacial climate change, with significant changes in vegetation composition occurring within the lifespan of individual trees. At all sites, vegetation lagged climate by less than 200 years, and at two-thirds of the sites, the initial vegetational response occurred within 100 years. The finding of rapid vegetational responses is consistent across sites and continents, and is similar to the 100-200 year response times predicted by gap-scale forest models. Likely mechanisms include 1) increased susceptibility of mature trees to disturbances such as fire, wind, and disease, thereby opening up gaps for colonization, 2) the proximity of these sites to late-glacial treeline, where climate may directly control plant population densities and range limits, 3) the presence of herbaceous taxa with short generation times in these plant communities, and 4) rapid migration due to rare long-distance seed dispersals. Our results are consistent with reports that plant ranges are already shifting in response to recent climate change, and suggest that these shifts will persist for the next several centuries. Widespread changes in plant distributions may affect surface-atmosphere interactions and will challenge attempts to manage ecosystems and conserve biodiversity.

  7. Late glacial 10Be ages for glacial landforms in the upper region of the Taibai glaciation in the Qinling Mountain range, China

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Liu, Liang; Chen, Yixin; Liu, Beibei; Harbor, Jonathan M.; Cui, Zhijiu; Liu, Rui; Liu, Xiao; Zhao, Xu

    2016-01-01

    Glacial landforms are well preserved on Taibai Mountain (3767 m), the main peak of the Qinling mountain range located south of the Loess Plateau and east of the Qinghai-Tibet Plateau. The timing and extent of Quaternary glaciation in the study area is important for reconstructing Quaternary environmental change however numerical ages for glaciation in this study area have not previously been well resolved. Using terrestrial in situ cosmogenic nuclides we dated four samples collected from two glacially eroded rock steps in the upper part of a valley near the main peak, in an area previously identified as having been occupied by ice during the Taibai glaciation. The 10Be results are all late glacial in age: 18.6 ± 1.1 ka, 16.9 ± 1.0 ka, 16.9 ± 1.1 ka and 15.1 ± 1.0 ka. The spatial pattern of ages in the valley suggests fast retreat, with horizontal and vertical retreat rates estimated to be on the order of 0.4 and 0.09 m a-1, respectively. A simple extrapolation of these retreat rates from the ages at the two sample sites suggests that the glacier retreat began during Last Glacial Maximum and that glaciers disappeared from the main peak by about 15 ka.

  8. Accelerator-mass spectrometer ages for late-glacial events at Ballybetagh, Ireland

    NASA Astrophysics Data System (ADS)

    Cwynar, Les C.; Watts, W. A.

    1989-05-01

    Although the character of late-glacial vegetation development in Ireland is well known, the dating is weak for a number of reasons. We report six accelerator-mass spectrometer (AMS) 14C dates of hand-picked organic material from Ballybetagh. Several of the dates are based on terrestrial plant remains, thus eliminating the commonly encountered problem associated with Irish sites of errors due to the hard-water effect. The two most significant indicate that (1) the Rumex-Salix zone, which represents the initial establishment of vegetation following deglaciation, began about 12,600 yr B.P. and (2) the classic Younger Dryas began at 10,600 yr B.P., somewhat younger than the traditionally accepted age of 11,000 yr B.P.

  9. Quantitative Morphometric Analysis of Terrestrial Glacial Valleys and the Application to Mars

    NASA Astrophysics Data System (ADS)

    Allred, Kory

    Although the current climate on Mars is very cold and dry, it is generally accepted that the past environments on the planet were very different. Paleo-environments may have been warm and wet with oceans and rivers. And there is abundant evidence of water ice and glaciers on the surface as well. However, much of that comes from visual interpretation of imagery and other remote sensing data. For example, some of the characteristics that have been utilized to distinguish glacial forms are the presence of landscape features that appear similar to terrestrial glacial landforms, constraining surrounding topography, evidence of flow, orientation, elevation and valley shape. The main purpose of this dissertation is to develop a model that uses quantitative variables extracted from elevation data that can accurately categorize a valley basin as either glacial or non-glacial. The application of this model will limit the inherent subjectivity of image analysis by human interpretation. The model developed uses hypsometric attributes (elevation-area relationship), a newly defined variable similar to the equilibrium line altitude for an alpine glacier, and two neighborhood search functions intended to describe the valley cross-sectional curvature, all based on a digital elevation model (DEM) of a region. The classification model uses data-mining techniques trained on several terrestrial mountain ranges in varied geologic and geographic settings. It was applied to a select set of previously catalogued locations on Mars that resemble terrestrial glaciers. The results suggest that the landforms do have a glacial origin, thus supporting much of the previous research that has identified the glacial landforms. This implies that the paleo-environment of Mars was at least episodically cold and wet, probably during a period of increased planetary obliquity. Furthermore, the results of this research and the implications thereof add to the body of knowledge for the current and past

  10. Glacial history of the Polar Urals inferred from terrestrial and lacustrine data

    NASA Astrophysics Data System (ADS)

    Svendsen, J. I.; Astakhov, V. I.; Bakke, J.; Gyllencreutz, R.; Henriksen, M.; Karlsen, L.; Lohne, Ø.; Mangerud, J.; Nazarov, D.

    2009-04-01

    A lake coring campaign in the Polar Urals is carried out within the framework of the Russian-Norwegian IPY-project "The Ice Age Development and Human Settlement in Northern Eurasia" (ICEHUS). The purpose is to improve the description and understanding of the Late Quaternary glacial and climate changes in this part of the Russian Arctic. Sediment cores are being obtained from selected mountain lakes that according to our hypothesis were not reached by local glaciers during the Last Glacial Maximum (LGM) some 25-20,000 years ago. The results are compared with other terrestrial data used to constrain the timing and extent of the former glaciers. This includes moraines, ice-dammed lakes, outwash sediments and other observations. The chronology is based on radiocarbon dating, cosmogenic isotope dating of erratics, and a large number of optically stimulated luminescence (OSL) dating of sediments. Judged from geomorphologic as well as stratigraphic observations it seems clear that the last major glaciation that affected the northern part of the Ural Mountains was a shelf-centred ice sheet that inundated the mountain valleys during the Early Weichselian. The OSL-dates of this event cluster around 75-80 ka. Following this glaciations the local glaciers appears to have been rather small and there is nothing to suggest that extensive valley glaciers existed, not even during the LGM. Coring results from the eastern foothills of the Polar Urals indicate that this area was affected by a major ice sheet advance during the Early Weichselian, but that the final deglaciation took place more than 70,000 yrs ago. This summer we will equip another field expedition aiming at retrieving long sediment cores from a 140 m deep lake (Bol. Schuchye) in the central part of the Polar Urals. Seismic profiles show that this basin contains more than a hundred meters of soft lacustrine sediments above bedrock. Radiocarbon dates from a short core that was collected in 2007 indicate that the upper 3

  11. Glacial-Interglacial and Holocene N2O Stable Isotope Changes Constrain Terrestrial N Cycling

    NASA Astrophysics Data System (ADS)

    Schmitt, J.; Spahni, R.; Bock, M.; Seth, B.; Stocker, B. D.; Ri, X.; Schilt, A.; Brook, E.; Otto-Bliesner, B. L.; Liu, Z.; Prentice, I. C.; Fischer, H.; Joos, F.

    2015-12-01

    The land biosphere contributes most to the natural source of the long-lived greenhouse gas nitrous oxide (N2O), with N2O emissions being dependent on the turnover rate of both the terrestrial nitrogen (N) and carbon (C) cycle. The C:N stoichiometry of vegetation and soil organic matter links the cycles intimately. Sustained plant productivity increase must be supported by biological N fixation. Intensified N cycling in turn enhances N loss and thereby N2O emissions. The temporal and spatial dynamics of terrestrial N and C cycles and related terrestrial N2O emissions are poorly constrained over the glacial-interglacial transition and the Holocene. Here we reconstruct increased terrestrial N2O emissions since the Last Glacial Maximum based on N2O concentration and isotope measurements on several ice cores and show that this N2O increase can be explained by N cycle modelling - provided N fixation is allowed to respond dynamically to increasing N demand and turnover. The Ice core reconstructions suggest a deglacial increase of 1.1 ± 0.4 Tg N/yr in terrestrial and 0.6 ± 0.4 Tg/yr in oceanic N2O emissions, but relatively constant terrestrial emissions over the Holocene. Transient simulations with a Dynamic Global Vegetation Model are shown to represent the climate and CO2 induced changes in terrestrial N2O emission, and suggest a deglacial increase in biological N fixation by 20%, independently of its absolute magnitude. Deciphering the response of biological N fixation during climatic changes is an important factor for our understanding of plant growth and the land carbon sink, alongside anthropogenic greenhouse gas emissions.

  12. Holocene and Late Glacial varved sediments from Czechowskie Lake (Poland)

    NASA Astrophysics Data System (ADS)

    Ott, Florian; Brauer, Achim; Słowiński, Michał; Dulski, Peter; Plessen, Birgit; Blaszkiewicz, Miroslaw

    2013-04-01

    Annual laminated (varved) sediment records are essential for detailed paleoclimate and environmental reconstructions as they function as a natural memory beyond instrumental datasets. In order to determine Holocene inter-annual and decadal-scale variability we investigated varved Lake Czechowskie (53°52' N/ 18°14' E, 108 m asl.), northern Poland. During two coring campaigns in 2009 and 2012 we recovered several long and short cores with the longest core reaching 14.5 m. Based on correlation with a biostratigraphically and tephrochronologically dated neighboring paleolake sediment record (Trzechowskie mire) the record extends back in to the Late Glacial. Lake Czechowskie is well suited for climate reconstruction as varves are almost entirely well (88 %) or poorly (5%) preserved. Only 7 % of the sediment profile are non-varved. Detailed investigations have been carried out for the last 2000 years of the sediment profile applying micro-facies analyses combined with X-ray fluorescence element scanning (µ-XRF) at 200 µm resolution and carbon and nitrogen analyses (TOC, TC, TN) at five-varveresolution. The chronology has been established by a multiple dating approach with 137Cs (for the last ca. 50 years), AMS 14C on plant macro remains (back to 2800 cal BP) and varve counting. Varve formation and preservation ceases at the beginning of the 20th century whereas the younger sediments are again faintly varved. Micro-facies analyses reveal that the sediment consists of biogenic calcite varves with intercalated diatom rich layers. Three distinct 100 to 200 years long periods of up to threefold thicker varves (approx. 1.4 to 5.0 mm/year) are predominantly caused by an increase in the diatom sub-layers and indicate distinct short-term climatic and environmental fluctuations. Possible reasons for these changes that occurred abruptly with only few years are either changes in lake water circulation or in nutrient supply to the lake. This study is a contribution to the Virtual

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

    USGS Publications Warehouse

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

    2006-01-01

    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.

  14. Evolution of the Indian Summer Monsoon eastern branch and terrestrial vegetation since the Last Glacial

    NASA Astrophysics Data System (ADS)

    Contreras-Rosales, Astrid; Jennerjahn, Tim; Tharammal, Thejna; Lückge, Andreas; Meyer, Vera; Paul, André; Schefuß, Enno

    2014-05-01

    The Indian summer monsoon (ISM) is one of the major climatic phenomena on the planet and supports the living of over a billion people. Thus, understanding its natural driving forces and ecological consequences are a matter of first importance. We provide a continuous record of the ISM precipitation and continental vegetation over the Ganges-Brahmaputra-Meghna lower catchment and the Indo-Burman ranges for the last 18,000 years (18 ka), based on terrestrial biomarkers of a sediment core from the northern Bay of Bengal (NBoB). Compound-specific stable isotope analysis of hydrogen (δD) and carbon (δ13C) on plant wax-derived n-alkanes was conducted to reconstruct changes in precipitation and vegetation composition, respectively. The results are compared to results from an isotope-enabled general atmospheric circulation model (IsoCAM) for selected time-slices (pre-industrial, mid-Holocene and Heinrich Stadial 1 [HS1]). Our findings indicate that changes in the δD of precipitation and plant waxes around the NBoB were mainly driven by the amount effect, and strongly influenced by summer monsoon precipitation. Model results also support the hypothesis of a constant moisture source (i.e. the NBoB) throughout the study period. Qualitative precipitation changes inferred from our alkane δD record suggest that, overall, the Holocene (last 10 ka) was moister than the late glacial (18-10 ka BP). Precipitation was strongest during the early Holocene (8.6-8.4 ka BP), whereas the most arid conditions were recorded during the HS1 (16.9-15.4 ka BP). These changes are comparable in timing and magnitude to those detected in other ISM records from central and western Asia [1, 2, 3, 4], suggesting simultaneous variability of the western (Arabian Sea) and eastern (Bay of Bengal) ISM branches. Downcore n-alkane δD anomalies were used to evaluate past changes in the precipitation isotopic signature and the observed anomalies were similar to those obtained from the IsoCAM model

  15. Late-stage accretion of the terrestrial planets

    NASA Astrophysics Data System (ADS)

    Agnor, Craig Bruce

    2002-08-01

    I have studied late stage accretion of the terrestrial planets using both analytic and numerical methods, modeling terrestrial planet accretion from a system of planetary embryos using three-dimensional N-body integrations. The simulations are generally successful in producing 1 2 large terrestrial planets (similar to Earth and Venus) and are usually accompanied by a smaller planet. Despite the general successes of the model, simulations of the late stage performed under a broad range of conditions tend to produce large terrestrial planets with eccentricities 2 5 times greater than those of Earth or Venus. My results show that the spin angular momentum states of the planets produced are generally the result of contributions made by the last few large impacts. This suggests that the current angular momentum of the Earth/Moon system may be the result of more than one large impact rather than a single impact. These results also suggest that the proto-Earth may have been rotating rapidly prior to the Moon-forming impact event. I have also examined the damping of terrestrial planet eccentricities via density wave interactions with a remnant gas disk that post-dated the accretionary epoch. My results suggest that the terrestrial planet eccentricities could be reduced from values permitting crossing orbits to the present day values by a remnant disk with gas surface densities of ˜10-3 10 -1 times the minimum mass solar nebula value and characteristic dissipation timescales of 106 107 years.

  16. Bayesian analysis of radiocarbon chronologies: examples from the European Late-glacial

    NASA Astrophysics Data System (ADS)

    Blockley, S. P. E.; Lowe, J. J.; Walker, M. J. C.; Asioli, A.; Trincardi, F.; Coope, G. R.; Donahue, R. E.

    2004-02-01

    Although there are many Late-glacial (ca. 15 000-11 000 cal. yr BP) proxy climate records from northwest Europe, some analysed at a very high temporal resolution (decadal to century scale), attempts to establish time-stratigraphical correlations between sequences are constrained by problems of radiocarbon dating. In an attempt to overcome some of these difficulties, we have used a Bayesian approach to the analysis of radiocarbon chronologies for two Late-glacial sites in the British Isles and one in the Adriatic Sea. The palaeoclimatic records from the three sites were then compared with that from the GRIP Greenland ice-core. Although there are some apparent differences in the timing of climatic events during the early part of the Late-glacial (pre-14 000 cal. yr BP), the results suggest that regional climatic changes appear to have been broadly comparable between Greenland, the British Isles and the Adriatic during the major part of the Late-glacial (i.e. between 14 000 and 11 000 cal. yr BP). The advantage of using the Bayesian approach is that it provides a means of testing the reliability of Late-glacial radiocarbon chronologies that is independent of regional chronostratigraphical (climatostratigraphical) frameworks. It also uses the full radiocarbon inventory available for each sequence and makes explicit any data selection applied. Potentially, therefore, it offers a more objective basis for comparing regional radiocarbon chronologies than the conventional approaches that have been used hitherto. Copyright

  17. Glacial geomorphic evidence for a late climatic change on Mars

    NASA Technical Reports Server (NTRS)

    Kargel, J. S.; Strom, R. G.

    1992-01-01

    In a series of preliminary reports, we documented evidence of former glacial epochs on Mars. Apparent glacial landforms seemed to be concentrated primarily at middle to high southern latitudes. We now have additional evidence supporting the view that Martian glaciation appears to have been more extensive than previously recognized. The growth and collapse of ice sheets on Mars seems closely analogous to the growth and decline of Earth's great Pleistocene ice sheets. This implies that climate change was probably somewhat comparable on the two planets, although in the case of Mars the entire planet seems to have changed rapidly to a cold, dry present-day environment after the collapse of the ice sheets.

  18. Late glacial climate estimates for southern Nevada: The ostracode fossil record

    SciTech Connect

    Forester, R.M.; Smith, A.J.

    1995-10-01

    Climate change plays an important role in determining as possible long term hydrological performance of the potential high level nuclear waste repository within Yucca Mountain, Nevada. Present-day global circulation results in this region having an arid to semi-arid climate characterized by hot and relatively dry summers. Global circulation during the late glacial (about 14 to 20 ka) was very different from the present-day. Preliminary study of late-glacial fossil ostracodes from {open_quotes}marsh deposits{close_quotes} in the upper Las Vegas Valley suggests mean annual precipitation may have been four times higher, while mean annual temperature may have been about 10{degrees}C cooler than today. A major difference between present-day and late-glacial climate was likely the existence of cooler, cloudier, and wetter summers in the past.

  19. Submarine glacial landforms record Late Pleistocene ice-sheet dynamics, Inner Hebrides, Scotland

    NASA Astrophysics Data System (ADS)

    Dove, Dayton; Arosio, Riccardo; Finlayson, Andrew; Bradwell, Tom; Howe, John A.

    2015-09-01

    We use ∼7000 km2 of high-resolution swath bathymetry data to describe and map the submarine glacial geomorphology, and reconstruct Late Pleistocene ice sheet flow configurations and retreat dynamics within the Inner Hebrides, western Scotland. Frequently dominated by outcrops of structurally complex bedrock, the seabed also comprises numerous assemblages of well-preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice-margin retreat. The occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography, however these factors alone cannot account for the location, orientation, and configuration of the observed landforms. We attribute the distribution of these elongate streamlined landforms to the onset zone of the former Hebrides Ice Stream (HIS) - part of a major ice stream system that drained 5-10% of the last British-Irish Ice Sheet (BIIS). We suggest this geomorphic signature represents the transition from slow 'sheet flow' to 'streaming flow' as ice accelerated out from an environment characterized by numerous bedrock obstacles (e.g. islands, headlands), towards the smooth, sediment dominated shelf. The majority of streamlined landforms associated with the HIS indicate ice sheet flow to the southwest, with regional-scale topography clearly playing a major role in governing the configuration of flow. During maximal glacial conditions (∼29-23 ka) we infer that the HIS merged with the North Channel-Malin Shelf Ice Stream to form a composite ice stream system that ultimately reached the continental shelf edge at the Barra-Donegal Trough-Mouth Fan. Taken collectively however, the pattern of landforms now preserved at seabed (e.g. convergent flow indicators, cross-cutting flow sets) is more indicative of a thinning ice mass, undergoing reorganization during overall ice sheet retreat (during latter stages of Late Weischselian glaciation). Suites of moraines overprinting the

  20. Late Cretaceous terrestrial vertebrate fauna, North Slope, Alaska

    SciTech Connect

    Clemens, W.A.; Allison, C.W.

    1985-01-01

    Closely related terrestrial vertebrates in Cretaceous mid-latitude (30/sup 0/ to 50/sup 0/) faunas of North America and Asia as well as scattered occurrences of footprints and skin impressions suggested that in the Late Mesozoic the Alaskan North Slope supported a diverse fauna. In 1961 abundant skeletal elements of Cretaceous, Alaskan dinosaurs (hadrosaurids) were discovered by the late R.L. Liscomb. This material is being described by K.L. Davies. Additional fossils collected by E.M. Brouwers and her associates include skeletal elements of hadrosaurid and carnosaurian (.tyrannosaurid) dinosaurs and other vertebrates. The fossil locality on the North Slope is not at about 70/sup 0/N. In the Late Cretaceous the members of this fauna were subject to the daylight regime and environment at a paleolatitude closer to 80/sup 0/N. Current hypotheses attributing extinctions of dinosaurs and some other terrestrial vertebrates to impact of an extraterrestrial object cite periods of darkness, decreased temperature (possibly followed by extreme warming) and acid rain as the direct causes of their demise. Unless members of this North Slope fauna undertook long-distance migrations, their high latitude occurrence indicates groups of dinosaurs and other terrestrial vertebrates regularly tolerated months of darkness.

  1. Glacial landforms of the southern Ungava Bay region (Canada): implications for the late-glacial dynamics and the damming of glacial Lake Naskaupi

    NASA Astrophysics Data System (ADS)

    Dube-Loubert, Hugo; Roy, Martin

    2014-05-01

    The Laurentide ice sheet played an important role in the late Pleistocene climate, notably through discharges of icebergs and meltwater. In this context, the Ungava Bay region in northern Quebec-Labrador appears particularly important, especially during the last deglaciation when the retreating ice margin dammed major river valleys, creating large proglacial lakes (e.g., McLean, aux Feuilles). The history of these lakes is closely related to the temporal evolution of the Labrador-Quebec ice dome. There are, however, large uncertainties regarding the position of its ice divide system through time, thereby limiting our understanding of the history of these glacial lakes. Here we focus on glacial and deglacial landforms present in the George River valley, south of Ungava Bay, in order to bring additional constraints on the late-glacial ice dynamics of this region, which also comprised glacial Lake Naskaupi. This work is based on surficial mapping using aerial photos and satellite imagery, combined with extensive fieldwork and sediment sampling. Our investigation showed significant differences in the distribution of glacial landforms across the region. The area east of the George River is characterized by well-developed Naskaupi shorelines while the elevated terrains show a succession of geomorphological features indicative of cold-based ice or ice with low basal velocities. In the easternmost part of this sector, ice flow directional data indicate that the ice was flowing towards ENE, against the regional slope. Eskers show paleocurrent directions indicating a general ice retreat from east to west. In the western part of this sector, near the George River valley, eskers are absent and the region is covered by felsenmeer and ground moraine that likely reflect the presence of a residual ice mass that was no longer dynamic. The presence of a stagnant ice represents the best mechanism to explain the formation of glacial lakes in the George River valley and its main

  2. Glacial inception during the late Holocene without carbon emissions from early agriculture: lessons from the stage-19 glacial inception

    NASA Astrophysics Data System (ADS)

    He, F.; Vavrus, S. J.; Kutzbach, J. E.; Ruddiman, W. F.; Tzedakis, P. C.

    2013-12-01

    Decreases in orbitally-forced summer insolation along with downward trends in greenhouse gases (GHG) have been precursors to incipient glaciation in the past. In the last several thousand years of the current interglacial, while summer insolation has decreased, there was a reversal of the downward trends in CH4 and CO2 concentration within the Holocene around 5,000 and 7,000 years ago. While the cause of this reversal remains unresolved, a leading hypothesis is Ruddiman's Early Anthropogenic Hypothesis that early agriculture, starting several thousand years ago, caused emissions of GHG large enough to reverse natural downward trends in CO2 and CH4 and kept Earth's climate anomalously warm, with the corollary that this may have prevented incipient glaciation during the late Holocene. Here we use the 1-degree, fully coupled Community Climate System Model version 4 (CCSM4) with climate forcings (orbital parameters and GHG) of a previous glacial inception to investigate whether glacial inception should have occurred prior to the industrial revolution if the concentrations of CH4 and CO2 had followed their natural downward trends throughout the Holocene. Tzedakis et al. [2012] show that for the previous eight interglacials, Stage 11 and Stage 19 are the best analogs of the Holocene because of their low eccentricities, and Stage 19 is a better analog than Stage 11 for the Holocene due to the in-phase relationship between obliquity and precession. Furthermore, their study suggests that 777 ka BP (777,000 years before present) is the timing of glacial inception for Stage 19, based on the occurrence of the earliest bipolar seesaw event associated with glacial melting. Not only do the orbital parameters at 777 ka BP resemble pre-industrial conditions, but the concentrations of CO2 at that time were essentially the same as their expected 'natural' pre-industrial values in the absence of anthropogenic greenhouse emissions. Our multi-millennial coupled CCSM4 simulations show

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

    NASA Astrophysics Data System (ADS)

    Deschamps, Rémy; Eschard, Rémi; Roussé, Stéphane

    2013-05-01

    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

  4. Evidence of late glacial runoff in the lower Mississippi Valley

    NASA Astrophysics Data System (ADS)

    Saucier, Roger T.

    Thousands of cubic kilometers of massive coarse-grained glacial outwash underlie the alluvial plain of the Lower Mississippi Valley between Cairo, Illinois, and the Gulf of Mexico. However, valley trains deposited by braided streams characterize less than one-third of the valley area, and those attributable to runoff from the Laurentide Ice Sheet cover less than 15,000 km2, mostly in the St. Francis Basin segment of the valley. There they form a series of subdued terraces that reflect episodes of meltwater release and possibly catastrophic flood events. Radiocarbon-dated sediment cores establish that the initial runoff entered the basin about 16.3 ka BP and continued without a significant lull for about 5000 years. The distribution of archeological sites tends to support an effective brief cessation of runoff to the valley about 11.0 ka BP when meltwater is thought to have been diverted from the Mississippi River Valley to the St. Lawrence Valley. Both radiocarbon dates and archeological evidence document a final pulse of outwash to the (Lower) Mississippi Valley about 10.0 ka BP when the Mississippi River occupied Thebes Gap near Cairo and created the Charleston Fan. All outwash deposition ended, and the river adopted a meandering regime not later than 9.8 ka BP.

  5. Hypoxia, global warming, and terrestrial late Permian extinctions.

    PubMed

    Huey, Raymond B; Ward, Peter D

    2005-04-15

    A catastrophic extinction occurred at the end of the Permian Period. However, baseline extinction rates appear to have been elevated even before the final catastrophe, suggesting sustained environmental degradation. For terrestrial vertebrates during the Late Permian, the combination of a drop in atmospheric oxygen plus climate warming would have induced hypoxic stress and consequently compressed altitudinal ranges to near sea level. Our simulations suggest that the magnitude of altitudinal compression would have forced extinctions by reducing habitat diversity, fragmenting and isolating populations, and inducing a species-area effect. It also might have delayed ecosystem recovery after the mass extinction.

  6. Influence of dynamic vegetation on climate change and terrestrial carbon storage in the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    O'ishi, R.; Abe-Ouchi, A.

    2013-07-01

    When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM.

  7. Late Glacial to Holocene paleoenvironmental change on the northwestern Pacific seaboard, Kamchatka Peninsula (Russia)

    NASA Astrophysics Data System (ADS)

    Pendea, Ionel Florin; Ponomareva, Vera; Bourgeois, Joanne; Zubrow, Ezra B. W.; Portnyagin, Maxim; Ponkratova, Irina; Harmsen, Hans; Korosec, Gregory

    2017-02-01

    We used a new sedimentary record from a small kettle wetland to reconstruct the Late Glacial and Holocene vegetation and fire history of the Krutoberegovo-Ust Kamchatsk region in eastern Kamchatka Peninsula (Russia). Pollen and charcoal data suggest that the Late Glacial landscape was dominated by a relatively fire-prone Larix forest-tundra during the Greenland Interstadial complex (GI 1) and a subarctic steppe during the Younger Dryas (GS1). The onset of the Holocene is marked by the reappearance of trees (mainly Alnus incana) within a fern and shrub dominated landscape. The Holocene Thermal Maximum (HTM) features shifting vegetational communities dominated by Alnus shrubs, diverse forb species, and locally abundant aquatic plants. The HTM is further defined by the first appearance of stone birch forests (Betula ermanii) - Kamchatka's most abundant modern tree species. The Late Holocene is marked by shifts in forest dynamics and forest-graminoid ratio and the appearance of new non-arboreal taxa such as bayberry (Myrica) and meadow rue (Filipendula). Kamchatka is one of Earth's most active volcanic regions. During the Late Glacial and Holocene, Kamchatka's volcanoes spread large quantities of tephra over the study region. Thirty-four tephra falls have been identified at the site. The events represented by most of these tephra falls have not left evidence of major impacts on the vegetation although some of the thicker tephras caused expansion of grasses (Poaceae) and, at least in one case, forest die-out and increased fire activity.

  8. A stable-isotope tree-ring timescale of the Late Glacial/Holocene boundary

    NASA Astrophysics Data System (ADS)

    Becker, Bernd; Kromer, Bernd; Trimborn, Peter

    1991-10-01

    LATE Glacial and Holocene tree-ring chronologies, like deep-sea sediments or polar ice cores, contain information about past environments. Changes in tree-ring growth rates can be related to past climate anomalies and changes in the isotope composition of tree-ring cellulose reflect changes in the composition of the atmosphere and the hydrosphere. We have established a 9,928-year absolutely dated dendrochronological record of Holocene oak (Quercus robur, Quercus petraea)-and a 1,604-year floating Late Glacial and Early Holocene chronology of pine (Pinus sylvestris) from subfossil tree remnants deposited in alluvial terraces of south central European rivers. The pine sequence provides records of dendro-dated 14C, 13C and 2H patterns for the late Younger Dryas and the entire Preboreal (10,100-9,000 yr BP). Through the use of dendrochronology, radiocarbon age calibration and stable isotope analysis, we suggest that the Late Glacial/Holocene transition may be identified and dated by 13C and 2H tree-ring chronologies.

  9. Mid-late Pleistocene glacial evolution in the Grove Mountains, East Antarctica, constraints from cosmogenic 10Be surface exposure dating of glacial erratic cobbles

    NASA Astrophysics Data System (ADS)

    Dong, Guocheng; Huang, Feixin; Yi, Chaolu; Liu, Xiaohan; Zhou, Weijian; Caffee, Marc W.

    2016-08-01

    Glacial histories from the East Antarctic Ice Sheet (EAIS) provide keys to understanding correlations between the EAIS and global climate. They are especially helpful in the assessment of global sea level change, and as a means of quantifying the magnitude of past glacial activity and the rate at which ice responded to climate change. Given the significance of EAIS glacial histories, it is imperative that more glacial chronologic data for this region be obtained, especially for the mid-to-late Pleistocene. We report cosmogenic 10Be surface exposure dating results from glacially transported cobbles embedded in blue-ice moraine material at Mount Harding, the Grove Mountains, EAIS. Forty exotic cobbles sampled along two profiles (A and B) on this blue-ice moraine present apparent exposure-ages ranging from 7.2 to 542.2 ka. We explore this scattered dataset by using Principal Component Analysis (PCA) to identify statistically significant trends in the data. We identify a correlation between exposure-age and distance of the cobbles from Mount Harding. In profile A, cobbles further from Mount Harding yield older exposure-ages than those that are relatively close. In profile B, cobbles closer to Mount Harding are found to have relatively older exposure-ages. In term of glacial history we suggest that the direction of ice flow changed during the period from ∼60 to 200 ka, and that multiple glacial fluctuations occurred in the mid-late Pleistocene.

  10. Late glacial stage and holocene tropical ice core records from Huascaran, Peru

    SciTech Connect

    Thompson, L.G.; Henderson, K.A.; Bolzan, J.F.

    1995-07-07

    Two ice cores from the col of Huascaran in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Wuerm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8{degree} to 12{degree}C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio {delta}{sup 18}O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5{degree} to 6{degree}C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.

  11. Late Pliocene to Late Quaternary Apparent Exposure Ages from Glacial Deposits in Ak-Shyrak, Central Kyrgyz Tian Shan

    NASA Astrophysics Data System (ADS)

    Blomdin, R.; Harbor, J.; Stroeven, A. P.; Petrakov, D. A.; Gribenski, N.; Heyman, J.; Ivanov, M.; Caffee, M. W.; Hättestrand, C.; Lifton, N. A.; Rogozhina, I.; Usubaliev, R.

    2014-12-01

    The Tian Shan in central Asia is one of the world's highest mountain ranges. The 2500 km-long WSW-ENE-trending arc of mountains extends from the western Kyrgyz Republic across northwestern China and almost to the border with Mongolia. Understanding the glacial history of this vast region is important because there is a general lack of paleoclimatic data from this highly continental location, at the confluence of major climate systems, and because glaciers are sensitive monitors of climate change. We examine the glacial history of the Ak-Shyrak massif and surrounding plateaus with average altitudes of ~3500 m a.s.l. To reconstruct the glacial history of this area we use a combined approach including geomorphological mapping, and cosmogenic nuclide surface exposure dating of erratic boulders on glacial landforms. We observe large site-specific scatter in our 10Be and 26Al exposure ages. Apparent minimum surface exposure ages range from ~2 ka to ~2.5 Ma, with early Quaternary- late Pliocene apparent exposure ages relating to some of the highest 10Be concentrations ever recorded for glacial deposits. Most dated boulders, however, fall in the apparent exposure age range of 100 ka to 300 ka. Consistent with previous results from the western and central Tian Shan, none of our boulders record a global last glacial maxima expansion of glaciers, and this contrasts to data from the eastern Kyrgyz Tian Shan. This spatial variation in glacier extent might be due to differences in paleoclimate. However, local physiographic conditions (e.g. altitude, slope, aspect) or external forcing factors other than climate (e.g., landslides) may cause local or regional differences in glacier response. We refrain from assigning mapped glacial advances to marine oxygen isotope stages because of the considerable age scatter. Finally we assess and discuss possible reasons for the observed age scatter and early Quaternary-late Pliocene apparent exposure ages in terms of prior and/or incomplete

  12. Thriving in the Cold: Glacial Expansion and Post-Glacial Contraction of a Temperate Terrestrial Salamander (Plethodon serratus)

    PubMed Central

    Newman, Catherine E.; Austin, Christopher C.

    2015-01-01

    The dynamic geologic history of the southeastern United States has played a major role in shaping the geographic distributions of amphibians in the region. In the phylogeographic literature, the predominant pattern of distribution shifts through time of temperate species is one of contraction during glacial maxima and persistence in refugia. However, the diverse biology and ecology of amphibian species suggest that a “one-size-fits-all” model may be inappropriate. Nearly 10% of amphibian species in the region have a current distribution comprised of multiple disjunct, restricted areas that resemble the shape of Pleistocene refugia identified for other temperate taxa in the literature. Here, we apply genetics and spatially explicit climate analyses to test the hypothesis that the disjunct regions of these species ranges are climatic refugia for species that were more broadly distributed during glacial maxima. We use the salamander Plethodon serratus as a model, as its range consists of four disjunct regions in the Southeast. Phylogenetic results show that P. serratus is comprised of multiple genetic lineages, and the four regions are not reciprocally monophyletic. The Appalachian salamanders form a clade sister to all other P. serratus. Niche and paleodistribution modeling results suggest that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species. PMID:26132077

  13. Thriving in the Cold: Glacial Expansion and Post-Glacial Contraction of a Temperate Terrestrial Salamander (Plethodon serratus).

    PubMed

    Newman, Catherine E; Austin, Christopher C

    2015-01-01

    The dynamic geologic history of the southeastern United States has played a major role in shaping the geographic distributions of amphibians in the region. In the phylogeographic literature, the predominant pattern of distribution shifts through time of temperate species is one of contraction during glacial maxima and persistence in refugia. However, the diverse biology and ecology of amphibian species suggest that a "one-size-fits-all" model may be inappropriate. Nearly 10% of amphibian species in the region have a current distribution comprised of multiple disjunct, restricted areas that resemble the shape of Pleistocene refugia identified for other temperate taxa in the literature. Here, we apply genetics and spatially explicit climate analyses to test the hypothesis that the disjunct regions of these species ranges are climatic refugia for species that were more broadly distributed during glacial maxima. We use the salamander Plethodon serratus as a model, as its range consists of four disjunct regions in the Southeast. Phylogenetic results show that P. serratus is comprised of multiple genetic lineages, and the four regions are not reciprocally monophyletic. The Appalachian salamanders form a clade sister to all other P. serratus. Niche and paleodistribution modeling results suggest that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species.

  14. Response of Terrestrial Vegetation to Variations in Temperature and Aridity Since the Last Glacial Maximum in Lake Chalco, Mexico

    NASA Astrophysics Data System (ADS)

    Werne, J. P.; Rubesch, M.; Brown, E. T.; Ortega, B.; Caballero, M.; Lozano-Garcia, S.

    2011-12-01

    The water balance of the Southwestern United States and most of Mexico is dependent on regional climate systems, including the Mexican (or North American) Monsoon. The Mexican Monsoon leads to significant summer rainfall across a broad swath of the continent, which constitutes the major source of annual precipitation over much of this region. The position of the ITCZ and the strength of the accompanying monsoon are affected by variability in insolation. Stronger northern hemisphere summer insolation shifts the ITCZ northward, bringing about a more intense monsoon. Here we discuss a new geochemical climate record from Lake Chalco, Mexico, which couples inorganic (X-ray fluorescence) and organic (biomarkers and stable isotopes) geochemical proxies to reconstruct temperature and aridity over the past 45,000 years, as well as the response of terrestrial vegetation to such climate changes. The Basin of Mexico is a high altitude closed lacustrine basin (20°N, 99°W; 2240 m.a.s.l.) in the Trans Mexican Volcanic Belt. The plain of Lake Chalco, located near Mexico City in the southern sub-basin, has an area of 120 km2 and a catchment of 1100 km2. Though the present-day lake has been reduced to a small marsh due to historic diversion of its waters, over longer timescales the lake has been a sensitive recorder of hydroclimatic variations. Low Ca concentrations indicate more arid periods during the late glacial (34 - 15 kybp) compared to the last interstadial or early Holocene. This observation is supported by the ratio of terrestrial to aquatic lipid biomarkers (long vs. short chain n-alkanes), which indicate greater relative inputs of aquatic biomarkers during wetter periods. The changes in aridity as shown in these geochemical proxies are compared with temperature as reflected in glycerol dialkyl glycerol tetraether (GDGT) based paleotemperature proxies to assess the extent to which insolation may have driven aridity variations, and with terrestrial and aquatic biomarker

  15. Response of Terrestrial Vegetation to Variations in Temperature and Aridity Since the Last Glacial Maximum in Lake Chalco, Mexico

    NASA Astrophysics Data System (ADS)

    Werne, J. P.; Halbur, J.; Rubesch, M.; Brown, E. T.; Ortega, B.; Caballero, M.; Correa-Metrio, A.; Lozano, S.

    2013-05-01

    The water balance of the Southwestern United States and most of Mexico is dependent on regional climate systems, including the Mexican (or North American) Monsoon. The Mexican Monsoon leads to significant summer rainfall across a broad swath of the continent, which constitutes the major source of annual precipitation over much of this region. The position of the ITCZ and the strength of the accompanying monsoon are affected by variability in insolation. Stronger northern hemisphere summer insolation shifts the ITCZ northward, bringing about a more intense monsoon. Here we discuss a new geochemical climate record from Lake Chalco, Mexico, which couples inorganic (X-ray fluorescence) and organic (biomarkers and stable isotopes) geochemical proxies to reconstruct temperature and aridity over the past 45,000 years, as well as the response of terrestrial vegetation to such climate changes. The Basin of Mexico is a high altitude closed lacustrine basin (20°N, 99°W; 2240 m.a.s.l.) in the Trans Mexican Volcanic Belt. The plain of Lake Chalco, located near Mexico City in the southern sub-basin, has an area of 120 km2 and a catchment of 1100 km2. Though the present-day lake has been reduced to a small marsh due to historic diversion of its waters, over longer timescales the lake has been a sensitive recorder of hydroclimatic variations. Low Ca concentrations indicate more arid periods during the late glacial (34 - 15 kybp) compared to the last interstadial or early Holocene. This observation is supported by the ratio of terrestrial to aquatic lipid biomarkers (long vs. short chain n-alkanes), which indicate greater relative inputs of aquatic biomarkers during wetter periods. The changes in aridity as shown in these geochemical proxies are compared with temperature as reflected in glycerol dialkyl glycerol tetraether (GDGT) based paleotemperature proxies to assess the extent to which insolation may have driven aridity variations, and with terrestrial and aquatic biomarker

  16. Incursions of southern-sourced water into the deep North Atlantic during late Pliocene glacial intensification

    NASA Astrophysics Data System (ADS)

    Lang, David C.; Bailey, Ian; Wilson, Paul A.; Chalk, Thomas B.; Foster, Gavin L.; Gutjahr, Marcus

    2016-05-01

    The circulation and internal structure of the oceans exert a strong influence on Earth's climate because they control latitudinal heat transport and the segregation of carbon between the atmosphere and the abyss. Circulation change, particularly in the Atlantic Ocean, is widely suggested to have been instrumental in the intensification of Northern Hemisphere glaciation when large ice sheets first developed on North America and Eurasia during the late Pliocene, approximately 2.7 million years ago. Yet the mechanistic link and cause/effect relationship between ocean circulation and glaciation are debated. Here we present new records of North Atlantic Ocean structure using the carbon and neodymium isotopic composition of marine sediments recording deep water for both the Last Glacial to Holocene (35-5 thousand years ago) and the late Pliocene to earliest Pleistocene (3.3-2.4 million years ago). Our data show no secular change. Instead we document major southern-sourced water incursions into the deep North Atlantic during prominent glacials from 2.7 million years ago. Our results suggest that Atlantic circulation acts as a positive feedback rather than as an underlying cause of late Pliocene Northern Hemisphere glaciation. We propose that, once surface Southern Ocean stratification and/or extensive sea-ice cover was established, cold-stage expansions of southern-sourced water such as those documented here enhanced carbon dioxide storage in the deep ocean, helping to increase the amplitude of glacial cycles.

  17. Late Glacial-Holocene Pollen-Based Vegetation History from Pass Lake, Prince of Wales Island, Southeastern Alaska

    USGS Publications Warehouse

    Ager, Thomas A.; Rosenbaum, Joseph G.

    2009-01-01

    A radiocarbon-dated history of vegetation development since late Wisconsin deglaciation has been reconstructed from pollen evidence preserved in a sediment core from Pass Lake on Prince of Wales Island, southeastern Alaska. The shallow lake is in the south-central part of the island and occupies a low pass that was filled by glacial ice of local origin during the late Wisconsin glaciation. The oldest pollen assemblages indicate that pine woodland (Pinus contorta) had developed in the area by ~13,715 cal yr B.P. An abrupt decline in the pine population, coinciding with expansion of alder (Alnus) and ferns (mostly Polypodiaceae) began ~12,875 yr B.P., and may have been a response to colder, drier climates during the Younger Dryas climatic interval. Mountain hemlock (Tsuga mertensiana) began to colonize central Prince of Wales Island by ~11,920 yr B.P. and was soon followed by Sitka spruce (Picea sitchensis). Pollen of western hemlock (Tsuga heterophylla) began to appear in Pass Lake sediments soon after 11,200 yr B.P. The abundance of western hemlock pollen in the Pass Lake core during most of the Holocene appears to be the result of wind transport from trees growing at lower altitudes on the island. The late Holocene pollen record from Pass Lake is incomplete because of one or more unconformities, but the available record suggests that a vegetation change occurred during the late Holocene. Increases in pollen percentages of pine, cedar (probably yellow cedar, Chamaecyparis nootkatensis), and heaths (Ericales) suggest an expansion of muskeg vegetation occurred in the area during the late Holocene. This vegetation change may be related to the onset of cooler, wetter climates that began as early as ~3,774 yr B.P. in the region. This vegetation history provides the first radiocarbon-dated Late Glacial-Holocene terrestrial paleoecological framework for Prince of Wales Island. An analysis of magnetic properties of core sediments from Pass Lake suggests that unconformities

  18. Late-glacial and postglacial history of the hill'', Norwich University campus, Northfield, Vermont

    SciTech Connect

    Larsen, F.D. . Dept. of Geology)

    1993-03-01

    The central part of the Norwich University campus at Northfield is built on a kame about 60 ft high on the side of the Dog River valley. Significant excavations made between 1979 and 1991 in the flank of the hill provide details about its glacial origin. Collapsed ice-contact lake deposits on the northwestern flank of the kame are overlain by undisturbed lake sediments formed by turbidity currents that moved southward in glacial Lake Roxbury. Lake Roxbury formed when the retreating ice margin blocked the north-draining Dog River valley and caused melt water to drain south over a 1,010-foot threshold at Roxbury. The lowest deposits exposed on the southeast flank of the kame are highly deformed and include a chaotic slide breccia overlain by progressively less deformed lake-bottom sediments. Northward retreat of the ice margin permitted Lake Roxbury to drop 80 ft to the level of glacial Lake Winooski, which still left 80 ft of lake water over the top of the hill''. Following the lowering of Lake Winooski, stream terraces were cut on the west flank of the hill''. The terraces are underlain by imbricated pebble gravel deposited by the north-flowing Dog River that probably was graded to a lower glacial lake in the Winooski River valley to the north. Downcutting by the Dog River and subsequent lateral migration of its meanders produced the topography the authors see today. The late-glacial and postglacial history can be summarized as follows: (1) deposition of lake sediments in contact with buried ice, (2) collapse and continued deposition of lake sediments during melting of buried ice, (3) deposition of undeformed lake sediments, (4) drainage of glacial lakes, and (5) development of stream terraces and the modern flood plain.

  19. Magnetic Properties of Bermuda Rise Sediments Controlled by Glacial Cycles During the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Roud, S.

    2015-12-01

    Sediments from ODP site 1063 (Bermuda Rise, North Atlantic) contain a high-resolution record of geomagnetic field behavior during the Brunhes Chron. We present rock magnetic data of the upper 160 mcd (<900 ka) from hole 1063D that show magnetic properties vary in concert with glacial cycles. Magnetite appears to be the main magnetic carrier in the carbonate-dominated interglacial horizons, yet exhibits contrasting grain size distributions depending on the redox state of the horizons. Higher contributions of single domain magnetite exist above the present day sulfate reduction zone (ca. 44 mcd) with relatively higher multidomain magnetite components below that likely arise from the partial dissolution of SD magnetite in the deeper, anoxic horizons. Glacial horizons on the other hand, characterized by enhanced terrigenous deposition, show no evidence for diagenetic dissolution but do indicate the presence of authigenic greigite close to glacial maxima (acquisition of gyro-remanence, strong magnetostatic interactions and SD properties). Glacial horizons contain hematite (maxima in HIRM and S-Ratio consistent with a reddish hue) and exhibit higher ARM anisotropy and pronounced sedimentary fabrics. We infer that post depositional processes affected the magnetic grain size and mineralogy of Bermuda rise sediments deposited during the late Pleistocene. Hematite concentration is interpreted to reflect primary terrigenous input that is likely derived from the Canadian Maritime Provinces. A close correlation between HIRM and magnetic foliation suggests that changes in sediment composition (terrigenous vs. marine biogenic) were accompanied by changes in the depositional processes at the site.

  20. Dating the Late Cenozoic glacial sequence, Pieman River basin, western Tasmania, Australia

    NASA Astrophysics Data System (ADS)

    Augustinus, Paul C.

    1999-10-01

    The Pieman River basin, western Tasmania, displays one of the most complete Middle to Early Pleistocene glacial sequences from a Southern Hemisphere mid-latitude site. Most of the glacial deposits exceed the 14C limit, although mapping of the depositional units using morphostratigraphic, post-depositional weathering criteria and magnetostratigraphy, shows that the sediments of the Boco and Bobadil glaciation were deposited during the Brunhes normal chron (<783 kyr), whilst the reversed polarity of Bulgobac Glaciation deposits indicates deposition prior to 783 kyr. A maximum age of latest Pliocene for the Bulgobac Glaciation is suggested by magneto- and palynostratigraphy of underlying organic-rich silts. Refinement in dating the Middle Pleistocene glacial deposits has been achieved using U/Th methods on ferricretes and peat developed within and upon the sediment bodies whereby the deposits of the Boco and Bobadil glaciation are shown to be broadly correlative with Oxygen Isotope Stages 6 and 8, respectively. An older mid-Pleistocene glacial event (Animal Creek Glaciation) has also been recognised and dated to >275 kyr. Late Last (Margaret) Glaciation advances in the Pieman basin are much more restricted in extent and display evidence for multiple stillstand-readvance phases during the decay of the system, with most of the ice having disappeared by ˜14 kyr BP.

  1. Late Quaternary terrestrial vertebrate coprolites from New Zealand

    NASA Astrophysics Data System (ADS)

    Wood, Jamie R.; Wilmshurst, Janet M.

    2014-08-01

    Over the past decade, concerted efforts to find and study Late Quaternary terrestrial vertebrate coprolites in New Zealand have revealed new insights into the diets and ecologies of New Zealand's prehistoric birds. Here, we provide a broader review of the coprolites found in natural (non-archaeological) Late Quaternary deposits from New Zealand. We summarise the morphological diversity of the coprolites, and discuss the taphonomy of the sites in which they are found. Since the 1870s more than 2000 coprolites have been discovered from 30 localities, all restricted to the South Island. The distribution of coprolite localities appears to reflect the presence of geological and climatic factors that enhance the potential for coprolite preservation; coprolites require dry conditions for preservation, and have been found on the ground surface within drafting cave entrances and at shallow (<300 mm) depths beneath rock overhangs with a northerly aspect. We classify the coprolites into eleven morphotypes, each of which may represent a range of different bird and/or reptile species. A review of genetically identified specimens shows that coprolites of different bird species overlap in size and morphology, reinforcing the need for identifications to be based on ancient DNA analysis.

  2. Mitochondrial DNA Signals of Late Glacial Recolonization of Europe from Near Eastern Refugia

    PubMed Central

    Pala, Maria; Olivieri, Anna; Achilli, Alessandro; Accetturo, Matteo; Metspalu, Ene; Reidla, Maere; Tamm, Erika; Karmin, Monika; Reisberg, Tuuli; Kashani, Baharak Hooshiar; Perego, Ugo A.; Carossa, Valeria; Gandini, Francesca; Pereira, Joana B.; Soares, Pedro; Angerhofer, Norman; Rychkov, Sergei; Al-Zahery, Nadia; Carelli, Valerio; Sanati, Mohammad Hossein; Houshmand, Massoud; Hatina, Jiři; Macaulay, Vincent; Pereira, Luísa; Woodward, Scott R.; Davies, William; Gamble, Clive; Baird, Douglas; Semino, Ornella; Villems, Richard; Torroni, Antonio; Richards, Martin B.

    2012-01-01

    Human populations, along with those of many other species, are thought to have contracted into a number of refuge areas at the height of the last Ice Age. European populations are believed to be, to a large extent, the descendants of the inhabitants of these refugia, and some extant mtDNA lineages can be traced to refugia in Franco-Cantabria (haplogroups H1, H3, V, and U5b1), the Italian Peninsula (U5b3), and the East European Plain (U4 and U5a). Parts of the Near East, such as the Levant, were also continuously inhabited throughout the Last Glacial Maximum, but unlike western and eastern Europe, no archaeological or genetic evidence for Late Glacial expansions into Europe from the Near East has hitherto been discovered. Here we report, on the basis of an enlarged whole-genome mitochondrial database, that a substantial, perhaps predominant, signal from mitochondrial haplogroups J and T, previously thought to have spread primarily from the Near East into Europe with the Neolithic population, may in fact reflect dispersals during the Late Glacial period, ∼19–12 thousand years (ka) ago. PMID:22560092

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  4. Late Glacial climate and palaeoenvironment in the Southern Carpathian Mountains inferred by chironomid and pollen analyses

    NASA Astrophysics Data System (ADS)

    Tóth, M.; Heiri, O.; Magyari, E.; Braun, M.; Buczkó, K.; Bálint, M.; Jakab, G.

    2009-04-01

    The Southern Carpathian Mountains have several glacial lakes with their sediments extending back to the Late Glacial period (ca. 11,500-14,700 calibrated radiocarbon years BP). This area has so far missed quantitative palaeoclimate records that are however much needed in order to obtain a continental-scale picture of ecosystem reorganization in response to rapid climatic changes during the Late Glacial. High-resolution chironomid and pollen analyses can both provide such records. In this study these two methods are applied to the sediment sequence of a small sub-alpine lake, Taul dintre Brazi (Retezat Mts, 1740 m a.s.l., 0.5 ha). The lake is situated on base-poor, granite bedrock, within the Picea abies forest belt. Our aim was (1) to study changes in the chironomid fauna, (2) to obtain summer temperature estimates using a chironomid-mean July air temperature inference model, and finally (3) to compare the chironomid-inferred climate record with a pollen-based quantitative climate record (plant functional type method). Here we provide first results from this multi-proxy study. The Late Glacial and Early Holocene part of this core was analysed at 100-200 yr resolution. During the Oldest Dryas the chironomid fauna was dominated by Pseudodiamesa and Tanytarsini species; the start of the Lateglacial interstadial was marked by the diversification of Tanytarsini (Tanytarsus lugens-type, Tanytarsus pallidicornis-type, Paratanytarsus sp, Micropsectra insignilobus-type) and the disappearance of Pseudodiamesa suggesting a distinct increase in summer temperature. At the same time afforestation by Larix, Pinus cembra, Pinus mugo and Picea abies was signaled by the pollen, stomatal and plant macrofossil records. During the Younger Dryas reversal the chironomid fauna showed increasing abundance of Micropsectra insignilobus-type, a chironomid typical for cool, nutrient poor lakes whereas the pollen, plant macrofossil and stomatal records pointed to a decrease of Picea abies

  5. Glacial Lake Musselshell: Late Wisconsin slackwater on the Laurentide ice margin in central Montana, USA

    USGS Publications Warehouse

    Davis, N.K.; Locke, W. W.; Pierce, K.L.; Finkel, R.C.

    2006-01-01

    Cosmogenic surface exposure ages of glacial boulders deposited in ice-marginal Lake Musselshell suggest that the lake existed between 20 and 11.5 ka during the Late Wisconsin glacial stage (MIS 2), rather than during the Late Illinoian stage (MIS 6) as traditionally thought. The altitude of the highest ice-rafted boulders and the lowest passes on the modern divide indicate that glacial lake water in the Musselshell River basin reached at least 920-930 m above sea level and generally remained below 940 m. Exposures of rhythmically bedded silt and fine sand indicate that Lake Musselshell is best described as a slackwater system, in which the ice-dammed Missouri and Musselshell Rivers rose and fell progressively throughout the existence of the lake rather than establishing a lake surface with a stable elevation. The absence of varves, deltas and shorelines also implies an unstable lake. The changing volume of the lake implies that the Laurentide ice sheet was not stable at its southernmost position in central Montana. A continuous sequence of alternating slackwater lake sediment and lacustrine sheetflood deposits indicates that at least three advances of the Laurentide ice sheet occurred in central Montana between 20 and 11.5 ka. Between each advance, it appears that Lake Musselshell drained to the north and formed two outlet channels that are now occupied by extremely underfit streams. A third outlet formed when the water in Lake Musselshell fully breached the Larb Hills, resulting in the final drainage of the lake. The channel through the Larb Hills is now occupied by the Missouri River, implying that the present Missouri River channel east of the Musselshell River confluence was not created until the Late Wisconsin, possibly as late as 11.5 ka. ?? 2005 Elsevier B.V. All rights reserved.

  6. Craniometric analysis of European Upper Palaeolithic and Mesolithic samples supports discontinuity at the Late Glacial Maximum

    PubMed Central

    Brewster, Ciarán; Meiklejohn, Christopher; von Cramon-Taubadel, Noreen; Pinhasi, Ron

    2014-01-01

    The Last Glacial Maximum (LGM) represents the most significant climatic event since the emergence of anatomically modern humans (AMH). In Europe, the LGM may have played a role in changing morphological features as a result of adaptive and stochastic processes. We use craniometric data to examine morphological diversity in pre- and post-LGM specimens. Craniometric variation is assessed across four periods—pre-LGM, late glacial, Early Holocene and Middle Holocene—using a large, well-dated, dataset. Our results show significant differences across the four periods, using a MANOVA on size-adjusted cranial measurements. A discriminant function analysis shows separation between pre-LGM and later groups. Analyses repeated on a subsample, controlled for time and location, yield similar results. The results are largely influenced by facial measurements and are most consistent with neutral demographic processes. These findings suggest that the LGM had a major impact on AMH populations in Europe prior to the Neolithic. PMID:24912847

  7. History of late glacial flow through the middle Mississippi and Illinois Valleys

    SciTech Connect

    Hajic, E.R. ) Bettis, E.A. III )

    1992-01-01

    Nearly the entire late glacial is represented by the sedimentologic, stratigraphic and geomorphic record. Sources and types of discharge and sediment varied considerably in response to style and timing of retreat and readvance of glacial lobes; drainage diversions; magnitude and timing of glacial lake discharges; and non-meltwater inputs. Sedimentology of backflood, slackwater, and tributary and main stem fluvial sediments associated with late Wisconsinan terraces, preserved in Mississippi tributary valley mouths, suggests that from before 16,000 until about 13,300 B.P., when the valleys were undergoing net aggradation during ice retreat, floods were of relatively small to moderate magnitude. Catastrophic flooding out of moraine--dammed lakes occurred down the Illinois Valley between about 16,000 and 15,500 B.P., and down the Mississippi Valley out of Lake Wisconsin around 15,000 B.P. Large-scale, but not necessarily catastrophic, paleochannels in the Illinois Valley were active at least intermittently between 15,500 and about 9,800 B.P. After about 12,200 B.P., the character of Mississippi River discharge changed greatly. Between 12,200 and about 9,500 B.P., multiple relatively large magnitude floods, some catastrophic, from Lake Agassiz, Des Moines lobe englacial or subglacial lakes, and other glacial lakes, passed through the valley causing downcutting, terrace formation, and locally extensive valley widening and left remnants of large-scale paleochannels and streamlined bars. Either catastrophic floods did not pass through the Illinois Valley after 13,300 B.P. or they were sharply attenuated by the time they reached the lower valley; the reverse sloping clayey surface of the Savanna Terrace and associated lacustrine deposits in the lower Illinois Valley show no depositional or erosional evidence suggestive of modification by catastrophic flooding.

  8. Effect of the Long-Term Warming Since the Last Glacial Maximum on Terrestrial Heat Flow

    NASA Astrophysics Data System (ADS)

    Huang, S.; Duan, W.; Wang, H.

    2013-12-01

    Terrestrial heat flow is a geophysical parameter enumerating the outward energy flux from the interior of Earth. It is conventionally measured in boreholes as the product of thermal conductivity of rocks and geothermal gradient, which is subject to the influence from the variations in ground surface temperature condition. As such, on the one hand variation of heat flow density with depth is a direct temperature record of paleoclimate change; on the other hand ground surface temperature history imposes transient perturbation on a heat flow measurement. The assessment of the paleoclimate effect on a heat flow measurement requires a good understanding of the paleoclimate history. In this study, we evaluate the transient effect of the long-term warming since the last glacial maximum on the continental heat flow with both forward and inversion approaches. With the forward approach, we calculate the subsurface temperature response to climate change based on the latest reconstruction of the last 30,000 year paleoclimate history. We then translate the thermal response to the perturbation to a heat flow measurement. With the inversion approach, we use a set of 6,144 qualified data selected from more than 13,000 reported continental heat flow measurements to synthesize a global profile of heat flow versus depth. We then invert this synthesized profile for a paleoclimate history and a steady-state heat flow profile. Our result shows that continental heat flow measurements within the depths down to around 2000 m are systematically lower than the steady state heat flow because of the effect of the last deglacial warming. If this transient perturbation is leaved uncorrected, the mean continental heat flow could be underestimated by as much as twenty percents. This study is supported by the NSF Grant 1202673 and Grant SKLLQG1201 of the Institute of Earth Environment, Chinese Academy of Sciences.

  9. Impact of Glacial Isostatic Adjustment on North America Plate Specific Terrestrial Reference Frame

    NASA Astrophysics Data System (ADS)

    Herring, Thomas; Melbourne, Tim; Murray, Mark; Floyd, Mike; Szeliga, Walter; King, Robert; Phillips, David; Puskas, Christine

    2017-04-01

    We examine the impact of incorporating glacial isostatic adjustment (GIA) models in determining the Euler poles for plate specific terrestrial reference frames. We will specifically examine the impact of GIA models on the realization of a North America Reference frame. We use a combination of the velocity fields determined by the Geodesy Advancing Geosciences and EarthScope (GAGE) Facility which analyzes GPS data from the Plate Boundary Observatory (PBO) and other geodetic quality GPS sites in North America, and from the ITRF2014 re-analysis. Initial analysis of the GAGE velocity field shows reduced root-mean-square (RMS) scatter of velocity estimate residuals when the North America Euler pole is estimated including the ICE-6G GIA mode. The reduction in the north-south direction is from 0.69 mm/yr to 0.52 mm/yr, in the east-west direction from 0.34 mm/yr to 0.30 mm/yr and in height from 0.93 mm/yr to 0.72 mm/yr. The reduction in the height RMS is not surprising since the contemporary geodetic height velocity estimates are used in the developing the ICE-6G model. Contemporary horizontal motions are not used the GIA model development, and the reduction in horizontal RMS provides a partial validation of the model. There is no reduction in the horizontal velocity residual when the ICE-5G model is used. Although removing the ICE-6G model before fitting an Euler pole for the North American plate reduces the RMS of the residuals, the pattern of residuals is still systematic suggesting possibly that a spherically symmetric viscosity model might not be adequate for accurate modeling of the horizontal motions associated with GIA in North America. This presentation in focus on the prospects and impacts of incorporating GIA models in plate-specific Euler poles with emphasis on North America.

  10. Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai

    NASA Astrophysics Data System (ADS)

    Gribenski, Natacha; Jansson, Krister N.; Lukas, Sven; Stroeven, Arjen P.; Harbor, Jonathan M.; Blomdin, Robin; Ivanov, Mikhail N.; Heyman, Jakob; Petrakov, Dmitry A.; Rudoy, Alexei; Clifton, Tom; Lifton, Nathaniel A.; Caffee, Marc W.

    2016-10-01

    The Southern part of the Russian Altai Mountains is recognized for its evidence of catastrophic glacial lake outbursts. However, little is known about the late Pleistocene paleoglacial history, despite the interest in such reconstructions for constraining paleoclimate. In this study, we present a detailed paleoglaciological reconstruction of the Chagan Uzun Valley, in the Russian Altai Mountains, combining for the first time detailed geomorphological mapping, sedimentological logging, and in situ cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. The Chagan Uzun Valley exhibits the most impressive glacial landforms of this sector of the Altai, with extensive lobate moraine belts deposited in the intramontane Chuja Basin, reflecting a series of pronounced former glacial advances. Observations of "hillside-scale" folding and extensive faulting of pre-existing soft sediments within the outer moraine belts, together with the geomorphology, strongly indicate that these moraine belts were formed during surge-like events. Identification of surge-related features is essential for paleoclimate inference because these features correspond to a glacier system that is not in equilibrium with the contemporary climate, but instead largely influenced by various internal and external factors. Therefore, no strict relationship can be established between climatic variables and the pronounced distal glacial extent observed in the Chagan Uzun Valley/Chuja basin. In contrast, the inner (up-valley) glacial landforms of the Chagan Uzun valley were likely deposited during retreat of temperate valley glaciers, close to equilibrium with climate, and so most probably triggered by a general warming. Cosmogenic ages associated with the outermost, innermost, and intermediate moraines all indicate deposition times clustered around 19 ka. However, the actual deposition time of the outermost moraine may slightly predate the 10Be ages due to shielding caused by

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    1996-01-01

    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

  14. Late Quaternary glacial relief evolution revealed by luminescence thermochronometry (Granite Range, Alaska)

    NASA Astrophysics Data System (ADS)

    Valla, P.; Guralnik, B.; Lowick, S.; Champagnac, J.; Herman, F.; Jain, M.; Murray, A.

    2012-12-01

    Long-term exhumation and topographic evolution of mountain belts arise from complex coupling between tectonics, climate and surface processes. Glacial and periglacial processes are especially potent agents to reshape the alpine landscapes by valley carving and/or limiting topography. The recent development of luminescence thermochronometry (e.g., Herman et al., 2010) and its very low closure temperature (0-60°C) opens a new spatial and temporal "window" for the study of latest stages of rock exhumation and thus to address potential topographic relief changes during the late Quaternary. We apply this new method in the Wrangell-St Elias National Park (Alaska), an alpine landscape that exhibits typical glacial features (U-shaped valleys, cirques, moraines). This setting provides an exceptional opportunity to infer potential differences in relief evolution under a gradient of glacial forcing. The Granite Range presents a consistent and progressive eastward increase in the mean elevation, glacier activity, and topographic relief, while low-temperature thermochonometry data display rather homogeneous, yet largely scattered (apatite (U-Th)/He ages of ~15±7 Ma) throughout the massif (e.g., Spotila and Berger, 2010 and references therein). We sampled four elevation profiles over an 80-km East-West transect across the Granite Range (bounded by Tana River to the West and Chitina River to the North). Feldspar separates from 15 bedrock surface samples were dated using an IR-50 SAR protocol (e.g., Murray et al., 2000), and exhibit good internal reproducibility. Apparent ages vary from ~250 ka in the western part of the range, towards younger ages of ~30 ka in the east, thus supporting the notion of high rates of erosion correlated with intense glacial/periglacial activity. We then use a kinetic model to convert apparent ages in mean cooling histories, and couple it with Pecube model (Braun et al., 2012) to extract tectono-geomorphic scenarios. Our results reveal spatially

  15. Late Pleistocene glacial chronology of the Retezat Mts, Southern Carpathians, using 10Be exposure ages

    NASA Astrophysics Data System (ADS)

    Ruszkiczay-Rüdiger, Zsófia; Kern, Zoltán; Urdea, Petru; Braucher, Régis; Madarász, Balázs; Schimmelpfennig, Irene

    2015-04-01

    Our knowledge on the timing of glacial advances in the Southern Carpathians is limited. Recently, some attempts have been made to develop an improved temporal framework for the glaciations of the region using cosmogenic 10Be exposure dating. However, glacial chronology of the Romanian Carpathians remains contradictory. E.g. the timing of the maximum ice advance appears to be asynchronous within the area and also with other dated glacial events in Europe. Main objective of our study is to utilize cosmogenic in situ produced 10Be dating to disentangle the contradictions of the Southern Carpathian Late Pleistocene glacial chronology. Firstly, previously published 10Be data are recalculated in accordance with the new half-life, standardization and production rate of 10Be. The recalculated 10Be exposure ages of the second largest (M2) moraines in the Retezat Mts. appear to be ca. 19-24% older than exposure ages calculated by Reuther et al. (2007, Quat. Int. 164-165, 151-169). This contradicts the earlier conclusions suggesting post LGM age of M2 glacial advance and suggests that M2 moraines can be connected to the end of the LGM with final stabilization possibly at the beginning of the Late Glacial. We emphasize that it is ambiguous to correlate directly the exposure-dated glacier chronologies with millennial scale climate changes due to uncertainties in sample collection and in computation of exposure ages from measured nuclide concentrations. New 10Be samples were collected in order to determine the 10Be exposure age of moraines outside the most prominent generation (M2) including the largest and oldest moraine (M1) and the landforms connected to the smallest ice advances (M4), which remained undated so far. The new exposure ages of M2 moraines are well in harmony with the recalculated ages of Reuther at al. (2007). 10Be exposure age of boulders on the smallest moraine suggest that the last glaciers disappeared in the area during the Late Glacial, indicating no

  16. Late Glacial And Holocene Glacier Fluctuations In Lyngen, Troms, Northern Norway

    NASA Astrophysics Data System (ADS)

    Bakke, J.; Dahl, S. O.; Nesje, A.

    The area north of the Kjosen fjord on the Lyngen Peninsula is mapped focused on glacial geomorphological features, and 13 cirque glaciers and their catchments are in- vestigated in detail. The four lakes Aspevatnet (Holocene glacier fluctuations), Barhei- vatnet (bio-proxy lake), Elvejordsvatnet (Holocene glacier fluctuations) and Trollvat- net (early deglaciation, Holocene slope processes) are investigated and bathymetric maps produced. Based on the laboratory analyses it is possible to reconstruct detailed Holocene glacier fluctuations on glaciers with aspects both to the east and west on the Lyngen Peninsula. From lake Aspevatn at the western side, it seems possible to reconstruct at least 14 local glacial events during the last c. 10 200 cal. yr BP (basin isolated from the sea). Some major glacial events are recorded during the Preboreal, while the glaciers seem to have advanced due to an increase in winter precipitation (as snow) during the Holocene climatic temperature optimum. The final neo-glaciation(s) started c. 3800 cal. yr BP with a marked maximum in the late 18-century. The reconstructed TPW- ELAs for the Aspevatn catchment are situated at altitudes of 790 to 1200 m. By using radiocarbon dated shorelines as age control, it is possible to date reconstructed val- ley glaciers with fossil ice-cored moraines in front, existing from c. 16000 to 11500 cal. yr BP (termination of the Younger Dryas). These glaciers are reconstructed with TPW-ELAs situated between 130 and 650 m when adjusted for land uplift. As these glaciers most likely existed in a cold and dry climate regime, they are suggested to have been polythermal (subpolar). The results show that there is a great potential for reconstructing the complete glacial history of the northern Lyngen Peninsula from the early deglaciation after the LGM to at present. This is so far the northernmost complete Holocene glacier record in Scandinavia.

  17. Fundamentals of Glacial-Interglacial Variability in Tropical Pangaean Aridity during the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Heavens, N. G.; Mahowald, N. M.; Soreghan, G. S.; Soreghan, M. J.

    2011-12-01

    Isotopic and sedimentological evidence suggests that the Late Carboniferous and Early Permian Periods were the most recent era of widespread glaciation prior to the Cenozoic; many aspects of the late Paleozoic glaciations remain disputed. Was glacial deposition on Gondwanaland due to a single ice sheet or multiple ice sheets? Did Milankovitch-scale orbital forcing drive expansion and contraction of ice sheets analogous to the Laurentide and Fennoscandian ice sheets? Or were Gondwanan ice sheets more stable, like the East Antarctic ice sheet? Did variability in Gondwanan ice sheet thickness and extent drive the sea level fluctuations evident in tropical cyclothem sequences from the late Paleozoic? One approach to answering some of these broad questions has been to identify and measure various aspects of sedimentary deposits containing dust (paleoloessites etc.) in order to reconstruct aridity at dust sources and sinks and wind patterns along the path between them. Moreover, glacial processes may be very efficient generators of dust particles. Dust deposits appear to have been widespread and thickly accumulating during late Paleozoic time, suggesting the Early Permian may have been the dustiest time in planetary history. There is strong high-frequency variability in dust deposition/wind patterns, possibly driven by Milankovitch-scale orbital variability and related climate feedbacks, and lower frequency variability driven by tectonic and/or other changes. Yet the sign of the correlation of aridity in tropical Pangaea with glacial extent in Gondwanaland and globally cooler climate in general is still unclear. Broadly speaking, some reconstructions (such as those based on dust) favor glacial aridity, while others favor glacial humidity. To investigate the dynamics of aridity in tropical Pangaea, we have designed and implemented simulations of the Earth's climate during the Asselian-Sakmarian of the Permian using the Community Climate System Model. These simulations

  18. Glacially influenced sedimentation in the late Neoproterozoic Mechum River Formation, Blue Ridge province, Virginia

    NASA Astrophysics Data System (ADS)

    Bailey, Christopher M.; Peters, Shanan E.

