Sample records for pleistocene glacial oscillations

  1. Interhemispheric correlation of late pleistocene glacial events

    SciTech Connect

    Lowell, T.V. [Univ. of Cincinnati, OH (United States); Heusser, C.J. [Clinton Woods, Tuxedo, NY (United States); Andersen, B.G. [Univ. of Oslo (Norway)] [and others

    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.

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

    E-print Network

    Ingólfsson, �lafur

    Quaternary Science Reviews 20 (2001) 405}417 Geomorphological correlation of Late Pleistocene Beringia. However, geomorphological analysis, complemented by palynological studies and radiocarbon age glaciation throughout North-East Rus- sia is largely based on the geomorphological analysis of glacial

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

    NASA Astrophysics Data System (ADS)

    Zimov, N.; Zimov, S. A.

    2011-12-01

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

  4. Glacial and climatic events in iceland reflecting regional north atlantic climatic shifts during the Pleistocene-Holocene transition

    NASA Astrophysics Data System (ADS)

    Ingólfsson, Ólafur; Björck, Svante; Haflidason, Haflidi; Rundgren, Mats

    This paper presents a summary of the evidence for glacial and climatic changes during the late Pleistocene-early Holocene transition in Iceland. The deglaciation during the Bølling-Allerød event was interrupted by a short-lived Older Dryas glacial advance. A biostratigraphical record from northern Iceland shows significant climate warming in late Allerød, when mean July temperatures were at least as warm as those of today. An abrupt cooling marked the beginning of the Younger Dryas event. It was characterised by a cold and stable polar climate and an extensive glaciation, before the postglacial warming of climate set in. The Icelandic paleoclimatic record is discussed in the light of climatic oscillations recorded from the GRIP ice-core, from the Greenland Inland Ice, and with reference to major shifts in the oceanic front systems, recorded in the Troll 8903 marine sediment core from the North Sea. The Vedde Ash gives a unique opportunity to address the chronological problems and correlate event stratigraphies of the different proxies. It is concluded that the Icelandic record of glacial and climatic changes during the late Pleistocene—early Holocene transition largely reflects the climatic development in the North Atlantic region.

  5. The late Pleistocene glacial sequence in the middle Maruia valley, southeast Nelson, New Zealand

    Microsoft Academic Search

    M. C. G. Mabin

    1983-01-01

    Glacial and fluvioglaciallandforms and deposits preserved in the middle reaches of the Maruia valley, southeast Nelson, New Zealand, record the activity of the Maruia glacier during the late Pleistocene Otira Glaciation. Five advances are recognised, from oldest to youngest: Creighton 1, 2, 3, and the Reid Stream 1, 2 advances. !bere was an interstadial interval between the Creighton 3 and

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

    Microsoft Academic Search

    O. Yu. Glushkova

    2001-01-01

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

  7. Case for periodic, colossal jokulhlaups from Pleistocene glacial Lake Missoula.

    USGS Publications Warehouse

    Waitt, R.B., Jr.

    1985-01-01

    Lake Missoula (2500 km3) remained sealed as long as any segment of the glacial dam remained grounded; when the lake rose to a critical level c.600 m in depth, the glacier bed at the seal became buoyant, initiating underflow from the lake. Subglacial tunnels then grew exponentially, leading to catastrophic discharge. Calculations of the water budget for the lake basin (including input from the Cordilleran ice sheet) suggest that the lake filled every three to seven decades. -from Author

  8. Volumetrically significant recharge of Pleistocene glacial meltwaters into epicratonic basins: Constraints imposed by solute mass balances

    Microsoft Academic Search

    J. C. McIntosh; L. M. Walter

    2005-01-01

    Melting of kilometer-thick continental ice sheets, during Pleistocene glaciation, profoundly altered regional-scale groundwater flow in the low-lying stable interior of the North American craton. In this paper, we show that large volumes of glacial meltwater penetrated to great depths in underlying sedimentary basins through regionally extensive Silurian–Devonian carbonate aquifers, disrupting relatively stagnant saline fluids, and creating a strong disequilibrium pattern

  9. Mitochondrial DNA variation in Pleistocene and modern Atlantic salmon from the Iberian glacial refugium.

    PubMed

    Consuegra, S; García de Leániz, C; Serdio, A; González Morales, M; Straus, L G; Knox, D; Verspoor, E

    2002-10-01

    Current understanding of the postglacial colonization of Nearctic and Palearctic species relies heavily on inferences drawn from the phylogeographic analysis of contemporary generic variants. Modern postglacial populations are supposed to be representative of their Pleistocene ancestors, and their current distribution is assumed to reflect the different colonization success and dispersal patterns of refugial lineages. Yet, testing of phylogeographic models against ancestral genomes from glacial refugia has rarely been possible. Here we compare ND1 mitochondrial DNA variation in late Pleistocene (16,000-40,000 years before present), historical and contemporary Atlantic salmon (Salmo salar) populations from northern Spain and other regions of western Europe. Our study demonstrates the presence of Atlantic salmon in the Iberian glacial refugium during the last 40,000 years and points to the Iberian Peninsula as the likely source of the most common haplotype within the Atlantic lineage in Europe. However, our findings also suggest that there may have been significant changes in the genetic structure of the Iberian refugial stock since the last ice age, and question whether modern populations in refugial areas are representative of ice age populations. A common haplotype that persisted in the Iberian Peninsula during the Pleistocene last glacial maximum is now extremely rare or absent from European rivers, highlighting the need for caution when making phylogeographic inferences about the origin and distribution of modern genetic types. PMID:12296947

  10. North Atlantic Glacial-Interglacial Ostracode Faunal Patterns through the Mid-Pleistocene Transition at ODP Site 980 and 982

    NASA Astrophysics Data System (ADS)

    Warner, J. S.; Schellenberg, S. A.

    2007-12-01

    Glacial-interglacial cycles through the Mid-Pleistocene Transition (MPT; 1.2 to 0.6 Ma) are characterized by a frequency decrease from 41 to 100 kyr and an amplitude increase via more extreme glaciations. This major transition has been the focal point of much North Atlantic paleoceanographic and micropaleontological research, yet little is know about North Atlantic deep-ocean benthic ostracode faunas through the MPT. One might predict such glacial-interglacial cycles to affect ostracode assemblages, yet North Atlantic ODP Sites 980 (1,145 m) and 982 (2,168 m) reveal no major or consistent changes in ostracode accumulation rates, resampled (abundance- corrected) richness, or taxon percent abundances, with the exception of an increase in ostracode accumulation rates late in the MPT at the deeper Site 980. This ostracode faunal stability is consistent with Raymo et al.'s (2004) interpretation of relatively stable North Atlantic thermohaline circulation through the MPT based on carbon-isotope depth-profiles. However, this ostracode faunal stability stands in stark contrast to other North Atlantic ostracode studies of the latest Pleistocene (Didie and Bauch, 2000) and Late Pliocene (Cronin et al., 1996), which show strong faunal variations in response to presumed oscillations in surface export production and intermediate water ventilation associated with glacial-interglacial cycles. Late in the MPT interval (0.8 to 0.6 Ma), benthic foraminifera experience a major decline and preferential extinction of infaunal taxa at Site 980 and 982 (Kawagata et al., 2002). Coeval ostracode assemblages show no comparable taxonomic loss through this enhanced extinction interval, but ostracode accumulation rates do markedly increase at the deeper Site 980. Such differential biotic response under presumably stable benthic environmental conditions remains difficult to reconcile with current paleoceanographic data.

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

    SciTech Connect

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

    1992-01-01

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

  12. 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 unusually high frequency of the relative sea-level oscillations (20 kyr), the concentration of sediment supply during low stands and early transgressions, and the correspondence of sea-level change with climatic change could be used to infer their relationship to a nearby ice sheet. Geologists studying deposits formed during times of widespread continental glaciation should consider possible glacial influences on the stratigraphy of mid-latitude deposits, even in the absence of sediments directly deposited by ice. ?? 2005 Elsevier B.V. All rights reserved.

  13. North Atlantic Glacial-Interglacial Ostracode Faunas During the Mid-Pleistocene Transition (MPT)

    NASA Astrophysics Data System (ADS)

    Warner, J. J.; Schellenberg, S. A.

    2006-12-01

    Latest Pleistocene and Late Pliocene studies of North Atlantic deep-ocean ostracodes have revealed strong glacial-interglacial fauna cycles, but little is know about ostracodes from the mid-Pleistocene transition (MPT) - an interval when global climate cycles increased in frequency and intensified in magnitude. Kawagata et al. (2005) identified an MPT-associated decline and extinction of numerous benthic foraminifer species with low- oxygen and high-export-production affinities, and attributed this faunal pattern to thermohaline circulation changes. As an initial assessment of North Atlantic MPT ostracodes, we analyzed the >150 ?m size-fraction of three pairs of Kawagata et al.'s (2005) glacial-interglacial samples (i.e. MIS 15/16; 21/22; 25/26) from ODP Site 980 (northwest Rockall Trough; 2,168 m). MPT ostracode abundances (i.e. typically <6 valves/g bulk sediment with an MIS 15 outlier of 18 valves/g bulk sediment) are marginally lower than latest Pleistocene ostracode abundances (Didie et al. 2002). MPT ostracode abundances show no significant correlation with associated Site 980 benthic foraminifer abundances (i.e. typically two to three orders-of-magnitude higher; Kawagata et al., 2005). MPT ostracode richness is strongly correlated with abundance (r2 = 0.73), which suggests caution in interpreting intersample differences among relatively rare taxa. Major faunal constituent patterns include (1) a strong and persistent presence (25-76%) of Krithe among all interglacial-glacial; (2) a variable, but often abundant, presence (3-21%) of Cytheropteron; and (3) a greater relative presence of Rockallia and Henryhowella within interglacial samples. These faunal patterns are broadly consistent with those established by Didie et al.'s (2002) high-resolution study of MIS 1-7 in the Rockall area. Ongoing MPT ostracode analyses include (1) assessing abundance and richness within the 63-150 ?m size-fractions, which are typically not analyzed, but here may contain up to five times more specimens than the >150 ?m size-fractions; (2) assessment of other glacial-interglacial extrema; and (3) replicate analyses from within individual glacial-interglacial extrema.

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

    SciTech Connect

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

    2008-01-01

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

  15. The influence of Pleistocene glacial refugia on tawny owl genetic diversity and phylogeography in western Europe.

    PubMed

    Brito, Patrícia H

    2005-09-01

    The glacial refugia hypothesis indicates that during the height of the Pleistocene glaciations the temperate species that are today widespread in western Europe must have survived in small and climatically favourable areas located in the southern peninsulas of Iberia, Italy and Balkans. One such species is the tawny owl, a relatively sedentary, nonmigratory bird presently distributed throughout Europe. It is a tree-nesting species closely associated with deciduous and mixed coniferous woodlands. In this study I used control region mtDNA sequences from 187 individuals distributed among 14 populations to determine whether current genetic patterns in tawny owl populations were consistent with postglacial expansion from peninsular refugia. European, North African and Asian tawny owls were found to represent three distinct lineages, where North Africa is the sister clade to all European owls. Within Europe, I found three well-supported clades that correspond to each of the three allopatric refugia. Expansion patterns indicate that owls from the Balkan refugium repopulated most of northern Europe, while expansion out of Iberia and Italy had only regional effects leading to admixture in France. Estimates of population divergence times between refugia populations are roughly similar, but one order of magnitude smaller between Greece and northern Europe. Based on a wide range of mutation rates and generation times, divergence between refugia appears to date to the Pleistocene. PMID:16101775

  16. 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.

  17. 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 ?18O 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.

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

    PubMed Central

    2012-01-01

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

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

    SciTech Connect

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

    1985-01-01

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

  20. The major Australian cool temperate rainforest tree Nothofagus cunninghamii withstood Pleistocene glacial aridity within multiple regions: evidence from the chloroplast.

    PubMed

    Worth, James R P; Jordan, Gregory J; McKinnon, Gay E; Vaillancourt, René E

    2009-01-01

    Glacial aridity of the Pleistocene was inhospitable for the cool temperate rainforest tree Nothofagus cunninghamii over most of its current range in southeastern Australia, particularly in eastern Tasmania. A chloroplast DNA phylogeographic study was undertaken to investigate whether this species was likely to have survived in situ or conforms to a dispersal model of postglacial recovery. Twenty-three chloroplast haplotypes were identified by PCR-RFLP and direct sequencing of 2164 base pairs from 213 N. cunninghamii individuals collected in a range-wide survey. Fine-scale haplotype distribution was investigated using PCR-RFLP in eastern Tasmania. Deep chloroplast divergence occurred in N. cunninghamii. The single haplotype of the sister species, N. moorei, was nested among N. cunninghamii haplotypes. The distribution of N. cunninghamii haplotypes supports: multiple glacial refugia in coastal and inland western Tasmania, the centre of haplotype diversity; glacial survival in the central highlands of Victoria, corroborating pollen data; and the long-term occupation of eastern Tasmania because of the presence of a unique deeply diverged chloroplast lineage. Nothofagus cunninghamii withstood glacial aridity within multiple regions in apparently nonequable climates. This finding contributes to a growing understanding of how the resilience of temperate species during glacial periods has shaped modern biota. PMID:19210718

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  2. Dating Plio-Pleistocene glacial sediments using the cosmic-ray-produced radionuclides 10Be and 26Al

    USGS Publications Warehouse

    Balco, G.; Stone, J.O.H.; Jennings, C.

    2005-01-01

    We use the cosmic-ray-produced radionuclides 26Al and 10Be to date Plio-Pleistocene glacial sediment sequences. These two nuclides are produced in quartz at a fixed ratio, but have different decay constants. If a sample is exposed at the surface for a time and then buried by overburden and thus removed from the cosmic-ray flux, the 26Al/10Be ratio is related to the duration of burial. We first attempted to date pre-Wisconsinan tills by measuring 26Al and 10Be in fluvial sediments beneath them and applying the method of "burial dating," which previous authors have used to date river sediment carried into caves. This method, however, requires simplifying assumptions about the 26Al and 10Be concentrations in the sediment at the time of burial. We show that these assumptions are not valid for river sediment in glaciated regions. 26Al and 10Be analyses of such sediment do not provide accurate ages for these tills, although they do yield limiting ages in some cases. We overcome this difficulty by instead measuring 26Al and 10Be in quartz from paleosols that are buried by tills. We use a more general mathematical approach to determine the initial nuclide concentrations in the paleosol at the time it was buried, as well as the duration of burial. This technique provides a widely applicable improvement on other means of dating Plio-Pleistocene terrestrial glacial sediments, as well as a framework for applying cosmogenic-nuclide dating techniques in complicated stratigraphic settings. We apply it to pre-Wisconsinan glacial sediment sequences in southwest Minnesota and eastern South Dakota. Pre-Wisconsinan tills underlying the Minnesota River Valley were deposited 0.5 to 1.5 Ma, and tills beneath the Prairie Coteau in eastern South Dakota and adjacent Minnesota were deposited 1 to 2 Ma.

  3. Loess, soil stratigraphy and Aokautere Ash on Late Pleistocene surfaces in south Westland, New Zealand: Interpretation and correlation with the glacial stratigraphy

    Microsoft Academic Search

    P. C. Almond

    1996-01-01

    The detailed stratigraphy and chronology for Late Pleistocene glaciations in north Westland have not previously been applied to glacial deposits and landforms of south Westland, in part because of lack of exposure. A stratigraphy for loess coverbeds offers the potential for discriminating and correlating landforms in this region. This study, in Saltwater Forest and surrounding areas in south Westland, confirms

  4. Millennial-Scale Climate Variability During a mid-Pleistocene Glacial (MIS 12) from a Terrestrial Lacustrine Record in the Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Fawcett, P. J.; Brown, E. T.; Werne, J. P.; Contreras, S.; Anderson, R. S.; Dodd, J. P.; Sharp, Z. D.; Heikoop, J. M.; Allen, C. D.

    2011-12-01

    We present a high-resolution terrestrial climate record from the Valles Caldera, New Mexico which spans some 200,000 years from mid MIS 14 to early MIS 10. The glacial periods represented in the record exhibit millennial-scale Dansgaard-Oeschger like variability, especially in MIS 12, one of the coldest glacials in the Pleistocene. High resolution proxies from core VC-3 including scanning XRF data, sediment density, color, and magnetic susceptibility show approximately 23 millennial-scale oscillations in MIS 12 with an average duration of 2,300 years. Many of these oscillations are characterized by relatively slow coolings followed by abrupt warmings, similar to D-O events in the Greenland ice core record. MBT/CBT MAT estimates in the MIS 12 portion of the core show stadial to interstadial warmings of up to 6 °C. The VC-3 stadials correlate with high percentages of boreal taxa pollen ( Picea, Abies ) (up to 25%) while interstadials have lower boreal pollen percentages (~5%) and many correlate with local maxima in Juniperus> and Quercus> . Significant changes in the hydrologic cycle also occur at these millennial timescales. Oxygen isotope data from diatom silica record changes of up to 10 per mil from stadial to interstadial, probably reflecting a combination of changes in moisture source (Pacific vs. Gulf of Mexico), moisture transport pathway, and the seasonality of precipitation. Several interstadials correlate with increases in Cyperaceae (sedge) pollen suggesting a shallower lake with a broad marshy zone around its margin. This zone was minimized during stadials when the lake was deeper. Interstadial shallowing probably resulted from higher evaporation rates and/or a reduction in winter precipitation. This combination of proxies from the Valles Caldera suggests that glacial stage millennial-scale climate variability in the American southwest was strongly driven by changes in the strength and location of the winter polar jet, which in turn affected the local hydrologic cycle and isotopic composition of precipitation, regional temperature change, watershed vegetation, the amount of fluvial runoff vs. atmospheric dust loading in the Valles Caldera lake, and contributed to the abrupt warmings ending the D-O like cycles.

  5. 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.

  6. 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.

  7. Sedimentological controls on gold in a late Pleistocene glacial placer deposit, Cariboo Mining District, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Eyles, Nicholas; Kocsis, Stephen P.

    1989-11-01

    It is a widely perceived notion that glaciation results in dispersal of mineralized bedrock and that sedimentary concentrates of economic minerals (placers) rarely occur in glaciated basins. This paper describes economic gold placers within late Pleistocene glacial and related fluvial sediments of the Cariboo Mining District in central British Columbia, Canada. The area has been defined as a "giant" gold placer; total production since 1858 is over 93,000 kg. The oldest and volumetrically largest placers occur in fluvial gravels and valley-side fan deposits deposited during a long non-glacial interval from as early as 125,000 to 30,000years B.P. The richest placers are found along bedrock "gutters" in the deepest parts of valleys, indicating repeated fluvial reworking of the valley infills. Braided and "wandering gravel bed" fluvial facies can be identified. Glacial placers, that overlie the fluvial placers, occur within lodgement till complexes deposited below the late Wisconsin Cordilleran ice sheet after 30,000 years B.P. The basal portions of lodgement tills are commonly enriched in gold as a result of incorporation from older gravels. Subglacial meltwaters created a highly effective sluicing system and left lucrative pay zones along meltwater-cut channels on bedrock benches, within intraformational gravels in lodgement till and within "lee-side" deposits down-ice of bedrock highs. "Lee-side" deposits are essentially water-worked talus slopes that accumulated in subglacial cavities. Finally, postglacial "wandering gravel-bed rivers" have repeatedly reworked older placers resulting in rich pay zones at the base of extensive bar platform deposits. Similar sedimentological controls on gold distribution can be identified in other glacial placers of late Cenozoic and Paleozoic age in North America, southern Africa and Australia. A distinction is drawn between these placers, all characterized by coarse-grained, nuggety gold, and the more well-known Precambrian and Paleozoic placers where finely-comminuted gold is dispersed through large thicknesses of rock. Episodes of glaciation typically occur after long periods of tropical and subtropical weathering when supergene processes were active and glaciers were able to remove and concentrate coarse gold. In contrast, gold in non-glacial placers of Precambrian and Paleozoic age has been through many cycles of erosion and transport and coarse gold is uncommon.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  9. The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S

    NASA Astrophysics Data System (ADS)

    Glasser, Neil F.; Jansson, Krister N.; Harrison, Stephan; Kleman, Johan

    2008-02-01

    This paper presents new mapping of the glacial geomorphology of southern South America between latitudes 38°S and 56°S, approximately the area covered by the former Patagonian Ice Sheets. Glacial geomorphological features, including glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques, were mapped from remotely sensed images (Landsat 7 ETM+, pan-sharpened Landsat 7 and ASTER). The landform record indicates that the Patagonian Ice Sheets consisted of 66 main outlet glaciers, together with numerous local cirque glaciers and independent ice domes in the surrounding mountains. In the northern part of the mapped area, in the Chilean Lake District (38-42°S), large piedmont glaciers developed on the western side of the Andes and the maximum positions of these outlet glaciers are, in general, marked by arcuate terminal moraines. To the east of the Andes between 38°S and 42°S, outlet glaciers were more restricted in extent and formed "alpine-style" valley glaciers. Along the eastern flank of the Andes south of ˜45°S a series of large fast-flowing outlet glaciers drained the ice sheet. The location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes. West of the Andes at this latitude, there is geomorphological evidence for an independent ice cap close to sea level on the Taitao Peninsula. The age of this ice cap is unclear but it may represent evidence of glacier growth during the Antarctic Cold Reversal and/or Younger Dryas Chronozone. Maximum glacier positions are difficult to determine along much of the western side of the Andes south of 42°S because of the limited land there, and it is assumed that most of these glaciers had marine termini. In the south-east of the mapped area, in the Fuegan Andes (Cordillera Darwin), the landform record provides evidence of ice-sheet initiation. By adding published dates for glacier advances from the literature we present maps of pre-Last Glacial Maximum (LGM) glacier extent, LGM extent and the positions of other large mapped moraines younger than LGM in age. A number of large moraines occur within the known LGM limits. The age of these moraines is unknown but, since many of them lie well outside the established maximum Neoglacial positions, the possibility that they reflect a return to glacial climates during the Younger Dryas Chronozone or Antarctic Cold Reversal cannot be discounted.

  10. 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 stasis (stabilizing selection, canalization) fail in this setting where climate is changing. One possible explanation is that most large birds and mammals are very broadly adapted and relatively insensitive to changes in their environments, although even the small mammals of the Pleistocene show stasis during climate change, too.

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

    NASA Astrophysics Data System (ADS)

    Peltier, W. Richard; Vettoretti, Guido

    2014-10-01

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

  12. Speciation of two desert poplar species triggered by Pleistocene climatic oscillations.

    PubMed

    Wang, J; Källman, T; Liu, J; Guo, Q; Wu, Y; Lin, K; Lascoux, M

    2014-02-01

    Despite the evidence that the Pleistocene climatic fluctuations have seriously affected the distribution of intraspecific diversity, less is known on its impact on interspecific divergence. In this study, we aimed to test the hypothesis that the divergence of two desert poplar species Populus euphratica Oliv. and P. pruinosa Schrenk. occurred during the Pleistocene. We sequenced 11 nuclear loci in 60 individuals from the two species to estimate the divergence time between them and to test whether gene flow occurred after species separation. Divergence time between the two species was estimated to be 0.66-1.37 million years ago (Ma), a time at which glaciation was at its maximum in China and deserts developed widely in central Asia. Isolation-with-Migration model also indicated that the two species had diverged in the presence of gene flow. We also detected evidence of selection at GO in P. euphratica and to a lesser extent at PhyB2. Together, these results underscore the importance of Pleistocene climate oscillations in triggering plant speciation as a result of habitats divergence. PMID:24065180

  13. Periodic jo??kulhlaups from Pleistocene glacial Lake Missoula-New evidence from varved sediment in northern Idaho and Washington

    USGS Publications Warehouse

    Waitt, R.B., Jr.

    1984-01-01

    Newly examined exposures in northern Idaho and Washington show that catastrophic floods from glacial Lake Missoula during late Wisconsin time were repeated, brief jo??kulhlaups separated by decades of quiet glaciolacustrine and subaerial conditions. Glacial Priest Lake, dammed in the Priest River valley by a tongue of the Purcell trench lobe of the Cordilleran ice sheet, generally accumulated varved mud; the varved mud is sharply interrupted by 14 sand beds deposited by upvalley-running currents. The sand beds are texturally and structurally similar to slackwater sediment in valleys in southern Washington that were backflooded by outbursts from glacial Lake Missoula. Beds of varved mud also accumulated in glacial Lake Spokane (or Columbia?) in Latah Creek valley and elsewhere in northeastern Washington; the mud beds were disrupted, in places violently, during emplacement of each of 16 or more thick flood-gravel beds. This history corroborates evidence from southern Washington that only one graded bed is deposited per flood, refuting a conventional idea that many beds accumulated per flood. The total number of such floodlaid beds in stratigraphic succession near Spokane is at least 28. The mud beds between most of the floodlaid beds in these valleys each consist of between 20 and 55 silt-to-clay varves. Lacustrine environments in northern Idaho and Washington therefore persisted for two to six decades between regularly recurring, colossal floods from glacial Lake Missoula. ?? 1984.

  14. Numerical chronology of Pleistocene coastal plain and valley development; extensive aggradation during glacial low sea-levels

    Microsoft Academic Search

    Ervin G. Otvos

    2005-01-01

    Based on more than 60 newly acquired luminescence ages, field information, and sediment granulometry data, a comprehensive chronostratigraphic framework is presented for Pleistocene alluvial coastal plain and valley terraces and coastal barrier trends on the northern Gulf of Mexico between Texas and NW Florida. Luminescence ages 216–188ka from the second youngest coastal terrace coincide with the highstand during the second

  15. New insights into Late Pleistocene glacial and postglacial history of northernmost Ungava (Canada) from Pingualuit Crater Lake sediments

    E-print Network

    Long, Bernard

    t The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada) from Pingualuit Crater Lake sediments Hervé Guyard a,b,*, Guillaume St-Onge a,b , Reinhard Pienitz c sediments Stratigraphy Multiproxy Late Pleistocene Ungava Crater Lake Subglacial Lake a b s t r a c

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

    PubMed

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

    2015-01-16

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

  17. Reduced El Niño–Southern Oscillation during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    PubMed Central

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

    2011-01-01

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

  19. Does an asymmetric thermohaline-ice-sheet oscillator drive 100 000-yr glacial cycles?

    NASA Astrophysics Data System (ADS)

    Denton, George H.

    2000-05-01

    A hypothesis is presented that late Quaternary 100 000-yr glacial cycles are driven by an asymmetric thermohaline-ice-sheet oscillator that emerged in the global climate system 650 000-950 000 yr ago, perhaps when the main source of Northern Hemisphere deep-water production shifted south from the Arctic into the Nordic seas. It is hypothesised that the asymmetry is due to the increasing difficulty after 950 000 years ago of resetting an interglacial mode of the critical Nordic limb of the salinity conveyor once it switches off and an ensuing iceberg flux enters the areas of downwelling. A possible reason for both a southward shift and the resulting asymmetry is uplift of the Greenland-Scotland submarine ridge from activity of the Iceland mantle plume.In this hypothesis an individual 100 000-yr glacial cycle begins when the northernmost limb of the salinity conveyor in the Nordic seas is curtailed, or even switched off, perhaps due to the growing strength of competing Antarctic Bottom Water (AABW) generated by interglacial recession of the West Antarctic Ice Sheet (WAIS) from the West Antarctic Rift System. Such recession produces southern marginal seas where dense shelf water can collect and overflow into the abyss. When northern ice sheets, nucleated by this circulation switch, develop marine components that calve icebergs into the Nordic seas, the salinity conveyor can no longer revert to an interglacial mode from orbital forcing, as it did prior to 950 000 yr ago. In order to reset an interglacial circulation mode of the conveyor, ice sheets must continue to grow for 100 000 years until they capture enough excess volume to produce a gravitational collapse of marine-based components, so massive that all grounded ice is flushed from North Atlantic continental shelves. The outburst of icebergs produced by this collapse cripples the glacial mode of overturning in the northern North Atlantic. Once this collapse ends, however, the Nordic seas become nearly free of icebergs for the first time in 100 000 years because of the depletion of adjacent marine-based components. As a consequence, North Atlantic salinity increases rapidly, switching the conveyor into a vigorous interglacial mode of operation and hence terminating the glacial cycle.By lowering sea-level, the prolonged growth of Northern Hemisphere ice sheets during each 100 000-yr cycle drives Antarctic grounding lines seaward across continental shelves, squeezing off the source of densified shelf waters that feed AABW. Sea-level rise and increased basal melting, however, caused by the subsequent collapse of northern ice sheets and the reintroduction of North Atlantic Deep Water into the Southern Ocean, reverses the process, forcing retreat of Antarctic grounding lines from their advanced last-glacial maximum positions. This retreat opens marginal seas for renewed formation of dense shelf water. By expanding marginal seas and hence the source of dense shelf water, ongoing recession of the WAIS strengthens AABW during the course of an interglaciation, eventually forcing a thermohaline circulation switch in the Nordic seas and initiating yet another 100 000-yr glacial cycle.The 100 000-yr duration of each cycle is set by two factors. Inertia is built into the system by the long time required for ice sheets to grow to the excess volume necessary for a marine collapse that resets the salinity conveyor into an interglacial mode. Eccentricity-driven changes in the amplitude of the precession or tropical half-precession signal give rise to warming events that trigger such a collapse of excess ice about each 100 000 yr.

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

    PubMed

    Ornelas, Juan Francisco; Rodríguez-Gómez, Flor

    2015-01-01

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

  1. Did glacial advances during the Pleistocene influence differently the demographic histories of benthic and pelagic Antarctic shelf fishes? – Inferences from intraspecific mitochondrial and nuclear DNA sequence diversity

    PubMed Central

    Janko, Karel; Lecointre, Guillaume; DeVries, Arthur; Couloux, Arnaud; Cruaud, Corinne; Marshall, Craig

    2007-01-01

    Background Circum-Antarctic waters harbour a rare example of a marine species flock – the Notothenioid fish, most species of which are restricted to the continental shelf. It remains an open question as to how they survived Pleistocene climatic fluctuations characterised by repeated advances of continental glaciers as far as the shelf break that probably resulted in a loss of habitat for benthic organisms. Pelagic ecosystems, on the other hand, might have flourished during glacial maxima due to the northward expansion of Antarctic polar waters. In order to better understand the role of ecological traits in Quaternary climatic fluctuations, we performed demographic analyses of populations of four fish species from the tribe Trematominae, including both fully benthic and pelagic species using the mitochondrial cytochrome b gene and an intron from the nuclear S7 gene. Results Nuclear and cytoplasmic markers showed differences in the rate and time of population expansions as well as the likely population structure. Neutrality tests suggest that such discordance comes from different coalescence dynamics of each marker, rather than from selective pressure. Demographic analyses based on intraspecific DNA diversity suggest a recent population expansion in both benthic species, dated by the cyt b locus to the last glacial cycle, whereas the population structure of pelagic feeders either did not deviate from a constant-size model or indicated that the onset of the major population expansion of these species by far predated those of the benthic species. Similar patterns were apparent even when comparing previously published data on other Southern Ocean organisms, but we observed considerable heterogeneity within both groups with regard to the onset of major demographic events and rates. Conclusion Our data suggest benthic and pelagic species reacted differently to the Pleistocene ice-sheet expansions that probably significantly reduced the suitable habitat for benthic species. However, the asynchronous timing of major demographic events observed in different species within both "ecological guilds", imply that the species examined here may have different population and evolutionary histories, and that more species should be analysed in order to more precisely assess the role of life history in the response of organisms to climatic changes. PMID:17997847

  2. Dansgaard-Oeschger Oscillations and the Bi-Polar SeeSaw in a Comprehensive Model of Glacial Climate

    NASA Astrophysics Data System (ADS)

    Peltier, W. R.; Vettoretti, G.

    2013-12-01

    The millennial timescale variability characteristic of Marine Oxygen Isotopic Stage 3 that is observed most clearly in Summit, Greenland ice-cores has never been adequately explained. The mechanism responsible for the bi-polar seesaw relationship between the Polar Regions that accompanies these events has remained similarly enigmatic. This situation has continued to exist in large part as a consequence of the fact that the D-O oscillation has never been shown to arise in a comprehensive coupled model of glacial climate. We will describe a series of very long timescale high resolution integrations of the NCAR CESM1 model under glacial boundary conditions in which the continental ice cover is assumed to be fixed to that of the new ICE-6G (VM5a) model. Greenhouse gases are also fixed to those inferred in the basis of Antarctic ice-core measurements. In order that the equilibrium dynamical state of the ocean not be prejudiced by the initial conditions, the ocean is initialized from a state of rest with modern ocean heat content. The spin-up of the model to statistical equilibrium is characterized by the existence of a series of cooling thresholds which, once crossed, lead the climate system into full glacial cold conditions in which sea ice cover has significantly expanded. In the high spatial resolution version of CESM1, the same resolution employed in CMIP5 experiments, we find that the glacial state is unsteady and characterized by millennium timescale oscillations, each of which has the form of a relaxation oscillation with the fast timescale warming phase of the oscillation caused by a rapid onset of deep water production in the North Atlantic due to convective instability of the water column. The subsequent slow timescale phase of each oscillation is associated with a slow expansion of sea ice cover which leads the system back into stadial conditions. These characteristics accurately mimic the GRIP and NGRIP records of individual D-O oscillations, not only in terms of the period of the individual oscillations but also concerning their amplitude. We compare the model predicted temperature variations for the Summit, Greenland and Dronning Maud Land, Antarctica sites and thereby show that the model replicates the bi-polar seesaw behavior inferred on the basis of the ?18O records from the collocated ice cores. The 'bare' D-O oscillation is thereby shown not to require co-variation of land ice volume for its existence, although negative feedback associated with freshwater forcing during the fast transitions into the interstadial state is expected to be important in sculpting the detailed form of individual Bond cycles.

  3. 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. PMID:10769156

  4. Water versus ice: The competing roles of modern climate and Pleistocene glacial erosion in the Central Alps of Switzerland

    NASA Astrophysics Data System (ADS)

    Schlunegger, Fritz; Norton, Kevin P.

    2013-08-01

    Recent studies have identified relationships between landscape form, erosion and climate in regions of landscape rejuvenation, associated with increased denudation. Most of these landscapes are located in non-glaciated mountain ranges and are characterized by transient geomorphic features. The landscapes of the Swiss Alps are likewise in a transient geomorphic state as seen by multiple knickzones. In this mountain belt, the transient state has been related to erosional effects during the Late Glacial Maximum (LGM). Here, we focus on the catchment scale and categorize hillslopes based on erosional mechanisms, landscape form and landcover. We then explore relationships of these variables to precipitation and extent of LGM glaciers to disentangle modern versus palaeo controls on the modern shape of the Alpine landscape. We find that in grasslands, the downslope flux of material mainly involves unconsolidated material through hillslope creep, testifying a transport-limited erosional regime. Alternatively, strength-limited hillslopes, where erosion is driven by bedrock failure, are covered by forests and/or expose bedrock, and they display oversteepened hillslopes and channels. There, hillslope gradients and relief are more closely correlated with LGM ice occurrence than with precipitation or the erodibility of the underlying bedrock. We relate the spatial occurrence of the transport- and strength-limited process domains to the erosive effects of LGM glaciers. In particular, strength-limited, rock dominated basins are situated above the equilibrium line altitude (ELA) of the LGM, reflecting the ability of glaciers to scour the landscape beyond threshold slope conditions. In contrast, transport-limited, soil-mantled landscapes are common below the ELA. Hillslopes covered by forests occupy the elevations around the ELA and are constrained by the tree line. We conclude that the current erosional forces at work in the Central Alps are still responding to LGM glaciation, and that the modern climate has not yet impacted on the modern landscape.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  6. Correlating tidewater glacial meltwater discharge with El Niño-Southern Oscillation in Southern Alaska

    NASA Astrophysics Data System (ADS)

    Jaeger, J. M.; Cowan, E.; Jackolski, C.; Powell, R. D.; Chapman, G.

    2007-12-01

    Over the past two decades coincident with Arctic climate warming, Alaskan glaciers have experienced significant volume loss with the resulting discharge substantially contributing to rising sea level. This thinning has occurred during a period of pronounced variability in regional climatology and oceanography. However, the meteorological parameters forcing melting have not been well established, as there are few annual records of meltwater discharge directly from large cliff-calving glaciers. To test how meltwater production varies in response to climate forcing, a multi-decadal proxy record of meltwater discharge was established for tidewater glaciers in Disenchantment Bay and in Muir Inlet, Glacier Bay National Park, southern coastal Alaska. 33 piston cores and 8 multicores were collected from 24 stations to measure annual sediment deposition rates over the last several decades. Sedimentary facies, physical properties, and short-lived radioisotopes were used to delineate summertime sediment deposition rates on fortnightly to annual time scales, as tidal and seasonal forcing create distinctly laminated (cyclopels) and annually varved deposits. Magnetic susceptibility, sortable silt, and sediment floc characteristics were used as proxies of meltwater plume competence. Complete varves were identified from cores collected in Disenchantment Bay for up to 22 years (1981-2003) and the period of highest and most variable summer layer thickness at Hubbard Glacier coincides with El Ni ñ o-dominated conditions in the North Pacific from 1990-1995 and a warm phase of the Pacific Decadal Oscillation (PDO). The velocity and competence of the meltwater plume increased in the period 1987-1992, likely associated with the numerous ENSO events that resulted in higher winter precipitation. Hubbard Glacier summer sediment thickness data follow a similar temporal trend as the Alsek River discharge hydrograph, the only currently glacierized basin gaged by the USGS in the region, suggesting that the two drainage basins respond similarly to regional climate forcing. Cross-correlation time-series of Alsek River discharge with temperature and precipitation data from the weather station at Yakutat, AK show that summers with higher mean temperatures correlate with increased discharge and to a lesser extent with the amount of precipitation accumulated during the preceding winter. Two 17-m-long jumbo cores from Muir Inlet contain up to 75 years of complete melt-season deposits and associated spring-neap packages. Multi-taper method and singular spectrum analysis spectral estimation techniques were used to calculate statistically significant periodicity in both the melt season deposit thicknesses and spring-neap package thicknesses for each core. Periodicity in melt season deposit thickness shows that both cores contain significant ENSO signals and that one core (EW0408 60JC) contains significant PDO signals. This research has shown that high-resolution records of fjord sedimentation from tidewater glaciers may be a reliable proxy for past magnitude, duration, and temporal distribution of annual meltwater discharge into Alaskan glacial fjords, thus adding to the climate change record in a sensitive area.

  7. Facies and ground-penetrating radar characteristics of coarse-grained beach deposits of the uppermost Pleistocene glacial Lake Algonquin, Ontario, Canada

    Microsoft Academic Search

    VINCENZO PASCUCCI; I. PETER; ANTHONY L. ENDRES

    2008-01-01

    The lithofacies of the uppermost Pleistocene (ca 11 800 to 10 400 14 Cy rbp), cold-temperate, coarse-grained beach deposits of Lake Algonquin, the precursor of the present Lake Huron of North America, have been studied and interpreted based on analogous features of modern beaches from the same region. Ice foot and ice-cementation develop during winter but, unlike Arctic beaches, ice-related

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

    NASA Technical Reports Server (NTRS)

    Saltzman, Barry; Maasch, Kirk A.

    1988-01-01

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

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

    PubMed Central

    2011-01-01

    Background Pleistocene glacial oscillations have significantly affected the historical population dynamics of temperate taxa. However, the general effects of recent climatic changes on the evolutionary history and genetic structure of extant subtropical species remain poorly understood. In the present study, phylogeographic and historical demographic analyses based on mitochondrial and nuclear DNA sequences were used. The aim was to investigate whether Pleistocene climatic cycles, paleo-drainages or mountain vicariance of Taiwan shaped the evolutionary diversification of a subtropical gossamer-wing damselfly, Euphaea formosa. Results E. formosa populations originated in the middle Pleistocene period (0.3 Mya) and consisted of two evolutionarily independent lineages. It is likely that they derived from the Pleistocene paleo-drainages of northern and southern Minjiang, or alternatively by divergence within Taiwan. The ancestral North-central lineage colonized northwestern Taiwan first and maintained a slowly growing population throughout much of the early to middle Pleistocene period. The ancestral widespread lineage reached central-southern Taiwan and experienced a spatial and demographic expansion into eastern Taiwan. This expansion began approximately 30,000 years ago in the Holocene interglacial period. The ancestral southern expansion into eastern Taiwan indicates that the central mountain range (CMR) formed a barrier to east-west expansion. However, E. formosa populations in the three major biogeographic regions (East, South, and North-Central) exhibit no significant genetic partitions, suggesting that river drainages and mountains did not form strong geographical barriers against gene flow among extant populations. Conclusions The present study implies that the antiquity of E. formosa's colonization is associated with its high dispersal ability and larval tolerance to the late Pleistocene dry grasslands. The effect of late Pleistocene climatic changes on the subtropical damselfly's historical demography is lineage-specific, depending predominantly on its colonization history and geography. It is proposed that the Riss and Würm glaciations in the late Pleistocene period had a greater impact on the evolutionary diversification of subtropical insular species than the last glacial maximum (LGM). PMID:21486452

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

    USGS Publications Warehouse

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

    1997-01-01

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

  11. A GCM comparison of Plio-Pleistocene interglacial-glacial periods in relation to Lake El'gygytgyn, NE Arctic Russia

    NASA Astrophysics Data System (ADS)

    Coletti, A. J.; DeConto, R. M.; Brigham-Grette, J.; Melles, M.

    2014-08-01

    Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stage (MIS) 1 (9 ka), 5e (127 ka), 11c (409 ka), and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the Mean Temperature of the Warmest Month (MTWM) indicate conditions 2.1, 0.5 and 3.1 °C warmer than today during MIS 5e, 11c, and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer orbital forcing, the extraordinary warmth of MIS 11c relative to the other interglacials in the proxy records remain difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice, and circum-Arctic land ice feedbacks on the climate of the Beringian interior. Simulations accounting for climate-vegetation-land surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on Northeast Asian temperature during the warmth of stage 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic ocean has some effect on Beringian climate, suggesting intrahemispheric coupling seen in comparisons between Lake El'gygytgyn and Antarctic sediment records might be related to linkages between Antarctic ice volume and ocean circulation. The exceptional warmth of MIS 11c remains enigmatic however, relative to the modest orbital and greenhouse gas forcing during that interglacial. Large Northern Hemisphere ice sheets during Plio-Pleistocene glaciation causes a substantial decrease in Mean Temperature of the Coldest Month (MTCM) and Mean Annual Precipitation (PANN) causing significant Arctic aridification. Aridification and cooling can be linked to a combination of mechanical forcing from the Laurentide and Fennoscandian ice sheets on mid-tropospheric westerly flow and expanded sea ice cover causing albedo-enhanced feedback.

  12. Early Pleistocene to Holocene glacial activity along the southern Alaska continental shelf inferred from the sedimentary record in the northern Gulf of Alaska - preliminary results

    NASA Astrophysics Data System (ADS)

    Forwick, M.; Cowan, E. A.; Bahlburg, H.; Childress, L. B.; Jaeger, J. M.; Moy, C. M.; Müller, J.; Ribeiro, F.; Ridgway, K. D.; Gulick, S. P.; Worthington, L. L.; Reece, R.

    2013-12-01

    Preliminary analyses of the lithology at Site U1418 (IODP Expedition 341), located on the proximal Surveyor Fan, provide evidence of continuous presence of tidewater glaciers on the southern Alaska continental shelf for more than c. 1.2 Ma, as well as evidence of prolonged presence of grounded ice at the shelf break and/or the initiation of ice streams. The lowermost lithostratigraphic unit (Unit IV) of the 941 m long record is composed of heavily deformed sediments that are interpreted to be the top of the recently discovered Surveyor mass-transport deposit. Unit III contains mostly laminated mud with thin interbeds of sand, silt and clast-rich muddy diamict with rip-up clasts. A few lonestones of granule and pebble size are present. Massive and laminated mud with scattered lonestones, as well as interbedded intervals of clast-poor diamict (clasts of granule and pebble size) compose Unit II. Unit I contains massive mud with interbedded silt laminae and sand beds. Most silt laminae have the same color as the matrix, but some are lighter. Diatom oozes and graded sand beds occur infrequently and lonestones are present below 3 m. The dominance of mud suggests that sedimentation at Site U1418 was strongly influenced by suspension settling from turbid meltwater plumes emanating into the Gulf of Alaska during the past c. 1.2 Ma. Laminated intervals may reflect temporal variations in meltwater runoff from a single sediment source and/or supply from several sources during the deposition of Units II and III. Lonestones and clasts of granule and pebble size are regarded to be mostly iceberg-rafted debris, indicating that tidewater glaciers have been present on the continental shelf for most of the time since the onset of the deposition of Unit III. Diamicts in Unit II most probably reflect periods of enhanced ice rafting and/or reduced meltwater runoff. Minor silt and sand beds provide evidence of occasional sediment reworking during the deposition of Units II and III. The abrupt occurrence of silt laminae and sand beds at the transition from Unit II to Unit I is suggested to reflect a major reorganization of the sediment delivery system to Site U1418. We suggest that these deposits reflect increased turbidity-flow activity related to the first expansion of grounded ice to the shelf break and/or the initiation of ice streams during the Late Pleistocene, transporting large amounts of sediment across the shelf. Slope failures most probably resulted from oversteepening and/or seismicity related to either glacio-isostatic adjustments or tectonic processes. Occasionally occurring different-colored silt laminae indicate that sediments probably originated from multiple sources.

  13. Arctic ocean sediment texture and the Pleistocene climate cycle

    SciTech Connect

    Clark, D.L.; Morris, T.H.

    1985-01-01

    Arctic Ocean sediment texture accurately reflects the Plio-Pleistocene climate cycle. The precision of paleoclimate interpretation is improved when deglaciation is recognized as a distinct climate stage, overlapping both glacial and interglacial stages, and for the later Pleistocene, perhaps never completed. Oxygen isotope stratigraphy and foraminifera productivity are out of phase but can be understood in the context of the transitional nature of the glacial, deglacial and interglacial climate stages of the Arctic Ocean.

  14. Phylogeography of the Alcippe morrisonia (Aves: Timaliidae): long population history beyond late Pleistocene glaciations

    PubMed Central

    Song, Gang; Qu, Yanhua; Yin, Zuohua; Li, Shouhsien; Liu, Naifa; Lei, Fumin

    2009-01-01

    Background The role of Pleistocene glacial oscillations in current biodiversity and distribution patterns varies with latitude, physical topology and population life history and has long been a topic of discussion. However, there had been little phylogeographical research in south China, where the geophysical complexity is associated with great biodiversity. A bird endemic in Southeast Asia, the Grey-cheeked Fulvetta, Alcippe morrisonia, has been reported to show deep genetic divergences among its seven subspecies. In the present study, we investigated the phylogeography of A. morrisonia to explore its population structure and evolutionary history, in order to gain insight into the effect of geological events on the speciation and diversity of birds endemic in south China. Results Mitochondrial genes cytochrome b (Cytb) and cytochrome c oxidase I (COI) were represented by 1236 nucleotide sites from 151 individuals from 29 localities. Phylogenetic analysis showed seven monophyletic clades congruent with the geographically separated groups, which were identified as major sources of molecular variance (90.92%) by AMOVA. TCS analysis revealed four disconnected networks, and that no haplotype was shared among the geographical groups. The common ancestor of these populations was dated to 11.6 Mya and several divergence events were estimated along the population evolutionary history. Isolation by distance was inferred by NCPA to be responsible for the current intra-population genetic pattern and gene flow among geographical groups was interrupted. A late Pleistocene demographic expansion was detected in the eastern geographical groups, while the expansion time (0.2–0.4 Mya) was earlier than the Last Glacial Maximum. Conclusion It is proposed that the complicated topology preserves high genetic diversity and ancient lineages for geographical groups of A. morrisonia in China mainland and its two major islands, and restricts gene exchange during climate oscillations. Isolation by distance seems to be an important factor of genetic structure formation within geographical populations. Although glacial influence to population fluctuation was observed in late Pleistocene, it seems that populations in eastern China were more susceptible to climate change, and all geographical groups were growing stably through the Last Glacial Maximum. Coalescence analysis suggested that the ancestor of A. morrisonia might be traced back to the late Miocene, and the current phylogeographical structure of A. morrisonia is more likely to be attributable to a series geological events than to Pleistocene glacial cycles. PMID:19558699

  15. Correlation of Late-Pleistocene Lake-Level Oscillations in Mono Lake, California, with North Atlantic Climate Events

    USGS Publications Warehouse

    Benson, L.V.; Lund, S.P.; Burdett, J.W.; Kashgarian, M.; Rose, T.P.; Smoot, J.P.; Schwartz, M.

    1998-01-01

    Oxygen-18 (18O) values of sediment from the Wilson Creek Formation, Mono Basin, California, indicate three scales of temporal variation (Dansgaard-Oeschger, Heinrich, and Milankovitch) in the hydrologic balance of Mono Lake between 35,400 and 12,900 14C yr B.P. During this interval, Mono Lake experienced four lowstands each lasting from 1000 to 2000 yr. The youngest low-stand, which occurred between 15,500 and 14,000 14C yr B.P., was nearly synchronous with a desiccation of Owens Lake, California. Paleomagnetic secular variation (PSV) data indicate that three of four persistent lowstands occurred at the same times as Heinrich events H1, H2, and H4. 18O data indicate the two highest lake levels occurred ???18,000 and ???13,100 14C yr B.P., corresponding to passages of the mean position of the polar jet stream over the Mono Basin. Extremely low values of total inorganic carbon between 26,000 and 14,000 14C yr B.P. indicate glacial activity, corresponding to a time when summer insolation was much reduced. ?? 1998 University of Washington.

  16. Glacial Landforms

    NSDL National Science Digital Library

    Mark Sweeney

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

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

    PubMed Central

    2012-01-01

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

  18. Investigating the effects of Pleistocene events on genetic divergence within Richardsonius balteatus, a widely distributed western North American minnow

    PubMed Central

    2014-01-01

    Background Biogeographers seek to understand the influences of global climate shifts and geologic changes to the landscape on the ecology and evolution of organisms. Across both longer and shorter timeframes, the western North American landscape has experienced dynamic transformations related to various geologic processes and climatic oscillations, including events as recently as the Last Glacial Maximum (LGM; ~20 Ka) that have impacted the evolution of the North American biota. Redside shiner is a cyprinid species that is widely distributed throughout western North America. The species’ native range includes several well-documented Pleistocene refugia. Here we use mitochondrial DNA sequence data to assess phylogeography, and to test two biogeographic hypotheses regarding post-glacial colonization by redside shiner: 1) Redside shiner entered the Bonneville Basin at the time of the Bonneville Flood (Late Pleistocene; 14.5 Ka), and 2) redside shiner colonized British Columbia post-glacially from a single refugium in the Upper Columbia River drainage. Results Genetic diversification in redside shiner began in the mid to late Pleistocene, but was not associated with LGM. Different clades of redside shiner were distributed in multiple glacial age refugia, and each clade retains a signature of population expansion, with clades having secondary contact in some areas. Conclusions Divergence times between redside shiner populations in the Bonneville Basin and the Upper Snake/Columbia River drainage precedes the Bonneville Flood, thus it is unlikely that redside shiner invaded the Bonneville Basin during this flooding event. All but one British Columbia population of redside shiner are associated with the Upper Columbia River drainage with the lone exception being a population near the coast, suggesting that the province as a whole was colonized from multiple refugia, but the inland British Columbia redside shiner populations are affiliated with a refugium in the Upper Columbia River drainage. PMID:24885371

  19. Age of the crowfoot advance in the Canadian Rocky Mountains. A glacial event coeval with the Younger Dryas oscillation

    SciTech Connect

    Reasoner, M.A.; Rutter, N.W. (Univ. of Alberta, Edmonton, Alberta (Canada)); Osborn, G. (Univ. of Calgary, Alberta (Canada))

    1994-05-01

    A suite of sediment core samples was recovered from two lakes, Crowfoot and Bow lakes, that are adjacent to the Crowfoot moraine type locality, to identify and radiocarbon date sediments related to the Crowfoot advance. The Crowfoot moraine system, widely recognized throughout northwestern North America, represents a glacial advance that is post-Wisconsin and pre-Mazama tephra in age. An interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca. 11,330 and 10,100 [sup 14]C yr B.P. is associated with the Crowfoot moraine. The Crowfoot advance is therefore approximately synchronous with the European Younger Dryas cold event (ca. 11,000-10,000 [sup 14]C yr B.P.). Furthermore, the termination of the Crowfoot advance also appears to have been abrupt. These findings illustrate that the climatic change responsible for the European Younger Dryas event extended beyond the northern Atlantic basin and western Europe. Equilibrium-line altitude (ELA) depressions associated with the Crowfoot advance are similar to those determined for the Little Ice Age advance, whereas Younger Dryas ELA depressions in Europe significantly exceed Little Ice Age ELA depressions. 26 refs., 3 figs., 1 tab.

  20. Vicariance Biogeography in the Pleistocene and Speciation in North American Wood Warblers: A Test of Mengel's Model

    Microsoft Academic Search

    Eldredge Bermingham; Scott Freeman; Chris Wood

    1992-01-01

    It is widely believed that habitat fragmentation during the Pleistocene initiated speciation events in many songbird genera. One such vicariance model for avian speciation in the Pleistocene was developed by R. M. Mengel for North American birds. This model suggests that the first Pleistocene glacial advance reduced the area of an extensive, eastern North American deciduous forest, forcing adaptation by

  1. Persistence across Pleistocene ice ages in Mediterranean and extra-Mediterranean refugia: phylogeographic insights from the common wall lizard

    PubMed Central

    2013-01-01

    Background Pleistocene climatic oscillations have played a major role in structuring present-day biodiversity. The southern Mediterranean peninsulas have long been recognized as major glacial refugia, from where Northern Europe was post-glacially colonized. However, recent studies have unravelled numerous additional refugia also in northern regions. We investigated the phylogeographic pattern of the widespread Western Palaearctic lizard Podarcis muralis, using a range-wide multilocus approach, to evaluate whether it is concordant with a recent expansion from southern glacial refugia or alternatively from a combination of Mediterranean and northern refugia. Results We analyzed DNA sequences of two mitochondrial (cytb and nd4) and three nuclear (acm4, mc1r, and pdc) gene fragments in individuals from 52 localities across the species range, using phylogenetic and phylogeographic methods. The complex phylogeographic pattern observed, with 23 reciprocally monophyletic allo- parapatric lineages having a Pleistocene divergence, suggests a scenario of long-term isolation in multiple ice-age refugia across the species distribution range. Multiple lineages were identified within the three Mediterranean peninsulas – Iberia, Italy and the Balkans - where the highest genetic diversity was observed. Such an unprecedented phylogeographic pattern - here called “refugia within all refugia” – compasses the classical scenario of multiple southern refugia. However, unlike the southern refugia model, various distinct lineages were also found in northern regions, suggesting that additional refugia in France, Northern Italy, Eastern Alps and Central Balkans allowed the long-term persistence of this species throughout Pleistocene glaciations. Conclusions The phylogeography of Podarcis muralis provides a paradigm of temperate species survival in Mediterranean and extra-Mediterranean glacial refugia. Such refugia acted as independent biogeographic compartments for the long-term persistence of this species, for the differentiation of its genetic lineages, and for the short-distance post-glacial re-colonization of neighbouring areas. This finding echoes previous findings from recent phylogeographic studies on species from temperate ecoregions, thus suggesting the need for a reappraisal of the role of northern refugia for glacial persistence and post-glacial assembly of Holarctic biota. PMID:23841475

  2. 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 composed of a lower light lamina, progressively grading upwards to a dark lamina. Light laminae are composed by diatom valves of a single species (Cyclostephanos cf. andinus), accumulated during short-term extraordinary diatom blooms when water column mixing took place under abrupt and short-term climatic events. Dark laminae contain a complex diatom assemblage and are rich in organic matter representing the baseline limnological conditions during several years of deposition. Spectral analyses (Fast Fourier Transformation - FFT - and Time Frequency - TF - analyses) were performed on the isolated paleohydrological curve and on the gray color curve calculated for these laminated sediments. The FFT analyses of the paleohydrological signal obtained from the PCA highlights the record of 35-51 years cycles, that might correspond to the solar Bruckner cycle as well as to the inter-decadal changes in the variance of the ENSO phenomena. The results of the FFT analyses carried out on the gray curve reinforce the hypothesis of the solar control on the variations in the lake productivity: the 11-years Schwabe, 22-23-years Hale, 35-years Bruckner and the approx. 90-years Gleissberg cycles, as well as a strong to very strong ENSO phenomena (8.2 and 7.5-years cycles) are recorded. The TF analyses developed on the variations of the gray-colour curve reveal that all solar frequencies have modified intensities during the Late Glacial and Early Holocene. During the low activity periods of the 11-years Schwabe cycles, strong to very strong ENSO phenomena took place. These results show that ENSO-like variability was present during the late Glacial and early Holocene in the Altiplano.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  4. The mid-Pleistocene transition in the subtropical southwest Pacific

    Microsoft Academic Search

    T. Russon; M. Elliot; A. Sadekov; G. Cabioch; T. Corrège; P. De Deckker

    2011-01-01

    Reconstructions of subtropical southwest Pacific climate variability over the Pleistocene were derived from coupled planktic foraminiferal ?18O-Mg\\/Ca measurements taken from a southern Coral Sea sediment core. A clear shift from ?40 kyr to ?100 kyr modes of reconstructed glacial-interglacial sea surface temperature (SST) variability is seen over the mid-Pleistocene transition, and these fluctuations are shown to have remained coherent with

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

    E-print Network

    Montgomery, David R.