    1998-07-01

    The late Neoproterozoic (ca. 700 730 Ma) Mechum River Formation is exposed as a structural inlier within Grenvillian basement in the Blue Ridge province of central Virginia, United States. The southern portion of the Mechum River belt preserves evidence of glaciomarine sedimentation at the margin and basinward of grounding-line fans. Subaqueous glacial till, coarse-grained rhythmites, and dropstones record the incursion of ice into the basin. Marine deposition is evidenced by persistent laminations (cyclopsams) in rhythmically bedded diamictite and possibly by tidally pumped, distal turbidites in laminated mudstones. Glaciomarine sedimentation in the Mechum River Formation may have been coeval with Sturtian-Rapitan glaciations in northwestern Laurentia and Australia, and provides further evidence for a globally cold climate during the late Neoproterozoic.

  19. Early and late Holocene glacial fluctuations and tephrostratigraphy, Cabin Lake, Alaska

    USGS Publications Warehouse

    Zander, Paul D.; Kaufman, Darrell S.; Kuehn, Stephen C.; Wallace, Kristi L.; Anderson, R. Scott

    2013-01-01

    Marked changes in sediment types deposited in Cabin Lake, near Cordova, Alaska, represent environmental shifts during the early and late Holocene, including fluctuations in the terminal position of Sheridan Glacier. Cabin Lake is situated to receive meltwater during periods when the outwash plain of the advancing Sheridan Glacier had aggraded. A brief early Holocene advance from 11.2 to 11.0 cal ka is represented by glacial rock flour near the base of the sediment core. Non-glacial lake conditions were restored for about 1000 years before the water level in Cabin Lake lowered and the core site became a fen. The fen indicates drier-than-present conditions leading up to the Holocene thermal maximum. An unconformity spanning 5400 years during the mid-Holocene is overlain by peat until 1110 CE when meltwater from Sheridan Glacier returned to the basin. Three intervals of an advanced Sheridan Glacier are recorded in the Cabin Lake sediments during the late Holocene: 1110–1180, 1260–1540 and 1610–1780 CE. The sedimentary sequence also contains the first five reported tephra deposits from the Copper River delta region, and their geochemical signatures suggest that the sources are the Cook Inlet volcanoes Redoubt, Augustine and Crater Peak, and possibly Mt Churchill in the Wrangell Volcanic field.

  20. Late-glacial vegetation associated with caribou and mastodon in central Indiana

    NASA Astrophysics Data System (ADS)

    Whitehead, Donald R.; Jackson, Stephen T.; Sheehan, Mark C.; Leyden, Barbara W.

    1982-03-01

    The Christensen Mastodon Site, located in central Indiana, contains a rich assemblage of vertebrates (including mastodon, caribou, and giant beaver), invertebrates, and plant macrofossils in situ in lake and bog sediments of late-glacial age. Studies of pollen and plant macrofossils suggest the existence of open, white spruce-dominated boreal forests from >; 14,000 yr B.P. to ca. 13,000 yr B.P. The regional decline of spruce, local occurrence of black spruce, white spruce, and larch, immigration of many hardwood taxa (e.g., ash, oak, elm), and the initiation of bog development are recorded beginning about 13,000 yr B.P. Recent reconstructions of late-glacial and early postglacial vegetational changes provide a context for understanding the disappearance of mastodons. The dramatic and rapid restriction of boreal forests along the retreating ice margin from 11,000 to 9000 yr B.P. may have caused a substantial reduction of mastodon populations. A diminished population would be more susceptible to small-scale, stochastic events such as short-term extremes of weather, outbreaks of disease, or predation pressure from paleoindian hunters.

  1. A 500-year dual stable isotope tree ring chronology of a Late Glacial cooling event

    NASA Astrophysics Data System (ADS)

    Pauly, Maren; Helle, Gerhard; Büntgen, Ulf; Friedrich, Michael; Heinrich, Ingo; Kromer, Bernd; Nievergelt, Daniel; Reinig, Frederick; Riedel, Frank; Sookdeo, Adam; Treydte, Kerstin; Wacker, Lukas; Brauer, Achim

    2017-04-01

    A recent discovery of over 250 subfossil pine trees in Zürich (dated 14 000 - 11 000 cal BP) has provided the opportunity to study the inconsistent warming transition from the last ice age to the current interglacial. This period (the Late Glacial) has been extensively studied through the development of mostly non-tree ring palaeoclimate proxy records due to the intrigue of numerous prominent climate oscillations. However, such existing (lake sediment and ice core) records often lack the temporal resolution required to interpret rapid environmental changes. Tree rings can help to resolve such events due to their high resolution (annually-resolved) growth banding and absolute dating potential. Moreover, the analysis of stable isotopes can strongly improve the climate signal implemented in tree-ring width. Since numerous environmental conditions are all integrated in the rather simple ring-width series, measurements of chemical tree responses (via stable isotopes) can greatly refine the climate-growth-dynamics. In this study, we are developing a well replicated 500-year annually resolved dual stable isotope (δ18O, δ13C) chronology from tree-ring cellulose, in an effort to reconstruct the environmental dynamics of a short-term Late Glacial cooling event (13 950 - 13 450 cal BP) in an otherwise naturally warming world. We will present and discuss the biological response to this rapid climate oscillation in the face of low atmospheric CO2 concentrations and other site conditions without any human fingerprint.

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

    NASA Astrophysics Data System (ADS)

    Lacey, Jack; Francke, Alexander; Leng, Melanie; Vane, Chris; Wagner, Bernd

    2015-04-01

    Lake Ohrid (Macedonia/Albania) is one of the world's oldest lakes and is renowned for its high degree of biological diversity. It is the target site for the ICDP SCOPSCO (Scientific Collaboration on Past Speciation Conditions in Lake Ohrid) project, an international research initiative to study the links between geology, environment and the evolution of endemic taxa. In 2011 a 10-meter core was recovered from the western shore of Lake Ohrid adjacent to the Lini Peninsula. Here we present high-resolution stable isotope and geochemical data from this core through the Late Glacial to Holocene to reconstruct past climate and hydrology (TIC, δ18Ocalcite, δ13Ccalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock-Eval pyrolysis). The data identify 3 main zones: (1) the Late Glacial-Holocene transition represented by low TIC, TOC and higher isotope values, (2) the early to mid-Holocene characterised by higher TOC, TOC/N and lower δ18Ocalcite, and (3) the late Holocene which shows a marked decrease in TIC and TOC. In general there is an overall trend of increasing δ18Ocalcite from 9 ka to present, suggesting progressive aridification through the Holocene, which is 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 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 SCOPSCO project cores recovered in spring-summer 2013 dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, 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 δ18Ocalcite 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.

  4. Late Glacial and Holocene Record of Hydroclimate in the San Luis Valley, Southern Colorado, USA

    NASA Astrophysics Data System (ADS)

    Yuan, F.; Koran, M.

    2012-12-01

    Lake sediments from the San Luis Valley, south-central Colorado, archive a detailed record of Late Glacial and Holocene climatic fluctuations in the southern Rocky Mountains. Together with radiometric dating analysis, measurements of grain size, magnetic susceptibility, total inorganic carbon (TIC), oxygen and carbon isotopic composition of the TIC fraction on sediment samples from San Luis Lake (at an average resolution of 60 years per sample) allow us to generate a sediment record of climatic change in the region spanning the last 16ka (1 ka=1000 cal yrs). This record documents the timing and duration of major climate episodes and trends, comparable to the existing paleoclimate records from the American Southwest. The Late Glacial record of San Luis Lake contains a big wet episode in the late part of the Mystery Interval (MI), a relatively dry climate during Bølling-Allerød (B/A) warm interval, and a relatively wet episode during the Younger Dryas (YD) interval, similar to the lake-level record found in the Estancia basin in central New Mexico. The early to middle Holocene record of d18O in the San Luis Lake parallels the calcite d18O record of Bison Lake in northern Colorado, documenting a history of significant change in precipitation seasonality across the northern boundary of the North American monsoon (NAM). The middle Holocene epoch is characterized by greater variations in magnetic susceptibility, d18O and d13C, suggesting the prevalence of wet, variable or transitional climate conditions. In contrast, the late Holocene climate is relatively dry, as indicated by more positive values of d18O in San Luis Lake. The results of this study reveal a complex history of climate evolution due to the interactions of two seasonally distinct precipitation regimes with mountainous landforms in the region.

  5. A Late Glacial Environmental Reconstruction performed on Lacustrine Sediments from the Southern Tibetan Plateau identifies regional Monsoon Variations

    NASA Astrophysics Data System (ADS)

    Henkel, K.; Ahlborn, M.; Haberzettl, T.; Alivernini, M.; Kasper, T.; Thiele, A.; St-Onge, G.; Daut, G.; Frenzel, P.; Gleixner, G.; Wang, J.; Zhu, L.; Maeusbacher, R.

    2014-12-01

    The Tibetan Plateau (TP) is very sensitive to climate variations and is therefore an ideal study site to investigate past climate changes. Influenced by the Asian Monsoon system, the numerous lake systems on the TP serve as valuable archives for past hydrological changes, which are assumed to be caused by variations in strength and extent of the monsoonal impact. The lacustrine record from the terminal lake Tangra Yumco (4540 m a.s.l., 31°13'N, 86°43'E) consists of an interbedding of fine-grained silty sediments with laminations of different thicknesses (sub-mm to cm) and partly intercalated blackish sandy layers. Thin section analysis in the laminated areas reveals cyclic laminations composed of a carbonate and a detrital layer. Homogenous intervals represent turbidite deposits which are further detected based on lithology, radiography as well as changes in the water content, grain size, Ti-values (XRF) and in the paleomagnetic parameter median destructive field. The chronology is based on 27 AMS-radiocarbon ages on bulk organic matter and one piece of wood, which is of terrestrial origin. To determine a possible carbon reservoir effect, additional surface sediment samples and one modern aquatic plant were measured. The calculated reservoir effect of 2,120 +110/-90 years is assumed to be constant over the time and thus the base of the record reveals a corrected radiocarbon age of 17,270 +325/-310 cal BP. Additionally, investigations on paleomagnetic secular variations were carried out, showing that since 15,900 cal BP the record preserved a well-defined magnetization recording a genuine paleomagnetic signal. Regarding the geochemical (organic and inorganic), sedimentological, mineralogical and micropaleontological analyses, a low lake level with a high terrestrial input is observed for the Late Glacial. At 15.6 ka cal BP, a change in the sediment accumulation rate, increased allochthoneous input and changing ostracod fauna point to an increasing lake level. In

  6. 3D-seismic observations of Late Pleistocene glacial dynamics on the central West Greenland margin

    NASA Astrophysics Data System (ADS)

    Hofmann, Julia; Knutz, Paul; Cofaigh, Colm Ó.

    2016-04-01

    Fast-flowing ice streams and outlet glaciers exert a major control on glacial discharge from contemporary and palaeo ice sheets. Improving our understanding of the extent and dynamic behaviour of these palaeo-ice streams is therefore crucial for predictions of the response of ice sheets to present and future climate warming and the associated implications for global sea level. This poster presents results from two 3D-seismic surveys located on the shelf adjoining the Disko Bay trough-mouth fan (TMF), one of the largest glacial outlet systems in Greenland. Located at the seaward terminus of the c. 370 km long cross-shelf Disko Trough, the Disko Bay TMF was generated by highly efficient subglacial sediment delivery onto the continental slopes during repeated ice-stream advances. A variety of submarine glacial landform assemblages are recognised on the seabed reflecting past ice-stream activity presumably related to glacial-interglacial cycles. The 3D-seismic volumes cover the shallow banks located north and south of the Disko Trough. The focus of this study is the seabed and the uppermost stratigraphic interval associated with the Late Stage of TMF development, presumably covering the late Pleistocene (Hofmann et al., submitted). Seabed morphologies include multiple sets of ridges up to 20 m high that extend in NW-SE direction for c. 30 km, and cross-cutting curvilinear furrows with maximum lengths of c. 9 km and average depths of c. 4.5 m. Back-stepping, arcuate scarps facing NW define the shelf break on the northern survey, comprising average widths of c. 4.5 km and incision depths of c. 27.5 m. The large transverse ridge features on the southern survey are likely ice-marginal and are interpreted as terminal moraine ridges recording the existence of a shelf-edge terminating, grounded Late Weichselian ice sheet. The furrows, most prominent on the outer shelf adjoining the shallow banks and partly incising the moraine ridges, are interpreted as iceberg ploughmarks

  7. Marine palynological record for tropical climate variations since the late last glacial maximum in the northern South China Sea

    NASA Astrophysics Data System (ADS)

    Dai, Lu; Weng, Chengyu

    2015-12-01

    The upper part (191-1439 cm) of the marine sediment core MD05-2906 from the northern South China Sea (SCS) was palynologically investigated. The chronology suggested that it covered the record since ~19 calendar kiloyears before present (cal ka BP) and revealed a detailed environmental change history since the late last glacial maximum (LGM). During the late LGM, due to the lowered sea level (~100 m lower) and the shortened distance from the shore to the study site, the pollen concentration was very high. The pollen assemblages were dominated by non-arboreal taxa, especially Artemisia pollen, before ~15 cal ka BP. Abundant subtropical and tropical pollen taxa were still important components and a south subtropical climate prevailed during the late LGM. The coexistent rich Artemisia pollen possibly was not derived from near shores, but was derived mainly from the northern exposed continental shelf in the East China Sea (ECS). After ~15 cal ka BP, with the rise in the sea level and enhanced distance from the pollen source areas to the core site, pollen concentrations started to decline gradually. However, during the late deglaciation and early Holocene, the higher concentrations of many pollen taxa reoccurred, which cannot be attributed to the sea level changes. Pinus pollen deposited in the core, which is considered to be mostly water-carried based on many modern pollen surveys, also started to dramatically increase at the same time. Therefore, the higher pollen concentration, with more Pinus and Typha (an aquatic plant) pollen indicated a notably enhanced terrestrial runoff and precipitation during the last deglaciation/Holocene transition (~11.3-9.4 cal ka BP). We inferred that a strong summer monsoon occurred at this time. During the late LGM/deglaciation transition period, the pollen assemblage reflected a gradually warming climate, and the climate fluctuations derived from the high-latitudes were not well-identified. This study suggests that solar insolation

  8. Atmospheric radiocarbon calibration to 45,000 yr B.P.: late glacial fluctuations and cosmogenic isotope production

    PubMed

    Kitagawa; van der Plicht J

    1998-02-20

    More than 250 carbon-14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from Lake Suigetsu (Japan) provide a first atmospheric calibration for almost the total range of the radiocarbon method (45,000 years before the present). The results confirm the (recently revised) floating German pine chronology and are consistent with data from European and marine varved sediments, and combined uranium-thorium and carbon-14 dating of corals up to the Last Glacial Maximum. The data during the Glacial show large fluctuations in the atmospheric carbon-14 content, related to changes in global environment and in cosmogenic isotope production.

  9. Atmospheric radiocarbon calibration to 45,000 yr B.P.: Late glacial fluctuations and cosmogenic isotope production

    SciTech Connect

    Kitagawa, H.; Plicht, J. van der

    1998-02-20

    More than 250 carbon-14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from Lake Suigetsu (Japan) provide a first atmospheric calibration for almost the total range of the radiocarbon method (45,000 years before the present). The results confirm the (recently revised) floating German pine chronology and are consistent with data from European and marine varved sediments, and combined uranium-thorium and carbon-14 dating of corals up to the Last Glacial Maximum. The data during the Glacial show large fluctuations in the atmospheric carbon-14 content, related to changes in global environment and in cosmogenic isotope production. 3 refs., 3 figs.

  10. Reconstruction of hydrologic responses to late-Glacial (9-33ka) abrupt climate transitions in the coastal southwest United States

    NASA Astrophysics Data System (ADS)

    Wu, M.; Feakins, S. J.; Kirby, M. E.

    2013-12-01

    A sediment core retrieved from Lake Elsinore, the largest natural freshwater lake in southern California, spans an age of 9 to 33ka BP. The period includes several late-Glacial abrupt climate transitions such as the Heinrich events (HEs) 1-3, the Bølling-Allerød (B-A), and the Younger Dryas (YD). This terrestrial site provides a unique opportunity to evaluate changes in hydrology in coastal southwest United States across these key abrupt climate transition events. Hydrogen isotopic ratios (δDwax) of the long-chain C28 alkanoic acid, a biomarker for terrestrial leaf wax, extracted from the sediments, were analyzed to reveal the δD of precipitation water in the past (δDprecip). In the modern climate, higher δDprecip values are associated with moisture sourced from the tropical Pacific, which brings a drier and warmer climate, whereas lower δDprecip values are associated with moisture sourced from north Pacific brought by polar jet stream, causing a wetter and colder climate. δDwax ranges from about -210‰ to -100‰ between late-Glacial HEs and the beginning of Holocene. The pattern generally correlates with Greenland ice core and regional speleothem records, with lower δDwax values corresponding to colder periods (HEs), and higher δDwax values corresponding to warmer periods (B-A and early Holocene). We infer cold and wet climate with north Pacific sourced moisture during the glacial, followed by gradual warming and drying into the B-A and Holocene, when the moisture sources shifted to the tropical Pacific. There is no substantive response to the YD. The fluctuations of δDwax into and out of the HEs can be as large as about 60‰, suggesting greatly variable hydrology across these late-Glacial abrupt climate transition events. The large shifts in δDwax signal during deglaciation and HEs indicate that hydrology in the coastal southwest US has responded sensitively to climate change, and therefore has important implications for water resources in this

  11. Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings

    NASA Astrophysics Data System (ADS)

    Bayon, Germain; de Deckker, Patrick; Magee, John W.; Germain, Yoan; Bermell, Sylvain; Tachikawa, Kazuyo; Norman, Marc D.

    2017-03-01

    Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use neodymium isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.

  12. Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

    USGS Publications Warehouse

    Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

    1995-01-01

    Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

  13. Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile.

    PubMed

    Moreno, P I; Jacobson, G L; Lowell, T V; Denton, G H

    2001-02-15

    Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.

  14. Extensive wet episodes in Late Glacial Australia resulting from high-latitude forcings

    PubMed Central

    Bayon, Germain; De Deckker, Patrick; Magee, John W.; Germain, Yoan; Bermell, Sylvain; Tachikawa, Kazuyo; Norman, Marc D.

    2017-01-01

    Millennial-scale cooling events termed Heinrich Stadials punctuated Northern Hemisphere climate during the last glacial period. Latitudinal shifts of the intertropical convergence zone (ITCZ) are thought to have rapidly propagated these abrupt climatic signals southward, influencing the evolution of Southern Hemisphere climates and contributing to major reorganisation of the global ocean-atmosphere system. Here, we use neodymium isotopes from a marine sediment core to reconstruct the hydroclimatic evolution of subtropical Australia between 90 to 20 thousand years ago. We find a strong correlation between our sediment provenance proxy data and records for western Pacific tropical precipitations and Australian palaeolakes, which indicates that Northern Hemisphere cooling phases were accompanied by pronounced excursions of the ITCZ and associated rainfall as far south as about 32°S. Comparatively, however, each of these humid periods lasted substantially longer than the mean duration of Heinrich Stadials, overlapping with subsequent warming phases of the southern high-latitudes recorded in Antarctic ice cores. In addition to ITCZ-driven hydroclimate forcing, we infer that changes in Southern Ocean climate also played an important role in regulating late glacial atmospheric patterns of the Southern Hemisphere subtropical regions.

  15. Glacial geomorphology of terrestrial-terminating fast flow lobes/ice stream margins in the southwest Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Evans, David J. A.; Young, Nathaniel J. P.; Ó Cofaigh, Colm

    2014-01-01

    Glacial geomorphological mapping of southern Alberta, Canada, reveals landform assemblages that are diagnostic of terrestrial-terminating ice streams/fast flowing outlet glaciers with lobate snouts. Spatial variability in features that comprise the landform assemblages reflects changes in (a) palaeo-ice stream activity (switch on/off); and (b) snout basal thermal regimes associated with climate sensitive, steady state flow. Palaeo-ice stream tracks reveal distinct inset sequences of fan-shaped flowsets indicative of receding lobate ice stream margins. Former ice lobe margins are demarcated by (a) major, often glacially overridden transverse moraine ridges, commonly comprising glacitectonically thrust bedrock; and (b) minor, closely spaced recessional push moraines and hummocky moraine arcs. Details of these landform types are well exhibited around the former southern margins of the Central Alberta Ice Stream, where larger scale, more intensive mapping identifies a complex glacial geomorphology comprising minor transverse ridges (MTR types 1-3), hummocky terrain (HT types 1-3), flutings, and meltwater channels/spillways. The MTR type 1 constitute the summit corrugation patterns of glacitectonic thrust moraines or major transverse ridges and have been glacially overrun and moderately streamlined. The MTR type 2 sequences are recessional push moraines similar to those developing at modern active temperate glacier snouts. The MTR type 3 document moraine construction by incremental stagnation because they occur in association with hummocky terrain. The close association of hummocky terrain with push moraine assemblages indicates that they are the products of supraglacial controlled deposition on a polythermal ice sheet margin, where the HT type 3 hummocks represent former ice-walled lake plains. The ice sheet marginal thermal regime switches indicated by the spatially variable landform assemblages in southern Alberta are consistent with palaeoglaciological

  16. Radiocarbon chronology of the late-glacial Puerto Bandera moraines, Southern Patagonian Icefield, Argentina

    NASA Astrophysics Data System (ADS)

    Strelin, J. A.; Denton, G. H.; Vandergoes, M. J.; Ninnemann, U. S.; Putnam, A. E.

    2011-09-01

    We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages ( n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 14C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 14C yrs BP to 13,450 ± 150 14C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance. Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 14C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 14C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 14C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 14C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini

  17. Validation of climate model-inferred regional temperature change for late-glacial Europe.

    PubMed

    Heiri, Oliver; Brooks, Stephen J; Renssen, Hans; Bedford, Alan; Hazekamp, Marjolein; Ilyashuk, Boris; Jeffers, Elizabeth S; Lang, Barbara; Kirilova, Emiliya; Kuiper, Saskia; Millet, Laurent; Samartin, Stéphanie; Toth, Monika; Verbruggen, Frederike; Watson, Jenny E; van Asch, Nelleke; Lammertsma, Emmy; Amon, Leeli; Birks, Hilary H; Birks, H John B; Mortensen, Morten F; Hoek, Wim Z; Magyari, Enikö; Muñoz Sobrino, Castor; Seppä, Heikki; Tinner, Willy; Tonkov, Spassimir; Veski, Siim; Lotter, André F

    2014-09-11

    Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized palaeoclimate data sets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth's recent past. Here we present a new chironomid-based palaeotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our palaeotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe.

  18. Validation of climate model-inferred regional temperature change for late-glacial Europe

    PubMed Central

    Heiri, Oliver; Brooks, Stephen J.; Renssen, Hans; Bedford, Alan; Hazekamp, Marjolein; Ilyashuk, Boris; Jeffers, Elizabeth S.; Lang, Barbara; Kirilova, Emiliya; Kuiper, Saskia; Millet, Laurent; Samartin, Stéphanie; Toth, Monika; Verbruggen, Frederike; Watson, Jenny E.; van Asch, Nelleke; Lammertsma, Emmy; Amon, Leeli; Birks, Hilary H.; Birks, H. John B.; Mortensen, Morten F.; Hoek, Wim Z.; Magyari, Enikö; Sobrino, Castor Muñoz; Seppä, Heikki; Tinner, Willy; Tonkov, Spassimir; Veski, Siim; Lotter, André F.

    2014-01-01

    Comparisons of climate model hindcasts with independent proxy data are essential for assessing model performance in non-analogue situations. However, standardized paleoclimate datasets for assessing the spatial pattern of past climatic change across continents are lacking for some of the most dynamic episodes of Earth's recent past. Here we present a new chironomid-based paleotemperature dataset designed to assess climate model hindcasts of regional summer temperature change in Europe during the late-glacial and early Holocene. Latitudinal and longitudinal patterns of inferred temperature change are in excellent agreement with simulations by the ECHAM-4 model, implying that atmospheric general circulation models like ECHAM-4 can successfully predict regionally diverging temperature trends in Europe, even when conditions differ significantly from present. However, ECHAM-4 infers larger amplitudes of change and higher temperatures during warm phases than our paleotemperature estimates, suggesting that this and similar models may overestimate past and potentially also future summer temperature changes in Europe. PMID:25208610

  19. Adaptation and niche construction in human prehistory: a case study from the southern Scandinavian Late Glacial

    PubMed Central

    Riede, Felix

    2011-01-01

    The niche construction model postulates that human bio-social evolution is composed of three inheritance domains, genetic, cultural and ecological, linked by feedback selection. This paper argues that many kinds of archaeological data can serve as proxies for human niche construction processes, and presents a method for investigating specific niche construction hypotheses. To illustrate this method, the repeated emergence of specialized reindeer (Rangifer tarandus) hunting/herding economies during the Late Palaeolithic (ca 14.7–11.5 kyr BP) in southern Scandinavia is analysed from a niche construction/triple-inheritance perspective. This economic relationship resulted in the eventual domestication of Rangifer. The hypothesis of whether domestication was achieved as early as the Late Palaeolithic, and whether this required the use of domesticated dogs (Canis familiaris) as hunting, herding or transport aids, is tested via a comparative analysis using material culture-based phylogenies and ecological datasets in relation to demographic/genetic proxies. Only weak evidence for sustained niche construction behaviours by prehistoric hunter–gatherer in southern Scandinavia is found, but this study nonetheless provides interesting insights into the likely processes of dog and reindeer domestication, and into processes of adaptation in Late Glacial foragers. PMID:21320895

  20. Late Wisconsinan glacial, lacustrine and marine stratigraphy in the Champlain Valley, New York and Vermont

    SciTech Connect

    Franzi, D.A. . Center for Earth and Environmental Science); Hunt, A.S. . Dept. of Geology)

    1993-03-01

    The stratigraphy of late-glacial, and postglacial deposits and landforms in the Champlain Lowland is interpreted from high-resolution (3.5 khz transducer) acoustical profiling and piston core analysis of sediments beneath Lake Champlain in conjunction with detailed morphologic sequence mapping of surficial deposits. The sediments of Lake Champlain have been grouped by acoustic, lithologic, and biostratigraphic criteria into three stratigraphic units that were deposited successively into Lake Vermont, the Champlain Sea, and Lake Champlain. The maximum thickness of unconsolidated sediment is known to exceed 200 meters locally. Biostratigraphic subdivision of these units using pollen, diatoms, ostracodes, and foraminifera provides further definition of late-glacial and postglacial events in the region and indicates that transitional environments occurred as conditions changed from proglacial lake to marine estuary to freshwater lake. The stratigraphy of surficial deposits records proglacial lake sequences in the Champlain Valley and its tributaries. Interbasinal correlation of the tributary proglacial lake sequences and reconstructed ice marginal positions, is consistent with a model of generally synchronous, northward recession controlled primarily by backwasting of active continental ice lobes. Minor asynchroneity of retreat rates may be attributed to local differences in subglacial topography and changes in proglacial lake level, both of which may affect calving rates. Northward ice recession of the Champlain Lobe allowed successive inundation of tributary valleys by Lake Vermont. Elevations of deltaic sandplains reveal at least three distinct lake levels in the northwestern Champlain Valley. The highest level corresponds to the Coveville Stage while the lower two represent levels of the Fort Ann Stage.

  1. Late glacial and Holocene history of the Greenland Ice Sheet margin, Nunatarssuaq, Northwestern Greenland

    NASA Astrophysics Data System (ADS)

    Farnsworth, L. B.; Kelly, M. A.; Axford, Y.; Bromley, G. R.; Osterberg, E. C.; Howley, J. A.; Zimmerman, S. R. H.; Jackson, M. S.; Lasher, G. E.; McFarlin, J. M.

    2015-12-01

    Defining the late glacial and Holocene fluctuations of the Greenland Ice Sheet (GrIS) margin, particularly during periods that were as warm or warmer than present, provides a longer-term perspective on present ice margin fluctuations and informs how the GrIS may respond to future climate conditions. We focus on mapping and dating past GrIS extents in the Nunatarssuaq region of northwestern Greenland. During the summer of 2014, we conducted geomorphic mapping and collected rock samples for 10Be surface exposure dating as well as subfossil plant samples for 14C dating. We also obtained sediment cores from an ice-proximal lake. Preliminary 10Be ages of boulders deposited during deglaciation of the GrIS subsequent to the Last Glacial Maximum range from ~30-15 ka. The apparently older ages of some samples indicate the presence of 10Be inherited from prior periods of exposure. These ages suggest deglaciation occurred by ~15 ka however further data are needed to test this hypothesis. Subfossil plants exposed at the GrIS margin on shear planes date to ~ 4.6-4.8 cal. ka BP and indicate less extensive ice during middle Holocene time. Additional radiocarbon ages from in situ subfossil plants on a nunatak date to ~3.1 cal. ka BP. Geomorphic mapping of glacial landforms near Nordsø, a large proglacial lake, including grounding lines, moraines, paleo-shorelines, and deltas, indicate the existence of a higher lake level that resulted from a more extensive GrIS margin likely during Holocene time. A fresh drift limit, characterized by unweathered, lichen-free clasts approximately 30-50 m distal to the modern GrIS margin, is estimated to be late Holocene in age. 10Be dating of samples from these geomorphic features is in progress. Radiocarbon ages of subfossil plants exposed by recent retreat of the GrIS margin suggest that the GrIS was at or behind its present location at AD ~1650-1800 and ~1816-1889. Results thus far indicate that the GrIS margin in northwestern Greenland

  2. Post-Late Glacial calcareous tufas from the Kurai fault zone (Southeastern Gorny Altai, Russia)

    NASA Astrophysics Data System (ADS)

    Kokh, Svetlana N.; Sokol, Ella V.; Deev, Evgeny V.; Ryapolova, Yuliya M.; Rusanov, Gennady G.; Tomilenko, Anatoliy A.; Bul'bak, Taras A.

    2017-06-01

    Calcareous tufa deposits have been discovered in the Chibitka River valley near Lake Cheybek-Kohl, at the junction of the Kurai and Teletsk-Kurai large active faults in the southeastern Gorny Altai, Russia, at an altitude of 1800-2000 m. Fossil tufa is composed of calcite and cements Holocene grey colluvium and glacial till deposited by the Late Glacial Chibitka Glacier. Current tufa precipitation has been observed from a low-flow spring with cold (10 °C) HCO3-SO4-Ca-Mg water, pH = 6.86. The stable isotope composition of spring water is - 5.8‰ VPDB δ13C of dissolved inorganic carbon and - 14.5‰ VSMOW δ18O. Modern tufa consists of thin laminated Mg-calcite and Sr-aragonite crusts, with abundant algae and biofilms on their surfaces. Both modern and fossil tufas are depleted in REE (a total of 0.40-16.4 ppm and 0.40-3.80 ppm, respectively) and share similar PAAS-normalised REE + Y spectra with HREE enrichment and slight progressive LREE depletion. The modern tufas show positive δ13C values of 0.1‰ to 0.9‰ VPDB while the fossil ones have an isotopically lighter composition of δ13C = - 4.1‰ to - 1.9‰ VPDB; the δ18O range is very narrow (- 13.0 to - 13.8‰ VPDB). Both stable isotope and trace-element signatures (including REE patterns) of the tufas indicate precipitation from cold groundwaters subjected to prolonged interaction with a carbonate aquifer (the Baratal Group of limestone and dolostone) in a cold continental climate similar to the present conditions. Tufa deposition in the Lake Cheybek-Kohl area began with the onset of post-Late Glacial global warming and permafrost degradation. Unlike the fossil tufa formation, current precipitation of freshwater carbonates has been microbially mediated. The discovered tufa deposits provide new palaeoclimatic and active tectonic proxies in the southeastern Gorny Altai.

  3. Late-stage accretion and habitability of terrestrial planets

    NASA Astrophysics Data System (ADS)

    Raymond, Sean Neylon

    The final stage in the formation of terrestrial planets consists of the accumulation of ~1000 km "planetary embryos" and ~1 km planetesimals via collisional accretion., under the mutual gravity of other solid bodies and the gas giant planets (if any). Water is delivered to planets via collisions with volatile-rich bodies that condensed past the snow line, beyond about 2.5 AU. We present results of a large number of relatively low-resolution simulations, designed to assess the predictability of systems of terrestrial planets as a function of "observables" such as the orbit of gas giant planets. These show that a variety of terrestrial planets can form, from small, dry, Mars-like worlds to planets with similar properties to Earth, to >3 Earth mass "water worlds" with >=30 times as much water as the Earth. The terrestrial planets are largely shaped by the influence of the giant planets and the surface density of material. We have uncovered trends between the terrestrial planets and (i) the mass, (ii) the orbital distance and (iii) the orbital eccentricity of a giant planet, (iv) the surface density of the disk, and (v) the disk's density profile. Five simulations with 1000-2000 particles reveal new aspects of the accretion process Water is delivered to the terrestrial planets as a few large planetesimals in a "hit or miss" process, and as billions of planetesimals in a robust way. The water delivery process is therefore more robust than previously thought, implying that the range of water contents of extra-solar Earths is less stochastic than indicated in previous studies; most planets accrete water- rich bodies. We simulate terrestrial accretion in the presence of close-in giant planets (e.g., "hot jupiters"), assuming these form and migrate quickly. Potentially habitable planets can form in these systems, but are likely to be iron-poor. Asteroid belts may exist between the terrestrial planets and hot jupiters in these systems. We have also tested the accretion

  4. The large late-glacial Ho eruption of the Hudson volcano, southern Chile

    NASA Astrophysics Data System (ADS)

    Weller, D.; Miranda, C. G.; Moreno, P. I.; Villa-Martínez, R.; Stern, C. R.

    2014-06-01

    Lakes formed in the Aysén region of southern Chile after the retreat of mountain glaciers, established by ~17,900 calendar years before present (cal years BP) or earlier, contain numerous late-glacial and Holocene tephra layers derived from >70 eruptions of the volcanoes in the region, including Hudson, the southernmost in the Andean Southern Volcanic Zone (SVZ). Sediment cores from seven of these lakes contain an unusually thick late-glacial age tephra layer, which based on its distribution and bulk trace-element composition was derived from a large explosive eruption of Hudson volcano between 17,300 and 17,440 cal years BP and is termed Ho. In 13 cores from six of these lakes, each located ~100 km generally northeast of Hudson, the Ho tephra layer ranges between 50 and 88 cm in thickness, and contains pumice grains up to 2 cm in maximum diameter. Comparison with three previously documented large explosive Holocene Hudson eruptions (H1 at 7,750 cal years BP, H2 at 3,920 cal years BP, and H3 in 1991 AD) suggests that Ho was larger, with an estimated tephra volume of >20 km3, the largest post-glacial eruption documented for any volcano in the southern Andes and most likely responsible for the formation of the Hudson caldera. In total, Hudson has erupted ≥45 km3 of pyroclastic material in the last ~17,500 years, making it the most productive volcano in the southern Andes in terms of the total volume erupted since the beginning of deglaciation in the region. Chemical stratification is not seen in the waterlain Ho tephra, but these deposits are bi-modal, consisting of a much greater proportion of dark glassy basaltic-trachyandesite dense fragments and pumice, with glasses which range between 55 and 59 wt.% SiO2, along with volumetrically less-significant lighter-colored trachydacite pumice, with glass of 66 wt.% SiO2. In contrast, H1 products are trachyandesitic in composition, H2 ones are more felsic than H1, being composed essentially of trachydacite, and although

  5. Extensive deposits on the Pacific plate from Late Pleistocene North American glacial lake outbursts

    USGS Publications Warehouse

    Normark, W.R.; Reid, J.A.

    2003-01-01

    One of the major unresolved issues of the Late Pleistocene catastrophic-flood events in the northwestern United States (e.g., from glacial Lake Missoula) has been what happened when the flood discharge reached the ocean. This study compiles available 3.5-kHz high-resolution and airgun seismic reflection data, long-range sidescan sonar images, and sediment core data to define the distribution of flood sediment in deepwater areas of the Pacific Ocean. Upon reaching the ocean at the mouth of the Columbia River near the present-day upper continental slope, sediment from the catastrophic floods continued flowing downslope as hyperpycnally generated turbidity currents. The turbidity currents resulting from the Lake Missoula and other latest Pleistocene floods followed the Cascadia Channel into and through the Blanco Fracture Zone and then flowed west to the Tufts Abyssal Plain. A small part of the flood sediment, which was stripped off the main flow at a bend in the Cascadia Channel at its exit point from the Blanco Fracture Zone, continued flowing more than 400 km to the south and reached the Escanaba Trough, a rift valley of the southern Gorda Ridge. Understanding the development of the pathway for the Late Pleistocene flood sediment reaching Escanaba Trough provides insight for understanding the extent of catastrophic flood deposits on the Pacific plate.

  6. Late-glacial vegetation and climate at the Manis Mastodon site, Olympic Peninsula, Washington

    NASA Astrophysics Data System (ADS)

    Petersen, Kenneth L.; Mehringer, Peter J.; Gustafson, Carl E.

    1983-09-01

    As the late Wisconsin Cordilleran Ice Sheet retreated, sediment accumulated in shallow depressions at the Manis Mastodon Archaeological site on the Olympic Peninsula, near Sequim, Washington. Pollen, plant macrofossils, and bones of mastodon, caribou, and bison occur within the lower 47 cm of these deposits. The fossil pollen and seed assemblages indicate persistence for 1000 yr (11,000-12,000 yr B.P.) of an herb-and-shrub-dominated landscape at a time when forest species appear elsewhere in Washington and in adjacent British Columbia. At present, Sequim is near the northern coastal limits of both Cactaceae and Ceratophyllum. Mean annual precipitation is 42.7 cm and summer temperatures average 15°-16°C in July. The absence of coniferous trees and the presence of cactus and Ceratophyllum in late-glacial sediments are explained by a regional climate that was drier and at least as warm as today. These conditions persisted in the rain shadow of the Olympic Mountains until at least 11,000 yr B.P.

  7. 10Be cosmic-ray exposure dating of moraines and rock avalanches in the Upper Romanche valley (French Alps): Evidence of two glacial advances during the Late Glacial/Holocene transition

    NASA Astrophysics Data System (ADS)

    Chenet, Marie; Brunstein, Daniel; Jomelli, Vincent; Roussel, Erwan; Rinterknecht, Vincent; Mokadem, Fatima; Biette, Melody; Robert, Vincent; Léanni, Laëtitia

    2016-09-01

    Cosmic-ray exposure (CRE) dating of moraines allow glacier fluctuations and past climate change reconstructions. In the French Alps, there is a lack of moraine dating for the Late Glacial/Holocene transition period. Here we present a chronology of glacier advances in the Upper Romanche valley (French Alps - Massif des Ecrins) based on 10Be CRE dating. CRE ages of moraines of 13.0 ± 1.1 ka and 12.4 ± 1.5 ka provide evidence for two stages of glacial advance or standstill at the end of the Late Glacial. The CRE dating of a rock avalanche deposit at 12.2 ± 1.5 ka is attributed to post-glacial debuttressing and reveals rapid deglaciation at the end of the Late Glacial. A CRE age of 7.1 ± 0.7 ka of a second mass-wasting, whose triggering factor is unidentified so far, indicates that up to an altitude of 2300 m a.s.l., the valley was ice-free as of ∼7 kyr at the latest. The re-evaluation of 21 moraine 10Be CRE ages from nine glacial valleys across the Alps shows multiple glacial advances occurring at the Late Glacial/Holocene transition. These results lead to a re-evaluation of the importance of cooling events during the Allerød and the Younger Dryas in the Alps.

  8. Testing a new temperature proxy using the late-glacial and early Holocene chironomid record of Rotsee, Switzerland

    NASA Astrophysics Data System (ADS)

    Verbruggen, F.; Heiri, O.; Reichart, G.-J.; Lotter, A. F.

    2009-04-01

    High concentrations of chironomid head capsules in late-glacial and early Holocene sediments from Rotsee, a lake in Central Switzerland, provide an excellent opportunity to study past climatic change and its effects on biota. Chironomids (non-biting midges) have been widely used as palaeoecological indicators of environmental change. In this study, we are testing the potential of these chitinous microfossils as a proxy to produce d18O records. Background information on the Rotsee record is provided by high-resolution records of organic matter and carbonate content. Periods of rapid climatic change are reflected by variations in stable oxygen isotope concentrations analyzed on bulk carbonates. For this record a high-resolution age model is based on wiggle-match dating using over 60 AMS radiocarbon dates on terrestrial plant macrofossils. In addition, changes in bulk carbonate d18O are correlated to similar variations observed in the Greenland ice core records to obtain an independent age control, which is additionally supported by pollen analysis and tephrochronology. Shifts in taxonomic composition of chironomid assemblages are apparent throughout the record. They coincide with changes in bulk carbonate d18O and are, therefore, thought to be related to climatic changes. Carbonate particles adhering to chironomid head capsules caused a noisy d18O record. After adequate carbonate removal a reliable d18O record based on chironomid head capsules was produced, which agrees well with the bulk carbonate record. The close agreement between variations in d18O of bulk carbonates and d18O in chironomid head capsules indicates that chironomid d18O can provide reliable reconstructions of past changes in lake water d18O, and indirectly climate, also in lakes where carbonates are absent. In future studies analyses of fossil chironomids can therefore produce reconstructions based on past assemblage changes and chironomid-temperature transfer functions, while at the same time

  9. Was the Sun especially active at the end of the late glacial epoch?

    NASA Astrophysics Data System (ADS)

    Alekseeva, Liliya

    In their pioneering work, the geophysicists A. Brekke and A. Egeland (1983) collected beliefs of different peoples, associated with northern lights. Our analyses of this collection show that these beliefs are mainly related to the mythological idea of ``abnormal'' deads (dead, childless old maids in Finnish beliefs; killed people; spirits dangerous to children). We find similar motifs in Slavic fairy tales about the ``Thrice-Nine Land,'' regarded as the other world in folkloric studies (in the Land where mobile and agitated warlike girls live, whose Head Girl is characterized by the words ``white snow, pretty light, the prettiest in the World,'' but whose name ``Mariya Morevna'' refers to the word ``mort''; where a river flows with its banks covered by human bones; where the witch Baba-Yaga dwells, being extremely dangerous for children). Moreover, it can be noted that similar narrative fabulous myths deal with the concept of auroral oval northern lights, since some specific features of the natural auroral forms are mentioned there, with their particular spatial orientations (to the North or West). This resembles the manner in which Ancient Greek myths describe the real properties of the heavenly phenomena in a mythological language. It is interesting that myths on the high-latitude northern lights spread even to the South of Europe (and, might be, to India and Iran). This fact can be understood in view of the following. It has been established that, during the late glacial epoch, the environmental and cultural conditions were similar over the area from Pyrenean to the Ural Mountains; the pattern of hunters' settlements outlined the glacial sheet from the outside. Relics of the hunters' beliefs can now be found in Arctic, where the environment and lifestyle remain nearly unchanged. The ethnographer Yu.B. Simchenko (1976) has reconstructed the most archaic Arctic myths. According to them, the World of dead is associated with the world of ice governed by the ``Ice

  10. An Assessment of Glacial Contributions to Lake Dynamics across the Tibetan Plateau since the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Sheng, Y.

    2014-12-01

    The Tibetan Plateau is one of the world's most vulnerable areas to global warming, and is home of the world's largest group of mountain glaciers and high-altitude lakes. These lakes in general have shrunk significantly since the late Pleistocene, and are currently continuing to experience changes in their distribution and inundation area. In the meantime, Tibetan glaciers have also gone through dramatic changes as evidenced by paleo glacial relics and recent accelerated melting. The paper provides a regional-scale systematic assessment of both paleo and contemporary lake changes across the plateau using geo-spatial information and optically stimulated luminescence (OSL) dating technologies. Using high-resolution satellite imagery of the plateau together with topographic data, this research recovered paleo lake extents for hundreds of contemporary lakes with visible paleo shore relics and estimated the amount of paleo lake shrinkage at regional scales. Both the basin-based water mass balance analysis using glacier/lake sizes and OSL dating of paleo shores suggest that paleo glaciers played a crucial role in the observed paleo lake shrinkage. Recent ~40 year lake dynamics was monitored by tracking thousands of Tibetan lakes using hundreds of satellite images. The results reveal that the overall total lake area has increased by ~26% between 1976 and 2009. The detected lake dynamics exhibit a strong spatial pattern generally but with local variations. The climate change and its regional glacier variations explain the general trend and the regional patterns of lake dynamics, respectively. The glacier mass monitored by GRACE satellites suggests a thinning trend over the past 12 years in the south while a gaining along the northern rim of the plateau. Basin-based analysis identifies glacial impacts on lake dynamics and explains many local variations. It can be concluded that glaciers play an important role in detected paleo as well as recent lake changes, and will

  11. SW Barents Sea sediment composition in response to Late Glacial-Holocene ice sheet retreat and provenance changes

    NASA Astrophysics Data System (ADS)

    Kaparulina, Ekaterina; Junttila, Juho; Pekka Lunkka, Juha; Strand, Kari

    2015-04-01

    The SW Barents Sea sediments preserve the data of Late Glacial to Holocene development in this area. The marine sediment components are the most reliable recorders for climatic and environmental changes, providing valuable information for reconstructions of past ice sheet dynamics in high latitudes. Detailed investigations of the distribution of clay minerals, geochemical composition of heavy minerals and ice-rafted debris (IRD) of Late Glacial-Holocene sediments from the SW Barents Sea provide important new information about the prominent provenances and retreat of Scandinavian Ice Sheet (SIS). Our particular interest is a study of geochemical composition of Late Glacial-Holocene sediments from the SW Barents Sea via mineralogical proxies and compilation the final results. This may help to advance the knowledge on distribution, pathways and sources of sediment components in these sediments which are currently poorly studied. The mineralogical and geochemical data were generated from the three sediment cores located in Nordkappbanken, SW Barents Sea and display mostly sedimentation cycles from the last deglaciation and Holocene. Sediment analysis will include clay mineral content analysed using X-ray diffraction (XRD), IRD counting and heavy minerals compositions obtained by Electron Probe Microanalyzer (EPMA). It will represent an integrated input function over time which will provide a chronological record of glacial history and paleoclimate. Furthermore, integrated study of these sediment components will elucidate the development of SIS during Late Glacial time. Preliminary results show variations in content of clay minerals. The Barents Sea sources of kaolinite are referred to Franz Josef Land, rock outcroppings on the sea floor, and to a lesser extent the Fennoscandian Shield weathering crust. This can be supported by the lithologies of IRD and heavy mineral contents.

  12. Reconstruction of Late Glacial summer temperatures from chironomid assemblages in Lac Lautrey (Jura, France)

    NASA Astrophysics Data System (ADS)

    Heiri, Oliver; Millet, Laurent

    2005-01-01

    A chironomid-July air temperature inference model based on chironomid assemblages in the surface sediments of 81 Swiss lakes was used to reconstruct Late Glacial July air temperatures at Lac Lautrey (Jura, Eastern France). The transfer-function was based on weighted averaging-partial least squares (WA-PLS) regression and featured a leave-one-out cross-validated coefficient of determination (r2) of 0.80, a root mean square error of prediction (RMSEP) of 1.53 ° C, and was applied to a chironomid record consisting of 154 samples covering the Late Glacial period back to the Oldest Dryas. The model reconstructed July air temperatures of 11-12 ° C during the Oldest Dryas, increasing temperatures between 14 and 16.5 ° C during the Bølling, temperatures around 16.5-17.0 ° C for most of the Allerød, temperatures of 14-15 ° C during the Younger Dryas and temperatures of ca. 16.5 ° C during the Preboreal. The Lac Lautrey record features a two-step July air temperature increase after the Oldest Dryas, with an abrupt temperature increase of ca. 3-3.5 ° C at the Oldest Dryas/Bølling transition followed by a more gradual warming between ca. 14 200 and 13 700 BP. The transfer-function reconstructs a less rapid cooling at the Allerød/Younger Dryas transition than other published records, possibly an artefact caused by the poor analogue situation during the earliest Younger Dryas, and an abrupt warming at the Younger Dryas/Holocene transition. During the Allerød, two centennial-scale 1.5-2.0 ° C coolings are apparent in the record. Although chronologically not well constrained, the first of these cold events may be synchronous with the beginning of the Gerzensee Oscillation. The second is inferred just before deposition of the Laachersee tephra at Lac Lautrey and is therefore coeval with the end of the Gerzensee Oscillation. In contrast to the Greenland oxygen isotope records, the Lac Lautrey palaeotemperature reconstruction lacks a clearly defined Greenland

  13. Numerical studies on the Impact of the Last Glacial Cycle on recent borehole temperature profiles: implications for terrestrial energy balance

    NASA Astrophysics Data System (ADS)

    Beltrami, H.; Matharoo, G. S.; Tarasov, L.; Rath, V.; Smerdon, J. E.

    2014-09-01

    Reconstructions of past climatic changes from borehole temperature profiles are important independent estimates of temperature histories over the last millennium. There remain, however, multiple uncertainties in the interpretation of these data as climatic indicators and as estimates of the changes in the heat content of the continental subsurface due to long-term climatic change. One of these uncertainties is associated with the often ignored impact of the last glacial cycle (LGC) on the subsurface energy content, and on the estimate of the background quasi steady-state signal associated with the diffusion of accretionary energy from the Earth's interior. Here, we provide the first estimate of the impact of the development of the Laurentide ice sheet on the estimates of energy and temperature reconstructions from measurements of terrestrial borehole temperatures in North America. We use basal temperature values from the data-calibrated Memorial University of Newfoundland glacial systems model (MUN-GSM) to quantify the extent of the perturbation to estimated steady-state temperature profiles, and to derive spatial maps of the expected impacts on measured profiles over North America. Furthermore, we present quantitative estimates of the potential effects of temperature changes during the last glacial cycle on the borehole reconstructions over the last millennium for North America. The range of these possible impacts is estimated using synthetic basal temperatures for a period covering 120 ka to the present day that include the basal temperature history uncertainties from an ensemble of results from the calibrated numerical model. For all the locations, we find that within the depth ranges that are typical for available boreholes (≈600 m), the induced perturbations to the steady-state temperature profile are on the order of 10 mW m-2, decreasing with greater depths. Results indicate that site-specific heat content estimates over North America can differ by as much

  14. Palaeoclimate: CO2 and late Palaeozoic glaciation

    NASA Astrophysics Data System (ADS)

    Myers, Timothy S.

    2016-11-01

    Large glacial-interglacial fluctuations occurred during the late Palaeozoic. Geochemical and fossil data show these cycles were marked by coincident shifts in the carbon cycle and terrestrial biosphere.

  15. Environmental transformations and cultural changes: A multidisciplinary case study for the Late Glacial and Final Palaeolithic from Northern Germany

    NASA Astrophysics Data System (ADS)

    Turner, F.; Tolksdorf, J. F.; Viehberg, F.; Schwarz, A.; von Bramann, U.; Bittmann, F.; Kaiser, K.; Schwalb, A.; Staesche, U.; Breest, K.; Pott, R.; Veil, S.

    2012-04-01

    In contrast to younger periods, studies integrating archaeological and environmental records for the Palaeolithic are still rare. Especially our knowledge about interactions between the drastic climatic/environmental changes and cultural developments during the Late Glacial is very limited. This multidisciplinary case study from river Jeetzel, a western Elbe tributary in Northern Germany, combines high resolution palaeoenvironmental investigations with fine-scaled archaeological research on stratified and surface sites. Various dating methods (palynostratigraphy, radiocarbon- and OSL-dating) and analyses of environmental and climatological proxies (pollen and plant macro-remains, ostracods, diatoms and green algae) on river palaeochannel sediments allow detailed reconstruction of interactions between Late Glacial climate, vegetation and fluvial developments. Biostratigraphical analyses on stratified archaeological sites and dating of charcoal / bone fragments from artefact scatters place the Late Palaeolithic occupation of Early Federmesser groups in an environmental context. Thus the former production of hitherto unknown amber art (amongst others a figurine representing a moose) can be ascribed to the Older Dryas and Early Allerød, which are the periods of main Late Glacial afforestation. Therewith our investigations suggest that Final Palaeolithic cultural changes may have been triggered by climatic and environmental transformations.

  16. Mycological evidence of coprophagy from the feces of an Alaskan Late Glacial mammoth

    NASA Astrophysics Data System (ADS)

    van Geel, Bas; Guthrie, R. Dale; Altmann, Jens G.; Broekens, Peter; Bull, Ian D.; Gill, Fiona L.; Jansen, Boris; Nieman, Aline M.; Gravendeel, Barbara

    2011-08-01

    Dung from a mammoth was preserved under frozen conditions in Alaska. The mammoth lived during the early part of the Late Glacial interstadial (ca 12,300 BP). Microfossils, macroremains and ancient DNA from the dung were studied and the chemical composition was determined to reconstruct both the paleoenvironment and paleobiology of this mammoth. Pollen spectra are dominated by Poaceae, Artemisia and other light-demanding taxa, indicating an open, treeless landscape ('mammoth steppe'). Fruits and seeds support this conclusion. The dung consists mainly of cyperaceous stems and leaves, with a minor component of vegetative remains of Poaceae. Analyses of fragments of the plastid rbcL gene and trnL intron and nrITS1 region, amplified from DNA extracted from the dung, supplemented the microscopic identifications. Many fruit bodies with ascospores of the coprophilous fungus Podospora conica were found inside the dung ball, indicating that the mammoth had eaten dung. The absence of bile acids points to mammoth dung. This is the second time that evidence for coprophagy of mammoths has been derived from the presence of fruit bodies of coprophilous fungi in frozen dung. Coprophagy might well have been a common habit of mammoths. Therefore, we strongly recommend that particular attention should be given to fungal remains in future fossil dung studies.

  17. Late Glacial vegetation reconstruction based on leaf waxes from the Gemündener Maar, Germany

    NASA Astrophysics Data System (ADS)

    Wüthrich, Lorenz; Lutz, Selina; Zech, Michael; Hepp, Johannes; Sirocko, Frank; Zech, Roland

    2015-04-01

    Lake sediments are valuable archives for the reconstruction of past changes in climate and vegetation. In the present study, we analyse samples from the Gemündener Maar, a lake situated in the western Eiffel, Germany, for their leaf wax composition: In the bottom part of the core, corresponding to the Oldest Dryas (i.e. older than ~15 ka), n-alkanes have a high average chain length (ACL), which points to a vegetation dominated by grass. During the Bölling/Alleröd, a decrease of the ACL can be interpreted as signal of more deciduous trees. During the Younger Dryas (~12.8 to 11.5 ka), the ACL increases again. Trees probably became again less abundant, before finally, the ACL records the return of deciduous trees during the early Holocene. In general, the total concentrations of both, n-alkanes and sugar biomarkers are high enough to measure compound-specific isotopes on n-alkanes (deuterium) and sugars (18-O). Combined, these two isotopes might help to obtain more information about the relative humidity and mean air temperature during the late glacial.

  18. Late-glacial environmental changes south of the Wisconsinan terminal moraine in the Eastern United States

    USGS Publications Warehouse

    Russell, E.W.B.; Stanford, S.D.

    2000-01-01

    Palynological analyses of two sediment cores, one 2.4 m long from northern Delaware, dated about 16,300 to 14,700 14C yr B.P., and one 1.8 m long from New Jersey just south of the Wisconsinan terminal moraine and dated about 13,600 to 12,500 14C yr B.P., give the first detailed evidence of vegetation in this area during these periods. The overall assemblages are similar to each other, with Picea and Pinus dominating the arboreal pollen and Poaceae and Cyperaceae the herbaceous flora. Nonarboreal pollen contributes about 30-50% of the total, indicating a very open vegetation or a mix of forest patches and open areas. Especially in Delaware, there is a diversity of other herbaceous pollen, including members of the Asteraceae, Fabaceae, and Ranunculaceae. The assemblages do not resemble current North American tundra or boreal forest assemblages; rather, they resemble assemblages characteristic of tundra on recently exposed land surfaces north of the Wisconsinan terminal moraine. The persistence of the assemblages for 1500-2000 years in late-glacial time suggests stable and cold climate during this time of glacier retreat.

  19. Late-Glacial to Early Holocene Climate Changes from a Central Appalachians Pollen and Macrofossil Record

    NASA Technical Reports Server (NTRS)

    Kneller, Margaret; Peteet, Dorothy

    1997-01-01

    A Late-glacial to early Holocene record of pollen, plant macrofossils and charcoal, based on two cores, is presented for Browns Pond in the central Appalachians of Virginia. An AMS radiocarbon chronology defines the timing of moist and cold excursions, superimposed upon the overall warming trend from 14,200 to 7,500 C-14 yr B.P. This site shows cold, moist conditions from approximately 14,200 to 12,700 C-14 yr B.P., with warming at 12,730, 11,280 and 10,050 C-14 yr B.P. A decrease in deciduous broad-leaved tree taxa and Pinus strobus (haploxylon) pollen, simultaneous with a re-expansion of Abies denotes a brief, cold reversal from 12,260 to 12,200 C-14 yr B.P. A second cold reversal, inferred from increases in montane conifers, is centered at 7,500 C-14 yr B.P. The cold reversals at Browns Pond may be synchronous with climate change in Greenland, and northwestern Europe. Warming at 11,280 C-14 yr B.P. shows the complexity of regional climate responses during the Younger Dryas chronozone.

  20. Late-Glacial Environmental Changes South of the Wisconsinan Terminal Moraine in the Eastern United States

    NASA Astrophysics Data System (ADS)

    Russell, Emily W. B.; Stanford, Scott D.

    2000-01-01

    Palynological analyses of two sediment cores, one 2.4 m long from northern Delaware, dated about 16,300 to 14,700 14C yr B.P., and one 1.8 m long from New Jersey just south of the Wisconsinan terminal moraine and dated about 13,600 to 12,500 14C yr B.P., give the first detailed evidence of vegetation in this area during these periods. The overall assemblages are similar to each other, with Picea and Pinus dominating the arboreal pollen and Poaceae and Cyperaceae the herbaceous flora. Nonarboreal pollen contributes about 30-50% of the total, indicating a very open vegetation or a mix of forest patches and open areas. Especially in Delaware, there is a diversity of other herbaceous pollen, including members of the Asteraceae, Fabaceae, and Ranunculaceae. The assemblages do not resemble current North American tundra or boreal forest assemblages; rather, they resemble assemblages characteristic of tundra on recently exposed land surfaces north of the Wisconsinan terminal moraine. The persistence of the assemblages for 1500-2000 years in late-glacial time suggests stable and cold climate during this time of glacier retreat.

  1. Late-glacial and Holocene history of changes in Quelccaya Ice Cap, Peru

    NASA Astrophysics Data System (ADS)

    Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.; Finkel, R. C.

    2008-12-01

    Quelccaya Ice Cap in the southeastern Peruvian Andes (~13-14° S latitude) is an icon for climate change. Its rapidly receding outlet, Qori Kalis Glacier, has been monitored since the 1970's. Cores from Quelccaya Ice Cap provide high-resolution information about temperature and precipitation during the past 1,500 years. We extend the understanding of past changes in Quelccaya Ice Cap based on mapping and dating of glacial moraines and associated deposits. Our results include fifty 10Be ages of moraines and bedrock as well as twenty-nine 14C ages of organic material associated with moraines. These results form the basis of a chronology of changes in Quelccaya Ice Cap from ~16,000 yr BP to late Holocene time. Results from 10Be and 14C dating indicate that Quelccaya Ice Cap experienced a significant advance at 12,700-11,400 yr BP. Subsequent to this advance, the ice margin deposited at least three recessional moraine sets. Quelccaya Ice Cap receded to near its present-day margin by ~10,000 yr BP. Neoglacial advances began by ~3,000 yr BP and culminated with a maximum advance during the Little Ice Age. This chronology fits well with prior work which indicates a restricted Quelccaya Ice Cap during middle Holocene time. Moreover, the overlap between moraine and ice core data for the last 1,500 years provides a unique opportunity to assess the influences of temperature and precipitation on past ice cap extents.

  2. Toward a late Holocene glacial chronology for the eastern Nyainqêntanglha Range, southeastern Tibet

    NASA Astrophysics Data System (ADS)

    Loibl, David; Hochreuther, Philipp; Schulte, Philipp; Hülle, Daniela; Zhu, Haifeng; Bräuning, Achim; Lehmkuhl, Frank

    2015-01-01

    Monsoonal-affected temperate glaciers in the eastern Nyainqêntanglha Range, southeastern Tibet, are highly sensitive to climate change. Knowledge about their late Holocene dynamics is still, however, widely lacking. The few studies on glacial chronology which are available for this region tend to mainly focus on dating results without sufficiently considering the geomorphological setting, often leading to misinterpretations in this complex high mountain environment. In this study, two selected glacier forelands are investigated using a multi-proxy approach encompassing detailed geomorphological mapping, dendrochronology, sedimentology, and optically stimulated luminescence as well as radiocarbon dating. The starting point was the creation of a consistent morphosequence which was validated by remote sensing of further glacier forelands from the wider region. Similarities and differences between the investigated settings were analyzed in detail to identify the relevant morphological and topoclimatic forcing mechanisms. We found evidence of climatic events affecting the whole region during the Little Ice Age, resulting in similar configurations and numbers of moraines. The geomorphological settings of the glacier forelands are, however, remarkably different, making investigations of the landform and sediment configuration an indispensable condition for their interpretation. Subsequently, constraints from different methods of relative and numerical dating were evaluated critically and included into a conceptual chronosequence if applicable. Our results suggest that the late Holocene maximum glacier advance comprised several successive advances from mid-17th to mid-18th century. None of our observations supports an earlier Neoglacial advance reaching further than the LIA maximum. After the LIA maximum, continued retreat that was only interrupted by short phases of stability followed, as evidenced by 2-3 recessional moraines in the investigated settings.

  3. Ecosystem responses during Late Glacial period recorded in the sediments of Lake Łukie (East Poland)

    NASA Astrophysics Data System (ADS)

    Zawiska, Izabela; Słowiński, Michał; Correa-Metrio, Alex; Obremska, Milena; Luoto, Tomi; Nevalainen, Liisa; Woszczyk, Michał; Milecka, Krystyna

    2014-05-01

    The main objectives of this study was to reconstruct climate impact on the functioning of Lake Łukie and its catchment (Łęczna Włodawa Lake District, East European Plain) during Late Glacial period. In order to reconstruct climatic fluctuations and corresponding ecosystem responses, we analysed lake sediments for pollen, subfossil Cladocera, plant macrofossils and chemical composition of the sediment. Of these, plant macrofossils and Cladocera were used to infer minimum and mean July temperatures and ordination analysis was used to examine biotic community shifts. Multiproxy analyses of late-glacial sediments of Lake Łukie clearly show that the main driver of aquatic and terrestrial ecosystems as well as geomorphological processes in the catchment was climate variation. The history of the lake initiated during the Older Dryas. In that period, Łęczna Włodawa Lake District was covered by open habitats dominated by grasses (Poaceae), humid sites were occupied by tundra plant communities with less clubmoss (Selaginella selaginoides), dry sites by dominated by steppe-like vegetation with light-demanding species such as Helianthemum, Artemisia, Chenopodiaceae, and juniper bushes (Juniperus). Cold climate limited the growth and development of organisms in the lake, Cladocera community species composition was poor, with only few species present there all the time. During this time period, permafrost was still present in the ground limiting infiltration of rainwater and causing high erosion in the catchment area. Surface runoff is confirmed by the presence of sclerotia of Cenococcum geophilum and high terrigenous silica content. The warming of the early Allerød caused a remarkable change in the natural environment of this area. This is in accordance with the temperature rise reconstructed with the use of plant macrofossils though the Cladocera reconstruction did not recorded the rise than. This temperature increase resulted in turnover of vegetation in the

  4. Unexpected spontaneous ignition of Late Glacial sediments from the palaeolake Wukenfurche (NE Germany)

    NASA Astrophysics Data System (ADS)

    Dräger, Nadine; Brademann, Brian; Theuerkauf, Martin; Wulf, Sabine; Tjallingii, Rik; Słowiński, Michał; Schlaak, Norbert; Błaszkiewicz, Mirosław; Brauer, Achim

    2015-04-01

    A new finely laminated sediment archive has been recovered from the palaeolake Wukenfurche, NE Germany, comprising the last Glacial to Interglacial transition. The site is located within the Eberswalde ice-marginal valley and south of the terminal moraine that was formed during the Pomeranian phase of the Weichselian glaciation. Two sediment cores were obtained from the presently swampy area in July 2014. From these individual profiles a 14.7 m long continuous composite profile has been compiled by correlation of distinct marker layers. Glacial sand deposits covered by basal peat are found at the base of the cores. A visible volcanic ash layer 6 cm above the transition from basal peat into the overlaying finely laminated lake sediments corresponds most likely to the late Allerød Laacher See Tephra (LST). Preliminary counting on core photographs of the 3.5 m thick package of reddish and black alternating laminae above the LST yields a total of ca. 2500 layer couplets. Further micro-facies analyses on large-scale thin sections will be applied to test if these couplets are of annual origin (i.e. varves). Standard preparation for large-scale thin sections involves freeze-drying (for 48 hours) of 10 cm-long sediment slabs stored in aluminum boxes. Immediately after releasing the vacuum of the freeze-dryer chamber we observed an unexpected spontaneous combustion of the sediment from a particular interval of the profile. The exothermic combustion process lasted for approximately 10 to 20 minutes during which temperatures of up to 350°C have been measured with an infrared camera. Preliminary results suggest that oxidation of iron sulfides contributes to the observed reaction. To our knowledge this is the first time that such spontaneous combustion of lake sediments after freeze-drying has been observed. Details of the combustion process and sediment characteristics will be provided. This study is a contribution to the Virtual Institute of Integrated Climate and Landscape

  5. New constrains on Late Glacial pluvial events on the Southern Bolivian Altiplano

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    Two large paleolakes (33,000 and 60,000 km2) occupied dry basins on the southern Bolivian Altiplano during the Late Glacial, providing evidence of dramatic changes in low-latitude moisture. It is now apparent that the Tauca (18.1-14.1 ka) and Coipasa (13-11 ka) lake cycles are part of a regional wet interval, the Central Andean Pluvial Event (CAPE). Proposed driving mechanisms for CAPE include changes in: summer solar insolation, Pacific SST gradients (ENSO variability), Atlantic SST gradients (the Younger Dryas and Heinrich I), and moisture levels in the eastern lowlands. The region impacted by CAPE may extend from 10 to 26°S. The Southern Altiplano (18-22°S) is at the center of this region. Regional climate histories, however, highlight existing uncertainties and contradictions about the timing, magnitude, and synchrony of the CAPE both across the region and within Altiplano lake basins. Are differing conclusions about the timing and mechanisms of central Andean climate change related to regional variability, or are these differences, instead, a result of different chronological or proxy methods? An improved understanding of climate history on the Southern Bolivian Altiplano is critical to addressing the cause of the CAPE. The Coipasa lake cycle coincides with the Younger Dryas (12.8-11 ka) and new insight into lake extent is aided by distinct 87Sr/86Sr values for this lake cycle. Carbonate crusts from this lake cycle produce exceptionally precise U-Th ages (some with uncertainties <150 years). Sediments associated with the Tauca and Coipasa lake cycles are clearly separated stratigraphically in some locations, but at the highest and lowest elevations these crusts often superimposed in a manner that is not obviously disconformable. Both field and geochemical evidence now suggest that the Coipasa lake cycle was ~55 meters deep (~33,000 km2) and began to expand at 12.8 ka. Quantitative assessment of the precipitation/evaporation balance necessary to maintain

  6. Late-Post-Glacial Tilt of the Lake Ladoga - Gulf of Finland Region and Rheology Models

    NASA Astrophysics Data System (ADS)

    Amantov, Aleksey; Amantova, Marina; Fjeldskaar, Willy

    2017-04-01

    Numerous Earth rheology models attempt to explain features of late- and post-glacial isostatic adjustment of Fennoscandia. An area of specific interest is the peripheral areas to the former ice sheet. We used geological-geomorphological observations of relevant elements of the Lake Ladoga - Eastern Gulf of Finland for verification of our modeling studies. New revised glaciation- deglaciation were tested together with thin ice model scenario, with only 10-11 000 years total last ice-age duration on largest highs. On this basis we expect an uplift pattern which differ from what is generally usually assumed, with more distinct northern trend eastward from the Ladoga basin, and subsidence in the Lake Onega region. Hydro-isostasy (HI) was a very noticeable factor in the post-glacial adjustment, both in local and regional scale. The local one is connected with water load changes of the Baltic-Ladoga system. Its details are extremely important for the verification of Earth rheology parameters. Gulf of Finland and Ladoga regions have probably experienced several dramatic water level changes, and expected HI pattern was sophisticated. In the modeling we have incorporated drops of large local ice lakes. Another one due to ice sheet retreat in Sweden probably happened 13000 cal. BP, with smaller influence due to posterior readvance and Baltic Ice Lake water rise untill the final drop at 11600 cal. BP. The minimum water level in the region from the model culminated 10800 cal. BP, with expected extensive dry land areas in south-eastern parts of the basin. Ancyllus Lake transgression could have two peaks, with another deep level fall in both separated basins at culmination of Baltic Ancyllus Lake regression 8700-8900 cal. BP. This could be synchronous with the known most pronounced largest sea level fall in Great Lakes of North America, being also caused by global climatic changes. Final dramatic changes influenced south-eastern Ladoga, with transgression and final drop took

  7. Late Pliocene-Pleistocene environments and glacial history of the northern North Sea

    NASA Astrophysics Data System (ADS)

    Reinardy, Benedict T. I.; Hjelstuen, Berit O.; Sejrup, Hans Petter; Augedal, Hans; Jørstad, Arild

    2017-02-01

    Based on new geochronological (amino acids and Sr-isotopes) and lithological data combined with analyses of 3D seismic data, the Pliocene-Pleistocene development of the central northern North Sea has been investigated. At the start of the Plio-Pleistocene Transition the study area was dominated by a deltaic, shallow marine or tidal depositional environment with sediments mainly sourced from the west. These sand-rich sediments include green glauconitic grains that belong to the Utsira Sand with a local provenance. Directly above the base Quaternary (R2) a 60 m thick layer of mud-rich sediments of glacimarine origin were deposited at a rate of ∼12 cm/ka between ∼2-1.5 Ma and up to 80 cm/ka between 1.5 and 1.2 Ma possibly reflecting glacial ice advancing to the Norwegian coastline. The high rate of deposition in the Early Pleistocene occurred immediately before the initiation of the Norwegian Channel Ice Stream at ∼1.1 Ma. Following this, a large part of the sediment input from Fennoscandia seems to have been directed away from the study area to the shelf break. At the start of the Mid Pleistocene Transition (MPT), subaerial conditions allowed the formation of a >50 km long fluvial channel across the study area draining water from the east to the south west. The earliest evidence of grounded ice in the investigated area comes from mega scale glacial lineations formed during the MPT, at or just after ∼1.2 Ma. Following this, a regional unconformity (R4) was formed by one or more grounded ice advances across the study area possibly during or directly after the MPT and likely marks the boundary between the Early and Mid Pleistocene glacimarine sediments. The Mid to Late Pleistocene stratigraphy is dominated by glacimarine sediments and tills and is associated with multiple generations of tunnel valleys observed within the seismic data. A high shear strength till containing chalk clasts transported from the west and/or south of the study area was likely deposited

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

    USGS Publications Warehouse

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

    2005-01-01

    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

  9. The North American Late Wisconsin ice sheet and mantle viscosity from glacial rebound analyses

    NASA Astrophysics Data System (ADS)

    Lambeck, Kurt; Purcell, Anthony; Zhao, S.

    2017-02-01

    Observations of sea level and crustal response to glacial loading cycles provide constraints on the mantle rheology function, E, and as well as on the ice load, I, with the latter being largely free from a-priori glaciological or climate assumptions and appropriate, therefore, for testing any such hypotheses. This paper presents new results for both continental-mantle E and I for the Late Wisconsin ice sheet, using geological evidence for relative sea-level change (rsl) and tilting of palaeo-lake shorelines, complemented with loose constraints from observations of present-day radial crustal displacement across North America. The focus is on evidence from near or within the former maximum ice margins and the resulting earth response is representative of sub-continental mantle conditions. The inversion of the sea-level information has limited resolution for earth rheology and simple three-layer models, characterized by depth-averaged effective lithospheric thickness (H) and upper- and lower-mantle viscosities (ηum and ηum respectively) adequately describe the response function, yielding parameters (earth model E-6) of H = 102 (85-120) km, ηum = 5.1 × 1020 (3.5-7.5)x1020, ηlm = 1.3 × 1022 (0.8-2.8)x1022 where the numbers in parenthesis are 95% confidence limits. The details of the ice sheet, with one exception, are not strongly dependent on the rheological assumptions within this range. The exception is the lower mantle viscosity that remains correlated with the magnitude scaling of the ice sheet: a link that is largely broken by introducing constraints from glacial loading effects on the Earth's rotation and dynamic flattening. The difference between the continental ηum and the comparable estimate of (1-2.5)x1020 for ocean mantle is statistically significant. Shoreline gradient information from Glacial Lakes McConnell, Agassiz, Algonquin and Ojibway provide strong constraints on the response within the interior of the ice sheet and the resulting ice sheet

  10. Late Influx: Evidence from Siderophile Elements in Terrestrial Peridotites and Lunar Breccias

    NASA Technical Reports Server (NTRS)

    Morgan, J. W.; Brandon, A. D.; Walker, R. J.; Horan, M. F.

    2001-01-01

    In terrestrial peridotites, Pd is sometimes enhanced relative to other PGE. This observation is taken to imply a "non-chondritic" HSE signature in the mantle. A similar pattern is seen in some Apollo 17 breccias suggesting it to be a primordial feature of late influx. Additional information is contained in the original extended abstract.

  11. Initial Results from a New Lake Elsinore Sediment Core Reveal Evidence for Hydrologic Change During the Late-Glacial/Holocene Transition

    NASA Astrophysics Data System (ADS)

    Fantozzi, J. M.; Kirby, M. E.; Lund, S.; Hiner, C.

    2010-12-01

    While there are several well-developed records of marine climate from Southern California that span the late-Glacial/Holocene transition, there are currently no high-resolution terrestrial counterparts. In June 2010, a 20 meter sediment core covering 10-30 meters below the sediment-water interface was extracted from the depocenter of Lake Elsinore, California - the largest natural, permanent lake in the region. Here, we present the initial results of a multi-proxy study on the section of this sediment core that spans the late-Glacial/Holocene transition (10-18.5 m below the sediment-water line [bswl]). Initial results reveal three distinct sediment units. Unit I (10-15m bswl) is composed of a homogeneous, often mottled (bioturbated?), gray mud with high and moderately variable magnetic susceptibility values (avg=1.20±0.29x10-7m3/kg), low organic matter content (6.50±0.83%), and highly variable carbonate content (12.21±4.89%). Unit II (15-17m bswl) is a transitional unit that begins as a gray mud similar to that of Unit I and transitions into a massive to laminated brown mud with low and variable magnetic susceptibility values (0.88±0.38x10-7m3/kg), increasing organic matter content (11.52±2.19%), and highly variable carbonate content (10.84±4.75%). Unit III (17-18.5m bswl) is characterized by a massive to laminated brown mud with very low and stable magnetic susceptibility values (0.87±0.19x10-7m3/kg), declining organic matter content (11.21±2.02%), and low to negligible carbonate content (5.0±0.87%). Together, these data indicate a significant change in Lake Elsinore’s depositional environment that is likely related to hydrologic change (i.e. average lake level) during the late Glacial to Holocene transition - a change that has not previously been documented in Southern California.

  12. Sedimentary record from the Canada Basin, Arctic Ocean: implications for late to middle Pleistocene glacial history

    NASA Astrophysics Data System (ADS)

    Dong, Linsen; Liu, Yanguang; Shi, Xuefa; Polyak, Leonid; Huang, Yuanhui; Fang, Xisheng; Liu, Jianxing; Zou, Jianjun; Wang, Kunshan; Sun, Fuqiang; Wang, Xuchen

    2017-05-01

    Sediment core ARC4-BN05 collected from the Canada Basin, Arctic Ocean, covers the late to middle Quaternary (Marine Isotope Stage - MIS - 1-15, ca. 0.5-0.6 Ma) as estimated by correlation to earlier proposed Arctic Ocean stratigraphies and AMS14C dating of the youngest sediments. Detailed examination of clay and bulk mineralogy along with grain size, content of Ca and Mn, and planktic foraminiferal numbers in core ARC4-BN05 provides important new information about sedimentary environments and provenance. We use increased contents of coarse debris as an indicator of glacier collapse events at the margins of the western Arctic Ocean, and identify the provenance of these events from mineralogical composition. Notably, peaks of dolomite debris, including large dropstones, track the Laurentide Ice Sheet (LIS) discharge events to the Arctic Ocean. Major LIS inputs occurred during the stratigraphic intervals estimated as MIS 3, intra-MIS 5 and 7 events, MIS 8, and MIS 10. Inputs from the East Siberian Ice Sheet (ESIS) are inferred from peaks of smectite, kaolinite, and chlorite associated with coarse sediment. Major ESIS sedimentary events occurred in the intervals estimated as MIS 4, MIS 6 and MIS 12. Differences in LIS vs. ESIS inputs can be explained by ice-sheet configurations at different sea levels, sediment delivery mechanisms (iceberg rafting, suspension plumes, and debris flows), and surface circulation. A long-term change in the pattern of sediment inputs, with an apparent step change near the estimated MIS 7-8 boundary (ca. 0.25 Ma), presumably indicates an overall glacial expansion at the western Arctic margins, especially in North America.

  13. Late glacial and Holocene sedimentary environments of Quesnel Lake, British Columbia

    NASA Astrophysics Data System (ADS)

    Gilbert, Robert; Desloges, Joseph R.

    2012-12-01

    At 512 m Quesnel Lake is the third deepest in North America and at 100 km long its drainage basin spans from the arid interior plateau to the high mountains of the eastern Cordillera where small glaciers are a significant source of sediment. In most of the lake sediment is 0 to 40 m thick, reaching a maximum of just over 100 m thick near the junction of the three arms. Cores from three locations in the lake provide evidence that the entire Holocene record is contained in the upper 4 to 6 m of the sedimentary record where rates of accumulation have been constant or have decreased slowly. The highest rates (0.35 to 0.72 mm/a) occur near points of inflow, while the lowest rate (0.22 mm/a) occurs in a sheltered environment with limited inflow, and significant hypolimnic circulation which may flush water and suspended sediment from the water column. Late Pleistocene sediment beneath has a similar acoustic signature to the cored Holocene record above, suggesting that the sedimentary processes governing its deposition were not greatly different than in the present lake but that extensive glacial and paraglacial sources contributed to a significantly higher rate of accumulation. Mazama ash analyzed from two locations near points of inflow has an age of 7576 ± 60 cal. BP according to our chronology. Vivianite, which is uncommon in lakes of the Cordillera, occurs in the middle of the cores mainly associated with macroscopic wood fragments and indicates reducing conditions within the sediment.

  14. History of late glacial runoff from the southern Laurentide ice sheet in Indiana

    SciTech Connect

    Fraser, G.S. ); Fleming, A.H. )

    1992-01-01

    The history of late glacial runoff from the southern Laurentide ice sheet in Indiana is one of long periods of normal'' meltwater flow punctuated by extreme flows. Meltwater flow down the Wabash began about 26 ka when ice of the Lake Michigan lobe entered the headwaters of its northern and western tributaries. This flow was augmented by meltwater from the Huron-Erie lobe which entered the basin about 24 ka, and there ensued a period when normal meltwater flow and outwash sedimentation prevailed through successive advances from these two sources. This ended about 17 ka ( ) when two extreme flow events occurred. The first involved a subglacial breakout of stored water in a stagnating sheet of Erie-Huron lobe ice and the second occurred when a proglacial lake stored behind a Huron-Erie Lobe recessional moraine in northeastern Indiana drained catastrophically into the Wabash. A second period of normal flow and sedimentation followed as successive episodes of advance and active backwasting of Huron-Erie lobe ice left a series of recessional moraines in northeastern Indiana. Lake Maumee (of ancestral Lake Erie) formed behind the last of these, and the final extreme flow down the Wabash occurred about 14 ka ( ) when this moraine was breached. During the final stages of glaciation in Indiana, very large volumes of meltwater were supplied to the Illinois river system through the Kankakee sluiceway by both the Lake Michigan lobe and the Saginaw lobe. For the most part, these were not extreme flows, but catastrophic subglacial outburst(s) of water from the Lake Michigan lobe did occur about 13 ka ( ) along the Valparaiso Moraine. Most of this meltwater was directed down the Kankakee sluiceway and into the Illinois River, but some may have flowed around the east end of the iroquois Moraine and into the Wabash River.

  15. A new varved late Glacial and Holocene sediment record from Lake Jelonek (North Poland) - preliminary results

    NASA Astrophysics Data System (ADS)

    Kramkowski, Mateusz; Filbrandt-Czaja, Anna; Ott, Florian; Słowiński, Michał; Tjallingii, Rik; Błaszkiewicz, Mirosław; Brauer, Achim

    2015-04-01

    Anually laminated (varved) lake deposits are suitable natural archives for reconstructing past climatic and environmental changes at seasonal resolution. A major advantage of such records is that varve counting allows constructing robust and independent chronologies, a key challenge for paleoclimate research. Recently, a new annually laminated sediment record has been obtained from Lake Jelonek, located in the eastern part of the Pomeranian Lakeland in northern Poland (Tuchola Pinewoods). The lake is surrounded by forest and covers an area of 19,9 ha and has a maximum depth of 13,8 m. Three overlapping series of 14,3 m - long sediment records have been cored with an UWITEC 90 mm diameter piston corer from the deepest part of the lake. A continuous master composite profile has been established comprising the entire postglacial lacustrine sediment infill. Preliminary analyses including micro-facies analyses on thin sections from selected intervals as well as X-ray fluorescence element scanning (µ-XRF) reveal that the sediments are to a large part annually laminated. Here we present detailed varve models for different sediment intervals and discuss high-resolution geochemical variation in the entire sediment record. A preliminary age model based on radiocarbon dating and major biostratigraphical boundaries based on pollen data will be presented as well. These data will form the fundament for the planned multi-proxy study for detailed reconstructions of climatic and environmental variability during the late glacial and Holocene in the southern Baltic. This study is a contribution to the Virtual Institute ICLEA (Integrated Climate and Landscape Evolution Analysis) funded by the Helmholtz Association and National Science Centre Poland NCN 2011/01/B/ST10/07367.

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

    PubMed Central

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

    2014-01-01

    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

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

    PubMed

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

    2014-08-12

    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.

  18. Late glacial history of central Aroostook County, Maine: The younger Dryas problem

    SciTech Connect

    Ashley, K.; Borns, H.W. Jr. . Inst. for Quaternary Studies)

    1993-03-01

    Previous work in Nova Scotia and New Brunswick, Canada has proven that a late-glacial climatic oscillation expressed itself in North America. Despite physical and palynological evidence in Canada for an event centered on the Alleroed-Younger Dryas chronozones, little conclusive evidence has been found for an equivalent oscillation in Maine. The only physical evidence for an Alleroed-Younger Dryas event so far in Maine is a deformed peat layer within a diamicton near Oxbow. Newman et al. reported ages on the peat ranging from 10,395 [plus minus] 85 to 11,760 [plus minus] 145 [sup 14]C yrs B.P. New excavation of the site in 1992 did not reveal the peat. Newman et al. reported a strong NNW-SSE stone fabric in the diamicton, which is consistent with regional flow directions and suggests that the diamicton may be a till. Regional basal organic [sup 14]C dates suggest that the area was ice-free by Younger Dryas time. The authors strategy for trying to solve this problem has been to investigate the stratigraphy of the Oxbow region, in conjunction with ice-flow directions as determined by bedrock striae and till fabrics. Ongoing fieldwork has shown that the direction of strongest bedrock erosion records a Late-Wisconsin ice flow event which occurred along a mean trend of s26E, based on 261 striation measurements at 36 localities. The NNW-SSE-trending striae cross-cut a W-E set at some localities. Faint striation sets which cross-cut the NNW-SSE-trending striae have no consistent orientation. This is in agreement with the striation data. A major drag fold found at the contact between the surface till and underlying gravel also indicates ice flow from the NNW (fold axis trend:s66W). The surface till has not been dated directly. The genesis of the diamicton at Oxbow and its relationship to the regional surface till remains unclear.

  19. THE LAST STAGES OF TERRESTRIAL PLANET FORMATION: DYNAMICAL FRICTION AND THE LATE VENEER

    SciTech Connect

    Schlichting, Hilke E.; Warren, Paul H.; Yin Qingzhu

    2012-06-10

    The final stage of terrestrial planet formation consists of the clean-up of residual planetesimals after the giant impact phase. Dynamically, a residual planetesimal population is needed to damp the high eccentricities and inclinations of the terrestrial planets to circular and coplanar orbits after the giant impact stage. Geochemically, highly siderophile element (HSE) abundance patterns inferred for the terrestrial planets and the Moon suggest that a total of about 0.01 M{sub Circled-Plus} of chondritic material was delivered as 'late veneer' by planetesimals to the terrestrial planets after the end of giant impacts. Here, we combine these two independent lines of evidence for a leftover population of planetesimals and show that: (1) a residual population of small planetesimals containing 0.01 M{sub Circled-Plus} is able to damp the high eccentricities and inclinations of the terrestrial planets after giant impacts to their observed values. (2) At the same time, this planetesimal population can account for the observed relative amounts of late veneer added to the Earth, Moon, and Mars provided that the majority of the accreted late veneer was delivered by small planetesimals with radii {approx}< 10 m. These small planetesimal sizes are required to ensure efficient damping of the planetesimal's velocity dispersion by mutual collisions, which in turn ensures sufficiently low relative velocities between the terrestrial planets and the planetesimals such that the planets' accretion cross sections are significantly enhanced by gravitational focusing above their geometric values. Specifically, we find that, in the limit that the relative velocity between the terrestrial planets and the planetesimals is significantly less than the terrestrial planets' escape velocities, gravitational focusing yields a mass accretion ratio of Earth/Mars {approx}({rho}{sub Circled-Plus }/{rho}{sub mars})(R{sub Circled-Plus }/R{sub mars}){sup 4} {approx} 17, which agrees well with the mass

  20. The Last Stages of Terrestrial Planet Formation: Dynamical Friction and the Late Veneer

    NASA Astrophysics Data System (ADS)

    Schlichting, Hilke E.; Warren, Paul H.; Yin, Qing-Zhu

    2012-06-01

    The final stage of terrestrial planet formation consists of the clean-up of residual planetesimals after the giant impact phase. Dynamically, a residual planetesimal population is needed to damp the high eccentricities and inclinations of the terrestrial planets to circular and coplanar orbits after the giant impact stage. Geochemically, highly siderophile element (HSE) abundance patterns inferred for the terrestrial planets and the Moon suggest that a total of about 0.01 M⊕ of chondritic material was delivered as "late veneer" by planetesimals to the terrestrial planets after the end of giant impacts. Here, we combine these two independent lines of evidence for a leftover population of planetesimals and show that: (1) a residual population of small planetesimals containing 0.01 M⊕ is able to damp the high eccentricities and inclinations of the terrestrial planets after giant impacts to their observed values. (2) At the same time, this planetesimal population can account for the observed relative amounts of late veneer added to the Earth, Moon, and Mars provided that the majority of the accreted late veneer was delivered by small planetesimals with radii <~ 10 m. These small planetesimal sizes are required to ensure efficient damping of the planetesimal's velocity dispersion by mutual collisions, which in turn ensures sufficiently low relative velocities between the terrestrial planets and the planetesimals such that the planets' accretion cross sections are significantly enhanced by gravitational focusing above their geometric values. Specifically, we find that, in the limit that the relative velocity between the terrestrial planets and the planetesimals is significantly less than the terrestrial planets' escape velocities, gravitational focusing yields a mass accretion ratio of Earth/Mars ~(ρ⊕/ρmars)(R⊕/Rmars)4 ~ 17, which agrees well with the mass accretion ratio inferred from HSEs of 12-23. For the Earth-Moon system, we find a mass accretion ratio of

  1. Late Quaternary Stratigraphy, Glacial Limits, and Paleoenvironments of the Marresale Area, Western Yamal Peninsula, Russia

    NASA Astrophysics Data System (ADS)

    Forman, Steven L.; Ingólfsson, Ólafur; Gataullin, Valery; Manley, William; Lokrantz, Hanna

    2002-05-01

    Stratigraphic records from coastal cliff sections near the Marresale Station on the Yamal Peninsula, Russia, yield new insight on ice-sheet dynamics and paleoenvironments for northern Eurasia. Field studies identify nine informal stratigraphic units from oldest to youngest (the Marresale formation, Labsuyakha sand, Kara diamicton, Varjakha peat and silt, Oleny sand, Baidarata sand, Betula horizon, Nenets peat, and Chum sand) that show a single glaciation and a varied terrestrial environment during the late Pleistocene. The Kara diamicton reflects regional glaciation and is associated with glaciotectonic deformation from the southwest of the underlying Labsuyakha sand and Marresale formation. Finite radiocarbon and luminescence ages of ca. 35,000 to 45,000 yr from Varjakha peat and silt that immediately overlies Kara diamicton place the glaciation >40,000 yr ago. Eolian and fluvial deposition ensued with concomitant cryogenesis between ca. 35,000 and 12,000 cal yr B.P. associated with the Oleny and the Baidarata sands. There is no geomorphic or stratigraphic evidence of coverage or proximity of the Yamal Peninsula to a Late Weichselian ice sheet. The Nenets peat accumulated over the Baidarata sand during much of the past 10,000 yr, with local additions of the eolian Chum sand starting ca. 1000 yr ago. A prominent Betula horizon at the base of the Nenets peat contains rooted birch trees ca. 10,000 to 9000 cal yr old and indicates a >200-km shift northward of the treeline from the present limits, corresponding to a 2° to 4°C summer warming across northern Eurasia.

  2. Palaeoenvironmental interpretation of an ice-contact glacial lake succession: an example from the late Devensian of southwest Wales, UK

    NASA Astrophysics Data System (ADS)

    Etienne, James L.; Jansson, Krister N.; Glasser, Neil F.; Hambrey, Michael J.; Davies, Jeremy R.; Waters, Richard A.; Maltman, Alex J.; Wilby, Philip R.

    2006-04-01

    During the late Devensian (late Weichselian) glaciation, a number of large proglacial lakes developed in dammed river valleys along the southwest coast of Wales, U.K. This paper presents sedimentological data, together with a Digital Terrain Model, to establish the sedimentation history, dynamics and evolution of the largest lake, glacial Llyn (Lake) Teifi. Buried valley-fill sequences within the margins of the former lake basin reveal a thick succession of glaciolacustrine muds which coarsen upward into, or are locally abruptly overlain by, proximal deltaic, subglacial and glaciofluvial deposits. Sediment delivery pathways represented in the lacustrine succession include gravity flows, suspension settling, deltaic aggradation and iceberg rafting, the latter indicating ice-contact conditions. The lacustrine muds are variably deformed, with a range of syn- and post-depositional structures, some of which indicate subglacial deformation associated with overriding of the lacustrine succession. Syn-depositional structures indicate high sedimentation rates, which may explain an absence of bioturbation structures. The overall coarsening-upward succession and cap of subglacial and/or glaciofluvial deposits support recent theories suggesting that glacial Llyn Teifi formed during glacial advance. There is no evidence to support glaciomarine conditions of sedimentation in this area of the Irish Sea basin.

  3. Stratigraphy and sedimentology of pre-late Wisconsin catastrophic glacial flood sediments, western Walla Walla Valley, Washington

    SciTech Connect

    Robertson, J.L.; Spencer, P.K. . Geology Dept.)

    1993-04-01

    The Cummins Bridge site in the western Walla Walla Valley exhibits clear evidence for pre-late Wisconsin catastrophic glacial flooding. The section consists of an unstratified, poorly sorted diamict with angular basaltic clasts in a matrix of sand and silt, and a large number of well-rounded clasts of exotic lithology in the coarse fraction, gradationally overlain by a coarse, angular gravel that is matrix poor and exotic-free; this unit grades upward into a matrix-rich diamict with a well-developed caliche in the upper portion. Above this is a sand and silt unit showing vague cross-stratification, lamination, and graded beds; this unit may represent local temporary ponding of the ancestral drainage. Overlying this on a pronounced erosional surface are rhythmically stratified sand-to-salt beds assigned to the late Wisconsin Toughet Beds. The section is capped by a thin bed of Holocene loess. Stratigraphic and sedimentologic criteria suggest that the lowermost units represent an indirect record of catastrophic glacial flooding. Flood sediments were deposited on an adjacent topographic high and subsequently mass-wasted via mudflow into their present position. Normal fluvial processes alternated with mass-wasting events to concentrate the angular, matrix-poor basaltic gravel. The lower diamict shows characteristics similar to documented pre-late Wisconsin catastrophic flood sediments at a nearby site, including rounded exotic clasts, angular basaltic clasts, lack of stratification, and poor sorting. The two sites may represent the same pre-late Wisconsin flood event.

  4. Late Quaternary geomorphic history of a glacial landscape - new sedimentary and chronological data from the Cordillera de Cochabamba (Bolivia)

    NASA Astrophysics Data System (ADS)

    May, J.-H.; Preusser, F.; Zech, R.; Ilgner, J.; Veit, H.

    2009-04-01

    Throughout the Central Andes, glacial landscapes have long been used for the reconstruction of Late Quaternary glaciations and landscape evolution. Much work has focused on the Andes in Peru, Chile and the Bolivian Altiplano, whereas relatively little data has been published on glaciation history in the eastern Andean ranges and slopes. Even less is known with regard to the postglacial evolution of these glacial landscapes. In the Cordillera de Cochabamba (Bolivia), local maximum advances probably peaked around 20-25 ka BP and were followed by significant readvances between ~12-16 ka BP. This generally points to temperature controlled maximum glacial advances along the humid eastern slopes of the Central Andes, which is supported by glacier-climate-modelling studies. However, most studies include only marginal information with regard to the complex geomorphic and sedimentary situation in the Cordillera de Cochabamba. Furthermore, the chronological results are afflicted with several methodological uncertainties inherent to surface exposure dating and call for application of alternative, independent age dating methods. Therefore this study aims at i) documenting and interpreting the complex glacial geomorphology of the Huara Loma valley in the Cordillera de Cochabamba (Bolivia), ii) analyzing the involved units of glacial sediments, and iii) improving the chronological framework by applying optically stimulated luminescence (OSL) and radiocarbon dating (14C). For this purpose, geomorphic mapping was combined with field documentation of sedimentary profiles. The involved sediments were subject to geochemical and mineralogical analysis in order to deduce information on their erosional and weathering histories. In addition, the interpretation of OSL ages from glacial and proglacial sediments integrated several methodological procedures with regard to sample preparation and statistical analysis of the measurements in order to increase the degree of confidence. These

  5. Isotopically-depleted late Pleistocene groundwater in Columbia River Basalt aquifers: Evidence for recharge of glacial Lake Missoula floodwaters?

    NASA Astrophysics Data System (ADS)

    Brown, Kyle B.; McIntosh, Jennifer C.; Baker, Victor R.; Gosch, Damian

    2010-11-01

    Late Pleistocene outburst flooding of ice-dammed glacial Lake Missoula, and possible discharge from the Cordilleran Ice Sheet (CIS), catastrophically altered the northwestern United States landscape, yet little is known about potential infiltration of flood waters into the subsurface. This study provides compelling evidence for the presence of late Pleistocene CIS-related recharge waters in the Columbia River Basalt Aquifers (CRBAs) in central Washington. CRBA groundwaters with corrected 14C ages from 15.7 and 33.3 k yrs BP (during periods of flood events) have anomalously low δ18O values (-18.9 to -17.6‰), compared to late Pleistocene soil waters (-16.1 to -13.4‰) and modern precipitation in the region (average -15.9‰), consistent with CIS-related meltwater recharge. These results have implications for our understanding of megaflood phenomena on earth and Mars.

  6. Glacial chronology and palaeoclimate in the Bystra catchment, Western Tatra Mountains (Poland) during the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Makos, Michał; Rinterknecht, Vincent; Braucher, Régis; Żarnowski, Michał

    2016-02-01

    Deglaciation chronology of the Bystra catchment (Western Tatra Mountains) has been reconstructed based on 10Be exposure age dating. Fourteen rock samples were collected from boulders located on three moraines that limit the horizontal extent of the LGM maximum advance and the Lateglacial recessional stage. The oldest preserved, maximum moraine was dated at 15.5 ± 0.8 ka, an age that could be explained more likely by post-depositional erosion of the moraine. Such scenario is supported by geomorphologic and palaeoclimatological evidence. The younger cold stage is represented by well-preserved termino-lateral moraine systems in the Kondratowa and Sucha Kasprowa valleys. The distribution of the moraine ridges in both valleys suggest a complex history of deglaciation of the area. The first Late-glacial re-advance (LG1) was followed by a cold oscillation (LG2), that occurred at around 14.0 ± 0.7-13.7 ± 1.2 ka. Glaciers during both stages had nearly the same horizontal extent, however, their thickness and geometry changed significantly, mainly due to local climatic conditions triggered by topography, controlling the exposition to solar radiation. The LG1 stage occurred probably during the pre-Bølling cold stage (Greenland Stadial 2.1a), however, the LG2 stage can be correlated with the cooling at around 14 ka during the Greenland Interstadial 1 (GI-1d - Older Dryas). This is the first chronological evidence of the Older Dryas in the Tatra Mountains. The ELA of the maximum Bystra glacier was located at 1480 m a.s.l. in accordance with the ELA in the High Tatra Mountains during the LGM. During the LG1 and LG2 stages, the ELA in the catchment rose up to 1520-1530 m a.s.l. and was located approximately 100-150 m lower than in the eastern part of the massif. Climate modelling results show that the Bystra glacier (maximum advance) could have advanced in the catchment when mean annual temperature was lower than today by 11-12 °C and precipitation was reduced by 40-60%. This

  7. Late Glacial and Holocene Geomagnetic secular variation in Western Lake Geneva (Switzerland)

    NASA Astrophysics Data System (ADS)

    Baster, I.; Heller, F.; Egli, R.; Rachoud-Schneider, A. M.; Wildi, W.

    2003-04-01

    Lacustrine sediments can provide excellent records of paleomagnetic secular variation which can be used as a powerful dating tool. We present the first paleosecular variation record from Lake Geneva (Switzerland) that extends back beyond 16 cal. kyr BP. Several cores up to 10 m long were collected in the delta area of the Promentouse and Asse rivers, close to the city of Nyon. Whole-core declination and horizontal intensity component of the natural remanent magnetization (NRM) were first measured in two cores retrieved from an area without slumps about 1050 and 1400 m from the coast, respectively. In addition, individual samples were extracted from the longest core for further detailed analysis. These samples are characterized by one single NRM component which is stable up to 20 mT. No secondary components (low-stability) have been recognized. As demonstrated by component analysis of IRM acquisition curves, fine-grained magnetite of biogenic origin is the dominant magnetic carrier with additional small amounts of detrital hematite. The declination values obtained from these subsamples display well-defined oscillations within a range of ± 44°. Thirteen major paleosecular declination swings can be distinguished. The inclination curve varies between 30° and 70° and is characterized by a more complex structure. However, nine pronounced features can be recognized. NRM intensity and initial susceptibility correlate well with the stratigraphy showing different trends for the Holocene and the Late Glacial periods. The inclination and declination variations are in excellent agreement with the records from Lac du Joux (Creer et al., 1980) and Lake Windermere (Turner &Thompson, 1981). The paleosecular variation curve of Lake Geneva, combined with lithostratigraphic features, pollen counting analyses and C14 dating, provides a well dated high quality reference curve for central Europe. References Creer, K.M., Hogg, T.E., Readman, P.W. &Reynaud, C. (1980) Palaeomagnetic

  8. Chronostratigraphical Subdivision of the Late Glacial and the Holocene for the Alaska Region

    NASA Astrophysics Data System (ADS)

    Michczynska, D. J.; Hajdas, I.

    2009-04-01

    Our work is a kind of so called data mining. The first step of our work was collection of the radiocarbon data for samples coming from Alaska. We construct data base using Radiocarbon Measurements Lists published by different radiocarbon laboratories (mainly in the journal 'Radiocaron'). The next step was careful analysis of collected dates. We excluded from our analysis all dates suspected of contamination by younger or older organic matter. Such fact could be stated, for instance, on the base of inconsistency of radiocarbon age and stratigraphy or palynology. Finally, we calibrated whole large set of chosen radiocarbon dates and construct probability density function (PDF). Analysis of the shape of PDF was the subject of the previous research (eg. Michczynska and Pazdur, 2004; Macklin et al., 2006; Starkel et al., 2006, Michczynska et al., 2007). In our analysis we take into account the distinct tendency to collect samples from specific horizons. It is a general rule to take samples for radiocarbon dating from places of visible sedimentation changes or changes in palynological diagram. Therefore the culminations of the PDF represent periods of environmental changes and could be helpful in identifying the chronostratigraphical boundaries on the calendar time scale. References: Michczyńska D.J., Pazdur A., 2004. A shape analysis of cumulative probability density function of radiocarbon dates set in the study of climate change in Late Glacial and Holocene. Radiocarbon 46(2): 733-744. Michczyńska D.J., Michczyński A., Pazdur A. 2007. Frequency distribution of radiocarbon dates as a tool for reconstructing environmental changes. Radiocarbon 49(2): 799-806. Macklin M.G., Benito G., Gregory K.J., Johnstone E., Lewin J., Michczyńska D.J., Soja R., Starkel L., Thorndycraft V.R., 2006. Past hydrological events reflected in the Holocene fluvial record of Europe. CATENA 66: 145-154. Starkel L., Soja R., Michczyńska D.J., 2006. Past hydrological events reflected in

  9. High-resolution study of Late Glacial and Early Holocene vegetation and tree line changes in the Southern Carpathian Mountains

    NASA Astrophysics Data System (ADS)

    Magyari, E.; Jakab, G.; Braun, M.; Buczkó, K.; Bálint, M.

    2009-04-01

    The Retezat Massif of the S Carpathian Mountains abounds in glacial lakes, mainly above 1900 m a.s.l., just above the present day tree limit formed by Picea abies and Pinus cembra in the northern slopes. For the reconstruction of Late Glacial and Early Holocene vegetation and tree line changes in this mountain, two lakes were selected: Taul dintre Brazi (1740 m a.s.l.) and Lake Gales (1990 m a.s.l.). Sediments obtained from these lakes extend back to the Late Glacial, and so provide us an exceptional opportunity to study 1) when trees were first established locally around the lower lake following glacial retreat and 2) what tree and shrub species were present and replaced each other in the Late Glacial and early postglacial forests in response to the high-amplitude climatic fluctuation, and in case of the Early Holocene, the high-amplitude climatic amelioration. Pollen, conifer stomata and plant macrofossils were studied from both lake sediments at approximately 100 years resolution. Sediment chronologies were based on multiple AMS radiocarbon dates. Preliminary results from this study show that Pinus mugo, Pinus cembra, Picea abies and Betula nana appeared very early during the lateglacial interstadial, ca. 14,500 cal yr BP followed by Larix decidua around 14,200 cal yr BP. Pinus cembra gained dominance in the Latglacial interstadial forest and survived locally during the Younger Dryas reversal unlike Picea abies. Another important result was the reconstruction of the Early Holocene forest composition around the lower lake that proved much more species rich than the present-day forest; Picea abies grew together with Larix decidua, Pinus mugo, Pinus cembra, Alnus viridis, Juniperus, Betula nana and Betula pubescens during the Early Holocene, furthermore the stomatal record suggested that conifer species were evenly distributed around the lake. In light of our data, the position of the Early Holocene tree line reached 1990 m a.s.l. by ca. 10,700 cal yr BP (i

  10. Glacial stratigraphy of the Bulkley River region: A depositional framework for the late Pleistocene in central British Columbia

    USGS Publications Warehouse

    Stumpf, A.J.; Broster, B.E.; Levson, V.M.

    2004-01-01

    A depositional framework for late Pleistocene sediments in central British Columbia was developed from the composite stratigraphy of glacial sediments found in the Bulkley River region. Nonglacial deposits correlated to the Olympia Nonglacial Interval, are overlain in succession by sub-till, ice-advance sediments, Late Wisconsinan (Fraser Glaciation) till, and late-glacial sediments. Due to local erosion and depositional variability, some of the units are not continuous throughout the region and differ locally in their thickness and complexity. At the onset of the Fraser Glaciation, ice advance was marked by rising base levels in rivers, lake ponding, and ice marginal sub-aqueous deposition. Physiography and glacier dynamics influenced the position of drainage outlets, direction of water flow, and ponding. The region was completely ice covered during this glaciation and ice-flow directions were variable, being dominantly influenced by the migrating position of ice divides. Deglaciation was marked by the widespread deposition of fine-grained sediments in proglacial lakes and glaciofluvial sands and gravels at locations with unrestricted drainage.

  11. Seismic Stratigraphy Of The Sabrina Coast Shelf, East Antarctica: History Of Late Paleogene To Early Neogene Glacial Evolution

    NASA Astrophysics Data System (ADS)

    Montelli, A.; Gulick, S. P. S.; Frederick, B. C.; Blankenship, D. D.; Leventer, A.; Shevenell, A.; Domack, E. W.

    2015-12-01

    Sedimentary architecture of the Sabrina Coast (SC) shelf, East Antarctica is studied for the first time using 754 km of high (up to 3 m) vertical resolution multichannel seismic data and four piston cores acquired on board of RVIB Palmer in 2014. We interpret the sedimentary record of early glacial SC shelf stratigraphy based on analysis of seismic facies and morphological features. We identify at least nine erosional surfaces that indicate advances of the Totten Glacier - Moscow University Ice Shelf system, part of the East Antarctic Ice Sheet (EAIS), to the SC shelf. The most prominent features include two series of undulating, channelized erosional surfaces truncating strata below and showing highly irregular morphology with elevation amplitudes of up to ~120 m and widths of individual undulations of up to ~10 km. These surfaces are located stratigraphically above a core bearing IRD and assigned biostratigraphically to the Late Eocene and below a regional erosional surface of Late Miocene age. Our major results show that: (1) Oligocene-early Miocene evolution of EAIS consists of low-frequency, high-amplitude glacial expansions followed by long periods of ice-distal to open marine conditions; (2) the presence of grounded EAIS expansions on shelf is expressed in a series of deep, hummocky undulations and first Antarctic sedimentary tunnel valley system, suggestive of presence of subglacial meltwater and hence, a polythermal glacial regime; (3) at least nine erosional unconformities representing major ice advances have been found on the inner shelf; (4) the most intensive polythermal glaciations have occurred in late Eocene-early Oligocene; (5) no evidence of focused paleo- ice stream(s) draining Aurora Basin Complex prior to the middle Miocene was found in the study area.

  12. Late glacial and Holocene development of Lake Donggi Cona on the NE Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Opitz, S.; Wünnemann, B.; Dietze, E.; Hartmann, K.; Lehmkuhl, F.; Stauch, G.; Ijmker, J.; Diekmann, B.

    2010-12-01

    Lake Donggi Cona is located in the north-eastern part of the Tibetan Plateau at the boundary between monsoon and westerly climate influence on an elevation of 4090m. Donggi Cona is an oligotrophic freshwater lake with a recent open-basin system. The 30 km long, 8 km wide, and up to 98 m deep lake basin is a tectonic pull-apart structure as part of Kunlun fault. Sub-bottom profiling of the lake basin revealed the presence of graben structures, conjugate faults, subaquatic terraces, and ancient fan systems, draped by 4 to 5 m thick postglacial lacustrine sediments. The aim of our investigations is the reconstruction of palaeo-environmental changes of the lake catchment. After analysis of the seismic pre-survey, five sediment cores have been retrieved at 35-40 m and at 2 m water depth. The cores are partly laminated and composed of calcareous muds with changing amounts of carbonate micrite, organic matter and detrital silt and clay. Furthermore, the cores contains remarkable amounts of ostracods and plant remains. Dating results from the top of three sediment cores obtain a hardwater effect of about 2000 years. Nineteen AMS dates from the entire cores suggest a sedimentary history throughout the Holocene. Despite possible reservoir errors the sandy bottom sediments were deposited during or after the last glacial maximum (LGM). With a multi-proxy approach using grain size, XRF, XRD, CNS, TOC and multivariate statistical endmember-modelling (EMMA) we hereby represent an interpretation concerning changes in hydrological conditions and sedimentation processes during the last about 20 kyears: Prior to 18 kyears, terrestrial loess and sand suggest a very low lake level. From 18 to 13 kyrs. BP the lake level rise during a period of climate-driven glacier melt. For the same time period the detrital supply is at its maximum and seems to control the high sedimentation rate. Grain-size coarsening and hiatuses in four sediment cores, document a repeated lake-level fall after 13

  13. Trophic pathways supporting juvenile Chinook and Coho salmon in the glacial Susitna River, Alaska: patterns of freshwater, marine, and terrestrial resource use across a seasonally dynamic habitat mosaic

    USGS Publications Warehouse

    Rine, Kristin M.; Wipfli, Mark S.; Schoen, Erik R.; Nightengale, Timothy L.; Stricker, Craig A.

    2016-01-01

    Contributions of terrestrial-, freshwater-, and marine-derived prey resources to stream fishes vary over time and space, altering the energy pathways that regulate production. In this study, we determined large-scale use of these resources by juvenile Chinook and coho salmon (Oncorhynchus tshawytscha and Oncorhynchus kisutch, respectively) in the glacial Susitna River, Alaska. We resolved spatial and temporal trophic patterns among multiple macrohabitat types along a 97 km segment of the river corridor via stable isotope and stomach content analyses. Juvenile salmon were supported primarily by freshwater-derived resources and secondarily by marine and terrestrial sources. The relative contribution of marine-derived prey to rearing salmon was greatest in the fall within off-channel macrohabitats, whereas the contributions of terrestrial invertebrate prey were generally greatest during midsummer, across all macrohabitats. No longitudinal (upstream–downstream) diet pattern was discernable. These results highlight large-scale spatial and seasonal patterns of energy flow and the dynamic interplay of pulsed marine and terrestrial prey subsidies to juvenile Chinook and coho salmon in a large, complex, and relatively pristine glacial river.

  14. 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)

    Verkulich, Sergey; Pushina, Zina; Tatur, Andrej

    2010-05-01

    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.

  15. INTegration of Ice-core, MArine, and TErrestrial records (INTIMATE): refining the record of the Last Glacial Interglacial Transition

    NASA Astrophysics Data System (ADS)

    Hoek, W. Z.; Yu, Z. C.; Lowe, J. J.

    2008-01-01

    INTegration of Ice-core, MArine and TErrestrial records (INTIMATE) is a core project of the INQUA Palaeoclimate Commission, the primary goal of which is to synchronise records of the Last Glacial-Interglacial Transition (LGIT). Through a series of international workshops, INTIMATE has encouraged direct collaboration between scientists with interests and expertise in a wide range of palaeoenvironmental approaches. The workshops have focused on the dissemination of good practice in the dating, correlation and synthesis of diverse palaeoenvironmental records that span the LGIT. This special issue of Quaternary Science Reviews presents some of the outcomes of the 8th INTIMATE International Workshop held in Iceland in September 2005, and focuses on four themes considered vital to INTIMATE's long-term strategy. (1) An event stratigraphy approach, which uses the Greenland oxygen isotope record as a stratotype sequence, lies at the core of INTIMATE's operations. A revised event stratigraphy scheme for application to North Atlantic LGIT records is presented, which is based on the new GICC05 Greenland ice-core chronology. (2) New tree-ring data from Switzerland and the application of Bayesian-based procedures in the analysis of comprehensive radiocarbon data sets provide much potential for reducing the uncertainties in radiocarbon-based age models. (3) Three of the contributions present new evidence that helps to refine the tephrostratigraphy of the LGIT in the NE Atlantic and New Zealand regions. (4) Establishing the precise order and synchroneity of events during the LGIT is vital to understand the causes and effects of abrupt climate change. Data are presented from the Baltic region and Alaska, which vary in degree of compatibility with North Atlantic records. Two final papers consider the roles of Dansgaard-Oeschger events on thermokarst during the Middle Weichselian and of solar activity variations during the mid-Holocene; both illustrate how the INTIMATE event

  16. The evolution of the Dogger Bank, North Sea: A complex history of terrestrial, glacial and marine environmental change

    NASA Astrophysics Data System (ADS)

    Cotterill, Carol J.; Phillips, Emrys; James, Leo; Forsberg, Carl Fredrik; Tjelta, Tor Inge; Carter, Gareth; Dove, Dayton

    2017-09-01

    This paper presents a summary of the results of a detailed multidisciplinary study of the near surface geology of the Dogger Bank in the southern central North Sea, forming part of a site investigation for a major windfarm development undertaken by the Forewind consortium. It has revealed that the Dogger Bank is internally complex rather than comprising a simple ;layer cake; of the Quaternary sediments as previously thought. Regional and high-resolution seismic surveys have enabled a revised stratigraphic framework to be established for the upper part of this sequence which comprises the Eem (oldest), Dogger Bank, Bolders Bank formations and Botney Cut Formation (youngest), overlain by a typically thin Holocene sequence. Detailed mapping of key horizons identified on the high-resolution seismic profiles has led to the recognition of a series of buried palaeo-landsystems which are characterised by a range of features including; glacial, glacifluvial and fluvial channels, a large-scale glacitectonic thrust-moraine complex with intervening ice-marginal basins, a lacustrine basin and marine ravinement surfaces. Interpretation of these buried landscapes has enabled the development of an environmental change model to explain the evolution of the Dogger Bank. This evolution was driven by the complex interplay between climate change, ice sheet dynamics and sea level change associated with the growth and subsequent demise of the British and Irish and Fennoscandian ice sheets during the Weichselian glaciation. Following the decay of these ice sheets the Dogger Bank entered a period of significant climatic and environmental flux which saw a terrestrial landscape being progressively inundated as sea levels rose during the Holocene.

  17. Paleogeography, glacially induced crustal displacement, and Late Quaternary coastlines on the continental shelf of British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Hetherington, Renée; Barrie, J. Vaughn; Reid, Robert G. B.; MacLeod, Roger; Smith, Dan J.

    2004-02-01

    Subsequent to the Last Glacial Maximum (LGM), complex isostatic adjustments resulted from deglaciation, eustatic sea level change, tectonic faulting, and a relatively thin, flexible lithosphere in the Queen Charlotte Islands (QCI) region. A geostatistical interpolation model charts the sequence of evolving landscapes and displays temporal changes in the magnitudes and extent of crustal flexure that accompanied forebulge development on the Late Quaternary northeast Pacific continental shelf between 14.2 and 8.7 ka BP. Wavelength and forebulge amplitude are consistent with thermal modeling implying low upper mantle viscosity and thin elastic lithospheric thickness beneath Queen Charlotte (QC) Sound and Hecate Strait. Glacial ice ˜690 m thick began retreating from Dixon Entrance after 14.5 ka BP ( 14C years ago) and prior to 12.6 ka BP, permitting over 100 m of crustal uplift in northern Hecate Strait. A forebulge persisted in Hecate Strait and QC Sound from 13.2 until after 9.7 ka BP, implying fixed glacial ice on the British Columbia (BC) mainland until ˜10 ka BP. Paleogeographic reconstructions show two emergent ice-free terrains, one extending eastward from the QCI and the other in QC Sound. By ˜11.7 ka BP, a landbridge connected the BC mainland and the QCI.

  18. Lithic technological responses to Late Pleistocene glacial cycling at Pinnacle Point Site 5-6, South Africa

    PubMed Central

    Brown, Kyle S.; Oestmo, Simen; Pereira, Telmo; Ranhorn, Kathryn L.; Schoville, Benjamin J.; Marean, Curtis W.

    2017-01-01

    There are multiple hypotheses for human responses to glacial cycling in the Late Pleistocene, including changes in population size, interconnectedness, and mobility. Lithic technological analysis informs us of human responses to environmental change because lithic assemblage characteristics are a reflection of raw material transport, reduction, and discard behaviors that depend on hunter-gatherer social and economic decisions. Pinnacle Point Site 5–6 (PP5-6), Western Cape, South Africa is an ideal locality for examining the influence of glacial cycling on early modern human behaviors because it preserves a long sequence spanning marine isotope stages (MIS) 5, 4, and 3 and is associated with robust records of paleoenvironmental change. The analysis presented here addresses the question, what, if any, lithic assemblage traits at PP5-6 represent changing behavioral responses to the MIS 5-4-3 interglacial-glacial cycle? It statistically evaluates changes in 93 traits with no a priori assumptions about which traits may significantly associate with MIS. In contrast to other studies that claim that there is little relationship between broad-scale patterns of climate change and lithic technology, we identified the following characteristics that are associated with MIS 4: increased use of quartz, increased evidence for outcrop sources of quartzite and silcrete, increased evidence for earlier stages of reduction in silcrete, evidence for increased flaking efficiency in all raw material types, and changes in tool types and function for silcrete. Based on these results, we suggest that foragers responded to MIS 4 glacial environmental conditions at PP5-6 with increased population or group sizes, ‘place provisioning’, longer and/or more intense site occupations, and decreased residential mobility. Several other traits, including silcrete frequency, do not exhibit an association with MIS. Backed pieces, once they appear in the PP5-6 record during MIS 4, persist through MIS

  19. Mitogenomes from two uncommon haplogroups mark late glacial/postglacial expansions from the near east and neolithic dispersals within Europe.

    PubMed

    Olivieri, Anna; Pala, Maria; Gandini, Francesca; Hooshiar Kashani, Baharak; Perego, Ugo A; Woodward, Scott R; Grugni, Viola; Battaglia, Vincenza; Semino, Ornella; Achilli, Alessandro; Richards, Martin B; Torroni, Antonio

    2013-01-01

    The current human mitochondrial (mtDNA) phylogeny does not equally represent all human populations but is biased in favour of representatives originally from north and central Europe. This especially affects the phylogeny of some uncommon West Eurasian haplogroups, including I and W, whose southern European and Near Eastern components are very poorly represented, suggesting that extensive hidden phylogenetic substructure remains to be uncovered. This study expanded and re-analysed the available datasets of I and W complete mtDNA genomes, reaching a comprehensive 419 mitogenomes, and searched for precise correlations between the ages and geographical distributions of their numerous newly identified subclades with events of human dispersal which contributed to the genetic formation of modern Europeans. Our results showed that haplogroups I (within N1a1b) and W originated in the Near East during the Last Glacial Maximum or pre-warming period (the period of gradual warming between the end of the LGM, ∼19 ky ago, and the beginning of the first main warming phase, ∼15 ky ago) and, like the much more common haplogroups J and T, may have been involved in Late Glacial expansions starting from the Near East. Thus our data contribute to a better definition of the Late and postglacial re-peopling of Europe, providing further evidence for the scenario that major population expansions started after the Last Glacial Maximum but before Neolithic times, but also evidencing traces of diffusion events in several I and W subclades dating to the European Neolithic and restricted to Europe.

  20. Mitogenomes from Two Uncommon Haplogroups Mark Late Glacial/Postglacial Expansions from the Near East and Neolithic Dispersals within Europe

    PubMed Central

    Olivieri, Anna; Pala, Maria; Gandini, Francesca; Kashani, Baharak Hooshiar; Perego, Ugo A.; Woodward, Scott R.; Grugni, Viola; Battaglia, Vincenza; Semino, Ornella; Achilli, Alessandro; Richards, Martin B.; Torroni, Antonio

    2013-01-01

    The current human mitochondrial (mtDNA) phylogeny does not equally represent all human populations but is biased in favour of representatives originally from north and central Europe. This especially affects the phylogeny of some uncommon West Eurasian haplogroups, including I and W, whose southern European and Near Eastern components are very poorly represented, suggesting that extensive hidden phylogenetic substructure remains to be uncovered. This study expanded and re-analysed the available datasets of I and W complete mtDNA genomes, reaching a comprehensive 419 mitogenomes, and searched for precise correlations between the ages and geographical distributions of their numerous newly identified subclades with events of human dispersal which contributed to the genetic formation of modern Europeans. Our results showed that haplogroups I (within N1a1b) and W originated in the Near East during the Last Glacial Maximum or pre-warming period (the period of gradual warming between the end of the LGM, ∼19 ky ago, and the beginning of the first main warming phase, ∼15 ky ago) and, like the much more common haplogroups J and T, may have been involved in Late Glacial expansions starting from the Near East. Thus our data contribute to a better definition of the Late and postglacial re-peopling of Europe, providing further evidence for the scenario that major population expansions started after the Last Glacial Maximum but before Neolithic times, but also evidencing traces of diffusion events in several I and W subclades dating to the European Neolithic and restricted to Europe. PMID:23936216

  1. The Late Glacial Chronology from Lake Suigestu: A new approach to varve interpolation using frequency distributions of annual sub-layers

    NASA Astrophysics Data System (ADS)

    Schlolaut, Gordon; Marshall, Michael; Brauer, Achim; Nakagawa, Takeshi; Lamb, Henry; Staff, Richard; Bronk Ramsey, Christopher; Brock, Fiona; Bryant, Charlotte; 2006 Project Members, Suigetsu

    2010-05-01

    The 1993 sediment core from Lake Suigetsu is one of the most comprehensive terrestrial radiocarbon records. It is extremely rich in leaf fossils, providing a unique, truly atmospheric record of radiocarbon for the last 10-50 kyr BP (Kitagawa & van der Plicht, 2000). Since the Lake Suigetsu sediment is annually laminated (varved) for much of its depth it is suitable for extending the terrestrial radiocarbon calibration model up to 50 kyr BP. However, the data presented by Kitagawa & van der Plicht (2000) significantly diverged from alternative, marine-based calibration datasets, due to gaps in the sediment profile and varve counting uncertainties (Staff et al., 2009). In 2006 four new parallel cores were recovered from Lake Suigetsu and combined to construct a new complete and continuous master profile (SG06). Along with a new program of AMS radiocarbon measurement, varve counting is being carried out using two different techniques: i) thin section microscopy and ii) high-resolution X-ray fluorescence and X-radiography. In addition, a novel interpolation approach has been developed. First results are presented for the Late Glacial (10,200 - 15,000 kyr BP). The U-Oki Tephra at the top of this interval is used as tie point for the floating varve count chronology. Initially, the two counting methods are carried out independently. The results are then compared in detail to identify the differences down to the sub-mm scale. This new approach substantially reduces internal error and results in a greater degree of accuracy than previously possible. Due to poor varve preservation in some sediment intervals, the counts of these sections have to be interpolated. Commonly, interpolation is carried out manually using sedimentation rate estimates from neighbouring sections. The new approach presented here is based on an automated analysis of frequency distributions of annual sub-layers from the compromised section itself, allowing an estimate of the sedimentation rate unbiased

  2. Late Glacial to Holocene abrupt temperature changes recorded by Crenarchaeota in Lake Lucerne (Vierwaldstättersee, Switzerland)

    NASA Astrophysics Data System (ADS)

    Blaga, Cornelia I.; Reichart, Gert-Jan; Lotter, André F.; Anselmetti, Flavio; Sinninghe Damsté, Jaap S.

    2010-05-01

    In this study we applied the TEX86 (TetraEther Index of 86 carbon atoms) temperature proxy to a sediment core from Lake Lucerne (Vierwaldstättersee) to reconstruct, in almost decadal resolution, temperature changes during the Younger Dryas and the Early Holocene (ca. 14600 to 10600 cal. BP). The TEX86 proxy suggests a sequence of shifts during the late glacial period that strongly resemble the shifts in δ18O values from the Greenland ice core record. The TEX86-reconstructed lake temperature record indicates a step-wise pattern of climate changes across the studied interval with a shift from colder to warmer temperatures at the onset of the late-glacial interstadial, followed by an abrupt cooling at the onset of Younger Dryas and a rapid warming from 5.5 to 9°C at the Younger Dryas/Holocene transition in less than 200 years. The temperature change associated with the Interstadial-Younger Dryas alternation is ca. 4 °C and is in line with previous temperature reconstructions based on different proxies. The rapid changes in temperature associated with the last deglaciation are reflected in the highest possible detail in the TEX86 record. It is thus clear that our proxy, based on the isoprenoidal GDGTs (Glycerol Dialkyl Glycerol Tetraethers), is capable to reflect high resolution records of rapid (decadal to century scale oscillations) environmental fluctuations comparable with those obtained from ice cores.

  3. Late Glacial and Early Holocene Climatic Changes Based on a Multiproxy Lacustrine Sediment Record from Northeast Siberia

    SciTech Connect

    Kokorowski, H D; Anderson, P M; Sletten, R S; Lozhkin, A V; Brown, T A

    2008-05-20

    Palynological (species assemblage, pollen accumulation rate), geochemical (carbon to nitrogen ratios, organic carbon and biogenic silica content), and sedimentological (particle size, magnetic susceptibility) data combined with improved chronology and greater sampling resolution from a new core from Elikchan 4 Lake provide a stronger basis for defining paleoenvironmental changes than was previously possible. Persistence of herb-dominated tundra, slow expansion of Betula and Alnus shrubs, and low percentages of organic carbon and biogenic silica suggest that the Late-Glacial transition (ca. 16,000-11,000 cal. yr BP) was a period of gradual rather than abrupt vegetation and climatic change. Consistency of all Late-Glacial data indicates no Younger Dryas climatic oscillation. A dramatic peak in pollen accumulation rates (ca. 11,000-9800 cal. yr BP) suggests a possible summer temperature optimum, but finer grain-sizes, low magnetic susceptibility, and greater organic carbon and biogenic silica, while showing significant warming at ca. 11,000 cal. yr BP, offer no evidence of a Holocene thermal maximum. When compared to trends in other paleo-records, the new Elikchan data underscore the apparent spatial complexity of climatic responses in Northeast Siberia to global forcings between ca. 16,000-9000 cal. yr BP.

  4. Late Devonian glacial deposits from the eastern United States signal an end of the mid-Paleozoic warm period

    USGS Publications Warehouse

    Brezinski, D.K.; Cecil, C.B.; Skema, V.W.; Stamm, R.

    2008-01-01

    A Late Devonian polymictic diamictite extends for more than 400??km from northeastern Pennsylvania across western Maryland and into east-central West Virginia. The matrix-supported, unbedded, locally sheared diamictite contains subangular to rounded clasts up to 2??m in diameter. The mostly rounded clasts are both locally derived and exotic; some exhibit striations, faceting, and polish. The diamictite commonly is overlain by laminated siltstone/mudstone facies associations (laminites). The laminites contain isolated clasts ranging in size from sand and pebbles to boulders, some of which are striated. The diamictite/laminite sequence is capped by massive, coarse-grained, pebbly sandstone that is trough cross-bedded. A stratigraphic change from red, calcic paleo-Vertisols in strata below the diamictite to non-calcic paleo-Spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite. The diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the Late Devonian of the Appalachian basin. These deposits record a Late Devonian episode of climatic cooling so extreme that it produced glaciation in the Appalachian basin. Evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite, overlain by glaciolacustrine varves containing dropstones, and capped by sandstone interpreted as braided stream outwash. The Appalachian glacigenic deposits are contemporaneous with glacial deposits in South America, and suggest that Late Devonian climatic cooling was global. This period of dramatic global cooling may represent the end of the mid-Paleozoic warm interval that began in the Middle Silurian. ?? 2008 Elsevier B.V. All rights reserved.

  5. Late-glacial recolonization and phylogeography of European red deer (Cervus elaphus L.).

    PubMed

    Meiri, Meirav; Lister, Adrian M; Higham, Thomas F G; Stewart, John R; Straus, Lawrence G; Obermaier, Henriette; González Morales, Manuel R; Marín-Arroyo, Ana B; Barnes, Ian

    2013-09-01

    The Pleistocene was an epoch of extreme climatic and environmental changes. How individual species responded to the repeated cycles of warm and cold stages is a major topic of debate. For the European fauna and flora, an expansion-contraction model has been suggested, whereby temperate species were restricted to southern refugia during glacial times and expanded northwards during interglacials, including the present interglacial (Holocene). Here, we test this model on the red deer (Cervus elaphus) a large and highly mobile herbivore, using both modern and ancient mitochondrial DNA from the entire European range of the species over the last c. 40,000 years. Our results indicate that this species was sensitive to the effects of climate change. Prior to the Last Glacial Maximum (LGM) haplogroups restricted today to South-East Europe and Western Asia reached as far west as the UK. During the LGM, red deer was mainly restricted to southern refugia, in Iberia, the Balkans and possibly in Italy and South-Western Asia. At the end of the LGM, red deer expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, Scandinavia, Germany, Poland and Belarus. Ancient DNA data cannot rule out refugial survival of red deer in North-West Europe through the LGM. Had such deer survived, though, they were replaced by deer migrating from Iberia at the end of the glacial. The Balkans served as a separate LGM refugium and were probably connected to Western Asia with genetic exchange between the two areas.

  6. High-Resolution Isotope Records of the Late Ordovician and Late Carboniferous: A Comparative Perspective on Glacial Carbon and Sulfur Cycles

    NASA Astrophysics Data System (ADS)

    Gill, B. C.; Lyons, T. W.; Saltzman, M. R.

    2005-12-01

    Carbonate-associated sulfate (CAS) faithfully tracks the sulfur isotope composition of seawater in both modern and ancient environments. Therefore, analyses of carbonate rocks permit the generation of parallel, high-resolution carbon and sulfur isotope data for seawater spanning geologic history. Our previous work in the early and middle Paleozoic has revealed parallel, short-term (1-4 Myrs) carbon and sulfur isotope excursions. The relationship between the two isotope systems seems to change over time, perhaps tracking longer-term evolution of the marine sulfur reservoir and of the primary loci of carbon burial, including increased burial on land. CAS isotope records therefore have the potential to shed essential mechanistic light on the causes (global versus regional) for carbon isotope excursions observed throughout the geological record. Previous work on the Late Carboniferous and Late Ordovician documented the existence of carbon isotope excursions of varying magnitude during these glacial episodes. The Late Carboniferous glaciations classically show evidence for multiple glacial-interglacial cycles with repeated, low magnitude (1 to 3 per mil) carbon isotope excursions. By contrast, the Late Ordovician was characterized by a short-lived glaciation with a corresponding single 4-6 per mil carbon isotope excursion. The modes and rates of carbon cycling reflected in the differing styles of C isotope behavior are the subject of debate, making these time-slices ideal for the CAS isotope approach. Carbon and sulfur isotope data from Pennsylvanian (Missourian Stage) cyclothems exposed in Kansas City, Missouri, show rapid isotope variability. We have preliminarily attributed these rapid changes to local reservoir effects linked to fluctuating sea level and its relationship to black shale deposition within the midcontinent basin and weathering on the basin margin during lowstands. Other work on the cyclic Carboniferous Bird Spring Formation, Nevada, is also

  7. Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition.

    PubMed

    Pound, Matthew J; Salzmann, Ulrich

    2017-02-24

    Rapid global cooling at the Eocene - Oligocene Transition (EOT), ~33.9-33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT.

  8. Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition

    PubMed Central

    Pound, Matthew J.; Salzmann, Ulrich

    2017-01-01

    Rapid global cooling at the Eocene – Oligocene Transition (EOT), ~33.9–33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT. PMID:28233862

  9. Heterogeneity in global vegetation and terrestrial climate change during the late Eocene to early Oligocene transition

    NASA Astrophysics Data System (ADS)

    Pound, Matthew J.; Salzmann, Ulrich

    2017-02-01

    Rapid global cooling at the Eocene – Oligocene Transition (EOT), ~33.9–33.5 Ma, is widely considered to mark the onset of the modern icehouse world. A large and rapid drop in atmospheric pCO2 has been proposed as the driving force behind extinctions in the marine realm and glaciation on Antarctica. However, the global terrestrial response to this cooling is uncertain. Here we present the first global vegetation and terrestrial temperature reconstructions for the EOT. Using an extensive palynological dataset, that has been statistically grouped into palaeo-biomes, we show a more transitional nature of terrestrial climate change by indicating a spatial and temporal heterogeneity of vegetation change at the EOT in both hemispheres. The reconstructed terrestrial temperatures show for many regions a cooling that started well before the EOT and continued into the Early Oligocene. We conclude that the heterogeneous pattern of global vegetation change has been controlled by a combination of multiple forcings, such as tectonics, sea-level fall and long-term decline in greenhouse gas concentrations during the late Eocene to early Oligocene, and does not represent a single response to a rapid decline in atmospheric pCO2 at the EOT.

  10. Geomorphic investigation of craters in Alba Mons, Mars: Implications for Late Amazonian glacial activity in the region

    NASA Astrophysics Data System (ADS)

    Sinha, Rishitosh K.; Vijayan, S.

    2017-09-01

    Evidence for mid-high latitude glacial episodes existing within the Late Amazonian history of Mars has been reported from analysis of variety of glacial/periglacial landforms and their stratigraphic relationships. In this study, using the Context Camera (CTX) images, we have surveyed the interior of craters within the Alba Mons region of Mars (30°-60°N; 80°-140°W) to decipher the presence of ice-related flow features. The primary goals of this study are to (1) suggest from observations that the flow features identified in the interior of Alba Mons craters have flow characteristic possibly different from concentric crater fill (CCF) landforms and (2) interpret the extent of glacial activity that led to formation of flow features with respect to previously described mid-latitude ice-related landforms. Our geomorphic investigation revealed evidence for the presence of tongue-like or lobate shaped ice-related flow feature from the interior of ∼346 craters in the study region. The presence of ring-mold crater morphologies and brain-terrain texture preserved on the surface of flow features suggests that they are possibly formed of near-surface ice-rich bodies. We found that these flow features tend to form inside both the smaller (<5 km) and larger (>5 km) diameter craters emplaced at a wide range of elevation (from ∼ -3.3 km to 6.1 km). The measurement of overall length and flow direction of flow features is suggestive that they are similar to pole-facing small-scale lobate debris apron (LDA) formed inside craters. Crater size-frequency distribution of these small-scale LDAs reveals a model age of ∼10-100 Ma. Together with topographic and geomorphic observations, orientation measurements, and distribution within the study region, we suggest that the flow features (identified as pole-facing small-scale LDAs in the interior of craters) have flow characteristic possibly different from CCF landforms. Our observations and findings support the results of previous

  11. Pleistocene Mitochondrial Genomes Suggest a Single Major Dispersal of Non-Africans and a Late Glacial Population Turnover in Europe.

    PubMed

    Posth, Cosimo; Renaud, Gabriel; Mittnik, Alissa; Drucker, Dorothée G; Rougier, Hélène; Cupillard, Christophe; Valentin, Frédérique; Thevenet, Corinne; Furtwängler, Anja; Wißing, Christoph; Francken, Michael; Malina, Maria; Bolus, Michael; Lari, Martina; Gigli, Elena; Capecchi, Giulia; Crevecoeur, Isabelle; Beauval, Cédric; Flas, Damien; Germonpré, Mietje; van der Plicht, Johannes; Cottiaux, Richard; Gély, Bernard; Ronchitelli, Annamaria; Wehrberger, Kurt; Grigorescu, Dan; Svoboda, Jiří; Semal, Patrick; Caramelli, David; Bocherens, Hervé; Harvati, Katerina; Conard, Nicholas J; Haak, Wolfgang; Powell, Adam; Krause, Johannes

    2016-03-21

    How modern humans dispersed into Eurasia and Australasia, including the number of separate expansions and their timings, is highly debated [1, 2]. Two categories of models are proposed for the dispersal of non-Africans: (1) single dispersal, i.e., a single major diffusion of modern humans across Eurasia and Australasia [3-5]; and (2) multiple dispersal, i.e., additional earlier population expansions that may have contributed to the genetic diversity of some present-day humans outside of Africa [6-9]. Many variants of these models focus largely on Asia and Australasia, neglecting human dispersal into Europe, thus explaining only a subset of the entire colonization process outside of Africa [3-5, 8, 9]. The genetic diversity of the first modern humans who spread into Europe during the Late Pleistocene and the impact of subsequent climatic events on their demography are largely unknown. Here we analyze 55 complete human mitochondrial genomes (mtDNAs) of hunter-gatherers spanning ∼35,000 years of European prehistory. We unexpectedly find mtDNA lineage M in individuals prior to the Last Glacial Maximum (LGM). This lineage is absent in contemporary Europeans, although it is found at high frequency in modern Asians, Australasians, and Native Americans. Dating the most recent common ancestor of each of the modern non-African mtDNA clades reveals their single, late, and rapid dispersal less than 55,000 years ago. Demographic modeling not only indicates an LGM genetic bottleneck, but also provides surprising evidence of a major population turnover in Europe around 14,500 years ago during the Late Glacial, a period of climatic instability at the end of the Pleistocene. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Surface-exposure Dating of Late Quaternary Glacial Advances in the Cordillera Blanca, Peruvian Andes (9°-10°S)

    NASA Astrophysics Data System (ADS)

    Smith, J. A.; Zehner, S. P., Jr.; Bowen, D. R.; Rodbell, D. T.

    2013-12-01

    New 10Be surface-exposure ages from boulders on lateral moraines bordering Querococha Valley (9°44.6' S, 77°21.6' W) in the southern Cordillera Blanca, Peru, indicate that late-glacial (˜16 ka) ice extended as much as 15 km downvalley from the headwall(s). With the glacier terminus at ˜3900 masl and the headwall at ˜5200 masl, THAR reconstruction (THAR=0.45) places the late-glacial equilibrium-line altitude (ELA) at ˜4485 masl, as compared to an estimated modern ELA of ˜5100 masl. The late-glacial Querococha advance was coeval with late-glacial advances at the Nevado Jeulla Rajo (NJR) massif at the southern end of the Cordillera Blanca (10°00'S, 77°16'W; peaks ˜5600 masl), ˜35 km to the south, where we have dated multiple moraines. Surface-exposure ages (10Be) indicate that the largest lateral moraines from Jeullesh Valley at NJR are compound features deposited during both the local last glacial maximum (˜30 ka) and a late-glacial readvance (˜15 ka). Late-glacial moraines are the largest lateral moraines in neighboring Quenua Ragra and Tuco valleys. The timing of the late-glacial advances in the Cordillera Blanca suggests a link to increased precipitation associated with Heinrich Event I (˜17 ka). Additional new 10Be surface-exposure ages from boulders on a moraine crossing a side valley in the upper reaches of Jeullesh Valley are early Holocene (˜9-11 ka), suggesting retreat of 3-4 km from the late-glacial terminal position in ˜4 kyr. Using the same THAR methodology, the late-glacial ELA in Jeullesh Valley was ˜4815 masl and the early Holocene ELA was ˜4995 masl. The active, west-dipping Cordillera Blanca Normal Fault (CBNF) vertically offsets the crests of 10Be-dated moraines in six valleys where we have profiled CBNF scarps: Jeullesh, Quenua Ragra, and Tuco valleys in the NJR massif; and Llaca, Cojup, and Querococha valleys in the south-central Cordillera Blanca (9°28'-45'S, 77°28'-21'W). In Jeullesh Valley, the CBNF scarp offsets both late-glacial

  13. Calibrating Late Quaternary terrestrial climate signals: radiometrically dated pollen evidence from the southern Sierra Nevada, USA

    USGS Publications Warehouse

    Litwin, Ronald J.; Smoot, Joseph P.; Durika, Nancy J.; Smith, George I.

    1999-01-01

    We constructed a radiometrically calibrated proxy record of Late Pleistocene and Holocene climate change exceeding 230,000 yr duration, using pollen profiles from two cores taken through age-equivalent dry lakes - one core having greater age control (via 230Th alpha mass-spectrometry) and the other having greater stratigraphic completeness. The better dated of these two serial pollen records (Searles Lake) served as a reference section for improving the effective radiometric age control in a nearby and more complete pollen record (Owens Lake) because they: (1) are situated ~90 km apart in the same drainage system (on, and immediately leeward of, the eastern flank of the Sierra Nevada), and (2) preserved strikingly similar pollen profiles and concordant sequences of sedimentological changes. Pollen assemblages from both lakes are well preserved and diverse, and document serial changes in Late Pleistocene and Holocene plant zone distribution and composition in the westernmost Great Basin; they consist of taxa now inhabiting montane forest, woodland, steppe, and desert-scrub environments. The studied core intervals are interpreted here to be the terrestrial equivalent of marine δ18O stages 1 through 9; these pollen profiles now appear to be among the best radiometrically dated Late Pleistocene records of terrestrial climate change known.