    Spawning sockeye salmon fossils in Pleistocene lake beds of Skokomish Valley, Washington Gerald R Available online 15 June 2007 Abstract An assemblage of fossil sockeye salmon was discovered in Pleistocene abundant near the head of a former glacial lake at 115 m elevation. Large adult salmon are concentrated

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

    Microsoft Academic Search

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

    2004-01-01

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

  7. Pleistocene speciation in the genus Populus (salicaceae).

    PubMed

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

    2012-05-01

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

  8. Early to Mid-Pleistocene Variability at IODP Site U1387 (Faro Drift): Surface and Mediterranean Outflow Water Responses

    NASA Astrophysics Data System (ADS)

    Voelker, A. H.; Jimenez, F. J.; Bahr, A.

    2013-12-01

    During the mid-Pleistocene transition (MPT; 500-1250 ka) the dominant pacing of glacial/ interglacial cycles changed from the 41 ky obliquity to the 100 ky eccentricity cycle. Superimposed on the orbital-scale changes are millennial-scale climate instabilities that in the mid-latitude Atlantic are related to insolation. In the Mediterranean Sea, on the other hand, sapropel layers were formed during insolation maxima and the associated circulation changes in the basin also affected the water exiting through the Strait of Gibraltar and forming the Mediterranean Outflow Water (MOW). MOW's hydrographic history is unknown prior to 100 ka but this is changing now with the complete sequences of Plio-/Pleistocene contourite deposits recovered by IODP Exp. 339 in the Gulf of Cádiz. Hydrographic changes during Marine Isotope Stages 16 to 32 (630-1100 ka) are being reconstructed at IODP Site U1387 (36.8°N; 7.7°W; 559 m). Variations in the Atlantic-sourced surface waters are revealed by G. bulloides stable isotope data and carbonate and organic carbon concentrations. Upper MOW core history is extracted from benthic stable isotope records, the weight percent of the sand fraction, and XRF data. Besides the glacial/ interglacial cycles both surface water and MOW records show millennial-scale stadial/ interstadial oscillations, in particular during the interglacials. Planktonic and benthic oxygen isotope records are strongly correlated on the orbital but not the millennial-scale level indicating that during the latter the subsurface North Atlantic Central Water played an important role in modifying the MOW signal. Ventilation in the MOW level varied significantly with better ventilation occurring during glacial and stadial intervals and periods of contouritic layer formation. The new records indicate that MOW was sensitive to abrupt climate instabilities during the MPT and, like during the last glacial cycle, provided an important component to the stability of the Atlantic's overturning circulation.

  9. Onset of major Pleistocene glaciations in the Alps

    NASA Astrophysics Data System (ADS)

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

    2003-04-01

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

  10. Glacial marine sedimentation: Paleoclimatic significance

    SciTech Connect

    Anderson, J.B.; Ashley, G.M. (eds.)

    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.

  11. The case for an ice shelf in the pleistocene Arctic Ocean

    Microsoft Academic Search

    Mikhail G. Grosswald; Terence J. Hughes

    1999-01-01

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

  12. The case for an ice shelf in the pleistocene Arctic Ocean

    Microsoft Academic Search

    Mikhail G. Grosswald; Terence J. Hughes

    2008-01-01

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

  13. Evolution of Lake Nikolay, Arga Island, Western Lena River Delta, during Late Pleistocene and Holocene Time

    Microsoft Academic Search

    Georg Schwamborn; Andrei A. Andreev; Volker Rachold; Hans-Wolfgang Hubberten; Mikhail N. Grigoriev; Volodya Tumskoy; Elena Yu

    2002-01-01

    Summary: The Late Pleistocene and Holocene history of Lake Nikolay on Arga Island, western Lena River delta, is reconstructed using shallow seismic and radio-eehe sounding (RES) profiles and sedimentary analyses including granulometry, biogeochemistry and pollen analysis. The main objective of this study is directed to the controversy about a glacial 01' a periglacial origin of Arga Island and a glacial

  14. Middle Pleistocene glaciation in Patagonia dated by cosmogenic-nuclide measurements on outwash gravels

    E-print Network

    Middle Pleistocene glaciation in Patagonia dated by cosmogenic-nuclide measurements on outwash beryllium-10 Last Glacial Maximum The well-preserved glacial record in Argentine Patagonia offers a ~1 Ma in other parts of Patagonia. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The aim

  15. Patterns of Diversity, Areas of Endemism, and Multiple Glacial Refuges for Freshwater Crabs of the Genus Sinopotamon in China (Decapoda: Brachyura: Potamidae)

    PubMed Central

    Fang, Fang; Sun, Hongying; Zhao, Qiang; Lin, Congtian; Sun, Yufang; Gao, Wei; Xu, Juanjuan; Zhou, Junying; Ge, Feng; Liu, Naifa

    2013-01-01

    Previous research has shown that the geographical distribution patterns of freshwater fishes and amphibians have been influenced by past climatic oscillations in China resulting from Pleistocene glacial activity. However, it remains unknown how these past changes have impacted the present-day distribution of Chinese freshwater crabs. This work describes the diversity and endemism of freshwater crabs belonging to Sinopotamon, a highly speciose genus endemic to China, and evaluates its distribution in terms of topography and past climatic fluctuations. Species diversity within Sinopotamon was found to be concentrated in an area from the northeastern edge of the Yunnan-Guizhou Plateau to the Jiangnan Hills, and three areas of endemism were identified. Multiple regression analysis between current climatic variables and Sinopotamon diversity suggested that regional annual precipitation, minimum temperature in the coldest month, and annual temperature range significantly influenced species diversity and may explain the diversity patterns of Sinopotamon. A comparison of ecological niche models (ENMs) between current conditions and the last glacial maximum (LGM) showed that suitable habitat for Sinopotamon in China severely contracted during the LGM. The coincidence of ENMs and the areas of endemism indicated that southeast of the Daba Mountains, and central and southeastern China, are potential Pleistocene refuges for Sinopotamon. The presence of multiple Pleistocene refuges within the range of this genus could further promote inter- and intraspecific differentiations, and may have led to high Sinopotamon species diversity, a high endemism rate and widespread distribution. PMID:23308152

  16. Glacial earthquakes

    Microsoft Academic Search

    G. Ekström; M. Nettles; G. A. Abers

    2003-01-01

    We have identified a new class of moderate earthquakes (seismic magnitude around 5) that occur beneath glaciers. The previously unknown glacial earthquakes generate long-period (20--60~sec) seismic surface waves that are well recorded on globally distributed seismic stations, but which have previously gone undetected because they do not generate the high-frequency seismic waves on which traditional earthquake detection and location methodologies

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

    E-print Network

    Cooper, David Matthew

    2013-11-28

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

  18. ROCK WEATHERING CHARACTERISTICS AS RELATIVE-AGE INDICATORS FOR GLACIAL AND POSTGLACIAL LANDFORMS ON MARION ISLAND

    Microsoft Academic Search

    P. SUMNER; W. NEL; S. HOLNESS; J. BOELHOUWERS

    2002-01-01

    Rock weathering characteristics as relative-age indicators are tested on rock surfaces of generally known chronological sequence on Marion Island in the sub-Antarctic. Relict Late Pleistocene glacial bedrock surfaces and glacial deposit rock surfaces provide both Schmidt hammer rebound values and weathering rind thickness indicative of the longest exposure to weathering. While the weathering characteristics could not establish any chronosequence in

  19. The timing of the Last Glacial Maximum in Australia

    Microsoft Academic Search

    Timothy T Barrows; John O Stone; L. Keith Fifield; Richard G Cresswell

    2002-01-01

    Late Pleistocene glaciation of Australia was restricted to the Snowy Mountains and the Tasmanian highlands. Glaciers were most extensive in Tasmania where ice caps formed on the Central Plateau and West Coast Ranges, and systems of valley and cirque glaciers formed on surrounding mountains. To investigate the timing of maximum glacier advance during the Last Glacial Maximum (LGM), we dated

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

    NASA Astrophysics Data System (ADS)

    Khélifi, N.; Frank, M.

    2013-12-01

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

  1. Pleistocene variability of Antarctic Ice Sheet extent in the Ross Embayment

    NASA Astrophysics Data System (ADS)

    McKay, Robert; Naish, Tim; Powell, Ross; Barrett, Peter; Scherer, Reed; Talarico, Franco; Kyle, Philip; Monien, Donata; Kuhn, Gerhard; Jackolski, Chris; Williams, Trevor

    2012-02-01

    Cores acquired by the ANDRILL McMurdo Ice Shelf Project (AND-1B) provide the basis for a new sedimentation model for glacimarine depositional sequences that reflect cyclic glacial-interglacial fluctuations of a marine-based ice sheet in the western Ross Embayment over the past 2.0 Ma. Notwithstanding periodic erosion during advances of the ice sheet, uncertainties inherent to the sedimentological interpretation, and a limited number of chronological datums, it is clear that subglacial to grounding-zone sedimentation was dominant at the AND-1B site during the Late Pleistocene with interglacials being represented only by thin intervals of ice-shelf sediment. Each sequence is characterised by subglacial, massive diamictite that pass upwards into glacimarine diamictites and mudstones. This provides the first direct evidence that the marine-based Antarctic Ice Sheet has oscillated between a grounded and floating state at least 7 times in the Ross Embayment over the last 780ka, implying a Milankovitch orbital influence. An unconformity in AND-1B, that spans most (˜200 kyr) of the Mid-Pleistocene Transition is inferred to represent widespread expansion of a marine-based ice sheet in the Ross Embayment at 0.8 Ma. Prior to 1.0 Ma, interglacial periods are characterised by open-water conditions at the drill site with high abundances of volcanoclastic deposits and occasional diatomaceous sediments. These may have responded to precession (˜20-kyr) or obliquity (˜40-kyr) orbital control. The occurrence of 6.7 m of phonolitic glass reworked from Mt Erebus in interglacial deposits beneath Last Glacial Maximum till requires open ocean or ice shelf conditions in the western Ross Sea around the drill site within the past 250 ka and implies a Ross Ice Shelf similar to or less extensive than today during Marine Isotope Stage 7 or 5.

  2. Glacial outburst floods and loess sedimentation documented during Oxygen Isotope Stage 4 on the Columbia Plateau, Washington State

    E-print Network

    Glacial outburst floods and loess sedimentation documented during Oxygen Isotope Stage 4 s t r a c t Stratigraphy and age control of late Pleistocene loess, associated glacial outburst flood deposits and flood-cut unconformities in the Channeled Scabland, Washington State, United States, indicate

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

    Microsoft Academic Search

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

    2008-01-01

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

  4. Hybridization among Arctic white-headed gulls (Larus spp.) obscures the genetic legacy of the Pleistocene.

    PubMed

    Sonsthagen, Sarah A; Chesser, R Terry; Bell, Douglas A; Dove, Carla J

    2012-06-01

    We studied the influence of glacial oscillations on the genetic structure of seven species of white-headed gull that breed at high latitudes (Larus argentatus, L. canus, L. glaucescens, L. glaucoides, L. hyperboreus, L. schistisagus, and L. thayeri). We evaluated localities hypothesized as ice-free areas or glacial refugia in other Arctic vertebrates using molecular data from 11 microsatellite loci, mitochondrial DNA (mtDNA) control region, and six nuclear introns for 32 populations across the Holarctic. Moderate levels of genetic structure were observed for microsatellites (F(ST)= 0.129), introns (?(ST)= 0.185), and mtDNA control region (?(ST)= 0.461), with among-group variation maximized when populations were grouped based on subspecific classification. Two haplotype and at least two allele groups were observed across all loci. However, no haplotype/allele group was composed solely of individuals of a single species, a pattern consistent with recent divergence. Furthermore, northernmost populations were not well differentiated and among-group variation was maximized when L. argentatus and L. hyberboreus populations were grouped by locality rather than species, indicating recent hybridization. Four populations are located in putative Pleistocene glacial refugia and had larger ? estimates than the other 28 populations. However, we were unable to substantiate these putative refugia using coalescent theory, as all populations had genetic signatures of stability based on mtDNA. The extent of haplotype and allele sharing among Arctic white-headed gull species is noteworthy. Studies of other Arctic taxa have generally revealed species-specific clusters as well as genetic structure within species, usually correlated with geography. Aspects of white-headed gull behavioral biology, such as colonization ability and propensity to hybridize, as well as their recent evolutionary history, have likely played a large role in the limited genetic structure observed. PMID:22833800

  5. Hybridization among Arctic white-headed gulls (Larus spp.) obscures the genetic legacy of the Pleistocene

    PubMed Central

    Sonsthagen, Sarah A; Chesser, R Terry; Bell, Douglas A; Dove, Carla J

    2012-01-01

    We studied the influence of glacial oscillations on the genetic structure of seven species of white-headed gull that breed at high latitudes (Larus argentatus, L. canus, L. glaucescens, L. glaucoides, L. hyperboreus, L. schistisagus, and L. thayeri). We evaluated localities hypothesized as ice-free areas or glacial refugia in other Arctic vertebrates using molecular data from 11 microsatellite loci, mitochondrial DNA (mtDNA) control region, and six nuclear introns for 32 populations across the Holarctic. Moderate levels of genetic structure were observed for microsatellites (FST= 0.129), introns (?ST= 0.185), and mtDNA control region (?ST= 0.461), with among-group variation maximized when populations were grouped based on subspecific classification. Two haplotype and at least two allele groups were observed across all loci. However, no haplotype/allele group was composed solely of individuals of a single species, a pattern consistent with recent divergence. Furthermore, northernmost populations were not well differentiated and among-group variation was maximized when L. argentatus and L. hyberboreus populations were grouped by locality rather than species, indicating recent hybridization. Four populations are located in putative Pleistocene glacial refugia and had larger ? estimates than the other 28 populations. However, we were unable to substantiate these putative refugia using coalescent theory, as all populations had genetic signatures of stability based on mtDNA. The extent of haplotype and allele sharing among Arctic white-headed gull species is noteworthy. Studies of other Arctic taxa have generally revealed species-specific clusters as well as genetic structure within species, usually correlated with geography. Aspects of white-headed gull behavioral biology, such as colonization ability and propensity to hybridize, as well as their recent evolutionary history, have likely played a large role in the limited genetic structure observed. PMID:22833800

  6. Hybridization among Arctic white-headed gulls (Larus spp.) obscures the genetic legacy of the Pleistocene

    USGS Publications Warehouse

    Sonsthagen, Sarah A.; Chesser, R. Terry; Bell, Douglas A.; Dove, Carla J.

    2012-01-01

    We studied the influence of glacial oscillations on the genetic structure of seven species of white-headed gull that breed at high latitudes (Larus argentatus, L. canus, L. glaucescens, L. glaucoides, L. hyperboreus, L. schistisagus, and L. thayeri). We evaluated localities hypothesized as ice-free areas or glacial refugia in other Arctic vertebrates using molecular data from 11 microsatellite loci, mitochondrial DNA (mtDNA) control region, and six nuclear introns for 32 populations across the Holarctic. Moderate levels of genetic structure were observed for microsatellites (FST= 0.129), introns (?ST= 0.185), and mtDNA control region (?ST= 0.461), with among-group variation maximized when populations were grouped based on subspecific classification. Two haplotype and at least two allele groups were observed across all loci. However, no haplotype/allele group was composed solely of individuals of a single species, a pattern consistent with recent divergence. Furthermore, northernmost populations were not well differentiated and among-group variation was maximized when L. argentatus and L. hyberboreus populations were grouped by locality rather than species, indicating recent hybridization. Four populations are located in putative Pleistocene glacial refugia and had larger t estimates than the other 28 populations. However, we were unable to substantiate these putative refugia using coalescent theory, as all populations had genetic signatures of stability based on mtDNA. The extent of haplotype and allele sharing among Arctic white-headed gull species is noteworthy. Studies of other Arctic taxa have generally revealed species-specific clusters as well as genetic structure within species, usually correlated with geography. Aspects of white-headed gull behavioral biology, such as colonization ability and propensity to hybridize, as well as their recent evolutionary history, have likely played a large role in the limited genetic structure observed.

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

    Microsoft Academic Search

    W. B. Curry; D. W. Oppo

    1997-01-01

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

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

    Microsoft Academic Search

    W. B. Curry; D. W. Oppo

    1997-01-01

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

  9. Pleistocene Niche Stability and Lineage Diversification in the Subtropical Spider Araneus omnicolor (Araneidae)

    PubMed Central

    Peres, Elen A.; Sobral-Souza, Thadeu; Perez, Manolo F.; Bonatelli, Isabel A. S.; Silva, Daniel P.; Silva, Márcio J.; Solferini, Vera N.

    2015-01-01

    The influence of Quaternary climate oscillations on the diversification of the South American fauna is being increasingly explored. However, most of these studies have focused on taxa that are endemic to tropical environments, and relatively few have treated organisms restricted to subtropical biomes. Here we used an integrative phylogeographical framework to investigate the effects of these climate events on the ecological niche and genetic patterns of the subtropical orb-weaver spider Araneus omnicolor (Araneidae). We analyzed the mitochondrial (Cytochrome Oxidase I, COI) and nuclear (Internal Transcribed Subunit II, ITS2) DNA of 130 individuals throughout the species’ range, and generated distribution models in three different climate scenarios [present, Last Glacial Maximum (LGM), and Last Interglacial Maximum (LIG)]. Additionally, we used an Approximate Bayesian Computation (ABC) approach to compare possible demographic scenarios and select the hypothesis that better explains the genetic patterns of A. omnicolor. We obtained high haplotype diversity but low nucleotide variation among sequences. The population structure and demographic analyses showed discrepancies between markers, suggesting male-biased dispersal in the species. The time-calibrated COI phylogenetic inference showed a recent diversification of lineages (Middle/Late Pleistocene), while the paleoclimate modeling indicated niche stability since ~120 Kya. The ABC results agreed with the niche models, supporting a panmictic population as the most likely historical scenario for the species. These results indicate that A. omnicolor experienced no niche or population reductions during the Late Pleistocene, despite the intense landscape modifications that occurred in the subtropical region, and that other factors beside LGM and LIG climate oscillations might have contributed to the demographic history of this species. This pattern may be related to the high dispersal ability and wide environmental tolerance of A. omnicolor, highlighting the need for more phylogeographical studies with invertebrates and other generalist taxa, in order to understand the effects of Quaternary climate changes on Neotropical biodiversity. PMID:25856149

  10. Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

    NASA Astrophysics Data System (ADS)

    Krabbendam, Maarten; Bradwell, Tom

    2014-07-01

    Vast areas previously covered by Pleistocene ice sheets consist of rugged bedrock-dominated terrain of innumerable knolls and lake-filled rock basins - the ‘cnoc-and-lochan' landscape or ‘landscape of areal scour'. These landscapes typically form on gneissose or granitic lithologies and are interpreted (1) either to be the result of strong and widespread glacial erosion over numerous glacial cycles; or (2) formed by stripping of a saprolitic weathering mantle from an older, deeply weathered landscape. We analyse bedrock structure, erosional landforms and weathering remnants and within the ‘cnoc-and-lochan' gneiss terrain of a rough peneplain in NW Scotland and compare this with a geomorphologically similar gneiss terrain in a non-glacial, arid setting (Namaqualand, South Africa). We find that the topography of the gneiss landscapes in NW Scotland and Namaqualand closely follows the old bedrock-saprolite contact (weathering front). The roughness of the weathering front is caused by deep fracture zones providing a highly irregular surface area for weathering to proceed. The weathering front represents a significant change in bedrock physical properties. Glacial erosion (and aeolian erosion in Namaqualand) is an efficient way of stripping saprolite, but is far less effective in eroding hard, unweathered bedrock. Significant glacial erosion of hard gneiss probably only occurs beneath palaeo-ice streams. We conclude that the rough topography of glaciated ‘cnoc-and-lochan' gneiss terrains is formed by a multistage process: 1) Long-term, pre-glacial chemical weathering, forming deep saprolite with an irregular weathering front; 2) Stripping of weak saprolite by glacial erosion during the first glaciation(s), resulting in a rough land surface, broadly conforming to the pre-existing weathering front (‘etch surface'); 3) Further modification of exposed hard bedrock by glacial erosion. In most areas, glacial erosion is limited, but can be significant beneath palaeo-ice stream. The roughness of glaciated gneiss terrains is crucial for modelling of the glacial dynamics of present-day ice sheets. This roughness is shown here to depend on the intensity of pre-glacial weathering as well as glacial erosion during successive glaciations.

  11. The middle Pleistocene transition as a generic bifurcation on a slow manifold

    NASA Astrophysics Data System (ADS)

    Ashwin, Peter; Ditlevsen, Peter

    2015-02-01

    The Quaternary period has been characterised by a cyclical series of glaciations, which are attributed to the change in the insolation (incoming solar radiation) from changes in the Earth's orbit around the Sun. The spectral power in the climate record is very different from that of the orbital forcing: prior to 1000 kyr before present most of the spectral power is in the 41 kyr band while since then the power has been in the 100 kyr band. The change defines the middle Pleistocene transition (MPT). The MPT does not indicate any noticeable difference in the orbital forcing. The climate response to the insolation is thus far from linear, and appears to be structurally different before and after the MPT. This paper presents a low order conceptual model for the oscillatory dynamics of the ice sheets in terms of a relaxation oscillator with multiple levels subject to the Milankovitch forcing. The model exhibits smooth transitions between three different climate states; an interglacial (i), a mild glacial (g) and a deep glacial (G) as proposed by Paillard (Nature 391:378-381, 1998). The model suggests a dynamical explanation in terms of the structure of a slow manifold for the observed allowed and "forbidden" transitions between the three climate states. With the model, the pacing of the climate oscillations by the astronomical forcing is through the mechanism of phase-resetting of relaxation oscillations in which the internal phase of the oscillation is affected by the forcing. In spite of its simplicity as a forced ODE, the model is able to reproduce not only general features but also many of the details of oscillations observed in the climate record. A particular novelty is that it includes a slow drift in the form of the slow manifold that reproduces the observed dynamical change at the MPT. We explain this change in terms of a transcritical bifurcation in the fast dynamics on varying the slow variable; this bifurcation can induce a sudden change in periodicity and amplitude of the cycle and we suggest that this is associated with a branch of "canard oscillations" that appear for a small range of parameters. The model is remarkably robust at simulating the climate record before, during and after the MPT. Even though the conceptual model does not point to specific mechanisms, the physical implication is that the major reorganisation of the climate response to the orbital forcing does not necessarily imply that there was a big change in the environmental conditions.

  12. Millennial-scale climate change and oceanic processes in the late Pliocene and early Pleistocene

    Microsoft Academic Search

    Katherine McIntyre; Margaret L. Delaney; A. Christina Ravelo

    2001-01-01

    We generated 200-500 year resolution records of oceanic processes in the North Atlantic (Ocean Drilling Program Site 983, 60°24'N, 23°38'W, 1983 meters water depth) for intervals in the latest Pliocene (1.86-1.93 Ma) and the earliest Pleistocene (1.75-1.83 Ma) in order to examine the linkages between millennial-scale variations in the ocean and background glacial-interglacial climate change. Within glacial intervals we find

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

    PubMed Central

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

    2011-01-01

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

  14. Pleistocene and Holocene Iberian flora: a complete picture and review

    NASA Astrophysics Data System (ADS)

    González Sampériz, Penélope

    2010-05-01

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

  15. Examining the effects of glacial erosion on the extent of glaciation

    NASA Astrophysics Data System (ADS)

    Pedersen, V. K.; Egholm, D.

    2012-12-01

    Landscapes modified by warm-based glacial activity in alpine settings show a distinct distribution of surface area with elevation (hypsometry), with a maximum in surface area just below the local snowline altitude. The emergence of this distinct hypsometric signature seems to be a consequence of effective glacial and periglacial erosion above the local snowline. Here we examine the response of mountain range glaciations to this distinct topographic distribution, and investigate how its formation influences patterns of glacial extent, and therefore also patterns of glacial erosion, over several glacial cycles. We use numerical modeling experiments, and show first how the hypsometry of characteristic natural landscapes affects glaciations for a simple climate forcing. The results suggest that glacial extent is highly sensitive to the hypsometry of glacially modified landscapes in addition to the climate forcing. Secondly, we show, using a synthetic landscape, how the gradual development of the distinct glacial hypsometric maximum influences the extent of glaciations on a timescale comparable to the Quaternary period. A Quaternary-like climate forcing results in two different phases of glacial erosion, suggesting a first phase of cirque formation followed by a phase of main valley deepening after the mid-Pleistocene transition. The numerical modeling experiments therefore suggest a significant increase in glacial extent and glacial erosion across the mid-Pleistocene transition. The results are obtained using iSOSIA, a higher-order ice sheet model approach, for simulating the flow of ice. Glacial erosion, represented by abrasion and quarrying processes, is approximated as functions of both sliding velocity, the amount of entrained sediment in the ice, and the bed slope in the direction of sliding. Temperature is linked to elevation through a constant lapse rate, ablation is a linear function of positive temperatures, and accumulation is a linear function of negative temperatures up to a maximum value.

  16. History of late Pleistocene glaciations in the central Sayan-Tuva Upland (southern Siberia)

    E-print Network

    and geomorphological analysis as well as 10 Be surface-exposure dating revealed the glacier fluctuations 10 Be data associated to a detailed geomorphologic study have then been used to constrain the chronology of the late Pleistocene glaciations in this region. The analysis of Quaternary glacial deposits

  17. Latest Pleistocene and Holocene river network evolution in the Ethiopian Lakes Region

    Microsoft Academic Search

    Mario Sagri; Carlo Bartolini; Paolo Billi; Giovanni Ferrari; Marco Benvenuti; Stefano Carnicelli; Francesco Barbano

    2008-01-01

    River network, geomorphologic, paleohydrologic, stratigraphic and sedimentologic analyses document a dramatic reorganization of the drainage pattern in the northern part of the Main Ethiopian Rift (MER) during latest Pleistocene and early Holocene. The river network modification was induced by tectonic deformation, volcanic activity, and by the arid conditions connected with the Last Glacial Maximum (LGM). This arid phase triggered the

  18. Demographic Processes Influencing Population Viability of the Iowa Pleistocene snail (Discus macclintocki)

    E-print Network

    Clark, William R.

    influence local dynamics most substantially, long-term threats of habitat loss or climatic change will likely affect survival of adults and persistence of the populations. INTRODUCTION The Iowa Pleistocene to as the ``driftless area,'' escaped the last glacial advances leaving the Paleozoic-age bedrock subject to erosion

  19. Pleistocene Precipitation Balance in the Amazon Basin Recorded in Deep Sea Sediments

    Microsoft Academic Search

    Sara E. Harris; Alan C. Mix

    1999-01-01

    Terrigenous sediments from Ceara Rise in the western tropical Atlantic Ocean record Pleistocene Amazon Basin climate variability. Iron oxides and oxyhydroxides in this region originate mainly from chemically leached Amazon lowland soils. Concentrations of goethite and hematite in the terrigenous fraction consistently peak during transitions from glacial to interglacial periods, suggesting an increased proportion of erosive products derived from the

  20. Glaciers and rivers: Pleistocene uncoupling in a Mediterranean mountain karst

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  1. What caused glacial abrupt climate changes?