  14. Was the Late-glacial advance at ~14.0 ka B.P. in Torres del Paine (Patagonia, 51S) the most extensive glacial pulse of Oxygen Isotope Stage 2?

    NASA Astrophysics Data System (ADS)

    Garcia, J.; Hall, B. L.; Kaplan, M. R.; Schaefer, J. M.; Vega, R. M.; Schwartz, R.; Finkel, R. C.

    2010-12-01

    Uncovering the timing and spatial extent of glaciers and associated climate changes in the southern hemisphere provide key foundations in the understanding of the origin and termination of ice ages and new insights regarding the Milankovitch model of ice ages. Here, we discuss paleoclimatological implications from our preliminary 10Be-dating program of moraines in Torres del Paine National Park (TDP), in southern Chilean Patagonia (51S). Four main moraine belts (TDP I-IV, from outer to inner) expose geomorphological evidence for ice extent and fluctuations during the last glacial cycle in Torres del Paine. We collected 24 boulders embedded in the outer two moraines (TDP I-II moraines) for 10Be cosmogenic-exposure dating to reconstruct the Quaternary glacial and climate history. The 10Be exposure data show that the mean ages of TDP I moraine, at least in Laguna Azul basin, is about 40 ka BP (n=5) (ka BP= 1,000 years before present) and TDP II is about 14 ka BP. Although most of the 10Be glacial records in Patagonia have documented that the local Last Glacial Maximum (LGM) occurred between 25-17.5 ka BP, in Torres del Paine the maximum extent of the Southern Patagonian Icefield during the last glacial cycle may have occurred as early as ~40 ka BP. This is one of the first lines of (moraine-based) evidence that suggests the existence of an early LGM in Patagonia. The apparent age of the TDP II moraine dating to the late-glacial seems to imply that there are no distinct moraines in Torres del Paine dating to the time of the global LGM, a unique case revealed here. Scattered boulders from TDP II moraine dates to the late LGM and seems to suggest that late-glacial ice overrode the LGM moraines in Torres del Paine. Both glacial pulses at 40 ka BP and 14 ka BP in Torres del Paine occurred during stadial phases in West Antarctica suggesting the existing of an Antarctic climate control on southern Patagonian during the last glacial cycle. Physical mechanisms allowing climate

  15. Radiocarbon dating late Quaternary loess deposits using small terrestrial gastropod shells

    USGS Publications Warehouse

    Pigati, Jeff S.; McGeehin, John P.; Muhs, Daniel R.; Bettis, E. Arthur

    2013-01-01

    Constraining the ages and mass accumulation rates of late Quaternary loess deposits is often difficult because of the paucity of organic material typically available for 14C dating and the inherent limitations of luminescence techniques. Radiocarbon dating of small terrestrial gastropod shells may provide an alternative to these methods as fossil shells are common in loess and contain ∼12% carbon by weight. Terrestrial gastropod assemblages in loess have been used extensively to reconstruct past environmental conditions but have been largely ignored for dating purposes. Here, we present the results of a multi-faceted approach to understanding the potential for using small terrestrial gastropod shells to date loess deposits in North America. First, we compare highly resolved 14C ages of well-preserved wood and gastropod shells (Succineidae) recovered from a Holocene loess section in Alaska. Radiocarbon ages derived from the shells are nearly identical to wood and plant macrofossil ages throughout the section, which suggests that the shells behaved as closed systems with respect to carbon for at least the last 10 ka (thousands of calibrated 14C years before present). Second, we apply 14C dating of gastropod shells to late Pleistocene loess deposits in the Great Plains using stratigraphy and independent chronologies for comparison. The new shell ages require less interpretation than humic acid radiocarbon ages that are commonly used in loess studies, provide additional stratigraphic coverage to previous dating efforts, and are in correct stratigraphic order more often than their luminescence counterparts. Third, we show that Succineidae shells recovered from historic loess in the Matanuska River Valley, Alaska captured the 20th century 14C bomb spike, which suggests that the shells can be used to date late Holocene and historic-aged loess. Finally, results from Nebraska and western Iowa suggest that, similar to other materials, shell ages approaching ∼40 ka should

  16. The Late Glacial/Holocene transition and its consequences on coastal environment in northwestern Greece (Epirus) : geoarchaeological and palaeogeographical prospects

    NASA Astrophysics Data System (ADS)

    Chabrol, A.; Fouache, E.; Le Coeur, C.; Ghilardi, M.

    2009-04-01

    At the scale of the Mediterranean Basin, the Glacial/Interglacial transition (15 000 - 6 000 BP) corresponds successively to the hunthers-gatherers from the Late Upper Paleolithic societies, to the Mesolithic and then to the farming societies from the Neolithic. The area of research (Epirus and particularly the Ionian coast) reveals original archaeological data: in this area, archaeologists didn't find much prehistoric settlements comparing to other places in Greece. Furthermore, the neolithisation became later than in Thessaly or in Boeotia. Geomorphologic researches and regional palaeogeographical reconstructions should help us to explain the prehistoric human dynamics and the adaptation of these societies to a rapid changing area due in particular to the post glacial sea level rise. The research focuses on Northwestern Epirus: the island of Corfu and the delta of the Kalamas river correspond to a promising area of research. Indeed, this area revealed us different interesting and complementary sedimentary archives for our study: the probable palaeo-lake between Corfu and the continental Greece and the delta of the Kalamas river. The poster for the scientific congress will explain the originality of the area of research and the originality of the geoarchaeological prospects in northwestern Greece. Particularly, the methodology will be explained: archaeological and geomorphologic cartography, geophysical prospection in the delta (electric vertical profiles, seismic profiles) and core sampling activities. Palaeogeographical and geoarchaeological prospects and the first results will be discussed.

  17. Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America.

    PubMed

    Vanneste, Heleen; De Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

    2015-07-01

    Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions.

  18. Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America

    NASA Astrophysics Data System (ADS)

    Vanneste, Heleen; de Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

    2015-07-01

    Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions.

  19. Evidence of late glacial paleoseismicity from submarine landslide deposits within Lac Dasserat, northwestern Quebec, Canada

    NASA Astrophysics Data System (ADS)

    Brooks, Gregory R.

    2016-09-01

    An integrated seismo- and chronostratigraphic investigation at Lac Dasserat, northwestern Quebec, identified 74 separate failures within eight event horizons. Horizons E and B, and H and G have strong or moderately-strong multi-landslide signatures, respectively, composed of 11-23 failures, while horizons F, D, C, and A have minor landslide signatures consisting of a single or pair of deposit(s). Cores collected at six sites recovered glacial Lake Ojibway varve deposits that are interbedded with the event horizons. The correlation of the varves to the regional Timiskaming varve series allowed varve ages or ranges of varve ages to be determined for the event horizons. Horizons H, G, E, and B are interpreted to be evidence of paleoearthquakes with differing levels of interpretative confidence, based on the relative strength of the multi-landslide signatures, the correlation to other disturbed deposits of similar age in the region, and the lack or possibility of alternative aseismic mechanisms. The four interpreted paleoearthquakes occurred between 9770 ± 200 and 8470 ± 200 cal yr BP, when glacial Lake Ojibway was impounded behind the Laurentide Ice Sheet during deglaciation. They probably represent an elevated period of seismicity at deglaciation that was driven by crustal unloading.

  20. Late-glacial elevated dust deposition linked to westerly wind shifts in southern South America

    PubMed Central

    Vanneste, Heleen; De Vleeschouwer, François; Martínez-Cortizas, Antonio; von Scheffer, Clemens; Piotrowska, Natalia; Coronato, Andrea; Le Roux, Gaël

    2015-01-01

    Atmospheric dust loadings play a crucial role in the global climate system. Southern South America is a key dust source, however, dust deposition rates remain poorly quantified since the last glacial termination (~17 kyr ago), an important timeframe to anticipate future climate changes. Here we use isotope and element geochemistry in a peat archive from Tierra del Fuego, to reconstruct atmospheric dust fluxes and associated environmental and westerly wind changes for the past 16.2 kyr. Dust depositions were elevated during the Antarctic Cold Reversal (ACR) and second half of the Younger Dryas (YD) stadial, originating from the glacial Beagle Channel valley. This increase was most probably associated with a strengthening of the westerlies during both periods as dust source areas were already available before the onset of the dust peaks and remained present throughout. Congruent with glacier advances across Patagonia, this dust record indicates an overall strengthening of the wind belt during the ACR. On the other hand, we argue that the YD dust peak is linked to strong and poleward shifted westerlies. The close interplay between dust fluxes and climatic changes demonstrates that atmospheric circulation was essential in generating and sustaining present-day interglacial conditions. PMID:26126739

  1. New records of temperate mollusks in two Late Pleistocene terrestrial localities from northeastern Oaxaca, Southern Mexico

    NASA Astrophysics Data System (ADS)

    Guerrero-Arenas, Rosalía; Jiménez-Hidalgo, Eduardo; García-Barrera, Pedro

    2013-11-01

    The Mixteca Alta Oaxaqueña is in the state of Oaxaca, southern Mexico. This region is characterized by numerous Pleistocene fossiliferous localities. The objective of this study is to describe a diverse assemblage of Late Pleistocene freshwater and terrestrial mollusks in two localities from northeastern Oaxaca, Coixtlahuaca District. We identified 10 taxa of gastropods and one of bivalves. By the sedimentological characteristics and the mollusks assemblage, it is possible to relate the first locality with meandriform river deposits, without vegetation. The second locality was associated with a floodplain with short-lived associated vegetation. Five identified species constitute the most austral records of these taxa in Neartic Realm. In all the taxa, the Late Pleistocene occurrences constitute the last records of the identified mollusks in the study zone.

  2. Multiproxy, Cross-Biome Analysis Of Ecosystem Dynamics During Late-Glacial And Holocene Climatic Change In North-Central North America

    NASA Astrophysics Data System (ADS)

    Camill, P.; Umbanhowar, C. E.; Geiss, C. E.; Teed, R. E.; Dorale, J. A.; Lynch, J. A.

    2010-12-01

    Vegetation ecotones and lake ecosystem dynamics have the potential to change dramatically with rapid climate warming. We present data for 15 proxies from eight well-dated lake sediment cores documenting late glacial and Holocene changes in both terrestrial and lake processes across a latitudinal gradient in central North America spanning grassland, aspen parkland, boreal, and tundra biomes. Our goal was to examine the timing and magnitude of terrestrial and aquatic ecosystem proxies across known climatic gradients in space and time. Results indicate that fire and vegetation dynamics were influenced by how climate controlled the relative abundance of arboreal vs. herbaceous taxa. Fire severity was greatest during the Holocene Thermal Maximum (HTM, 8500-5000 BP) only in forest-dominated boreal and northern parkland landscapes. At the grassland-woodland border and tundra-woodland ecotones, fire severity peaked after the HTM, presumably during more mesic conditions that supported greater landscape productivity. Lake ecosystems differed across the latitudinal gradient, with warmer grassland lakes showing a potential shift from diatoms to cyanobacteria following HTM aridity, P inputs, N:P (molar) declines to < 5-15, and N limitation, leading to poor or negative overall correlations among biogenic silica, nutrients, and organic matter. At the northernmost parkland and boreal and tundra sites, there was no indication from the pollen, magnetics, grain size, TP, or N:P data of significant mineral transport to these lakes or shifts in lake stoichiometry at or following the HTM, suggesting that aridity was less severe in higher latitudes. Unlike the grassland sites, which may have experienced a state change in the plankton community from diatoms to cyanobacteria as a result of HTM mineral inputs, cyanobacteria probably played a smaller role in the northernmost parkland, boreal, and tundra sites because the strong positive correlations between organic matter and bSi (P < 0

  3. Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation

    USGS Publications Warehouse

    Carrara, Paul E.; Ager, Thomas A.; Baichtal, James F.; VanSistine, D. Paco

    2003-01-01

    During the late Wisconsin glaciation (circa 26,000-13,000 carbon-14 yr BP) the Cordilleran glacier complex formed vast ice fields and large glaciers along the crest of the Coast Mountains. As these glaciers flowed west to the Pacific Ocean, they were joined by local glaciers originating on the higher reaches of the Alexander Archipelago (Mann and Hamiltion, 1995). This extensive volume of ice was channeled into deep troughs (present-day fiords) that formed major outlet glaciers, such as the glaciers that occupied Chatham Strait and Dixon Entrance. In several places along the coast, deep glacially scoured submarine troughs indicate that glaciers reached to the edge of the continental shelf. For instance, the glacier that extended into the Dixon Entrance trough is known to have extended to the edge of the continental shelf. Its retreat began sometime after 16,000-15,000 carbon-14 yr BP (Barrie and Conway, 1999).

  4. A first Late Glacial and Early Holocene coupled 18O and 2H biomarker isotope record from Gemuendener Maar, Germany

    NASA Astrophysics Data System (ADS)

    Zech, Michael; Bromm, Tobias; Hepp, Johannes; Benesch, Marianne; Sirocko, Frank; Glaser, Bruno; Zech, Roland

    2015-04-01

    During the last years, we developed a method for compound-specific d18O analyses of hemicellulose-derived sugars from plants, soils and sediment archives (Zech and Glaser, 2009; Zech et al., 2014). The coupling of respective d18O sugar results with d2H alkane results from paleosol and sediment climate archives proved to be a valuable innovative approach towards quantitative paleoclimate reconstruction (Hepp et al., 2014; Zech et al., 2013). Here we present a first coupled d18O sugar and d2H alkane biomarker record obtained for Late Glacial and Early Holocene sediments from the Gemuendener Maar in the Eifel, Germany. The d18O sugar biomarker record resembles the d18O ice core records of Greenland. The coupling with the d2H alkane biomarker results allows drawing further more quantitative paleocimate information in terms of (i) paleohumidity and (ii) d18O of paleoprecipitation.

  5. Multiple instabilities and modes of glacial rhythmicity in the Plio-Pleistocene: A general theory of late Cenozoic climatic change

    SciTech Connect

    Saltzman, B.; Verbitsky, M.Ya.

    1993-10-01

    Several distinct modes of glacial oscillation have existed during the past few million years, ranging from low-amplitude, high-frequency oscillations in the early Pliocene, through relatively high amplitude, predominantly near 40 ky period, oscillations in the late Pliocene and early Pleistocene, to the major near 100 ky period oscillations of the late Pleistocene. In addition to other plausible mechanisms, this study illustrates another possible contributor based on the hypothesis that the slow-response climatic system is bistable and that two kinds of internal instability may be operative along with externally imposed forcing due to earth-orbital (Milankovitch) radiation changes and slow, tectonically-induced changes in atmospheric carbon dioxide. Within the framework of a dynamical model containing the possibility for these two instabilities, as well as for stable modes, the study shows (1) how Milankovitch radiative changes or stochastic forcing influencing ice sheets can induce aperiodic (chaotic) transitions between the possible stable and unstable modes, and (2) how progressive, long-term, tectonically-induced, changes in carbon dioxide, acting in concert with earth-orbital radiative variations in high Northern Hemisphere latitudes, can force systematic transitions between the modes. This is a minimum dynamical model of the late Cenozoic climatic changes, containing the main physical factors determining these changes: ice mass, bedrock depression, atmospheric carbon dioxide concentration, deep ocean thermohaline state, Milankovitch radiation forcing, and slow tectonically-induced carbon dioxide forcing. 34 refs., 13 figs., 2 tabs.

  6. New insights into late Neogene glacial dynamics, tectonics, and hydrocarbon migrations in the Atlantic-Arctic gateway region.

    NASA Astrophysics Data System (ADS)

    Knies, J.; Baranwal, S.; Fabian, K.; Grøsfjeld, K.; Andreassen, K.; Husum, K.; Mattingsdal, R.; Gaina, C.; De Schepper, S.; Vogt, C.; Andersen, N.

    2012-04-01

    Notwithstanding the recent IODP drilling on the Lomonosov Ridge, the Late Cenozoic history of the Arctic Ocean still remains elusive. The tectonic processes leading to the development of the only deep-water connection to the Arctic Ocean via the Fram Strait are still poorly understood. Also, the influence of the gateway region on changes in Arctic-Atlantic ocean circulation, uplift/erosion on the adjacent hinterland, as well as glacial initiation and its consequences for the petroleum systems in the regions, remain unclear. By revisiting Ocean Drilling Program (ODP) Leg 151, holes 911A and 910C and interpreting new multi-channel seismic data, we have now established a new comprehensive chronological framework for the Yermak Plateau and revealed important paleoenvironmental changes for the Atlantic-Arctic gateway during the late Neogene. The improved chronostratigraphic framework is established through continuous paleomagnetic and biostratigraphic data as well as selected intervals with stable ?18O and ?13C data derived from benthic foraminifera Cassidulina teretis. Supported by acoustic profiling, the new data indicate a continuous late Miocene/early Pliocene age (~5-6 Ma) for the base of both holes. The depositional regime north (Yermak Plateau) and south of the Fram Strait (Hovgaard Ridge) was rather shallow during the late Miocene and water mass exchange between the Arctic and Atlantic was restricted. Ice sheets on the Svalbard Platform evolved during the late Miocene, however did not reach the coastline before 3.3 Ma. Migration of gaseous hydrocarbons occurred prior to the intensification of the Northern Hemisphere Glaciations (~2.7 Ma) as indicated by high-amplitude reflections, corroborating the occurrence of greigite mineralization and stable carbon isotope excursions in planktic/benthic foraminifera. The data indicate that Pleistocene erosion and uplift in the Barents Sea region had probably only minor effects on reservoir leakages than previously thought.

  7. Late Pleistocene glacial stratigraphy of the Kumara-Moana region, West Coast of South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Barrows, Timothy T.; Almond, Peter; Rose, Robert; Keith Fifield, L.; Mills, Stephanie C.; Tims, Stephen G.

    2013-08-01

    On the South Island of New Zealand, large piedmont glaciers descended from an ice cap on the Southern Alps onto the coastal plain of the West Coast during the late Pleistocene. The series of moraine belts and outwash plains left by the Taramakau glacier are used as a type section for interpreting the glacial geology and timing of major climatic events of New Zealand and also as a benchmark for comparison with the wider Southern Hemisphere. In this paper we review the chronology of advances by the Taramakau glacier during the last or Otira Glaciation using a combination of exposure dating using the cosmogenic nuclides 10Be and 36Cl, and tephrochronology. We document three distinct glacial maxima, represented by the Loopline, Larrikins and Moana Formations, separated by brief interstadials. We find that the Loopline Formation, originally attributed to Oxygen Isotope Chronozone 4, is much younger than previously thought, with an advance culminating around 24,900 ± 800 yr. The widespread late Pleistocene Kawakawa/Oruanui tephra stratigraphically lies immediately above it. This Formation has the same age previously attributed to the older part of the Larrikins Formation. Dating of the Larrikins Formation demonstrates there is no longer a basis for subdividing it into older and younger phases with an advance lasting about 1000 years between 20,800 ± 500 to 20,000 ± 400 yr. The Moana Formation represents the deposits of the last major advance of ice at 17,300 ± 500 yr and is younger than expected based on limited previous dating. The timing of major piedmont glaciation is restricted to between ˜25,000 and 17,000 yr and this interval corresponds to a time of regionally cold sea surface temperatures, expansion of grasslands at the expense of forest on South Island, and hemisphere wide glaciation.

  8. The oldest caseid synapsid from the Late Pennsylvanian of Kansas, and the evolution of herbivory in terrestrial vertebrates.

    PubMed

    Reisz, Robert R; Fröbisch, Jörg

    2014-01-01

    The origin and early evolution of amniotes (fully terrestrial vertebrates) led to major changes in the structure and hierarchy of terrestrial ecosystems. The first appearance of herbivores played a pivotal role in this transformation. After an early bifurcation into Reptilia and Synapsida (including mammals) 315 Ma, synapsids dominated Paleozoic terrestrial vertebrate communities, with the herbivorous caseids representing the largest vertebrates on land. Eocasea martini gen. et sp. nov., a small carnivorous caseid from the Late Carboniferous, extends significantly the fossil record of Caseidae, and permits the first clade-based study of the origin and initial evolution of herbivory in terrestrial tetrapods. Our results demonstrate for the first time that large caseid herbivores evolved from small, non-herbivorous caseids. This pattern is mirrored by three other clades, documenting multiple, independent, but temporally staggered origins of herbivory and increase in body size among early terrestrial tetrapods, leading to patterns consistent with modern terrestrial ecosystem.

  9. The Oldest Caseid Synapsid from the Late Pennsylvanian of Kansas, and the Evolution of Herbivory in Terrestrial Vertebrates

    PubMed Central

    Reisz, Robert R.; Fröbisch, Jörg

    2014-01-01

    The origin and early evolution of amniotes (fully terrestrial vertebrates) led to major changes in the structure and hierarchy of terrestrial ecosystems. The first appearance of herbivores played a pivotal role in this transformation. After an early bifurcation into Reptilia and Synapsida (including mammals) 315 Ma, synapsids dominated Paleozoic terrestrial vertebrate communities, with the herbivorous caseids representing the largest vertebrates on land. Eocasea martini gen. et sp. nov., a small carnivorous caseid from the Late Carboniferous, extends significantly the fossil record of Caseidae, and permits the first clade-based study of the origin and initial evolution of herbivory in terrestrial tetrapods. Our results demonstrate for the first time that large caseid herbivores evolved from small, non-herbivorous caseids. This pattern is mirrored by three other clades, documenting multiple, independent, but temporally staggered origins of herbivory and increase in body size among early terrestrial tetrapods, leading to patterns consistent with modern terrestrial ecosystem. PMID:24739998

  10. Late Glacial Tropical Savannas in Sundaland Inferred From Stable Carbon Isotope Records of Cave Guano

    NASA Astrophysics Data System (ADS)

    Wurster, C. M.; Bird, M. I.; Bull, I.; Dungait, J.; Bryant, C. L.; Ertunç, T.; Hunt, C.; Lewis, H. A.; Paz, V.

    2008-12-01

    During the Last Glacial Period (LGP), reduced global sea level exposed the continental shelf south of Thailand to Sumatra, Java, and Borneo to form the contiguous continent of Sundaland. However, the type and extent of vegetation that existed on much of this exposed landmass during the LGP remains speculative. Extensive bird and bat guano deposits in caves throughout this region span beyond 40,000 yr BP, and contain a wealth of untapped stratigraphic palaeoenvironmental information. Stable carbon isotope ratios of insectivorous bird and bat guano contain a reliable record of the animal's diet and, through non-specific insect predation, reflect the relative abundance of major physiological pathways in plants. Various physiological pathways of carbon fixation in plants yield differing stable carbon isotope ratios. Stable carbon isotope values of C3 plants are lower than C4 vegetation due to different enzymatic discriminations of the heavy isotope through the carbon fixing pathways. In tropical locales, grasses nearly always follow the C4 photosynthetic pathway, whereas tropical rainforest uses C3 photosynthesis, providing a proxy for vegetation and therefore climate change in the past. Here we discuss four guano stable-isotope records, based on insect cuticle and n-alkane analysis, supplemented by pollen analysis. All sites suggest a C3 dominated ecosystem for the Holocene, consistent with the wet tropical forest vegetation present at all locations. Two sites from Palawan Island, Philippines, record stable carbon isotope values of guano that document a drastic change from C3 (forest) to C4 (savanna) dominated ecosystems during the Last Glacial Maximum (LGM). A third location, at Niah Great Cave, Malaysia, indicates C3-dominant vegetation throughout the record, but does display variation in stable carbon isotope values likely linked to humidity changes. A fourth location, Batu Caves in Peninsular Malaysia, also indicates open vegetation during the LGM. Vegetation

  11. Linking glacial melting to Late Quaternary sedimentation in climatically sensitive mountainous catchments of the Mount Chlemos compex, Kalavryta, southern Greece

    NASA Astrophysics Data System (ADS)

    Pope, Richard; Hughes, Philip

    2014-05-01

    Compared to the mountainous areas of northern Greece (e.g. Woodward et al., 2008), the influence of deglaciation cycles on sedimentation in mountainous catchments in southern Greece remains poorly understood due to the poor preservation of small moraines and limited opportunities to date glacial and fluvial sediment dynamics fluvial sediments (Pope, unpublished data). Nevertheless, intriguing new insight into links between glacial cycles and sediment transfer/deposition phases in upland catchments have emerged by applying multiple dating techniques to well-preserved multiple generations of moraines and extensive glacio-fluvial fan systems on Mount Chelmos (2355 m a.s.l.). U-series dating of calcites within proximal fan sediments constrain the earliest phase of glacio-fluvial sedimentation to 490 (±21.0)(ka (MIS 12), while OSL dating of fine sands constrains the deposition of extensive medial glacio-fluvial gravels in (valley we walked down through trees) to between 250.99 (±20.67) and 160.82 (±11.08) ka. By comparison, cosmogenic dating of moraine boulders indicates that three generations of well-preserved moraines in the highest cirque areas date to 31-23 ka, 17-16 ka and 12-11.5 ka. OSL dating also provides ages of 18 and 17 (±11.08) for an extensive glacio-fluvial terrace in a major valley draining the southern flanksof Mount Chelmos. The initial Mount Chelmos geochronology suggests that the earliest and middle phases of glacio-fluvial sedimentation are coincident with the Middle Pleistocene glacial stages stages recorded in the Pindus range (Hughes et al, 2006). These include the Skamnellian (MIS 12) and the Vlasian (MIS 6) Stages as well as other cold stage between these (e.g. MIS 8).Evidence of glacio-fluvial outwash in MIS 8 is interesting since evidence for this in the moraine records has remained elusive although is suggested further north in the Balkans (Hughes et al., 2011). The valley moraines and glacio-fluvial terraces (late MIS 2) post-date the

  12. Detailed view into the dynamics of the Late Miocene glaciation episode that accompanied terrestrial evolution

    NASA Astrophysics Data System (ADS)

    Tzanova, A.; Herbert, T.; Lawrence, K. T.; Peterson, L.; Kelly, C. S.

    2015-12-01

    We focus on the period of ~ 9 - 5 Ma when an episode of notably cool temperatures corresponds to evidence of high latitude Northern Hemisphere glaciation and mid-latitude terrestrial evolution. Alkenone-based sea surface temperatures (SST) from six globally distributed sites: ODP Sites 907 and 982 in the North Atlantic, ODP Site 1088 in the South Atlantic and ODP Sites 883, 884 and 887 in the North Pacific, and the Monte dei Corvi marine section in the Mediterranean unequivocally establish a dramatic, Late Miocene cold episode that persisted over approximately 2.5 Myr. In this work we establish the timing and synchronization of temperature decrease as well as rebound at orbital timescales. All sites were notably warmer than their modern annual average at ~9 Ma and exhibit sustained cooling beginning at ~8 Ma. SSTs rebound close to ~5.9 Ma at most locations suggesting that the cooling trend that began in the Late Miocene slowed down or even reversed in some locations in the Pliocene. The newly reconstructed SSTs highlight the role of cooling and an increase in equator to pole temperature gradients in terrestrial evolution at this pivotal time.

  13. Late Impacts and the Origins of the Atmospheres on the Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, S.; Stewart, S. T.; Lock, S. J.; Parai, R.; Tucker, J. M.

    2014-12-01

    Models for the origin of terrestrial atmospheres typically require an intricate sequence of events, including hydrodynamic escape, outgassing of mantle volatiles and late delivery. Here we discuss the origin of the atmospheres on the terrestrial planets in light of new ideas about the formation of the Moon, giant impact induced atmospheric loss and recent noble gas measurements. Our new measurements indicate that noble gases in the Earth's atmosphere cannot be derived from any combination of fractionation of a nebular-derived atmosphere followed by outgassing of deep or shallow mantle volatiles. While Ne in the mantle retains a nebular component, the present-day atmosphere has no memory of nebular gases. Rather, atmospheric noble gases have a close affinity to chondrites. On the other hand, Venus's atmosphere has 20 and 70 times higher abundance of 20Ne and 36Ar, respectively, and a 20Ne/22Ne ratio closer to the solar value than Earth's atmosphere. While the present atmosphere of Mars is significantly fractionated in the lighter noble gases due to long term atmospheric escape, the Kr isotopic ratios in Martian atmosphere are identical to solar. Thus, while Earth's atmosphere has no memory of accretion of nebular gases, atmospheres on both Venus and Mars preserve at least a component of nebular gases. To explain the above observations, we propose that a common set of processes operated on the terrestrial planets, and that their subsequent evolutionary divergence is simply explained by planetary size and the stochastic nature of giant impacts. We present geochemical observations and simulations of giant impacts to show that most of Earth's mantle was degassed and the outgassed volatiles were largely lost during the final sequence of giant impacts onto Earth. Earth's noble gases were therefore dominantly derived from late-accreting planetesimals. In contrast, Venus did not suffer substantial atmospheric loss by a late giant impact and retains a higher abundance of

  14. Late Miocene Global Ocean Cooling Linked to Terrestrial Aridification and Evolutionary Events

    NASA Astrophysics Data System (ADS)

    Herbert, T.; Lawrence, K. T.; Tzanova, A.; Kelly, C. S.; Peterson, L.

    2015-12-01

    The path of global temperatures between the permanent establishment of the East Antarctic ice sheet at ~13.9 Ma and the onset of cyclical northern hemisphere glaciation at circa 2.7 Ma is poorly known. Enormous changes to terrestrial environments and ecosystems occurred approximately halfway between these polar glaciation milestones. What is perplexing is that this environmental upheaval on land occurred without any substantial evidence for late Miocene temperature change. Our single best marine index of the global climate state, the marine oxygen isotope record derived from benthic foraminifera is singularly devoid of a strong trend that would suggest notable climatic change during this time period. We present a globally distributed data set of estimated marine sea surface temperatures (SST) for the past 12 Ma reconstructed via the alkenone unsaturation method. Our reconstruction reveals what may be the strongest directional cooling of the Neogene, which occurred broadly synchronously in both hemispheres and culminated with ocean temperatures dipping to values close to the present between ~7 and 5.8 Ma before rebounding to warmer conditions in the Pliocene. The cold interval from circa 7-5.8 Ma that we reconstruct coincides very closely in time with previously enigmatic evidence of late Miocene glaciations of southeast Greenland, southeastern Alaska, and South America, with pulses of ice rafted detritus off Wilkes Land and Adelie Land and, perhaps the formation of an ice sheet on West Antarctica. A large scale forcing mechanism, such as a previously hypothesized decline in atmospheric CO2 levels from 8-6 Ma [T.E. Cerling and colleagues] seems required to coordinate the increase in late Miocene Equator-Pole temperature gradients with evidence for a contemporaneous increase in aridity on land, restructuring of terrestrial plant and animal communities, and a pronounced shift in the marine carbon cycle.

  15. Reconstructing Climate Change Since The Late Glacial At Amsterdamøya, NW Svalbard (80°N), Based On Lake Sediments From Lake Hakluytvatnet

    NASA Astrophysics Data System (ADS)

    Gjerde, Marthe; Bakke, Jostein; D'Andrea, William J.; Balascio, Nicholas L.; Hormes, Anne; Bradley, Raymond S.

    2015-04-01

    order to constrain the different sediment contributions to the lake infill at different times throughout the Late Glacial and the Holocene. The investigated sedimentary archive has recorded the last ~ 13,000 years of climate change, and is the first terrestrial record going back to the Late Glacial at this site. According to older studies, the island of Amsterdamøya remained ice-free during the LGM. Our novel findings show that a glacier was present at the study site during the OD/YD. Our work also contributes with new data on the sea-level history for NW Svalbard based on geochemical indices from the lake sediments, results from the geomorphic mapping as well as from d13C results. Furthermore, the robust age chronology is of importance for high-Arctic studies as it can be used as basis for subsequent chronological work at NW Svalbard.

  16. Late Wisconsin and early holocene glacial history, inner Ross Embayment, Antarctica

    NASA Technical Reports Server (NTRS)

    Denton, George H.; Bockheim, James G.; Wilson, Scott C.; Stuiver, Minze

    1991-01-01

    Lateral drift sheets of outlet glaciers that pass through the Transantarctic Mountains constrain past changes of the huge Ross ice drainage system of the Antarctic Ice Sheet. Drift stratigraphy suggests correlation of Reedy III (Reedy Glacier), Beardmore, Britannia (Hatherton/Darwin Glaciers), Ross Sea (McMurdo Sound), and younger (Terra Nova Bay) drifts; radiocarbon dates place the outer limits of Ross Sea drift in late Wisconsin time at 24,000 to 13,000 yr B.P. Outlet glacier profiles from these drifts constrain late Wisconsin ice sheet surface elevations. Within these constraint, two extreme late Wisconsin reconstructions are given of the Ross ice drainage system. Both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner Ross Embayment. However, in the central Ross Embayment, one reconstruction shows floating shelf ice, where as the other shows a grounded ice sheet. Massive late Wisconsin/Holocene recession of grounded ice from the western Ross Embayment, which was underway at 13,040 yr B.P. and completed by 6600 to 6020 yr B.P., was accompanied by little change in plateau ice levels inland of the Transantarctic Mountains.

  17. Late Wisconsin and early holocene glacial history, inner Ross Embayment, Antarctica

    NASA Astrophysics Data System (ADS)

    Denton, George H.; Bockheim, James G.; Wilson, Scott C.; Stuiver, Minze

    1991-05-01

    Lateral drift sheets of outlet glaciers that pass through the Transantarctic Mountains constrain past changes of the huge Ross ice drainage system of the Antarctic Ice Sheet. Drift stratigraphy suggests correlation of Reedy III (Reedy Glacier), Beardmore, Britannia (Hatherton/Darwin Glaciers), Ross Sea (McMurdo Sound), and younger (Terra Nova Bay) drifts; radiocarbon dates place the outer limits of Ross Sea drift in late Wisconsin time at 24,000 to 13,000 yr B.P. Outlet glacier profiles from these drifts constrain late Wisconsin ice sheet surface elevations. Within these constraint, two extreme late Wisconsin reconstructions are given of the Ross ice drainage system. Both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner Ross Embayment. However, in the central Ross Embayment, one reconstruction shows floating shelf ice, where as the other shows a grounded ice sheet. Massive late Wisconsin/Holocene recession of grounded ice from the western Ross Embayment, which was underway at 13,040 yr B.P. and completed by 6600 to 6020 yr B.P., was accompanied by little change in plateau ice levels inland of the Transantarctic Mountains.

  18. High-Resolution Geochemical and Paleoecological Records of Climate Change Since the Late Glacial at Lake Tanganyika, East Africa

    NASA Astrophysics Data System (ADS)

    Alin, S. R.; Cohen, A. S.

    2002-12-01

    We used high-resolution geochemical and paleoecological records from shallow-water sediment cores to refine previous descriptions of climatic conditions at Lake Tanganyika, East Africa, for the period from the Late Glacial to the present. Radiocarbon and 210Pb dating were used to establish chronologies for the cores. Sedimentological changes indicate that lake level has risen approximately 50-70 m since the Late Glacial. A depositional hiatus occurred between 6.4 and 11.4 ka BP (all dates in calendar years) in several of the shallow-water cores. Elemental abundance (%C, %N) and stable isotopic (δ15N, δ13C) data for one core suggest that substantial changes in primary productivity and nutrient recycling regimes have occurred since 6.4 ka BP. Carbonate and ostracode crustacean preservation were low and nil, respectively, prior to 2.4 ka BP. Generally, these data support previous interpretations of regional paleoclimate and lake conditions, with wet and warm conditions during the interval from 6.4 to 4.0 ka, and increasingly arid conditions since 2.4 ka. However, for the interval from 4.0 to 2.4 ka, paleoenvironmental indicators (δ15N, reduced carbonate and ostracode preservation) suggest that the central part of Lake Tanganyika was stably stratified at a shallower depth than present as a result of diminished southerly trade winds. After 2.4 ka BP, sedimentary carbonate concentrations increase, and δ13C values become enriched, suggesting that lacustrine productivity increased with the resumption of deeper wind-driven mixing, lasting until 1 ka BP. For post-2.4 ka samples, species abundance data for ostracodes were used to generate an ostracode water depth index (OWDI). OWDI indicated that severe drought conditions were persistent or recurred at Lake Tanganyika between 1550 and 1850 A.D. Droughts resulted in marked lowstands at Lake Tanganyika at 1580+/-15 A.D., 1730+/-35 A.D., and 1800+/-30 A.D. These data contribute new information on the timing of Little Ice Age

  19. New observations on lower than present relative sea-levels since the late Glacial from the British Isles

    NASA Astrophysics Data System (ADS)

    Cooper, J. Andrew; Long, Antony; Plets, Ruth; Callard, Louise; Quinn, Rory; Kelley, Joseph; Belknap, Daniel; Jackson, Derek; Edwards, Robin; Long, David; Monteys, Xavier; Milne, Glenn

    2014-05-01

    Relative sea-level change around the British Isles shows marked spatial variability in response to ice sheet history and crustal response to loading/offloading. The area thus offers an ideal natural laboratory for the investigation of such interactions and has formed the basis of several models of earth-ice-ocean interaction. RSL data with which to test models is, however, largely restricted to the late Holocene. The paucity of data from much lower than present sea levels is reflected in large (tens of metres) discrepancies between different modelled RSL curves for the late-glacial to early Holocene period. WE report on two years intensive fieldwork on six sites around the Irish Sea (at Bantry Bay, Waterford, Cardigan Bay, offshore Louth, Isle of Man, and Belfast Lough) on a north-south gradient. These were selected to target lower than present sea-level indicators from ice-proximal to ice-distal locations. The initial investigation using multibeam bathymetry and shallow seismic profiling identified wave-cut platforms and associated cliffs in bedrock, planation surfaces on drumlins, incised valley termini and the seaward limit of the transgressive unconformity. Subsequent coring of seabed targets yielded over 450m of core from 150 sites. Palaeoenvironmental interpretation and radiocarbon dating of material has yielded new observational data on lower than present sea levels that challenge existing model simulations.

  20. Delayed CO2 emissions from mid-ocean ridge volcanism as a possible cause of late-Pleistocene glacial cycles

    NASA Astrophysics Data System (ADS)

    Huybers, Peter; Langmuir, Charles H.

    2017-01-01

    The coupled 100,000 year variations in ice volume, temperature, and atmospheric CO2 during the late Pleistocene are generally considered to arise from a combination of orbital forcing, ice dynamics, and ocean circulation. Also previously argued is that changes in glaciation influence atmospheric CO2 concentrations through modifying subaerial volcanic eruptions and CO2 emissions. Building on recent evidence that ocean ridge volcanism responds to changes in sea level, here it is suggested that ocean ridges may play an important role in generating late-Pleistocene 100 ky glacial cycles. If all volcanic CO2 emissions responded immediately to changes in pressure, subaerial and ocean-ridge volcanic emissions anomalies would oppose one another. At ocean ridges, however, the egress of CO2 from the mantle is likely to be delayed by tens-of-thousands of years, or longer, owing to ascent time. A simple model involving temperature, ice, and CO2 is presented that oscillates at ∼100 ky time scales when incorporating a delayed CO2 contribution from ocean ridge volcanism, even if the feedback accounts for only a small fraction of total changes in CO2. Oscillations readily become phase-locked with insolation forcing associated with changes in Earth's orbit. Under certain parameterizations, a transition from ∼40 ky to larger ∼100 ky oscillations occurs during the middle Pleistocene in response to modulations in orbital forcing. This novel description of Pleistocene glaciation should be testable through ongoing advances in understanding the circulation of carbon through the solid earth.

  1. Late Glacial to Holocene evolution and sea-level history of Gulf of Gemlik, Sea of Marmara, Turkey

    NASA Astrophysics Data System (ADS)

    Sabuncu, Asen; Kadir Eriş, K.; Kaslilar, Ayse; Namık Çaǧatay, M.; Gasperini, Luca; Filikçi, Betül

    2016-04-01

    The Gulf of Gemlik is an E-W elongated trans-tensional basin with a maximum depth of 113 m, located on the middle strand of the North Anatolian Fault (NAF) in the south eastern part of the Sea of Marmara (SoM). While during the Holocene the sea level in the Gulf of Gemlik changed in tandem with the water level changes in the SoM, it may have been different in the late glacial when the Sea of Marmara was lacustrine. Beside the tectonic activity related to the NAFZ, eustatic sea level changes would have controlled the basin evolution and consequent sedimentary history during the different paleocanographic phases of the SoM. Considering the limited studies on the late glacial-Holocene stratigraph of the Gulf of Gemlik, this study aims to investigate the depositional units and their environments with respect to different allogenic and autogenic controls. For these purposes, we analyzed over 300 2 - 7 kHz bandwidth high-resolution gridded seismic sub-bottom CHIRP profiles together with 70 kHz high resolution multibeam bathymetry with backscatter data. Four seismic stratigraphic units were defined and correlated with chronstratigraphic units in five piston cores covering the last 15.8 ka BP according to radiocarbon ages (14C). The depth-scale accuracy of chronostratigraphic units in cores is of key importance for the precise calculation of sedimentation rates. Correlation between the seismic profiles and cores were made by matching Multi-Sensor Core-Logger (MSCL) data and seismic reflection coefficients and amplitudes for different stratigraphic units. The impedance data derived from the logger were used to generate a synthetic seismogram. We used an approach to display, estimate, and correct the depth-scale discrepancies due to oversampling affecting the upper part of sedimentary series during piston coring. The method is based on the resynchronization of synthetic seismograms computed from high-quality physical property logs to the corresponding CHIRP profiles. Each

  2. Timing of late Pleistocene glaciation in Mongolia: Surface exposure dating reveals a differentiated pattern of glacial forcing

    NASA Astrophysics Data System (ADS)

    Pötsch, Steffen; Rother, Henrik; Lorenz, Sebastian; Walther, Michael; Lehmkuhl, Frank

    2015-04-01

    of atmospheric circulation and its significance for controlling regional precipitation results in a more differentiated pattern of late Pleistocene glaciation in Mongolia than previously recognized. Compared to other glacial records from High Asia, the observed patterns of past glaciations in Mongolia show similar results (i.e. ice maxima during interstadial wet phases) compared to monsoon influenced regions in southern Central Asia and NE-Tibet, while major expansion during insolation minima (MIS-4 and MIS-2) are more in tune with glacier responses known from western Central Asia and Siberia.

  3. Autogenic incision and terrace formation resulting from abrupt late-glacial base-level fall, lower Chippewa River, Wisconsin, USA

    NASA Astrophysics Data System (ADS)

    Faulkner, Douglas J.; Larson, Phillip H.; Jol, Harry M.; Running, Garry L.; Loope, Henry M.; Goble, Ronald J.

    2016-08-01

    A paucity of research exists regarding the millennial-scale response of inland alluvial streams to abrupt base-level fall. Studies of modern systems indicate that, over short time scales, the response is a diffusion-like process of upstream-propagating incision. In contrast, evidence from the lower Chippewa River (LCR), located in the upper Midwest of the USA, suggests that autogenic controls operating over time scales of several millennia can overwhelm diffusion, resulting in incision that is prolonged and episodic. During the Last Glacial Maximum, the LCR drained the Chippewa Lobe of the Laurentide Ice Sheet to the glacial upper Mississippi River (UMR). As a meltwater stream, it aggraded and filled its valley with glacial outwash, as did its largest tributaries, which were also meltwater streams. Its nonglacial tributaries aggraded, too, filling their valleys with locally derived sediment. During deglaciation, the UMR incised at least twice, abruptly lowering the LCR's base level - ~ 15 m at 16 ka or earlier and an additional 40 m at ca. 13.4 ka. Each of these base-level falls initiated incision of the LCR, led by upstream migrating knickpoints. The propagation of incision has, however, been a lengthy process. The optically stimulated luminescence (OSL) ages of terrace alluvium indicate that, by 13.5 ka, incision had advanced up the LCR only 15 km, and by 9 ka, only 55 km. The process has also been episodic, resulting in the formation of fill-cut terraces (inferred from GPR surveys and exposures of terrace alluvium) that are younger and more numerous in the upstream direction. Autogenic increases in sediment load and autogenic bed armoring, the result of periodic tributary-stream rejuvenation and preferential winnowing of fines by the incising river, may have periodically caused knickpoint migration and incision to slow and possibly stop, allowing lateral erosion and floodplain formation to dominate. A decline in sediment flux from stabilizing incised tributary

  4. New insights on the late-stage history of glacial Lake Ojibway: implications for meltwater discharges of the last deglaciation

    NASA Astrophysics Data System (ADS)

    Roy, Martin; Veillette, Jean J.; Godbout, Pierre-Marc

    2016-04-01

    The decay of the Laurentide ice sheet is believed to be responsible for abrupt climate variations during the last deglaciation and early Holocene, notably through massive discharges of meltwater that had accumulated in large ice-dammed lakes such as Lake Agassiz and Lake Ojibway. Indeed, high-resolution North Atlantic marine records indicate that the ocean's circulation was affected by several outbursts of meltwater during the late deglacial interval. Yet, field evidence and geological data supporting multi-step drawdowns of Lake Agassiz-Ojibway are relatively limited, underlying important uncertainties in the late-stage history of these glacial lakes. Furthermore, physical evidence for the drainage of glacial lakes remains relatively rare in depositional records, giving rise to much debate on the location of outlets and discharge pathways, as well as on the climate impact of the attendant meltwater forcing. Recent investigations of geomorphological and sedimentary records in northern Ontario and Quebec (Canada) have revealed new insights on the late-stage evolution of Lake Ojibway. The number of Ojibway lake phases have so far remained poorly documented mainly because of the dominance of fine-grained glaciolacustrine sediments in the lake basin that prevented the formation of extensive sandy/bouldery strandlines. We thus developed an alternative approach based on the study of a complex sequence of relict terraces carved in the Ojibway clay plain. The elevation measurement of 154 raised wave-cut scarps provided evidence for four distinct shorelines, three of which projecting well below the main outlet that controlled the elevation of the lake during the deglaciation. The elevation, uplift gradients, and areal extent of these shorelines indicate that these low-elevation lake levels formed during the late stages of the deglaciation, following abrupt drawdowns of the lake's surface. Insights on the origin of these late-stage phases are provided from sediment sequences

  5. Arctic greenhouse-gas storage and release modulated by late-glacial ice sheet fluctuations

    NASA Astrophysics Data System (ADS)

    Portnov, Alexey; Mienert, Jurgen; Vadakkepuliyambatta, Sunil; Patton, Henry; Andreassen, Karin; Winsborrow, Monica; Knies, Jochen; Hubbard, Alun I.

    2016-04-01

    The subglacial footprint of the Barents Sea Ice sheet which advanced across northern Eurasia from 26 to 22 ka BP had a major impact on the underlying gas hydrate stability zone (GHSZ) leading to storage of methane and other hydrocarbons. With the onset of deglaciation, these hydrocarbon rich hydrates dissociated, releasing potent greenhouse gas into the ocean and possibly atmosphere over a period of thousands of years. We present a wide-range of observational data acquired from offshore western Svalbard and the Barents Sea to robustly constrain a coupled model of the subglacial evolution of gas hydrate reservoirs during and after the Last Glacial Maximum (LGM). Our results indicate that even under minimum ice thickness reconstructions, an extensive, ~500-meter thick GHSZ existed beneath the ice sheet in our study area offshore of western Svalbard (Portnov et al., 2016). An offshore corridor of methane release did though also persist throughout maximum ice conditions on the upper continental margin. Throughout the LGM a marine ice sheet directly comparable to those of Greenland and Antarctica today inundated the continental margin offshore of western Svalbard and the vast shelf areas of the Barents Sea. However, with climatic amelioration the Barents Sea ice sheet experienced a 4ka period of dynamic retreat with concurrent flooding of the shelf by rising sea levels, which provided a high magnitude perturbation to the substrate pressure and temperature domains. By analogy, the future response of Polar ice sheets is an emerging concern as their ongoing thinning and retreat will likewise perturb the present day subglacial GHSZ leading to potential widespread gas hydrate destabilisation and release. Portnov, Alexey, et al. "Ice-sheet-driven methane storage and release in the Arctic", Nature Comm. DOI: 10.1038/ncomms10314. (2016).

  6. Late Post-glacial Sea Level Rise and Its Effects On Human Activity In Asia

    NASA Astrophysics Data System (ADS)

    Oppenheimer, S. J.

    Three rapid post-glacial sea-level rises flooded coastlines with large continental shelves. The last of these, shortly before the interglacial optimum c.7,500BP, not only changed coastal Neolithic societies, but may also have stimulated maritime skills. Two Asian examples explore these aspects. First, during the Mid-Holocene, the Arabian Gulf transgressed as far inland as Ur probably laying down Woolley's famous Ur Flood silt layer between 7,000-5,500 BP. Stratigraphy and dating suggests the phase of rapid sea level rise immediately preceded the start of the 'Ubaid pottery period. Red-slipped Uruk pottery and copper items then appear from about 6,000BP, but above Woolley's silt layer. The Sumerian King Lists also record a major upheaval and dynastic change after 'the Flood'. Second, the final flooding of the Sunda shelf in Southeast Asia was followed by a maritime extension of human occupation from Northern Melanesia south into the Solomon Islands 6,000 years ago. Simultaneously, further west on the north coast of New Guinea, new archaeological assemblages ap- pear beneath a silt layer left by a pro-grading 6,000 year-old inland sea. The presence of arboriculture items such as betel nuts and the contemporary arrival of dogs and pigs in the same region suggests intrusion from Southeast Asia. This supports Solheim's suggestion that rapid sea-level rise on the eastern edge of the Sunda Shelf stimulated maritime skills and invention in Southeast Asia. This may have provided the initial stimulus to the first maritime expansion that was later to colonise the whole Pacific.

  7. Water mass evolution of the Greenland Sea since late glacial times

    NASA Astrophysics Data System (ADS)

    Telesiński, M. M.; Spielhagen, R. F.; Bauch, H. A.

    2014-01-01

    Four sediment cores from the central and northern Greenland Sea basin, a crucial area for the renewal of North Atlantic deep water, were analyzed for planktic foraminiferal fauna, planktic and benthic stable oxygen and carbon isotopes as well as ice-rafted debris to reconstruct the environmental variability in the last 23 kyr. During the Last Glacial Maximum, the Greenland Sea was dominated by cold and sea-ice bearing surface water masses. Meltwater discharges from the surrounding ice sheets affected the area during the deglaciation, influencing the water mass circulation. During the Younger Dryas interval the last major freshwater event occurred in the region. The onset of the Holocene interglacial was marked by an increase in the advection of Atlantic Water and a rise in sea surface temperatures (SST). Although the thermal maximum was not reached simultaneously across the basin, benthic isotope data indicate that the rate of overturning circulation reached a maximum in the central Greenland Sea around 7 ka. After 6-5 ka a SST cooling and increasing sea-ice cover is noted. Conditions during this so-called "Neoglacial" cooling, however, changed after 3 ka, probably due to enhanced sea-ice expansion, which limited the deep convection. As a result, a well stratified upper water column amplified the warming of the subsurface waters in the central Greenland Sea, which were fed by increased inflow of Atlantic Water from the eastern Nordic Seas. Our data reveal that the Holocene oceanographic conditions in the Greenland Sea did not develop uniformly. These variations were a response to a complex interplay between the Atlantic and Polar water masses, the rate of sea-ice formation and melting and its effect on vertical convection intensity during times of Northern Hemisphere insolation changes.

  8. In-situ cosmogenic 10 Be production rate at Lago Argentino, Patagonia: Implications for late-glacial climate chronology

    NASA Astrophysics Data System (ADS)

    Kaplan, Michael R.; Strelin, Jorge A.; Schaefer, Joerg M.; Denton, George H.; Finkel, Robert C.; Schwartz, Roseanne; Putnam, Aaron E.; Vandergoes, Marcus J.; Goehring, Brent M.; Travis, Scott G.

    2011-09-01

    for late-glacial moraine systems. Both chronologies then indicate that outlet glaciers of the Southern Patagonian Icefield achieved a late-glacial maximum in the western reaches of Lago Argentino at 13,000 cal. yr BP at the end of the Antarctic Cold Reversal (14,500-12,900 cal. yr BP). Outlet glaciers subsequently receded to near present-day ice margins during the Younger Dryas stadial (12,900-11,700 cal. yr BP). This general retreat was interrupted about 12,200 cal. yr BP when Upsala Glacier constructed an interlobate complex of moraine ridges on Herminita Peninsula. Mountain glaciers in Patagonia and New Zealand, on both sides of the South Pacific Ocean, exhibited a coherent pattern of late-glacial ice-margin fluctuations.

  9. A Late-Glacial sedimentary sequence at KIlkeel, Northern Ireland: implications for the glaciation of the Irish Sea Basin

    NASA Astrophysics Data System (ADS)

    Merritt, Jon; Roberson, Sam; Cooper, Mark

    2017-04-01

    This paper re-evaluates the nature and timing of a Late-Glacial ice sheet re-advance in the north western sector of the Irish Sea basin. The sedimentary archive in the region records the collapse of the Irish Sea Ice Stream, a major outlet glacier of the British-Irish Ice Sheet. The region documents the interplay between southerly flowing Scottish ice, ice flowing southeast from Lough Neagh and locally sourced Mournes ice. We present the results of sedimentological analysis of a glacigenic sequence exposed in a modern cliff section 3 km long between Derryoge and Kilkeel, Co. Down, Northern Ireland. The interaction between an advancing ice-sheet outlet lobe and rapidly changing sea levels are examined using facies analysis and micromorphology. The section is composed of four lithofacies associations (LAs). These are, from the base, a laminated, fossiliferous and deformed silt (LA1) at least 4.5 m thick that contains lenses of diamicton and discontinuous rafts of sandy gravel. Marine shells form the axis of a fold hinge, part of a lightly tectonised channel fill within the raft. LA1 is overlain by a sandy diamict (LA2) up to 14 m thick containing mainly local clasts with some of northern provenance. Within LA2 are wide channel structures infilled by laminated clayey silts (LA2b). These form deposits up to 14 m thick and contain small-scale folds, discrete shear zones and ball-and-pillow structures. LA2b forms a lithofacies association with LA2, consisting of a lower subfacies of sheared and deformed silts, overlain by sandy diamicton, capped by a striated boulder pavement. These are interpreted to represent retreat/advance cycles of a marine terminating ice margin. Up to five such cycles are identified. LA2 is widely punctuated by fissures and conduits infilled by loose sands and gravels. These are inferred to be emplaced by subglacial meltwater during the final stages of ice sheet advance. Covering both LA2 and LA2b, LA3 is a unit of glaciofluvial outwash, composed

  10. Integrating terrestrial and marine archives of Late Wisconsinan ice stream dynamics in the Canadian Arctic Archipelago

    NASA Astrophysics Data System (ADS)

    Lakeman, Thomas; Blasco, Steve; MacLean, Brian; Bennett, Robbie; England, John; Hughes Clarke, John; Covill, Bob; Patton, Eric

    2014-05-01

    During Late Wisconsinan glaciation the northern Laurentide and Innuitian ice sheets converged over the Canadian Arctic Archipelago. This ice sheet complex included several major ice streams, which constituted important dynamical components. Discharging into the Beaufort Sea and Baffin Bay, these ice streams were a primary control on ice sheet mass balance and ice age sedimentation on adjacent continental margins, including the Arctic Ocean basin. This study presents a new compilation of multibeam echosounder data, sub-bottom profiler data, radiocarbon ages, and marine sediment cores acquired primarily during regional surveys with the CCGS Amundsen. These data characterize the nature and thickness of seafloor sediments in Parry Channel (and many of its connecting channels) and Amundsen Gulf. When combined with the results of terrestrial geomorphological mapping of the adjacent islands, this dataset constrains the maximum extent, chronology, and behaviour of former ice streams in M'Clure Strait, Viscount Melville Sound, Lancaster Sound, and Amundsen Gulf. Importantly, these data highlight complex patterns of past ice stream flow during regional deglaciation. These results contribute to a better understanding of the causal mechanisms that occasioned retreat of the terrestrial and marine sectors of the Laurentide and Innuitian ice sheets. As well, this study helps to quantify past iceberg fluxes to the Arctic Ocean, which has implications for assessing past climate, and the origin of ice-rafted sediment and deep iceberg scours in the Arctic Ocean basin.

  11. History of late glacial runoff along the southwestern margin of the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Kehew, Alan E.; Teller, James T.

    The routing of runoff from the retreating Laurentide Ice Sheet was controlled by a combination of ice-marginal position and topography; isostatic depression also played an important role in the evolution of the ice-marginal landscape. A major redirection of drainage occurred after ice retreated north of the Missouri Escarpment about 12 ka BP. Runoff that had previously flowed south to the Missouri River could then be routed eastward to Lake Agassiz, which in turn drained to the upper Mississippi River valley. Changes in drainage routing in the region west of glacial Lake Agassiz typically were abrupt, as new and lower paths along the retreating ice margin became available. Each new basin was larger than its predecessor and its headwaters extended farther west. Four distinct, sequential phases of ice-marginal drainage occurred between 12 and 10.7 ka BP: the James, Sheyenne, Souris-Pembina and Qu'Appelle-Assiniboine. Starting with the Qu'Appelle-Assiniboine phase about 11.2 ka BP, Lake Agassiz collected runoff from as far west as the Rocky Mountains. By about 10.7 ka BP, ice had retreated north of the lower reaches of the Saskatchewan River, allowing meltwater to by-pass the Qu'Appelle-Assiniboine basin. At about the same time, the eastern outlets of Lake Agassiz opened, initiating drainage to the North Atlantic Ocean from this vast region. Drainage routes evolved by a common sequence of events, beginning with the impoundment of proglacial lakes along the ice margin. Most of these lakes drained catastrophically, resulting in the formation of spillways with distincitve geomorphic features that include broad, scoured and streamlined subupland channels along with subsequently incised narrow, deep inner channels. Characteristic deposits of these outbursts include boulder mantles on subupland channel floors, boulder-gravel bars within the inner channels, and large, primarily subaqueous fans in lake basins that received the flood bursts. These outbursts progressed from

  12. Multiproxy reconstruction of rapid paleooceanographic changes in the SW Barents Sea during the Late Glacial- Early Holocene transition

    NASA Astrophysics Data System (ADS)

    Soerensen, S. A.; Husum, K.; Hald, M.; Knies, J.

    2009-12-01

    The main objective of this study is to examine the Late Glacial - Early Holocene variability of the North Atlantic Current with focus on the zonal component of this meridional transport during the transition from glacial to interglacial conditions. The investigated sediment core is from 409 m water depth, SW Barents Sea, and the site is today influenced by Atlantic Water from the zonal branch of North Atlantic Current, the North Cape Current, and fresher water masses from the Norwegian Coastal Current. Both the North Atlantic Current and the North Cape Current are important components in the meridional overturning circulation system of the North Atlantic. Eight AMS 14C dates show that the core covers the last 20.000 cal yr BP with a resolution of centennial scale during Late Glacial - Early Holocene. The core has been analyzed with regard to planktic foraminiferal assemblages using the larger than 100 μm size fraction, number of IRD, and planktic and benthic δ13C and δ18O isotopes. Furthermore, a range of physical and chemical analyses have been carried out on the bulk sediment samples; δ13C, MSCL, grain size distributions, TOC and CaCO3. The results show that between 13.700-12.700 cal yr BP (Allerød) planktic foraminifera are found indicating seasonally open water conditions. The fauna is dominated by the species Neogloboquadrina pachyderma (sin) reflecting very cold surface water conditions while high flux of planktic foraminifera and increased values of TOC and CaCO3 generally indicate enhanced primary production. High amounts of IRD indicate transportation by sea ice or icebergs while relatively large difference between benthic and planktic δ18O isotope values signals stratified water masses. High production and stratified water masses are probably caused by a combination of a close position to the sea ice edge and an increased subsurface influx of the Atlantic water mass. The time interval between ca. 12.700-11.000 cal yr BP (Younger Dryas) is a low

  13. Low post-glacial rebound rates in the Weddell Sea due to Late Holocene ice-sheet readvance

    NASA Astrophysics Data System (ADS)

    Bradley, Sarah L.; Hindmarsh, Richard C. A.; Whitehouse, Pippa; Bentley, Michael J.; King, Matt

    2014-05-01

    The Holocene deglaciation of West Antarctica resulted in widespread ice surface lowering. While many ice-sheet reconstructions generally assume a monotone Holocene retreat for the West Antarctica Ice sheet (WAIS) [Ivins et al., 2013; Peltier, 2004; Whitehouse et al., 2012], an increasing number of glaciological observations infer it is readvancing, following retreat behind the present-day margin[Siegert et al., 2013]. We will show that a readvance in the Weddell Sea region can reconcile two outstanding problems: (i) the present-day widespread occurrence of seemingly stable ice-streams grounded on beds that deepen inland in apparent contradiction to theory [Schoof, 2007]; and (ii) the inability of models of Glacial Isostatic Adjustment (GIA) to match present-day uplift rates [Whitehouse et al., 2012]. Combining a suite of ice loading histories that include a readvance with a model of GIA provides significant improvements to predictions of present-day uplift rates, and we are able to reproduce previously unexplained observations of subsidence in the southern sector of the Weddell Sea. We hypothesize that retreat behind present grounding lines occurred when the bed was lower, and isostatic recovery led to shallowing, ice sheet re-grounding and readvance. We will conclude that some sections of the current WAIS grounding line that are theoretically unstable, may be advancing and that the volume change of the WAIS may have been more complex in the Late Holocene than previously posited. This revised Holocene ice-loading history would have important implications for the GIA correction applied to Gravity Recovery and Climate Experiment (GRACE) data, likely resulting in a reduction in the GIA correction and a smaller estimate of present-day ice mass loss within the Weddell Sea region of the WAIS. Ivins, E. R., T. S. James, J. Wahr, E. J. O. Schrama, F. W. Landerer, and K. M. Simon (2013), Antarctic contribution to sea level rise observed by GRACE with improved GIA correction

  14. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-Glacial-Holocene Transition

    NASA Technical Reports Server (NTRS)

    Han, Y. M.; Peteet, D. M.; Arimoto, R.; Cao, J. J.; An, Z. S.; Sritrairat, S.; Yan, B. Z.

    2016-01-01

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.

  15. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition.

    PubMed

    Han, Y M; Peteet, D M; Arimoto, R; Cao, J J; An, Z S; Sritrairat, S; Yan, B Z

    2016-02-10

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.

  16. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition

    PubMed Central

    Han, Y.M.; Peteet, D.M.; Arimoto, R.; Cao, J.J.; An, Z.S.; Sritrairat, S.; Yan, B.Z.

    2016-01-01

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role. PMID:26860820

  17. Climate and Fuel Controls on North American Paleofires: Smoldering to Flaming in the Late-glacial-Holocene Transition

    NASA Astrophysics Data System (ADS)

    Han, Y. M.; Peteet, D. M.; Arimoto, R.; Cao, J. J.; An, Z. S.; Sritrairat, S.; Yan, B. Z.

    2016-02-01

    Smoldering and flaming fires, which emit different proportions of organic (OC) and black carbon (BC, in the form of char and soot), have long been recognized in modern wildfire observations but never in a paleo-record, and little is known about their interactions with climate. Here we show that in the late glacial-early Holocene transition period, when the climate was moist, relatively high quantities of char were deposited in Linsley Pond, Connecticut, USA while soot was more abundant during the warmer and drier early Holocene interval. The highest soot mass accumulation rates (MARs) occurred at the beginning of the Holocene as fuel availability increased through the climatic transition when boreal forests were locally extirpated. These variations with time are related to the different formation pathways of char and soot, which are governed by combustion efficiency. This study provides an approach for differentiating smoldering from flaming combustion in paleo-wildfire reconstructions. Our results suggest that climate and fuel loads control the occurrence of different wildfire types and precipitation may play a key role.

  18. Upper Ocean Variability in the Indo-Pacific Warm Pool during the Late Holocene, Early Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xu, J.; Kuhnt, W.; Holbourn, A. E.; Andersen, N.

    2009-12-01

    We analyzed oxygen isotopes and Mg/Ca ratios in the surface dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to improve understanding of upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka) and the late Holocene (0-2 ka). Our records from twenty-four stations in the South China Sea, Timor Sea, Indonesian seas and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. Warm surface waters (>28 Celsius degree) spread over the entire region during the early Holocene, indicating substantial expansion of the IPWP. However in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow. Increased precipitation over the South China Sea appears related to an intensified summer monsoon and northward displacement of the Intertropical Convergence Zone. Increased freshwater export from the South China Sea through the Java Sea also contributed to a change in the vertical structure of the Indonesian Throughflow from surface- to thermocline-dominated flow and a freshening of Timor Sea waters during the early Holocene.

  19. Late Glacial-Holocene ecostratigraphy of the south-eastern Aegean Sea, based on plankton and pollen assemblages

    NASA Astrophysics Data System (ADS)

    Triantaphyllou, M. V.; Antonarakou, A.; Kouli, K.; Dimiza, M.; Kontakiotis, G.; Papanikolaou, M. D.; Ziveri, P.; Mortyn, P. G.; Lianou, V.; Lykousis, V.; Dermitzakis, M. D.

    2009-08-01

    Quantitative analyses of coccolithophores, planktonic foraminifers, dinoflagellate cysts and pollen assemblages were carried out on shallow (NS-14) and deeper (NS-40) sediment cores from the south-eastern Aegean Sea. Nine coccolithophore (ACE 1-9) and nine planktonic foraminifer (APFE 1-9) ecozones, correlated with dinoflagellate cyst evidence, have been defined for the last ~14.5 cal. ka. Additionally, eight pollen assemblage zones (PAZ 1-8) have been recognised and correlated with the plankton ecozones. Although generally consistent with existing schemes for the central and eastern Mediterranean, the established high-resolution ecostratigraphy has led to an expanded palaeoecological reconstruction of the Late Glacial-Holocene archive in the south-eastern Aegean Sea, defining two warm and humid phases at 9.3-8.6 and 7.6-6.4 cal. ka b.p., associated with the deposition of the early Holocene sapropel S1, and a third one between 5.2 and 4.2 cal. ka b.p. The high sedimentation rates which characterise the study area enabled the detection of even minor and brief climatic events in the Aegean Sea during S1 deposition times. [InlineMediaObject not available: see fulltext.

  20. Late-glacial and Holocene record of vegetation and climate from Cynthia Bay, Lake St Clair, Tasmania

    NASA Astrophysics Data System (ADS)

    Hopf, F. V. L.; Colhoun, E. A.; Barton, C. E.

    2000-10-01

    A Late-glacial-Holocene pollen record was obtained from a 3.96 m sediment core taken from Lake St Clair, central Tasmania. Modern vegetation and pollen analyses formed the basis for interpretation of the vegetation and climate history. Following deglaciation and before ca. 18450 yr BP Podocarpus lawrencei coniferous heath and Astelia-Plantago wet alpine herbfield became established at Lake St Clair. A distinct Poaceae-Plantago peak occurs between 18450 and 11210 yr BP and a mean annual temperature depression from ca. 6.2°C to 3°C below present is inferred for this period. The marked reduction in Podocarpus and strong increase of Poaceae suggests reduced precipitation levels during the period of widespread deglaciation (ca. 18.5-11 kyr BP). The local Late Pleistocene-Holocene non-forest to forest biostratigraphical boundary is dated at 11.2 kyr BP. It is characterised by expansion of the subalpine taxa Athrotaxis/Diselma with Nothofagus gunnii, and by the establishment of Nothofagus cunninghamii with Eucalyptus spp. A Phyllocladus bulge prior to the expansion of Nothofagus cunninghamii, reported at other Tasmanian sites, is not present at Lake St Clair. Nothofagus cunninghamii cool temperate rainforest peaked at 7800 yr BP, probably under wetter climatic conditions than present. The maximum development of rainforest in the early-middle Holocene may indicate that the temperature was slightly warmer than present, but the evidence is not definitive. The expansion of Eucalyptus spp. and Poaceae after 6000 yr BP may be partly a disclimax effect as a result of Aboriginal burning, but appears also to reflect reduced precipitation. The changes in vegetation and inferred climate can be explained by major changes in synoptic patterns of southern Australia and the adjacent southwest Pacific.

  1. Provenance of Greenland Ice Sheet icebergs constrained by Ar-Ar radioisotope data from late glacial-early Holocene records

    NASA Astrophysics Data System (ADS)

    Knutz, P. C.; Storey, M.; Kuijpers, A.

    2009-12-01

    Radiogenic Ar-Ar dating of hornblende has been used to constrain the sources of ice-rafted detritus on the southwest Greenland margin and central Davis Strait. Single hornblende grains (total of 248) were picked from sand-size fractions of two marine cores, DA04-31P and TTR462G, covering the early Holocene to late glacial interval including Heinrich events (HE) 1-3. Paleoceanographic analyses of DA04-31P have indicated that the last deglaciation of the southern Greenland Ice Sheet occurred in multiple steps during the early deglacial/HE1, Allerød and early Holocene intervals (Knutz et al., in review). Each of these collapse stages were preceded by upper ocean warming related to enhanced Irminger Current activity. Pre-HE1, Allerød and Holocene hornblende samples show a bimodal signature of late Archean (2.5-3.0 Ga) and early Proterozoic (1.6-2.2 Ga) ages consistent with southern Greenland bedrock sources. In contrast hornblende grains from detrital carbonate HE layers and within the Younger Dryas interval show a dominant early Proterozoic spectrum that is similar to results obtained from the central North Atlantic IRD belt. The early Proterozoic age of Younger Dryas samples from the Davis Strait site and the high amounts of basalt in this core, presumably derived from the Disko-Nussuaq province, suggests that icebergs carrying Archean material from southern Greenland did not enter the Baffin Bay or at least not for this specific time interval. The conclusion of our study is that the Greenland Ice Sheet appears to have been a much larger contributor to non-Heinrich IRD in the North Atlantic than thought previously. P. C. Knutz, H. Ebbesen, S. Christiansen, M.-A. Sicre and A. Kuijpers. Multiple deglaciation steps of the southern Greenland Ice Sheet driven by vigorous Irminger Current: Significance for the Younger Dryas cooling. Submitted to Quaternary Science Reviews.

  2. Delayed CO2 emissions from mid-ocean ridge volcanism as a possible cause of late-Pleistocene glacial cycles

    NASA Astrophysics Data System (ADS)

    Huybers, P. J.

    2016-12-01

    The coupled variations in ice volume, temperature, and atmospheric CO2 during the late Pleistocene are most often represented as involving some combination of orbital forcing, ice dynamics, and ocean circulation. Also previously argued is that changes in glaciation influence atmospheric CO2 concentrations through modifying subaerial volcanic eruptions and CO2 emissions. Building on recent evidence that ocean ridge volcanism responds to changes in sea level, a conceptual model is presented wherein ocean ridges play an important role in generating late-Pleistocene 100 ky glacial cycles on account of an inherent delay in their feedback response. If all volcanic CO2 emissions responded immediately to changes in pressure, subaerial and ocean-ridge volcanic emissions anomalies would merely oppose one another. At ocean ridges, however, the egress of CO2 from the mantle is delayed by tens-of-thousands of years, or longer, owing to ascent time. The simple model involves temperature, ice, and CO2 and is shown to oscillates at 100 ky time scales when incorporating a delayed CO2 contribution from ocean ridge volcanism, even if the feedback accounts for only a small fraction of total changes in CO2. Features of the model that are consistent with observations include that it readily become phase-locked with insolation forcing associated with changes in Earth's orbit, and that temperature variations lead changes in CO2 by several centuries during deglaciation. Under certain parameterizations, a transition from 41 ky to larger 100 ky oscillations occurs during the middle Pleistocene in response to modulations in orbital forcing. This novel description of Pleistocene glaciation should be testable through ongoing advances in understanding the circulation of carbon through the solid earth.

  3. Late-Glacial to Holocene Hydroclimatic Change in the Mojave Desert: Silver Lake, CA

    NASA Astrophysics Data System (ADS)

    Kirby, M. E.; Knell, E. J.; Anderson, W. T., Jr.; Lachniet, M. S.; Eeg, H.; Lucero, R.; Murrieta, R.; Arevalo, A.; Silveira, E.; Hiner, C.; Palermo, J. A.

    2014-12-01

    Silver Lake is the modern terminal playa of the Mojave River. As a result, it is well located to record both influences from the winter precipitation dominated San Bernardino Mountains - the source of the Mojave River - as well as the late-summer to early-fall North American monsoon. Here, we present various physical and geochemical data from a new 8.2 m sediment core taken from Silver Lake, CA that spans modern through 14.8 kcal yrs BP. Age control is based on six bulk organic C radiocarbon dates processed with Bacon v2.2 to generate an age model. Texturally, the core varies between a silty clay and a silty sand, often with abrupt sedimentological transitions. Our working hypothesis states that high percent clay values indicate persistent standing water wherein the deposition, accumulation, and preservation of fine grain sediment exceeds some undefined thickness that inhibits deflation during succeeding desiccation events or ephemeral lake environments. Based on this clay - lake status hypothesis, the sediment core is divided into five lake status intervals. Clay values are highest between 14.4 - 13.5 kcal yrs BP, coeval to Lake Mojave II. Clay values decrease abruptly at 13.5 kcal yrs BP (encapsulating the Younger Dryas) indicating a return to an ephemeral lake. At 11.3 kcal yrs BP, clay values rise abruptly indicating a return to a perennial lake; this early Holocene pluvial ended abruptly at 7.8 kcal yrs BP. From 7.8 - 4.2 kcal yrs BP, clay is low, but variable and mudcracks are common. At 4.2 kcal yrs BP, clay values increase but only moderately indicating a return to more frequent sustained perennial lakes. The early Holocene pluvial is likely a result of higher summer insolation, which generated a more intense and spatially expansive North American monsoon. Coupled with lower winter insolation and thus more winter storms across the region, Silver Lake flourished. A comparison to stable carbon isotope data from Leviathan Cave (NV), support our interpretation

  4. Midlatitude land surface temperature impacts the timing and structure of glacial maxima

    NASA Astrophysics Data System (ADS)

    Thomas, Elizabeth K.; Clemens, Steven C.; Sun, Youbin; Huang, Yongsong; Prell, Warren; Chen, Guangshan; Liu, Zhengyu; Loomis, Shannon

    2017-01-01

    Orbitally modulated insolation is thought to be among the key mechanisms driving ice sheet change. Yet, late Pleistocene ice sheets attained maximum marginal extents prior to summer insolation minima, suggesting that additional mechanisms influenced ice growth and decay. Continuous orbital-scale terrestrial temperature records can help define the role that temperature near ice sheet margins plays on the timing and structure of glacial maxima. We hypothesize, based on a 360 kyr long air temperature record from the Chinese Loess Plateau and shorter records from North America and Europe, that midlatitude terrestrial temperature influenced the rate of ice sheet growth prior to and during glacial maxima; cold conditions prior to glacial maxima enhanced ice sheet growth, while warming during glacial maxima inhibited further growth, despite low summer insolation. Thus, the midlatitude surface energy budget may be an important component of understanding and modeling ice volume, particularly for intervals prior to and during glacial maxima, when ice sheet margins reached midlatitudes.

  5. Faunal migration in late-glacial central Italy: implications for human resource exploitation.

    PubMed

    Pellegrini, Maura; Donahue, Randolph E; Chenery, Carolyn; Evans, Jane; Lee-Thorp, Julia; Montgomery, Janet; Mussi, Margherita

    2008-06-01

    The hunter-gatherer transhumance model presents foragers as specialised hunters of migratory ungulates, which moved seasonally between coastal lowlands and interior uplands. We studied six animal teeth of horse (Equus hydruntinus) and red deer (Cervus elaphus) from four different archaeological sites: the Grotta di Vado all'Arancio, Grotta di Settecannelle, Grotta Polesini and Grotta di Pozzo, in central Italy to test whether the migratory patterns and seasonal variations recorded in their teeth were consistent with expectations of the transhumance model for this region during the late Upper Palaeolithic. Sequential sub-samples of enamel were analysed from each tooth for oxygen, carbon and strontium isotope ratios to reconstruct mobility and yearly seasonal variations. The results show little evidence that these animals were moving over different geological terrains throughout the year, although small variations in Sr isotope ratios and concentrations were detected that corresponded to probable seasonal variations as shown by variability in oxygen isotope sequences. The results do, however, demonstrate that Cervus elaphus and Equus hydruntinus had different ranging behaviours, with the former moving over wider areas than the latter. This methodology produces results appropriate to assess animal migratory behaviour and, in turn, to test the consistency of proposed models of hunter-gatherer subsistence and mobility strategies. John Wiley & Sons, Ltd

  6. Paleoenvironmental implications of a late glacial insect assemblage from northwestern New York

    NASA Astrophysics Data System (ADS)

    Schwert, Donald P.; Morgan, Alan V.

    1980-01-01

    The Winter Gulf site near North Collins, New York is a 0.8-m sequence of organic detritus dated at approximately 12,700 yr B.P. A 260-kg sample produced over 500 identified individuals representing five orders of insects. Three insect zones were recognized, the lowest representing an open mire with sparse numbers of carices and other sedges; aquatic beetles were rare, and no trees were in the vicinity of the sample site. The middle zone indicated an extensive marsh or moist meadow environment with spruce nearby. The upper zone represented a mixed riparian and spruce forest insect assemblage. The results of the Winter Gulf insect analyses support published hypotheses that the site was probably a protected embayment of early lake Warren. Although the flora at the site has been previously interpreted as representing parkland tundra, temperature analyses of the fauna indicate that the thermal conditions were much warmer than parkland tundra regions of North America today. These results have important significance for the region immediately south of the Laurentide Ice Sheet during this period of the Late Wisconsinan.

  7. Late Wisconsinan sub-glacial clastic intrusive sheets along Lake Erie bluffs, at Bradtville, Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Dreimanis, Aleksis; Rappol, Martin

    1997-07-01

    Numerous clastic intrusive sheets, a few decimetres to more than 16 m long, 1-120 cm thick, and extending one to more than 25 m laterally, occur along a 350 m long section of the late Wisconsinan Catfish Creek Drift in the Lake Erie bluffs at Bradtville, southwestern Ontario. Most of them are downglacier-dipping dikes, the largest one terminating in the underlying middle Wisconsinan Tyrconnell Formation. Most dikes strike NNE-SSW, at right angles to the local direction of glacier movement during the deposition of Catfish Creek Drift. The tops of some of them are truncated or displaced downglacier by shearing. The main concentration of clastic intrusive sheets is on the upglacier side of a glaciotectonically folded anticline of Tyrconnell Formation clays and silts underlying the Catfish Creek Drift. The host sediments are Catfish Creek till, gravel, sand and silt, and Tyrconnell Formation silt and clay. Most intrusive sheets, particularly the small to medium ones, consist of massive to crudely laminated sand and silt, intruded from below by a dewatering process. The largest dike reflects in its composition mainly the adjoining or higher-lying host-sediment materials, and its main part was formed by downward infilling, or by gravity flows into an open fracture. The large dike is flanked by small laminated silty sand sheets and several small apophyses, some of them injected downward and sideways, others upward by dewatering. The clastic intrusive sheets were formed under a moving glacier, the Erie lobe, probably both at the beginning and towards the end of the deposition of Catfish Creek till. Their location and position was predetermined by glaciotectonically induced listric planar structures and zones of weakness, mainly tension fractures, that strike transverse to glacier movement and dip downglacier and also by confinement of pore-water in a permeable sediment wedge between the less pervious Tyrconnell Formation and massive Catfish Creek basal till.

  8. Late Glacial to Holocene environmental variabilities: A new multi-proxy paleolimnological study of sedimentary sequences from Como (northern Italy)

    NASA Astrophysics Data System (ADS)

    Höbig, N.; Martinelli, E.; Motella, S.; Michetti, A. M.; Livio, F.; Tinner, W.; Reicherter, K.; Castelletti, L.

    2012-04-01

    Lake Como (northern Italy) is the deepest Italian lake, reaching a depth of about 425 m. The lambda-shaped lake expands about 45 km in NE-SW direction. Southwards of the hydrologically closed western branch, two sediment cores of 70 m (S1) and 65 m length (S2) were taken in the year 2005 close to the cathedral of Como (Piazza Verdi). The drilling sites are located in the middle of the Southern Alps, some 300 m from the present-day lakeshore. The cores provide the first detailed Late Glacial to Holocene multi-proxy record for the Lake Como basin. Our research is aimed at investigating the environmental and geological evolution of the Insubria Region. The multi-proxy study of the stratigraphic sequences contain geophysical, geotechnical, sedimentological, paleobotanical, and radiocarbon analyses. They have been performed for core S1 and are still in progress on core S2. With this data the working group focuses on two main issues. The first topic is the reconstruction of the natural and anthropogenic processes controlling the ground subsidence in the Como urban area (e.g., Comerci et al., 2007) and another aim is to reconstruct vegetation and land-use dynamics. In particular, 150 samples of vegetal macroremains have been collected in the palustrine deposits along S1 core, down to 31,00 m. Below this depth (dated 14C 12,496 ± 55 yr BP - 15,050 - 14,250 cal yr BP), the amount of plant macroremains in the sediment drops dramatically. The taxonomic determination was carried out on more than 800 macroremains. They are represented by fragments of wood, leaves, needles, seeds, fruits, mosses and tiny charcoals (Motella, 2009, unpublished PhD Thesis). Picea/Larix, Pinus sp., Juniperus with Betula, found in the deeper levels (30.80 - 30.00 m), are the first arboreal taxa that colonized the shores of Lake Como, and show that the reforestation began in this area about 16,000 years ago. During the early Holocene (25.10 m) Abies alba expanded and further upwards the sequence

  9. Fossil shrews from Honduras and their significance for late glacial evolution in body size (Mammalia: Soricidae: Cryptotis)

    USGS Publications Warehouse

    Woodman, N.; Croft, D.A.

    2005-01-01

    failure to obtain reliable radiometric dates on remains restrict our opportunities to place the site in a firm temporal context. However, the morphometrical differences we document for fossil C. orophila and C. goodwini show them to be distinct from modern populations of these shrews. Some other species of fossil mammals from McGrew Cave exhibit distinct size changes of the magnitudes experienced by many northern North American and some Mexican mammals during the transition from late glacial to Holocene environmental conditions, and it is likely that at least some of the remains from the cave are late Pleistocene in age. One curious factor is that, whereas most mainland mammals that exhibit large-scale size shifts during the late glacial/postglacial transition experienced dwarfing, C. goodwini increased in size. The lack of clinal variation in modern C. goodwini supports the hypothesis that size evolution can result from local selection rather than from cline translocation. Models of size change in mammals indicate that increased size, such as that observed for C. goodwini, are a likely consequence of increased availability of resources and, thereby, a relaxation of selection during critical times of the year.

  10. Episodic speleothem deposition tracks the terrestrial impact of millennial-scale last glacial climate variability in SW Ireland

    NASA Astrophysics Data System (ADS)

    Fankhauser, Adelheid; McDermott, Frank; Fleitmann, Dominik

    2016-11-01

    Eighty four new U-Th ages are presented for twenty randomly selected broken, displaced and reworked calcite speleothems retrieved from clastic sedimentary fill and from isolated bedding-plane shelves in Crag cave (SW Ireland). The dated pre-Holocene samples span much of the last glacial, ranging in age from 85.15 ± 0.60 to 23.45 ± 0.17 ka. Speleothem deposition requires the presence of liquid water, and because Crag cave is a shallow system, deposition is considered likely only when mean annual air temperatures (MAAT) exceed the freezing point of water. Deposition at this mid-latitude ocean-marginal site occurred episodically during MIS5a through to MIS2, synchronously within dating uncertainties, with the timing of Greenland Interstadials (GI). In the latter part of Marine Isotope Stage 3 (MIS3), deposition was particularly intense, consistent with regional scale climate amelioration inferred previously from radiocarbon ages for sparse MIS3 organic and freshwater surficial deposits in N. Ireland. A brief episode of speleothem deposition at c.23.40 ± 0.22 ka coincides with GI-2, demonstrating the sensitivity of the site to brief climate amelioration episodes in Greenland during MIS2. Conditions favourable for speleothem deposition occurred periodically during the last glacial, indicating temperature changes of at least 10 °C between stadials and interstadials at this mid-latitude site. Deposition ceased during Greenland Stadials (GS), including during periods of ice-rafting in the adjacent N. Atlantic Ocean (Heinrich events). Oxygen and carbon isotope ratios of the last glacial speleothems are generally elevated, reflecting non-equilibrium isotope fractionation effects. However, establishment of low δ13C values often occurred within a few decades of climate amelioration, indicating that biogenic CO2 production resumed rapidly at this site, particularly during MIS3. Speleothem δ18O variability was driven largely by long-term changes in the δ18O value of the

  11. A beryllium-10 chronology of late-glacial moraines in the upper Rakaia valley, Southern Alps, New Zealand supports Southern-Hemisphere warming during the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Koffman, Tobias N. B.; Schaefer, Joerg M.; Putnam, Aaron E.; Denton, George H.; Barrell, David J. A.; Rowan, Ann V.; Finkel, Robert C.; Rood, Dylan H.; Schwartz, Roseanne; Plummer, Mitchell A.; Brocklehurst, Simon H.

    2017-08-01

    Interhemispheric differences in the timing of pauses or reversals in the temperature rise at the end of the last ice age can help to clarify the mechanisms that influence glacial terminations. Our beryllium-10 (10Be) surface-exposure chronology for the moraines of the upper Rakaia valley of New Zealand's Southern Alps, combined with glaciological modeling, show that late-glacial temperature change in the atmosphere over the Southern Alps exhibited an Antarctic-like pattern. During the Antarctic Cold Reversal, the upper Rakaia glacier built two well-defined, closely-spaced moraines on Reischek knob at 13,900 ± 120 [1σ; ± 310 yrs when including a 2.1% production-rate (PR) uncertainty] and 13,140 ± 250 (±370) yrs ago, in positions consistent with mean annual temperature approximately 2 °C cooler than modern values. The formation of distinct, widely-spaced moraines at 12,140 ± 200 (±320) and 11,620 ± 160 (±290) yrs ago on Meins Knob, 2 km up-valley from the Reischek knob moraines, indicates that the glacier thinned by ∼250 m during Heinrich Stadial 0 (HS 0, coeval with the Younger Dryas 12,900 to 11,600 yrs ago). The glacier-inferred temperature rise in the upper Rakaia valley during HS 0 was about 1 °C. Because a similar pattern is documented by well-dated glacial geomorphologic records from the Andes of South America, the implication is that this late-glacial atmospheric climate signal extended from 79°S north to at least 36°S, and thus was a major feature of Southern Hemisphere paleoclimate during the last glacial termination.

  12. Chronology of Late Quaternary Glacial Cycles in the Bering Trough, Gulf of Alaska: Constraints from Core-Log-Seismic Integration across the Continental Shelf and Slope

    NASA Astrophysics Data System (ADS)

    Clary, W. A.; Worthington, L. L.; Daigle, H.; Slagle, A. L.; Gulick, S. P. S.

    2016-12-01

    Sediments offshore Southern Alaska offer a natural laboratory to study glacial erosion, sediment deposition, and orogenesis. A major goal of Integrated Ocean Drilling Program (IODP) Expedition 341 was investigation of interrelationships among tectonic processes, paleoclimate, and glacial activity. Here, we focus on core-log-seismic integration of IODP Sites U1420 and U1421 on the shallow shelf and slope near the Bering Trough, a glacially derived shelf-crossing landform. These sites sample glacial and marine sediments that record a history of sedimentation following the onset of glacial intensification near the mid-Pleistocene transition (1.2 Ma) and Yakutat microplate convergence with North America. Ocean drilling provides important stratigraphic, physical properties, and age data in depth which support development of a stratigraphic model that can be extended across the shelf if carefully calibrated to local and regional seismic surveys. We use high resolution multichannel seismic, core, and logging data to develop a time-depth relationship (TDR) and update the developing chronostratigraphic model based on correlation of seismic sequence boundaries and drilling-related data, including biostratigraphic and paleomagnetic age controls. We calibrate, combine, and interpolate core and logging data at each site to minimize gaps in physical property information and generate synthetic seismic traces. At Site U1421, vertical seismic profiling further constrains the TDR, and provides input for the initial velocity model during the tie. Finally, we match reflectors in the synthetic trace with events in nearby seismic reflection data to establish a TDR at each site. We can use this relationship to better interpret the development of the Bering Trough, a recurring and favored path for ice streams and glacial advance. Initial results suggest late Pleistocene sedimentation rates of at least 1 km/m.y. on average, and variable sedimentation rates which are possibly correlated

  13. Late Glacial to Holocene Sealevel changes in the Sea of Marmara; evidence from high-resolution seismic and core studies

    NASA Astrophysics Data System (ADS)

    Eris, K. K.

    2009-04-01

    Late Glacial to Holocene sedimentary record of the northern shelf of the Sea of Marmara (SoM) is documented by detailed stratigraphic analysis of sub-bottom (Chirp) profiles and sediment cores. The reflection profiles reveal the presence of four seismic stratigraphic units S4-S1 that are equivalent to lithostratigraphic units L4-L1, separated from each other by shelf-crossing unconformities of Q1 to Q3. The seismic profiles from the SoM entrance to the Strait of İstanbul (SoI) allow us to divide the Holocene sediments of Unit S1 into seven sub-units, therefore, we can estimate high-frequency sealevel fluctuations. The SoM was converted into freshwater lake in the beginning of the marine isotope stage 3 (MIS-3) due to global sealevel fall below the Dardanelles outlet (-83 m). During the MIS-3 and main part of the MIS-2, disconnection with the Mediterranean Sea and the forced regression in the SoM gave rise to deposition of progradational units (seismic units S4 and S3) as sediment wedges thickening towards the shelf edge. The maximum lowstand of the ‘Marmara lake' is associated with river incisions below to 105 m water depth, above which a prominent erosional surface formed on the shelf. In contrast to the LGM disconnection with the Mediterranean Sea, the SoM experienced a period of Black Sea outflow between 15-13.5 14C ka BP, when the Black Sea level rised above the sill depth (-35 m) of the SoI. This gave rise to a freshwater transgression in the lake leading to rise the water level to -85 m by 13 ka BP. Following the reconnection with the Mediterranean Sea at 12 ka BP, the Younger Dryas (YD) cold period in the SoM was associated by a Black Sea outflow at 11.5 ka BP leading to formation of a levee within the axis of the paleo Bosphorus shelf valley. During the YD, the sealevel increase was interrupted by stillstands at -76 m and -71 m. In the seismic profiles from the SoM entrance to the SoI, the colonization of algal-serpulid bioherms across the reflector

  14. The Carnian (Late Triassic) carbon isotope excursion: new insights from the terrestrial realm

    NASA Astrophysics Data System (ADS)

    Miller, Charlotte; Kürschner, Wolfram; Peterse, Francien; Baranyi, Viktoria; Reichart, Gert-Jan

    2016-04-01

    The geological record contains evidence for numerous pronounced perturbations in the global carbon cycle, some of which are associated with eruptions from large igneous provinces (LIP), and consequently, ocean acidification and mass extinction. In the Carnian (Late Triassic), evidence from sedimentology and fossil pollen points to a significant change in climate, resulting in biotic turnover: during a period termed the 'Carnian Pluvial Event' (CPE). Additionally, during the Carnian, large volumes of flood basalts were erupted from the Wrangellia LIP (western North America). Evidence from the marine realm suggests a fundamental relationship between the CPE, a global 'wet' period, and the injection of light carbon into the atmosphere from the LIP. Here we provide the first evidence from the terrestrial realm of a significant negative δ13C excursion through the CPE recorded in the sedimentary archive of the Wiscombe Park Borehole, Devon (UK). Both total organic matter and plant leaf waxes reflect a gradual carbon isotope excursion of ~-5‰ during this time interval. Our data provides evidence for the global nature of this isotope excursion, supporting the hypothesis that the excursion was likely the result of an injection of light carbon into the atmosphere from the Wrangellia LIP.

  15. Quantitative Temperature Reconstructions from Holocene and Late Glacial Lake Sediments in the Tropical Andes using Chironomidae (non-biting midges)

    NASA Astrophysics Data System (ADS)

    Matthews-Bird, F.; Gosling, W. D.; Brooks, S. J.; Montoya, E.; Coe, A. L.

    2014-12-01

    Chironomidae (non-biting midges) is a family of two-winged aquatic insects of the order Diptera. They are globally distributed and one of the most diverse families within aquatic ecosystems. The insects are stenotopic, and the rapid turnover of species and their ability to colonise quickly favourable habitats means chironomids are extremely sensitive to environmental change, notably temperature. Through the development of quantitative temperature inference models chironomids have become important palaeoecological tools. Proxies capable of generating independent estimates of past climate are crucial to disentangling climate signals and ecosystem response in the palaeoecological record. This project has developed the first modern environmental calibration data set in order to use chironomids from the Tropical Andes as quantitative climate proxies. Using surface sediments from c. 60 lakes from Bolivia, Peru and Ecuador we have developed an inference model capable of reconstructing temperatures, with a prediction error of 1-2°C, from fossil assemblages. Here we present the first Lateglacial and Holocene chironomid-inferred temperature reconstructions from two sites in the tropical Andes. The first record, from a high elevation (4153 m asl) lake in the Bolivian Andes, shows persistently cool temperatures for the past 15 kyr, punctuated by warm episodes in the early Holocene (9-10 kyr BP). The chironomid-inferred Holocene temperature trends from a lake sediment record on the eastern Andean flank of Ecuador (1248 m asl) spanning the last 5 millennia are synchronous with temperature changes in the NGRIP ice core record. The temperature estimates suggest along the eastern flank of the Andes, at lower latitudes (~1°S), climate closely resemble the well-established fluctuations of the Northern Hemisphere for this time period. Late-glacial climate fluctuations across South America are still disputed with some palaeoecological records suggesting evidence for Younger Dryas

  16. Glacial and tectonic influence on terrestrial organic carbon delivery to high latitude deep marine systems: IODP Site U1417, Surveyor Fan, Gulf of Alaska

    NASA Astrophysics Data System (ADS)

    Childress, L. B.; Ridgway, K. D.

    2014-12-01

    Glacial and tectonic processes on active margins are intrinsically coupled to the transport of sediment and associated organic carbon (OC). Glaciation/deglaciation and the formation of ice sheets can alter the quantity and composition of OC delivered to the marine environment. Over geologic time scales (>1 Ma), exhumation and mass wasting of sedimentary rock from uplifted accretionary wedges inject recycled OC (e.g. kerogen), along with modern OC into the marine environment. The sedimentary record of glacial and tectonic processes along the southern Alaska margin is particularly well preserved at Integrated Ocean Drilling Program (IODP) Site U1417. Lithofacies of Site U1417 can be divided into 3 sedimentary packages that we interpret as linked to the onset of tidewater glaciation along, and tectonic convergence of the Yakutat Terrane with, the continental margin of northwestern Canada and southern Alaska. Based on previous studies linking the development of the Cordilleran Ice Sheet and the movement of the Yakutat Terrane to the development of the Surveyor Fan System, we hypothesize biogeochemical variations in the deposited sediments as a result of changing provenance. Preservation of terrestrial OC that has been documented in sediments of the Alaskan continental shelf margin and sediment routing through the deep-sea Surveyor Channel from the Pleistocene to modern time implies a long-term conduit for this OC to reach the distal portion of the Surveyor Fan system. To correlate marine deposits with terrestrial formations, bulk geochemical and detailed biomarker analyses are used to delineate source material. Preliminary bulk OC content and stable carbon isotope analyses of the Yakataga, Poul Creek, and Kultheith Fms. reveal notable differences. Detailed biomarker analysis by pyrolysis-gas chromatograph-mass spectrometry has revealed further differences between the three primary formations. Using the biogeochemical fingerprints of the Yakataga, Poul Creek, and coal

  17. Late Glacial-Holocene sequence of Lake Saint-Point (Jura Mountains, France): Detrital inputs as records of climate change and anthropic impact

    NASA Astrophysics Data System (ADS)

    Leroux, Aurélie; Bichet, Vincent; Walter-Simonnet, Anne-Véronique; Magny, Michel; Adatte, Thierry; Gauthier, Émilie; Richard, Hervé; Baltzer, Agnès

    2008-12-01

    A sediment sequence (SP05, 12.5 m long) was taken from the deep zone of Lake Saint-Point (850 m a.s.l.). Sedimentological analyses highlight two main contrasted periods of sedimentation: the Last Glacial Maximum (LGM)/Late Glacial characterized by high silicates and quartz contents the Holocene dominated by the carbonated fraction. At the beginning of the Holocene (11 400 years cal. BP), silicates fraction flux abruptly decreased. The shift between the Late Glacial and the Holocene periods may be explained by forest development in the catchment. From 10 200 to 6800 years cal. BP, silicates and detrital carbonate fractions remained stable before they progressively increased steady till 5000 years cal. BP. Both increases cannot be totally attributed to an anthropic impact since pollen data indicate continuous anthropic activities only dated back from 3000 years cal. BP. They thus resulted from a dominant climatic control. From 5000 years cal. BP, silicates content still increased while detrital carbonates input became steady due to a change in pedogenetic processes affecting the catchment. During the last millennium, silicates and detrital carbonate decreased, probably due to pastureland development.

  18. Environmental and climatic changes in Central Chilean Patagonia since the Late Glacial (Mallín El Embudo, 44° S)

    NASA Astrophysics Data System (ADS)

    de Porras, M. E.; Maldonado, A.; Quintana, F. A.; Martel-Cea, A.; Reyes, O.; Méndez, C.

    2013-10-01

    Multi-millennial environmental and climatic changes in Central Chilean Patagonia (44-49° S) during the Last Glacial-Interglacial cycle have been of particular interest as changes in the position and strength of the Southern Westerlies are the major forcing factor conditioning the environmental dynamics. Recent attempts to reconstruct regional environmental and climatic signals from Central Chilean Patagonia reveal some discrepancies and unclear issues among the records. This paper presents the 13 ka pollen and charcoal records from Mallín El Embudo (44°40' S; 71°42' W) located in the deciduous Nothofagus forest in the middle Río Cisnes valley. The paper aims to (1) establish the timing and magnitude of local vegetation changes and fire activity since the Late Glacial and (2) integrate these results at the regional scale in order to discuss the discrepancies and depict the Central Chilean Patagonia environmental and climatic dynamics since Late Glacial. Open landscapes dominated by grasses associated with scattered Nothofagus forest patches dominated middle Río Cisnes valley between 13-11.2 ka suggesting low effective moisture but also reflecting that landscape configuration after glacial retreat was still ongoing. At 11.2 ka, a sudden development of an open and quite dynamic Nothofagus forest probably associated to the synchronous high fire activity occurred suggesting a rise in effective moisture. Since 9.5 ka, the record reflects the presence of a closed Nothofagus forest related to higher/similar effective moisture conditions than before but under an unmarked precipitation seasonality. The forest experienced a slight canopy opening since 5.7 ka, probably due to slightly drier conditions than before followed by a sudden change around 4.2 ka associated with fire and volcanic disturbances. The recovery of an open Nothofagus forest related to slight wetter conditions (similar to present) occurred around 2 ka and persisted under highly variable climatic

  19. Environmental and climatic changes in central Chilean Patagonia since the Late Glacial (Mallín El Embudo, 44° S)

    NASA Astrophysics Data System (ADS)

    de Porras, M. E.; Maldonado, A.; Quintana, F. A.; Martel-Cea, A.; Reyes, O.; Méndez, C.

    2014-05-01

    Multi-millennial environmental and climatic changes in central Chilean Patagonia (44-49° S) during the Last Glacial-Interglacial cycle have been of particular interest as changes in the position and strength of the southern westerlies are the major forcing factor conditioning the environmental dynamics. Recent attempts to reconstruct regional environmental and climatic signals from central Chilean Patagonia reveal some discrepancies and unclear issues among the records. This paper presents the 13 ka pollen and charcoal records from Mallín El Embudo (44° 40' S, 71° 42' W) located in the deciduous Nothofagus forest in the middle Río Cisnes valley. The paper aims to (1) establish the timing and magnitude of local vegetation changes and fire activity since the Late Glacial and (2) integrate these results at the regional scale in order to discuss the discrepancies and depict the environmental and climatic dynamics in central Chilean Patagonia since the Late Glacial. Open landscapes dominated by grasses associated with scattered Nothofagus forest patches dominated the middle Río Cisnes valley between 13 and 11.2 ka suggesting low effective moisture but also indicating that landscape configuration after glacial retreat was still ongoing. At 11.2 ka, the sudden development of an open and quite dynamic Nothofagus forest probably associated with the synchronous high fire activity occurred, suggesting a rise in effective moisture associated with dry summers. Since 9.5 ka, the record reflects the presence of a closed Nothofagus forest related to higher effective moisture conditions than before combined with moderate dry summers that may have triggered a high frequency of low-magnitude crown fires that did not severely affect the forest. The forest experienced a slight canopy opening after 5.7 ka, probably due to slightly drier conditions than before followed by a sudden change to open forest conditions around 4.2 ka associated with fire and volcanic disturbances. Around

  20. Glacial isostatic adjustment in response to changing Late Holocene behaviour of ice streams on the Siple Coast, West Antarctica

    NASA Astrophysics Data System (ADS)

    Nield, Grace A.; Whitehouse, Pippa L.; King, Matt A.; Clarke, Peter J.

    2016-04-01

    The Siple Coast region of Antarctica contains a number of fast-flowing ice streams, which control the dynamics and mass balance of the region. These ice streams are known to undergo stagnation and reactivation cycles, which lead to ice thickness changes that may be sufficient to excite a viscous solid Earth response (glacial isostatic adjustment; GIA). This study aims to quantify Siple Coast ice thickness changes during the last 2000 yr in order to determine the degree to which they might contribute to GIA and associated present-day bedrock uplift rates. This is important because accurate modelling of GIA is necessary to determine the rate of present-day ice-mass change from satellite gravimetry. Recently-published reconstructions of ice-stream variability were used to create a suite of kinematic models for the stagnation-related thickening of Kamb Ice Stream since ˜1850 AD, and a GIA model was used to predict present-day deformation rates in response to this thickening. A number of longer-term loading scenarios, which include the stagnation and reactivation of ice streams across the Siple Coast over the past 2000 yr, were also constructed, and used to investigate the longer term GIA signal in the region. Uplift rates for each of the ice loading histories, based on a range of earth models, were compared with regional GPS-observed uplift rates and an empirical GIA estimate. We estimate Kamb Ice Stream to have thickened by 70-130 m since stagnation ˜165 years ago. Modelled present-day vertical motion in response to this load increase peaks at -17 mm yr-1 (i.e. 17 mm yr-1 subsidence) for the weakest earth models tested here. Comparison of the solid Earth response to ice load changes throughout the last glacial cycle, including ice stream stagnation and reactivation across the Siple Coast during the last 2000 yr, with an empirical GIA estimate suggests that the upper mantle viscosity of the region is greater than 1 × 1020 Pa s. When upper mantle viscosity values of

  1. Glacial landforms on German Bank, Scotian Shelf: evidence for Late Wisconsinan ice-sheet dynamics and implications for the formation of De Geer moraines

    USGS Publications Warehouse

    Todd, Brian J.; Valentine, Page C.; Longva, Oddvar; Shaw, John

    2007-01-01

    The extent and behaviour of the southeast margin of the Laurentide Ice Sheet in Atlantic Canada is of significance in the study of Late Wisconsinan ice sheet-ocean interactions. Multibeam sonar imagery of subglacial, ice-marginal and glaciomarine landforms on German Bank, Scotian Shelf, provides evidence of the pattern of glacial-dynamic events in the eastern Gulf of Maine. Northwest-southeast trending drumlins and megaflutes dominate northern German Bank. On southern German Bank, megaflutes of thin glacial deposits create a distinct northwest-southeast grain. Lobate regional moraines (>10km long) are concave to the northwest, up-ice direction and strike southwest-northeast, normal to the direction of ice flow. Ubiquitous, overlying De Geer moraines (

  2. Late quaternary distribution of the Cycladophora davisiana radiolarian species: Reflection of possible ventilation of the North Pacific intermediate water during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Matul, A. G.; Abelmann, A.; Gersonde, R.; Nürnberg, D.; Tiedemann, R.; Kruglikova, S. B.

    2015-02-01

    A comparison of micropaleontological data on the distribution of the Cycladophora davisiana radiolarian species in the surface sediment layer and the Late Quaternary sediments from the Subarctic Pacific and Far East marginal seas allowed conclusions concerning the possible conditions and occurrence of intermediate waters during the last glacial maximum. We used the modern data on the C. davisiana species, which is a micro-paleontological indicator of the cold oxygen-rich upper intermediate water mass, which is now forming only in the Sea of Okhotsk. The high amount of C. davisiana in sediments of the last glacial maximum may point to the possible formation and expansion of the ventilated intermediate water in the most part of the Subarctic paleo-Pacific: the Bering Sea, the Sea of Okhotsk, within the NW Gyre, and in the Gulf of Alaska.

  3. Using submarine landforms to investigate glacial history, chronology and evolution during the Late Cenozoic: A 3D seismic case study of the mid-Norwegian shelf.

    NASA Astrophysics Data System (ADS)

    Newton, Andrew; Huuse, Mads

    2014-05-01

    The mid-Norwegian continental shelf and its succession through time has in places preserved a detailed geomorphological record of glacial and interglacial ice dynamics. Most work has concentrated on the most recent glaciations and therefore the full extent and dynamics of older glaciations is poorly understood. In this work several 3D seismic volumes, from across the mid-Norwegian shelf, are used together to image the glacial-interglacial sequences and piece together a chronology of shelf edge glaciation throughout the Late Cenozoic up until the most recent Weichselian glaciation. The 3D seismic data are supplemented with a large number of 2D seismic profiles and oil industry boreholes are used for calibration and horizon dating. The work presented here will help in the effort to establish a better detailed and more tightly constrained chronology of the extent and timings of different glaciations throughout the Late Cenozoic. Developing a better chronology is of critical importance for helping to calibrate current models of ice sheet and landscape evolution so that contemporary changes may be better understood. The basic geology of the system shows a progradation of the shelf edge towards the basin. The stratigraphical succession comprises evidence for several erosional events associated with the Elsterian, Saalian and Weichselian glaciations during the mid- to late Pleistocene. At depth the pre-glacial Neogene deposits are characterized by widespread polygonal faulting. Within the 3D seismic blocks several glaciogenic structures are visible. Most notably these include an abundance of linear and curvilinear mega-scale glacial lineations, which reach lengths of over 50 km, and iceberg scours that vary in length from 100 m to over 7 km. An array of different sized channels offer insight into the flow characteristics of pro-glacial and subglacial regimes during previous glaciations. Lateral moraines are also present in the seismic data and help to delineate past

  4. Hydrological and Vegetation Shifts in the Equatorial Sulawesi since the Last Glacial Maximum: Perspectives from Hydrogen and Carbon Isotopes of Terrestrial Leaf Wax Compounds

    NASA Astrophysics Data System (ADS)

    Wicaksono, Satrio; Russell, James; Holbourn, Ann; Kuhnt, Wolfgang

    2014-05-01

    The Indo-Pacific Warm Pool (IPWP) is a major epicenter of the tropical convective activity that drives both the Walker and Hadley circulations. The island of Sulawesi is situated at the heart of the Maritime Continent within the IPWP, and despite the region's importance, published proxy records and numerical simulations of convection and precipitation patterns from Sulawesi and across the Maritime Continent since the Last Glacial Maximum (LGM) display some substantial disagreement. Today, precipitation over Sulawesi is strongly influenced by variations in topography and wind pattern, which include land-sea breezes, orographically-forced winds, and monsoonal winds related to the seasonal migration of the Intertropical Convergence Zone. To better understand the interplay between such variations and high latitude climate dynamics during the last deglaciation, we developed high resolution records of the deuterium isotopic composition of terrestrial leaf waxes (long-chain n-alkanoic acids; δDwax) from a marine core (3.63 ºS, 119.36 ºE, water depth: 688 m) retrieved 10 km west of Sulawesi in close proximity to a major river delta. At low latitudes, δDwax has been used to reconstruct the δD of catchment-integrated precipitation, often interpreted as an indicator of regional rainfall amounts and large-scale convective activity. Our record displays relatively depleted values during the height of LGM, followed by a gradual enrichment that reached its peak (up to 10o enrichment) during the Younger Dryas (YD). Following the YD, δDwax becomes more depleted into the Holocene, reaching values nearly identical to the LGM. The deglacial pattern observed in our δDwax, derived from a predominantly high-altitude catchment in the southwestern arm of Sulawesi, is similar to that of δDwax record from Lake Towuti (2.5 ºS, 121.5 ºE, surface elevation: 319 m) in the southeastern arm of Sulawesi. The synoptic deglacial shifts seen in both catchments demonstrate that the equatorial

  5. The Terrestrial Fossil Organic Matter Record of Global Carbon Cycling: A Late Paleozoic through Early Mesozoic Perspective

    NASA Astrophysics Data System (ADS)

    Montanez, I. P.

    2006-12-01

    The carbon isotope composition of terrestrial fossil organic matter (δ13Corg) has been widely used as a proxy of global carbon cycling and to reconstruct perturbations to the ocean-atmosphere carbon budget. The degree to which terrestrial δ13Corg records local to regional environmental conditions versus the evolution of the global carbon cycle has been highly debated. The high-resolution (104 to 106 m.y.) terrestrial δ13Corg record presented here defines a long-term trend through the latest Devonian to Late Triassic that reveals significant and systematic variations that track independently inferred changes in climate, paleo-atmospheric pCO2, and major restructuring in paleotropical flora. This newly derived record is based on 350 carbon isotope analyses of compressed and permineralized plants, cuticle, charcoal and coal (including vitrinite and fusinite) collected from paleo-wetland mudstones and claystones, claystone-filled abandoned fluvial channels, floodplain mudstones, and ephemeral lacustrine deposits at paleo-tropical to paleo-temperate latitudes. Morphologic and geochemical analysis of contemporaneous paleosols and fluvial-alluvial deposits allow for correlation of terrestrial δ13Corg values to reconstructed paleo-environmental conditions. Terrestrial δ13Corg values of contemporaneous fossil organic matter exhibit systematic inter- and intra-basinal variation of up to 2‰ associated with differences in paleo-precipitation and burial history, and geomorphic position within depositional basins and paleo-fluvial systems. Variation in δ13Corg by organic matter type is minimal to less than 1.5‰; specifically, charcoal δ13Corg values overlap to are slightly less negative than those of thermally less mature organic components analyzed. Overall, variation within contemporaneous populations is significantly less than defined by the long-term terrestrial δ13Corg record. Moreover, paleo-floral pi/pa ratios, an established proxy of water-use efficiency of

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    imparted pervasive deformation throughout all underlying units, highlighted by a previously unrecognized raft of Cretaceous bedrock. During this advance, Laurentide ice from the interior of Banks Island coalesced with an ice stream in Amundsen Gulf, depositing the interlobate Sachs Moraine that contains shells as young as ˜24 cal ka BP (Late Wisconsinan). During deglaciation, meltwater emanating from these separating ice lobes deposited outwash that extended to deglacial marine limit (11 m asl) along the west coast of Banks Island. Our new stratigraphic synthesis fundamentally revises and simplifies the record of past Quaternary environments preserved on southwest Banks Island, which serves as a key terrestrial archive for palaeoenvironmental change.

  7. Reconstruction of Late Glacial and Holocene landscape-climatic changes in the central Selenga Middle Mountains based on the isotopic composition of organic matter

    NASA Astrophysics Data System (ADS)

    Golubtsov, V. A.; Ryzhov, Yu. V.

    2017-02-01

    The results of investigation into the composition of stable carbon and nitrogen isotopes of organic matter in the soils developed within soil-sedimentary sequences in the central part of the Selenga Middle Mountains in the Late Glacial and Holocene are presented. In the past 15000 years, the organic matter of the investigated soils has only been formed from the biomass of C3 plants (without the participation of C4 plants). This is confirmed by the of δ13C values from-27.00 to-23.35‰. A combined analysis of the parameters of the organic matter (Corg, Ntotal, C/N, δ13C, and δ15N) of soils formed in different periods makes it possible to assume that the isotopic composition of carbon and nitrogen reflects changes in the climate humidity during the Late Glacial and Holocene periods. The specified intervals of soil formation correspond to the climate humidification and stabilization of the surface owing to the development of dense vegetation. Aridization periods were characterized by the accumulation of sediments that buried soil horizons. The most pronounced stages of climate aridization occurred at the transition from the Late Glacial to the Holocene, from the Boreal to the Atlantic, and from the Atlantic to the Subboreal periods. The optimum soil-forming conditions existed in the periods of 11700-11000, 8800-6900, and 4700-1000 years ago, which is confirmed by the published data on the landscape-climatic changes in the adjacent areas in the past 15000 years.

  8. Exceptionally well-preserved giant spermatozoa in male and female specimens of an ostracod Cypria ophtalmica (Crustacea: Ostracoda) from Late Glacial lacustrine sediments of Southern Carpathians, Romania.

    PubMed

    Iepure, Sanda; Namiotko, Tadeusz; Valdecasas, Antonio G; Magyari, Enikö K

    2012-07-01

    Exceptionally well-preserved giant spermatozoa observed between abundant decalcified carapace valves of ostracods (Crustacea: Ostracoda) were found in Late Glacial to Holocene (14,400 to 10,000 cal years BP) lacustrine sediments in the southern Romanian Carpathians. Analysis by scanning electron microscopy and laser scanning confocal microscopy revealed good preservation of the appendages enabling specific identification as Cypria ophtalmica (Candonidae) and indication of the presence of both female and male specimens based on the sexual dimorphism of the second antenna. This record represents the oldest and richest direct evidence of virtually morphologically unaltered animal spermatozoa preserved in females after mating.

  9. Exceptionally well-preserved giant spermatozoa in male and female specimens of an ostracod Cypria ophtalmica (Crustacea: Ostracoda) from Late Glacial lacustrine sediments of Southern Carpathians, Romania

    NASA Astrophysics Data System (ADS)

    Iepure, Sanda; Namiotko, Tadeusz; Valdecasas, Antonio G.; Magyari, Enikö K.

    2012-07-01

    Exceptionally well-preserved giant spermatozoa observed between abundant decalcified carapace valves of ostracods (Crustacea: Ostracoda) were found in Late Glacial to Holocene (14,400 to 10,000 cal years bp) lacustrine sediments in the southern Romanian Carpathians. Analysis by scanning electron microscopy and laser scanning confocal microscopy revealed good preservation of the appendages enabling specific identification as Cypria ophtalmica (Candonidae) and indication of the presence of both female and male specimens based on the sexual dimorphism of the second antenna. This record represents the oldest and richest direct evidence of virtually morphologically unaltered animal spermatozoa preserved in females after mating.

  10. Increased delivery of condensation nuclei during the Late Heavy Bombardment to the terrestrial and martian atmospheres

    NASA Astrophysics Data System (ADS)

    Losiak, Anna

    2014-05-01

    During the period of the Late Heavy Bombardment (LHB), between 4.1 and 3.8 Ga, the impact rate within the entire Solar System was up to a few thousand times higher than the current value (Ryder 2002, Bottke et al. 2012, Fassett and Minton 2013). Multiple basin-forming events on inner planets that occurred during this time had a strong but short-lasting (up to few thousands of years) effect on atmospheres of Earth and Mars (Sleep et al. 1989, Segura et al. 2002, 2012). However, the role of the continuous flux of smaller impactors has not been assessed so far. We calculated the amount of meteoric material in the 10^-3 kg to 106 kg size range delivered to Earth and Mars during the LHB based on the impact flux at the top of the Earth's atmosphere based on results from Bland and Artemieva (2006). Those values were recalculated for Mars based on Ivanov and Hartmann (2009) and then recalculated to the LHB peak based on estimates from Ryder (2002), Bottke et al. (2012), Fassett and Minton (2013). During the LHB, the amount of meteoritic material within this size range delivered to Earth was up to ~1.7*10^10 kg/year and 1.4*10^10 kg/year for Mars. The impactors that ablate and are disrupted during atmospheric entry can serve as cloud condensation nuclei (Rosen 1968, Hunten et al. 1980, Ogurtsov and Raspopov 2011). The amount of material delivered during LHB to the upper stratosphere and lower mezosphere (Hunten et al. 1980, Bland and Artemieva 2006) is comparable to the current terrestrial annual emission of mineral cloud condensation nuclei of 0.5-8*10^12 kg/year (Tegen 2003). On Mars, the availability of condensation nuclei is one of the main factors guiding water-ice cloud formation (Montmessin et al. 2004), which is in turn one of the main climatic factors influencing the hydrological cycle (Michaels et al. 2006) and radiative balance of the planet (Haberle et al. 1999, Wordsworth et al. 2013, Urata and Toon 2013). Increased delivery of condensation nuclei during the

  11. Glacial-interglacial variability in Tropical Pangaean Precipitation during the Late Paleozoic Ice Age: simulations with the Community Climate System Model

    NASA Astrophysics Data System (ADS)

    Heavens, N. G.; Mahowald, N. M.; Soreghan, G. S.; Soreghan, M. J.; Shields, C. A.

    2012-05-01

    The Late Paleozoic Ice Age (LPIA), the Earth's penultimate "icehouse climate", was a critical time in the history of biological and ecological evolution. Many questions remain about the connections between high-latitude glaciation in Gondwanaland and low-latitude precipitation variability in Pangaea. We have simulated the Earth's climate during Asselian-Sakmarian time (299-284 Ma) with the Community Climate System Model version 3 (CCSM3), a coupled dynamic atmosphere-ocean-land-sea-ice model. Our simulations test the sensitivity of the model climate to direct and indirect effects of glaciation as well as variability in the Earth's orbit. Our focus is on precipitation variability in tropical (30° S-30° N) Pangaea, where there has been the most interpretation of glacial-interglacial climate change during the LPIA. The results of these simulations suggest that glacials generally were drier than interglacials in tropical Pangaea, though exceptional areas may have been wetter, depending on location and the mode of glaciation. Lower sea level, an indirect effect of changes in glacial extent, appears to reduce tropical Pangaean precipitation more than the direct radiative/topographic effects of high-latitude glaciation. Glaciation of the Central Pangaean Mountains would have greatly reduced equatorial Pangaean precipitation, while perhaps enhancing precipitation at higher tropical latitudes and in equatorial rain shadows. Variability evident in strata with 5th order stratigraphic cycles may have resulted from precipitation changes owing to precession forcing of monsoon circulations and would have differed in character between greenhouse and icehouse climates.

  12. Late Quaternary glacial relief evolution and fracture-density control on erosion revealed by low-temperature thermochronometry and remote sensing (Granite Range, Alaska)

    NASA Astrophysics Data System (ADS)

    Valla, Pierre; Champagnac, Jean-Daniel; Herman, Frédéric; Lowick, Sally; Guralnik, Benny; Shuster, David; Fellin, Giuditta

    2013-04-01

    Long-term erosion and topographic evolution of mountain belts arise from complex coupling between tectonics, climate and surface processes. The Granite Range (Wrangell-St Elias National Park, Alaska) presents an ideal setting to study such interactions. Its alpine landscape, preserving typical glacial features (U-shaped valleys, cirques), appears highly smoothed in the west, and progressively more rugged towards the east. In the field, this is evidenced by minor and only localized faulting of massive bedrock (granite and paragneiss) in the west, while the eastern part shows highly fractured bedrock (penetrative faults, fault gouges). Remote-sensing analysis confirms that fracture density is much higher towards east, and also reveals high post-glacial incision only in areas associated with high fracture density. To quantify our morphometric observations, we sampled four elevation profiles (~15 samples in total) over an 80-km East-West transect for low-temperature thermochrometry. Apatite (U-Th-Sm)/He dating provides ages between ~10 and 30 Ma, in agreement with published data, and shows apparent low long-term exhumation rates (~0.05-0.1 km/Ma). Preliminary 4He/3He thermochronometry data reveal a more complex exhumation history, with a significant increase since ~6-5 Ma which can be related to either onset of glaciations in Alaska or a major change in tectonic activity occurring at that period. Further data collected within the Granite Range will help to decipher the origin of this late-Miocene acceleration in exhumation. We also performed luminescence thermochronometry measured on feldspar separates from bedrock samples. Our results show a strong East-West gradient in samples saturation ratio. Apparent ages vary from ~250 ka in the western part of the range, towards younger ages of ~30 ka in the east. This pattern reveals spatially variable erosion rates during the late Quaternary associated with a major fracture-density control on erosion, and further supports the

  13. Terrestrial and submarine evidence for the extent and timing of the Last Glacial Maximum and the onset of deglaciation on the maritime-Antarctic and sub-Antarctic islands

    NASA Astrophysics Data System (ADS)

    Hodgson, Dominic A.; Graham, Alastair G. C.; Roberts, Stephen J.; Bentley, Michael J.; Cofaigh, Colm Ó.; Verleyen, Elie; Vyverman, Wim; Jomelli, Vincent; Favier, Vincent; Brunstein, Daniel; Verfaillie, Deborah; Colhoun, Eric A.; Saunders, Krystyna M.; Selkirk, Patricia M.; Mackintosh, Andrew; Hedding, David W.; Nel, Werner; Hall, Kevin; McGlone, Matt S.; Van der Putten, Nathalie; Dickens, William A.; Smith, James A.

    2014-09-01

    This paper is the maritime and sub-Antarctic contribution to the Scientific Committee for Antarctic Research (SCAR) Past Antarctic Ice Sheet Dynamics (PAIS) community Antarctic Ice Sheet reconstruction. The overarching aim for all sectors of Antarctica was to reconstruct the Last Glacial Maximum (LGM) ice sheet extent and thickness, and map the subsequent deglaciation in a series of 5000 year time slices. However, our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub-Antarctic sector. Therefore, in this paper we focus on an assessment of the terrestrial and offshore evidence for the LGM ice extent, establishing minimum ages for the onset of deglaciation, and separating evidence of deglaciation from LGM limits from those associated with later Holocene glacier fluctuations. Evidence included geomorphological descriptions of glacial landscapes, radiocarbon dated basal peat and lake sediment deposits, cosmogenic isotope ages of glacial features and molecular biological data. We propose a classification of the glacial history of the maritime and sub-Antarctic islands based on this assembled evidence. These include: (Type I) islands which accumulated little or no LGM ice; (Type II) islands with a limited LGM ice extent but evidence of extensive earlier continental shelf glaciations; (Type III) seamounts and volcanoes unlikely to have accumulated significant LGM ice cover; (Type IV) islands on shallow shelves with both terrestrial and submarine evidence of LGM (and/or earlier) ice expansion; (Type V) Islands north of the Antarctic Polar Front with terrestrial evidence of LGM ice expansion; and (Type VI) islands with no data. Finally, we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme.

  14. Reflection of global late glacial and Holocene paleoclimate oscillations in the palynological record from bottom sediments of Tavatui Lake (Middle Urals)

    NASA Astrophysics Data System (ADS)

    Maslennikova, A. V.; Udachin, V. N.; Anfilogov, V. N.; Deryagin, V. V.

    2016-06-01

    The palynological analysis of the reliably dated core section of bottom sediments from Tavatui Lake revealed consistency between the chronology and succession of Late Pleistocene and Early Pliocene events (GI-a/b, CS-1, GH-11.2) in the Middle Urals and the North Atlantic region. It is established that the Holocene thermal maximum (5.3-8.0 cal. ka ago) in the Middle Urals was characterized by high temperatures and humidity. The initial stage of the Subboreal cooling was reffered to the interval of 4.5-5.3 cal. ka ago. The data obtained provided grounds for the conclusion that the palynological record in the Tavatui Lake section reflects in detail global and regional climate oscillations, which allows it to be used as a Holocene and late glacial reference section, as well as for predicting the behavior of the natural system of the Middle Urals in response to future climate change.

  15. Oligocene sea water temperatures offshore Wilkes Land (Antarctica) indicate warm and stable glacial-interglacial variation and show no 'late Oligocene warming'

    NASA Astrophysics Data System (ADS)

    Hartman, Julian; Bijl, Peter; Peterse, Francien; Schouten, Stefan; Salabarnada, Ariadna; Bohaty, Steven; Escutia, Carlota; Brinkhuis, Henk; Sangiorgi, Francesca

    2017-04-01

    At present, warming of the waters below the Antarctic ice shelves is a major contributor to the instability of the Antarctic cryosphere. In order to get insight into future melt behavior of the Antarctic ice sheet, it is important to look at past warm periods that can serve as an analogue for the future. The Oligocene ( 34-23 Ma) is a period within the range of CO2 concentrations predicted by the latest IPCC report for the coming century and is characterized by a very dynamic Antarctic ice sheet, as suggested by benthic δ18O records from ice-distal sites. We suspect that, like today, environmental changes in the Southern Ocean are in part responsible for this dynamicity. To gain more insight into this, we have reconstructed sea water temperatures (SWT) based on Thaumarchaeotal lipids (TEX86) for the Oligocene record obtained from the ice-proximal Site U1356 (Integrated Ocean Drilling Program), offshore Wilkes Land. Part of our record shows a strong coupling between the lithology and SWT, which we attribute to glacial-interglacial variation. Our data shows that both glacial and interglacial temperatures are relatively warm throughout the Oligocene: 14°C and 18°C respectively, which is consistent with previously published estimates based on UK'37 and clumped isotopes for the early Oligocene. Our SST records show only a minor decline between 30 and 24 Ma, and thus show no evidence for a 'late Oligocene warming' as was suggested based on benthic δ18O records from low latitudes. Instead, the discrepancy between our SST trend and the δ18O trend suggests that the late-Oligocene benthic δ18O decrease is likely related to a decline in ice volume. After 24 Ma, however, glacial-interglacial temperature variation appears to increase. In particular, some large temperature drops occur, one of which can be related to the Mi-1 event and a major expansion of the Antarctic ice sheet.

  16. Bottom-current and wind-pattern changes as indicated by Late Glacial and Holocene sediments from western Lake Geneva (Switzerland)

    USGS Publications Warehouse

    Girardclos, S.; Baster, I.; Wildi, W.; Pugin, A.; Rachoud-Schneider, A. -M.

    2003-01-01

    The Late-Glacial and Holocene sedimentary history of the Hauts-Monts area (western Lake Geneva, Switzerland) is reconstructed combining high resolution seismic stratigraphy and well-dated sedimentary cores. Six reflections and seismic units are defined and represented by individual isopach maps, which are further combined to obtain a three-dimensional age-depth model. Slumps, blank areas and various geometries are identified using these seismic data. The sediment depositional areas have substantially changed throughout the lake during the end of the Late-Glacial and the Holocene. These changes are interpreted as the result of variations in the intensity of deep lake currents and the frequency of strong winds determining the distribution of sediment input from the Versoix River and from reworking of previously deposited sediments within the lacustrine basin. The identified changes in sediment distribution allowed us to reconstruct the lake's deep-current history and the evolution of dominant strong wind regimes from the Preboreal to present times.

  17. Glacial and deglacial climatic patterns in Australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near-shore proxy data

    NASA Astrophysics Data System (ADS)

    Williams, Martin; Cook, Ellyn; van der Kaars, Sander; Barrows, Tim; Shulmeister, Jamie; Kershaw, Peter

    2009-11-01

    This study forms part of a wider investigation of late Quaternary environments in the Southern Hemisphere. We here review the terrestrial and near-shore proxy data from Australia, Indonesia, Papua New Guinea (PNG), New Zealand and surrounding oceans during 35-10 ka, an interval spanning the lead-up to the Last Glacial Maximum (LGM), the LGM proper (21 ± 2 ka), and the ensuing deglaciation. Sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval, a stratigraphically consistent chronology, and one or more sources of proxy climatic data. Tropical Australia, Indonesia and PNG had LGM mean annual temperatures 3-7 °C below present values and summer precipitation reduced by at least 30%, consistent with a weaker summer monsoon and a northward displacement of the Intertropical Convergence Zone. The summer monsoon was re-established in northwest Australia by 14 ka. Precipitation in northeast Australia was reduced to less than 50% of present values until warmer and wetter conditions resumed at 17-16 ka, followed by a second warmer, wetter phase at 15-14 ka. LGM temperatures were up to 8 °C lower than today in mainland southeast Australia and up to 4 °C cooler in Tasmania. Winter rainfall was much reduced throughout much of southern Australia although periodic extreme flood events are evident in the fluvial record. Glacial advances in southeast Australia are dated to 32 ± 2.5, 19.1 ± 1.6 and 16.8 ± 1.4 ka, with periglacial activity concentrated towards 23-16 ka. Deglaciation was rapid in the Snowy Mountains, which were ice-free by 15.8 ka. Minimum effective precipitation in southern Australia was from 14 to 12 ka. In New Zealand the glacial advances date to ∼28, 21.5 and 19 ka, with the onset of major cooling at ∼28 ka, or well before the LGM. There is no convincing evidence for a Younger Dryas cooling event in or around New Zealand, but there are signs of the Antarctic Cold Reversal in and around New

  18. Simulated Trends in African Glacial and Interglacial Vegetation: Implications for Late-Pleistocene Hominid-Plant Interactions

    NASA Astrophysics Data System (ADS)

    Cowling, S. A.; Cox, P. M.; Jones, C. D.; Maslin, M. A.; Spall, S. A.

    2004-12-01

    Most theories of human evolution in south, central and eastern Africa are predicated on the assumption that savannas and grasslands almost exclusively dominated Pleistocene (glacial) landscapes. It was our aim to evaluate this assumption using a state-of-the-art fully-coupled earth system model (HadCM3LC), which we used to predict potential palaeovegetation following representative glacial and interglacial climate-forcing. Our glacial simulations indicate that tropical broadleaf forest was not severely displaced by grassland expanding into central Africa, although the outer extent of closed forest decreases, particularly in the north. Our vegetation-climate simulations also indicate that the extent of closed tropical forest during typical interglacials is not represented by today's observed vegetation distributions. Simulated interglacial climate results in expansion of tropical forest from coast-to-coast across much of central Africa. Our modelling experiments have implications for interpreting biogeography and phylogenies of various African plant and animal species, including the evolution of our own species, Homo sapiens sapiens.

  19. On the Timing and Forcing Mechanisms of Late Pleistocene Glacial Terminations: Insights from a New High-Resolution Benthic Stable Oxygen Isotope Record of the Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Lourens, L. J.; Konijnendijk, T.; Ziegler, M.

    2015-12-01

    We present the first long (~1.2 Ma) benthic oxygen isotope record from the eastern Mediterranean, based on ODP Sites 967 and 968, which clearly reflects the behavior of global climate on a glacial-interglacial scale. The age model for our record is based on tuning the elemental ratio of titanium versus aluminum (Ti/Al) against insolation. The Ti/Al record is dominated by the precession-related changes in northern African climate, i.e. monsoonal forcing, and hence largely independent of glacial-interglacial variability. We found the largest offset between our chronology and that of the widely applied, open ocean stacked record LR04 (Lisiecki and Raymo, 2005) for TVII (~624 ka), which occurred ~9 kyr earlier according to our estimates, though in agreement with the AICC2012 δDice chronology of EPICA Dome C (Bazin et al., 2013). Spectral cross-correlation analysis between our benthic δ18O record and 65°N summer insolation reveals significant amounts of power in the obliquity and precession range, with an average lag of 5.5±0.8 kyr for obliquity, and 6.0±1.0 kyr for precession. In addition, our results show that the obliquity-related time lag was smaller (3.0±3.3 kyr) prior to ~900 ka than after (5.7±1.1 kyr), suggesting that on average the glacial response time to obliquity forcing increased during the mid-Pleistocene transition, much later than assumed by Lisiecki and Raymo (2005). Finally, we found that almost all glacial terminations have a consistent phase relationship of ~45±45 degrees with respect to the precession and obliquity-driven increases in 65°N summer insolation, consistent with the general consensus that both obliquity and precession are important for deglaciation during the Late Pleistocene. Exceptions are glacial terminations TIIIb, T36 and potentially T32 (and TVII T24 and T34), which show this consistent phase relationship only with precession (only with obliquity). Our findings point towards an early (>1200 ka) onset of the Mid Pleistocene

  20. Late glacial to Holocene climatic and oceanographic record of sediment facies from the South Scotia Sea off the northern Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Yoon, H. I.; Khim, B. K.; Yoo, K.-C.; Bak, Y. S.; Lee, J. I.

    2007-10-01

    Two gravity cores were collected from the South Scotia Sea located off the northern Antarctic Peninsula during the 2002/2003 Korea Antarctic Research Program (KARP) expedition to determine the late Quaternary climatic and oceanographic history. Reassessment of previous sedimentological, geochemical and micropaleontological analyses combined with established age model of AMS 14C dates represent the reliable record of late Pleistocene climatic/oceanographic change for the Scotia Sea region of Antarctica. During the Last Glacial Maximum (LGM), the South Scotia Sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated Weddell Sea continental margin. Drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area. The bottom current deposits during the glacial phase comprise two lithologic units: (1) bioturbated gravelly sandy mud (Facies 1), formed by sluggish bottom current caused by reduced dense-water production originated from the ice sheet on the Weddell Shelf, (2) indistinctly layered diatomaceous mud as shown by total organic carbon (TOC) highs in the Facies 1, deposited by sporadic bottom currents caused by intensified sea-ice formation in polynya during the glacial stage. The LGM is characterized by greater and longer sea-ice coverage and a restricted Weddell/Scotia summer communication, as evidenced by a relative decrease in percentage Thalssiosira antarctica and Chaetoceros resting spores, which are more abundant close to the Weddell Ice Shelf. Deglaciation (about 13,000-9000 14C yr BP) in the South Scotia Sea was characterized by increasing TOC, diatom abundance, and decreasing magnetic susceptibility and sand contents up core. At this time, subglacial meltwater streams began to emanate from the Weddell Ice Sheet with peak of ice rafting. Sediment-laden turbid plumes from melting glacier and deglaciated Weddell

  1. Terrestrial cosmogenic surface exposure dating of glacial and associated landforms in the Ruby Mountains-East Humboldt Range of central Nevada and along the northeastern flank of the Sierra Nevada

    USGS Publications Warehouse

    Wesnousky, Steven G.; Briggs, Richard; Caffee, Marc W.; Ryerson, Rick J.; Finkel, Robert C.; Owen, Lewis A.

    2016-01-01

    Deposits near Lamoille in the Ruby Mountains-East Humboldt Range of central Nevada and at Woodfords on the eastern edge of the Sierra Nevada each record two distinct glacial advances. We compare independent assessments of terrestrial cosmogenic nuclide (TCN) surface exposure ages for glacial deposits that we have determined to those obtained by others at the two sites. At each site, TCN ages of boulders on moraines of the younger advance are between 15 and 30 ka and may be associated with marine oxygen isotope stage (MIS) 2. At Woodfords, TCN ages of boulders on the moraine of the older advance are younger than ~ 60 ka and possibly formed during MIS 4, whereas boulders on the correlative outwash surface show ages approaching 140 ka (~ MIS 6). The TCN ages of boulders on older glacial moraine at Woodfords thus appear to severely underestimate the true age of the glacial advance responsible for the deposit. The same is possibly true at Lamoille where clasts sampled from the moraine of the oldest advance have ages ranging between 20 and 40 ka with a single outlier age of ~ 80 ka. The underestimations are attributed to the degradation and denudation of older moraine crests. Noting that boulder ages on the older advances at each site overlap significantly with MIS 2. We speculate that erosion of the older moraines has been episodic, with a pulse of denudation accompanying the inception of MIS 2 glaciation.

  2. Terrestrial cosmogenic surface exposure dating of glacial and associated landforms in the Ruby Mountains-East Humboldt Range of central Nevada and along the northeastern flank of the Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Wesnousky, Steven G.; Briggs, Richard W.; Caffee, Marc W.; Ryerson, F. J.; Finkel, Robert C.; Owen, Lewis A.

    2016-09-01

    Deposits near Lamoille in the Ruby Mountains-East Humboldt Range of central Nevada and at Woodfords on the eastern edge of the Sierra Nevada each record two distinct glacial advances. We compare independent assessments of terrestrial cosmogenic nuclide (TCN) surface exposure ages for glacial deposits that we have determined to those obtained by others at the two sites. At each site, TCN ages of boulders on moraines of the younger advance are between 15 and 30 ka and may be associated with marine oxygen isotope stage (MIS) 2. At Woodfords, TCN ages of boulders on the moraine of the older advance are younger than ~ 60 ka and possibly formed during MIS 4, whereas boulders on the correlative outwash surface show ages approaching 140 ka (~ MIS 6). The TCN ages of boulders on older glacial moraine at Woodfords thus appear to severely underestimate the true age of the glacial advance responsible for the deposit. The same is possibly true at Lamoille where clasts sampled from the moraine of the oldest advance have ages ranging between 20 and 40 ka with a single outlier age of ~ 80 ka. The underestimations are attributed to the degradation and denudation of older moraine crests. Noting that boulder ages on the older advances at each site overlap significantly with MIS 2. We speculate that erosion of the older moraines has been episodic, with a pulse of denudation accompanying the inception of MIS 2 glaciation.

  3. Soil stratigraphy and plant soil interactions on a Late Glacial Holocene fluvial terrace sequence, Sierra Nevada National Park, northern Venezuelan Andes

    NASA Astrophysics Data System (ADS)

    Mahaney, William C.; Dirszowsky, Randy W.; Milner, Michael W.; Harmsen, Rudolf; Finkelstein, Sarah A.; Kalm, Volli; Bezada, Maximilano; Hancock, R. G. V.

    2007-01-01

    Analysis of a flight of alluvial terraces in the Sierra Nevada National Park near Pico Mucuñuque in the Eastern Mérida Andes has yielded information on geomorphic, pedogenic, and vegetational changes from Late Glacial time to the present. The terraces formed in large part due to stream incision/migration triggered by neotectonic uplift (>7000 yr BP) of a Late Glacial/Early Holocene glaciolacustrine lithosequence and, with the exception of the oldest/highest terrace, exhibit near-uniform lithology/parent materials. Soils developed in the terrace materials range from thin, weakly developed profiles (O/C/Cu horizons) to Entisols with O/Ah/Cox/Cu horizons and similar buried counterparts representing former short periods of floodplain stability or slow aggradation. The buried soils provide organic-rich material that yields radiocarbon ages, which provide time constraints on individual pedons and the geomorphic development of the site. Iron and aluminum extracts of soil matrix material provide information on the formation and accumulation of goethite and hematite, the relative accumulation of ferrihydrite (gain/loss), and the downward translocation of organically complexed Al as a function of soil development and age. SEM analysis of heavy mineral grains indicates varying material sources and degrees of weathering in the soil chronosequence. A qualitative study of plant functional types across the terrace sequence shows that older surfaces support greater plant diversity. The study also suggests ways in which the plant communities influence soil development at the site through varying organic matter inputs and varying soil moisture use by specific species (e.g., ferns on the oldest terrace), which may explain the absence of B horizons in the Late Pleistocene/Early Holocene soils.

  4. Terrestrial biome distribution in the Late Neogene inferred from a black carbon record in the northeastern equatorial Pacific

    PubMed Central

    Kim, Donghyun; Lee, Yong Il; Hyeong, Kiseong; Yoo, Chan Min

    2016-01-01

    The appearance and expansion of C4 plants in the Late Cenozoic was a dramatic example of terrestrial ecological change. The fire hypothesis, which suggests fire as a major cause of C4 grassland is gaining support, yet a more detailed relationship between fire and vegetation-type change remains unresolved. We report the content and stable carbon isotope record of black carbon (BC) in a sediment core retrieved from the northeastern equatorial Pacific that covers the past 14.3 million years. The content record of BC suggests the development process of a flammable ecosystem. The stable carbon isotope record of BC reveals the existence of the Late Miocene C4 expansion, the ‘C4 maximum period of burned biomass’ during the Pliocene to Early Pleistocene, and the collapse of the C4 in the Late Pleistocene. Records showing the initial expansion of C4 plants after large fire support the role of fire as a destructive agent of C3-dominated forest, yet the weak relationships between fire and vegetation after initial expansion suggest that environmental advantages for C4 plants were necessary to maintain the development of C4 plants during the late Neogene. Among the various environmental factors, aridity is likely most influential in C4 expansion. PMID:27604853

  5. Terrestrial biome distribution in the Late Neogene inferred from a black carbon record in the northeastern equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Kim, Donghyun; Lee, Yong Il; Hyeong, Kiseong; Yoo, Chan Min

    2016-09-01

    The appearance and expansion of C4 plants in the Late Cenozoic was a dramatic example of terrestrial ecological change. The fire hypothesis, which suggests fire as a major cause of C4 grassland is gaining support, yet a more detailed relationship between fire and vegetation-type change remains unresolved. We report the content and stable carbon isotope record of black carbon (BC) in a sediment core retrieved from the northeastern equatorial Pacific that covers the past 14.3 million years. The content record of BC suggests the development process of a flammable ecosystem. The stable carbon isotope record of BC reveals the existence of the Late Miocene C4 expansion, the ‘C4 maximum period of burned biomass’ during the Pliocene to Early Pleistocene, and the collapse of the C4 in the Late Pleistocene. Records showing the initial expansion of C4 plants after large fire support the role of fire as a destructive agent of C3-dominated forest, yet the weak relationships between fire and vegetation after initial expansion suggest that environmental advantages for C4 plants were necessary to maintain the development of C4 plants during the late Neogene. Among the various environmental factors, aridity is likely most influential in C4 expansion.