    NASA Astrophysics Data System (ADS)

    Banderas Carreño, Rubén; Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2014-05-01

    The last glacial period was punctuated by abrupt climate changes that are widely considered to result from millennial-scale variability of the Atlantic meridional overturning circulation (AMOC). However, the origin of these AMOC reorganizations remains poorly understood. The climatic connection between both hemispheres suggested by proxies indicates that the Southern Ocean (SO) could regulate this variability through changes in winds and atmospheric CO2 concentration. Here, we investigate this hypothesis by using a coupled climate model in an experimental setup inspired by proxy data, in which CO2 and SO wind-stress respond to AMOC variations. The evolution of the simulated climatic patterns matches the amplitude and timing of the largest events that occurred during the last glacial period. Our results indicate that glacial abrupt climate events are part of an internal interhemispheric oscillation and provide an explanation for the pervasive Antarctic-like climate signal found in proxy records worldwide.

  2. Damping of glacial-interglacial cycles from anthropogenic forcing

    NASA Astrophysics Data System (ADS)

    Haqq-Misra, Jacob

    2014-09-01

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

  3. The role of deep ocean circulation in setting glacial climates Jess F. Adkins1

    E-print Network

    The role of deep ocean circulation in setting glacial climates Jess F. Adkins1 Received 2 January cycles of the Pleistocene involve changes in the circulation of the deep ocean in important ways in the Atlantic, expanded southern source water in the abyss and deep ocean, salt (rather than heat

  4. The glacial sequence in part of the Rakaia Valley, Canterbury, New Zealand

    Microsoft Academic Search

    Jane M. Soons

    1963-01-01

    From examination of the glacial deposits and landforms of the Rakaia Valley, four major ice advances have been recognised. In chronological order, these are the Woodlands, Tui Creek, Bayfield, and Acheron Advances. The Bayfield Advance was double, and the Acheron triple. All are regarded as of late Pleistocene age, the Waimaunga Glaciation being represented by the Woodlands Advance, and the

  5. Correlation of Upper Pleistocene sediments in northern West Siberia

    NASA Astrophysics Data System (ADS)

    Astakhov, Valery; Nazarov, Dmitry

    2010-12-01

    A geochronometric database, comprising 121 optically stimulated luminescence and 59 radiocarbon dates plus U/Th date on peat from 24 key sections in northern West Siberia is presented and discussed. These data have been obtained during Russian-Norwegian joint research for the past 15 years and are augmented by reports on radiocarbon dated mammoth carcasses in West Siberia. Together they provide the basis for revising the regional stratigraphic scheme and for correlation to the European Quaternary chronostratigraphy and marine oxygen isotope record. The geochronologic correlation of sedimentary formations across West Siberia involves classical stratotypes of fluvial, shallow limnic and temperate marine sediments of the Karginsky Horizon, ca 130 ka, which was previously attributed to MIS 3. The older Kazantsevo marine formation is thus assigned a Middle Pleistocene age. The uppermost glacial sedimentary complex containing glacial ice was deposited by shelf-based ice sheets between ca 100 and 60 ka BP. The postglacial Pleistocene sediments are mostly ice-bound loess-like deposits and sink-hole silts containing numerous mammoth carcasses that are radiocarbon dated to between ca 42 and 25 ka BP. There are no traces of glacial activity on the Siberian plains during MIS 2, a period for which palaeoclimatic proxies suggest a cold and dry environment. This synthesis indicates that the prior usage of the Siberian correlation horizons of Kazantsevo and Karginsky as equivalents of the Eemian and Middle Pleniglacial is stratigraphically invalid.

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

    PubMed Central

    Spellman, Garth M; Klicka, John

    2006-01-01

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

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

    PubMed

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

    2011-09-01

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

  8. Subsurface warming in the subpolar North Atlantic during rapid climate events in the Early and Mid-Pleistocene

    NASA Astrophysics Data System (ADS)

    Hernández-Almeida, Iván; Sierro, Francisco; Cacho, Isabel; Abel Flores, José

    2014-05-01

    A new high-resolution reconstruction of the temperature and salinity of the subsurface waters using paired Mg/Ca-?18O measurements on the planktonic foraminifera Neogloboquadrina pachyderma sinistrorsa (sin.) was conducted on a deep-sea sediment core in the subpolar North Atlantic (Site U1314). This study aims to reconstruct millennial-scale subsurface hydrography variations during the Early and Mid-Pleistocene (MIS 31-19). These rapid climate events are characterized by abrupt shifts between warm/cold conditions, and ice-sheet oscillations, as evidenced by major ice rafting events recorded in the North Atlantic sediments (Hernández-Almeida et al., 2012), similar to those found during the Last Glacial period (Marcott et al, 2011). The Mg/Ca derived paleotemperature and salinity oscillations prior and during IRD discharges at Site U1314 are related to changes in intermediate circulation. The increases in Mg/Ca paleotemperatures and salinities during the IRD event are preceded by short episodes of cooling and freshening of subsurface waters. The response of the AMOC to this perturbation is an increased of warm and salty water coming from the south, transported to high latitudes in the North Atlantic beneath the thermocline. This process is accompanied by a southward shift in the convection cell from the Nordic Seas to the subpolar North Atlantic and better ventilation of the North Atlantic at mid-depths. Poleward transport of warm and salty subsurface subtropical waters causes intense basal melting and thinning of marine ice-shelves, that culminates in large-scale instability of the ice sheets, retreat of the grounding line and iceberg discharge. The mechanism proposed involves the coupling of the AMOC with ice-sheet dynamics, and would explain the presence of these fluctuations before the establishment of high-amplitude 100-kyr glacial cycles. Hernández-Almeida, I., Sierro, F.J., Cacho, I., Flores, J.A., 2012. Impact of suborbital climate changes in the North Atlantic on ice sheet dynamics at the Mid-Pleistocene Transition. Paleoceanography 27, PA3214. Marcott, S.A., Clark, P.U., Padman, L., Klinkhammer, G.P., Springer, S.R., Liu, Z., Otto-Bliesner, B.L., Carlson, A.E., Ungerer, A., Padman, J., He, F., Cheng, J., Schmittner, A., 2011. Ice-shelf collapse from subsurface warming as a trigger for Heinrich events. Proceedings of the National Academy of Sciences 108, 13415-13419

  9. Pleistocene climatic changes and landscape evolution in the Kashmir Basin, India: Paleopedologic and chronostratigraphic studies

    NASA Astrophysics Data System (ADS)

    Bronger, Arnt; Pant, Rajendra K.; Singhvi, Ashok K.

    1987-03-01

    The Kashmir Basin is filled with Pliocene-Pleistocene fluvio-lacustrine sediments. On the flank of the Pir Panjal these sediments, called "Lower Karewas", are covered with loess deposits up to 25 m thick that contain numerous middle and late Pleistocene paleosols, mostly polygenetic pedocomplexes, which were classified by micromorphological studies. Thermoluminescence dates provide a chronostratigraphy of the late Pleistocene loess-paleosol sequences. On the Himalayan flank, the "Upper Karewas" are covered only with late Pleistocene loess-paleosol sequences. Their base is the last interglacial soil, developed ca. 110,000 ± 10,000 yr B.P. This soil is genetically comparable to the modern soil and, therefore, is thought to have developed under a deciduous forest in a "xeric" soil moisture regime. The loesses of last glacial age on both flanks of the basin contain three humus-rich Ah, mostly Aht, horizons, indicating three warm and mostly humid climatic episodes between ca. 80,000 and 50,000 yr B.P. The middle Pleistocene loesses contain at least four Bwt, or thick Bt, horizons developed during four interglacial periods, having climates similar to the present. Large parts of the Karewa Lake must have lasted until the end of the penultimate glacial age.

  10. The role of deep ocean circulation in setting glacial climates

    NASA Astrophysics Data System (ADS)

    Adkins, Jess F.

    2013-09-01

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

  11. Glacial landscape evolution and sediment export: insights from digital topographic analyses and numerical modelling (Invited)

    NASA Astrophysics Data System (ADS)

    Brocklehurst, S. H.; MacGregor, K. R.

    2013-12-01

    Sediment accumulation rates in the Gulf of Alaska and low-temperature thermochronology from the European Alps, amongst other lines of evidence, indicate accelerated glacial incision and sediment export associated with the Middle Pleistocene Transition (MPT), ~1 Ma. At this time, the change from symmetrical 40-kyr temperature cycles to larger amplitude, asymmetric 100-kyr cycles would have allowed larger, longer lived glaciers to develop, which is inferred as a key contributor to accelerated glacial erosion. Digital topographic analyses comparing glaciated drainage basins of different sizes in the Southern Alps, New Zealand, and Teton Range, western US, amongst others, indicate the importance of scale in glacial landscape development. In smaller drainage basins, or those at the limit of glaciation, landscape modification is primarily restricted to carving characteristic cirques at the heads of valleys. Glaciers may have occasionally spilled from these to carve U-shaped cross-sections downvalley, but without substantial vertical incision. In larger drainage basins with a longer history of glacial occupation, glacial incision has produced shallower downvalley profiles with characteristic glacial steps, presumably accompanied by greater sediment export. A numerical glacial longitudinal profile evolution model, driven by temperature cycles representing either side of the MPT, is used to compare glacial erosion and sediment export from initial Pleistocene glaciations with post-MPT behaviour. The modelled landscape response to the MPT is strongly dependent on the tectonic setting and the behaviour of the fluvial system downstream of the glacier. With no imposed tectonic rock uplift, the major change in the landscape is the carving of cirque forms and glacial longitudinal profiles at the start of the Pleistocene; the MPT would have had little impact on landscape morphology or sediment export. Imposing tectonic as well as isostatic rock uplift, alongside inefficient fluvial transport and erosion downstream of the glacier, the MPT causes more substantial erosion and sediment production than initial glaciation. However, if fluvial processes downstream of the glacier can keep pace with the imposed uplift, the impact of the MPT is dramatically reduced; once again, the major landscape modification is at the onset of glaciation. As such, the history of glacial sediment export during the Pleistocene is a function of drainage basin scale, tectonic setting, and fluvial behaviour downstream of glaciers.

  12. Glacial Lake Hides Bacteria

    NSDL National Science Digital Library

    2010-03-01

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

  13. Glacial lake hides bacteria

    NSDL National Science Digital Library

    Mark Peplow

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

  14. Evidence against a Pleistocene desert refugium in the Lower Colorado River Basin

    USGS Publications Warehouse

    Holmgren, Camille A.; Betancourt, Julio L.; Peñalba, M. Cristina; Delgadillo, José; Zuravnsky, Kristin; Hunter, Kimberly L.; Rylander, Kate A.; Weiss, Jeremy L.

    2014-01-01

    The assemblage of chaparral, woodland and select desert elements refutes the hypothesis that the Lower Colorado River Basin served as a late Pleistocene refugium for Sonoran Desert flora. The rapid arrival of most missing desert species by the early Holocene suggests they did not have far to migrate. They probably survived the last glacial period as smaller, disparate populations in dry microsites within chaparral and pinyon–juniper–oak woodlands. Diploid and tetraploid races of Larrea tridentata were present during the Pleistocene, but hexaploids did not appear until the mid-Holocene. This demonstrates that individualistic responses to climate involved genetic variants, in this case cytotypes, and not just species.

  15. Long-term climate record inferred from early-middle Pleistocene amphibian and squamate reptile assemblages at the Gran Dolina Cave, Atapuerca, Spain.

    PubMed

    Blain, Hugues-Alexandre; Bailon, Salvador; Cuenca-Bescós, Gloria; Arsuaga, Juan Luis; Bermúdez de Castro, José Maria; Carbonell, Eudald

    2009-01-01

    The Gran Dolina cave site is famous for having delivered some of the oldest hominin remains of Western Europe (Homo antecessor, ca. 960 ka). Moreover, the evidence of lithic industries throughout the long vertical section suggests occupation on the part of hominins from the latest early Pleistocene (levels TD3/4, TD5, and TD6) to the late middle Pleistocene (level TD10). The Gran Dolina Sondeo Sur (TDS) has furnished a great number of small-vertebrate remains; among them some 40,000 bones are attributed to amphibians and squamates. Although they do not differ specifically from the extant herpetofauna of the Iberian Peninsula, the overlap of their current distribution areas (= mutual climatic range method) in Spain can provide mean annual temperatures (MAT), the mean temperatures of the coldest (MTC) and warmest (MTW) months, and mean annual precipitation (MAP) estimations for each sub-level, and their change can be studied throughout the sequence. Results from the squamate and amphibian study indicate that during hominin occupation the MAT (10-13 degrees C) was always slightly warmer than at present in the vicinity of the Gran Dolina Cave, and the MAP (800-1000mm) was greater than today in the Burgos area. Climatic differences between "glacial" and "interglacial" phases are poorly marked. Summer temperatures (MTW) show stronger oscillations than winter temperatures (MTC), but seasonality remains almost unchanged throughout the sequence. These results are compared with those for large mammals, small mammals, and pollen analysis, giving a scenario for the palaeoclimatic conditions that occurred during the early to middle Pleistocene in Atapuerca, and hence a scenario for the hominins that once lived in the Sierra de Atapuerca. PMID:18986681

  16. A northern glacial refugium for bank voles (Clethrionomys glareolus)

    PubMed Central

    Kotlík, Petr; Deffontaine, Valérie; Mascheretti, Silvia; Zima, Jan; Michaux, Johan R.; Searle, Jeremy B.

    2006-01-01

    There is controversy and uncertainty on how far north there were glacial refugia for temperate species during the Pleistocene glaciations and in the extent of the contribution of such refugia to present-day populations. We examined these issues using phylogeographic analysis of a European woodland mammal, the bank vole (Clethrionomys glareolus). A Bayesian coalescence analysis indicates that a bank vole population survived the height of the last glaciation (?25,000–10,000 years B.P.) in the vicinity of the Carpathians, a major central European mountain chain well north of the Mediterranean areas typically regarded as glacial refugia for temperate species. Parameter estimates from the fitted isolation with migration model show that the divergence of the Carpathian population started at least 22,000 years ago, and it was likely followed by only negligible immigration from adjacent regions, suggesting the persistence of bank voles in the Carpathians through the height of the last glaciation. On the contrary, there is clear evidence for gene flow out of the Carpathians, demonstrating the contribution of the Carpathian population to the colonization of Europe after the Pleistocene. These findings are consistent with data from animal and plant fossils recovered in the Carpathians and provide the clearest phylogeographic evidence to date of a northern glacial refugium for temperate species in Europe. PMID:17001012

  17. Glacial modification of granite tors in the Cairngorms, Scotland

    USGS Publications Warehouse

    Hall, A.M.; Phillips, W.M.

    2006-01-01

    A range of evidence indicates that many granite tors in the Cairngorms have been modified by the flow of glacier ice during the Pleistocene. Comparisons with SW England and the use of a space-time transformation across 38 tor groups in the Cairngorms allow a model to be developed for progressive glacial modification. Tors with deeply etched surfaces and no, or limited, block removal imply an absence of significant glacial modification. The removal of superstructure and blocks, locally forming boulder trains, and the progressive reduction of tors to stumps and basal slabs represent the more advanced stages of modification. Recognition of some slabs as tor stumps from which glacial erosion has removed all superstructure allows the original distribution of tors to be reconstructed for large areas of the Cairngorms. Unmodified tors require covers of non-erosive, cold-based ice during all of the cold stages of the Middle and Late Pleistocene. Deformation beneath cold-based glacier ice is capable of the removal of blocks but advanced glacial modification requires former wet-based glacier ice. The depth of glacial erosion at former tor sites remains limited largely to the partial or total elimination of the upstanding tor form. Cosmogenic nuclide exposure ages (Phillips et al., 2006) together with data from weathering pit depths (Hall and Phillips, 2006), from the surfaces of tors and large erratic blocks require that the glacial entrainment of blocks from tors occurred in Marine Isotope Stages (MIS) 4-2, 6 and, probably, at least one earlier phase. The occurrence of glacially modified tors on or close to, the main summits of the Cairngorms requires full ice cover over the mountains during these Stages. Evidence from the Cairngorms indicates that tor morphology can be regarded as an important indicator of former ice cover in many formerly glaciated areas, particularly where other evidence of ice cover is sparse. Recognition of the glacial modification of tors is important for debates about the former existence of nunataks and refugia. Copyright ?? 2006 John Wiley & Sons, Ltd.

  18. Vegetation context and climatic limits of the Early Pleistocene hominin dispersal in Europe

    NASA Astrophysics Data System (ADS)

    Leroy, S. A. G.; Arpe, K.; Mikolajewicz, U.

    2011-06-01

    The vegetation and the climatic context in which the first hominins entered and dispersed in Europe during the Early Pleistocene are reconstructed, using literature review and a new climatic simulation. Both in situ fauna and in situ pollen at the twelve early hominin sites under consideration indicate the occurrence of open landscapes: grasslands or forested steppes. The presence of ancient hominins ( Homo of the erectus group) in Europe is only possible at the transition from glacial to interglacial periods, the full glacial being too cold for them and the transition interglacial to glacial too forested. Glacial-interglacial cycles forced by obliquity showed paralleled vegetation successions, which repeated c. 42 times during the course of the Early Pleistocene (2.58-0.78 Ma), providing 42 narrow windows of opportunity for hominins to disperse into Europe. The climatic conditions of this Early Pleistocene vegetation at glacial-interglacial transitions are compared with a climatic simulation for 9 ka ago without ice sheet, as this time period is so far the best analogue available. The climate at the beginning of the present interglacial displayed a stronger seasonality than now. Forest cover would not have been hampered though, clearly indicating that other factors linked to refugial location and soils leave this period relatively free of forests. Similar situations with an offset between climate and vegetation at the beginning of interglacials repeated themselves throughout the Quaternary and benefitted the early hominins when colonising Europe. The duration of this open phase of vegetation at the glacial-interglacial transition was long enough to allow colonisation from the Levant to the Atlantic. The twelve sites fall within rather narrow ranges of summer precipitation and temperature of the coldest month, suggesting the hominins had only a very low tolerance to climate variability.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  20. Hydrological characteristics of an Alpine glacial valley in the North Italian Dolomites

    NASA Astrophysics Data System (ADS)

    Van de Griend, A. A.; Seyhan, E.; Engelen, G. B.; Geirnaert, W.

    1986-11-01

    Hydrogeological characteristics of Alpine regions generally are determined to a large extent by the geomorphological development during the Quaternary period (Pleistocene and Holocene). This development and the hydrogeological characteristics were studied for a glacial trough-valley San Vigilio, developed in a Dolomite limestone complex in the Alps of North Italy. Geo-electrical soundings were successful for detecting the shape of the glacial valley-bottom and to interpret the depth and sediment type distribution of the glacial valley fill, composed of ground moraine, fluvio-glacial deposits, fluvial fans, talus cones and lake deposits. Hydrochemical analyses and environmental isotopes ( 3H and 18O) were used to further interpret the groundwater flow systems.

  1. Cool glacial temperatures and changes in moisture source recorded in oman groundwaters

    PubMed

    Weyhenmeyer; Burns; Waber; Aeschbach-Hertig; Kipfer; Loosli; Matter

    2000-02-01

    Concentrations of atmospheric noble gases (neon, argon, krypton, and xenon) dissolved in groundwaters from northern Oman indicate that the average ground temperature during the Late Pleistocene (15,000 to 24,000 years before present) was 6.5 degrees +/- 0.6 degrees C lower than that of today. Stable oxygen and hydrogen isotopic groundwater data show that the origin of atmospheric water vapor changed from a primarily southern, Indian Ocean source during the Late Pleistocene to a dominantly northern, Mediterranean source today. The reduced northern water vapor source is consistent with a drier Last Glacial Maximum through much of northern Africa and Arabia. PMID:10657295

  2. Glacial cycles drive variations in the production of oceanic crust

    NASA Astrophysics Data System (ADS)

    Crowley, John W.; Katz, Richard F.; Huybers, Peter; Langmuir, Charles H.; Park, Sung-Hyun

    2015-03-01

    Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of Earth’s interior. Using Plio-Pleistocene sea-level variations as a forcing function, theoretical models of mid-ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters. New bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills, one of the most common bathymetric features on Earth, record the magmatic response to changes in sea level. The models and data support a link between glacial cycles at the surface and mantle melting at depth, recorded in the bathymetric fabric of the sea floor.

  3. Glacial cycles drive variations in the production of oceanic crust.

    PubMed

    Crowley, John W; Katz, Richard F; Huybers, Peter; Langmuir, Charles H; Park, Sung-Hyun

    2015-03-13

    Glacial cycles redistribute water between oceans and continents, causing pressure changes in the upper mantle, with consequences for the melting of Earth's interior. Using Plio-Pleistocene sea-level variations as a forcing function, theoretical models of mid-ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters. New bathymetry from the Australian-Antarctic ridge shows statistically significant spectral energy near the Milankovitch periods of 23, 41, and 100 thousand years, which is consistent with model predictions. These results suggest that abyssal hills, one of the most common bathymetric features on Earth, record the magmatic response to changes in sea level. The models and data support a link between glacial cycles at the surface and mantle melting at depth, recorded in the bathymetric fabric of the sea floor. PMID:25766231

  4. 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.

  5. Alaska PaleoGlacier Atlas: A Geospatial Compilation of Pleistocene Glacier Extents

    NSDL National Science Digital Library

    William Manley

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

  6. Kennebunk glacial advance: A reappraisal

    Microsoft Academic Search

    Geoffrey W. Smith

    1981-01-01

    Evidence for the Kennebunk glacial advance (readvance) in southwestern Maine is discussed in light of recent geologic mapping. Orientations of glacially produced lineations record the response of ice to major topographic controls and do not indicate glacial readvance. Minor end moraines and large stratified end moraines associated with deformed marine sediments of the Presumpscot Formation occur throughout the southwestern coastal

  7. The mid-Pleistocene transition in the subtropical southwest Pacific

    NASA Astrophysics Data System (ADS)

    Russon, T.; Elliot, M.; Sadekov, A.; Cabioch, G.; Corrège, T.; De Deckker, P.

    2011-03-01

    Reconstructions of subtropical southwest Pacific climate variability over the Pleistocene were derived from coupled planktic foraminiferal ?18O-Mg/Ca measurements taken from a southern Coral Sea sediment core. A clear shift from ˜40 kyr to ˜100 kyr modes of reconstructed glacial-interglacial sea surface temperature (SST) variability is seen over the mid-Pleistocene transition, and these fluctuations are shown to have remained coherent with the orbital obliquity cycle across the transition. The likely origin of this strong obliquity signal in subtropical southwest Pacific SST is shown to be the southern high latitudes, and comparison with existing SST reconstructions from the equatorial Pacific is consistent with the communication of the signal occurring principally by greenhouse gas forcing. In contrast to the SST reconstruction, regional hydrological cycle variability (based on the calculated local component of ?18Osw change) does not show significant coherence with obliquity after ˜1000 ka. The decoupling of the SST and hydrological cycle responses over the mid-Pleistocene transition allows constraints to be placed on the evolution and extent of orbitally paced fluctuations within the coupled low-latitude ocean-atmosphere system.

  8. Stratigraphy of Late Pleistocene formations of the Mezen river valley

    NASA Astrophysics Data System (ADS)

    Maksimov, Anton; Semenova, Ljudmila

    2014-05-01

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

  9. Giant glacial cirques of non-mountainous terrains

    NASA Astrophysics Data System (ADS)

    Amantov, A.; Amantova, M.

    2012-04-01

    Cirques are usually considered as specific landforms of hill and mountain terrains produced by alpine glaciers, and/or slope failures (landslides). However, glacial cirques seem to be present also in non-mountainous terrains that underwent extensive Pleistocene ice-sheet glaciations and strong glacial and fluvio-glacial erosion. The largest form in the Baltic region is Severoladozhsky (North Lake Ladoga) cirque, probably the world's largest representative, with the length and width close to 100 km. Another example is the deepest Landsort basin of the Baltic Sea. In those cases Meso-Neoproterozoic sediments were subject to selected erosion, with evident overdeepening of the bedrock surface in comparison with surrounding crystalline frame. The bowl headwall shape of the cirque-like landforms was determined by the outline of the margin of exhumed basin. The origin of the major basins of margins of the Baltic and Canadian shields are similar. However, direct analogues of giant cirques are not well developed in this part of North America due to geological deviations and dominant directions of ice movement. Comparable landforms (like the South Chippewa basin of the Lake Michigan) are therefore less mature. We define glacial cirque as an amphitheatre-shape depression with comparable values of length and width, steep headwall with adjacent side slopes and gentle lip with commonly increased glacial accumulation. They are usually located within an ice stream that created typical relief profile with normal horseshoe overdeepening, and in areas predefined by geological and geomorphological peculiarities. This definition likely fits both classic mountain cirques, and giant ones created in favorable conditions in domains that underwent extensive glaciations and relevant selective glacial erosion. Length/width ratio typical for giant cirques group is close to 1:1, being comparable with classical alpine ones. Major differences (like length/height ratio of other order and possible larger internal landscape complications) are related to the extreme size of typical representatives of giant cirques of non-mountainous terrains.

  10. Quaternary glacial landforms and evolution in the Cantabrian Mountains (Northern Spain): a synthesis from current data

    NASA Astrophysics Data System (ADS)

    Serrano, Enrique; José González-Trueba, Juan; Pellitero, Ramón; González-García, María; Gómez-Lende, Manuel

    2014-05-01

    In Northern Iberian Peninsula are located the Cantabrian Mountains, a mountain system of 450 km length, reaching 2648 m in the Picos de Europa. It is an Atlantic mountain in the North slope, with a Atlantic Mediterranean transitional climate in the South slope.More than thirty-five massifs developed glaciers during the Pleistocene. Studies on glacial morphology are known from the XIX century and they have focused mainly on the maximum extent of glaciers. Nowadays there are detailed geomorphological maps, morphostratigraphic surveys and estimation of Equilibrium Line Altitude in different massifs and on different stages. During the last decade studies on glacial evolution and glaciation phases have been made, and the first chronological data have been published. In this work we presents the reconstruction of the glacial evolution in the Cantabrian Mountains during the Pleistocene and Holocene, based on recent chronological data (30 dates made using OSL, AMS and C14) and morphostratigraphic correlations obtained by several research groups. The number of reconstructed glacial stages varies among the different massifs, form one to four different stages. The highest massifs located in the central portion of the Cantabrian Mountains have the most complex glacial features, with at least four different moraine complexes stepped between the 400 m a.s.l in the Northern slope and 800 m a.s.l. in the Southern slope for the lowest moraine complexes, and the highest and youngest, located above 2100 m a.s.l. An ancient glacial phase has been pointed to MIS 12 -more than 400 ka-, disconnected from the present day glacial morphology. During Upper Pleistocene three main stages have been identified. The first one, the local glacial maximum, could be prior to the LGM, as all dates refer to chronologies prior to 28-38 ka. Some authors locate this stage prior to 45 and 65 ka, during the 50-70 ka cold stage. It could be a wet stage, when the main fronts reached the Iberian Peninsula from the SW. The second stage is located to around 30 ka, and point to a dryer stage when glaciers was shorter but thicker. The third stage is located at 20-18 ka, contemporary from the LGM. Glaciers are located inside of glacier-shaped mountain valleys. A few moraine complexes located in the highest massif have been related to Lateglacial, coinciding with cold phases (Dryas) recorded in the Picos de Europa lakes and paleolakes. Finally, during the Holocene only small glaciers developed in the Picos de Europa, which have been assigned to LIA. Nowadays there are still glacial ice remains in four glacial cirques of Picos de Europa, close to the LIA moraines.