  6. Systematic Uncertainties of Glacial Chronologies Based on Surface Exposure Dating

    NASA Astrophysics Data System (ADS)

    Ilgner, J.; Zech, R.; Baechtiger, C.; Kubik, P. W.; Veit, H.

    2008-12-01

    Surface exposure dating using terrestrial cosmogenic nuclides provides the opportunity to establish glacial chronologies in semi-arid high mountain regions, where the lack of organic material for radiocarbon dating has limited our knowledge about the timing and the causes of glacial advances so far. However, several scaling systems and calculation schemes exist. This can result in significant systematic uncertainties, particularly at high altitudes as e.g. in the Central Andes. We present and discuss previously published exposure ages from Bolivia and Argentina in order to illustrate the extent of the current uncertainties. It is neither possible to unambiguously determine whether the local Last Glacial Maximum (local LGM) in the tropics occurred in-phase with or predated the global LGM, nor can the subsequent Late Glacial stages be dated accurately enough to infer temperature or precipitation changes at millennial-scale timescales. We then also present new results from the Tres Lagunas in the Sierra de Santa Victoria, NW Argentina. There we can compare our glacial exposure age chronology with bracketing radiocarbon ages from lake sediments. The Tres Lagunas may thus serve as a high-altitude calibration site for 10Be dating. Paleoclimatically, we conclude that glacial deposits in NW-Argentina document glacial advances in-phase with the global LGM, but that the prominent moraines there date to the Late Glacial. This coincides with the well-documented intensification and/or southward shift of the tropical circulation and reflects the strong precipitation-sensitivity of glaciers in arid and semi-arid environments.

  7. The potential of the latest developments in terrestrial laser scanning technologies for monitoring and investigating periglacial and glacial processes in Alpine environments

    NASA Astrophysics Data System (ADS)

    Micheletti, Natan; Gabbud, Chrystelle; Maxime, Capt; Lambiel, Christophe; Lane, Stuart

    2014-05-01

    Three-dimensional data obtained using Light Detection And Raging (LiDAR) methods are a valuable resource for many geosciences studies, as proven by the rapid growth of LiDAR applications for monitoring processes shaping the Earth's surface. The analysis of LiDAR data is particularly attractive for geomorphologists as it offers the opportunity to measure surface topography and monitor morphological changes at resolutions not previously possible. The derived three-dimensional data not only enable geomorphological investigations at unprecedented spatial resolutions with fast measurement acquisition, but also allows for repeated surveys where high temporal resolution is required. Accordingly, the potential of LiDAR techniques grants the detection of morphological changes in landforms at centimeter scale even at very short temporal scale. Nevertheless, laser-derived data remain subject to a number of issues that will generate errors in the resulting point cloud if left unchecked. Moreover, in glacial and periglacial environments, there are significant limits in LiDAR application because at the wavelengths typical of most LiDAR systems, ice and snow cover absorbs rather than reflects the laser signal. With this in mind, in 2012 RIEGL announced the new Terrestrial Laser Scanner VZ-6000. This high-speed (up to 222,000 meas./sec), high-accuracy device offers ultra-long measurement range of more than 6,000 m for static applications, allowing easier survey of larger zones than previous TLS devices. In addition, due to its laser wavelength, it is particularly well suited for measuring snowy and icy terrain (RIEGL, 2013). In the present contribution we test the potential of this device for monitoring morphological changes in a Swiss Alpine setting, where the landscape comprises a complex set of surface types, and hence reflectors. The characteristics of the VZ-6000 device together with the efficiency of the associated software allows for the generation of precise 3D models of

  8. Late Holocene glacial history of the Copper River Delta, coastal south-central Alaska, and controls on valley glacier fluctuations

    NASA Astrophysics Data System (ADS)

    Barclay, David J.; Yager, Elowyn M.; Graves, Jason; Kloczko, Michael; Calkin, Parker E.

    2013-12-01

    Fluctuations of four valley glaciers in coastal south-central Alaska are reconstructed for the past two millennia. Tree-ring crossdates on 216 glacially killed stumps and logs provide the primary age control, and are integrated with glacial stratigraphy, ages of living trees on extant landforms, and historic forefield photographs to constrain former ice margin positions. Sheridan Glacier shows four distinct phases of advance: in the 530s to c.640s in the First Millennium A.D., and the 1240s to 1280s, 1510s to 1700s, and c.1810s to 1860s during the Little Ice Age (LIA). The latter two LIA advances are also recorded on the forefields of nearby Scott, Sherman and Saddlebag glaciers. Comparison of the Sheridan record with other two-millennia long tree-ring constrained valley glacier histories from south-central Alaska and Switzerland shows the same four intervals of advance. These expansions were coeval with decreases in insolation, supporting solar irradiance as the primary pacemaker for centennial-scale fluctuations of mid-latitude valley glaciers prior to the 20th century. Volcanic aerosols, coupled atmospheric-oceanic systems, and local glacier-specific effects may be important to glacier fluctuations as supplemental forcing factors, for causing decadal-scale differences between regions, and as a climatic filter affecting the magnitude of advances.

  9. High resolution dating of moraines on Kodiak Island, Alaska links Atlantic and North Pacific climatic changes during the late glacial

    SciTech Connect

    Mann, D.H. . Alaska Quaternary Center)

    1992-01-01

    Much less is known about the paleoclimate and paleoceanography of the North Pacific than the North Atlantic despite the North Pacific's important role in the global ocean-climate system. Kodiak Island lies in the northwestern Gulf of Alaska astride the eastern end of the Aleutian Low. On southwestern Kodiak Island, coastal bluffs section a series of moraines, kettle ponds, and bogs formed between 15 and 9 ka BP. Distinctive tephras from volcanoes on the Alaska Peninsula provide time-lines within the stratigraphy. Deformation events recorded in sediment stacks from basins within glaciotectonic landforms allows precise dating of glacial events. An ice cap occupied the Kodiak archipelago during the last glaciation. Three glacial advances of the southwestern margin of this ice cap occurred after 15 ka BP. At 13.4 ka, piedmont ice lobes formed large push moraines extending into Shelikof Strait during the Low Cape Advance. The less-extensive Tundra Advance culminated between 12 and 11.7 ka BP followed by glacier retreat then readvance to form the prominent Olga Moraine system between 11 and 10 ka BP. The timing of the Tundra and Olga Advances correlates closely with that of the Older and Younger Dryas cold episodes in northwestern Europe suggesting that these climatic oscillations were synchronous throughout the northern hemisphere.

  10. Late-glacial to Early Holocene lake basin and river valley formation within Pomeranian moraine belt near Dobbertin (Mecklenburg-Vorpommern, NE Germany)

    NASA Astrophysics Data System (ADS)

    Zawiska, Izabela; Lorenz, Sebastian; Börner, Andreas; Niessner, Dominique; Słowiński, Michał; Theuerkauf, Martin; Pieper, Hagen; Lampe, Reinhard

    2014-05-01

    In central Mecklenburg-Vorpommern vast areas between the terminal moraine belts of the Frankfurt (W1F) and Pomeranian Phase (W2) were covered by glaciolacustrine basins which were embedded in the outwash plains. With deglaciation of the Pomeranian Phase around 17-18 ka BP the basins north to the villages Dobbertin and Dobbin were part of a glaciofluvial river system in combination with ice-dammed lake basins. During the late-glacial after ~14 ka cal BP the melting of buried dead ice reshaped the lake basin morphology by new depressions, in- and outlets. We study late-glacial basin and landscape development using cores collected along a pipeline trench crossing the Dobbin-Dobbertin basin. Core analysis includes sedimentological (carbon content, grainsize distribution) and palaeoecological (pollen, plant macrofossils, Cladocera) proxies. Radiocarbon dates indicate that peat formation started soon after the start of the Weichselian late-glacial. High resolution analysis of a basal peat layer indicates that initial organic and lacustrine sedimentation started in shallow ponding mires, evolving from buried dead ice sinks in the glaciofluvial sequence, in which telmatic plants (Carex aquatilis, Schoenoplectus lacustris) dominated. Chydorus sphaericus, the only cladocera species recorded, is ubiquitous and can survive in almost all reservoir types in very harsh conditions. Findings of Characeae than point at the formation of shallow lakes. The expansion of rich fen communities, including Scorpidium scorpoides, and a decline in Cladocera diversity show that these lakes soon again terrestrialised with peat formation. The appearance of Alona costata points at a lowering of pH values in that process. A tree trunk of birch (14.2 ka cal. BP) shows that first trees established during this first telmatic period. At this position in the basin, the basal peat layer is covered by minerogenic sediments, which points at a period of higher water levels and fluvial dynamics, possibly

  11. Geomorphological evolution of Mediterranean enclosed depressions in the Late glacial and Holocene: The example of Canohès (Roussillon, SE France)

    NASA Astrophysics Data System (ADS)

    Carozza, Jean-Michel; Llubes, Muriel; Danu, Mihaela; Faure, Elodie; Carozza, Laurent; David, Mélodie; Manen, Claire

    2016-11-01

    The origin and evolution of the enclosed depressions (pans) of southern France during the period from the Late Glacial to the Holocene are discussed on the basis of new stratigraphical, geophysical and chronological (14C) data from the Canohès depression (Roussillon, Southern of France) and its nearby environment. The Canohès depression is non-karstic, excavated from Pliocene arkosic sands that were shaped by eolian erosion during cold stages of the Middle and Upper Pleistocene. The timing and controlling factors of eolian carving of the depression are discussed on the basis of geomorphological data, surrounding alluvial terrace chronology, preserved ledge within the depression and alluvial infill of the depression. Formation of the depression was controlled, locally, by climate variability and its consequences on vegetation and water table position and, regionally, by the sea base level. The enclosed depression probably started to form during MIS 6, reaching its maximum depth during MIS 2. Climate variability in the region is recorded in the depression's infill. The basal deposits are of fluvial origin and record the increase of moisture and temperature during the Early Late-Glacial. The first lacustrine deposits are observed during the Bölling/GI-1e stage, while continental sedimentation and drying occurred during the Alleröd and Younger Dryas stages. During the Early and Middle Holocene, lacustrine conditions prevailed, except during short periods of drying. The specific evolution of the Canohès depression as regards other such formations is discussed in light of regional deglaciation and climate chronology. A regional synthesis of eolian erosion is proposed.

  12. Evolution of habitat and environment of deer during the Late-glacial and early Holocene: the case of red deer in French Jura.

    NASA Astrophysics Data System (ADS)

    Drucker, Dorothée.; Bridault, Anne; Hujic, Alisa; Bocherens, Hervé

    2010-05-01

    The Late-glacial and early Holocene transition is a key period of environmental changes in a context of to a global warming. In northwestern Europe, extensive studies have documented the vegetation and faunal recomposition with the replacement of the cold steppe-tundra ecosystem by the forested temperate ecosystem we can still observe. Paleoecological interest focused on the extinct large mammals species like the Mammoth. In comparison, little has been done to decipher the ecological adaptation of the surviving species, especially those that are still present in the very same region than in the past. A better knowledge of the impact of changing environmental conditions on the ecology would be useful to define the degree of selective pressure. Thus, we have studied the habitat and environment evolution of red deer (Cervus elaphus) during the Late-glacial and early Holocene using stable isotopes and radiocarbon investigations. The analyzed bone material was selected from archaeological sites in French Jura. Performing direct radiocarbon dating on the bone collagen of the selected remains solved the problem of possible chronological uncertainties of the stratigraphical record of the sites. The same bone collagen samples were used for stable isotope measurements. We investigated the relative abundances in 13C to examine changes in habitat closure (canopy effect), in 15N to decipher changes in pedogenic activities (soil maturation) of the animals dwelling, and in 18O to track changes in altitude and/or local temperatures of the occupied territories. The results demonstrate that the stable isotopic composition of red deer bone collagen can be a valuable and sensitive indicator of habitat use and environmental conditions. The associated direct dating allows us to reconstruct the chronology of ecological changes. The combined chronological and ecological results evidence local differences in red deer adaptation at a small geographical scale.

  13. Late Holocene glacial history of Petermann Fjord, Northwest Greenland: Non-destructive CT, XRF, and magnetic results from OD1507 sediment cores

    NASA Astrophysics Data System (ADS)

    Reilly, B. T.; Stoner, J. S.; Mix, A. C.; Jakobsson, M.; Jennings, A. E.; Walczak, M.; Dyke, L. M.; Cheseby, M.; Albert, S. W.; Wiest, J.

    2016-12-01

    An international and interdisciplinary expedition to Nares Strait and Petermann Fjord, Northwest Greenland, onboard the Swedish Icebreaker Oden July-September 2015 (OD1507) sought to understand the Holocene history of the Petermann glacial system among other research objectives. Petermann Glacier, which terminates as a floating ice-tongue in Petermann Fjord, is thought to be especially sensitive to ice-ocean interactions. While limited historical observations dating back to 1876 suggest the Petermann Ice Tongue extends about 70-90 km from the grounding-line, large calving events in 2010 and 2012 reduced the ice-tongue extent to about 45 km from the grounding-line. A suite of 14 marine sediment cores recovered a range of glacio-marine facies that form an along fjord (15-80 km from the grounding-line) and an across fjord depth (473-1041 meters water depth) transect. CT scans clearly identify four primary fjord facies, including bioturbated, IRD-rich, laminated and mud with stratified graded sand layers. The latter of these occurs near the modern grounding-line. Additionally, a new MATLAB routine is used to quantify clasts >2 mm in size from the CT scans. XRF sediment geochemical changes mirror magnetic mineral concentrations and are driven by varying contribution of Ca-rich and Ca-poor sources, which we interpret as a reflection of the mixing of the local carbonate rocks and crystalline basement excavated by the ice sheet. Initial paleomagnetic results isolate a strong and stable characteristic remanent magnetization which show remarkable similarity to paleosecular variation (PSV) recorded in nearby mid-late Holocene varved lakes on Ellesmere Island. This non-destructive dataset provides robust correlations, indicating a coherent and dynamic record of changes in the Petermann glacial system during the late Holocene, including evidence for a significant grounding-line retreat followed by the growth and relative paleo-extent of the modern Petermann Ice Tongue.

  14. Linking Late Pleistocene alpine glacial erosion and continental margin sedimentation: Insights from 40Ar/39Ar dating of silt-sized sediment, Canterbury Basin, New Zealand

    NASA Astrophysics Data System (ADS)

    Villaseñor, Tania; Jaeger, John M.; Foster, David A.

    2016-01-01

    Quaternary climatic and eustatic cycles in mid-latitude regions have led to more extensive alpine glaciations and continental shelf progradation, respectively. However, the glacial influence on sediment fluxes to the ocean creating continental margin strata is poorly documented. This contribution analyzes the provenance of fine sediment accumulating on the continental shelf during the Late Pleistocene to evaluate the influence of glacial cycles on sediment erosion and routing to the continental shelf. Taking advantage of the contrasting bedrock ages exposed across the Southern Alps, New Zealand, we perform 40Ar/39Ar incremental heating on the bulk silt-size sediment from three drill sites of IODP Expedition 317, Canterbury Basin, New Zealand. The results suggest that a large proportion of sediment accumulating on the continental shelf results from erosion within the Main Divide fault zone of the Southern Alps. Sediment 40Ar/39Ar age fluctuations over this time period suggest that bedrock with various 40Ar/39Ar cooling ages has been differentially eroded in the upper Waitaki River catchment and mixed in the Waitaki-Canterbury sediment-routing system. Across-shelf variations in sediment 40Ar/39Ar age reflect changing modes of sediment dispersal on the continental shelf. Fluvial material, likely derived from the main drainage divide zone, preferentially accumulates in the middle continental shelf, whereas material representing erosion of older bedrock (Torlesse Terrane), located lower in the drainage basin, is dispersed uniformly across the shelf. The age signature of the muddy sediment accumulating on the continental shelf reflects Late Pleistocene landscape evolution of the Southern Alps and its influence on sediment dispersal to the continental shelf.

  15. Sediment production and transport in the New Zealand Southern Alps - Canterbury sedimentary system during the Late Pleistocene: the influence of alpine glacial erosion on the marine stratigraphic record.

    NASA Astrophysics Data System (ADS)

    Villaseñor, T. G.; Jaeger, J. M.; Foster, D. A.

    2014-12-01

    Quaternary mountain glaciations have greatly modified landscape and sediment production, especially after the Mid Pleistocene Transition. However, the impact of increased glacigenic sediment yields on continental margin sedimentation is poorly documented during this period in which eustasy is proposed as the dominant control on margin development. We study the provenance of sediment accumulated in the continental shelf during the Late Pleistocene, by performing 40Ar/39Ar geochronology of the bulk silt-size fraction on sediment samples from three sites drilled during IODP Expedition 317 to Canterbury Basin, New Zealand. The results show ages that range from 25 to 90 Ma, which are significantly younger than the cooling ages of the potential rock sources (>100 Ma). Bedrock cooling ages similar to our results are found adjacent to the Main Divide Fault Zone, located near the main drainage divide in Central Southern Alps. This suggests that a large proportion of sediment accumulating in the continental shelf is sourced in this region of highest elevation and maximum glacial erosion. Sediment bulk ages in the cores show younger ages up-section, suggesting that contribution of young sediment has increased and/or that glaciers have eroded younger rocks with time. In addition, sediment ages are younger in the most landward site, while the most offshore site observes young ages later indicating that the input of young sediment across the continental shelf is progressive, likely by means of sediment reworking during sea level transgression and shoreline migration during sea level fall. We propose that sediment transfer from source to sink occurs in steps in which sediment undergoes several cycles of transport and storage until final accumulation. Glacial erosion plays a very important role in this sedimentary system, supplying sediment that is likely eroded in a zone of rock weakness. The age signature of the muddy sediment accumulating in the continental shelf likely

  16. The late-glacial fluvial terrace t7 at Raunheim (lower River Main), Germany. Constraining the chronological placement by optical stimulated luminescence dating.

    NASA Astrophysics Data System (ADS)

    Thiemeyer, Heinrich; Kadereit, Annette; Zipf, Lars; Flettner, Stephan

    2017-04-01

    The lower River Main valley exhibits up to seven fluvial terrace levels (t1 - t7, according to the stratigraphy of Semmel 1969). The lowermost terrace (t7) represents the most recently formed level which due to stratigraphical considerations is assumed to be of Late Pleistocene age (Semmel 1969). However, the chronological placement of the terrace has not been determined by numerical dating so far. The area was apparently roamed by Late Palaeolithic people as evidenced by artefacts which were discovered on a former sandy river bank between 87 m and 91 m above sea level on top of the t7 east of the town of Raunheim. We took this opportunity to open four trenches in order to localize additional in situ Palaeolithic artefacts and to investigate the stratigraphy of the sediments and soils and, for the first time, to provide numerical ages in order to narrow down the period of the t7 activity. Eight samples from three profiles in three of the trenches were collected for optical stimulated (OSL) dating. OSL dating occurred applying a blue light stimulated luminescence (BLSL) single aliquot regeneration (SAR) protocol (Murray & Wintle 2000) to small aliquots (few 102 grains) of quartz coarse grain separates (125 - 212 µm). The trenches showed that the t7 sediments consist of fluvial sand over gravel. They are overlain by calcareous loamy and sandy overbank deposits. At the investigated site the Holocene Cambisol at the surface passes into a Gleysol that has developed in a palaeochannel which is incised into the t7. The trenches revealed further that only parts of the Late Palaeolithic site are in situ and therefore contemporaneous with the fluvial sediments beneath the Cambisol. The upper part of the sections consists of colluvial deposits lying on truncated Cambisols. The OSL dating places the section into the period spanning the last glacial maximum (LGM) / late glacial to the late Holocene. The oldest investigated fluvial t7 sediments date around 24.7 ka. Slightly

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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

  18. On the timing and forcing mechanisms of late Pleistocene glacial terminations: Insights from a new high-resolution benthic stable oxygen isotope record of the eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Konijnendijk, T. Y. M.; Ziegler, M.; Lourens, L. J.

    2015-12-01

    Benthic oxygen isotope records of deep marine sedimentary archives have yielded a wealth of information regarding ice sheet dynamics and climate change during the Pleistocene. However, since they often lack independent age control, these records are generally bound by a fixed phase relationship between orbital forcing and the climate response, e.g. ice volume changes. We present the first long (∼1.2 Ma) benthic oxygen isotope record from the eastern Mediterranean, based on ODP Sites 967 and 968, which clearly reflects the behavior of global climate on a glacial-interglacial scale throughout the late Pleistocene time period. The age model for our record is based on tuning the elemental ratio of titanium versus aluminum (Ti/Al) against insolation. The Ti/Al record is dominated by the precession-related changes in northern African climate, i.e. monsoonal forcing, and hence largely independent of glacial-interglacial variability. We found the largest offset between our chronology and that of the widely applied, open ocean stacked record LR04 (Lisiecki and Raymo, 2005) for TVII (∼624 ka), which occurred ∼9 kyr earlier according to our estimates, though in agreement with the AICC2012 δDice chronology of EPICA Dome C (Bazin et al., 2013). Spectral cross-correlation analysis between our benthic δ18O record and 65°N summer insolation reveals significant amounts of power in the obliquity and precession range, with an average lag of 5.5 ± 0.8 kyr for obliquity, and 6.0 ± 1.0 kyr for precession. In addition, our results show that the obliquity-related time lag was smaller (3.0 ± 3.3 kyr) prior to ∼900 ka than after (5.7 ± 1.1 kyr), suggesting that on average the glacial response time to obliquity forcing increased during the mid-Pleistocene transition, much later than assumed by Lisiecki and Raymo (2005). Finally, we found that almost all glacial terminations have a consistent phase relationship of ∼45 ± 45° with respect to the precession and obliquity

  19. Turbidite megabeds in an Oceanic Rift Valley recording jokulhlaups of late Pleistocene glacial lakes of the western United States

    USGS Publications Warehouse

    Zuffa, G.G.; Normark, W.R.; Serra, F.; Brunner, C.A.

    2000-01-01

    Escanaba Trough is the southernmost segment of the Gorda Ridge and is filled by sandy turbidites locally exceeding 500 m in thickness. New results from Ocean Drilling Program (ODP) Sites 1037 and 1038 that include accelerator mass spectrometry (AMS) 14C dates and revised petrographic evaluation of the sediment provenance, combined with high-resolution seismic-reflection profiles, provide a lithostratigraphic framework for the turbidite deposits. Three fining-upward units of sandy turbidites from the upper 365 m at ODP Site 1037 can be correlated with sediment recovered at ODP Site 1038 and Deep Sea Drilling Program (DSDP) Site 35. Six AMS 14C ages in the upper 317 m of the sequence at Site 1037 indicate that average deposition rates exceeded 10 m/k.yr. between 32 and 11 ka, with nearly instantaneous deposition of one ~60-m interval of sand. Petrography of the sand beds is consistent with a Columbia River source for the entire sedimentary sequence in Escanaba Trough. High-resolution acoustic stratigraphy shows that the turbidites in the upper 60 m at Site 1037 provide a characteristic sequence of key reflectors that occurs across the floor of the entire Escanaba Trough. Recent mapping of turbidite systems in the northeast Pacific Ocean suggests that the turbidity currents reached the Escanaba Trough along an 1100-km-long pathway from the Columbia River to the west flank of the Gorda Ridge. The age of the upper fining-upward unit of sandy turbidites appears to correspond to the latest Wisconsinan outburst of glacial Lake Missoula. Many of the outbursts, or jokulhlaups, from the glacial lakes probably continued flowing as hyperpycnally generated turbidity currents on entering the sea at the mouth of the Columbia River.

  20. Late glacial to Holocene water level and climate changes in the Gulf of Gemlik, Sea of Marmara: evidence from multi-proxy data

    NASA Astrophysics Data System (ADS)

    Filikci, Betül; Eriş, Kürşad Kadir; Çağatay, Namık; Sabuncu, Asen; Polonia, Alina

    2017-10-01

    Multi-proxy analyses of new piston core M13-08 together with seismic data from the Gulf of Gemlik provide a detailed record of paleoceanographic and paleoclimatic changes with special emphasis on the timing of the connections between the Sea of Marmara (SoM) and the Gulf of Gemlik during the late Pleistocene to Holocene. The deposition of a subaqueous delta sourced from the Armutlu River to the north is attributed to the lowstand lake level at -60 m in the gulf prior to 13.5 cal ka BP. On the basis of the seismic data, it is argued that the higher lake level (-60 m) in the gulf compared to the SoM level (-85 m) attests to its disconnection from the SoM during the late glacial period. Ponto-Caspian assemblages in the lacustrine sedimentary unit covering the time period between 13.5 and 12 cal ka BP represent a relict that was introduced into the gulf by a Black Sea outflow during the marine isotope stage 3 interstadial. Contrary to the findings of previous studies, the data suggest that such an outflow into the Gulf of Gemlik during the late glacial period could have occurred only if the SoM lake level (-85 m) was shallower than the sill depth (-55 m) of the gulf in the west. A robust age model of the core indicates the connection of the gulf with the marine SoM at 12 cal ka BP, consistent with the sill depth (-55 m) of the gulf on the global sea level curve. Strong evidence of a marine incursion into the gulf is well documented by the μ-XRF Sr/Ca data. The available profiles of elemental ratios in core M13-08, together with the age-depth model, imply that a warm and wet climate prevailed in the gulf during the early Holocene (12-10.1 cal ka BP), whereas the longest drought occurred during the middle Holocene (8.2-5.4 cal ka BP). The base of the main Holocene sapropel in the gulf is dated at 10.1 cal ka BP, i.e., 500 years younger than its equivalent in the SoM. The late Holocene is earmarked by warm and wet climate periods (5.0-4.2 and 4.2-2.7 cal ka BP) with some

  1. Late glacial to Holocene water level and climate changes in the Gulf of Gemlik, Sea of Marmara: evidence from multi-proxy data

    NASA Astrophysics Data System (ADS)

    Filikci, Betül; Eriş, Kürşad Kadir; Çağatay, Namık; Sabuncu, Asen; Polonia, Alina

    2017-02-01

    Multi-proxy analyses of new piston core M13-08 together with seismic data from the Gulf of Gemlik provide a detailed record of paleoceanographic and paleoclimatic changes with special emphasis on the timing of the connections between the Sea of Marmara (SoM) and the Gulf of Gemlik during the late Pleistocene to Holocene. The deposition of a subaqueous delta sourced from the Armutlu River to the north is attributed to the lowstand lake level at -60 m in the gulf prior to 13.5 cal ka BP. On the basis of the seismic data, it is argued that the higher lake level (-60 m) in the gulf compared to the SoM level (-85 m) attests to its disconnection from the SoM during the late glacial period. Ponto-Caspian assemblages in the lacustrine sedimentary unit covering the time period between 13.5 and 12 cal ka BP represent a relict that was introduced into the gulf by a Black Sea outflow during the marine isotope stage 3 interstadial. Contrary to the findings of previous studies, the data suggest that such an outflow into the Gulf of Gemlik during the late glacial period could have occurred only if the SoM lake level (-85 m) was shallower than the sill depth (-55 m) of the gulf in the west. A robust age model of the core indicates the connection of the gulf with the marine SoM at 12 cal ka BP, consistent with the sill depth (-55 m) of the gulf on the global sea level curve. Strong evidence of a marine incursion into the gulf is well documented by the μ-XRF Sr/Ca data. The available profiles of elemental ratios in core M13-08, together with the age-depth model, imply that a warm and wet climate prevailed in the gulf during the early Holocene (12-10.1 cal ka BP), whereas the longest drought occurred during the middle Holocene (8.2-5.4 cal ka BP). The base of the main Holocene sapropel in the gulf is dated at 10.1 cal ka BP, i.e., 500 years younger than its equivalent in the SoM. The late Holocene is earmarked by warm and wet climate periods (5.0-4.2 and 4.2-2.7 cal ka BP) with some

  2. Depositional environments of late glacial to Holocene sediments on the deep water levees of Setúbal and Nazaré Canyons, offshore Portugal: preliminary results

    NASA Astrophysics Data System (ADS)

    Pascoletti, F. C.; Masson, D.; Innocenti, C.

    2010-12-01

    The west Iberian margin is indented by a network of submarine canyons that create rugged seafloor morphology and act as major pathways for the transport of sediment from land to the abyssal plains. The Setúbal and Nazaré Canyons are part of this complex environment and strongly influence sediment distribution, capturing sediments from the Tagus River and the littoral cell transport respectively. Deep submarine sedimentary sequences thus reflect changes in sediment input and depositional environments. The high-resolution sedimentological study here presented was applied in four cores of the deep water levees of Nazaré and Setúbal Canyons in order to explore how sediment input to the canyons changed during the last glacial - interglacial transition, and how this reflects changing environmental conditions on land. By means of non-destructive corelogger measurements and analyses of spectral signatures, geochemical compositions and colour variations, it was possible to identify ice-rafted debris (IRD) deposits, to characterize hemipelagic and turbidite layers and to investigate terrestrial-derived sediments input variation during the last 26 ka. Preliminary results from the sedimentological and turbidite frequency analyses show that highest turbidite occurrence is recorded during the glacial stage, confirming that the generation of turbidity flows in submarine canyons is tightly related to low sea-level stands. We found that major peaks in frequency and thickness of turbidite deposits in the deep Portuguese margin are mainly coeval with abrupt climatic (H2 and 1) and sea-level changes (~ 19 and ~ 23 ka BP), as a consequence of which a major amount of continentally-derived material was transported into the deep sea. During the Holocene, the inception of sea-level rises, independent of their magnitude, has been found to be sufficient to generate turbidity currents, particularly in the Nazaré system. Moreover, a multiple regression analysis was attempted in order to

  3. Evidence for coeval Late Triassic terrestrial impacts from the Rochechouart (France) meteorite crater

    NASA Astrophysics Data System (ADS)

    Gilder, S. A.; Carporzen, L.

    2006-12-01

    High temperature impact melt breccias from the Rochechouart (France) meteorite crater record a magnetization component with antipodal, normal and reverse polarities. The corresponding paleomagnetic pole for this component lies between the 220 Ma and 210 Ma reference poles on the Eurasian apparent polar wander path, consistent with the 214 ± 8 Ma ^{40} Ar/ ^{39} Ar age of the crater [Kelley and Spray, 1997]. Late Triassic tectonic reconstructions of the Eurasian and North American plates place this pole within 95 % confidence limits of the paleomagnetic pole from the Manicouagan (Canada) meteorite impact crater, which is dated at 214 ± 1 Ma [Hodych and Dunning, 1992]. Together, these observations reinforce the hypothesis of Spray et al. [1998] for a Late Triassic, multiple meteorite impact event on Earth. References: Hodych, J. P., and G. R. Dunning (1992), Did the Manicouagan impact trigger end-of-Triassic mass extinction?, Geology, 20, 51-54. Kelley, S. P., and J. G. Spray (1997), A late Triassic age for the Rochechouart impact structure, France, Meteor., 32, 629-636. Spray, J. G., S. P. Kelley, and D. B. Rowley (1998), Evidence for a late Triassic multiple impact event on Earth, Nature, 392, 171-173.

  4. Late Glacial, Early Holocene and Late Holocene life at the interface of a distinct landscape — relationship of humans and environments in the Sub-Carpathian region (N Hungary)

    NASA Astrophysics Data System (ADS)

    Bácsmegi, Gábor; Sümegi, Pál; Törőcsik, Tünde

    2012-12-01

    Relationships between the communities and environment surrounding these communities can be disclosed by the application of different archeological, geological and environmental historical methods. This includes the deployment of numerous tools in scientific investigation including the application of chronological, sedimentological, geochemical and paleoecological analytical methods on sequences accumulated in historical catchment basins of peat-bog. The Nádas-tó at Nagybárkány is a small peatbog in the northern part of Hungary, on the Sub-Carpathian region. The formation of the lake can be traced back to the Late Glacial period. The sediments deposited in the lakebed provide a record of climatic and hydrologic changes. A higher water level could be demonstrated from the Late Glacial to the Mid-Holocene, when the reed-beds covered a small area only. This was followed by a hiatus spanning ca. 4400 years, caused by the deepening and cleaning of the lakebed during the Late Iron / Imperial Age, between 2100 - 1900 cal BP years. After this change the water level decreased and the water quality was more eutrophic. A reed-bed evolved around the lake. Paludification started with a bulrush floating mat phase at the close of the Middle Age, ca. 1500 cal AD years. The endowments and settlement pattern persisted from the Neolithic onwards until the terminal Modern Age, when measures aimed to ordain the area substantially altered the natural landscape. Although some anthropogenic disturbances can be reconstructed in the development of the peatland, some climatic effects and authogenic processes might be separated by paleoecological analyses.

  5. Late Glacial and Holocene environmental history of Wielkopolska region (western Poland) recorded in sediments of Strzeszyńskie Lake and Kierskie Lake

    NASA Astrophysics Data System (ADS)

    Pleskot, Krzysztof; Szczuciński, Witold; Tjallingii, Rik; Makohonienko, Mirosław; Nowaczyk, Norbert; Brauer, Achim

    2016-04-01

    The growing amount of publications concerning reconstructions of Late Glacial and Holocene environment based on analysis of lake sediments gives us robust insight into general patterns of that record. However, it is still challenging to decipher processes and events that occurred on local scale, as they record may be strongly affected by the type, catchment, size and depth of a lake. Therefore in the present study we focus on application of sedimentological and geochemical methods in order to reveal environmental history from two neighbouring lakes located within city of Poznań, Wielkopolska (western Poland). The lake sediments analysis cover Late Glacial and Holocene in case of smaller Strzeszyńskie Lake (SL) and the last 8 ka in deeper Kierskie Lake (KL). The study is based on two 8.5 (SL) and 14 (KL) m long sediment cores, which were described and analyzed in thin sections and on smear slides. The relative chemical composition variations within the cores were measured using an X-ray fluorescence (XRF). Moreover, the cores were measured for magnetic susceptibility and sampled for pollen analysis. The chronology has been established by a AMS 14C dating of bulk samples of lake sediments. To assess the reservoir effect, selected samples were analyzed for soluble and residual carbon fractions. Our results suggest the onset of authigenic sedimentation in SL in Allerød. The sediments from this period are characterized by high organic matter and low carbonate content. This trend changed into opposite at the beginning of the Younger Dryas, while at its termination sediments again became more organic. The transition to Holocene is marked by spread of Betula forest, gradual increase in magnetic susceptibility and Ca content together with decreasing organic matter and clastic input. During Preboreal and Boreal period the relatively stable conditions was noted. Then, ca. 8.5 ka BP, sharp decrease in magnetic susceptibility occurred coincided with deciduous forest

  6. LATE CENOZOIC INCREASE IN ACCUMULATION RATES OF TERRESTRIAL SEDIMENT: How Might Climate Change Have Affected Erosion Rates?

    NASA Astrophysics Data System (ADS)

    Molnar, Peter

    2004-05-01

    Accumulation rates of terrestrial sediment have increased in the past few million years both on and adjacent to continents, although not everywhere. Apparently, erosion has increased in elevated terrain regardless of when last tectonically active or what the present-day climate. In many regions, sediment coarsened abruptly in late Pliocene time. Sparser data suggest increased sedimentation rates at 15 Ma, approximately when oxygen isotopes in benthic foraminifera imply high-latitude cooling. If climate change effected accelerated erosion, understanding how it did so remains the challenge. Some obvious candidates, such as lowered sea level leading to erosion of continental shelves or increased glaciation, account for increased sedimentation in some, but not all, areas. Perhaps stable climates that varied slowly allowed geomorphic processes to maintain a state of equilibrium with little erosion until 34 Ma, when large oscillations in climate with periods of 20,00040,000 years developed and denied the landscape the chance to reach equilibrium.

  7. Mid- to late-Holocene El Niño-Southern Oscillation dynamics reflected in the subtropical terrestrial realm

    PubMed Central

    Donders, Timme H.; Wagner, Friederike; Dilcher, David L.; Visscher, Henk

    2005-01-01

    High resolution pollen analysis of mid- to late-Holocene peat deposits from southwest Florida reveals a stepwise increase in wetland vegetation that points to an increased precipitation-driven fresh water flow during the past 5,000 years. The tight coupling between winter precipitation patterns in Florida and the strength of the El Niño-Southern Oscillation (ENSO) strongly suggests that the paleo-hydrology record reflects changes in ENSO intensity. A terrestrial subtropical record outside the Indo Pacific Warm Pool both documents ecosystem response to the known onset of modern-day ENSO periodicities, between ≈7,000 and 5,000 years B.P., and subsequent ENSO intensification after 3,500 years B.P. The observed increases in “wetness” are sustained by a gradual rise in relative sea level that prevents a return to drier vegetation through natural succession. PMID:16043705

  8. The Osmium Isotopic Composition of Tagish Lake and Other Chondrites, Implications for Late Terrestrial Planetary Accretion

    NASA Technical Reports Server (NTRS)

    Brandon, A. D.

    2003-01-01

    The goals of this investigation are twofold. First, obtain high-precision Os isotope measurements of Tagish Lake and other chondrites by TIMS. Second, measure Re, Os, Pt, and other HSE concentrations by isotope dilution using TIMS and ICPMS. These measurements will determine whether this meteorite does in fact represent C-chondrite material with timeintegrated elevated Re/Os and Pt/Os with the implications to late accretion material characteristics.

  9. Terrestrial gastropod succession in a late Holocene stream deposit in South Texas

    NASA Astrophysics Data System (ADS)

    Neck, Raymond W.

    1987-03-01

    Investigation of snail-bearing alluvium from the Smyth Crossing site in Uvalde County, Texas, indicates that the terrestrial gastropod fauna of this area has been stable for at least 3000 yr. However, relative proportions and presence/absence variations indicate changes in the relative occurrence of preferred microhabitats of certain snails. Gastropods from an excavated soil column reveal a succession of gastropod associations in response to succession of the plant community of the site from a riverside gravel bar to an upland savannah/grassland. Human impact on the gastropods is mostly contemporary, with apparent local extirpations of some species having occurred. The recovered paleofaunas provide no evidence for regional climatic change since 3000 yr B.P.

  10. Late Cretaceous restructuring of terrestrial communities facilitated the end-Cretaceous mass extinction in North America

    NASA Astrophysics Data System (ADS)

    Mitchell, Jonathan S.; Roopnarine, Peter D.; Angielczyk, Kenneth D.

    2012-11-01

    The sudden environmental catastrophe in the wake of the end-Cretaceous asteroid impact had drastic effects that rippled through animal communities. To explore how these effects may have been exacerbated by prior ecological changes, we used a food-web model to simulate the effects of primary productivity disruptions, such as those predicted to result from an asteroid impact, on ten Campanian and seven Maastrichtian terrestrial localities in North America. Our analysis documents that a shift in trophic structure between Campanian and Maastrichtian communities in North America led Maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than Campanian communities. Of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of Maastrichtian ecosystems against environmental perturbations. Therefore, earlier ecological restructuring may have exacerbated the impact and severity of the end-Cretaceous extinction, at least in North America.

  11. Late Cretaceous restructuring of terrestrial communities facilitated the end-Cretaceous mass extinction in North America

    PubMed Central

    Roopnarine, Peter D.; Angielczyk, Kenneth D.

    2012-01-01

    The sudden environmental catastrophe in the wake of the end-Cretaceous asteroid impact had drastic effects that rippled through animal communities. To explore how these effects may have been exacerbated by prior ecological changes, we used a food-web model to simulate the effects of primary productivity disruptions, such as those predicted to result from an asteroid impact, on ten Campanian and seven Maastrichtian terrestrial localities in North America. Our analysis documents that a shift in trophic structure between Campanian and Maastrichtian communities in North America led Maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than Campanian communities. Of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of Maastrichtian ecosystems against environmental perturbations. Therefore, earlier ecological restructuring may have exacerbated the impact and severity of the end-Cretaceous extinction, at least in North America. PMID:23112149

  12. Late Cretaceous restructuring of terrestrial communities facilitated the end-Cretaceous mass extinction in North America.

    PubMed

    Mitchell, Jonathan S; Roopnarine, Peter D; Angielczyk, Kenneth D

    2012-11-13

    The sudden environmental catastrophe in the wake of the end-Cretaceous asteroid impact had drastic effects that rippled through animal communities. To explore how these effects may have been exacerbated by prior ecological changes, we used a food-web model to simulate the effects of primary productivity disruptions, such as those predicted to result from an asteroid impact, on ten Campanian and seven Maastrichtian terrestrial localities in North America. Our analysis documents that a shift in trophic structure between Campanian and Maastrichtian communities in North America led Maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than Campanian communities. Of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of Maastrichtian ecosystems against environmental perturbations. Therefore, earlier ecological restructuring may have exacerbated the impact and severity of the end-Cretaceous extinction, at least in North America.

  13. The late glacial paleoclimate of the central Altiplano constrained by cosmogenic 3He dating and 'clumped-isotope' paleothermometry

    NASA Astrophysics Data System (ADS)

    Blard, P.; Lave, J.; Farley, K. A.; Tripati, A.; Eiler, J.; Sylvestre, F.

    2007-12-01

    One of the ongoing debates in paleoclimatology is whether climate change in the tropics is simply a response to global climate change, or actually forces it. The Altiplano is a highland area (>3600 m) located in the tropical Andes that is particularly well-suited to address this question since both paleo-glacier footprints and paleolake shorelines are very well preserved in this region. Because glacier extents and lake levels have differential sensitivity to change in temperature and in precipitation, they can be used to place tight constraints on the amplitude of past changes in these atmospheric variables. However, because the timing of the deglaciation in this region is still uncertain and poorly documented, this task requires new chronological constraints on paleoglacier fluctuations. New cosmogenic 3He dates from several glacial moraines and striated rocks of the Cerro Tunupa (Bolivia, 20 ° S) show that, in the central part of the Altiplano, glaciers persisted at their maximum extent between 18 and 15 ka, synchronously with the highest level of paleolake Tauca at 17-15 ka (Placzek et al., 2006) (Clayton and Clapperton, 1997). Abrupt glacial retreat occurred approximately 15 ka and was followed by a small amplitude readvance during the Younger Dryas. This result is different from previous moraine dating (Smith et al., 2005) that indicates an earlier (~34 ka) local glacial maximum in the northern part of the Altiplano. This discrepancy most probably reflects spatial variations in past precipitation. Consequently, climatic conditions inferred from the past extent of mountain glaciers must take into account local atmospheric variations before being interpreted in a global context. To this end, we have coupled a numerical modeling approach with an independent estimate of past air temperature based on "clumped isotope" thermometry, a technique based on the temperature dependence of the abundances of 13C-18O bonds in carbonate minerals (Ghosh et al., 2006). This

  14. Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets.

    PubMed

    Gomes, R; Levison, H F; Tsiganis, K; Morbidelli, A

    2005-05-26

    The petrology record on the Moon suggests that a cataclysmic spike in the cratering rate occurred approximately 700 million years after the planets formed; this event is known as the Late Heavy Bombardment (LHB). Planetary formation theories cannot naturally account for an intense period of planetesimal bombardment so late in Solar System history. Several models have been proposed to explain a late impact spike, but none of them has been set within a self-consistent framework of Solar System evolution. Here we propose that the LHB was triggered by the rapid migration of the giant planets, which occurred after a long quiescent period. During this burst of migration, the planetesimal disk outside the orbits of the planets was destabilized, causing a sudden massive delivery of planetesimals to the inner Solar System. The asteroid belt was also strongly perturbed, with these objects supplying a significant fraction of the LHB impactors in accordance with recent geochemical evidence. Our model not only naturally explains the LHB, but also reproduces the observational constraints of the outer Solar System.

  15. Late Pleistocene ages for the most recent volcanism and glacial-pluvial deposits at Big Pine volcanic field, California, USA, from cosmogenic 36Cl dating

    USGS Publications Warehouse

    Vazquez, Jorge A.; Woolford, Jeff M

    2015-01-01

    The Big Pine volcanic field is one of several Quaternary volcanic fields that poses a potential volcanic hazard along the tectonically active Owens Valley of east-central California, and whose lavas are interbedded with deposits from Pleistocene glaciations in the Sierra Nevada Range. Previous geochronology indicates an ∼1.2 Ma history of volcanism, but the eruption ages and distribution of volcanic products associated with the most-recent eruptions have been poorly resolved. To delimit the timing and products of the youngest volcanism, we combine field mapping and cosmogenic 36Cl dating of basaltic lava flows in the area where lavas with youthful morphology and well-preserved flow structures are concentrated. Field mapping and petrology reveal approximately 15 vents and 6 principal flow units with variable geochemical composition and mineralogy. Cosmogenic 36Cl exposure ages for lava flow units from the top, middle, and bottom of the volcanic stratigraphy indicate eruptions at ∼17, 27, and 40 ka, revealing several different and previously unrecognized episodes of late Pleistocene volcanism. Olivine to plagioclase-pyroxene phyric basalt erupted from several vents during the most recent episode of volcanism at ∼17 ka, and produced a lava flow field covering ∼35 km2. The late Pleistocene 36Cl exposure ages indicate that moraine and pluvial shoreline deposits that overlie or modify the youngest Big Pine lavas reflect Tioga stage glaciation in the Sierra Nevada and the shore of paleo-Owens Lake during the last glacial cycle.

  16. Long-term demographic decline and late glacial divergence in a Californian paleoendemic: Sequoiadendron giganteum (giant sequoia).

    PubMed

    Dodd, Richard S; DeSilva, Rainbow

    2016-05-01

    Mediterranean ecosystems comprise a high proportion of endemic taxa whose response to climate change will depend on their evolutionary origins. In the California flora, relatively little attention has been given to the evolutionary history of paleoendemics from a molecular perspective, yet they number among some of the world's most iconic plant species. Here, we address questions of demographic change in Sequoiadendron giganteum (giant sequoia) that is restricted to a narrow belt of groves in the Sierra Nevada Mountains. We ask whether the current distribution is a result of northward colonization since the last glacial maximum (LGM), restriction of a broader range in the recent past (LGM) or independent colonizations in the deeper past. Genetic diversity at eleven microsatellite loci decreased with increasing latitude, but partial regressions suggested this was a function of smaller population sizes in the north. Disjunct populations north of the Kings River were divergent from those south of the Kings River that formed a single cluster in Bayesian assignment tests. Demographic inferences supported a demographic contraction just prior to the LGM as the most likely scenario for the current disjunct range of the species. This contraction appeared to be superimposed upon a long-term decline in giant sequoia over the last 2 million years, associated with increasing aridity due to the Mediterranean climate. Overall, low genetic diversity, together with competition in an environment to which giant sequoia is likely already poorly adapted, will pose major constraints on its success in the face of increasing aridity.

  17. Glacial History of Southernmost South America and Implications for Movement of the Westerlies and Antarctic Frontal Zone

    NASA Astrophysics Data System (ADS)

    Kaplan, M. R.; Fogwill, C. J.; Hulton, N. R.; Sugden, D. E.; Peter, K. W.

    2004-12-01

    The ~1 Myr glacial geologic record in southern South American is one of the few available terrestrial paleoclimate proxies at orbital and suborbital time scales in the middle latitudes of the Southern Hemisphere. Presently, southernmost Patagonia lies about 3\\deg north of the Antarctic frontal zone and within the middle latitude westerlies and the climate is controlled by the surrounding maritime conditions. Thus, the long-term glacial record provides insight into the history of climatic boundaries over the middle and high latitude southern ocean, including the upwind SE Pacific Ocean, tectonic-glacial evolution of the Andes, and global climate. To date, cosmogenic nuclide and 14C dating have focused on glacial fluctuations between 51 and 53\\deg S (Torres del Paine to northern Tierra del Fuego) during the last glacial cycle, including the late glacial period. At least 4 advances occurred between ca. 25 and 17 ka, with the maximum expansion of ice ca. 25-24 ka. Major deglaciation commenced after ca. 17.5 ka, which was interrupted by a major glacial-climate event ca. 14-12 ka. Modelling experiments suggest that the ice mass needed to form the glacial maximum moraines required about a 6\\deg cooling and a slight drying relative to the present. Such a fundamental temperature reduction, despite high summer isolation, strongly suggests northward movement of the westerlies and the polar front on millennial timescales. The Patagonian record also indicates that on orbital timescales equatorward movement of climate boundaries and glacial growth was in phase with major Northern Hemisphere ice volume change, despite high local summer insolation. At suborbital timescales, the picture is more complex. While major facets of the last glacial maximum appear to be in phase between the hemispheres, at least some late glacial events may be in step with Antarctic climate change. Present and future research will further constrain the timing of glacial events over the last 1 Myr and

  18. Discovery of laterally extensive drape of siliciclastic silt in the Northern Calcareous Alps, Austria: Late-glacial to ?early Holocene aeolian deposition.

    NASA Astrophysics Data System (ADS)

    Gild, Charlotte; Geitner, Clemens; Haas, Jean Nicolas; Sanders, Diethard

    2016-04-01

    Field surveys in the Northern Calcareous Alps (NCA, a nappe stack of Triassic carbonate rocks) revealed a drape, or drapes, typically 20-40 cm in thickness of siliciclastic silt over extensive landscape areas, from valley floors to LGM (Last Glacial Maximum) nunataks. The drape veneers substrates ranging from country rocks to diverse post-LGM deposits - the latter with depositional and/or erosional topographies. The drape mostly is overlain by vegetated organic material and, in turn, tops inactive/abandoned post-LGM successions of fluvial (including kame terrace), alluvial fan, scree slope, LGM basal till, and rock-avalanche origin. The drape extends over kilometers at least (limit of field investigation in specific areas), up to LGM nunatak plateaus. Deposystems (e.g., scree slopes, alluvial fans) on carbonate-rocky terrain that remained active until the Holocene are not topped by the drape; a level of siliciclastic silt, however, was spotted within a few of these successions. The possibility that several levels of silt are intercalated within or top post-glacial deposits cannot be excluded at present; the large lateral extent and the stratigraphic position, however, suggest that at least most locations pertain to a single widespread level (with that reservation, we prefer to speak in singular of the drape). Over the inspected area (~ 90 x 20 km), the drape consists mainly of silt-sized grains of quartz, feldspars, micas, and amphiboles; at a few sites, calci- or dolosilt are admixed. Most of the grains are angular to subrounded, some grains show features of corrosion. Preliminary palynological analyses of this silt - seven locations from LGM nunataks to kame terrace and alluvial fans - suggest vegetation types that, together, may be assigned to palaeoclimates ranging from the late-glacial (Younger Dryas?) to the middle Holocene. A few of the pollen spectra appear to record sparse vegetation cover allowing for enhanced aeolian deposition, but other spectra (e

  19. Widespread evidence for a late veneer on the terrestrial planets and planetisimals

    NASA Astrophysics Data System (ADS)

    Dale, C. W.; Burton, K.; Pearson, G.; Greenwood, R. C.

    2010-12-01

    Growth of the Earth from smaller planetisimals resulted in substantial partitioning of the iron-loving (siderophile) into the metallic core. However, some of the most highly siderophile elements in Earth’s silicate mantle are present in much greater concentrations than expected, even for high-pressure equilibration in a deep ‘magma ocean’ [1], and in broadly chondritic proportions. Consequently, it is often assumed that the highly siderophile elements require the late addition of extraterrestrial material (the so called ‘late veneer’) to the mantle after core formation was complete. Core formation on smaller asteroidal bodies cannot have been affected by high-pressure equilibration, and Hf-W chronology suggests that core formation was rapid [2] and, during global scale melting, was likely highly efficient [3]. This study presents new HSE abundance and 187Os/188Os isotope data for basaltic meteorites, the HEDs (Howardites, Eucrites and Diogenites thought to sample the asteroid 4 Vesta), anomalous Eucrites and Angrites (considered to be from distinct parent bodies) and SNCs (thought to be from Mars). The results show that these igneous meteorites all formed from mantle sources that possessed broadly chondritic (i.e. primitive solar system) inter-element ratios and Os isotope compositions, inconsistent with equilibrium partitioning of the PGE. Furthermore, there is a simple relationship where predicted mantle HSE concentrations are linked to the size of the parent body, and so Vesta (like the Moon [4]) has much lower HSE concentrations than Earth or Mars. These data can be most readily explained by the late addition of a chondritic meteorite flux to the silicate mantles of all these bodies, after core formation was complete, and suggests that the addition of a late veneer is a general feature of planetary accretion in the inner solar system, rather than being a unique temporal event that only affected the Earth. [1] Wood, B.J., Walter, M.J. & Wade, J. (2006

  20. Late Paleogene terrestrial fauna and paleoenvironments in Eastern Anatolia: New insights from the Kağızman-Tuzluca Basin

    NASA Astrophysics Data System (ADS)

    Métais, Grégoire; Sen, Sevket; Sözeri, Koray; Peigné, Stéphane; Varol, Baki

    2015-08-01

    In Eastern Turkey, relatively little work has been undertaken to characterize the sedimentologic and stratigraphical context of the Kağızman-Tuzluca Basin until now. Extending across the Turkey-Armenian border, this basin documents the syn- and post-collisional evolution of Eastern Anatolia, resulting from the closure of the Neotethyan Seaways and the final collision of the Afro-Arabian and Eurasian plates. From detailed sedimentological and paleontological studies, we propose an interpretation of the lithology and depositional environment of the Late Paleogene Alhan Formation located on the western bank of the Aras River. This sequence of terrestrial clastics rests directly and unconformably onto the ophiolitic mélange, and it documents several depositional sequences deposited in alluvial plain and lacustrine environments. At this stage, the age of the Alhan Formation can only be calibrated by fossil evidence. Several stratigraphic levels yielding fossil data along the section have been identified, but these poor assemblages of fauna and flora hamper extensive comparisons with roughly contemporaneous localities of Central and Southern Asia. Carnivorous and ruminant mammal remains are reported for the first time from the supposed Late Oligocene Güngörmez Formation. The identified fossil mammal taxa reveal biogeographic affinities between Central Anatolia and southern Asia, thus suggesting dispersal between these areas during the Oligocene or earlier. Further studies of the fossil assemblages from the Kağızman-Tuzluca Basin and other basins of Eastern Anatolia and lesser Caucasus regions are needed to better constrain the paleobiogeographic models.

  1. A late glacial record of ice-sheet dynamics and melt supply recovered in the sediments of IODP Expedition 347 in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Passchier, Sandra; Jensen, Jørn Bo; Kenzler, Michael; Johnson, Sean; Andrén, Thomas; Barker Jørgensen, Bo

    2015-04-01

    Modern observations of increased surface ablation, meltwater routing to the bed, and increases in glacial speeds point to feedbacks between ice-sheet dynamics, melt supply, and subglacial discharge. Paleorecords have the potential to explore the decadal to centennial variability of these systems, but until recently such records were short and discontinuous in ice-proximal settings and underutilized for this specific purpose. The Integrated Ocean Drilling Program Expedition 347 in the Baltic Sea recovered annually laminated sediments that document the dynamics of the Scandinavian Ice Sheet. Hydraulic piston cores recovered from Sites M0060, M0063, M0064, and M0065 allow us to reconstruct a nearly complete record of ca. 6000 years in ice retreat history at annual to decadal resolution between ca. 17 and 11ka. The late glacial successions of these four IODP drillsites comprise of a till or proglacial fluvioglacial sediment overlain by variable thicknesses of well-laminated deglacial successions within several high-recovery holes. As the Scandinavian Ice Sheet retreated from the western Baltic Sea, and to the North, the ice-sheet's grounding line migrated across the four sites and deposited overlapping sections of high-resolution ice-proximal to ice-distal successions. Laser particle size results from Sites M0060 and M0063, and inspection of line-scan images, show shifts in sedimentary facies and lithologies that were not recognized during initial visual core description. For example, at Site M0060 in the Kattegat, ice-rafting fluxes in silty clays decrease upward and are negligible in the overlying varved succession. These characteristics are interpreted as ice retreat within a calving bay environment from ca. 17ka onward, followed by distal glacial marine deposition from sediment plumes governed by meltwater discharge. Moreover, at Site M0063 in the Baltic Sea, laser particle size distributions record an abrupt shift from interlaminated clayey silt to laminated clay

  2. Late glacial river-bed changes on the Little Hungarian Plain based on preliminary chronological, geological and paleontological data

    NASA Astrophysics Data System (ADS)

    Sávai, Szilvia; Molnár, Dávid; Sümegi, Pál

    2015-10-01

    Comprehensive chronological, geological and paleontological investigations were conducted as part of archaeological excavations in 2011 and 2012, prior to the construction of the M85 motorway between Gyor and Csorna, Hungary. These studies clearly show that the alluvial fan that underlies much of the Little Hungarian Plain was built up by streams flowing in a southeasterly to northwesterly direction from the nearby Bakony Hills, and continued to form until the end of the last glacial period. The northern part of the fan, now named the Csorna Plain, became inactive (i.e. became a fossil river-bed system) at about 25-15 ka, when the Rába and Marcal rivers changed theirflowdirection fromsouth-north towest-east.As a result of this change in flow direction, the Rába and Marcal rivers became incised, capturing the Bakony stream beds, stopping sediment deposition on the northern side of the alluvial fan (essentially the left bank of the Rába-Marcal river system), although the southern part of the fan continue to form as before. On the northern side of the fan, the sediment surface dried out due to falling groundwater levels, and aeolian sand-drifts began to form. Eventually, accumulation of the sand-drift sediments ceased due to the deposition of loess-type sediments, which fixed the surface, conserved the sand-drift shapes, and contributed to the straightening and eventual canalization of the fluvial channels. Geoarchaeological examinations indicate that the development of present fluvial features were strongly affected by the settlement and tillage activity of human communities on the Csorna Plain.

  3. Modelling Regional Climate and Terrestrial Environmental Change during Interglacial Events of the Late Pliocene

    NASA Astrophysics Data System (ADS)

    Prescott, C.; Dolan, A. M.; Haywood, A. M.; Hunter, S. J.; Tindall, J. C.

    2016-12-01

    The mid-Pliocene Warm Period (mPWP; 3.264-3.025 Ma) is a valuable target for environmental reconstruction and modelling. In previous work modelling climate variability around two interglacials in the mPWP we found peak Marine Isotope Stage (MIS) KM5c and K1 interglacial temperatures were not globally synchronous, highlighting regional leads and lags in temperature. We demonstrated that orbitally-forced changes in temperature during interglacial events within the mPWP could be substantial and contribute to data/model discord. Here, we use new climate model simulations to analyze the mPWP vegetation cover and how this varies between four distinct interglacial events during the mPWP (MIS G17, K1, KM3 and KM5c), and we assess climate feedbacks associated with changes in vegetation. Increased spring/summer and reduced autumn/winter insolation in the Northern Hemisphere during MIS G17, K1 and KM3, relative to the modern orbit, leads to increased seasonality in temperature and precipitation. Two of the largest regional responses in climate and vegetation are seen in North America and continental Eurasia, where forests are replaced by more open-type vegetation for interglacials with the most extreme orbital forcing. With the addition of dynamic vegetation, this trend is amplified leading to a loss of forest to a degree not supported by available terrestrial palaeobotanical records. This demonstrates the importance of examining model performance under a range of palaeoclimate conditions even within the same time interval. Further high resolution proxy investigations of regional variability in vegetation throughout the mPWP is necessary to examine the validity of model predicted regional climate and vegetation responses.

  4. Late Glacial temperature and precipitation changes in the lowland Neotropics by tandem measurement of δ 18O in biogenic carbonate and gypsum hydration water

    NASA Astrophysics Data System (ADS)

    Hodell, David A.; Turchyn, Alexandra V.; Wiseman, Camilla J.; Escobar, Jaime; Curtis, Jason H.; Brenner, Mark; Gilli, Adrian; Mueller, Andreas D.; Anselmetti, Flavio; Ariztegui, Daniel; Brown, Erik T.

    2012-01-01

    We applied a new method to reconstruct paleotemperature in the tropics during the last deglaciation by measuring oxygen isotopes of co-occurring gypsum hydration water and biogenic carbonate in sediment cores from two lakes on the Yucatan Peninsula. Oxygen and hydrogen isotope values of interstitial and gypsum hydration water indicate that the crystallization water preserves the isotopic signal of the lake water, and has not undergone post-depositional isotopic exchange with sediment pore water. The estimated lake water δ18O is combined with carbonate δ18O to calculate paleotemperature. Three paired measurements of 1200-yr-old gypsum and gastropod aragonite from Lake Chichancanab, Mexico, yielded a mean temperature of 26 °C (range 23-29.5 °C), which is consistent with the mean and range of mean annual temperatures (MAT) in the region today. Paired measurements of ostracods, gastropods, and gypsum hydration water samples were measured in cores from Lake Petén Itzá, Guatemala, spanning the Late Glacial and early Holocene period (18.5-10.4 ka). The lowest recorded temperatures occurred at the start of Heinrich Stadial (HS) 1 at 18.5 ka. Inferred temperatures from benthic ostracods ranged from 16 to 20 °C during HS 1, which is 6-10 °C cooler than MAT in the region today, whereas temperatures derived from shallow-water gastropods were generally warmer (20-25 °C), reflecting epilimnetic temperatures. The derived temperatures support previous findings of greater tropical cooling on land in Central America during the Late Glacial than indicated by nearby marine records. Temperature increased in two steps during the last deglaciation. The first occurred during the Bolling-Allerod (B-A; from 14.7 to 13 ka) when temperature rose to 20-24 °C towards the end of this period. The second step occurred at 10.4 ka near the beginning of the Holocene when ostracod-inferred temperature rose to 26 °C, reflecting modern hypolimnetic temperature set during winter, whereas

  5. Late Glacial and Holocene Fire History From Radiocarbon Dating of Charcoal in Valley-Bottom Sediments in Small Watersheds of the Oregon Coast Range

    NASA Astrophysics Data System (ADS)

    Lancaster, S. T.; Frueh, W. T.

    2011-12-01

    . Although resolution in the late glacial to early Holocene is limited, the record shows a high relative fire frequency during the late glacial before dipping 10,000-9000 BP. The 7700 BP maximum and 1800 BP minimum are consistent with another fire history from lake sediments northeast of our sites in the Oregon Coast Range. Other features appear to contradict that record but to support of climate change inferences based on other climate proxies.

  6. History of ice-rafting and water mass evolution at the northern Siberian continental margin (Laptev Sea) during Late Glacial and Holocene times

    NASA Astrophysics Data System (ADS)

    Taldenkova, Ekaterina; Bauch, Henning A.; Gottschalk, Julia; Nikolaev, Sergei; Rostovtseva, Yuliana; Pogodina, Irina; Ovsepyan, Yaroslav; Kandiano, Evgeniya

    2010-12-01

    The Late Glacial and Holocene history of environmental changes in the western Laptev Sea is reconstructed on the basis of continuous records of ice-rafted debris (IRD) and Atlantic water indicative subpolar planktic foraminifers and benthic foraminifer Cassidulina neoteretis from the two AMS 14C dated sediment cores, one from the upper continental slope and another from the Khatanga paleoriver valley on the outer shelf. Since seasonal sea ice cover is a permanent feature in this high Arctic region the prominent IRD-rich intervals in the oldest (>15.4 ka) and youngest (<7.2 ka) sediment units are attributed to iceberg-rafting. Rock types like phyllites are used as indicators of sediment material supplied by icebergs from local ice caps of the Severnaya Zemlya Archipelago. Authigenic concretions of vivianite and rhodochrosite found in the basal, IRD-rich core section on the slope, point to strong water stratification likely caused by meltwater inputs. The oldest Late Glacial IRD peaks provide evidence for iceberg production by the local ice caps on Severnaya Zemlya. Subsequent meltwater influence is tentatively related to the freshwater release from a retreating Barents-Kara ice sheet in the northeastern Kara Sea. Already prior to 15.4 ka Atlantic-derived waters intermittently reached the western Laptev Sea continental slope probably facilitated by upwelling in coastal polynyas. While subsurface Atlantic-derived waters were constantly present at the continental slope between 15.4 and 12 ka, the disappearance of C. neoteretis together with reduced abundance of subpolar planktic foraminifers after 12 ka suggests establishment of a freshened shelf water mass on the flooded outer shelf which affected the water mass structure on the continental slope. After 7 ka climate cooling and enhanced Atlantic-derived water inflow caused re-growth of ice caps on Severnaya Zemlya leading to a recurrence of IRD. Peaks of this renewed IRD input are centered at 7.2, 6.4, 5.4, 3, and 2

  7. A new depositional model for glacial sediments in Killiney Bay during the Late Devensian deglaciation - East Central Ireland

    NASA Astrophysics Data System (ADS)

    Clerc, S.; Portier, E.; Buoncristiani, J. F.

    2009-04-01

    During the last glaciation in northwestern Europe, major studies are consistent with the hypothesis of an ice-stream flowing southward in the Irish Sea Basin, in connection with tributary flows on the eastern of the Irish Cap. During deglaciation, sediment deposition processes are predominant, leaving a record of glacially influenced environments. Evidence of such deposits still remains on the coast of the UK and Ireland today. Although these deposits have been studied for many decades, their depositional environment is still under debate and interpretations are evolving, together with new concepts. The present work focuses on the study of the Killiney Bay section, South Dublin, located in a topographic depression, expected to be a former subglacial tunnel valley in connection with an offshore canyon in the Irish Sea. Geometry and architecture have been approached by using panoramic photographs. In addition, fifteen detailed logs describe the stratigraphic succession, erosive surfaces and variations of small-scale sedimentary features. Seven Facies Associations were defined and used to reconstruct depositional environments. Although the section is affected by glaciotectonic deformation, primary sedimentological figures are well preserved. Within the section, a 600m long depression has been observed, in which a Gilbert-type delta has developed. Laterally, this delta evolves into prograding sheet-like structures interpreted as subaqueous fans. The corresponding facies association is composed of four main facies: -Matrix-supported coarse-grained facies (granules to cobbles) arranged in prograding sheet-like structures (dip angle 5-9° N160). -Massive sand to diffusely graded sand. -Coarse-to-medium sand facies with long wavelength ripples (1-2m), oriented N160. -Medium-to-coarse sand with climbing ripples and current ripples. These facies associations are characteristic of subaqueous (probably glaciolacustrine) environments. The transition from delta to fan delta has

  8. Late Glacial and Holocene avulsions of the Rio Pastaza Megafan (Ecuador-Peru): frequency and controlling factors

    NASA Astrophysics Data System (ADS)

    Bernal, Carolina; Christophoul, Frédéric; Darrozes, José; Soula, Jean-Claude; Baby, Patrice; Burgos, José

    2011-10-01

    The geomorphological study by means of remote sensing imagery of the Rio Pastaza Megafan (Ecuador and northern Peru) reveals the traces of numerous avulsions. One hundred and eight avulsion sites have been defined. The location of these sites, the available radiocarbon ages as well as historical maps of the seventeenth century, enable us to propose an evolution history of the migration and avulsions of the Rio Pastaza since the Last Glacial Maximum. The first avulsions of the Río Pastaza occurred after the LGM in a zone close to and roughly parallel to the sudandean front, where the developed avulsion gave a distributive pattern to the ancient stream of the Río Pastaza in an area located between the modern Río Morona and Pastaza, where they caused the Rio Pastaza to develop a fan-like distributary pattern. This is interpreted as a response to thrust-related forelimb tilt, progressively shifting eastward the Rio Pastaza and the apex of the megafan. This sequence of events ended with the Great Diversion of the Rio Pastaza towards the modern Rios Corrientes and Tigre. Avulsions occurred in the Tigre-Corrientes Area between 9200 and 8,500 years Cal BP. Afterwards, the Río Pastaza was diverted to its present-day north-south course. This last significant avulsion occurred before AD 1691. In the area located between the modern Río Morona and Pastaza, avulsion frequency—probably overestimated—ranges between 100 and 200 years. In the Ríos Tigre and Corrientes area, avulsion frequency—probably underestimated—ranges from 300 to 400 years. Regional tectonics is likely to have triggered most of the avulsions in the Morona Pastaza area but its influence is restricted to this area. The factors controlling the avulsions in the Tigre-Corrientes area are less clear because the frequently described "hydrologic"-driven avulsion as observed in areas characterized by contrasted hydrologic cycles are inconsistent with the characteristics of the hydrologic cycles of the Rio

  9. Paleoecology of late-glacial peats from the bering land bridge, Chukchi Sea shelf region, northwestern Alaska

    USGS Publications Warehouse

    Elias, S.A.; Short, S.K.; Phillips, R.L.

    1992-01-01

    Insect fossils and pollen from late Pleistocene nonmarine peat layers were recovered from cores from the shelf region of the Chukchi Sea at depths of about 50 m below sea level. The peats date to 11,300-11,000 yr B.P. and provide a limiting age for the regional Pleistocene-Holocene marine transgression. The insect fossils are indicative of arctic coastal habitats like those of the Mackenzie Delta region (mean July temperatures = 10.6-14??C) suggesting that 11,000 yr ago the exposed Chukchi Sea shelf had a climate substantially warmer than modern coastal regions of the Alaskan north slope. The pollen spectra are consistent with the age assignment to the Birch Interval (14,000-9000 yr B.P.). The data suggest a meadow-like graminoid tundra with birch shrubs and some willow shrubs growing in sheltered areas. ?? 1992.

  10. Impact of the Last Glacial Cycle on Common-Era temperature and energy reconstructions from terrestrial borehole temperatures in North America

    NASA Astrophysics Data System (ADS)

    Beltrami, H.; Matharoo, G. S.; Tarasov, L.; Rath, V.; Smerdon, J. E.

    2014-12-01

    Reconstructions of past climatic changes from borehole temperature profiles areimportant independent estimates of temperature histories over the lastmillennium. There remain, however, multiple uncertainties in theinterpretation of these data as climatic indicators and as estimates of thechanges in heat content of the continental subsurface due to long-termclimatic change. One of these uncertainties is associated with the oftenignored impact of the last glacial cycle on the subsurface energy content, andthe estimate of the background quasi steady-state signal associated withthe diffusion of accretionary energy from the Earth's interior. Here we providethe first quantification of the impact of the Laurentide ice sheeton energy and surface temperature reconstructions during the Common Era from measurements ofterrestrial borehole temperatures in North America. We use basal temperaturevalues from the data-calibrated Memorial University of Newfoundland GlacialSystems Model to quantify the extent of the perturbation tosteady-state temperature profiles and to derive spatial maps of the expectedimpacts on measured profiles over North America. Furthermore, we presentquantitative estimates of the potential effects of temperature changes duringthe last glacial cycle on Common-Era surface temperature reconstructions for North America. The range of these possible impacts areestimated using synthetic basal temperatures for a period covering 120 ka tothe present day that include the basal temperature history uncertainties froman ensemble of results from the calibrated numerical model. For all thelocations, we find that within the depth ranges that are typical for availableboreholes used to estimate surface temperature changes during the Common era (~600 m), the induced perturbations to the steady-state temperature profile are on the order of 10 mW/m2, decreasingwith greater depths. Results indicate that site-specific heat content estimatesover North America can differ by as much

  11. New Algorithm for Peat Carbon Accumulation Estimation Reveals and Quantifies the Global Importance of Northern Peatlands to the Late Glacial and Early Holocene Carbon Cycle

    NASA Astrophysics Data System (ADS)

    Nichols, J. E.; Peteet, D. M.

    2016-12-01

    Northern peatlands are vital to the global carbon cycle. Previous estimates of global peatland carbon accumulation rates were limited to data from peatlands with robust radiocarbon age models spanning the entire Holocene and Late Glacial periods. This stringent data policy eliminated large amounts of otherwise legitimate radiocarbon measurements. We introduce the AccumC algorithm for calculating carbon accumulation rate. This method has been used previously at single sites, but its flexibility allows it to be used to calculate carbon accumulation in multiple sites simultaneously. Using the AccumC algorithm, we are now able to include radiocarbon measurements from any peat, regardless of how many measurements were made from the same site. Our full dataset includes radiocarbon measurements from Loisel et al., 2014 (L-14), the Neotoma Paleoecology Database, the Canadian Archaeological Radiocarbon Database (CARD), and other published sources. With our expanded dataset, we have extended our record of northern peatland accumulation rates back to 22 ka, including the important deglacial period. We also now have sufficient data to divide carbon accumulation geographically into several peat-forming regions. The Holocene portion of the global record reinforces previous estimates, but the increased temporal resolution has uncovered new details, such as a previously unreported increase from 7 to 5 ka. We have also identified high rates of carbon accumulation during the Allerød warm interval and even a relative increase during the mystery interval (17.5 - 14.5 ka).

  12. Preliminary Vertical Slip Rate for the West Tahoe Fault from six new Cosmogenic 10Be Exposure Ages of Late Pleistocene Glacial Moraines at Cascade Lake, Lake Tahoe, California

    NASA Astrophysics Data System (ADS)

    Pierce, I. K. D.; Wesnousky, S. G.; Kent, G. M.; Owen, L. A.

    2015-12-01

    The West Tahoe Fault is the primary range bounding fault of the Sierra Nevada at the latitude of Lake Tahoe. It is a N-NW striking, east dipping normal fault that has a pronounced onshore quaternary scarp extending from highway 50 southwest of Meyers, CA to Emerald Bay. At Cascade Lake, the fault cuts and progressively offsets late Pleistocene right lateral moraines. The fault vertically offsets the previously mapped Tahoe moraine ~83 m and the Tioga moraine ~23 m, measured from lidar data. Seventeen samples were collected for 10Be cosmogenic age analysis from boulders on both the hanging and footwalls of the fault along the crests of these moraines.We report here the initial analysis of 6 of these boulders and currently await processing of the remainder. The 10Be exposure ages of 3 boulders each on the younger Tioga and older Tahoe moraines range from 12.7 +/- 1.6 to 20.7 +/- 3.3 ka and 13.3 +/- 2.1 to 72.5 +/- 8.8 ka, respectively. Using the oldest ages as minima, these preliminary results suggest that the slip rate has averaged ~1 mm/yr since the penultimate glaciation, in accord with estimates of previous workers, and place additional bounds on the age of glaciation in the Lake Tahoe basin. The Last Glacial Maxima and penultimate glaciation near Lake Tahoe thus appear to coincide with the Tioga and Tahoe II glaciations of the Eastern Sierra.

  13. Atmospheric production signal in 10Be from varved sediments of Lake Meerfelder Maar during the late glacial-early Holocene transition

    NASA Astrophysics Data System (ADS)

    Czymzik, Markus; Adolphi, Florian; Muscheler, Raimund; Brauer, Achim; Mekhaldi, Florian; Martin-Puertas, Celia; Tjallingii, Rik; Aldahan, Ala; Possnert, Göran

    2016-04-01

    Beryllium 10 concentrations (10Becon) were measured at 20-year resolution in annually laminated (varved) sediments of Lake Meerfelder Maar (western Germany) covering the late glacial-early Holocene transition 11310-13130 varve years before present. Comparing the 10Becon record to environmental proxy records from the same archive indicates that varying sediment accumulation and composition only slightly modify trends, but do not substantially influence multi-decadal to centennial 10Becon excursions. Corrected for potential environmental biases using multiple-regression analysis, the resulting 10Beatmosphere time-series likely represents an alternative mid-latitude 10Be production record, exhibiting broad similarities but also some differences to radionuclide records as 14C in tree rings and 10Be in polar ice cores. The preservation of the globally common atmospheric production signal in 10Be from varved lake sediments indicates the, to date, largely unexplored potential of these archives for the synchronization to other radionuclide records around the globe, complementing existing solar activity reconstructions and Sun-climate studies.

  14. A Reassessment of U-Th and 14C Ages for Late-Glacial High-Frequency Hydrological Events at Searles Lake, California

    USGS Publications Warehouse

    Lin, J.C.; Broecker, W.S.; Hemming, S.R.; Hajdas, I.; Anderson, Robert F.; Smith, G.I.; Kelley, M.; Bonani, G.

    1998-01-01

    U-Th isochron ages of tufas formed on shorelines suggest that the last pluvial event in Lake Lahontan and Searles Lake was synchronous at about 16,500 cal yr B.P. (equivalent to a radiocarbon age of between 14,000 and 13,500 yr B.P.), whereas the timing of this pluvial event determined by radiocarbon dating is on the order of 1000 yr younger. The timing of seven distinct periods of near desiccation in Searles Lake during late-glacial time has been reinvestigated for U-Th age determination by mass spectrometry. U-Th dating of evaporite layers in the interbedded mud and salt unit called the Lower Salt in Searles Lake was hampered by the uncertainty in assessing the initial 230Th/232Th of the samples. The resulting ages, corrected by a conservative range of initial 230Th/ 232Th ratios, suggest close correlation of the abrupt changes recorded in Greenland ice cores (Dansgaard-Oeschger events) and wet-dry conditions in Searles Lake between 35,000 and 24,000 Cal yr B.P. ?? 1998 University of Washington.

  15. Holocene and late glacial palaeoceanography and palaeolimnology of the Black Sea: Changing sediment provenance and basin hydrography over the past 20,000 years

    USGS Publications Warehouse

    Piper, David Z.; Calvert, S.E.

    2011-01-01

    The elemental geochemistry of Late Pleistocene and Holocene sediments of the Black Sea, recovered in box cores from the basin margins and a 5-m gravity core from the central abyssal region of the basin, identifies two terrigenous sediment sources over the last 20 kyrs. One source region includes Anatolia and the southern Caucasus; the second region is the area drained by rivers entering the Black Sea from Eastern Europe. Alkali metal:Al and heavy:light rare-earth element ratios reveal that the relative contribution of the two sources shifted abruptly every few thousand years during the late glacial and early Holocene lacustrine phase of the basin. The shifts in source were coeval with changes in the lake level as determined from the distribution of quartz and the heavy mineral-hosted trace elements Ti and Zr.The geochemistry of the abyssal sediments further recorded a sequence of changes to the geochemistry of the water column following the lacustrine phase, when high salinity Mediterranean water entered the basin beginning 9.3 kyrs BP. Bottom water that had been oxic throughout the lake phase became anoxic at approximately 8.4 kyrs BP, as recorded by the accumulation from the water column of several redox-sensitive trace metals (Mo, Re, U). The accumulation of organic carbon and several trace nutrients (Cd, Cu, Ni, Zn) increased sharply ca. 0.4 kyrs later, at 8.0 kyrs BP, reflecting an increase of primary productivity. Its increase was coeval with a shift in the dinoflagellate ecology from stenohaline to euryhaline assemblages. During this profound environmental change from the lacustrine to the marine phase, the accumulation rate of the lithogenous sediment fraction decreased as much as 10-fold in response to the rise of the water level in the basin from a low stand ca. 9.3 ka to its current level.

  16. Holocene and late glacial palaeoceanography and palaeolimnology of the Black Sea: Changing sediment provenance and basin hydrography over the past 20,000years

    USGS Publications Warehouse

    Piper, D.Z.; Calvert, S.E.

    2011-01-01

    The elemental geochemistry of Late Pleistocene and Holocene sediments of the Black Sea, recovered in box cores from the basin margins and a 5-m gravity core from the central abyssal region of the basin, identifies two terrigenous sediment sources over the last 20. kyrs. One source region includes Anatolia and the southern Caucasus; the second region is the area drained by rivers entering the Black Sea from Eastern Europe. Alkali metal:Al and heavy:light rare-earth element ratios reveal that the relative contribution of the two sources shifted abruptly every few thousand years during the late glacial and early Holocene lacustrine phase of the basin. The shifts in source were coeval with changes in the lake level as determined from the distribution of quartz and the heavy mineral-hosted trace elements Ti and Zr. The geochemistry of the abyssal sediments further recorded a sequence of changes to the geochemistry of the water column following the lacustrine phase, when high salinity Mediterranean water entered the basin beginning 9.3. kyrs BP. Bottom water that had been oxic throughout the lake phase became anoxic at approximately 8.4. kyrs BP, as recorded by the accumulation from the water column of several redox-sensitive trace metals (Mo, Re, U). The accumulation of organic carbon and several trace nutrients (Cd, Cu, Ni, Zn) increased sharply ca. 0.4. kyrs later, at 8.0. kyrs BP, reflecting an increase of primary productivity. Its increase was coeval with a shift in the dinoflagellate ecology from stenohaline to euryhaline assemblages. During this profound environmental change from the lacustrine to the marine phase, the accumulation rate of the lithogenous sediment fraction decreased as much as 10-fold in response to the rise of the water level in the basin from a low stand ca. 9.3. ka to its current level. ?? 2011.

  17. The Late Miocene Rise of C4 Vegetation in Eastern Africa Documented by Terrestrial Plant Waxes in Marine Cores

    NASA Astrophysics Data System (ADS)

    Uno, K. T.; Polissar, P. J.; Jackson, K.; deMenocal, P. B.

    2015-12-01

    C4 plants are predominantly grasses and they account for ~20% of global net primary productivity, serve as important sources of food, and are the dominant plant type in non-forested tropical ecosystems. Yet the reasons behind their rise to such a globally significant component of the terrestrial biosphere within the last 10 million years are not well understood. In eastern Africa, the expansion of C4 grasslands led to long-term changes in faunal distributions and resulted in major dietary shifts in mammalian lineages. Potential mechanisms leading to the rise of C4 plants include a decrease in atmospheric CO2, ecosystem perturbations by fire or large herbivores, and increased aridity or seasonality of precipitation. Improvement of the temporal and spatial coverage of vegetation records in the Late Neogene of East Africa may help elucidate the mechanisms responsible for regional and global C4 grassland expansion. It will also improve our ability to assess the relationship between vegetation change and mammalian evolution. To evaluate the evolution of C4 grasslands in East Africa, we measured carbon isotope ratios of n-alkanes from four DSDP cores stretching from the Red Sea (19.1° N) to the Somali Basin (2.4° S) that range in age from ~24 Ma to 0.5 Ma. Carbon isotope data from Somali Basin sites 235 and 241 indicate the appearance of C4 vegetation by ca. 10 Ma, followed by a relatively steady increase through the late Pleistocene. Odd numbered n-alkane homologues (C29 ­to C35) exhibit up to a 10‰ increase in δ13C. We also established end member molecular distributions of n-alkanes and tracked changes in their proportional contributions through time. Changes in molecular distribution are broadly synchronous with increases in carbon isotope ratios, suggesting that n-alkane distributions reflect changes in C3 and C4 vegetation types.

  18. The loss of late successional species has a disproportionate impact on terrestrial carbon storage in North America

    NASA Astrophysics Data System (ADS)

    Moore, D. J.; McLachlan, J. S.; Rocha, A. V.; Peters, J.; Dawson, A.; Raiho, A.; Blakely, B.; Heilman, K.; Paciorek, C. J.; Read, Q.; Feng, X.; Cogbill, C. V.; Goring, S. J.

    2015-12-01

    Annually, terrestrial vegetation absorbs more than 10 times the amount of carbon released by human activities, but the degree to which this contributed to net removal of carbon from the atmosphere depends on how much carbon uptake is allocated to long-lived pools. A significant fraction of carbon taken up by forests is allocated to wood where it is effectively removed from the atmosphere for the duration of the tree's life. In this study we derive forest biomass for the Upper Midwest USA from historical records of tree distribution and size and compare it to published values for old growth forests and also modern forest biomass in the same region. Our estimates of pre-settlement biomass are lower than small scale studies in the published literature. Despite this, we find substantial losses in forest biomass since European settlement, often associated with the loss of large, long lived conifers. The mean life span of tree species in pre-industrial forests was greater than on the modern landscape and that this change is strongly influenced by the loss of long lived, late successional tree species like Tsuga canadensis. Regrowth of forest cleared during the expansion of Europeans across the North American continent had led to net carbon sequestration over the past century. However, because land use change and subsequent land use policies have not permitted the recovery of long lived, late successional species, it is unclear whether pre-industrial forest carbon stocks will recover. Figure: Maps showing the biomass-weighted mean of maximum potential tree lifespan across the study area. The upper panel is pre-settlement forests, with biomass estimates output from an observation informed statistical reconstruction, and the right panel is the same analysis for modern forests.

  19. Can planetesimals left over from terrestrial planet formation produce the lunar Late Heavy Bombardment?

    NASA Astrophysics Data System (ADS)

    Bottke, William F.; Levison, Harold F.; Nesvorný, David; Dones, Luke

    2007-09-01

    The lunar Late Heavy Bombardment (LHB) defines a time between ˜3.8 to possibly 4.1 Gy ago when the Nectarian and early-Imbrium basins on the Moon with reasonably well-constrained ages were formed. Some have argued that these basins were produced by a terminal cataclysm that caused a spike in the inner Solar System impactor flux during this interval. Others have suggested the basins were formed by the tail end of a monotonically decreasing impactor population originally produced by planet formation processes in the inner Solar System. Here we investigate whether this so-called declining bombardment scenario of the LHB is consistent with constraints provided by planet formation models as well as the inferred ages of Nectaris, Serenitatis, Imbrium, and Orientale. We did this by modeling the collisional and dynamical evolution of the post-planet formation population (PPP) for a range of starting PPP masses. Using a Monte Carlo code, we computed the probability that the aforementioned basins were created at various times after the Moon-forming event approximately 4.54 Ga. Our results indicate that the likelihood that the declining bombardment scenario produced Nectaris, Serenitatis, Imbrium, and Orientale (or even just Imbrium and Orientale) at any of their predicted ages is extremely low and can be ruled out at the 3 σ confidence level, regardless of the PPP's starting mass. The reason is that collisional and dynamical evolution quickly depletes the PPP, leaving behind a paucity of large projectiles capable of producing the Moon's youngest basins between 3.8-4.1 Gy ago. If collisions are excluded from our model, we find that the PPP produces numerous South Pole-Aitken-like basins during the pre-Nectarian period. This is inconsistent with our understanding of lunar topography. Accordingly, our results lead us to conclude that the terminal cataclysm scenario is the only existing LHB paradigm at present that is both viable from a dynamical modeling perspective and

  20. New insights on Late Quaternary Asian palaeomonsoon variability and the timing of the Last Glacial Maximum in southwestern China

    NASA Astrophysics Data System (ADS)

    Cook, Charlotte G.; Jones, Richard T.; Langdon, Peter G.; Leng, Melanie J.; Zhang, Enlou

    2011-04-01

    A ˜6.35 m core (06SD) was retrieved from Lake Shudu, Yunnan Province, China. The sediments spanning the period ˜22.6-10.5 kcal. yr BP (6.35-1.44 m) were analysed using a combination of variables including pollen, charcoal, particle size, magnetic susceptibility and loss-on-ignition. The resulting palaeorecord provides a high-resolution reconstruction of Late Pleistocene to Early Holocene climatic and environmental changes in southwestern China. Our findings indicate that from c. 22.6 to 17.7 kcal. yr BP, vegetation assemblages were primarily aligned to sparse xerophytic grassland/tundra or cold-tolerant boreal Pinus forest, indicating that climatic conditions in southwestern China were cold and dry. However, from c. 17.7 to 17.4 kcal. yr BP, the Lake Shudu record is punctuated by marked environmental changes. These include the establishment of denser vegetation cover, a marked expansion of boreal Pinus forest and enhanced hydrological activity in the catchment over centennial timescales, perhaps suggesting that stepwise variations in the Asian Monsoon were triggering fundamental environmental changes over sub-millennial timescales. Thereafter, the pollen record captures a period of environmental instability reflected in fluctuations across all of the variables, which persists until c. 17.1 kcal. yr BP. After c. 17.1 kcal. yr BP, the expansion of steppe vegetation cover and cold-cool mixed forest consisting of mesophilous vegetation such as Tsuga and Picea, thermophilous trees including Ulmus and deciduous Quercus inferred from the Lake Shudu pollen record point to the establishment of warmer, wetter and perhaps more seasonal conditions associated with a strengthening Asian Summer Monsoon during the shift from Pleistocene to Holocene climatic conditions.

  1. Black Mats, Spring-Fed Streams, and Late-Glacial-Age Recharge in the Southern Great Basin

    NASA Astrophysics Data System (ADS)

    Quade, Jay; Forester, Richard M.; Pratt, William L.; Carter, Claire

    1998-03-01

    Black mats are prominent features of the late Pleistocene and Holocene stratigraphic record in the southern Great Basin. Faunal, geochemical, and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge, ranging from wet meadows to shallow ponds. Small land snails such as Gastrocopta tappanianaand Vertigo berryiare the most common mollusk taxa present. Semiaquatic and aquatic taxa are less abundant and include Catinellids, Fossaria parva, Gyraulus parvus,and others living today in and around perennial seeps and ponds. The ostracodes Cypridopsis okeechobiand Scottia tumida,typical of seeps and low-discharge springs today, as well as other taxa typical of springs and wetlands, are common in the black mats. Several new species that lived in the saturated subsurface also are present, but lacustrine ostracodes are absent. The δ 13C values of organic matter in the black mats range from -12 to -26‰, reflecting contributions of tissue from both C 3(sedges, most shrubs and trees) and C 4(saltbush, saltgrass) plants. Carbon-14 dates on the humate fraction of 55 black mats fall between 11,800 to 6300 and 2300 14C yr B.P. to modern. The total absence of mats in our sample between 6300 and 2300 14C yr B.P. likely reflects increased aridity associated with the mid-Holocene Altithermal. The oldest black mats date to 11,800-11,600 14C yr B.P., and the peak in the 14C black mat distribution falls at ˜10,000 14C yr B.P. As the formation of black mats is spring related, their abundance reflects refilling of valley aquifers starting no later than 11,800 and peaking after 11,000 14C yr B.P. Reactivation of spring-fed channels shortly before 11,200 14C yr B.P. is also apparent in the stratigraphic records from the Las Vegas and Pahrump Valleys. This age distribution suggests that black mats and related spring-fed channels in part may have formed in response to Younger Dryas (YD)-age recharge in the region. However, the

  2. Black Mats, Spring-Fed Streams, and Late-Glacial-Age Recharge in the Southern Great Basin

    USGS Publications Warehouse

    Quade, Jay; Forester, R.M.; Pratt, W.L.; Carter, C.

    1998-01-01

    Black mats are prominent features of the late Pleistocene and Holocene stratigraphic record in the southern Great Basin. Faunal, geochemical, and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge, ranging from wet meadows to shallow ponds. Small land snails such as Gastrocopta tappaniana and Vertigo berryi are the most common mollusk taxa present. Semiaquatic and aquatic taxa are less abundant and include Catinellids, Fossaria parva, Gyraulus parvus, and others living today in and around perennial seeps and ponds. The ostracodes Cypridopsis okeechobi and Scottia tumida, typical of seeps and low-discharge springs today, as well as other taxa typical of springs and wetlands, are common in the black mats. Several new species that lived in the saturated subsurface also are present, but lacustrine ostracodes are absent. The ??13C values of organic matter in the black mats range from -12 to -26???, reflecting contributions of tissue from both C3 (sedges, most shrubs and trees) and C4 (saltbush, saltgrass) plants. Carbon-14 dates on the humate fraction of 55 black mats fall between 11,800 to 6300 and 2300 14C yr B.P. to modern. The total absence of mats in our sample between 6300 and 2300 14C yr B.P. likely reflects increased aridity associated with the mid-Holocene Altithermal. The oldest black mats date to 11,800-11,600 14C yr B.P., and the peak in the 14C black mat distribution falls at ???10,000 14C yr B.P. As the formation of black mats is spring related, their abundance reflects refilling of valley aquifers starting no later than 11,800 and peaking after 11,000 14C yrB.P. Reactivation of spring-fed channels shortly before 11,200 14C yr B.P. is also apparent in the stratigraphic records from the Las Vegas and Pahrump Valleys. This age distribution suggests that black mats and related spring-fed channels in part may have formed in response to Younger Dryas (YD)-age recharge in the region. However, the

  3. Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group

    NASA Astrophysics Data System (ADS)

    Turney, C. S. M.; Haberle, S.; Fink, D.; Kershaw, A. P.; Barbetti, M.; Barrows, T. T.; Black, M.; Cohen, T. J.; Corrège, T.; Hesse, P. P.; Hua, Q.; Johnston, R.; Morgan, V.; Moss, P.; Nanson, G.; van Ommen, T.; Rule, S.; Williams, N. J.; Zhao, J.-X.; D'Costa, D.; Feng, Y.-X.; Gagan, M.; Mooney, S.; Xia, Q.

    2006-10-01

    The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric teleconnection and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. Copyright

  4. Evidence for the persistence of the land planarian species Microplana terrestris (Müller, 1774) (Platyhelminthes, Tricladida) in microrefugia during the Last Glacial Maximum in the northern section of the Iberian Peninsula.

    PubMed

    Álvarez-Presas, Marta; Mateos, Eduardo; Vila-Farré, Miquel; Sluys, Ronald; Riutort, Marta

    2012-09-01

    The land planarian species Microplana terrestris (Müller, 1774), shows a wide distribution in the north of the Iberian Peninsula, where mature humid forests can be found. Since most terrestrial planarians require the presence and good condition of wet forests to survive, a parallel evolution of the taxon and its habitat might be expected. Performing molecular analyses (mitochondrial cytochrome oxidase I and nuclear ITS-1 genes) we estimated the demography and biogeographic history of the species in that region. Our results show the species to present levels of genetic diversity likely originating before the Pleistocene. However, it presents a genetic structure that presumably resulted from its survival in various refugees during the Pleistocene glacial cycles. The two main genetic groups, present on the Iberian Peninsula, seem to have different origins: the western one being of Iberian origin, while the eastern group may have been the result of a re-colonization from the north. In both cases, their biogeographical history mirrors their habitat range movements, reinforcing the phylogeographical hypothesis put forward for its preferred habitat, i.e. humid forests. Copyright © 2012 Elsevier Inc. All rights reserved.

  5. New findings of Late Glacial Etna pumice fall deposits in NE Sicily and implications for distal tephra correlations in the Mediterranean area

    NASA Astrophysics Data System (ADS)

    Del Carlo, Paola; Branca, Stefano; D'Oriano, Claudia

    2017-07-01

    Pumice fall deposits found in the Nebrodi Mountains and along the Alcantara River, close to the town of Randazzo (NE Sicily), have been studied to derive information about their volcanic source and age. The geochemical Na-alkaline affinity of juvenile products, benmoreite to trachyte, clearly indicates they originated from Etna volcano (Sicily). Major (EMPA) and trace (LA-ICP-MS) element compositional data on matrix glasses indicate that the investigated deposits have a compositional affinity consistent with the tephra deposits of unit D produced by the Ellittico caldera-forming eruptions between ca. 17 and 19 cal ka BP. Furthermore, their compositions correspond to the distal tephra equivalent found in some lacustrine and marine cores in Central Italy (Y-1, TM-11), Tyrrhenian Sea (Et-1; MD10α) and Adriatic Sea (Pal94-66-358; Pal94-8-353). We applied the principal components analysis (PCA), a statistical tool able to reduce the variability of a complex system, to compare the compositions of the proximal samples with the possible distal counterparts found in drill cores of the Mediterranean area. On the basis of northward dispersal of the studied deposits and their geochemical features, we suggest they represent a previously unreported sub-Plinian/Plinian eruption of Ellittico volcano producing medial-distal pumice fall deposits in the Nebrodi Mountains and close to Randazzo, named here the D1c layer. The discovery of these deposits helps solve the problem of distal correlations of the northerly dispersed tephra from Etna related to unit D, for which no definitive attribution with proximal units was given in previous studies. The results presented here add to the knowledge of the eruptive history of the volcano and contribute to expanding the proximal geochemical glass dataset for distal tephra correlation in the Mediterranean region during the Late Glacial period.

  6. High-Resolution Late Holocene Climatic Records From Kucukcekmece Lagoon and Uludag Glacial, Yeniçaga, Bafa Lakes in Western Turkey: Some Preliminary Results

    NASA Astrophysics Data System (ADS)

    Akcer On, S.; Cagatay, M.; Sakinc, M.

    2010-12-01

    This study focuses on climatic and environmental sedimentary records of the last 4000 years in Kucukcekmece Lagoon (Istanbul), Uludag glacial (Bursa) , Yenicaga (Bolu) and Bafa (Mugla) Lakes in western Turkey. The water bodies are located on a N-S transect in western Turkey, and as such the’r records are important for assesment of Late Holocene eastern Mediterranean climatic changes. A total of 12 cores varying between 0.6 and 4.8 m are analyzed at 5mm resolution using Multi Sensor Core Logger (MSCL) having magnetic susceptibilty, P-Wave, density and resistivity sensors, XRF(X-Ray Fluoresance) core scanner multi element analysis at a 0.2 mm resolution. The cores are then sampled at 20, 50 and 100 mm intervals for different analyses. The samples are analyzed for total inorganic (TIC) and organic carbon (TOC). The ostracoda and benthic foraminifera shells in the sand size fraction of the sediment samples are identified under binocular microscope and suitable species are picked and analyzed for the stable oxygen and carbon isotope analysis. The cores are dated using AMS 14C analysis. The data from these lakes and lagoon are interpreted for environmental and climatic changes and compared with historical and other regional and global climate signals. The results indicate dry periods during 3300 -2500 ka BP and 867-1790 AD and1070-1690 AD with some brief intervening humid periods. Abrupt environmental change starting around1950 due to mainly human activities has also been clearly detected. These changes in the sedimentds are well correlated with the historical records.

  7. A Lateglacial to late Holocene glacial chronology for the Cairngorm Mountains (Scotland): effects of boulder inheritance and snow shielding on age distributions.

    NASA Astrophysics Data System (ADS)

    Kirkbride, Martin; Everest, Jez; Benn, Doug

    2014-05-01

    It is thought that British glaciers disappeared after the Younger Dryas Stadial (YDS, 12.9 - 11.7 k yr). We present cosmogenic 10Be ages of cirque moraines in the Cairngorm Mountains which include two Lateglacial advances, a speculative early Holocene advance, and a late Holocene moraine probably deposited by a Little Ice Age glacier ( 17th - 18th century AD). One cirque (CLE) contains evidence of a YDS advance peaking at c. 12.3 k yr, and a probable Little Ice Age (LIA) advance dated to <0.9 k yr. Another cirque (CLW) has an outer moraine dated to between 15.3 and 12.0 k yr. An inner moraine, conventionally regarded as YDS in age, yields 10Be ages of 11.5 to 8.3 k yr (Lal/Stone time-dependent production model). The putative YDS moraines are well dated in cirque CLE, but appear too "young" in CLW. We consider how snow-shielding and boulder recycling may have affected age distributions. If these ages are minima from a YDS moraine, snow-shielding and delayed deposition from debris-covered ice may explain low 10Be concentrations, but this does not explain why similar adjustments are not needed in the neighbouring cirque. Alternatively, ages may be maxima from an early Holocene moraine which incorporated existing boulders. The LIA moraine in CLE contains a high proportion of inherited boulders, but the YDS moraine here contains few. Therefore the proportion of inherited boulders is estimated to be a function of the ratio of debris production during the glacial period and debris production during the preceding paraglacial period. The ratio describes the likelihood of sampling an inherited boulder if the geomorphological history is understood. By this reasoning, an alternative interpretation of the "YDS" moraine in CLW is that an early Holocene glacier (speculatively, the 8.2 k event?) incorporated post-YDS paraglacial rock fall debris.

  8. Late Miocene–Pliocene Paleoclimatic Evolution Documented by Terrestrial Mollusk Populations in the Western Chinese Loess Plateau

    PubMed Central

    Li, Fengjiang; Wu, Naiqin; Rousseau, Denis-Didier; Dong, Yajie; Zhang, Dan; Pei, Yunpeng

    2014-01-01

    The Neogene eolian deposits in the Chinese Loess Plateau (CLP) are one of the most useful continental deposits for understanding climatic changes. To decipher Late Neogene paleoclimatic changes in the CLP, we present a terrestrial mollusk record spanning the time interval between 7.1 and 3.5 Ma from the western CLP. The results indicate four stages of paleoclimatic evolution: From 7.1 to 6.2 Ma, cold and dry climatic conditions prevailed as evidenced by high values of the total number of cold-aridiphilous (CA) mollusk species and by low values of all of the thermo-humidiphilous (TH) mollusk indices. From 6.2 to 5.4 Ma, the climate remained cold and dry but was not quite as dry as during the preceding phase, as indicated by the dominance of CA mollusks and more TH species and individuals. From 5.4 to 4.4 Ma, a warm and moist climate prevailed, as indicated by high values of the TH species and individuals and by the sparsity of CA species and individuals. From 4.4 to 3.5 Ma, all of the CA indices increased significantly and maintained high values; all of the TH indices exhibit high values from 4.4 to 4.0 Ma, an abrupt decrease from 4.0 Ma and a further increase from 3.7 Ma. The CA species of Cathaica pulveraticula, Cathaica schensiensis, and Pupopsis retrodens are only identified in this stage, indicating that the CA species were diversified and that the climate was becoming drier. Moreover, the CA mollusk group exhibits considerable diversity from 7.1 to 5.4 Ma when a cold, dry climate prevailed; whereas the diversity of the TH group was high during the relatively warm, wet interval from 5.4 to 4.4 Ma. This indicates that variations in the diversity of the CA and TH mollusk groups were closely related to climatic changes during the Late Miocene to Pliocene. PMID:24752586

  9. The UV-B stimulon of the terrestrial cyanobacterium Nostoc commune comprises early shock proteins and late acclimation proteins.

    PubMed

    Ehling-Schulz, Monika; Schulz, Stefan; Wait, Robin; Görg, Angelika; Scherer, Siegfried

    2002-11-01

    The UV-B and desiccation-tolerant terrestrial cyanobacterium Nostoc commune was grown under defined UV irradiation. Proteome changes were monitored in the membrane and the cytosolic and the extracellular fractions. Tools were developed to separate stress-triggered from growth stage-dependent changes. UV-B changed the relative cellular concentration of 493 out of 1,350 protein spots at least by a factor of three, rendering the UV-B stimulon of N. commune the most complex one described so far. It comprises two different parts: an early shock response influencing 214 proteins and a late acclimation response involving 279 proteins. The shock response comprised many membrane or membrane-associated proteins, whereas the acclimation response mainly changed cytosolic proteins. Most of the shock-induced changes were transient and did not overlap with the acclimation response. In the extracellular fraction, UV irradiation induced superoxide dismutase and the water stress protein. In total, 27 intracellular, UV-B-induced proteins were partially sequenced by electrospray ionization tandem mass spectrometry. Three functional classes were identified: proteins involved in lipid metabolism, in carbohydrate metabolism and in regulatory pathways. About 50% of the sequenced proteins were homologous to cyanobacterial database entries with un-known function. Interestingly, all of these proteins belong to the UV-B acclimation response. We conclude that the UV-B shock response and the UV-B acclimation response represent two completely different and remarkably complex strategies of N. commune to protect itself against UV-B radiation in its natural environment.

  10. The relative roles of CO2 and palaeogeography in determining Late Miocene climate: results from a terrestrial model-data comparison

    NASA Astrophysics Data System (ADS)

    Bradshaw, C. D.; Lunt, D. J.; Flecker, R.; Salzmann, U.; Pound, M. J.; Haywood, A. M.; Eronen, J. T.

    2012-03-01

    The Late Miocene (∼11.6-5.3 Ma) palaeorecord provides evidence for a warmer and wetter climate than that of today and there is uncertainty in the palaeo-CO2 record of at least 150 ppmv. We present results from fully coupled atmosphere-ocean-vegetation simulations for the Late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of Late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that the data accurately reflects the Late Miocene climate, and that the Late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that the proxy-derived precipitation differences between the Late Miocene and modern can be largely accounted for by the palaeogeographic changes alone. However, the proxy-derived temperatures differences between the Late Miocene and modern can only begin to be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates.

  11. The relative roles of CO2 and palaeogeography in determining late Miocene climate: results from a terrestrial model-data comparison

    NASA Astrophysics Data System (ADS)

    Bradshaw, C. D.; Lunt, D. J.; Flecker, R.; Salzmann, U.; Pound, M. J.; Haywood, A. M.; Eronen, J. T.

    2012-08-01

    The late Miocene palaeorecord provides evidence for a warmer and wetter climate than that of today, and there is uncertainty in the palaeo-CO2 record of at least 200 ppm. We present results from fully coupled atmosphere-ocean-vegetation simulations for the late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO2 concentration in the determination of late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that these data accurately reflect the late Miocene climate, and that the late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that: 1. Both palaeogeography and atmospheric CO2 contribute to the proxy-derived precipitation differences between the late Miocene and modern reference climates. However these contributions exibit synergy and so do not add linearly. 2. The vast majority of the proxy-derived temperature differences between the late Miocene and modern reference climates can only be accounted for if we assume a palaeo-CO2 concentration towards the higher end of the range of estimates.

  12. Glacial and Holocene terrestrial temperature variability in subtropical east Australia as inferred from branched GDGT distributions in a sediment core from Lake McKenzie

    NASA Astrophysics Data System (ADS)

    Woltering, Martijn; Atahan, Pia; Grice, Kliti; Heijnis, Henk; Taffs, Kathryn; Dodson, John

    2014-07-01

    Branched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene.

  13. Changes in Terrestrial Organic Carbon Delivery to the Colville River Delta and Adjacent Simpson's Lagoon Over the Late Holocene

    NASA Astrophysics Data System (ADS)

    Schreiner, K. M.; Bianchi, T. S.; Allison, M. A.; Miller, A. J.; Marcantonio, F.

    2012-04-01

    The Colville River in Alaska is the largest river in North America that drains only continuously permafrosted tundra, and as such provides a unique signal of historical changes in one of the world's most vulnerable areas to climate changes. Additionally, the Colville flows into Simpson's Lagoon, a shallow area of the Alaskan Beaufort coast protected by a barrier island chain, lessening the impacts of Arctic storms and ice grounding on sediment mixing. Cores collected from the Colville river delta in August of 2010 were found to be composed of muddy, organic-rich, well-laminated sediments. The 2.5 to 3 meter length of each core spans about one to two thousand years of Holocene history, including the entire Anthropocene and much of the late Holocene. Three cores were sampled for this data set, arranged latitudinally from the mouth of the Colville River east into Simpson's Lagoon. Samples were taken every 2 cm for the entire length of all cores. Bulk analyses including percent organic carbon, percent nitrogen, and stable carbon isotopic analysis were performed, and compound specific analyses including lignin-phenol and algal pigment analyses were performed. These analyses showed significant changes in carbon storage over the past one to two thousand years. There were also significant spatial differences in organic carbon inputs across the ~20km distance between the Colville mouth and the easternmost core. Lignin-phenol concentrations in surface sediments nearest to the river mouth correlated positively with reconstructed Alaskan North Slope temperatures, suggesting more terrestrial organic matter was delivered during higher temperature regimes. Molar C:N ratios and plant pigments correlated negatively and positively, respectively, with reconstructed Alaskan North Slope moisture regime, indicating greater algal inputs during wetter time periods. These data may in part be consistent with observed woody shrub encroachment and increasing expanse of permafrost lakes on the

  14. An evaluation of Mesodon and other larger terrestrial gastropod shells for dating late Holocene and historic alluvium in the Midwestern USA

    USGS Publications Warehouse

    Rakovan, Monica T.; Rech, Jason A.; Pigati, Jeffery S.; Nekola, Jeffery C.; Wiles, Gregory C.

    2013-01-01

    Understanding the history of stream erosion and changes in channel morphology is important for managing and restoring unstable streams. One of the significant challenges in this type of research is establishing accurate dating of late Holocene and historic alluvium. Here we evaluate the potential of using 14C dating and amino acid racemization (AAR) to date large terrestrial gastropod shells that are often preserved within alluvial sediments. Many terrestrial gastropods incorporate old carbon from limestone or other carbonate rocks into their shells and therefore are unsuitable for radiocarbon dating. Recent studies, however, have shown that some taxa avoid this ‘limestone problem’ and can yield reliable 14C ages. In this study, we measured the 14C activity of specimens for the genera Mesodon, Ventridens, and Allogona collected live and from alluvial sequences dated independently by dendrochronology, 14C dating of wood, and/or 137Cs analyses. Mesodon zaletus contained old carbon in similar concentrations (up to ~ 30%) found in previous studies of other large taxa and should be avoided for 14C dating when possible. In contrast, shells of Ventridens ligera and Allogona profunda showed minimal limestone effects and therefore may be suitable for dating late Holocene alluvium. These results highlight the importance of taxonomic identification of gastropod taxa prior to their use for 14C dating and demonstrate that shell fragments that are not identifiable should be avoided. We also measured d/l ratios (n = 17) of aspartic and glutamic acid from eight different taxa of terrestrial gastropods recovered from four late Holocene and historic stratigraphic sequences. Average d/l ratios of aspartic and glutamic acid from historic sediments < 300 years old are lower in shells from younger stratigraphic units, indicating that AAR can be used to differentiate between multiple historic stratigraphic units.

  15. Compound Specific D/H Records of Marine and Terrestrial Biomarkers From Core MD972151 in the Southern South China Sea During the Last Glacial-Interglacial Cycle

    NASA Astrophysics Data System (ADS)

    Izawa, Y.; Yamamoto, M.; Seki, O.; Kawamura, K.; Chen, M.

    2006-12-01

    Hydrological changes in the Western Pacific Warm Pool are a recent central issue of the paleoclimate study for the tropical Pacific. Here we present 150-kyr records of deuterium/hydrogen ratios of short- and long-chain n-fatty acids, which derived from aquatic organisms and terrestrial higher plants, respectively, in the IMAGES MD972151 core. The delta D of short-chain fatty acids (C16 and C18) ranged from ~-220 to ~-150 permil vs SMOW. A strong negative shift of delta D occurred at ~17 ka, which is attributed to the decrease of salinity in the southern South China Sea, suggesting an enhanced riverine discharge. The delta D of long-chain fatty acids (C24 to C28) ranged from ~-160 to ~-120 permil. The delta D showed a minimum at ~17 ka. This phenomenon is attributed to changes in either moisture or precipitation D/H ratio. These findings suggest a drastic change of hydrological dynamics in the Western Pacific Warm Pool in the early stage of the last deglaciation.

  16. A Comparison of Re-Os Isotopes and Abundances of Highly Siderophile Elements in Chondritic Meteorites: Constraints on Terrestrial Late Accretion

    NASA Astrophysics Data System (ADS)

    Horan, M. F.; Walker, R. J.

    2001-12-01

    Understanding the distributions of refractory, highly-siderophile elements (HSE) in chondritic meteorites is necessary to better constrain the history and distributions of those elements in terrestrial and planetary mantles. It is now widely, although not unanimously, agreed that the bulk of the highly siderophile elements in the Earth's mantle were added subsequent to terrestrial core segregation, by late accretion of broadly chondritic materials. New, precise abundance data for the HSE in chondrites, coupled with Re-Os isotopic data for the same meteorites, indicate that each of the three major chondrite groups is uniquely defined. Re-Os isotopic data show isotopic evidence for a major difference in long-term Re/Os (as shown in their modern 187Os/188Os) between carbonaceous chondrites relative to and ordinary and enstatite chondrites. Ordinary chondrites have 187Os/188Os=0.1283+/-0.0031. Enstatite chondrites have 187Os/188Os=0.1281+/-0.0009; and carbonaceous chondrites have 187Os/188Os=0.1260+/-0.0021. These differences reflect 7-8% lower Re/Os ratio in carbonaceous chondrites, compared to enstatite and ordinary chondrites. This fractionation process occurred very early in the history of the solar system, possibly during condensation. It has been long recognized that enstatite chondrites have relatively high Pd concentrations, compared to the other highly siderophile elements. Our new data show that enstatite chondrites have Pd/Ru and Pd/Ir ratios of 0.987+/-0.102 and 1.48+/-0.18. Carbonaceous chondrites and ordinary chondrites have distinctly lower Pd/Ru and Pd/Ir ratios. Pd/Ru and Pd/Ir in carbonaceous chondrites average 0.754+/-0.104 and 1.08+/-0.17, respectively. Similarly, ordinary chondrites have average Pd/Ru and Pd/Ir ratios of 0.759+/-0.088 and 1.153+/-0.153. The cause of high relative Pd concentrations in enstatite chondrites is not well understood. Its ubiquitous presence, regardless of the presence of brecciation, degree of metamorphism and

  17. The contribution of micrometeorites to the iron stocks of buried podzols, developed in Late-glacial aeolian sand deposits (Brabant, The Netherlands)

    NASA Astrophysics Data System (ADS)

    van Mourik, Jan; de Vet, Sebastiaan

    2015-04-01

    The surface geology of an extensive part of NW-Europe is dominated by coversands (Late-glacial chemical poor aeolian sand deposits). The geomorphology of coversand landscapes is dominated by ridges and planes. Podzolation is the dominant soil forming process in coversands under moderate humid climatic conditions. Umbric Podzols developed on the ridges under Quercetum-mixtum, Gleyic and Histic Podzols developed in the planes under Alnetum. Even in chemical poor coversands, iron will be released by hydrolysis from iron containing silicate minerals (such as feldspars). It is well known that the vertical iron distribution in Podzols is effected by translocation of active iron from eluvial to illuvial horizons and that iron is leaching to the aquifer. Iron stocks of Podzols, in contrasts, have not been widely studied for comparison purposes of individual soil horizons or between soils. We determined the stocks of active and immobile iron in the horizons of buried xeromorphic Podzols (soils that developed without any contact with groundwater). The results show that the total amount of iron exceeds the potential amount which can be released by hydrolysis from the parent material. Furthermore, to amount of iron that leached to the groundwater is unknown. It is evident that we must find an additional source to explain the total iron stocks in buried Podzols. It is known from analysis of ice cores that the earth atmosphere is subjected to a continuous influx of (iron rich) micrometeorites. The precipitation of micrometeorites (and other aerosols) on the earth surface is concentrated in humid climatic zones with (intensive) rain fall. We analyzed minerals, extracted from the ectorganic horizon of the Initial Podzols, developed in driftsand that stabilized around 1900 AD, overlying Palaeopodzols, buried around 1200 AD. Among blown in quartz grains, we could determine also micrometeorites, embedded in the organic skeleton of the fermentation horizon of the Initial Podzol

  18. Periodic isolation of the southern coastal plain of South Africa and the evolution of modern humans over late Quaternary glacial to interglacial cycles

    NASA Astrophysics Data System (ADS)

    Compton, J. S.

    2012-04-01

    Humans evolved in Africa, but where in Africa and by what mechanisms remain unclear. The evolution of modern humans over the last million years is associated with the onset of major global climate fluctuations, glacial to interglacial cycles, related to the build up and melting of large ice sheets in the Northern Hemisphere. During interglacial periods, such as today, warm and wet climates favored human expansion but during cold and dry glacial periods conditions were harsh and habitats fragmented. These large climate fluctuations periodically expanded and contracted African ecosystems and led to human migrations to more hospitable glacial refugia. Periodic isolation of relatively small numbers of humans may have allowed for their rapid evolutionary divergence from the rest of Africa. During climate transitions these divergent groups may have then dispersed and interbred with other groups (hybridization). Two areas at the opposite ends of Africa stand out as regions that were periodically isolated from the rest of Africa: North Africa (the Maghreb) and the southern coastal plain (SCP) of South Africa. The Maghreb is isolated by the Sahara Desert which periodically greens and is reconnected to the rest of Africa during the transition from glacial to interglacial periods. The SCP of South Africa is isolated from the rest of Africa by the rugged mountains of the Cape Fold Belt associated with inedible vegetation and dry climates to the north. The SCP is periodically opened when sea level falls by up to 130 m during glacial maxima to expose the present day submerged inner continental shelf. A five-fold expansion of the SCP receiving more rainfall in glacial periods may have served as a refuge to humans and large migratory herds. The expansive glacial SCP habitat abruptly contracts, by as much as one-third in 300 yr, during the rapid rise in sea level associated with glacial terminations. Rapid flooding may have increased population density and competition on the SCP to

  19. 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)

    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

    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

  20. Marine record of late quaternary glacial-interglacial fluctuations in the Ross Sea and evidence for rapid, episodic sea level change due to marine ice sheet collapse

    NASA Technical Reports Server (NTRS)

    Anderson, John B.

    1991-01-01

    Some of the questions to be addressed by SeaRISE include: (1) what was the configuration of the West Antarctic ice sheet during the last glacial maximum; (2) What is its configuration during a glacial minimum; and (3) has it, or any marine ice sheet, undergone episodic rapid mass wasting. These questions are addressed in terms of what is known about the history of the marine ice sheet, specifically in Ross Sea, and what further studies are required to resolve these problems. A second question concerns the extent to which disintegration of marine ice sheets may result in rises in sea level that are episodic in nature and extremely rapid, as suggested by several glaciologists. Evidence that rapid, episodic sea level changes have occurred during the Holocene is also reviewed.

  1. Sorted (clastic) polygons in the Argyre region, Mars, and possible evidence of pre- and post-glacial periglaciation in the Late Amazonian Epoch

    NASA Astrophysics Data System (ADS)

    Soare, R. J.; Conway, S. J.; Gallagher, C.; Dohm, J. M.

    2016-01-01

    The Argyre basin and associated rim-materials in the southern highlands of Mars are ancient, having been formed by the impact of a large body ∼3.9 Gya. Despite its age, the regional landscape exhibits a wide range of geological/geomorphological modifications and/or features, e.g. fluvial, lacustrine, aeolian, glacial and periglacial. Collectively, this bears witness to the dynamic evolution of the Argyre region from the deep past through to, perhaps, the present day.

  2. Stratigraphy and palaeoclimatic significance of Late Quaternary loess-palaeosol sequences of the Last Interglacial-Glacial cycle in central Alaska

    USGS Publications Warehouse

    Muhs, D.R.; Ager, T.A.; Bettis, E. Arthur; McGeehin, J.; Been, J.M.; Beget, J.E.; Pavich, M.J.; Stafford, Thomas W.; Stevens, D.A.S.P.

    2003-01-01

    Loess is one of the most widespread subaerial deposits in Alaska and adjacent Yukon Territory and may have a history that goes back 3 Ma. Based on mineralogy and major and trace element chemistry, central Alaskan loess has a composition that is distinctive from other loess bodies of the world, although it is quartz-dominated. Central Alaskan loess was probably derived from a variety of rock types, including granites, metabasalts and schists. Detailed stratigraphic data and pedologic criteria indicate that, contrary to early studies, many palaeosols are present in central Alaskan loess sections. The buried soils indicate that loess sedimentation was episodic, or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input. As in China, loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess/soil formation cycle. Loess deposition in central Alaska took place before, and probably during the last interglacial period, during stadials of the mid-Wisconsin period, during the last glacial period and during the Holocene. An unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period. Our studies lead us to conclude that vegetation plays a key role in loess accumulation in Alaska. Factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods. The most important of these is vegetation; boreal forest serves as an effective loess trap, but sparsely distributed herb tundra does not. Thus, thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central Alaska. Much of the stratigraphic diversity of North American loess, including that found in the Central Lowlands, the Great Plains, and Alaska is explained by a new

  3. Extraterrestrial accretion and glacial cycles

    NASA Technical Reports Server (NTRS)

    Muller, R. A.

    1994-01-01

    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.

  4. Amplified Late Pliocene terrestrial warmth in northern high latitudes from greater radiative forcing and closed Arctic Ocean gateways

    NASA Astrophysics Data System (ADS)

    Feng, Ran; Otto-Bliesner, Bette L.; Fletcher, Tamara L.; Tabor, Clay R.; Ballantyne, Ashley P.; Brady, Esther C.

    2017-05-01

    Proxy reconstructions of the mid-Piacenzian warm period (mPWP, between 3.264 and 3.025 Ma) suggest terrestrial temperatures were much warmer in the northern high latitudes (55°-90°N, referred to as NHL) than present-day. Climate models participating in the Pliocene Model Intercomparison Project Phase 1 (PlioMIP1) tend to underestimate this warmth. For instance, the underestimate is ∼10 °C on average across NHL and up to 17 °C in the Canadian Arctic region in the Community Climate System Model version 4 (CCSM4). Here, we explore potential mPWP climate forcings that might contribute to this mPWP mismatch. We carry out seven experiments to assess terrestrial temperature responses to Pliocene Arctic gateway closure, variations in CO2 level, and orbital forcing at millennial time scale. To better compare the full range of simulated terrestrial temperatures with sparse proxy data, we introduce a pattern recognition technique that simplifies the model surface temperatures to a few representative patterns that can be validate with the limited terrestrial proxy data. The pattern recognition technique reveals two prominent features of simulated Pliocene surface temperature responses. First, distinctive patterns of amplified warming occur in the NHL, which can be explained by lowered surface elevation of Greenland, pattern and amount of Arctic sea ice loss, and changing strength of Atlantic meridional overturning circulation. Second, patterns of surface temperature response are similar among experiments with different forcing mechanisms. This similarity is due to strong feedbacks from responses in surface albedo and troposphere water vapor content to sea ice changes, which overwhelm distinctions in forcings from changes in insolation, CO2 forcing, and Arctic gateway closure. By comparing CCSM4 simulations with proxy records, we demonstrate that both model and proxy records show similar patterns of mPWP NHL terrestrial warmth, but the model underestimates the magnitude

  5. Shallow-source aeromagnetic anomalies observed over the West Antarctic Ice Sheet compared with coincident bed topography from radar ice sounding—new evidence for glacial "removal" of subglacially erupted late Cenozoic rift-related volcanic edifices

    NASA Astrophysics Data System (ADS)

    Behrendt, John C.; Blankenship, Donald D.; Morse, David L.; Bell, Robin E.

    2004-07-01

    Aeromagnetic and radar ice sounding results from the 1991-1997 Central West Antarctica (CWA) aerogeophysical survey over part of the West Antarctic Ice Sheet (WAIS) and subglacial area of the volcanically active West Antarctic rift system have enabled detailed examination of specific anomaly sources. These anomalies, previously interpreted as caused by late Cenozoic subglacial volcanic centers, are compared to newly available glacial bed-elevation data from the radar ice sounding compilation of the entire area of the aeromagnetic survey to test this hypothesis in detail. We examined about 1000 shallow-source magnetic anomalies for bedrock topographic expression. Using very conservative criteria, we found over 400 specific anomalies which correlate with bed topography directly beneath each anomaly. We interpret these anomalies as indicative of the relative abundance of volcanic anomalies having shallow magnetic sources. Of course, deeper source magnetic anomalies are present, but these have longer wavelengths, lower gradients and mostly lower amplitudes from those caused by the highly magnetic late Cenozoic volcanic centers. The great bulk of these >400 (40-1200-nT) anomaly sources at the base of the ice have low bed relief (60-600 m, with about 80%<200 m). We interpret this relief as an indication of residual topography after glacial removal of volcanic edifices comprising hyaloclastite, pillow breccia and other volcanic debris erupted into the moving ice during volcanism since the initiation of the WAIS >10 million years ago. Eighteen of the anomalies examined, about half concentrated in the area of the WAIS divide, have high-topographic expression (as great as 400 m above sea level) and high bed relief (up to 1500 m). All of these high-topography anomaly sources at the base of the ice would isostatically rebound to elevations above sea level were the ice removed. We interpret these 18 anomaly sources as evidence of subaerial eruption of volcanoes whose topography

  6. Arctic Climate and Terrestrial Vegetation Responses During the Middle to Late Eocene and Early Oligocene: Colder Winters Preceded Cool-Down.

    NASA Astrophysics Data System (ADS)

    Greenwood, D. R.; Eldrett, J.

    2006-12-01

    The late Eocene to early Oligocene is recognized as an interval of substantial change in the global climate, with isotopic proxies of climate indicating a significant drop in sea surface temperatures. Other studies have shown, however that at middle latitudes that terrestrial mean annual temperature did not change significantly over this interval, and that the major change was likely a shift towards a greater range of seasonal temperatures; colder winters and warmer summers. Previous analyses of high latitude (Arctic) middle Eocene climate using both leaf physiognomic analysis and qualitative analysis of identified nearest living relatives of terrestrial floras indicated upper microthermal environments (mean annual temp. or MAT ca 10°C but perhaps as high as 15°C, coldest month mean temp. or CMMT ca 0°C) for Axel Heiberg Island in the Arctic Archipelago, but did not address precipitation nor provide data on the Eocene-Oligocene transition in the Arctic. Presented here are new estimates of temperature and precipitation (annual and season amounts) for the Arctic based on NLR analysis of terrestrial plant palynomorphs (spores and pollen) from the ODP 913B and 985 cores from near Greenland. The record of climate for the Greenland cores show a similar climate in the middle Eocene to that previously estimated for Axel Heiberg Island further to the west, with MAT 10- 15°C but with CMMT >5°C. Precipitation was high (mean annual precip. or MAP >180 cm/yr), although with large uncertainties attached to the estimate. The climate proxy record for the late Eocene to early Oligocene shows a lack of change in MAT and MAP over the time interval. Consistent with other published records at middle latitudes, however, winter temperatures (as CMMT) show greater variability leading up to the E-O boundary, and consistently cooler values in the early Oligocene (CMMT <5°C) than recorded for most of the middle to late Eocene record (CMMT >5°C). Plant groups sensitive to freezing such

  7. High-resolution record of sea ice conditions in Fram Strait sheds new light on ice-ocean interactions and climate variability during the late glacial and Termination 1

    NASA Astrophysics Data System (ADS)

    Müller, Juliane; Stein, Ruediger

    2014-05-01

    Abrupt shifts in the palaeoceanographic setting in the subpolar North Atlantic and a hence significant climate variability characterised the transition from last glacial to deglacial and current interglacial conditions. Knowledge about the crucial role of sea ice coverage during these rapid climate reversals, however, is still limited. Herein we present a high-resolution reconstruction of the sea ice conditions that prevailed in eastern Fram Strait - the only deepwater passage permitting a substantial exchange of water and ice masses between the Arctic and the Atlantic Ocean - during the late glacial and deglacial period (i.e. from 29 ka to 9 ka BP). The joint analysis of the sea ice biomarker IP25 (Belt et al., 2007) and phytoplankton derived biomarkers allows to distinguish between different sea ice conditions and we further provide an even semi-quantitative assessment of the sea ice cover by means of the PIP25 index (Müller et al., 2011). Information about relative sea surface temperature changes is derived from the so-called DIP25 index (Cabedo-Sanz et al., 2013; Fahl & Stein, 2012). Importantly, the exceptional high temporal resolution of the studied sediment core permits the identification of a hitherto unknown variability in the sea ice coverage throughout the late glacial, which finally culminates in a permanent sea ice cover at the end of the Last Glacial Maximum (LGM). We suggest that the heat flow to the Nordic Seas during this critical time interval of Northern Hemisphere ice-sheet growth was rather pulse-like than continuous as is commonly assumed. This new observation of late glacial short-term fluctuations in the sea ice cover has considerable implications for palaeoceanographic proxy and model studies that focus on the LGM. Furthermore, we consider that the abrupt breakup of the perennial sea ice cover in Fram Strait at about 18 ka BP directly contributed to the weakening of the Atlantic Meridional Overturning Circulation (AMOC) during Heinrich

  8. Late Pleistocene Magnitude Glacial Incursions of Southern Component Water to the Deep North Atlantic Resolved Using Nd Isotopes during the Intensification of Northern Hemisphere Glaciation (3.3 to 2.4 Ma)

    NASA Astrophysics Data System (ADS)

    Lang, D.; Bailey, I.; Wilson, P. A.; Foster, G. L.; Gutjahr, M.

    2014-12-01

    The ocean, through its ability to globally redistribute heat and partition carbon dioxide, is believed to play a key role in driving and amplifying climate change during Quaternary glaciations on orbital to millennial timescales. Relatively little is known, however, about changes in Atlantic Meridional Overturning Circulation (AMOC) associated with the Pliocene intensification of Northern Hemisphere glaciation (iNHG). To help fill this gap in our knowledge we present a new high resolution (~6 ka) record of the Nd isotope composition of the deep North Atlantic between ~3.3 and 2.4 Ma, measured on fish debris at IODP Site U1313 (3426 m, 41°N, 32.5°W). This record represents the first orbital-resolution record of variations in watermass mixing in this region for iNHG independent of changes in the carbon cycle and, in contrast to existing benthic foraminiferal δ13C records for this time interval, our Nd dataset contains evidence for late Pleistocene magnitude incursions of Southern Component Waters to the deep North Atlantic Ocean during key glacial periods through this time. We therefore infer an important role for AMOC variability in amplifying Quaternary glacial-interglacial cycles

  9. Dynamics of the transfer of terrestrial organic matter in the late Quaternary turbiditic system of the Ogooué River (Gabon)

    NASA Astrophysics Data System (ADS)

    Mignard, Salomé; Mulder, Thierry; Martinez, Philippe; Garlan, Thierry

    2016-04-01

    -size sediments. This organic sedimentation is highly sensitive to the variations of the sea level due to the alternation between glacial and interglacial times. Glacial periods are characterized by higher amounts of organic matter in hemipelagic deposits, with a higher contribution of continental material, and by the presence of frequent organic rich turbiditic beds. On the contrary, during interglacial periods very few turbiditic events are recorded and the OM in hemipelagic sediments is mainly of marine origin and in lesser quantity. When the sea-level is high, the Ogooué delta is disconnected from the canyon heads and the sediments delivered by the river are deposited on the shelf and mobilized by the strong South-North coastal drift currents. During low sea-level periods, the river discharges its sediments rich in terrestrial OM directly in the canyons heads bypassing the shelf. The low sea level also generates increased erosion of the shelf sediments containing globally high rate of reworked continental OM.

  10. Late-Pleistocene precipitation δ18O interpolated across the global landmass

    NASA Astrophysics Data System (ADS)

    Jasechko, Scott

    2016-08-01

    Global water cycles, ecosystem assemblages, and weathering rates were impacted by the ˜4°C of global warming that took place over the course of the last glacial termination. Fossil groundwaters can be useful indicators of late-Pleistocene precipitation isotope compositions, which, in turn, can help to test hypotheses about the drivers and impacts of glacial-interglacial climate changes. Here, a global catalog of 126 fossil groundwater records is used to interpolate late-Pleistocene precipitation δ18O across the global landmass. The interpolated data show that extratropical late-Pleistocene terrestrial precipitation was near uniformly depleted in 18O relative to the late Holocene. By contrast, tropical δ18O responses to deglacial warming diverged; late-Pleistocene δ18O was higher-than-modern across India and South China but lower-than-modern throughout much of northern and southern Africa. Groundwaters that recharged beneath large northern hemisphere ice sheets have different Holocene-Pleistocene δ18O relationships than paleowaters that recharged subaerially, potentially aiding reconstructions of englacial transport in paleo ice sheets. Global terrestrial late-Pleistocene precipitation δ18O maps may help to determine 3-D groundwater age distributions, constrain Pleistocene mammal movements, and better understand glacial climate dynamics.

  11. Shallow-source aeromagnetic anomalies observed over the West Antarctic Ice Sheet compared with coincident bed topography from radar ice sounding - New evidence for glacial "removal" of subglacially erupted late Cenozoic rift-related volcanic edifices

    USGS Publications Warehouse

    Behrendt, John C.; Blankenship, D.D.; Morse, D.L.; Bell, R.E.

    2004-01-01

    Aeromagnetic and radar ice sounding results from the 1991-1997 Central West Antarctica (CWA) aerogeophysical survey over part of the West Antarctic Ice Sheet (WAIS) and subglacial area of the volcanically active West Antarctic rift system have enabled detailed examination of specific anomaly sources. These anomalies, previously interpreted as caused by late Cenozoic subglacial volcanic centers, are compared to newly available glacial bed-elevation data from the radar ice sounding compilation of the entire area of the aeromagnetic survey to test this hypothesis in detail. We examined about 1000 shallow-source magnetic anomalies for bedrock topographic expression. Using very conservative criteria, we found over 400 specific anomalies which correlate with bed topography directly beneath each anomaly. We interpret these anomalies as indicative of the relative abundance of volcanic anomalies having shallow magnetic sources. Of course, deeper source magnetic anomalies are present, but these have longer wavelengths, lower gradients and mostly lower amplitudes from those caused by the highly magnetic late Cenozoic volcanic centers. The great bulk of these >400 (40-1200-nT) anomaly sources at the base of the ice have low bed relief (60-600 m, with about 80%10 million years ago. Eighteen of the anomalies examined, about half concentrated in the area of the WAIS divide, have high-topographic expression (as great as 400 m above sea level) and high bed relief (up to 1500 m). All of these high-topography anomaly sources at the base of the ice would isostatically rebound to elevations above sea level were the ice removed. We interpret these 18 anomaly sources as evidence of subaerial eruption of volcanoes whose topography was protected from erosion by competent volcanic flows similar to prominent volcanic peaks that are exposed above the surface of the WAIS. Further, we infer these volcanoes as possibly erupted at a time when the WAIS was absent. In contrast, at the other extreme

  12. Constraints on Lake Agassiz discharge through the late-glacial Champlain Sea (St. Lawrence Lowlands, Canada) using salinity proxies and an estuarine circulation model

    USGS Publications Warehouse

    Katz, B.; Najjar, R.G.; Cronin, T.; Rayburn, J.; Mann, M.E.

    2011-01-01

    During the last deglaciation, abrupt freshwater discharge events from proglacial lakes in North America, such as glacial Lake Agassiz, are believed to have drained into the North Atlantic Ocean, causing large shifts in climate by weakening the formation of North Atlantic Deep Water and decreasing ocean heat transport to high northern latitudes. These discharges were caused by changes in lake drainage outlets, but the duration, magnitude and routing of discharge events, factors which govern the climatic response to freshwater forcing, are poorly known. Abrupt discharges, called floods, are typically assumed to last months to a year, whereas more gradual discharges, called routing events, occur over centuries. Here we use estuarine modeling to evaluate freshwater discharge from Lake Agassiz and other North American proglacial lakes into the North Atlantic Ocean through the St. Lawrence estuary around 11.5 ka BP, the onset of the Preboreal oscillation (PBO). Faunal and isotopic proxy data from the Champlain Sea, a semi-isolated, marine-brackish water body that occupied the St. Lawrence and Champlain Valleys from 13 to 9 ka, indicate salinity fell about 7-8 (range of 4-11) around 11.5 ka. Model results suggest that minimum (1600 km3) and maximum (9500 km3) estimates of plausible flood volumes determined from Lake Agassiz paleoshorelines would produce the proxy-reconstructed salinity decrease if the floods lasted <1 day to 5 months and 1 month to 2 years, respectively. In addition, Champlain Sea salinity responds very quickly to the initiation (within days) and cessation (within weeks) of flooding events. These results support the hypothesis that a glacial lake flood, rather than a sustained routing event, discharged through the St. Lawrence Estuary during the PBO. ?? 2011 Elsevier Ltd.

  13. Turbidite Megabeds in an Oceanic Rift Valley Recording Jökulhlaups of Late Pleistocene Glacial Lakes of the Western United States.

    PubMed

    Zuffa; Normark; Serra; Brunner

    2000-05-01

    Escanaba Trough is the southernmost segment of the Gorda Ridge and is filled by sandy turbidites locally exceeding 500 m in thickness. New results from Ocean Drilling Program (ODP) Sites 1037 and 1038 that include accelerator mass spectrometry (AMS) 14C dates and revised petrographic evaluation of the sediment provenance, combined with high-resolution seismic-reflection profiles, provide a lithostratigraphic framework for the turbidite deposits. Three fining-upward units of sandy turbidites from the upper 365 m at ODP Site 1037 can be correlated with sediment recovered at ODP Site 1038 and Deep Sea Drilling Program (DSDP) Site 35. Six AMS 14C ages in the upper 317 m of the sequence at Site 1037 indicate that average deposition rates exceeded 10 m/k.yr. between 32 and 11 ka, with nearly instantaneous deposition of one approximately 60-m interval of sand. Petrography of the sand beds is consistent with a Columbia River source for the entire sedimentary sequence in Escanaba Trough. High-resolution acoustic stratigraphy shows that the turbidites in the upper 60 m at Site 1037 provide a characteristic sequence of key reflectors that occurs across the floor of the entire Escanaba Trough. Recent mapping of turbidite systems in the northeast Pacific Ocean suggests that the turbidity currents reached the Escanaba Trough along an 1100-km-long pathway from the Columbia River to the west flank of the Gorda Ridge. The age of the upper fining-upward unit of sandy turbidites appears to correspond to the latest Wisconsinan outburst of glacial Lake Missoula. Many of the outbursts, or jökulhlaups, from the glacial lakes probably continued flowing as hyperpycnally generated turbidity currents on entering the sea at the mouth of the Columbia River.

  14. Separating the Effects of Northern Hemisphere Ice-Sheets, CO2 Concentrations and Orbital Parameters on Global Precipitation During the Late Pleistocene Glacial Cycles

    NASA Astrophysics Data System (ADS)

    Elison Timm, O.; Friedrich, T.; Timmermann, A.; Ganopolski, A.

    2015-12-01

    Global-scale changes in the hydrological cycle have been reconstructed in many parts of the world using various archives of proxy information. The signals found in proxies allow us to study the complex response of the global hydrological cycle to the combined forcing and feedback mechanisms. However, it remains a challenge to attribute the observed variations to specific causes, in particular, it is difficult to distinguish CO2 and ice-sheet response in time series. Here, we present new results from a set of transient paleoclimate simulation of the last eight glacial cycles (784,000 years) using accelerated forcing. In order to isolate the ice-sheet forcing from the CO2 -driven response and orbital forcing, we made use of additional transient experiments with varying forcing combinations covering the last 408,000 years: (a) keeping CO2 concentrations constant, (b) keeping the ice-sheet fixed, (c) orbital forcing only. The simulations show that orbital forcing has strongest impact in the tropical and subtropical regions. The northern hemisphere ice-sheets stamp a characteristic spatial footprint on the global precipitation variability. The ice-sheets mainly affect the extratropical northern hemisphere, but the cone of influence extends further into the North African monsoon regions, and to a weaker extent into the Asian monsoon. In an attempt to validate our model-specific results we compared our results with existing hydrological paleo proxy records. Despite the growing number of proxy archives, the aim to identify the ice-sheet influence in spatially limited networks of proxy time series remains as challenge. More records that cover at least two full glacial cycles could significantly increase the signal separation. In conclusion, our results suggest that the northern hemisphere ice-sheets played an important role in modulating the global hydrological cycle.

  15. Carbon isotopic record of terrestrial ecosystems spanning the Late Miocene extinction of Oreopithecus bambolii, Baccinello Basin (Tuscany, Italy).

    PubMed

    Matson, Samuel D; Rook, Lorenzo; Oms, Oriol; Fox, David L

    2012-07-01

    Oreopithecus bambolii is a Late Miocene hominoid with an extensive fossil record in the Baccinello Basin (Tuscany, Italy), and was the only western European hominoid to survive a major extinction event ca. 9.6 Ma (millions of years ago). Oreopithecus lived in the insular Tusco-Sardinian paleobioprovince, where it evolved many unique anatomical specializations that make it important for understanding the mechanisms and history of Late Miocene hominoid evolution. The eventual extinction of Oreopithecus and its associated fauna ca. 6.5 Ma has generally been attributed to interaction with species that arrived from continental Europe following tectonic collision of the Tusco-Sardinian province with mainland Italy, but palynological, paleontological, and sedimentological records indicate an environmental shift toward more variable climate across the extinction event. To explore the possibility of environmental change as a contributing factor in the extinction of Oreopithecus, we developed a stable carbon and oxygen isotope record from organic matter in paleosols from the Baccinello Basin. These data show very low temporal and spatial variability (indicating plant ecosystem stability through time and space) and provide no evidence for ecologically significant changes in floral composition spanning the extinction event, suggesting that environmental change was not an underlying cause for the extinction of Oreopithecus and its associated fauna. The carbon isotope values fall entirely within the range of isotopic variability for modern plants following the C(3) photosynthetic pathway (trees, shrubs, cool-season grasses), indicating that C(4) vegetation (warm-season grasses) was not an important component of biomass. When corrected for temporal variation in the carbon isotopic composition of atmospheric carbon dioxide, the paleosol carbon isotope values are consistent with predicted values based on modern plants and the Baccinello palynoflora, supporting the reliability of

  16. Using ice sheet models simulations of the last glacial period for the reconstruction of late Holocene ground surface temperatures from borehole temperature profiles

    NASA Astrophysics Data System (ADS)

    Rath, V.; Álvarez-Solas, J.; Robinson, A.; Montoya-Redondo, M.