  11. Early Pleistocene climate changes in the central Mediterranean region as inferred from integrated pollen and planktonic foraminiferal stable isotope analyses

    NASA Astrophysics Data System (ADS)

    Joannin, Sébastien; Quillévéré, Frédéric; Suc, Jean-Pierre; Lécuyer, Christophe; Martineau, François

    2007-03-01

    Vegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes ( ?18O and ?13C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events. Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. ?18O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova.

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

    PubMed

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

    2014-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  14. Should I stay or should I go: biogeographic and evolutionary history of a polyploid complex (Chrysanthemum indicum complex) in response to Pleistocene climate change in China.

    PubMed

    Li, Jing; Wan, Qian; Guo, Yan-Ping; Abbott, Richard J; Rao, Guang-Yuan

    2014-02-01

    Quaternary climatic oscillations greatly influenced the distribution and pattern of biodiversity in the Northern Hemisphere. Here we examine how such oscillations in South East Asia may have affected the demographic and evolutionary history of a polyploid plant complex associated with semi-dry habitats. We analyzed plastid and nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS) sequence variation within the Chrysanthemum indicum complex (Asteraceae), which comprises diploid and polyploid plants distributed throughout China. In total, 368 individuals from 47 populations across the geographical range of the complex were analyzed. We show that the relatively widespread tetraploid form of C. indicum expanded its range southward in the Pleistocene, possibly during the most recent or previous glacial period when conditions became drier and forests retreated in southern China. In marked contrast, diploid and other polyploid members of the complex failed to expand their ranges at these times or have since undergone range contractions in contrast to tetraploid C. indicum. We conclude that hybridization and gene flow between taxa occurred frequently during the evolutionary history of the complex, causing considerable sharing of chlorotypes and ITS types. Nevertheless, taxa within ploidy levels could be largely distinguished according to chlorotype and/or ITS type. PMID:24400906

  15. Glacial Geology of Wisconsin.

    ERIC Educational Resources Information Center

    Madison Public Schools, WI.

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

  16. Palaeoclimate: A glacial zephyr

    NASA Astrophysics Data System (ADS)

    Putnam, Aaron E.

    2015-03-01

    The hydrology of the North American west looked very different at the Last Glacial Maximum to today. A model-data comparison suggests the observed precipitation patterns are best explained if the storm track was squeezed and steered by high-pressure systems.

  17. Glacial-Interglacial Cycle

    NSDL National Science Digital Library

    This online lab exercise focuses on the causes, characteristics and effects of the glacial-interglacial cycle. The sixth in a 10-part lab series on weather and climate, this lab exercise is designed for first and second year college geoscience students (majors and non-majors) as well as pre-service STEM teachers.

  18. 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

    2014-05-01

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

  19. Large inert carbon pool in the terrestrial biosphere during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Ciais, P.; Tagliabue, A.; Cuntz, M.; Bopp, L.; Scholze, M.; Hoffmann, G.; Lourantou, A.; Harrison, S. P.; Prentice, I. C.; Kelley, D. I.; Koven, C.; Piao, S. L.

    2012-01-01

    During each of the late Pleistocene glacial-interglacial transitions, atmospheric carbon dioxide concentrations rose by almost 100ppm. The sources of this carbon are unclear, and efforts to identify them are hampered by uncertainties in the magnitude of carbon reservoirs and fluxes under glacial conditions. Here we use oxygen isotope measurements from air trapped in ice cores and ocean carbon-cycle modelling to estimate terrestrial and oceanic gross primary productivity during the Last Glacial Maximum. We find that the rate of gross terrestrial primary production during the Last Glacial Maximum was about 40+/-10 Pg C yr-1, half that of the pre-industrial Holocene. Despite the low levels of photosynthesis, we estimate that the late glacial terrestrial biosphere contained only 330 Pg less carbon than pre-industrial levels. We infer that the area covered by carbon-rich but unproductive biomes such as tundra and cold steppes was significantly larger during the Last Glacial Maximum, consistent with palaeoecological data. Our data also indicate the presence of an inert carbon pool of 2,300 Pg C, about 700 Pg larger than the inert carbon locked in permafrost today. We suggest that the disappearance of this carbon pool at the end of the Last Glacial Maximum may have contributed to the deglacial rise in atmospheric carbon dioxide concentrations.

  20. Late Pleistocene carbonate dissolution in the Venezuela Basin, Caribbean Sea

    SciTech Connect

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

    1985-01-01

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

  1. Polar front shift and atmospheric CO2 during the glacial maximum of the Early Paleozoic Icehouse

    PubMed Central

    Vandenbroucke, Thijs R. A.; Armstrong, Howard A.; Williams, Mark; Paris, Florentin; Zalasiewicz, Jan A.; Sabbe, Koen; Nõlvak, Jaak; Challands, Thomas J.; Verniers, Jacques; Servais, Thomas

    2010-01-01

    Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO2 (8 to 22× PAL: preindustrial atmospheric level). The paleobiogeographical distribution of chitinozoan (“mixed layer”) marine zooplankton biotopes for the Hirnantian glacial maximum (440 Ma) are reconstructed and compared to those from the Sandbian (460 Ma): They demonstrate a steeper latitudinal temperature gradient and an equatorwards shift of the Polar Front through time from 55°–70° S to ?40° S. These changes are comparable to those during Pleistocene interglacial-glacial cycles. In comparison with the Pleistocene, we hypothesize a significant decline in mean global temperature from the Sandbian to Hirnantian, proportional with a fall in pCO2 from a modeled Sandbian level of ?8× PAL to ?5× PAL during the Hirnantian. Our data suggest that a compression of midlatitudinal biotopes and ecospace in response to the developing glaciation was a likely cause of the end-Ordovician mass extinction. PMID:20696937

  2. The Last Glacial Maximum

    Microsoft Academic Search

    Peter U. Clark; Arthur S. Dyke; Jeremy D. Shakun; Anders E. Carlson; Jorie Clark; Barbara Wohlfarth; Jerry X. Mitrovica; Steven W. Hostetler; A. Marshall McCabe

    2009-01-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing

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

    PubMed Central

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

    2012-01-01

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

  4. Relative importance of meridional and zonal sea surface temperature gradients for the onset of the ice ages and PliocenePleistocene climate

    E-print Network

    midlatitudes and subpolar regions cooled, establishing a meridional sea surface temperature (SST) gradient of the changes in the meridional and zonal temperature gradients for the onset of glacial cycles and for Pliocene and zonal sea surface temperature gradients for the onset of the ice ages and PliocenePleistocene climate

  5. Pleistocene glaciation history of the Northern North Sea and Norwegian Channel documented by basin-scale 3D seismic analysis

    NASA Astrophysics Data System (ADS)

    Huuse, J.; Huuse, M.

    2012-04-01

    A regionally merged (c. 30,000 km2) 'megasurvey' 3D seismic dataset and an extensive set of 2D lines, tied to the Troll (89-03) core and wireline logs, was used to investigate the glacial and inter-glacial evolution of the northernmost North Sea through the Plio-Pleistocene. An extensive regional unconformity (URU) exists throughout the study area truncating the Naust Formation, a Plio-Pleistocene glacially-influenced progradational delta system, and older strata. This major erosion surface forms the base of the Norwegian Channel, a large (800 km long) cross-shelf trough located along the southern Norwegian coast. The evolution and exact erosion mechanism of this enigmatic feature is still debated. The stratigraphic succession above the URU consists of relatively flat-lying, alternating glacial and glacio-marine units of mid Pleistocene-Holocene age. This study is the first to present fully 3D seismic-constrained maps of the URU, the Naust clinoforms and all major glacial erosion surfaces within the Norwegian Channel infill. Furthermore it documents the geometries and sedimentary facies characteristics of the till and marine units preserved within the Norwegian Channel and the Norwegian sector of the Northern North Sea. Mapped erosional surfaces reveal a diverse assemblage of glacial morpologies interpreted as mega-scale glacial lineations, tunnel valleys, glaciotectonic thrust complexes, terminal moraines and meltwater conduits demarcating the terminus of successive grounded palaeo-ice sheets. Ice berg ploughing was common along the margin between 2.6 and 1.1 Ma with ice streaming commencing prior to 1.1 Ma. Repeated occupation of the NC by fast flowing ice streams, during the Elsterian, Saalian, and Weichselian (MIS 12, 10, 8, 6, 2), led to a progressively westward erosion of the channel margin, migrating approximately 60 km between 1.1 Ma and the LGM. Although well imaged by seismic data, the prolific record of glaciations and interglacials in the Northern North Sea require better age constraints to further fine tune the record of Pleistocene environmental changes. Whilst a large number of wells exist in the North Sea, giving basic lithological information, only very few have sufficiently detailed stratigraphic data in the Pleistocene section. Further research should thus include coring tied to high-resolution seismic data that can be linked to the basin-scale 3D seismic observations presented herein. As this study provides a unique insight into the spatial and temporal dynamics of shelf-edge glaciation in the northern North Sea and its Atlantic margin throughout the late Cenozoic, the plethora of features documented within the Northern North Sea may serve as a template for interpreting other less well imaged glaciated margins.

  6. Abrupt glacial climate shifts controlled by ice sheet changes

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Conor

    2014-08-01

    During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

  7. The Last Interglacial-Glacial cycle (MIS 5-2) re-examined based on long proxy records from central and northern Europe

    NASA Astrophysics Data System (ADS)

    Helmens, Karin F.

    2014-02-01

    Current multi-proxy studies on a long sediment sequence preserved at Sokli (N Finland), i.e. in the central area of Fennoscandian glaciations, are drastically changing classic ideas of glaciations, vegetation and climate in northern Europe during the Late Pleistocene. The sediments in the Sokli basin have escaped major glacial erosion due to non-typical bedrock conditions. In this review, the Sokli record is compared in great detail with other long proxy records from central, temperate and northern, boreal Europe. These comprise the classic records of La Grande Pile (E France) and Oerel (N Germany) and more recently obtained records from Horoszki Du?e (E Poland) and Lake Yamozero (NW Russia). The focus of the review is on pollen, lithology and macrofossil- and insect-based temperature inferences. The long records are further compared with recent proxy data from nearby terrestrial sites as well as with the rapidly accumulating high-resolution proxy data from the ocean realm. The comparison allows a re-examination of the environmental history and climate evolution of the Last Interglacial-Glacial (LI-G) cycle (MIS 5-2). It shows that environmental and climate conditions during MIS 5 (ca 130-70 ka BP) were distinctly different from those during MIS 4-2 (ca 70-15 ka BP). MIS 5 is characterized by three long forested intervals (broadly corresponding to MIS 5e, 5c, 5a), both in temperate and northern boreal Europe. These mild periods were interrupted by two short, relatively cold and dry intervals (MIS 5d and 5b) with mountain-centered glaciation in Fennoscandia. Millennial scale climate events were superimposed upon these longer lasting climate fluctuations. The time interval encompassing MIS 4-2 shows open vegetation. It is characterized by two glacial maxima (MIS 4 and 2) with sub-continental scale glaciation over northern Europe and dry conditions in strongly continental eastern European settings. High amplitude climate oscillations of millennial duration characterized the climate variability of MIS 3. Mild climate conditions in early MIS 3 caused large-scale deglaciation of the Fennoscandian Ice Sheet, and ice-free conditions with Betula-dominated vegetation (including tree birch) persisted over large parts of Fennoscandia, possibly interrupted by glaciation, during major part of MIS 3 till ca 35 ka BP. Overall, MIS 5 was mostly mild with warmest or peak interglacial conditions at the very start during MIS 5e. MIS 4-2 was mostly cold with most extreme or peak glacial conditions in the closing phase during MIS 2. This points to a subdivision of the last climate cycle into an early, overall mild interglacial half and a late, overall cold glacial half, each with duration of ca 50 ka. This review also shows that the climate variability in central and northern Europe during the LI-G cycle was mostly in degrees of continentality with major shifts in winter temperature and precipitation values; summer temperatures, on the other hand, remained largely unchanged. It points to the waxing and waning of sea-ice over the North Atlantic Ocean as a possible characteristic feature of the Late Pleistocene. The present compilation, based on long terrestrial sequences, high-resolution multi-proxy data from the oceans, and quantified paleo-climate data, strongly favors a definition of entire Marine Oxygen Isotope Stage 5 as the Last Interglacial similar as in the original marine stratigraphy and the stratigraphy at La Grande Pile in France. The proxy-based climate data places the start of the Last Glacial at the base of MIS 4 and the northwest European Pleniglacial. It shows that the division between the Eemian (MIS 5e) and the Early Weichselian (MIS 5d-a) is not useful, as not relevant from a climate point of view.

  8. Marine ice sheets of Pleistocene age on the East Siberian Continental Margin (Invited)

    NASA Astrophysics Data System (ADS)

    Niessen, F.; Hong, J.; Hegewald, A.; Matthiessen, J. J.; Stein, R. H.; Kim, H.; Kim, S.; Jensen, L.; Jokat, W.; Nam, S.; Kang, S.

    2013-12-01

    Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present results of the RV "Polarstern' cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA03B (2012), which investigated an area between the Chukchi Borderland and the East Siberian Sea between 165°W and 170°E. At the southern end of the Mendeleev Ridge, close to the Chukchi and East Siberian shelves, evidence is found for the existence of Pleistocene ice sheets/ice shelves, which have grounded several times in up to 1200 m present water depth. We found mega-scale glacial lineations associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, accentuated by a conspicuous truncation of pre-glacial strata typically capped with mostly thin layers of diamicton draped by pelagic sediments. Our tentative age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3. The oldest and deepest event predates MIS 6. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. They were possibly linked to previously suggested ice sheets on the Chukchi Borderland and the New Siberian Islands. We propose that the ice sheets extended northward as thick ice shelves, which grounded on the Mendeleev Ridge to an area up to 78°N within MIS 5 and/or earlier. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for global sea-level variations, albedo, ocean-atmosphere heat exchange, freshwater export from the Arctic Ocean at glacial terminations and the formation of submarine permafrost. The existence of km-thick Pleistocene ice sheets in the western Arctic Ocean during glacial times predating that of the Last Glacial Maximum (LGM) also implies significantly different atmospheric circulation patterns, in particular availability and distribution of moisture during pre-LGM glaciations.

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

    PubMed

    Steele, Craig A; Storfer, Andrew

    2006-08-01

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

  10. Geomorphic controls on Pleistocene knickpoint migration in Alpine valleys

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  11. Live birth among Iguanian lizards predates Pliocene–Pleistocene glaciations

    PubMed Central

    Schulte, James A.; Moreno-Roark, Franck

    2010-01-01

    Among tetrapods, viviparity is estimated to have evolved independently within Squamata (lizards and snakes) more than 100 times, most frequently in species occupying cold climate environments. Because of this relationship with cold climates, it is sometimes assumed that many origins of squamate viviparity occurred over the past 2.5–4 Myr during the Pliocene–Pleistocene glaciations; however, this hypothesis is untested. Divergence-dating analysis on a 733-species tree of Iguanian lizards recovers 20 independent lineages that have evolved viviparity, of which 13 multispecies groups derived live birth prior to glacial advances (8–66 Myr ago). These results place the transitions from egg-laying to live birth among squamates in a well-supported historical context to facilitate examination of the underlying phenotypic and genetic changes associated with this complex shift in reproduction. PMID:19812068

  12. Pleistocene changes in the fauna and flora of South america.

    PubMed

    Vuilleumier, B S

    1971-08-27

    In recent years, the view that Pleistocene climatic events played a major role in the evolution of the biotas of southern, primarily tropical continents has begun to displace the previously held conviction that these areas remained relatively stable during the Quaternary. Studies of speciation patterns of high Andean plant and avian taxa (7-14) have led to the conclusion that Pleistocene climatic events were the factors that ultimately shaped the patterns now observed in the paramo-puna and the related Patagonian flora and fauna. The final uplift of the Andes at the end of the Tertiary automatically limits the age of the high Andean habitats and their biotas to the Quaternary. Within this period, the number of ecological fluctuations caused by the glaciations could easily have provided the mechanism behind the patterns now present in these habitats (Appendix, 1; Figs. 1 and 2; Table 1). In glacial periods, when vegetation belts, were lowered, organisms in the paramo-puna habitat were allowed to expand their ranges. In interglacial periods, these taxa were isolated on disjunct peaks, where differentiation could occur. At times of ice expansion, glacial tongues and lakes provided local barriers to gene exchange, whereas in warm, interglacial times, dry river valleys were a major deterrent to the interbreeding of populations on different mountains (Fig. 2; Table 2). A preliminary analysis of about 10 to 12 percent of the total South American avifauna (14), subsequent to the study of the high Andean biota, suggested that the birds of all the major habitats of the continent possess, with about equal frequency, similar stages of speciation. This correspondence in levels of evolution indicated that the avifauna of vegetation zones which were thought to have been more stable (for example, tropical rainforests) are as actively speciating as are those of the more recent paramo-puna habitats. More intensive work on lowland tropical taxa (16, 19-21) and recent work on montane forest elements (40) now justify the conclusion that the floras and faunas of these areas were also greatly affected by Pleistocene climatic shifts. In the broad region of South America that lies within the tropics, a series of humid-arid cycles (Appendix, 6, 8-10) drastically and repeatedly altered vegetation patterns during the Quaternary. Both montane and lowland rainforests were fragmented during dry periods and were able to reexpand during humid phases. Speciation of forest elements was initiated-and sometimes completed-in isolated patches of the fragmented forest. Secondary contact, with hybridization or reunition of populations that did not become reproductively isolated, occurred in periods of reexpansion. These biological data, combined with supportive geological evidence (Appendix, 1-11), show that climatic events during the last million or so years have affected the biota of South America as much as the Pleistocene glacial changes affected the biotas of Eurasia and North America. Since most of South America lies within tropical latitudes, it is suggested here that part of the diversity of species in the tropical areas of this continent is due to two historical factors: the lack of wholesale elimination of species (compared with northern and high latitudes), and ample opportunity for speciation in successive periods of ecological isolation. The apparent paradox of the wealth of species in the "stable tropics" is partially explained by the fact that the tropics have probably been quite unstable, from the point of view of their biotas, during the Pleistocene and perhaps part of the Tertiary. PMID:17812182

  13. Pliocene-Pleistocene Evolution of Tropical Aridity

    NASA Astrophysics Data System (ADS)

    Demenocal, Peter Bedloe

    1992-09-01

    The goal of this research has been to determine the nature and origin of low-latitude terrestrial climate variability prior to and after the rapid expansion of high -latitude ice sheets near 2.4 Myr to understand the interactions between high- and low-latitude climate systems since the late Pliocene (ca. 3.5 Myr). Records of eolian dust variability were reconstructed from whole-core magnetic susceptibility data at Ocean Drilling Project Site 661 in the eastern equatorial Atlantic and Site 721 on the Owen Ridge in the Arabian Sea. Susceptibility is a rapidly-measured and conservative indicator of terrigenous (eolian) variations at both sites. Susceptibility correlations were used to construct well-dated, composite sequences extending to 3.5 Myr. Evolutive spectral analysis of the two susceptibility records demonstrate that prior to 2.4 Myr both eolian records are dominated by variance at the 23-19 kyr precessional periodicities, whereas after 2.4 Myr the records exhibit strong increases in 41 kyr power. Dominant 23-19 kyr variations at Site 721 extend from 2.4 Myr to at least the late Miocene (ca. 6 Myr). The increase in 41 kyr power after 2.4 Myr and the subsequent increase in 100 kyr power after 0.7 Myr are interpreted to reflect the onset of glacial aridity in African and Arabian dust source areas. We also present a 0.9 Myr record of eolian accumulation from ODP Site 663 in the tropical Atlantic; concentrations of two terrestrial eolian components, opal phytoliths (grass cuticles) and freshwater diatom (Melosira) valves from desiccated lake beds, were also measured. General circulation model (GCM) sensitivity tests were used to examine physical linkages between high and low latitude climate. These results demonstrate that the African and Asian monsoon circulations are very responsive to precessional insolation forcing in the absence of significant ice volume variability. However, full glacial ice cover caused significant precipitation and temperature decreases in monsoon dust source areas in Arabia and northeast Africa. The paleoclimate data and modeling results are combined to develop a generalized model for the Pliocene -Pleistocene evolution of low-latitude terrestrial climate. (Abstract shortened with permission of author.).

  14. Glacial isostasy and plate motion

    Microsoft Academic Search

    Volker Klemann; Zdenek Martinec; Erik R. Ivins

    2008-01-01

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

  15. A Holocene and latest Pleistocene pollen record from Lake Poukawa, Hawke's Bay, New Zealand

    NASA Astrophysics Data System (ADS)

    McGlone, M. S.

    2002-07-01

    Lake Poukawa is a small, shallow lake lying in the middle of extensive peatland in the Poukawa depression, central Hawke's Bay. Holocene peats (10 m at deepest point) overlie more than 200 m of sand, silt, clastic debris and infrequent thin peats and lacustrine sediments deposited during the late Pleistocene. Pollen analyses are presented for: a peat possibly dating to a late stage of the last interglacial or a warm interstadial of the last glacial; cool climate last glacial sediments; and a Holocene peat. The last interglacial or interstadial peat records a cool climate Nothofagus podocarp forest. During the last glacial, sparse shrubland and grassland grew within the depression under much drier and colder conditions than now. There is no pollen record for the Late Glacial and early Holocene period as conditions remained too dry for peat formation. Avian fossils indicate scrub and grassland persisted through until at least 10,600 years BP, and scrub or open forest may have prevailed until c. 6500 years BP. Closed podocarp broadleaved forest ( Prumnopitys taxifolia dominant) occupied the depression from at least 6500 years BP until its destruction by Polynesian settlers after 800 years BP. Water levels rose from 6500 to 4500 years BP, culminating in the establishment of the present fluctuating lake-peatland system. Dry conditions in the Late Glacial and early Holocene may reflect a predominant northwesterly air flow, and a change to more easterly and southerly air flow in the mid- to late Holocene resulted in increased rainfall.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  17. Hominin variability, climatic instability and population demography in Middle Pleistocene Europe

    NASA Astrophysics Data System (ADS)

    Dennell, Robin W.; Martinón-Torres, María; Bermúdez de Castro, José M.

    2011-06-01

    We propose a population model for Middle Pleistocene Europe that is based on demographic "sources" and "sinks". The former were a small number of "core" or populations in glacial refugia in southern Europe from which hominins expanded northwards in interstadial and interglacial periods; occupation outside glacial refugia would have been restricted to warm or temperate periods, and populations at the northern limit of the Middle Pleistocene range would have been "sink" populations in that they depended upon recruitment from source populations further south. Southwest Asia would also have been a likely source of immigrant, source populations. We argue as an alternative to an "ebb and flow" model in which groups retreated to refugia when conditions worsened that local extinction outside refugia would have been frequent. In extreme situations, Europe may have been a population "sink" (i.e. unpopulated) that was replenished from source populations in Southwest Asia. We suggest that this pattern of repeated colonisation and extinction may help explain the morphological variability of European Middle Pleistocene hominins, particularly Homo heidelbergensis and its apparent non-lineal evolution towards Homo neanderthalensis.

  18. Pleistocene pollen stratigraphy from borehole 81/34, devil's hole area, central north sea

    NASA Astrophysics Data System (ADS)

    Ekman, Sten R.

    1998-09-01

    Twelve pollen assemblage zones are identified in a 229 m deep borehole (BH 81/34) from the Devil's Hole area in the central North Sea (British sector). The sediment from this borehole is Early to Late Pleistocene in age and the observation of massulae from Azolla filiculoides in sediment with reversed polarity indicates an age younger than the Olduvai geomagnetic event for the entire sequence. The Early Pleistocene sediments were at least partly deposited in the vicinity of a river outlet and can be correlated either with the Eburonian or the Menapian cold stage and with the Bavel interglacial and the Linge glacial within the Bavelian stage in the Dutch stratigraphy. The Middle Pleistocene sequence contains an interval rich in Abies, Picea and Pinus, probably deposited during the end of either Cromerian Complex interglacial IV (Noordbergum) or possibly the Holsteinian. The uppermost 80 m of the core contains high frequencies of pre-Quaternary and deteriorated palynomorphs indicating extensive glacial or glaciofluvially reworked sediment.

  19. Pleistocene cycles and marine records of West Antarctic Ice Sheet expansion and retreat

    NASA Astrophysics Data System (ADS)

    Scherer, Reed; Konfirst, Matthew; Hillenbrand, Claus-Dieter; Kuhn, Gerhard

    2010-05-01

    The Pleistocene is very poorly represented in Antarctic continental shelf settings. Most piston cores do not penetrate last-glacial age diamictons. Moreover, nearly all sedimentary records have been subjected to the erosional effects of multiple expansions of the WAIS. No existing sediment core recovered from the continental shelf preserves a complete record of the last 1.2 Ma. The ANDRILL-MIS drillcore (AND-1B) from the southwestern Ross Sea may contain the best continental shelf record of the Late Pleistocene, but it is not well dated and probably incomplete. The upper 55 m of AND-1B contains sediments devoid of diatoms, including Pleistocene fragments or robust reworked Tertiary forms, suggestive of strong glacial shearing (Scherer et al., 2004, Geology). It is characterized by thick diamictites with very rare, thin mudstone units. The absence of diatoms, even in the mudstones, may result from (1) continuously expanded mid-Pleistocene ice (grounded or grounding-line proximal), (2) glacial erosion and removal of interglacial diatomaceous sediments, or (3) interglacial non-deposition of diatomaceous sediments, despite episodic open water with marine productivity. The southeastern Ross Sea, which has a non-winnowed relict glacial surface, despite high primary productivity, provides an analog for scenario 3 (Dunbar et al., 1985). McKay et al. (GSA Bull., 2009) interpret this interval as reflecting a nearly continuous Pleistocene record reflecting a predominance of grounded ice throughout much of the late Pleistocene, with the thin mudstones reflecting exclusively sub-ice shelf interglacial deposits. However, there is evidence of warmer than present interglacial conditions in Southern Ocean sediment cores (numerous references), and in East Antarctic ice cores (Sime et al., 2009, Nature). Furthermore, recent modeling of the WAIS suggests late Pleistocene instability, including episodic collapse of the Ross Ice Shelf and interior grounded ice (Pollard & Deconto, 2009, Nature). The enigmatic AND-1B record limits interpretation of Late Pleistocene interglacials and WAIS history in the Ross Sea. Although the Southern Ocean has a rich record of Pleistocene interglacial events, interpretation of WAIS collapse from these records is equivocal, in part due to lower latitude influences and their distance from the WAIS. The best sediment core available to date that is proximal to the WAIS is the Polarstern core PS58/254 from the Amundsen Sea (69°190S, 108°270W, water depth 4014 m), offshore from Pine Island Bay (Hillenbrand et al., 2009, QSR). The core is well-dated and contains a nearly continuous record of the last ca. 1.2 Ma. It's proximity to Pine Island Bay, the "weak underbelly" of the WAIS (Hughes, 1981), suggests that stratigraphic changes recognized in the core will have been strongly influenced by past WAIS collapse. We will present new diatom results from this core that bear on past WAIS fluctuations via the Pine Island Bay corridor.

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

    USGS Publications Warehouse

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

    2008-01-01

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

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

    PubMed

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

    2009-03-01

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

  2. DECIPHERING NORTH AMERICAN PLEISTOCENE EXTINCTIONS

    Microsoft Academic Search

    Donald K. Grayson

    2007-01-01

    The debate over the cause of North American Pleistocene extinctions may be further from resolution than it has ever been in its 200-year history and is certainly more heated than it has ever been before. Here, I suggest that the reason for this may lie in the fact that paleontologists have not heeded one of the key biogeographic concepts that

  3. Coupled Warming and Drought in the American Southwest During Long mid-Pleistocene Interglacials (MIS 11 and 13)

    Microsoft Academic Search

    P. J. Fawcett; J. Werne; R. Anderson; J. Heikoop; E. Brown; L. Hurley; S. Smith; M. Berke; H. Soltow; F. Goff; J. Geissman; G. Woldegabriel; J. Fessenden; M. Cisneros-Dozal; C. D. Allen

    2008-01-01

    An 82-m deep lacustrine sediment core from the Valles Caldera, northern New Mexico reveals details of climate change over two glacial cycles in the middle Pleistocene. Core VC-3, taken from the Valle Grande, has a basal 40Ar\\/39Ar date of 552 kyr from a tephra associated with the eruption of the South Mountain rhyolite which formed the lake. A variety of

  4. An introduction to the Middle and Upper Pleistocene loess–paleosol sequence at Ruma brickyard, Vojvodina, Serbia

    Microsoft Academic Search

    S. B. Markovi?; E. Oches; P. Sumegi; M. Jovanovic; T. Gaudenyi

    2006-01-01

    Six Loess units and five paleosols are preserved in the 20m thick exposure of Middle and Late Pleistocene sediments at Ruma brickyard, Vojvodina, Serbia. Amino acid geochronology provides stratigraphic correlations between Loess–Paleosol units SL L1-S1, SL L2-S2, SL L3-S3 and SL L4 at Ruma with loess of Glacial cycles B, C and D, and E, respectively, at other central and

  5. Hydrographic variations in deep ocean temperature over the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Bates, Stephanie L.; Siddall, Mark; Waelbroeck, Claire

    2014-03-01

    During the mid-Pleistocene transition the dominant 41 ka periodicity of glacial cycles transitioned to a quasi-100 ka periodicity for reasons not yet known. This study investigates the potential role of deep ocean hydrography by examining oxygen isotope ratios in benthic foraminifera. Oxygen isotope records from the Atlantic, Pacific and Indian Ocean basins are separated into their ice volume and local temperature/hydrography components using a piece-wise linear transfer function and a temperature calibration. Although our method has certain limitations, the deep ocean hydrography reconstructions show that glacial deep ocean temperatures approached freezing point as the mid-Pleistocene transition progressed. Further analysis suggests that water mass reorganisation could have been responsible for these temperature changes, leading to such stable conditions in the deep ocean that some obliquity cycles were skipped until precessional forcing triggered deglaciation, creating the apparent quasi-100 ka pattern. This study supports previous work that suggests multiples of obliquity cycles dominate the quasi-100 ka glacial cycles with precession components driving deglaciations.

  6. Pleistocene sea-level fluctuations and human evolution on the southern coastal plain of South Africa

    NASA Astrophysics Data System (ADS)

    Compton, John S.

    2011-03-01

    Humans evolved in Africa, but where and how remain unclear. Here it is proposed that the southern coastal plain (SCP) of South Africa may have served as a geographical point of origin through periodic expansion and contraction (isolation) in response to glacial/interglacial changes in sea level and climate. During Pleistocene interglacial highstands when sea level was above -75 m human populations were isolated for periods of 360-3400 25-yr generations on the SCP by the rugged mountains of the Cape Fold Belt, climate and vegetation barriers. The SCP expands five-fold as sea level falls from -75 to -120 m during glacial maxima to form a continuous, unobstructed coastal plain accessible to the interior. An expanded and wet glacial SCP may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups. 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 select for humans who expanded their diet to include marine resources or hunted large animals. Successful adaptations developed on an isolated SCP are predicted to widely disperse during glacial terminations when the SCP rapidly contracts or during the initial opening of the SCP in the transition to glacial maxima. The hypothesis that periodic expansion and contraction of the SCP, as well as the coastal plain of North Africa, contributed to the stepwise origin of our species over the last 800 thousand years (kyr) is evaluated by comparing the archeological, DNA and sea-level records. These records generally support the hypothesis, but more complete and well dated records are required to resolve the extent to which sea-level fluctuations influenced the complex history of human evolution.

  7. Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps)

    NASA Astrophysics Data System (ADS)

    Monegato, Giovanni; Ravazzi, Cesare; Donegana, Marta; Pini, Roberta; Calderoni, Gilberto; Wick, Lucia

    2007-09-01

    The glacial history of the Tagliamento morainic amphitheater (southeastern Alpine foreland, Italy) during the last glacial maximum (LGM) has been reconstructed by means of a geological survey and drillings, radiocarbon dating and pollen analysis in the amphitheater and in the sandur. Two phases of glacial culmination, separated by a distinct recession, are responsible for glacial landforms and related sediments in the outer part of the amphitheater. The age of the younger advance fits the chronology of the culmination of the last glaciation in the Alps, well established between 24 and 21 cal ka BP (20 to 17.5 14C ka BP), whereas the first pulse between 26.5 and 23 cal ka BP (22 to 21 14C ka BP), previously undated, was usually related to older (pre-LGM) glaciations by previous authors. Here, the first pulse is the most extensive LGM culmination, but is often buried by the subsequent pulse. The onset and final recession of the late Würm Alpine glaciation in the Tagliamento amphitheater are synchronous with the established global glacial maximum between 30 and 19 cal ka BP. The two-fold LGM glacial oscillation is interpreted as a millennial-scale modulation within the late Würm glaciation, caused by oscillations in inputs of southerly atmospheric airflows related to Dansgaard-Oeschger cycles. Phases of enhanced southerly circulation promoted increased rainfall and ice accumulation in the southern Alps.

  8. Quaternary glacial, lacustrine, and fluvial interactions in the western Noatak basin, Northwest Alaska

    NASA Astrophysics Data System (ADS)

    Hamilton, Thomas D.

    2001-01-01

    The 130 km long Noatak basin is surrounded by mountains of the western Brooks Range. Middle and late Pleistocene glaciers flowing southeast into the basin dammed a succession of proglacial lakes defined by shorelines, outlet channels, and upper limits of wave erosion. More than 60 bluffs along the Noatak River and its principal tributaries expose glacial and glaciolacustrine sediments that exhibit cut-and-fill relationships with interglacial and interstadial river-channel and floodplain deposits. This report focuses on the western Noatak basin, where high bluffs created by deep postglacial erosion record four major glacial advances. During the Cutler advance, a floating ice tongue terminated in a large proglacial lake that filled the Noatak basin. The retreating glacier abandoned a trough along the valley center that subsequently filled with about 40 m of sediment during several younger glaciations and probably two major interglacial episodes. Alluvium that formed near the beginning of the younger interglaciation contains the 140,000 yr old Old Crow tephra. The subsequent closely spaced Okak and Makpik advances are clearly younger than the maximum of the last interglaciation, but they preceded a middle Wisconsin (36-30 ka) nonglacial interval in the Noatak basin. The Okak advance terminated in an extensive lake, whereas glaciers of the Makpik and the subsequent Anisak advances flowed into much narrower lakes that filled only the basin center. The Anisak advance, bracketed by radiocarbon ages of about 35 and 13.6 ka, represents the Last Glacial Maximum (LGM) in the western Noatak basin. Correlations with the oldest and youngest glacial deposits of the central Brooks Range are clear, but relationships to events of intermediate age are more tenuous. Early Pleistocene and older glacial advances from the central Brooks Range must have filled the Noatak basin and overflowed northward through Howard Pass. A younger glacial advance, of inferred middle Pleistocene (Sagavanirktok River) age, extended down the Noatak valley into the basin center, but its deposits are deeply buried beneath the basin floor and must be older than the Cutler moraine. The Cutler advance may have been synchronous with the older of two advances of Itkillik I age in the Atongarak Creek area, but other evidence indicates that the Okak-Makpik moraine succession more likely was synchronous with the two Atongarak Creek moraines. Radiocarbon ages, surface morphology, soil and weathering profiles, and lake-level history all support correlation of the last (Anisak) major glacial advance in the western basin with the Douglas Creek moraine farther east and with Itkillik II (late Wisconsin) glaciation of the central Brooks Range.

  9. What drives glacial cycles

    SciTech Connect

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

    1990-01-01

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

  10. Millennial-scale varnish microlamination dating of late Pleistocene geomorphic features in the drylands of western USA

    NASA Astrophysics Data System (ADS)

    Liu, Tanzhuo; Broecker, Wallace S.

    2013-04-01

    Varnish microlamination (VML) dating is a climate-based correlative age determination technique used to correlate and date various geomorphic features in deserts. In this study, we establish a generalized late Pleistocene (18-74 ka) millennial-scale microlamination sequence in fine-grained, fast-accumulating rock varnish for the drylands of western USA, radiometrically calibrate the sequence and correlate it with the ?18O record in the GISP2 Greenland ice core. We then use this climate-correlated varnish microstratigraphy to estimate surface exposure ages for radiometrically dated late Pleistocene geomorphic features in the study region. The VML dating of debris flow deposits on the Sehoo recessional shorelines of Lake Lahontan at the Jessup embayment of central Nevada yields a minimum-limiting age of 14.95-15.95 ka, in good agreement with a calibrated 14C age of 15.22 ± 0.12 ka for the timing of the lake recession. The VML dating of a giant ejecta block on the rim of Meteor Crater in northern Arizona yields a minimum-limiting age of 49.15 ka, closely matching a thermoluminescence (TL) age of 49 ± 3 ka and slightly younger than a recently updated cosmogenic 36Cl age of 56.0 ± 2.4 ka for the meteor impact event. The VML dating of distal Q2c fan surfaces on Hanaupah Canyon alluvial fan in Death Valley, California, yields a minimum-limiting age of 73.55 ka, in accord with cosmogenic 36Cl depth-profile ages of 66 + 22/-14 ka and 72 + 24/- 20 ka for the same fan deposits. The close agreement between the VML age estimates and the independently derived radiometric ages for these geomorphic features attests to the validity and reliability of millennial-scale VML dating. To further assess its potential in desert geomorphological research, we use the VML method to study alluvial-fan responses to millennial-scale climatic changes. The VML dating of a small tributary fan in Death Valley reveals two episodes of fan aggradation, one ceasing at 73.55-86.75 ka during the dry period of the last interglacial (MIS 5a) and the other finishing at 66.15 ka during the wet period of the last glacial (MIS 4). The VML and 36Cl dating of the distal Q2c fan surfaces on Hanaupah Canyon fan reveal two episodes of large-scale fan aggradation ended at 72 + 24/- 20 ka and 73.55 ka during the wet period of MIS 4. Fanhead incision and associated within-channel or fantoe aggradation are found to take place during the relatively dry period of the glacial-to-interglacial climatic transition (12-24 ka) and the Holocene interglacial dry period (0-12 ka). These data indicate that, on the millennial to sub-Milankovitch timescale (~ 103-104 years), fan aggradation is a discrete sedimentational process under various climatic conditions. Because fan aggradation is ultimately controlled by the intensity and frequency of precipitation events - which in turn are modulated by major climatic oscillations such as Heinrich events, Dansgaard/Oeschger (DO) events, and glacial/interglacial shifts - these major climatic changes could be the pacemaker of regionally contemporaneous large-area fan segmentation.

  11. A 500 kyr record of global sea level oscillations in the Gulf of Lion, Mediterranean Sea: new insights into MIS 3 sea level variability

    NASA Astrophysics Data System (ADS)

    Frigola, J.; Canals, M.; Cacho, I.; Moreno, A.; Sierro, F. J.; Flores, J. A.; Berné, S.; Jouet, G.; Dennielou, B.; Herrera, G.; Pasqual, C.; Grimalt, J. O.; Galavazi, M.; Schneider, R.

    2011-12-01

    Borehole PRGL1-4 drilled in the upper slope of the Gulf of Lion provides an exceptional record to investigate the impact of Late Pleistocene orbitally-driven glacio-eustatic sea level oscillations on the sedimentary outbuilding of a river fed continental margin. High-resolution grain-size and geochemical records supported by oxygen isotope chronostratigraphy allow reinterpreting the last 500 ka upper slope seismostratigraphy of the Gulf of Lion which consists of five main sequences stacked during the sea level lowering phases of the last five glacial-interglacial 100-kyr cycles. The high sensitivity to sea level oscillations of the grain-size record along the borehole, favoured by the large width of the Gulf of Lion continental shelf, demonstrates that sea level driven changes in accommodation space over the shelf are able to cyclically modify the depositional mode of the entire margin. PRGL1-4 data also illustrate the imprint of sea level oscillations at millennial scale, as shown for Marine Isotopic Stage 3, and provide unambiguous evidence of relative high sea levels at the onset of each Dansgaard-Oeschger Greenland warm interstadial. The PRGL1-4 grain-size record represents the first evidence ever for a one-to-one coupling of millennial-scale sea level oscillations associated with each Dansgaard-Oeschger cycle.

  12. A 500 kyr record of global sea-level oscillations in the Gulf of Lion, Mediterranean Sea: new insights into MIS 3 sea-level variability

    NASA Astrophysics Data System (ADS)

    Frigola, J.; Canals, M.; Cacho, I.; Moreno, A.; Sierro, F. J.; Flores, J. A.; Berné, S.; Jouet, G.; Dennielou, B.; Herrera, G.; Pasqual, C.; Grimalt, J. O.; Galavazi, M.; Schneider, R.

    2012-06-01

    Borehole PRGL1-4 drilled in the upper slope of the Gulf of Lion provides an exceptional record to investigate the impact of late Pleistocene orbitally-driven glacio-eustatic sea-level oscillations on the sedimentary outbuilding of a river fed continental margin. High-resolution grain-size and geochemical records supported by oxygen isotope chronostratigraphy allow reinterpreting the last 500 ka upper slope seismostratigraphy of the Gulf of Lion. Five main sequences, stacked during the sea-level lowering phases of the last five glacial-interglacial 100-kyr cycles, form the upper stratigraphic outbuilding of the continental margin. The high sensitivity of the grain-size record down the borehole to sea-level oscillations can be explained by the great width of the Gulf of Lion continental shelf. Sea level driven changes in accommodation space over the shelf cyclically modified the depositional mode of the entire margin. PRGL1-4 data also illustrate the imprint of sea-level oscillations at millennial time-scale, as shown for Marine Isotopic Stage 3, and provide unambiguous evidence of relative high sea-levels at the onset of each Dansgaard-Oeschger Greenland warm interstadial. The PRGL1-4 grain-size record represents the first evidence for a one-to-one coupling of millennial time-scale sea-level oscillations associated with each Dansgaard-Oeschger cycle.

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

    PubMed

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

    2012-01-01

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

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

    PubMed Central

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

    2004-01-01

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

  15. Ancient DNA reveals that bowhead whale lineages survived Late Pleistocene climate change and habitat shifts.

    PubMed

    Foote, Andrew D; Kaschner, Kristin; Schultze, Sebastian E; Garilao, Cristina; Ho, Simon Y W; Post, Klaas; Higham, Thomas F G; Stokowska, Catherine; van der Es, Henry; Embling, Clare B; Gregersen, Kristian; Johansson, Friederike; Willerslev, Eske; Gilbert, M Thomas P

    2013-01-01

    The climatic changes of the glacial cycles are thought to have been a major driver of population declines and species extinctions. However, studies to date have focused on terrestrial fauna and there is little understanding of how marine species responded to past climate change. Here we show that a true Arctic species, the bowhead whale (Balaena mysticetus), shifted its range and tracked its core suitable habitat northwards during the rapid climate change of the Pleistocene-Holocene transition. Late Pleistocene lineages survived into the Holocene and effective female population size increased rapidly, concurrent with a threefold increase in core suitable habitat. This study highlights that responses to climate change are likely to be species specific and difficult to predict. We estimate that the core suitable habitat of bowhead whales will be almost halved by the end of this century, potentially influencing future population dynamics. PMID:23575681

  16. Glacial terminations and the global water budget

    SciTech Connect

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

    1992-01-01

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

  17. Kennebunk glacial advance: A reappraisal

    NASA Astrophysics Data System (ADS)

    Smith, Geoffrey W.

    1981-06-01

    Evidence for the Kennebunk glacial advance (readvance) in southwestern Maine is discussed in light of recent geologic mapping. Orientations of glacially produced lineations record the response of ice to major topographic controls and do not indicate glacial readvance. Minor end moraines and large stratified end moraines associated with deformed marine sediments of the Presumpscot Formation occur throughout the southwestern coastal zone. These features outline the general pattern of ice retreat from this part of the coastal zone and suggest that withdrawal of the last ice from southwestern Maine occurred with minor stillstands and local frontal fluctuations but without significant readvance. The Kennebunk glacial advance (readvance) appears to have been one of many local fluctuations of the ice front during general recession, occurring at about 13,200 yr B.P.

  18. Matuyama–Brunhes boundary in key sections of the loess–paleosol–glacial formations on the East European Plain

    Microsoft Academic Search

    A. A. Velichko; V. V. Semenov; G. A. Pospelova; T. D. Morozova; V. P. Nechaev; Yu. N. Gribchenko; K. G. Dlusskii; N. Rutter; N. Catto; E. Little

    2006-01-01

    Multidisciplinary studies of two key sections (parastratotypes) of the loess–soil–glacial formation (Strelitsa and Sebryakovo-Mikhailovka sections) located in the central part of the East European Plain placed the Matuyama–Brunhes reversal well below the Lower Pleistocene till. The till attributed to the Don glaciation (maximum glaciation on the East European Plain) is separated from the M\\/B reversal by several units, as follows:

  19. Origin and age of phosphorite from the Last Glacial Maximum to Holocene transgressive succession off the Orange River, South Africa

    Microsoft Academic Search

    John S Compton; Jeffrey Mulabisana; I. K McMillan

    2002-01-01

    A major erosional unconformity between upper Cretaceous sediments and the Last Glacial Maximum (LGM) transgressive succession occurs on the inner continental shelf off the Orange River. Vibracores from 122 m water-depth consist of upper Pleistocene shelly, phosphatic sands deposited in a high-energy shoreface environment during the LGM lowstand between 22 and 19 ka. The gravel-rich shoreface sand grades into condensed

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

    PubMed

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

    2013-08-23

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

  1. Science Sampler: Glacial ice action

    NSDL National Science Digital Library

    Virginia Bourdeau

    2008-10-01

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

  2. Glacial Features of North Dakota

    NSDL National Science Digital Library

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  4. Glacially Generated Overpressure Offshore Massachusetts, USA: Integration of Full Seismic Waveform Inversion and Overpressure Modeling

    NASA Astrophysics Data System (ADS)

    Siegel, J. E.; Lizarralde, D.; Dugan, B.; Person, M. A.

    2012-12-01

    Localized, high-amplitude reflections, overlying a late Pleistocene glacial erosion surface 100 km offshore Massachusetts, USA, have lower compressional wave velocities of up to 200 m/s compared to adjacent sediments of equal depth. This may be the result of lower effective stress from overpressures as high as 1 MPa. To investigate the origin of these low velocity zones, we compare the detailed velocity structure across the high-amplitude regions to adjacent, undisturbed regions through a full waveform inversion, and we forward model the effective stress and overpressure. We relate the full waveform inversion velocities to effective stress with a power-law model. This model predicts effective stresses are 0.6 MPa at 250 m below the sea floor, which equates to an overpressure of 1.0 MPa. To help understand the overpressure source, we model the pressure response to erosion, glacial loading, and sedimentation in 1D. Preliminary models show that late Pleistocene glaciations, including the Last Glacial Maximum (LGM), and rapid sedimentation from glacial lake drainage may be important mechanisms for the generation of the localized regions of high overpressure. Our geophysical observations and interpretations suggest overpressure exists offshore today. Our forward models predict that this overpressure originated during the LGM due to pore pressure generation from rapid loading by glacial ice, however these overpressures are dissipating in the modern, low sedimentation rate environment. These shallow overpressures provide a mechanism to explain the SGD inferred along the Northern Atlantic continental shelf. Our results also provide physical-property observables, specific to location, that can constrain ongoing 3D numerical modeling efforts to deterministically predict the hydrologic history of the continental shelf sediments based on detailed stratigraphic and ice-sheet evolution.

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

    PubMed

    Berkland, J O; Raymond, L A

    1973-08-17

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

  6. Pleistocene-Holocene transition in the central Mississippi River valley

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  8. Chronology for Fluctuations in Late Pleistocene Sierra Nevada Glaciers and Lakes

    Microsoft Academic Search

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

    1996-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

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

  11. 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 tributaries. In contrast, the area west of the George River valley shows very few shorelines, implying that Lake Naskaupi was mostly in contact with the decaying ice margin. The abundance ice-marginal meltwater channels allowed the reconstruction of the general ice retreat pattern. The area is also characterized by abundant WNW-trending drumlins and crag-and-tails indicating an important ice flow towards Ungava Bay. These glacial lineations may be linked with eskers further to west that terminated into the postglacial Iberville Sea, forming large ice-contact deltas. This setting suggests that this landform assemblage likely developed during the deglaciation. Our results thus underlie important differences in the subglacial regime across the ice divide of the Labrador sector during the late-glacial and early deglacial interval. The so-called horseshoe unconformity appear to delineate an inner area characterized by warm-based conditions that allowed a massive deglacial ice flow to developed in Ungava Bay, while the area under and proximal to the divide in the east appears to have evolved towards cold-based ice conditions, resulting with a stagnant ice mass that dammed the major proglacial lakes.

  12. The last glacial maximum

    USGS Publications Warehouse

    Clark, P.U.; Dyke, A.S.; Shakun, J.D.; Carlson, A.E.; Clark, J.; Wohlfarth, B.; Mitrovica, J.X.; Hostetler, S.W.; McCabe, A.M.

    2009-01-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level ???14.5 ka.

  13. The Last Glacial Maximum.

    PubMed

    Clark, Peter U; Dyke, Arthur S; Shakun, Jeremy D; Carlson, Anders E; Clark, Jorie; Wohlfarth, Barbara; Mitrovica, Jerry X; Hostetler, Steven W; McCabe, A Marshall

    2009-08-01

    We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level approximately 14.5 ka. PMID:19661421

  14. Glacial History of a Modern Invader: Phylogeography and Species Distribution Modelling of the Asian Tiger Mosquito Aedes albopictus

    PubMed Central

    Porretta, Daniele; Mastrantonio, Valentina; Bellini, Romeo; Somboon, Pradya; Urbanelli, Sandra

    2012-01-01

    Background The tiger mosquito, Aedes albopictus, is one of the 100 most invasive species in the world and a vector of human diseases. In the last 30 years, it has spread from its native range in East Asia to Africa, Europe, and the Americas. Although this modern invasion has been the focus of many studies, the history of the species’ native populations remains poorly understood. Here, we aimed to assess the role of Pleistocene climatic changes in shaping the current distribution of the species in its native range. Methodology/Principal Findings We investigated the phylogeography, historical demography, and species distribution of Ae. albopictus native populations at the Last Glacial Maximum (LGM). Individuals from 16 localities from East Asia were analyzed for sequence variation at two mitochondrial genes. No phylogeographic structure was observed across the study area. Demographic analyses showed a signature of population expansion that started roughly 70,000 years BP. The occurrence of a continuous and climatically suitable area comprising Southeast China, Indochinese Peninsula, and Sundaland during LGM was indicated by species distribution modelling. Conclusions/Significance Our results suggest an evolutionary scenario in which, during the last glacial phase, Ae. albopictus did not experience a fragmentation phase but rather persisted in interconnected populations and experienced demographic growth. The wide ecological flexibility of the species probably played a crucial role in its response to glacial-induced environmental changes. Currently, there is little information on the impact of Pleistocene climatic changes on animal species in East Asia. Most of the studies focused on forest-associated species and suggested cycles of glacial fragmentation and post-glacial expansion. The case of Ae. albopictus, which exhibits a pattern not previously observed in the study area, adds an important piece to our understanding of the Pleistocene history of East Asian biota. PMID:22970238

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

    SciTech Connect

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

    1990-02-20

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

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

    PubMed

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

    2002-08-01

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

  17. Glacial chronologies and past climate change in the tropical-subtropical Central Andes during the last glacial and deglacial periods

    NASA Astrophysics Data System (ADS)

    Clarke, B. A.; Strecker, M. R.

    2012-12-01

    Because glaciers advance or retreat in response to changes in temperature and precipitation, glacial chronologies derived from well-dated sequences of inset moraines provide insight into the timing and magnitude of past climate change within the terrestrial realm. During the last glacial and deglacial periods, glaciers at high northern latitudes waxed and waned in phase with orbital- and millennial-scale temperature oscillations. Although paleoclimate records suggest strong correlations between high-latitude temperature variability and low-latitude climate change, the timing and cause of glacial fluctuations at low, southern-latitudes remains unclear - limiting our understanding about the global synchronicity of past glaciations, the causes of abrupt climate change, and the relative importance of high- versus low-latitude forcing for developing and transmitting climate signals around the globe.. Here we present a compilation of cosmogenically dated glacial chronologies from the tropical-subtropical Central Andes (~9-24 °S). We demonstrate that episodes of glacial advance in the Central Andes coincide with Northern Hemisphere cold events, increased pole-to-equator sea-surface temperature gradients, and southward displacements of the Intertropical Convergence Zone. Although glacial fluctuations in the Central Andes were synchronous with Northern Hemisphere records, our data suggest strong contrasts in the cause of ice advance between the last glacial and deglacial periods. During the last glacial period, glaciers were at their greatest extent in the humid Northern Central Andes from ~35-19 ka, coeval with insolation-driven reductions in global temperatures and moderately increased southern summer monsoon intensity. Conversely, in the arid Southern Central Andes, there is no record of moraines deposited during the last glacial period, suggesting that, despite the cold temperatures, limited moisture availability in this region inhibited the growth of glaciers, such that the last glacial moraines were subsequently overridden by more extensive stages of deglacial advance. During deglaciation, all records from the Central Andes reveal that ice advance (or re-advance) was coincident with pronounced increases in precipitation and low-latitude warming during Heinrich Stadial 1 (~15-17 ka) and the Younger Drays (~11-14 ka). However, in the Northern Central Andes these deglacial episodes constitute only minor re-advances or standstills, whereas in the Southern Central Andes they represent the most extensive stages of glacial advance. The apparent contrast in the magnitude of ice advance in the Central Andes during the last glacial and deglacial periods supports the contention that glaciers in the humid Northern Central Andes predominantly respond to changes in temperature, whereas in the arid Southern Central Andes glaciers are most sensitive to changes in precipitation. Overall, the data suggest a distinct transition between temperature-driven ice advance during the last glacial period due to orbital-scale forcing, which favors extensive advance in the humid Northern Central Andes, and precipitation-driven stages of re-advance during deglaciation in response to large millennial-scale shifts in the Intertropical Convergence Zone, which favor more pronounced advances within the arid Southern Central Andes.

  18. Climatic implications of intermediate sized glacial advances in New Zeland valleys during OIS3.

    NASA Astrophysics Data System (ADS)

    Shulmeister, James; Thackray, Glenn; Rittenour, Tammy

    2014-05-01

    Recent work has greatly increased the number of known glacial oscillations during the last (Otiran) glaciation in South Island, New Zealand. Here we present summary stratigraphic and age results from a tectonic basin in the upper Rangitata Valley and a trough fill in the Rakaia Valley in Canterbury, New Zealand. The deposits constrain a series of intermediate scale glacial advances during OIS 3 that are not recorded in terminal moraine sequences in these valleys. These records demonstrate that ice limits oscillated substantially during the last glacial cycle but that very significant advances occurred at times other than the LGM, with glacial extents 80-95% of the local last glacial maximum. The timings of these advances appear to coincide with fragmentary evidence for glaciation in some other settings in New Zealand and SE Australia, indicating that the advances represent regionally significant climatic events. In the talk, I will summarise the evidence for the better constrained advances, consider the climate forcing required to maintain extended ice in these valleys through much of the last glacial cycle and consider the impact of antecedent ice limits on the climatic conditions at the LGM.

  19. Glacial discharge along the west Antarctic Peninsula during the Holocene

    NASA Astrophysics Data System (ADS)

    Pike, Jennifer; Swann, George E. A.; Leng, Melanie J.; Snelling, Andrea M.