    2012-12-01

    Borehole temperature profiles (BTP) are not only the source for estimates of the background geothermal heat flow, but also allow the reconstruction of past surface temperature changes. Though shallow boreholes (e. g. less than 500 m) are available nearly everywhere, their use is inhibited by the necessity of extracting the paleoclimatic signal present in the borehole temperature at any depth. However, assuming a long-term ground surface temperature history (GSTH), a generalized reduced temperature may be used for the interpretation of the shallow observations. To derive or test the required assumptions, very deep boreholes (say, > 2000 m) are highly important also for the investigation of shallow measurements. In areas which were influenced by the Last Glacial Period (LGP), the existence of the large scale ice sheets (e.g. the Laurentide or Weichselian), the spatial distribution of basal conditions, and the timing of their retreat have a major influence on the subsurface temperature regime. Though for parts of its history no longer directly related to atmospheric temperature, deep BTPs carry information on basal conditions and retreat histories, and can thus contribute to the confirmation/rejection, or even calibration of ice sheet models. From this it follows that a meaningful interpretation of the paleoclimatic signal can only proceed with a reasonable understanding of the regional ice sheet behavior, and, in order to quantify the effects, a calibrated numerical ice sheet model. From such a model, synthetic long term GSTHs may be generated, which can subsequently be used to derive the generalized reduced temperatures for the shallow BTPs. This approach is challenging in several aspects: (1) high-resolution, high-order/hybrid ice sheet models are only now emerging, and the physics at the base (e.g. ice streams) needs improvement; (2) a calibration in the sense of a Bayesian inverse problem are rare, and (3) appropriate sets of borehole data (including the

  17. Glacial Seismology.

    PubMed

    Aster, Richard; Winberry, Paul

    2017-08-07

    Seismic source and wave propagation studies contribute to understanding structure, transport, fracture mechanics, mass balance, and other processes within glaciers and their surrounding environments. Glaciogenic seismic waves readily couple with the bulk Earth, and can be recorded by seismographs deployed at local to global ranges. Although the fracturing, ablating, melting, and/or highly irregular environment of active glaciers can be highly unstable and hazardous, informative seismic measurements can commonly be made at stable proximal ice or rock sites. Seismology also contributes more broadly to emerging studies of elastic and gravity wave coupling between the atmosphere, oceans, solid Earth, and cryosphere, and recent scientific and technical advances have produced glaciological/seismological collaborations across a broad range of scales and processes. This importantly includes improved insight into the responses of cryospheric systems to changing climate and other environmental conditions. Here, we review relevant fundamental physics and glaciology, and provide a broad review of the current state of glacial seismology and its rapidly evolving future directions. © 2017 IOP Publishing Ltd.

  18. 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)

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

    2009-12-01

    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

  19. 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)

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

    2009-04-01

    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

  20. A Late-Glacial-to-modern reconstruction of the Southern Hemisphere westerly winds: New insights from a Lake Hayes, New Zealand sediment core

    NASA Astrophysics Data System (ADS)

    Hinojosa, J.; Moy, C. M.; Vandergoes, M.; Sessions, A. L.

    2016-12-01

    The Southern Hemisphere westerly winds strongly influence air-sea CO2 exchange in the Southern Ocean, one of the largest carbon sinks on Earth. The winds may have played a significant role in accelerating deep ocean CO2 release during the last glacial termination, thus creating a positive feedback leading to enhanced warming. However, the strength and position of the westerly winds remain unclear on multi-millennial timescales, especially in different sectors of the wind field. In particular, there are limited data from the southwest Pacific sector. Here, we present a new 18-kyr lacustrine sedimentary record of climate variability from Lake Hayes, New Zealand. Using a multiproxy approach in a 6 m core, we reconstruct precipitation, catchment and lake hydrology, and lake productivity, all of which inform us on regional wind strength and direction. Our proxies include compound-specific stable isotopes (n-alkane δD), bulk organic δ13C, magnetic susceptibility, and elemental concentrations. This new record provides a climate chronology that matches well with existing records from South America, indicating zonally symmetric wind patterns during the deglaciation and Holocene.

  1. Cosmogenic 36Cl exposure ages reveal a 9.3 ka BP glacier advance and the Late Weichselian-Early Holocene glacial history of the Drangajökull region, northwest Iceland

    NASA Astrophysics Data System (ADS)

    Brynjólfsson, Skafti; Schomacker, Anders; Ingólfsson, Ólafur; Keiding, Jakob K.

    2015-10-01

    We present twenty-four new cosmogenic isotope (36Cl) surface exposure ages from erratic boulders, moraine boulders and glacially eroded bedrock that constrain the late Weichselian to Holocene glacial history of the Drangajökull region, northwest Iceland. The results suggest a topographically controlled ice sheet over the Vestfirðir (Westfjords) peninsula during the last glaciation. Cold based non-erosive sectors of the ice sheet covered most of the mountains while fjords and valleys were occupied with erosive, warm-based ice. Old36Cl exposure ages from highlands and mountain plateaux (L8; 76.5 ka and H1; 41.6 ka) in combination with younger erratic boulders (L7; 26.2 and K1-K4; 15.0-13.8 ka) superimposed on such surfaces suggest the presence of non-erosive ice over uplands and plateaux in the Vestfirðir peninsula during the last glaciation. Glacially scoured terrain and erratic boulders yielding younger exposure ages (L1-L6; 11.3-9.1 ka and R1, R6-R7; 10.6-9.4 ka) in the lowland areas indicate that the valleys and fjords of the Vestfirðir peninsula were occupied by warm-based, dynamic ice during the last glaciation. The deglaciation of mountain Leirufjall by 26.2 ka BP suggests that ice thinning and deglaciation of some mountains and plateaux preceded any significant lateral retreat of the ice sheet. Subsequently this initial ice thinning was followed by break-up of the shelf based ice sheet off Vestfirðir about 15 ka BP. Hence, the new exposure ages suggest a stepwise asynchronous deglaciation on land, following the shelf break-up with some valleys and most of the highlands, ice free by 14-15 ka BP. The outermost moraine at the mouth of Leirufjörður is dated to 9.3 ka BP, and we suggest the moraine to be formed by a glacier re-advance in response to a cooler climate forced by the reduced Atlantic Meridional Overturning Circulation at around 9.3 ka BP. A system of moraines proximal to the 9.3 ka moraine in Leirufjörður as well as a 9.4 ka deglaciation age

  2. Palaeoglacial lake and outburst flood reconstructions along the southern late-glacial Cordilleran Ice Sheet margin: implications for ice sheet reconstruction and landscape evolution

    NASA Astrophysics Data System (ADS)

    Cripps, Jonathan; Brennand, Tracy

    2016-04-01

    Proglacial lakes are crucial in controlling the meltwater and sediment flux from decaying ice margins, affect local ice dynamics, and can influence local and regional weather and climate. They are also potential sources of outburst floods, which can have major impacts on regional geomorphology and drainage networks. As such, proglacial lakes are important components of deglacial environments, and reconstructing proglacial lakes during decay of past ice sheets will improve understanding of their potential influence in the future. The presence of palaeo-ice-dammed lakes in valleys dissecting the southern Interior Plateau of British Columbia (BC), is evident in abundant lake-bottom sediments, deltaic deposits and shorelines. To date, the palaeogeography of these lakes have not been well constrained, and the damming ice margins have been proposed under a paradigm of Cordilleran Ice Sheet (CIS) stagnation - lakes dammed by dead-ice lobes in valleys where ice was thickest; this paradigm has been challenged by recent studies elsewhere on the Interior Plateau that support generally active, systematic retreat of the ice margin to the north and west. This project reinvestigated glacial Lake Nicola (gLN) on the northern Thompson Plateau, the key site for development of the stagnation paradigm, to improve palaeogeographic and palaeohydrological reconstructions of this basin. Five lake stages for gLN have been identified on the basis of shoreline and delta elevations and the extent of lake-bottom sediments. Glacioisostatic tilts were reconstructed for the four most extensive stages of between 1.6 and 1.9 m/km up to the north-northwest. Areal extent and lake volume for each lake were extracted by plotting lake planes onto DEMs adjusted to these reconstructed tilts; maximum volumes for each stage are in the order of 10 km3, with the largest reconstructed at 260km3. These lakes expanded and lowered to the northwest, as progressively lower outlets were opened by ice recession in

  3. Marine and Terrestrial Evidence for Glaciation during the Pliocene - a Global Synthesis

    NASA Astrophysics Data System (ADS)

    De Schepper, S.; Gibbard, P. L.; Salzmann, U.; Ehlers, J.

    2014-12-01

    The Pliocene climate is globally warm and characterized by high atmospheric carbon dioxide concentrations. Nevertheless, considerable evidence for substantial glaciation events has been identified in both the Northern and Southern Hemisphere prior to the Quaternary. Evidence on land is fragmentary, but marine records of glaciation present a more complete history of Pliocene glaciation. A global compilation of glacial evidence (De Schepper et al. 2014) demonstrates that there are four large glaciation events in the Southern and/or Northern Hemisphere prior to the latest Pliocene intensification of Northern Hemisphere glaciation. Two global glacial events are identified in the early Pliocene, one around the early/late Pliocene transition, and one during the late Pliocene Marine Isotope Stage M2. ReferenceDe Schepper, S., Gibbard, P.L., Salzmann, U., Ehlers, J., 2014. A global synthesis of the marine and terrestrial evidence for glaciation during the Pliocene Epoch. Earth-Science Reviews 135, 83-102.

  4. Late Quaternary glacial/interglacial variability in Arctic sea ice and related organic carbon flux: A 180 ka record from Yermak Plateau

    NASA Astrophysics Data System (ADS)

    Kremer, A.; Stein, R. H.; Fahl, K.; Wiers, S.; Forwick, M.; Matthiessen, J. J.; O'Regan, M.; Snowball, I.

    2016-12-01

    The recent dramatic decline of Arctic sea over the last decades and its controlling processes are still poorly understood. In order to distinguish between natural and anthropogenic processes controlling these changes in sea ice, we have to look back to the past beyond the times of direct measurements. For this purpose, we carried out a multi-proxy approach combining organic-geochemical data (bulk parameters: C/N, TOC, δ13Corg; biomarkers: IP25, sterols, GDGTs) with sedimentological data (core lithology, physical properties, IRD counting, XRF scanning) determined in sediments of Yermak Plateau Core PS92/039-2. This core is situated close to the modern summer ice edge and thus very sensitive for environmental changes. Based on magnetostratigraphy and correlations with dated sediment cores, this core represents the time span from MIS 6 to 1 (ca. 180,000 years) and allows the reconstruction of sea ice variability and related changes in oceanic circulation patterns and the Svalbard Barents Ice Sheet (SBIS) fluctuations during glacial/interglacial changes. As sea ice and phytoplankton biomarkers occur throughout the entire sedimentary section but show some strong variability, a more seasonal sea ice cover was probably predominant during the entire time interval, superimposed by a distinct short-term variability in extent. Significant fluctuations in most of our proxy records indicate highly variable sea ice conditions over the Yermak Plateau during MIS 6. Based on our biomarker data, the SBIS could not have reached the Yermak Plateau during MIS 6. During MIS 4 and 2, coevally elevated concentrations of the sea ice proxy IP25 and the biomarkers for phytoplankton productivity and terrigenous input point to a stationary ice margin above the core position at that time. Strengthened Atlantic Water inflow possibly coupled with katabatic winds from the protruding SBIS may have created this stable ice edge situation and the related sedimentary regime.

  5. Modern and late Pleistocene glacial studies in the central Andes of Peru and Bolivia: Application of satellite remote sensing and digital terrain analysis

    NASA Astrophysics Data System (ADS)

    Klein, Andrew George

    Changes in the glaciers of the central Andes provide insight into changes in the region's climate on timescales ranging from decades to tens or hundreds of thousands of years. Satellite remote sensing was used to map the current extent of glaciers and snow cover as well as the maximum extent of late Pleistocene glaciation. The former extents of glaciers were reconstructed from the position of late Pleistocene moraines. Between 15sp° and 22sp°S, the central Andes contained approximately 11,000 paleo-glaciers with an area of 29,800 kmsp2 and an estimated volume of 3700 kmsp3. These reconstructed glaciers, combined with cirque floor elevations in Peru, were used to determine the late Pleistocene snowline for the central Andes which was 500 to 1200+ meters lower than at present. Mass balance modeling shows the 1200+ meter snowline depression observed in the humid portions of the central Andes to be consistent with a 5sp° to 9sp°C cooling. Extensive glacier expansion in the arid western portion of the central Andes, where the elevation of glaciers today is limited by precipitation, indicates wetter conditions existed during the late Pleistocene as well. This cooling is in agreement with paleoclimate proxy records from other continental sites in South America, but disagrees with current estimates of late Pleistocene sea surface temperatures which indicate only a 1 to 2sp°C cooling. Modern glaciers in the central Andes are presently rapidly retreating. This shrinking has economic implications because glaciers are a valuable water resource. However, no comprehensive monitoring program exists. The ablation and accumulation zones, as well as the transient snowline, were mapped at two tropical sites: Zongo Glacier, Bolivia, and the Quelccaya Ice Cap, Peru, using spectral mixture analysis applied to Landsat Thematic Mapper. Because the transient snowline is a proxy for the equilibrium line altitude (ELA), this technique shows promise in enabling the relative health of

  6. Glacial marine sedimentation: Paleoclimatic significance

    SciTech Connect

    Anderson, J.B.; Ashley, G.M.

    1991-01-01

    This publication resulted from a symposium held during the 1988 Annual Meeting of the Geological Society of America. Many, but not all, contributors to the symposium have papers in this volume. This Special Paper consists of 14 chapters and a Subject/Geographic index. Each chapter has is own list of references. The papers cover a wide range of modem climate/ ocean environments, including papers on glacial marine sediments from Antarctica, the fiords of Alaska, and sediments from the Canadian High Arctic. In addition, three papers discuss [open quote]old[close quotes] glacial marine records (i.e., pre-Tertiary), and one paper discusses the Yakataga Formation of the Gulf of Alaska which is a Miocene-to-late-Pleistocene sequence. The last chapter in the book includes a survey and summary of the evidence for the paleoclimatic significance of glacial marine sediments by the two editors, John Anderson and Gail Ashley. It is worth noting that Anderson and Domack state in the Foreword that there is a considerable variation in terminology; hence they employ a series of definitions which they urge the other authors to employ. They define and explain what they mean by [open quotes]polar ice cap,[close quotes] [open quote]polar tundra (subpolar),[close quotes] and [open quotes]temperate oceanic and boreal[close quotes] in terms of the dominant glacial and glacial marine processes. Although one might quarrel with the terminology, the broad differences between these three glaciological regimes are indeed fundamental and need to be sought in the geological record. The flavor of the volume can be judged by some of the chapter titles. Contributions on Antarctica include a paper by Anderson and other entitled [open quote]Sedimentary facies associated with Antarctica's floating ice masses[close quotes] and a companion paper by Anderson and Domack which deals with the extremely complex glacial marine facies (13 facies are delimited) in McMurdo Sound, Antarctica.

  7. Late Quaternary change in the North American (Mexican) Monsoon: variability in terrestrial and marine records and possible mechanisms

    NASA Astrophysics Data System (ADS)

    Metcalfe, S. E.; Barron, J. A.; Roy, P.; Davies, S.

    2013-05-01

    The Late Quaternary history of the North American (or Mexican) monsoon (NAM) remains poorly understood, with continuing debates about the relative importance of insolation forcing, the role of the Laurentide Ice Sheet (LIS), the expression of warm (D-O) and cold (H) events in the North Atlantic and the influence of the Pacific. To date, more information has been available from the southern and northern margins of the NAM region than from its tropical and subtropical core. This is significant because to the south of the NAM region, the direct effect of ITCZ location is likely to be stronger and any potential influence of the LIS weaker, and to the north, there is an important change in present day precipitation seasonality (from summer to winter), an opposite response to forcings such as ENSO/PDO and AMO and probably a stronger influence of the LIS. As a result, the interpretation of speleothem records from New Mexico (e.g. Asmerom et al., 2010) and Arizona (e.g. Wagner et al., 2010), in the southwestern USA and marine records such as Cariaco (Peterson and Haug, 2006) and lake records such as Peten Iztá (Hodell et al., 2008) may not be applicable to the tropical NAM core. Here we present results from two lacustrine sequences in Mexico (Sayula 20oN; Babicora 29oN) and a marine core record from the central part of the Gulf of California (27oN) all extending back at least through MIS3 (ca. 60 kyr BP). Although lacking the chronological precision of the speleothem sequences, these multiproxy records preserve evidence of centennial and millennial scale variability. MIS3 is marked by generally wetter conditions in the lake basins and warmer SSTs in the marine record, particularly during D/O events, which can be attributed to a stronger monsoon as well northward displacement of the ITCZ. This contrasts with the standard interpretation of the speleothem sequences where D/O events are dry. In contrast, H events are usually drier/cooler (weaker NAM, reduced summer

  8. Glacial history of Tranquilo glacier (Central Patagonia) since the Last Glacial Maximum through to the present.

    NASA Astrophysics Data System (ADS)

    Sagredo, E. A.; Araya, P. S.; Schaefer, J. M.; Kaplan, M. R.; Kelly, M. A.; Lowell, T. V.; Aravena, J. C.

    2014-12-01

    Deciphering the timing and the inter-hemispheric phasing of former glacial fluctuations is critical for understanding the mechanisms and climate signals underlying these glacial events. Here, we present a detailed chronology of glacial fluctuations for Río Tranquilo glacier (47°S), since the LGM, including up to the present. Río Tranquilo is a small glacial valley located on the northern flank of Monte San Lorenzo, an isolated granitic massif, ~70 km to the east of the southern limit of the Northern Patagonian Icefield. Although Mt. San Lorenzo is located on the leeward side of the Andes, it is one of the most glacierized mountains in the region, with an ice surface area of ~140 km2. Geomorphic evidence suggests that during past episodes of climate change several small glaciers that today occupy the headwalls of Río Tranquilo valley expanded and coalesced, depositing a series of moraines complexes along the flanks and bottom of the valley. We used two independent dating techniques to constrain the age of the glacial history of the area. 10Be surface exposure ages from boulders located atop moraine ridges reveal that Río Tranquilo valley underwent glacial expansion/stabilization during at least the LGM (late LGM?), Late glacial (ACR and Younger Dryas) and Mid-Holocene. Within the Mid-Holocene limits, tree-ring based chronology indicates that Río Tranquilo glacier expanded during the Late Holocene as well. Our results are the first detailed chronology of glacial fluctuations from a single valley glacier, spanning the entire period from the (end of the) LGM up to the present, in southern South America. By identifying different glacial episodes within a single alpine valley, this study provides baseline data for studying the relative magnitude of the climate events responsible for these glacial events.

  9. 38 kyr record of Asian dust deposition in Hawaii: its links to interglacial/glacial changes

    NASA Astrophysics Data System (ADS)

    Kim, S. H.; Hotchkiss, S.; Vitousek, P.; Chadwick, O.; Mason, J. A.

    2015-12-01

    Asian desert dust is the major inorganic fraction of late Cenozoic sediments in the North Pacific. Dust modelling, satellite observations and stable isotope data have contributed to understanding of the dust provenance, teleconnection and process mechanisms. Most paleo-aeolian data have suggested positive links between Asian dust input variability and glacial-interglacial cycles in the North Pacific. However, existing Pacific paleodust studies mostly depend on low-resolution marine records at mid- and high-latitudes. In this study, we reconstruct 38 kyr terrestrial records of Asian dust deposition from Hawaiian montane peat bogs. We also focus on interpreting temporal correlations of the Asian dust flux history with its local hydrological variability over late Quaternary interglacial/glacial changes because of the significant positive correlation between Asian dust mass in Hawaiian surface soils and annual precipitations (Figure A1 & A2). For a proxy for Asian dust in Hawaii, we use quartz, a continental igneous rock-driven mineral type absent in Hawaiian basaltic rocks. Using an X-ray diffraction method, we quantify quartz content and calculate quartz deposition rates. We also reconstruct Hawaiian paleoprecipitation history by using pollen assemblage and peat humification degree analyses. Our results present two significant quartz deposition peaks during the Last Glacial Maximum (0.134 g/cm3) and between 2.6 and 0.4 kyr BP (0.044 g/cm3). Our moisture varaition results show that Hawaii was drier during the LGM than the Holocene. Therefore, this study suggests that Asian dust input in Hawaii has negative temporal correlations with wet deposition-controlling climates, but positive correlations with the drier glacial period in the late Quaternary.

  10. Ice-free conditions on the queen charlotte islands, british columbia, at the height of late wisconsin glaciation.

    PubMed

    Warner, B G; Mathewes, R W; Clague, J J

    1982-11-12

    New radiocarbon dates and plant macrofossil data establish that parts of the Queen Charlotte Islands, British Columbia, were ice-free during and subsequent to the late Wisconsin glacial maximum on the Pacific coast of Canada. A paleoecological investigation of dated sediments at Cape Ball has indicated that a varied flora consisting of terrestrial and aquatic plants was present there about 16,000 years ago. This finding provides support for the existence of a heretofore questioned biotic refugium on the Queen Charlotte Islands during the last glaciation. These results shed new light on problems of glacial chronology, climatic change, biogeography, and archeology along the western margin of North America.

  11. Magnetostratigraphy and paleontology of Aït Kandoula Basin (High Atlas, Morocco) and the African-European late Miocene terrestrial fauna exchanges

    NASA Astrophysics Data System (ADS)

    Benammi, Mouloud; Calvo, Manuel; Prévot, Michel; Jaeger, Jean-Jacques

    1996-12-01

    A magnetostratigraphic study has been carried out on a middle Miocene to upper Pliocene lacustrine sedimentary deposit in the central part of the Aït Kandoula basin, which contains micromammal faunas and is situated in the southern High Atlas (Morocco). In total, 113 samples were subjected to paleomagnetic analysis: 60 out of the 113 studied samples representing 52 different stratigraphic levels yielded a paleomagnetic direction and at least the polarity could be recognized in 42 specimens. Eleven specimens were submitted to AF demagnetization. The mean direction for normal-polarity samples was D = 349.4, I = 50.7 (N = 36, α95 = 4.5, k = 27) and for reversed polarity samples D = 191.2, I = -53.4 (N = 16, α95 = 12.32, k = 9). These results yielded a polarity sequence which we interpret as spanning from Chron C5n.2n to the beginning of Chron C3n.4n. This interpretation relies on biostratigraphic data previously proposed for a part of the continental fauna found in the basin. This result is in agreement with the 40Ar/ 39Ar dating previously carried out on a volcanic ash layer, which provided an age of 5.9 ± 0.5 Ma [1] and which is shown here to be reversely magnetized. This layer is correlated here with the reverse polarity zone corresponding to Chron C3r. Biostratigraphic studies on the same section have shown that the micromammal levels extend here only from middle Vallesian to upper Turolian (upper Miocene). Four localities have yielded western European species of micromammals, indicating trans-Mediterranean terrestrial faunal exchanges between these two continents during the late Miocene. The European murid rodent Occitanomys is recorded for the first time in North Africa in level 8 of the Afoud section, an age younger than 5.32 Ma being assigned to this level by the present study. Level 1 of the same section yields the lagomorph Prolagus cf. michauxi, with an age of 6.1 Ma. The magnetostratigraphic data suggest therefore that the beginning of terrestrial

  12. Crustal uplifting rate associated with late-Holocene glacial-isostatic rebound at Skallen and Skarvsnes, Lützow-Holm Bay, East Antarctica: evidence of a synchrony in sedimentary and biological facies on geological setting

    NASA Astrophysics Data System (ADS)

    Takano, Y.; Yokoyama, Y.; Tyler, J. J.; Kojima, H.; Fukui, M.; Sato, T.; Ogawa, N. O.; Suzuki, N.; Kitazato, H.; Ohkouchi, N.

    2010-06-01

    We determined the mean crustal uplifting rate during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica, by dating a marine-lacustrine transition recorded in lake sediments. We focused on temporal variations in the chemical composition of sediments recovered from Lake Skallen Oike at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine (fresh water) settings, as indicated by analyses of sedimentary facies for carbon and nitrogen contents, nitrogen isotopic compositions (15N/14N), and major element concentrations. Changes in the dominant primary producers during the marine-lacustrine transition were also clearly revealed by biogenic Opal-A, diatom assemblages, and gradient gel electrophoresis (DGGE) with 16S rRNA gene analysis. Geochronology based on radiocarbon dating of acid-insoluble organic carbon suggested that the environmental transition from saline to fresh water occurred at 2940±100 cal yr BP at L. Skallen and 1060±90 cal yr BP at L. Oyako. Based on these data and a linear approximation model, we estimated a mean crustal uplifting rate of 3.6 mm yr-1 for the period since the marine-lacustrine transition via brackish condition; this uplift is attributed to glacial-isostatic rebound along the Soya Coast. The geological setting was the primary factor in controlling the emergence event and the occurrence of simultaneous changes in sedimentary and biological facies along the zone of crustal uplift.

  13. Linking the Holocene glacial and oceanographic variability in northern Spitsbergen

    NASA Astrophysics Data System (ADS)

    Bartels, Martin; Hebbeln, Dierk

    2015-04-01

    The Svalbard area can be considered as a key region for Arctic heat transfer. The archipelago is located where relatively warm Atlantic Water is reaching further north than at any other Arctic location at similar latitudes. The Holocene variability of Atlantic Water advection is well documented for the western coasts of Spitsbergen whereas records from northern Svalbard are still rare. Here we present a sedimentary record from Woodfjorden in northern Spitsbergen where the influence of Atlantic Water is fading out and glaciers are responding much more sensitive to oceanographic variations than at the western coasts of Spitsbergen. We analyzed the foraminiferal fauna and the distribution of Ice Rafted Debris (IRD) to trace the interplay between the oceanographic and glacial variability, respectively. The appearance of Nonionellina labradorica, a species which is adapted to warm Atlantic Water, shows that the advection of Atlantic-derived water correlates positively with summer insolation. The amount of IRD - increasing during the Allerød interstadial - diminished subsequently with intensifying inflow of Atlantic Water. During the Mid-Holocene, the strong influence of these relative warm water masses concurs with very low IRD values, possibly reflecting the retreat of tidewater glaciers from the coast to a further inland position disconnecting glacier dynamics from the respective marine archives at that time. With declining inflow of Atlantic Water during the late Holocene sea ice expanded, indicated by increased percentages of Islandiella norcrossi. The appearance of this species shows a similar trend as reported for sea-ice biomarkers in the eastern Fram Strait. Thus, variations of Atlantic Water inflow directly affected glacial activity as well as sea-ice coverage. Combining marine and terrestrial proxies enabled us to reconstruct regional (sea-ice) as well as local (glacial expansion) changes over time.

  14. Late-glacial and Holocene Vegetation and Climate Variability, Including Major Droughts, in the Sky Lakes Region of Southeastern New York State

    NASA Technical Reports Server (NTRS)

    Menking, Kirsten M.; Peteet, Dorothy M.; Anderson, Roger Y.

    2012-01-01

    Sediment cores from Lakes Minnewaska and Mohonk in the Shawangunk Mountains of southeastern New York were analyzed for pollen, plantmacrofossils, macroscopic charcoal, organic carbon content, carbon isotopic composition, carbon/nitrogen ratio, and lithologic changes to determine the vegetation and landscape history of the greater Catskill Mountain region since deglaciation. Pollen stratigraphy generally matches the New England pollen zones identified by Deevey (1939) and Davis (1969), with boreal genera (Picea, Abies) present during the late Pleistocene yielding to a mixed Pinus, Quercus and Tsuga forest in the early Holocene. Lake Minnewaska sediments record the Younger Dryas and possibly the 8.2 cal kyr BP climatic events in pollen and sediment chemistry along with an 1400 cal yr interval of wet conditions (increasing Tsuga and declining Quercus) centered about 6400 cal yr BP. BothMinnewaska andMohonk reveal a protracted drought interval in themiddle Holocene, 5700-4100 cal yr BP, during which Pinus rigida colonized the watershed, lake levels fell, and frequent fires led to enhanced hillslope erosion. Together, the records show at least three wet-dry cycles throughout the Holocene and both similarities and differences to climate records in New England and central New York. Drought intervals raise concerns for water resources in the New York City metropolitan area and may reflect a combination of enhanced La Niña, negative phase NAO, and positive phase PNA climatic patterns and/or northward shifts of storm tracks.

  15. Laguna Potrok Aike, Argentina: the first non-tropical environmental record in South America extending far beyond the Late-Glacial - a progress report

    NASA Astrophysics Data System (ADS)

    Zolitschka, B.; Anselmetti, F.; Ariztegui, D.; Corbella, H.; Francus, P.; Gebhardt, C.; Lücke, A.; Ohlendorf, C.; Schäbitz, F.; Pasado Science Team

    2009-04-01

    Within the framework of the ICDP-funded "Potrok Aike maar lake sediment archive drilling project" (PASADO) an international team of scientists carried out interdisciplinary research at the unique mid-Pleistocene (770 ka) maar lake of Laguna Potrok Aike in southern Patagonia (Province of Santa Cruz, Argentina). This lake is very sensitive to variations in southern hemispheric wind and pressure systems and thus holds a unique and continuous lacustrine record of climatic and ecological variability of global significance. Moreover, Southern Patagonia with its many active volcanoes is an ideal location to better understand the regional history of volcanism. These are two challenging geo-scientific themes that need to be tackled, especially as both of them have an increasing socio-economic relevance. Three months of drilling activities that finished last November 2008 were carried out by DOSECC from the drilling platform R/V "Kerry Kelts". More than 500 m of lacustrine sediments were recovered. This sedimentary archive will provide (1) new insights into the processes of regional back arc volcanism within the Pali Aike Volcanic Field itself as well as the more distant explosive volcanism of the Andean mountain chains; and, (2) high-resolution (decadal) quantitative climate and environmental reconstructions supported by multiple dating and stratigraphic correlations. Marine - ice core - terrestrial linkages will be emphasized as well as the incorporation of results from global climate modelling simulations for the last ca. 100 ka. The two drilled sites in the central deep basin of Laguna Potrok Aike have been selected based on four seismic surveys carried out between 2003 and 2005. Sediments were recovered at both drilled sites down to a subbottom depth of slightly more than 100 m using the GLAD800 drill rig with the hydraulic piston corer tool (HPC) at water depths varying between 95 and 100 m. The total core recovery is 94%. On-site core logging with the multi sensor

  16. New observations on relative sea-level change since the late Glacial from the British and Irish continental shelf and their implications for understanding earth-ice-ocean interactions

    NASA Astrophysics Data System (ADS)

    Cooper, J. A.; Long, A. J.; Plets, R. M.; Callard, L.; Kelley, J. T.; Belknap, D. F.; Quinn, R.; Edwards, R.; Jackson, D.; Long, D.; Monteys, X.; Milne, G. A.

    2013-12-01

    The pattern of relative sea-level (RSL) change around the British Isles shows marked spatial variability in response to ice sheet history and crustal response to loading/offloading. The area thus offers an ideal natural laboratory for the investigation of such interactions and has formed the basis of several models of earth-ice-ocean interaction. Data with which to test models is, however, largely restricted to the late Holocene for which period many RSL curves have been derived from salt marsh studies. There is a paucity of data from much lower than present sea levels and this is reflected in large (tens of metres) discrepancies between different modelled RSL curves for the late-glacial early Holocene period, despite close agreement of the models for the mid-late Holocene. Few data currently exist that can resolve these discrepancies. We have just completed two years intensive fieldwork on six sites around the Irish Sea (at Bantry Bay, Waterford, Cardigan Bay, offshore Louth, Isle of Man, and Belfast Lough) on a north-south gradient. These were selected to target lower than present sea-level indicators from ice-proximal to ice-distal locations. The detailed results from two sites are presented in separate posters. The initial investigation using multibeam bathymetry and shallow seismic profiling identified several sea-level indicators including wave-cut platforms and associated cliffs in bedrock, planation surfaces on drumlins, incised valley termini and terraces and the depth of the transgressive unconformity (and in some cases its seaward terminus). Subsequent coring of seabed targets yielded over 450m of core from 150 sites. The most consistently identified RSL indicator at all sites was the transgressive unconformity. It was penetrated in cores at most sites and has yielded age-dateable material. Palaeoenvironmental interpretation and radiocarbon dating of material is ongoing, but has already yielded new observational data on lower than present sea levels with

  17. A combined palaeomagnetic and environmental magnetic investigation of Late Glacial loess from the Middle Danube Basin (Süttö, Hungary)

    NASA Astrophysics Data System (ADS)

    Rolf, Christian; Hambach, Ulrich; Novothny, Agnes; Schnepp, Elisabeth; Worm, Kathrin

    2010-05-01

    In July 2008 and in August 2009 sampling for palaeomagnetic and environmental magnetic research was carried out at a 20 m thick Upper Pleistocene loess-palaeosol sequence near Süttö (North Hungary) in order to establish a high resolution palaeomagnetic record. Aeolian dust was deposited worldwide during dry/cold periods of the recent geological past. Alternating environmental conditions (dry/cold; humid/warm) after deposition led to loess-paleosol sequences (LPSS) covering wide parts of the continents and providing high resolution archives of palaeoclimatic changes during the Pleistocene. LPSS cover more than 30% of the surface of Hungary. In order to establish an absolute chronology for late Quaternary deposits from Hungary, different loess-palaeosol sequences have been investigated by luminescence dating performed by the Leibniz Institute for Applied Geophysics (LIAG) in Hannover in collaboration with the Department of Physical Geography of the Eötvös Loránd University of Budapest. The objectives of our study are: firstly, to establish a palaeomagnetic directional record for additional, independent dating; secondly, to construct a palaeosol-loess stratigraphy based on variations of the magnetic susceptibility (MS) and other rock magnetic proxies with depth in order to reconstruct the palaeoclimatic evolution; thirdly, to build a relative palaeointensity record and to compare this record with the high resolution global palaeointensity stack GLOPIS 75 (Laj et al. 2004). During our first sampling campaign we took small cylinders and overlapping blocks. Based on the results of this campaign we collected samples with narrow spacing (1 cm) at the most interesting part of the profile. Most samples show a clear palaeomagnetic signal and magnetic cleaning (thermal or alternating field) yielded stable characteristic remanences with well defined palaeodirections. Thus, the profile at Süttö represents a succession of palaeodirections characterised mainly by normal

  18. Holocene glacial fluctuations in southern South America

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    Understanding the timing and magnitude of former glacier fluctuations is critical to decipher long-term climatic trends and to unravel both natural cycles and human impact on the current glacial behavior. Despite more than seven decades of research efforts, a unifying model of Holocene glacial fluctuations in Southern South America remains elusive. Here, we present the state-of-the-art regarding the timing of Holocene glacial fluctuation in southern Patagonia-Tierra del Fuego, with a focus on a new generation of high-resolution radiocarbon and 10Be surface exposure dating chronologies. Recently acquired evidence suggest that after receding from advanced Late Glacial positions, Patagonian glaciers were for the most part close to, or even behind, present ice margins during the Early Holocene. On the other hand, emerging chronologies indicate that in some areas there were extensive expansions (century scale?) that punctuated the warm interval. Subsequently, we have evidence of multiple millennial timescale glacial advances starting in the middle Holocene. Several glacial maxima are defined by moraines and other landforms from 7000 years ago to the 19th century, with a gap sometime between 4,500 and 2,500 years ago. The last set of advances began around 800-600 years ago. Although glacial activity is documented in Patagonia at the same time as the European Little Ice Age, the extent of these glacial events are less prominent than those of the mid-Holocene. The causes that may explain these glacial fluctuations remain elusive. Finally, we discuss ongoing efforts to better define the timing and extent of Holocene glaciations in southern South America, and to establish the basis to test competing hypothesis of regional Holocene climate variability.

  19. Poorly ventilated deep ocean at the Last Glacial Maximum inferred from carbon isotopes: A data-model comparison study

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Yu, J.; Joos, F.; Mouchet, A.; Meissner, K. J.; England, M. H.

    2017-01-01

    Atmospheric CO2 was ˜90 ppmv lower at the Last Glacial Maximum (LGM) compared to the late Holocene, but the mechanisms responsible for this change remain elusive. Here we employ a carbon isotope-enabled Earth System Model to investigate the role of ocean circulation in setting the LGM oceanic δ13C distribution, thereby improving our understanding of glacial/interglacial atmospheric CO2 variations. We find that the mean ocean δ13C change can be explained by a 378 ± 88 Gt C(2σ) smaller LGM terrestrial carbon reservoir compared to the Holocene. Critically, in this model, differences in the oceanic δ13C spatial pattern can only be reconciled with a LGM ocean circulation state characterized by a weak (10-15 Sv) and relatively shallow (2000-2500 m) North Atlantic Deep Water cell, reduced Antarctic Bottom Water transport (≤10 Sv globally integrated), and relatively weak (6-8 Sv) and shallow (1000-1500 m) North Pacific Intermediate Water formation. This oceanic circulation state is corroborated by results from the isotope-enabled Bern3D ocean model and further confirmed by high LGM ventilation ages in the deep ocean, particularly in the deep South Atlantic and South Pacific. This suggests a poorly ventilated glacial deep ocean which would have facilitated the sequestration of carbon lost from the terrestrial biosphere and atmosphere.

  20. Multiple tropical Andean glaciations during a period of late Pliocene warmth

    PubMed Central

    Roberts, Nicholas J.; Barendregt, René W.; Clague, John J.

    2017-01-01

    The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene. PMID:28169346

  1. Multiple tropical Andean glaciations during a period of late Pliocene warmth

    NASA Astrophysics Data System (ADS)

    Roberts, Nicholas J.; Barendregt, René W.; Clague, John J.

    2017-02-01

    The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene.

  2. Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records

    NASA Astrophysics Data System (ADS)

    Bock, Michael; Schmitt, Jochen; Beck, Jonas; Seth, Barbara; Chappellaz, Jérôme; Fischer, Hubertus

    2017-07-01

    Atmospheric methane (CH4) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [δ13CH4 and δD(CH4)] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our δD(CH4) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.

  3. Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records.

    PubMed

    Bock, Michael; Schmitt, Jochen; Beck, Jonas; Seth, Barbara; Chappellaz, Jérôme; Fischer, Hubertus

    2017-07-18

    Atmospheric methane (CH4) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [δ(13)CH4 and δD(CH4)] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our δD(CH4) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.

  4. Paleoclimate of northern Guatemala during the Last Glacial Cycle

    NASA Astrophysics Data System (ADS)

    Hodell, D. A.; Anselmetti, F.; Ariztegui, D.; Brenner, M.; Curtis, J.; Gilli, A.; Mueller, A.

    2006-12-01

    Lake Peten Itza (zmax = 165 m) in northern Guatemala is the deepest lake in the lowlands of Central America. Annual rainfall averages ~1600 mm and is highly seasonal with over 90% occurring in the months from May to October. As part of an ICDP project, we recovered 1327 m of lake sediment at seven sites using the GLAD800 superbarge. Preliminary research has focused on Site PI-6 at a water depth of 71 m. Three holes were drilled and recovered a complete stratigraphic section to a maximum depth of 75.9 mblf. Radiocarbon dates on terrestrial organic matter display a regular increase in age with depth, and indicate a mean sedimentation rate of ~100 cm per 1000 yrs (1mm/yr). The top 10.8 mcd were deposited during the Holocene and consist primarily of gray carbonate clay with abundant charcoal. The Pleistocene/Holocene boundary at 10.8 mcd is marked by a transition to Holocene clay from underlying, interbedded dense gypsum sand and clay deposited during the Late Glacial period from ~17 to 9.3 kyrs. This transition represents a switch to moist climate during the early Holocene from more arid conditions during the Late Glacial. Arid conditions during the Late Glacial period may coincide with episodic delivery of seasonal meltwater to the Gulf of Mexico (Aharon, 2003, Paleoceanography, 18, 1079). In contrast to the Late Glacial period, the earlier Last Glacial Maximum (LGM), from 23 to 17 kyrs, consists of gray carbonate clay that is very similar to Holocene deposits, suggesting high detrital input and high lake level. This finding contradicts previous results suggesting that the LGM was dry in the Peten lowlands. We speculate that a cold, wet LGM may have been caused by increased winter precipitation when the Laurentide Ice Sheet (LIS) was at its southernmost extent. The mechanism may have been related to increased frequency of polar outbreaks and "Norte" winds, which occasionally bring rain to the Peten today during the dry season. Similar increases in winter

  5. Early local last glacial maximum in the tropical Andes.

    PubMed

    Smith, Jacqueline A; Seltzer, Geoffrey O; Farber, Daniel L; Rodbell, Donald T; Finkel, Robert C

    2005-04-29

    The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle approximately 34,000 years before the present and were retreating by approximately 21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle.

  6. Robustness of Quaternary glacial cycles

    NASA Astrophysics Data System (ADS)

    Ganopolski, Andrei; Brovkin, Victor; Calov, Reinhard

    2015-04-01

    In spite of significant progress in paleoclimate reconstructions and modeling some aspects of Quaternary climate cycles are still poorly understood. Among them is the question of whether glacial cycles are deterministic and solely externally forced or, at least partially, they are stochastic. The answer to this question can only be obtained using a comprehensive Earth system models which incorporates all major components of the Earth system - atmosphere, ocean, land surface, northern hemisphere ice sheets, terrestrial biota and soil carbon, aeolian dust and marine biogeochemistry. Here, we used the Earth system model of intermediate complexity CLIMBER-2. The model was optimally tuned to reproduce climate, ice volume and CO2 variability for the last 0.8 million years. Using the same model version, we performed a large set of simulations covering the entire Quaternary (3 million years). By starting the model at different times (with the time step of 100,000 years) and using identical initial conditions we run the model for 500,000 years using the Earth's orbital variations as the only prescribed radiative forcing. We show that within less than 100,000 years after the beginning of each experiment the modeling results converge to the same solution which depends only on the orbital forcing and boundary conditions, such as topography and terrestrial sediment thickness for the ice sheets or volcanic CO2 outgassing for the carbon cycle. By using only several sets of the Northern Hemisphere orography and sediment thickness which represent different stages of landscape evolution during Quaternary, we are able to reproduce all major regimes of Quaternary long-term climate variability. Our results thus strongly support the notion that Quaternary glacial cycles are deterministic and externally forced.

  7. Should precise numerical dating overrule glacial geomorphology?

    NASA Astrophysics Data System (ADS)

    Winkler, Stefan

    2016-04-01

    Numerical age dating techniques, namely different types of terrestrial cosmogenic nuclide dating (TCND), have achieved an impressive progress in both laboratory precision and regional calibration models during the past few decades. It is now possible to apply precise TCND even to young landforms like Late Holocene moraines, a task seemed hardly achievable just about 15 years ago. An increasing number of studies provide very precise TCND ages for boulders from Late Holocene moraines enabling related reconstruction of glacier chronologies and the interpretation of these glacial landforms in a palaeoclimatological context. These studies may also solve previous controversies about different ages assigned to moraines obtained by different dating techniques, for example relative-age dating techniques or techniques combining relative-age dating with few fixed points derived from numerical age dating. There are a few cases, for example Mueller Glacier and nearby long debris-covered valley glacier in Aoraki/Mt.Cook National Park (Southern Alps, New Zealand), where the apparent "supremacy" of TCND-ages seem to overrule glacial geomorphological principles. Enabled by a comparatively high number of individual boulders precisely dated by TCND, moraine ridges on those glacier forelands have been primarily clustered on basis of these boulder ages rather than on their corresponding morphological position. To the extreme, segments of a particular moraine complex morphologically and sedimentologically proven to be formed during one event have become split and classified as two separate "moraines" on different parts of the glacier foreland. One ledge of another moraine complex contains 2 TCND-sampled boulders apparently representing two separate "moraines"-clusters of an age difference in the order of 1,500 years. Although recently criticism has been raised regarding the non-contested application of the arithmetic mean for calculation of TCND-ages for individual moraines, this

  8. Paraglacial Geomorphology on Mars: A Conceptual Framework for Post-Glacial Geomorphic Processes

    NASA Astrophysics Data System (ADS)

    Jawin, E. R.; Head, J. W.; Marchant, D. R.

    2014-07-01

    The paraglacial period is a terrestrial post-glacial phase that describes the environmental response to deglaciation. We use this period as a framework for analyzing martian impact craters that bear evidence of ice accumulation, flow, and loss.

  9. Glacial Meltwater as a Source of Amorphous Silica on Early Mars

    NASA Astrophysics Data System (ADS)

    Rutledge, A. M.; Horgan, B.; Havig, J. R.; Rampe, E. B.; Scudder, N. A.; Hamilton, T. L.

    2017-10-01

    Cold-climate silica cycling on mafic volcanics due to glacial meltwater alteration is a significant terrestrial weathering process. Amorphous silica deposits on Mars could be interpreted as mineralogical evidence for past ice sheet melt.

  10. Post-glacial redistribution and shifts in productivity of giant kelp forests.

    PubMed

    Graham, Michael H; Kinlan, Brian P; Grosberg, Richard K

    2010-02-07

    Quaternary glacial-interglacial cycles create lasting biogeographic, demographic and genetic effects on ecosystems, yet the ecological effects of ice ages on benthic marine communities are unknown. We analysed long-term datasets to develop a niche-based model of southern Californian giant kelp (Macrocystis pyrifera) forest distribution as a function of oceanography and geomorphology, and synthesized palaeo-oceanographic records to show that late Quaternary climate change probably drove high millennial variability in the distribution and productivity of this foundation species. Our predictions suggest that kelp forest biomass increased up to threefold from the glacial maximum to the mid-Holocene, then rapidly declined by 40-70 per cent to present levels. The peak in kelp forest productivity would have coincided with the earliest coastal archaeological sites in the New World. Similar late Quaternary changes in kelp forest distribution and productivity probably occurred in coastal upwelling systems along active continental margins worldwide, which would have resulted in complex shifts in the relative productivity of terrestrial and marine components of coastal ecosystems.

  11. Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation.

    PubMed

    Schilt, Adrian; Brook, Edward J; Bauska, Thomas K; Baggenstos, Daniel; Fischer, Hubertus; Joos, Fortunat; Petrenko, Vasilii V; Schaefer, Hinrich; Schmitt, Jochen; Severinghaus, Jeffrey P; Spahni, Renato; Stocker, Thomas F

    2014-12-11

    Nitrous oxide (N2O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources. The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales. It is not well understood, however, how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations. Here we present N2O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the N2O cycle, we find a 30 per cent increase in total N2O emissions from the late glacial to the interglacial, with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation, even though there is no a priori connection between the drivers of the two sources. However, we find that terrestrial emissions dominated on centennial timescales, consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces. The results improve our understanding of the drivers of natural N2O emissions and are consistent with the idea that natural N2O emissions will probably increase in response to anthropogenic warming.

  12. Isotopic constraints on marine and terrestrial N2O emissions during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Schilt, Adrian; Brook, Edward J.; Bauska, Thomas K.; Baggenstos, Daniel; Fischer, Hubertus; Joos, Fortunat; Petrenko, Vasilii V.; Schaefer, Hinrich; Schmitt, Jochen; Severinghaus, Jeffrey P.; Spahni, Renato; Stocker, Thomas F.

    2014-12-01

    Nitrous oxide (N2O) is an important greenhouse gas and ozone-depleting substance that has anthropogenic as well as natural marine and terrestrial sources. The tropospheric N2O concentrations have varied substantially in the past in concert with changing climate on glacial-interglacial and millennial timescales. It is not well understood, however, how N2O emissions from marine and terrestrial sources change in response to varying environmental conditions. The distinct isotopic compositions of marine and terrestrial N2O sources can help disentangle the relative changes in marine and terrestrial N2O emissions during past climate variations. Here we present N2O concentration and isotopic data for the last deglaciation, from 16,000 to 10,000 years before present, retrieved from air bubbles trapped in polar ice at Taylor Glacier, Antarctica. With the help of our data and a box model of the N2O cycle, we find a 30 per cent increase in total N2O emissions from the late glacial to the interglacial, with terrestrial and marine emissions contributing equally to the overall increase and generally evolving in parallel over the last deglaciation, even though there is no a priori connection between the drivers of the two sources. However, we find that terrestrial emissions dominated on centennial timescales, consistent with a state-of-the-art dynamic global vegetation and land surface process model that suggests that during the last deglaciation emission changes were strongly influenced by temperature and precipitation patterns over land surfaces. The results improve our understanding of the drivers of natural N2O emissions and are consistent with the idea that natural N2O emissions will probably increase in response to anthropogenic warming.

  13. Luminescence Chronology for the Formation of Glacial Lake Calgary, Southern Alberta, Canada: Age Constraints for the Initiation of the Late Pleistocene Retreat of the Laurentide Ice Sheet from its Western Margin

    NASA Astrophysics Data System (ADS)

    Munyikwa, K.; Rittenour, T. M.

    2014-12-01

    Glacial Lake Calgary in southern Alberta, Canada, was a Late Pleistocene proglacial lake that formed along the southwest margin of the Laurentide Ice Sheet (LIS), dammed by the retreating ice sheet margin. Attempts to constrain the age of the lake using radiocarbon methods have been hampered by the lack of datable organic material. In an effort to apply an alternative chronometer, this study uses two optically stimulated luminescence (OSL) dating approaches to date fine grained sand and silt that were deposited in the lake during its existence. OSL dating determines the depositional ages of sediments by measuring the energy from ionizing radiation that is stored in mineral grains such as quartz and feldspar. Dividing the stored energy, also referred to as the paleodose, by the rate at which the dose accumulated, allows an age to be ascertained. In one method applied in this study, the paleodose stored in the feldspar component of the sediment is determined using normalized infrared stimulated luminescence signals acquired using a portable OSL reader. In the second method, blue optically stimulated luminescence signals obtained from quartz separates from the sediment by employing a regular OSL reader and standard protocols are used to determine the paleodose. After correcting the feldspar data for anomalous fading, the age results from the two dating approaches are compared. The ages signify a time period by which the LIS had retreated from the study area and, hence, serve as constraints for the initiation of the retreat of the ice sheet from its western limit. Advantages and limitations of the dating methods are briefly discussed. Constraining the chronology of the retreat of the LIS from western Canada allows for a better understanding of the driving forces behind ice sheet retreat. Secondly, assigning a temporal scale to the postglacial evolution of the environment of the region permits a better insight into the dynamics of the physical and biological

  14. High-resolution record of environmental changes and tephrochronological markers of the Last Glacial-Holocene transition at Lake Lautrey (Jura, France)

    NASA Astrophysics Data System (ADS)

    Vannière, Boris; Bossuet, Gilles; Walter-Simonnet, Anne-Véronique; Ruffaldi, Pascale; Adatte, Thierry; Rossy, Michel; Magny, Michel

    2004-12-01

    This paper presents the results of a multiproxy investigation including volume magnetic susceptibility (), mineral and pollen analyses of Late Glacial sediments from Lake Lautrey (Jura, France). Small-scale lithological variations have been identified with high stratigraphic resolution in order to establish lithostratigraphic correlations between cores. measurements, combined with mineralogical analyses, provide information on past sedimentary processes. This combined approach reflects major changes in terrestrial habitats and soil processes which may relate to the climatic events characterising the Late Glacial climatic warming and cooling phases. During warm intervals, the record indicates increased lake productivity via carbonate precipitation and decreased input of detrital material. In contrast, cooler intervals show reduced lake productivity, catchment area instability and increased detrital inputs. Several short interruptions in reforestation and in soil stabilisation can be identified and linked with abrupt colder events occurring through the Bølling. A general trend of warming is recorded from the coldest part of the Younger Dryas. Three tephra layers were also detected. The mineral composition analyses show that the upper tephra layer corresponds to the Laacher See eruption (Eifel, Germany) while the lower ones may relate to the volcanic activity of the Chaîne des Puys (Massif Central, France) around 13 000 cal. yr BP. These two events, recognised for the first time outside the Massif Central region, may provide additional chronostratigraphic markers for the Late Glacial sedimentary records of the Jura mountains and northern Alps. Copyright

  15. Terrestrial slopes in northern high latitudes: A paradigm shift regarding sediment origin, composition, and dynamic evolution

    NASA Astrophysics Data System (ADS)

    Lønne, Ida

    2017-01-01

    High-Arctic terrestrial slopes have received limited systematic research interest, but increased vulnerability related to regional warming has driven the call for better knowledge of the dynamics of these systems. Studies of sediment transport from a plateau area in Adventdalen, Svalbard, and associated slopes extending to sea level demonstrate that glacial processes play a more prominent role than earlier anticipated, - especially the impact of glacial meltwater. Traces of drainage at the plateau and the dissection of the plateau edge and upper slope were clearly initiated during various stages of Late Glacial runoff. Further, there is a close association between the sediment distribution and composition at the plateau and the evolution of various types of slopes. The reconstructed sedimentation history shows that the landscape will undergo four stages with contrasting modes of sediment transport: 1) subglacial processes related to active ice, 2) processes related to the margin of active ice, 3) processes related to the melting of inactive ice, and 4) nonglacial processes. These stages form four successions, referred to as supply regimes A-D, which control the supply of water and sediments to a given slope segment. In this landscape, traces of glacial meltwater occur at most altitudes, in "odd" positions and in slope segments "without" catchments. The associated depocenters (isolated, composite or coalescing into aprons), are often outsized compared to the apparent slope catchment. Reworked glacial sediments form a significant part of the slope-debris but are covered partly or entirely by products of physical weathering. Colluvium, senso stricto, thus masks a distinct system shift related to the local termination of glacial meltwater. Consequently, the weathering part of the slope sediment budget in this region is considerably overestimated.

  16. Cosmogenic beryllium-10 and neon-21 dating of late Pleistocene glaciations in Nyalam, monsoonal Himalayas

    NASA Astrophysics Data System (ADS)

    Schaefer, Joerg M.; Oberholzer, Peter; Zhao, Zhizhong; Ivy-Ochs, Susan; Wieler, Rainer; Baur, Heinrich; Kubik, Peter W.; Schlüchter, Christian

    2008-02-01

    We present cosmogenic 10Be and 21Ne chronologies from 21 erratic boulders on three moraine sequences in Nyalam county, monsoonal Himalayas, southern margin of the Tibetan Plateau. The surface exposure ages provide evidence for at least two distinct glacial advances during the late stage of the last glacial cycle and for one or more significantly older glaciations. The distribution of cosmogenic ages from the three ridges of the old moraine sequence is inconsistent with their stratigraphic order. Because exposure periods of the erratics prior to deposition on the moraine surface is shown to be small, the chronology-stratigraphy mismatch suggests that the cosmogenic ages do not date moraine deposition but most likely significant moraine ridge denudation and related boulder exhumation after initial deposition of the moraines during the penultimate glacial cycle or earlier. The surface exposure ages based on various currently accepted production rate scaling protocols yield age differences of up to 35% reflecting the poor knowledge of terrestrial cosmogenic production rates at low latitude/high altitude sites. Even within this conservative uncertainty range, our results do not yield evidence for late Pleistocene glaciations in monsoonal Tibet to be asynchronous to those in mid-latitudes on both hemispheres. There is an urgent need to improve the knowledge of terrestrial cosmogenic nuclide production rates and their scaling to low latitude regions to fully exploit the climate information archived in tropical moraine sequences.

  17. The Terrestrial Eocene-Oligocene Transition in North America

    NASA Astrophysics Data System (ADS)

    Prothero, Donald R.; Emry, Robert J.

    1996-06-01

    The transition from the Eocene to the Oligocene epoch, occurring approximately 47 to 30 million years ago, was the most dramatic episode of climatic and biotic change since the demise of the dinosaurs. The mild tropical climates of the Paleocene and early Eocene were replaced by modern climatic conditions and extremes, including glacial ice in Antarctica. The first part of this book summarizes the latest information in the dating and correlation of the strata of late middle Eocene through early Oligocene age in North America. The second part reviews almost all the important terrestrial reptiles and mammals found near the Eocene-Oligocene boundary, in the White River Chronofauna--from the turtles, snakes and lizards to the common rodents, carnivores, oreodonts and deer of the Badlands. This is the first comprehensive treatment of these topics in over sixty years, and will be invaluable to vertebrate paleontologists, geologists, mammalogists and evolutionary biologists.

  18. Oceanic role in terrestrial climate

    SciTech Connect

    Ellsaesser, H.W.

    1984-11-01

    A review is given of the role of the oceans in terrestrial climatogenesis. The review leads to development of a criterion for recognizing areas of potential climatogenesis through atmosphere-oceanic interaction and to speculations as to the causes of the El Nino-Southern Oscillation events, the Medieval Little Optimum, Little Ice Age and 20th Century Arctic Warming of the North Atlantic and the glacial-interglacial cycles. 29 references, 6 figures.

  19. Sources of glacial moisture in Mesoamerica

    USGS Publications Warehouse

    Bradbury, J.P.

    1997-01-01

    Paleoclimatic records from Mesoamerica document the interplay between Atlantic and Pacific sources of precipitation during the last glacial stage and Holocene. Today, and throughout much of the Holocene, the entire region receives its principal moisture in the summer from an interaction of easterly trade winds with the equatorial calms. Glacial records from sites east of 95?? W in Guatemala, Florida, northern Venezuela and Colombia record dry conditions before 12 ka, however. West of 95?? W, glacial conditions were moister than in the Holocene. For example, pollen and diatom data show that Lake Pa??tzcuaro in the central Mexican highlands was cool, deep and fresh during this time and fossil pinyon needles in packrat middens in Chihuahua, Sonora, Arizona, and Texas indicate cooler glacial climates with increased winter precipitation. Cold Gulf of Mexico sea-surface temperatures and reduced strength of the equatorial calms can explain arid full and late glacial environments east of 95?? W whereas an intensified pattern of winter, westerly air flow dominated hydrologic balances as far south as 20?? N. Overall cooler temperatures may have increased effective moisture levels during dry summer months in both areas. ?? 1997 INQUA/ Elsevier Science Ltd.

  20. Evidence against a late Wisconsinan ice shelf in the Gulf of Maine

    USGS Publications Warehouse

    Oldale, R.N.; Williams, R.S.; Colman, Steven M.

    1990-01-01

    Proposals for the formation of a late Wisconsinan ice shelf in the Gulf of Maine during the retreat of the Laurentide Ice Sheet are considered to be inappropriate. An Antarctic-type ice shelf does not fit the field data that indicate temperate glacial, terrestrial, and marine climates for the region between 18 ka and 12 ka. A temperate ice shelf has no modern analogues and may be physically impossible. The preponderance of stratified drift in the Gulf of Maine region supports temperate climates during late Wisconsinan time. It also indicates that glacial meltwater, rather than ice in either an ice sheet or ice shelf, was the primary transport mechanism of glacial sediment and the source for the glaciomarine mud. For these reasons we have proposed glacial analogues for the deglaciation of the Gulf of Maine that consist of temperate or subpolar marine-based glaciers, characterized by depositional environments dominated by meltwater discharge directly to the sea or the sea by way of subaerial meltwater streams. These analogues include Alaskan fjord glaciers, glaciers on the Alaskan continental shelf that discharged meltwater directly into the sea in the not too distant past, and Austfonna (Nordaustandet, Svalbard, Norway) that is presently discharging meltwater in the sea along a grounded ice wall. This last example is the best modern-day analogue for the depositional environment for most of the glaciomarine mud in the Gulf of Maine and deglaciation of the Gulf. 

  1. Evidence against a late Wisconsinan ice shelf in the Gulf of Maine

    NASA Astrophysics Data System (ADS)

    Oldale, R. N.; Williams, R. S.; Colman, S. M.

    Proposals for the formation of a late Wisconsinan ice shelf in the Gulf of Maine during the retreat of the Laurentide Ice Sheet are considered to be inappropriate. An Antarctic-type ice shelf does not fit the field data that indicate temperate glacial, terrestrial, and marine climates for the region between 18 ka and 12 ka. A temperate ice shelf has no modern analogues and may be physically impossible. The preponderance of stratified drift in the Gulf of Maine region supports temperate climates during late Wisconsinan time. It also indicates that glacial meltwater, rather than ice in either an ice sheet or ice shelf, was the primary transport mechanism of glacial sediment and the source for the glaciomarine mud. For these reasons we have proposed glacial analogues for the deglaciation of the Gulf of Maine that consist of temperate or subpolar marine-based glaciers, characterized by depositional environments dominated by meltwater discharge directly to the sea or the sea by way of subaerial meltwater streams. These analogues include Alaskan fjord glaciers, glaciers on the Alaskan continental shelf that discharged meltwater directly into the sea in the not too distant past, and Austfonna (Nordaustandet, Svalbard, Norway) that is presently discharging meltwater in the sea along a grounded ice wall. This last example is the best modern-day analogue for the depositional environment for most of the glaciomarine mud in the Gulf of Maine and deglaciation of the Gulf.

  2. Origin, paleoecology, and extirpation of bluebirds and crossbills in the Bahamas across the last glacial-interglacial transition.

    PubMed

    Steadman, David W; Franklin, Janet

    2017-09-12

    On low islands or island groups such as the Bahamas, surrounded by shallow oceans, Quaternary glacial-interglacial changes in climate and sea level had major effects on terrestrial plant and animal communities. We examine the paleoecology of two species of songbirds (Passeriformes) recorded as Late Pleistocene fossils on the Bahamian island of Abaco-the Eastern bluebird (Sialia sialis) and Hispaniolan crossbill (Loxia megaplaga). Each species lives today only outside of the Bahamian Archipelago, with S. sialis occurring in North and Central America and L. megaplaga endemic to Hispaniola. Unrecorded in the Holocene fossil record of Abaco, both of these species probably colonized Abaco during the last glacial interval but were eliminated when the island became much smaller, warmer, wetter, and more isolated during the last glacial-interglacial transition from ∼15 to 9 ka. Today's warming temperatures and rising sea levels, although not as great in magnitude as those that took place from ∼15 to 9 ka, are occurring rapidly and may contribute to considerable biotic change on islands by acting in synergy with direct human impacts.

  3. Beryllium-10 dating of the duration and retreat of the last pinedale glacial sequence

    SciTech Connect

    Gosse, J.C. |; Klein, J.; Evenson, E.B.

    1995-06-02

    Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 {+-} 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 {+-} 500 beryllium-10 years.

  4. Beryllium-10 dating of the duration and retreat of the last pinedale glacial sequence.

    PubMed

    Gosse, J C; Klein, J; Lawn, B; Middleton, R; Evenson, E B

    1995-06-02

    Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 +/- 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 +/- 500 beryllium-10 years.

  5. Glacial integrative modelling.

    PubMed

    Ganopolski, Andrey

    2003-09-15

    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.

  6. Terrestrial paleoclimatic changes in northeast Asia during OAE 3 in the Late Cretaceous: Organic geochemical evidences from the Songliao paleo-lake Basin, northeast China

    NASA Astrophysics Data System (ADS)

    Gao, Y.; Wang, C.; Huang, H.

    2016-12-01

    Oceanic anoxic events (OAEs) in the Cretaceous greenhouse world record significant paleoclimatic changes and represent major disturbances in the global carbon cycle. The Coniacian-Santonian oceanic anoxic event (OAE 3), the last of the Cretaceous OAEs, is characterized by restricted black shale deposits in equatorial to mid-latitude Atlantic and adjacent basins. Continental hydroclimate on tropical Africa and South America was proved have a strong effect on carbon burial in ocean basins during OAE 3, although terrestrial paleoclimatic changes on the other continents were not well understood. The Continental Scientific Drilling Project of the Songliao paleo-lake Basin (northeast China) recovered 500m thick, continuous, dark-colored, deep lacustrine mudstone of the Qingshankou Formation, with the age of 92.0-86.2Ma tightly constrained by radiometric dating on volcanic ashes, magnetostratigraphy and cyclostratigraphy. These sediments thus provide an opportunity to study terrestrial paleoclimate changes in northeast Asia during OAE 3. Our high-resolution ( 1m interval) TOC and δ13Corg data of the Qingshankou Formation in the Songliao Basin show several positive δ13Corg excursions over the OAE 3 time period. Spectrum analysis shows remarkable Milankovich cycles including eccentricity cycles ( 400kyr) and precession cycles ( 20 kyr). These data suggest that dark-colored mudstone deposition in the Songliao paleo-lake was probably controlled by regional hydroclimatic changes which were influenced by orbital forcing.

  7. Exploring biological constraints on the glacial history of Antarctica

    NASA Astrophysics Data System (ADS)

    Convey, Peter; Stevens, Mark I.; Hodgson, Dominic A.; Smellie, John L.; Hillenbrand, Claus-Dieter; Barnes, David K. A.; Clarke, Andrew; Pugh, Philip J. A.; Linse, Katrin; Cary, S. Craig

    2009-12-01

    The evolutionary and biogeographic history of the contemporary Antarctic terrestrial and marine biotas reveals many components of ancient origin. For large elements of the terrestrial biota, long-term isolation over timescales from hundreds of thousands to tens of millions of years, and thus persistence through multiple glacial cycles, now appears to be the norm rather than the exception. For the marine biota there are some parallels with benthic communities also including ancient components, together with an incidence of species-level endemism indicating long-term isolation on the Antarctic continental shelf. Although it has long been known that a few ice-free terrestrial locations have existed in Antarctica for up to 10-12 million years, particularly in the Dry Valleys of Victoria Land along with certain nunataks and higher regions of large mountain ranges, these do not provide potential refugia for the majority of terrestrial biota, which occur mainly in coastal and/or low-lying locations and exhibit considerable biogeographic regionalisation within the continent. Current glacial models and reconstructions do not have the spatial resolution to detect unequivocally either the number or geographical distribution of these glacial refugia, or areas of the continental shelf that have remained periodically free from ice scouring, but do provide limits for their maximum spatial extent. Recent work on the evolution of the terrestrial biota indicates that refugia were much more widespread than has been recognised and it is now clear that terrestrial biology provides novel constraints for reconstructing the past glacial history of Antarctica, and new marine biological investigations of the Antarctic shelf are starting to do likewise.

  8. Late Pleistocene coastal loess deposits of the central west coast of North America: Terrestrial facies indicators for marine low-stand intervals

    NASA Astrophysics Data System (ADS)

    Peterson, Curt D.; Grathoff, Georg H.; Reckendorf, Frank; Percy, David; Price, David M.

    2014-03-01

    Coastal loess deposits measured in sea cliffs, bay cliffs, road cuts and boreholes (62 sites) are compiled for the states of Washington, Oregon, and California in the central west coast of North America (1700 km in length). The loess-enriched deposits are recognized by (1) substantial abundances of silt (30-90% by weight) and (2) depositional settings in uplifted marine terraces or dune fields that are situated well above alluvial floodplains at the coast. Total loess thickness above the MIS5a marine terrace, or 80 ± 20 ka basal TL age, ranges from 0.1 to 8.0 m in 46 dated sites. Loess deposits reach maximum thickness (5-8 m) in the vicinities of glacial outwash plains in the highest latitudes. Loess thickness in the middle and lower latitudes increases with proximity to 1) large river mouths (>3 × 106 mt yr-1 modern suspended sediment discharge) and 2) broad shelf widths (>10 km distance from 0 to -100 m depth). Coastal loess deposits dated by TL or radiocarbon (37 samples) range from ˜250 to 11 ka in age, but generally fall into the MIS4-2 marine low-stand intervals (32 dates between 77-15 ka). The coastal loess facies represent marine low-stand intervals in coastal Quaternary sequences from the central west coast of North America.

  9. Reply to comment received from J. Herget et al. regarding ;Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai; by Gribenski et al. (2016), Quaternary Science Reviews 149, 288-305

    NASA Astrophysics Data System (ADS)

    Gribenski, Natacha; Lukas, Sven; Stroeven, Arjen P.; Jansson, Krister N.; Harbor, Jonathan M.; Blomdin, Robin; Ivanov, Mikhail N.; Heyman, Jakob; Petrakov, Dmitry A.; Rudoy, Alexei; Clifton, Tom; Lifton, Nathaniel A.; Caffee, Marc W.

    2017-07-01

    We thank Herget et al. (2017) for their keen interest in our study about the paleoglacial history of the Chagan Uzun Valley, in the Russian Altai (Gribenski et al., 2016). In our study, we proposed a detailed chronological and glaciodynamic reconstruction of a succession of glacial events represented by prominent moraine complexes, based on remotely-sensed data and field-geomorphological mapping, sedimentological logging, and cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. Herget et al. (2017) express skepticism about the outermost moraine complex dated in our study (CUMC 1; Gribenski et al., 2016), which slightly predates 19 thousand years (ka), during marine isotope stage (MIS) 2. To quote: ;we suspect that their claim of regional climatic significance-that the ∼19 ka Chagan-Uzun moraine they dated can be used to show that the local LGM and regional LGM were the same, and occurred during MIS 2-may be premature; (Herget et al., 2017: p. 1). Their comment appears to relate to an ongoing debate regarding the timing of maximum glaciation in Central Asia during the last glacial cycle, however it is based on misinterpretations of our paper.

  10. Terrestrial sequestration

    SciTech Connect

    Charlie Byrer

    2008-03-10

    Terrestrial sequestration is the enhancement of CO2 uptake by plants that grow on land and in freshwater and, importantly, the enhancement of carbon storage in soils where it may remain more permanently stored. Terrestrial sequestration provides an opportunity for low-cost CO2 emissions offsets.

  11. Terrestrial sequestration

    ScienceCinema

    Charlie Byrer

    2016-07-12

    Terrestrial sequestration is the enhancement of CO2 uptake by plants that grow on land and in freshwater and, importantly, the enhancement of carbon storage in soils where it may remain more permanently stored. Terrestrial sequestration provides an opportunity for low-cost CO2 emissions offsets.

  12. Quaternary glacial stratigraphy and chronology of Mexico

    NASA Astrophysics Data System (ADS)

    White, Sidney E.

    The volcano Iztaccihuatl in central Mexico was glaciated twice during the middle Pleistocene, once probably in pre-Illinoian (or pre-Bull Lake) time, and once in late Illinoian (or Bull Lake) time. Glaciation during the late Pleistocene was restricted to the late Wisconsin (or Pinedale). A maximum advance and one readvance are recorded in the early part, and one readvance in the latter part. Three or four small neoglacial advances occurred during the Holocene. Two other volcanoes nearby, Ajusco and Malinche, have a partial record of late Pleistocene and Holocene glaciations. Three others, Popocatépetl, Pico de Orizaba, and Nevado de Toluca, have a full Holocene record of three to five glacial advances during Neoglaciation.

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

    PubMed

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

    2004-02-29

    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.

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

    PubMed Central

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

    2004-01-01

    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 predic