    2013-03-01

    The causes for rising temperatures along the Antarctic Peninsula during the late Holocene have been debated, particularly in light of instrumental records of warming over the past decades. Suggested mechanisms range from upwelling of warm deep waters onto the continental shelf in response to variations in the westerly winds, to an influence of El Niño-Southern Oscillation on sea surface temperatures. Here, we present a record of Holocene glacial ice discharge, derived from the oxygen isotope composition of marine diatoms from Palmer Deep along the west Antarctic Peninsula continental margin. We assess atmospheric versus oceanic influences on glacial discharge at this location, using analyses of diatom geochemistry to reconstruct atmospherically forced glacial ice discharge and diatom assemblage ecology to investigate the oceanic environment. We show that two processes of atmospheric forcing--an increasing occurrence of La Niña events and rising levels of summer insolation--had a stronger influence during the late Holocene than oceanic processes driven by southern westerly winds and upwelling of upper Circumpolar Deepwater. Given that the evolution of El Niño-Southern Oscillation under global warming is uncertain, its future impacts on the climatically sensitive system of the Antarctic Peninsula Ice Sheet remain to be established.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  1. Molecular biogeography of Europe: Pleistocene cycles and postglacial trends

    PubMed Central

    Schmitt, Thomas

    2007-01-01

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

  2. 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. PMID:25071171

  3. 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

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

    USGS Publications Warehouse

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

    2004-01-01

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

  5. Mammal diversity during the Pleistocene-Holocene transition in Eastern Europe.

    PubMed

    Puzachenko, Andrei Yurievich; Markova, Anastasia Konstantinovna

    2014-08-01

    Fossil record data on the mammal diversity and species richness are of importance for the reconstruction of the evolution of terrestrial ecosystems during the Late Pleistocene-Holocene transition. In Eastern Europe, the transformations during the Pleistocene-Holocene transition consisted mainly in changes in zonal structure and local fauna composition (Markova & Kolfschoten 2008). We investigated the species richness and the analogues of the ?, ? diversity indexes (in the sense of Whittaker 1972) of large and medium size mammals for 13 climate-stratigraphic units dating to the Late Pleistocene and the Holocene, from the Hasselo Stadial (44-39 kBP) to the Subatlantic period and the present day. The biological diversity of the Last Glacial Maximum (LGM) and the Holocene thermal optimum was investigated in more detail using information about all mammalian taxa (PALEOFAUNA database; Markova 1995). One of our results show that the ?, ? diversity values show only a negative correlation with the temperature conditions during the Late Pleistocene, the period that is characterized by the so-called 'Mammoth Fauna' complex. For the Holocene faunas the diversity indexes are nearly independent from physical conditions; the ? diversity index decreased and the ? diversity index increased. The relatively low ? diversity and high ? diversity indexes for the present-day faunas are referred to the decrease of the population number of some forest species in historical time and the increase of the dominance of unspecialized species or the species connected with intra-zonal ecosystems. The study shows furthermore the occurrence of several East European 'centers' with a high mammal diversity, which are relatively stable during the Pleistocene-Holocene transition. The orientation of the boundaries between the large geographical mammal assemblages depended, particularly in the northwestern part of Eastern Europe, on the expansion of the Scandinavian ice sheet. PMID:25236416

  6. Managing the effects of accelerated glacial melting on volcanic collapse and debris flows: Planchon-Peteroa Volcano, Southern Andes

    NASA Astrophysics Data System (ADS)

    Tormey, Daniel

    2010-11-01

    Glaciated mountains are among the most sensitive environments to climatic changes, and recent work has shown that large-scale glacial melting, including at the end of the Pleistocene, caused a significant increase in the incidence of large volcanic sector collapse and debris flows on then-active volcanoes. With current accelerated rates of glacial melting, glaciated active volcanoes are at an increasing risk of sector collapse, debris flow and landslide. These catastrophic events are Earth's most damaging erosion phenomenon, causing extensive property damage and loss of life. This paper illustrates these effects in well-studied settings, focusing on the end-Pleistocene to Holocene glaciovolcanic growth and destruction of the cone of the active volcano Planchon-Peteroa in the Andean Southern Volcanic Zone at latitude 35° 15' S, along the border between Chile and Argentina. The development of the volcano over the last 14,000 years illustrates how glacial melting and magmatic activity can trigger landslides and sector collapses. Planchon had a large sector collapse that produced a highly mobile and erosive debris avalanche 11,000 years BP, and other slope instabilities during the end-Pleistocene/early Holocene deglaciation. The summit amphitheater left after the sector collapse was subject to alternating periods of glaciation and melting-induced lake formation. Breaching of the moraine dams then formed lahars and landslides originating at the western edge of the summit amphitheater, and the deposits are preserved along the western flank of the volcano. Deep incision of moraine deposits further down the western slope of the volcano indicates that the lahars and landslides were water-rich and had high erosive power. As illustrated by Planchon-Peteroa, the interplay among glacial growth and melting, magmatic activity, and slope stability is complex, but must be accounted for in volcanic hazard assessment. Planchon-Peteroa currently has the southernmost temperate zone mountain glacier in the Andes. Accelerated glacial melting at present rates of climate change could lead to a recurrence of many of these post-Pleistocene events. A framework for augmenting hazard assessments and countermeasures is also proposed based on the types of hazards presented by accelerated glacial melting. Glacial melting may lead to volcanic hazards in areas not previously considered at risk, and hence there may be a low level of preparedness. Compared to the end-Pleistocene accelerated glacial melting and sector collapses, present-day glacial melting in volcanic terrain has the potential to affect large human populations. Human settlements, hydropower production, forestry, mining and wilderness tourism are all concentrated near some glaciated volcanic areas. For example, the area covered by the debris avalanche from Volcan Planchon currently supports a rich agricultural economy in Chile. Effective risk management is needed to address the issues of changing patterns in vulnerability, the nature and redistribution of hazards, and the potential socioeconomic consequences of glaciovolcanic events. Since these events are infrequent, local communities frequently do not have a memory of past occurrences, and therefore have a low awareness of the potential effects. Systematic and structured impact assessment allows objective risk analysis, uncertainty analysis, and a framework for balancing countermeasures and contingency measures with public need and acceptance. An impact assessment approach similar to that used in land use planning is presented here, with the following major elements: (i) hazard characterization; (ii) consequence characterization; (iii) risk assessment; (iv) risk control and countermeasures; and (v) risk communication. The emphasis is on effective risk communication, supported by facts, in order to address the increased hazards posed by accelerated glacial melting on volcanic cone stability. Decision makers must then weigh societal acceptance of the risk control and countermeasures against their costs and consequences.

  7. The Yana RHS site: humans in the Arctic before the last glacial maximum.

    PubMed

    Pitulko, V V; Nikolsky, P A; Girya, E Yu; Basilyan, A E; Tumskoy, V E; Koulakov, S A; Astakhov, S N; Pavlova, E Yu; Anisimov, M A

    2004-01-01

    A newly discovered Paleolithic site on the Yana River, Siberia, at 71 degrees N, lies well above the Arctic circle and dates to 27,000 radiocarbon years before present, during glacial times. This age is twice that of other known human occupations in any Arctic region. Artifacts at the site include a rare rhinoceros foreshaft, other mammoth foreshafts, and a wide variety of tools and flakes. This site shows that people adapted to this harsh, high-latitude, Late Pleistocene environment much earlier than previously thought. PMID:14704419

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

    PubMed

    Kontula, Tytti; Väinölä, Risto

    2003-11-01

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

  9. Climate impacts on transocean dispersal and habitat in gray whales from the Pleistocene to 2100.

    PubMed

    Alter, S Elizabeth; Meyer, Matthias; Post, Klaas; Czechowski, Paul; Gravlund, Peter; Gaines, Cork; Rosenbaum, Howard C; Kaschner, Kristin; Turvey, Samuel T; van der Plicht, Johannes; Shapiro, Beth; Hofreiter, Michael

    2015-04-01

    Arctic animals face dramatic habitat alteration due to ongoing climate change. Understanding how such species have responded to past glacial cycles can help us forecast their response to today's changing climate. Gray whales are among those marine species likely to be strongly affected by Arctic climate change, but a thorough analysis of past climate impacts on this species has been complicated by lack of information about an extinct population in the Atlantic. While little is known about the history of Atlantic gray whales or their relationship to the extant Pacific population, the extirpation of the Atlantic population during historical times has been attributed to whaling. We used a combination of ancient and modern DNA, radiocarbon dating and predictive habitat modelling to better understand the distribution of gray whales during the Pleistocene and Holocene. Our results reveal that dispersal between the Pacific and Atlantic was climate dependent and occurred both during the Pleistocene prior to the last glacial period and the early Holocene immediately following the opening of the Bering Strait. Genetic diversity in the Atlantic declined over an extended interval that predates the period of intensive commercial whaling, indicating this decline may have been precipitated by Holocene climate or other ecological causes. These first genetic data for Atlantic gray whales, particularly when combined with predictive habitat models for the year 2100, suggest that two recent sightings of gray whales in the Atlantic may represent the beginning of the expansion of this species' habitat beyond its currently realized range. PMID:25753251

  10. Chronology for fluctuations in late pleistocene Sierra Nevada glaciers and lakes

    SciTech Connect

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

    1996-11-01

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

  11. Chronology for fluctuations in late Pleistocene Sierra Nevada glaciers and lakes

    USGS Publications Warehouse

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

    1996-01-01

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

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

    PubMed Central

    2013-01-01

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

  13. The Kråkenes late-glacial palaeoenvironmental project

    Microsoft Academic Search

    Hilary H. Birks; R. W. Battarbee; D. J. Beerling; H. J. B. Birks; S. J. Brooks; C. A. Duigan; S. Gulliksen; H. Haflidason; F. Hauge; V. J. Jones; B. Jonsgard; M. Kårevik; E. Larsen; G. Lemdahl; R. Løvlie; J. Mangerud; S. M. Peglar; G. Possnert; J. P. Smol; J. O. Solem; I. Solhøy; T. Solhøy; E. Sønstegaard; H. E. Wright

    1996-01-01

    Kråkenes is the site of a small lake on the west coast of Norway that contains a long sequence of late-glacial sediments. The Younger Dryas is well represented, as a cirque glacier developed in the catchment at this time. This site offers unique opportunities to reconstruct late-glacial environments from independent sources of evidence; physical evidence (glacial geomorphology, sedimentology, palaeomagnetism, radiocarbon

  14. DATING GLACIAL LANDFORMS Jason P. Briner

    E-print Network

    Briner, Jason P.

    D DATING GLACIAL LANDFORMS Jason P. Briner Department of Geological Sciences, University at Buffalo, Buffalo, NY, USA Definition Dating glacial landforms. Applying geochronological tools (e.g., relative- and absolute-dating methods, etc.) to glacial landforms (e.g., moraines) to yield the timing of past glaciation

  15. Last Glacial Maximum

    NSDL National Science Digital Library

    Kristine DeLong

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

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    Microsoft Academic Search

    José María Postigo Mijarra; Fernando Gómez Manzaneque; Carlos Morla

    2008-01-01

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

  18. A 10Be Chronology of Late Pleistocene and Holocene Glaciation in the Rwenzori Mountains, Uganda

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Although the retreat of glaciers in East Africa has been monitored over the last century, longer-term records of African glacier fluctuations are scarce. The Rwenzori Mountains, located on the border of Uganda and the Democratic Republic of Congo, host the largest glacial system in Africa and provide an opportunity for extensive investigation of past glaciations. We mapped and applied surface exposure (10Be) dating to glacial moraines deposited since the end of the last ice age in the Rwenzori Mountains to test the feasibility of 10Be dating at this site and to develop a chronology of glacial fluctuations. Our study is the first to use 10Be dating of glacial features in Africa and is possible because the Rwenzori host quartz-rich lithologies. By comparing the timing of Rwenzori glacial advances with other paleoclimate records from East Africa, we also will examine the climatic conditions which influenced tropical glacier fluctuations. Osmaston (1989) mapped moraines in the Rwenzori Mountains, documenting three stages of Pleistocene and Holocene glaciations, the Mahoma, Omurubaho and Lac Gris stages. The Mahoma stage moraines are estimated to be older than 17,980 ± 780 yr BP (D. M. Livingstone, 1962) by basal 14C dating of sediments from Lake Mahoma, situated in large lateral moraine at 2990 m asl. The age of the Omurubaho stage moraine is estimated from a basal 14C age (7,730 ± 150 yr BP) Lower Kitandara Lake (3990 m asl) and dammed by an Omurubaho stage moraine. The Lac Gris moraines are estimated at ~150-700 yr BP (de Heinzelin, 1953; Bergström, 1955) based on rates of lichen growth and plant colonization on moraines about 200 m below current glacial positions on Mt. Stanley. Though considerable uncertainty remains for the ages of these glacier deposits, these three stages most likely represent ages from the LGM to the LIA. We present two new 10Be ages of boulders from two moraines in the Nyamagusani Valley, ~4000 m asl. Sample KOP-2 (4033 m asl) is from the innermost moraine on the valley floor and yielded a 10Be age of 9,750 ± 110 yrs. Sample LA-1 (3870 masl) is from a moraine located ~1.8 km down valley and is 10,590 ± 120 yrs. Although the 10Be production rate is not well known in this region, these preliminary ages are in stratigraphic order and suggest glacial advance in the Rwenzori during late glacial to Early Holocene time. In June 2012, we sampled boulders from multiple valleys in the Rwenzori. We are currently processing fifteen samples from Nyamagusani to test the reproducibility of boulder ages on individual landforms and to test the age of Omurubaho stage moraines.

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

    NASA Astrophysics Data System (ADS)

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

    2007-02-01

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

  20. Pleistocene glaciation is implicated in the phylogeographical structure of Potamopyrgus antipodarum, a New Zealand snail.

    PubMed

    Neiman, Maurine; Lively, Curtis M

    2004-10-01

    Pleistocene glaciation has been identified as an important factor shaping present-day patterns of phylogeographical structure in a diverse array of taxa. The purpose of this study was to use mitochondrial sequence data to address whether Pleistocene glaciation is also a major determinant of phylogeographical patterns in Potamopyrgus antipodarum, a freshwater snail native to New Zealand. We found that haplotypes were separated by no more than 3.7% sequence divergence, and major genetic divisions tended to occur on a north-south axis. These data fit the predictions of the hypothesis that isolation of P. antipodarum in glacial refugia at the northern and southern tip of the South Island of New Zealand during the Pleistocene glaciation underlies the present-day phylogeographical structure. Because sexual P. antipodarum occasionally produce asexual offspring, we also used these data to show that the appearance of asexuality is not phylogeographically constrained. This means that the maintenance of sex in P. antipodarum cannot be wholly due to limited contact between sexual and asexual lineages and must instead be linked to a selective advantage of sexual reproduction. PMID:15367122

  1. Pleistocene evolution of closely related sand martins Riparia riparia and R. diluta.

    PubMed

    Pavlova, Alexandra; Zink, Robert M; Drovetski, Sergei V; Rohwer, Sievert

    2008-07-01

    Climatic fluctuations during the Quaternary resulted in a dynamic history of species' range shifts, fragmentations and expansions. Some of these events left traces in the genetic structures of plants and animals. Recent avian phylogeographic studies demonstrated that Holarctic birds responded idiosyncratically to Pleistocene climate fluctuations. We present phylogeographic analyses of the Holarctic collared sand martin (Riparia riparia) and the Asian pale sand martin (Riparia diluta), which were considered conspecific until recently. Mitochondrial and nuclear sequences confirm species status of the pale sand martin; the two species diverged sometime between late Pliocene and middle Pleistocene, but precise dates could not be provided without calibration of the substitution rate. Within the pale sand martin, we found two mitochondrial clades that are likely to have diverged in the Pleistocene, one from Central Siberia, and the other restricted to Mongolia. The two clades were sympatric with the collared sand martin in Buryatiya and Mongolia, respectively. The mitochondrial gene genealogy and phi(st) analysis of the collared sand martin haplotypes indicate recent, but not ongoing, gene exchange between North America and Eurasia, and restricted gene flow between western and eastern Siberia that likely resulted from historic fragmentation of the species' range during the last glacial maximum. PMID:18499482

  2. Nonlinear detection of large-scale transitions in Plio-Pleistocene African climate

    NASA Astrophysics Data System (ADS)

    Donges, J. F.; Donner, R. V.; Trauth, M. H.; Marwan, N.; Schellnhuber, H. J.; Kurths, J.

    2011-12-01

    Potential paleoclimatic driving mechanisms acting on human development present an open problem of cross-disciplinary scientific interest. The analysis of paleoclimate archives encoding the environmental variability in East Africa during the last 5 Ma (million years) has triggered an ongoing debate about possible candidate processes and evolutionary mechanisms. In this work, we apply a novel nonlinear statistical technique, recurrence network analysis, to three distinct marine records of terrigenous dust flux. Our method enables us to identify three epochs with transitions between qualitatively different types of environmental variability in North and East Africa during the (i) Mid-Pliocene (3.35-3.15 Ma BP (before present)), (ii) Early Pleistocene (2.25-1.6 Ma BP), and (iii) Mid-Pleistocene (1.1-0.7 Ma BP). A deeper examination of these transition periods reveals potential climatic drivers, including (i) large-scale changes in ocean currents due to a spatial shift of the Indonesian throughflow in combination with an intensification of Northern Hemisphere glaciation, (ii) a global reorganization of the atmospheric Walker circulation induced in the tropical Pacific and Indian Ocean, and (iii) shifts in the dominating temporal variability pattern of glacial activity during the Mid-Pleistocene, respectively. A statistical reexamination of the available fossil record demonstrates a remarkable coincidence between the detected transition periods and major steps in hominin evolution. This suggests that the observed shifts between more regular and more erratic environmental variability have acted as a trigger for rapid change in the development of humankind in Africa.

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

    SciTech Connect

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

    1993-03-01

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

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

    PubMed

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

    2014-03-01

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

  5. 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 invaded the valleys. Maximum ice retreat was associated with high water fluxes and sediment discharge, causing a sand-dominated outwash fan to prograde out over the valleys and interfluves. This outwash fan was supplied mainly by flood activity at the ice front, involving high-density sustained flows. The dominant facies consists of giant aggrading climbing dunes filling channels or constructing sandy lobes downstream.

  6. Pleistocene lake level changes in Western Mongolia

    Microsoft Academic Search

    P. S. Borodavko

    2009-01-01

    Global cooling in the Early Pleistocene caused extensive continental glaciation in the northern hemisphere including the arid areas of Central Asia. The reduction of temperatures (particularly summer temperatures) reduced evaporation and strengthened the importance of precipitation. The simultaneity of \\

  7. Predicting Pleistocene climate from vegetation

    NASA Astrophysics Data System (ADS)

    Loehle, C.

    2006-10-01

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

  8. An interhemispheric mechanism for glacial abrupt climate change

    NASA Astrophysics Data System (ADS)

    Banderas, Rubén; Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa

    2014-06-01

    The last glacial period was punctuated by abrupt climate changes that are widely considered to result from millennial-scale variability of the Atlantic meridional overturning circulation (AMOC). However, the origin of these AMOC reorganizations remains poorly understood. The climatic connection between both hemispheres indicated by proxies suggests that the Southern Ocean (SO) could regulate this variability through changes in winds and atmospheric CO2 concentration. Here, we investigate this hypothesis using a coupled climate model forced by prescribed CO2 and SO wind-stress variations. We find that the AMOC exhibits an oscillatory behavior between weak and strong circulation regimes which is ultimately caused by changes in the meridional density gradient of the Atlantic Ocean. The evolution of the simulated climatic patterns matches the amplitude and timing of the largest events that occurred during the last glacial period and their widespread climatic impacts. Our results suggest the existence of an internal interhemispheric oscillation mediated by the bipolar seesaw that could promote glacial abrupt climate changes through variations in atmospheric CO2 levels, the strength of the SO winds and AMOC reorganizations, and provide an explanation for the pervasive Antarctic-like climate signal found in proxy records worldwide.

  9. Late Pleistocene Vertebrates and Other Fossils from Epiguruk, Northwestern Alaska

    USGS Publications Warehouse

    Hamilton, T.D.; Ashley, G.M.; Reed, K.M.; Schweger, C.E.

    1993-01-01

    Sediments exposed at Epiguruk, a large cutbank on the Kobuk River about 170 km inland from Kotzebue Sound, record multiple episodes of glacial-age alluviation followed by interstadial downcutting and formation of paleosols. Vertebrate remains from Epiguruk include mammoth, bison, caribou, an equid, a canid, arctic ground squirrel, lemmings, and voles. Radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37,000 and 14,000 yr B.P. The late Pleistocene pollen record is dominated by Cyperaceae, with Artemisia, Salix, Betula, and Gramineae also generally abundant. The fossil record from Epiguruk indicates that the Kobuk River valley supported tundra vegetation with abundant riparian willows during middle and late Wisconsin time. Large herbivores were present during the height of late Wisconsin glaciation as well as during its waning stage and the preceding interstadial interval. The Kobuk River valley would have been a favorable refugium for plants, animals, and possibly humans throughout the last glaciation.

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

    PubMed Central

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

    2012-01-01

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

  11. 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 predicated upon their ability to extend their societies in space and time. We examine this difference further using a database of all available radiocarbon determinations from western Europe in the late glacial. These data act as proxies for population history, and in particular the expansion and contraction of regional populations as climate changed rapidly. Independent assessment of these processes is obtained from the genetic history of Europeans. The results indicate that climate affects population contraction rather than expansion. We discuss the consequences for genetic and cultural diversity which led to the legacy of the Ice Age: a single hominid species, globally distributed. PMID:15101580

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

    PubMed

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

    2007-04-01

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

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

    PubMed

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

    2015-01-01

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

  14. 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.

  15. A multi-locus species phylogeny of African forest duikers in the subfamily Cephalophinae: evidence for a recent radiation in the Pleistocene

    PubMed Central

    2012-01-01

    Background Duikers in the subfamily Cephalophinae are a group of tropical forest mammals believed to have first originated during the late Miocene. However, knowledge of phylogenetic relationships, pattern and timing of their subsequent radiation is poorly understood. Here we present the first multi-locus phylogeny of this threatened group of tropical artiodactyls and use a Bayesian uncorrelated molecular clock to estimate divergence times. Results A total of 4152 bp of sequence data was obtained from two mitochondrial genes and four nuclear introns. Phylogenies were estimated using maximum parsimony, maximum likelihood, and Bayesian analysis of concatenated mitochondrial, nuclear and combined datasets. A relaxed molecular clock with two fossil calibration points was used to estimate divergence times. The first was based on the age of the split between the two oldest subfamilies within the Bovidae whereas the second was based on the earliest known fossil appearance of the Cephalophinae and molecular divergence time estimates for the oldest lineages within this group. Findings indicate strong support for four major lineages within the subfamily, all of which date to the late Miocene/early Pliocene. The first of these to diverge was the dwarf duiker genus Philantomba, followed by the giant, eastern and western red duiker lineages, all within the genus Cephalophus. While these results uphold the recognition of Philantomba, they do not support the monotypic savanna-specialist genus Sylvicapra, which as sister to the giant duikers leaves Cephalophus paraphyletic. BEAST analyses indicate that most sister species pairs originated during the Pleistocene, suggesting that repeated glacial cycling may have played an important role in the recent diversification of this group. Furthermore, several red duiker sister species pairs appear to be either paraphyletic (C.callipygus/C. ogilbyi and C. harveyi/C. natalensis) or exhibit evidence of mitochondrial admixture (C. nigrifrons and C. rufilatus), consistent with their recent divergence and/or possible hybridization with each other. Conclusions Molecular phylogenetic analyses suggest that Pleistocene-era climatic oscillations have played an important role in the speciation of this largely forest-dwelling group. Our results also reveal the most well supported species phylogeny for the subfamily to date, but also highlight several areas of inconsistency between our current understanding of duiker taxonomy and the evolutionary relationships depicted here. These findings may therefore prove particularly relevant to future conservation efforts, given that many species are presently regulated under the Convention for Trade in Endangered Species. PMID:22823504

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

    NASA Astrophysics Data System (ADS)

    Mehl, A. E.; Zárate, M. A.

    2014-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Goyanes, Gabriel; Massabie, Armando

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  2. Glacial cycles drive variations in the production of oceanic crust

    NASA Astrophysics Data System (ADS)

    Crowley, J. W.; Katz, R. F.; Langmuir, C. H.; Huybers, P. J.

    2013-12-01

    Changes in sea level accompanying glacial cycles affect the static pressure within the asthenosphere; these variations could modulate melting rates beneath the mid-ocean ridge system as well as crustal thickness. These effects can be investigated and quantified using models of ridges based on conservation of mass, momentum, energy, and composition for two phases (magma & mantle) and two thermodynamic components (enriched & depleted). The models predict that the sensitivity of crustal thickness to oscillations in sea-level depends on the period of oscillation, the spreading rate of the ridge, and the assumed permeability scale of the melting regime. In contrast to previous studies (Huybers & Langmuir, 2009 and Lund & Asimow, 2011), the new results indicate that effects are larger for ridges with faster spreading rates. They also show that the dominant period of variations in crustal thickness changes with spreading rate and permeability. Sea-level variations with periods in the range of 10 ky - 100 ky can result in significant changes in crustal thickness that are orders of magnitude larger than the sea-level variations that drive them. Accurately modelling this process requires the inclusion of two previously unaccounted for processes: (1) determining the volume of the melting regime that is consistent with the ridge spreading rate and (2) properly treating the transport of melt. These enable us to capture the non-linear dependencies on spreading rate and other model parameters. Spectral analysis of bathymetry at two ridge segments that have a symmetric bathymetric signal and hence are undisturbed by off-axis volcanism or ridge jumps reveals the presence of variability at frequencies associated with precession, obliquity, and the 100 ky glacial/inter-glacial variability. Furthermore, the faster spreading ridge has larger amplitude responses to changes in sea level and shows a proportionately greater response at higher frequencies. These observations reinforce the possible links among climate cycles at the surface, mantle melting at depth and the crustal fabric of the sea floor.

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

    NASA Astrophysics Data System (ADS)

    Vaughan-Hirsch, David

    2013-04-01

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

  4. Late-glacial to holocene changes in winds, upwelling, and seasonal production of the northern California current system

    USGS Publications Warehouse

    Sancetta, C.; Lyle, M.; Heusser, L.; Zahn, R.; Bradbury, J.P.

    1992-01-01

    A core 120 km off the coast of southern Oregon was examined for changes in lithology, diatoms, and pollen over the past 30,000 yr. Primary production during the late Pleistocene was about half that of the Holocene. Evidence from diatoms and pollen indicates that summer upwelling was much weaker, implying an absence of strong northerly winds. Early Pliocene diatoms found throughout the late Pleistocene section were probably derived from diatomites east of the Cascades and provide evidence for strong easterly winds over a dry continental interior. The findings verify predictions of a climate model based on glacial maximum conditions. There is no compelling evidence for a climatic reversal corresponding to the European Younger Dryas chron. During the early Holocene (9000-7000 yr B.P.) there may have been years when winds were insufficiently strong to support upwelling, so that warm stratified waters lay closer to the coast. ?? 1992.

  5. Combining cosmogenic radionuclides and amino acid racemization to date late Pliocene glacial deposits exposed on Baffin Island, Nunavut, Canada

    NASA Astrophysics Data System (ADS)

    Refsnider, K. A.; Miller, G. H.

    2009-12-01

    Sequences of glacial deposits spanning the Quaternary are valuable archives recording the effects of glaciation on landscapes through time, but determining the age of such deposits has long challenged geologists. The recent advances in cosmogenic radionuclide (CRN) measurement has made it possible to date some of these deposits, but dating buried glacial sediments in most settings remains problematic. Here we explore a new approach to date the oldest glacial deposits in the Plio-Pleistocene Clyde Foreland Formation of Baffin Island. This formation, approximately 40 m thick, includes interlayered shell-bearing marine, glaciomarine, and glacial sediments deposited along the northern margin of the Laurentide Ice Sheet and earlier continental ice sheets. Previous work on foraminifera assemblages suggests that the deposits span the last ?2 Ma. By combining CRN measurements (10Be and 26Al) from the glacial units and measurements of the D-alloisoleucine:L-isoleucine ratios (A/I) in valves of the mollusk Hiatella arctica in the marine units overlying a particular glacial deposit, we can calculate the age of the glacial deposit. Because the post-burial temperature history for the mollusks preserved in the Clyde Foreland Formation is poorly constrained, A/I ratios alone cannot be used to determine absolute ages. Instead, we use A/I ratios to identify sediment packages of discrete ages and define a step-wise burial history function for glacial units. A/I ratios of all packages (<0.3 for the total hydrolysate fraction) fall within the A/I interval characterized by linear racemization kinetics, so the age of each package in the burial history function can simply be defined as a fractional age with respect to the total burial age for the glacial deposit of interest. The long duration of burial (26Al/10Be as low as 1.6±0.6 at 2?) and low initial CRN inventories require that post-burial muogenic production is accounted for using the burial history function. We apply a numerical model to calculate the duration of burial from the measured CRN concentrations for a given inherited CRN inventory. But because this initial inventory is unknown, a single CRN sample/burial history combination will not provide a unique age solution. Instead, measurements from multiple localities where a particular glacial deposit has differing burial histories (i.e., the thickness of overlying units or ages of overlying units differ) are required to statistically determine the total burial age that most closely matches the observed CRN inventories and burial histories.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  8. The Mid-Pliocene sea-level conundrum: Glacial isostasy, eustasy and dynamic topography

    NASA Astrophysics Data System (ADS)

    Rovere, A.; Raymo, M. E.; Mitrovica, J. X.; Hearty, P. J.; O'Leary, M. J.; Inglis, J. D.

    2014-02-01

    Determining eustatic sea level during the Mid-Pliocene warm period (?3.3 to 2.9 Ma) has been a central but elusive goal in the study of past warm climates. Estimates of eustatic sea level based on geologic data span a broad range; variation that we now recognize is due in part to geographically varying post-depositional displacement caused by glacial isostatic adjustment and dynamic topography. In this study, we combine field observations and glacial isostatic adjustment modeling to estimate the dynamic topography signal in three areas that are important to paleo-sea level studies of the Mid-Pliocene warm period (South Africa, West Australia and southeastern United States). We show that dynamic topography played a significant role in the post-depositional displacement of Pliocene, and even younger Pleistocene, shorelines. In this regard, we provide a robust paleo-sea level elevation data set, corrected for glacial isostatic adjustment, that can be used to evaluate predictions from mantle flow models of dynamic topography.

  9. Driving Regional Scale Groundwater Flow in the Deep Michigan Basin: Glacial Loading vs. Variable Density Flow

    NASA Astrophysics Data System (ADS)

    McPherson, B. J.; Saylor, B. Z.

    2001-12-01

    Recent hydrodynamic studies of the Michigan Basin detail mildly excessive fluid pressures and anomalous flow in deeper formations within the basin. Depending on the conceptual model applied, modeled or inferred flow directions in the deep Michigan Basin may be as much as 180o different than flow directions suggested by topographic driving forces alone. Observed anomalously high fluid pressures and anomalous flow directions at depth are attributed to two possible causes, by different workers: (1) Pleistocene glacial loading, inducing high pressures in a fashion similar to rapid sedimentation, and (2) sinking of high density brines from Silurian halite/anhydrite units into deeper formations below, driving flow of lower density groundwater at depth. We developed and applied a simplified numerical model of the Michigan basin to evaluate regional-scale hydrodynamics and to address glacial loading versus brine sinking as causes of apparent anomalous pressures and flow. Results of basin flow simulations suggest that glacial loading is likely responsible for observed regional-scale excessive fluid pressures. However, variable density flow simulations also suggest that local-scale anomalous flow directions may be induced by brine sinking. >http://www.ees.nmt.edu/Hydro/faculty/McPherson/ michiganbasin.html

  10. Surface exposure dating reveals MIS-3 glacial maximum in the Khangai Mountains of Mongolia

    NASA Astrophysics Data System (ADS)

    Rother, Henrik; Lehmkuhl, Frank; Fink, David; Nottebaum, Veit

    2014-09-01

    This study presents results from geomorphological mapping and cosmogenic radionuclide dating (10Be) of moraine sequences at Otgon Tenger (3905 m), the highest peak in the Khangai Mountains (central Mongolia). Our findings indicate that glaciers reached their last maximum extent between 40 and 35 ka during Marine Oxygen Isotope Stage (MIS) 3. Large ice advances also occurred during MIS-2 (at ~ 23 and 17-16 ka), but these advances did not exceed the limits reached during MIS-3. The results indicate that climatic conditions during MIS-3, characterized by a cool-wet climate with a greater-than-today input from winter precipitation, generated the most favorable setting for glaciation in the study region. Yet, glacial accumulation also responded positively to the far colder and drier conditions of MIS-2, and again during the last glacial-interglacial transition when precipitation levels increased. Viewed in context of other Pleistocene glacial records from High Asia, the pattern of glaciation in central Mongolia shares some features with records from southern Central Asia and NE-Tibet (i.e. ice maxima during interstadial wet phases), while other features of the Mongolian record (i.e. major ice expansion during the MIS-2 insolation minimum) are more in tune with glacier responses known from Siberia and western Central Asia.

  11. Synchronous extinction of North America's Pleistocene mammals.

    PubMed

    Faith, J Tyler; Surovell, Todd A

    2009-12-01

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

  12. Synchronous extinction of North America's Pleistocene mammals

    PubMed Central

    Faith, J. Tyler; Surovell, Todd A.

    2009-01-01

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

  13. Using Climate Models to Evaluate Mechanisms of Glacial Inception

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  14. Thermohaline Circulation Crisis and Changes Through the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Goldstein, S. L.; Pena, L.

    2013-12-01

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

  15. Latest Pleistocene and Holocene glacier fluctuations on Mount Baker, Washington

    NASA Astrophysics Data System (ADS)

    Osborn, Gerald; Menounos, Brian; Ryane, Chanone; Riedel, Jon; Clague, John J.; Koch, Johannes; Clark, Douglas; Scott, Kevin; Davis, P. Thompson

    2012-08-01

    Glaciers on stratovolcanoes of the Pacific Northwest of North America offer opportunities for dating late Pleistocene and Holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields. We capitalize on this opportunity by examining the Holocene glacial record at Mount Baker, an active stratovolcano in northwest Washington. Earlier workers concluded that glaciers on Mount Baker during the early Holocene were more extensive than during the Little Ice Age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes. We show that the main argument for an early Holocene glacier advance on Mount Baker, namely the absence of ca 10,000-year-old tephra on part of the south flank of the mountain, is incorrect. Moreover, a lake-sediment core indicates that a small cirque moraine previously thought be of early Holocene age is also likely older than the tephra and consequently of late Pleistocene age. Lateral and end moraines and wood mats ca 2 km downvalley of the present snout of Deming Glacier indicate that an advance during the Younger Dryas interval was little more extensive than the climactic Little Ice Age advance. Tephra and wood between tills in the left lateral moraine of Easton Glacier suggest that ice on Mount Baker was restricted in the early Holocene and that Neoglaciation began ca 6 ka. A series of progressively more extensive Neoglacial advances, dated to about 2.2, 1.6, 0.9, and 0.4 ka, are recorded by stacked tills in the right lateral moraine of Deming Glacier. Intervening retreats were long enough to allow establishment of forests on the moraine. Wood mats in moraines of Coleman and Easton glaciers indicate that Little Ice Age expansion began before 0.7 ka and was followed by retreat and a readvance ca 0.5 ka. Tree-ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid-1800s. The similarity between glacier fluctuations at Mount Baker and those elsewhere in the Cascades and in British Columbia suggests a coherent history of Holocene climate change over a broad area of the western Cordillera. We found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere.

  16. Remote identification of a gravel laden Pleistocene river bed

    NASA Technical Reports Server (NTRS)

    Scholen, Douglas E.

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  18. Post-glacial population expansion of the Monterey Spanish mackerel Scomberomorus concolor in the Gulf of California.

    PubMed

    Domínguez-López, M; Díaz-Jaimes, P; Uribe-Alcocer, M; Quiñonez-Velázquez, C

    2015-03-01

    The level of genetic homogeneity and demographic history of the Monterey Spanish mackerel Scomberomorus concolor was assessed by analyses using sequences of the mitochondrial (mt)DNA-control region of samples from the two oceanographic regions of the Gulf of California in order to define the stock structure for this exploited vulnerable species. The data were consistent with a single homogeneous population and revealed the hallmark of fluctuations in population size; these fluctuations appear to have occurred during glacial events of the middle to late Pleistocene, which may in turn be related to the colonization and expansion of S. concolor populations in the gulf. PMID:25583211

  19. Origin and age of phosphorite from the Last Glacial Maximum to Holocene transgressive succession o¡ the Orange River South Africa

    Microsoft Academic Search

    John S. Compton; Jerey Mulabisana; I. k. Mcmillan

    Abstract A major,erosional unconformity,between,upper,Cretaceous sediments,and,the Last Glacial Maximum,(LGM) transgressive succession occurs,on the inner continental,shelf off the Orange River. Vibracores from,122 m,water- depth consist of upper Pleistocene shelly, phosphatic sands deposited in a high-energy shoreface environment during the LGM lowstand,between,22 and 19 ka. The gravel-rich shoreface sand grades into condensed,shell-rich delta-front sands as sea level rose between,19 and 14.3 ka. An

  20. Glacial Lake Chicago Early Lake Michigan

    E-print Network

    Cochran-Stafira, D. Liane

    between the ice front and the moraines that circle the southern end of the Lake Michigan Basin. The lakeGlacial Lake Chicago Early Lake Michigan Ancient Shorelines This section refers to the phases of Glacial Lake Chicago. The title "Lake Michigan" refers to stages that occurred after ice had completely

  1. Sea-level variability over five glacial cycles.

    PubMed

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

    2014-01-01

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

  2. Seismic characterization of glacial sediments in central Illinois

    NASA Astrophysics Data System (ADS)

    Ismail, Ahmed; Stumpf, Andrew; Bauer, Robert

    2014-02-01

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

  3. Sea-level variability over five glacial cycles

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  4. Glacial isostatic adjustment in the static gravity field of Fennoscandia

    NASA Astrophysics Data System (ADS)

    Root, B. C.; Wal, W.; Novák, P.; Ebbing, J.; Vermeersen, L. L. A.

    2015-01-01

    In the central part of Fennoscandia, the crust is currently rising, because of the delayed response of the viscous mantle to melting of the Late Pleistocene ice sheet. This process, called Glacial Isostatic Adjustment (GIA), causes a negative anomaly in the present-day static gravity field as isostatic equilibrium has not been reached yet. Several studies have tried to use this anomaly as a constraint on models of GIA, but the uncertainty in crustal and upper mantle structures has not been fully taken into account. Therefore, our aim is to revisit this using improved crustal models and compensation techniques. We find that in contrast with other studies, the effect of crustal anomalies on the gravity field cannot be effectively removed, because of uncertainties in the crustal and upper mantle density models. Our second aim is to estimate the effects on geophysical models, which assume isostatic equilibrium, after correcting the observed gravity field with numerical models for GIA. We show that correcting for GIA in geophysical modelling can give changes of several kilometer in the thickness of structural layers of modeled lithosphere, which is a small but significant correction. Correcting the gravity field for GIA prior to assuming isostatic equilibrium and inferring density anomalies might be relevant in other areas with ongoing postglacial rebound such as North America and the polar regions.

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

    E-print Network

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

  6. Introduction 1.1 Glacial Isostatic Adjustment

    E-print Network

    Hanyk, Ladislav

    by glaciers during the late Pleistocene epoch and, hence, it is customary to refer to the whole process continuing with permanent intensity. Let us mention publications on analytical solutions to relaxation

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  9. Glacigenic erosion, sediment generation and transport routes in Fennoscandia during Pleistocene - evidence from South Norway

    NASA Astrophysics Data System (ADS)

    Hjelstuen, B. O.; Nygård, A.; Sejrup, H. P.; Haflidason, H.

    2009-04-01

    During the Northern Hemisphere glaciations ice sheets shaped the Fennoscandian landscape into its present form. Along the southwestern Fennoscandian coastline the prominent sub-marine Norwegian Channel has been the main transport route for Pleistocene glacigenic erosional products from SE Norway and SW Sweden to the Norwegian Sea. The Norwegian Channel reaches a maximum water depth of 700 m in the Skagerrak and has been occupied by repeated ice streams the last 1.1 million years. Glacigenic erosional products were also fed into the Norwegian Channel through the western Norwegian fjord systems during glacial stages. The main depocentre for the eroded products was the North Sea Fan complex at the mouth of the channel, where the sediments transported at the base of the Norwegian Channel Ice Stream were deposited as stacks of glacigenic debris flows. The Pleistocene part of the fan complex, reaches a maximum thickness of c. 1500 m and comprises nearly 40 000 km3 of sediments. Close to 85% of these sediments have however been deposited during the last 500 000 years, when ice-advances to the shelf edge occurred during each glacial stage. Our estimates show that only 20% of the 1.1 Ma North Sea Fan sediment volume could have been eroded from the channel itself, implying that erosion of the nearby land areas must have been significant. Assuming a North Sea Fan drainage area of between 165 000 km2 and 250 000 km2, we find that the landscape in the southwestern part of Fennoscandia has been lowered by 110-170 m since 1.1 Ma. This gives an average denudation rate of 10-15 cm/kyr. We suggest that most of this landscape denudation has taken place the last 0.5 million years.

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

    PubMed

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

    2014-12-30

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

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

    PubMed

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

    2014-03-01

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

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

    PubMed Central

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

    2014-01-01

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

  13. Late Pleistocene Faunal Extinctions in Southern Patagonia

    Microsoft Academic Search

    Vera Markgraf

    1985-01-01

    Major environmental changes recorded in pollen records from various sites in southern Patagonia and Tierra del Fuego are also reflected in pollen and cuticle data from dung of the late Pleistocene groundsloth. The most prominent change was the large-scale reduction of steppe environment about 10,000 years ago, which coincides with the latest dates for extinctions of many large grazers such

  14. Temporal labyrinths of eastern Eurasian Pleistocene humans

    PubMed Central

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

    2014-01-01

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

  15. Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska

    NASA Astrophysics Data System (ADS)

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

    1981-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  17. Late Pleistocene and Holocene climate and geomorphic histories as interpreted from a 23,000 14C yr B.P. paleosol and floodplain soils, southeastern West Virginia, USA

    NASA Astrophysics Data System (ADS)

    Driese, Steven G.; Li, Zheng-Hua; Horn, Sally P.

    2005-03-01

    Field, micromorphological, pollen, whole soil (XRF), and stable isotope geochemical methods were used to evaluate the latest Pleistocene to Holocene climate record from a floodplain-terrace system in southeastern West Virginia. A late Pleistocene (22,940 ± 150 14C yr B.P.) silt paleosol with low-chroma colors formed from fluviolacustrine sediment deposited during the last glacial maximum (Wisconsinan) and records a cooler full-glacial paleoclimate. Fluvial gravel deposited between the latest Pleistocene and earliest Holocene (prior to 6360 ± 40 14C yr B.P.) was weathered in the middle Holocene under warmer, drier climate conditions, possibly correlated with the Hypsithermal and Altithermal Events of the eastern and southwestern United States, respectively. The glacial to interglacial climate shift is recorded by: (1) changes from a poorly drained landscape with fine-textured soil, characterized by high organic C and redoximorphic features related to Fe removal and concentration, to a well-drained, coarse-textured setting without gley and with significant argillic (Bt) horizon development; (2) changes from a high Zr and Ti silt-dominated parent material to locally derived, coarse fluvial gravels lower in Zr and Ti; (3) a shift from dominantly conifer and sedge pollen in the paleosol to a modern oak/hickory hardwood assemblage; and (4) a shift in ? 13C values of soil organic matter from -28‰ to -24‰ PDB, suggesting an ecosystem shift from cooler, C3-dominated flora to one that was mixed C3 and C4, but still predominantly composed of C3 plants. A root-restrictive placic horizon developed between the late Pleistocene silt paleosol and the overlying fluvial gravel because of the high permeability contrast between the two textures of soil materials. This layer formed a barrier that effectively isolated the Pleistocene paleosol from later Holocene pedogenic processes.

  18. Expansion of Magellanic Moorland during the late Pleistocene: Palynological evidence from northern Isla de Chiloé, Chile

    NASA Astrophysics Data System (ADS)

    Villagrán, Carolina

    1988-11-01

    The late Quaternary vegetation of northern Isla de Chiloé is inferred from palynological analysis of a section in the Río Negro drainage (42°03'S, 73°50'W). At ca. 30,500 yr B.P., maxima of Astelia and Donatia occurred, suggesting wetland development. From that time until ca. 27,000 yr B.P., steppe indicators such as Compositae/Gramineae dominated, suggesting drier conditions. After 27,000 yr B.P., the moorland shrub Dacrydium gradually increased, reaching a maximum by 18,000 yr B.P. At this time Astelia increased again, suggesting development of cushion bog during cold and wet conditions. The glacial-postglacial transition is characterized by a marked change from peaty sediments to clays, a decrease in the cushion bog flora, and the prevalence of Gramineae/ Compositae and swamp taxa. This vegetation prevailed until ca.7000 yr B.P. when forest taxa became dominant. The floristic pattern inferred from the pollen spectra of the Rio Negro section suggests that the late Pleistocene vegetation of Chiloé resembled modern Magellanic Moorland vegetation (52°-56°lat S). Based on climatic conditions presently associated with Magellanic Moorland, its occurrence in Chiloé at low elevations during the late Pleistocene implies a decrease in average temperature of at least 4°C and an increase in annual precipitation of at least 1500 mm.

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

    PubMed Central

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  1. Glacio-eustatic Control on Plio-Pleistocene Sedimentation Along the Northern California Ocean Margin

    NASA Astrophysics Data System (ADS)

    Green Nylen, N. M.; Zinniker, D. A.; Ingle, J. C.; Moldowan, J. M.

    2002-12-01

    Over the last 3.5 million years major climatic and tectonic changes have resulted in high frequency fluctuations in relative sea level adjacent to the northern California shoreline. A detailed record of these changes is preserved in two sedimentary sequences currently exposed along the coast: the neritic to nonmarine Merced Formation near San Francisco and the bathyal to neritic Rio Dell Formation north of Cape Mendocino. With the goal of deciphering the Plio-Pleistocene paleoenvironmental histories of these expanded ocean margin sequences, detailed stratigraphic sections were measured and described from the lower portion of the Merced Formation and from the Upper Rio Dell Formation. Samples are being analyzed for benthic foraminiferal assemblage, palynological assemblage, stable carbon and oxygen isotope composition of foraminiferal carbonate, and organic geochemistry. These data provide insight into paleo-water characteristics and paleobathymetry, global ice volume and climate, terrestrial and marine ecosystem composition and structure, specific sources of sedimentary organic material, the frequency and magnitude of wildfires on land during deposition, and redox conditions during early diagenesis. Variations in these climate and environmental proxies appear to demarcate glacial and interglacial cycles. These results generally support previous interpretations of glacio-eustatic control on the cyclicity of sedimentary facies within the Merced and Rio Dell formations. Ongoing work aims to explore the relationship between local and global climate proxies and to develop a more detailed model of northern California ocean margin sedimentary response to rapid Plio-Pleistocene sea-level change.

  2. Pleistocene refugia in an arid landscape: analysis of a widely distributed Australian passerine.

    PubMed

    Toon, Alicia; Mather, Peter B; Baker, Andrew M; Durrant, Kate L; Hughes, Jane M

    2007-06-01

    While many studies have documented the effect that glacial cycles have had on northern hemisphere species, few have attempted to study the associated effect of aridification at low latitudes in the southern hemisphere. We investigated the past effects that cyclic aridification may have had on the population structure and history of a widespread endemic Australian bird species, the Australian magpie (Gymnorhina tibicen). One thousand one hundred and sixty-six samples from across its native range were analysed for mitochondrial control region sequence variation and variation at six microsatellite loci. Analysis of mitochondrial control region sequence data indicated monophyletic clades that were geographically congruent with an eastern and western region. The contemporary distribution of east and west clades is nonoverlapping but in close proximity. Populations were estimated to have diverged in the Pleistocene around 36,000 years ago. The putative Carpentarian and Nullarbor arid barriers appear to be associated with the divergence between east and west mainland populations. Nested clade analysis indicated a signature of range expansion in the eastern region suggesting movement possibly inland and northward subsequent to the last period of aridity. The island population of Tasmania was of very recent origin, possibly since sea levels rose 16,000 years ago. Given the east-west structure, there was no congruence between morphology and recent history of this species indicating a lack of support for morphological taxa. Overall mitochondrial DNA and microsatellite variation suggest that increasing aridity and Pleistocene refugia played a role in structuring populations of the Australian magpie; however, the dispersal ability and generalist habitat requirements may have facilitated the movement of magpies into an almost contiguous modern distribution across the continent. This study supports the idea that Pleistocene aridification played an important role in structuring intraspecific variation in low latitudinal southern hemisphere avian species. PMID:17561911

  3. Pleistocene climate and biome evolution modulated at orbital, millennial, and centennial time scales

    NASA Astrophysics Data System (ADS)

    Hooghiemstra, H.

    2013-05-01

    For the northern Andes we present a multi-proxy record of environmental and climatic change at millennial- to century-scale resolution of the full Pleistocene. The composite record includes the 540-m Funza core (2250-27 ka; 1050-yr resolution) from the Bogotá basin (~4°N, 2550 m asl, 2100 samples), the 58-mcd core (284-27 ka; 60-yr resolution) from the Fúquene basin (~5°N, 2540 m asl 4700 samples), and the 12-m core (last 14 ka; 25-yr resolution) from the La Cocha basin (1°N, 2780 m asl, 550 samples). At high elevations climatic variability is mainly driven by the 41-kyr component of orbital forcing changing into a dominant 100-kyr frequency during the last 0.9 Ma. High elevation intraAndean environments are mainly driven by temperature and atmospheric pCO2 while changes in moisture is an important driver of the Andean environments on the Amazonian flank. The Pleistocene is reflected by MIS 87 to 1, the last interglacial-glacial cycle by D/O-cycles 28 to 1 (and during MIS 7-6 another 15 D/O-style cycles), and the Holocene shows many events with an acceleration of climate change. Repeatedly the subpáramo shrub biome is temporarily lost suggesting vertical migration of forest exceeded the maximum migration capacity of the subpáramo biome. Continuous changes in altitidinal vegetation distribution caused mountains above ~1500 m were alternatingly covered by different biomes. Forests reached only ~125 ka modern species compositions indicating most of the Pleistocene record shows nonanalog vegetation associations, however not preventing modern ecological ranges can be applied to reconstruct past environments. Comparison with Greenland, Antarctic and marine climate records is demonstrated.

  4. A mid-Pleistocene record of monsoonal precipitation in southwestern US, insights into the occurrence of drought

    NASA Astrophysics Data System (ADS)

    Cisneros Dozal, L.; Huang, Y.; Heikoop, J. M.; Fawcett, P. J.; Fessenden, J. E.; Anderson, R. S.; Meyers, P. A.; Larson, T. E.; Perkins, G.; Toney, J. L.; Werne, J. P.; Goff, F.; WoldeGabriel, G. W.; Allen, C. D.; Berke, M. A.

    2012-12-01

    Accurate model predictions of drought require an understanding of human-induced as well as natural climate variability. Paleoclimate records of precipitation changes over glacial/interglacial periods are essential to gain insights into natural variability. However there is a lack of such records for the southwestern US, particularly of quantitative changes. Here we present a mid-Pleistocene record of changes in monsoonal precipitation in northern New Mexico spanning interglacials MIS 13 and 11, glacial MIS 12 and onset of MIS 10. We based our estimates on the reconstructed ?D record of precipitation in lacustrine sediments from the Valles Caldera, New Mexico. The ?D record of precipitation holds similarities to the global benthic ?18O record and the ?D record from the Antarctica Dome C ice core during glacial periods and at the glacial-interglacial boundaries. However marked differences to the global records during each of interglacials MIS 13 and 11 suggests the influence of a regional climate forcing on precipitation changes in the region. We show that monsoonal precipitation (as the proportion of annual precipitation) declined repeatedly during these interglacials from a maximum of up to 90% to less than 30%, resembling glacial periods. The variability in monsoonal precipitation during interglacial periods resembles a response to insolation cycles and its intensity correlates to the land-sea surface temperature contrast (LSTC). However, near the highest temperatures over land, there seems to be a failure of the LSTC mechanism leading to severe aridity. Our results suggest that current human-induced warming may worsen a natural state of monsoon minima leading to severe drought and this superimposed variability should be considered in climate predictions.

  5. Late Pleistocene age and archaeological context for the hominin calvaria from GvJm-22 (Lukenya Hill, Kenya)

    PubMed Central

    Tryon, Christian A.; Crevecoeur, Isabelle; Faith, J. Tyler; Ekshtain, Ravid; Nivens, Joelle; Patterson, David; Mbua, Emma N.; Spoor, Fred

    2015-01-01

    Kenya National Museums Lukenya Hill Hominid 1 (KNM-LH 1) is a Homo sapiens partial calvaria from site GvJm-22 at Lukenya Hill, Kenya, associated with Later Stone Age (LSA) archaeological deposits. KNM-LH 1 is securely dated to the Late Pleistocene, and samples a time and region important for understanding the origins of modern human diversity. A revised chronology based on 26 accelerator mass spectrometry radiocarbon dates on ostrich eggshells indicates an age range of 23,576–22,887 y B.P. for KNM-LH 1, confirming prior attribution to the Last Glacial Maximum. Additional dates extend the maximum age for archaeological deposits at GvJm-22 to >46,000 y B.P. (>46 kya). These dates are consistent with new analyses identifying both Middle Stone Age and LSA lithic technologies at the site, making GvJm-22 a rare eastern African record of major human behavioral shifts during the Late Pleistocene. Comparative morphometric analyses of the KNM-LH 1 cranium document the temporal and spatial complexity of early modern human morphological variability. Features of cranial shape distinguish KNM-LH 1 and other Middle and Late Pleistocene African fossils from crania of recent Africans and samples from Holocene LSA and European Upper Paleolithic sites. PMID:25730861

  6. Late Pleistocene age and archaeological context for the hominin calvaria from GvJm-22 (Lukenya Hill, Kenya).

    PubMed

    Tryon, Christian A; Crevecoeur, Isabelle; Faith, J Tyler; Ekshtain, Ravid; Nivens, Joelle; Patterson, David; Mbua, Emma N; Spoor, Fred

    2015-03-01

    Kenya National Museums Lukenya Hill Hominid 1 (KNM-LH 1) is a Homo sapiens partial calvaria from site GvJm-22 at Lukenya Hill, Kenya, associated with Later Stone Age (LSA) archaeological deposits. KNM-LH 1 is securely dated to the Late Pleistocene, and samples a time and region important for understanding the origins of modern human diversity. A revised chronology based on 26 accelerator mass spectrometry radiocarbon dates on ostrich eggshells indicates an age range of 23,576-22,887 y B.P. for KNM-LH 1, confirming prior attribution to the Last Glacial Maximum. Additional dates extend the maximum age for archaeological deposits at GvJm-22 to >46,000 y B.P. (>46 kya). These dates are consistent with new analyses identifying both Middle Stone Age and LSA lithic technologies at the site, making GvJm-22 a rare eastern African record of major human behavioral shifts during the Late Pleistocene. Comparative morphometric analyses of the KNM-LH 1 cranium document the temporal and spatial complexity of early modern human morphological variability. Features of cranial shape distinguish KNM-LH 1 and other Middle and Late Pleistocene African fossils from crania of recent Africans and samples from Holocene LSA and European Upper Paleolithic sites. PMID:25730861

  7. Evolution of Mediterranean sea surface temperature: Evidence for an intensification of European glaciation at the Pliocene-Pleistocene boundary?

    NASA Astrophysics Data System (ADS)

    Herbert, T.; Ng, G.; Cleaveland, L. C.

    2009-12-01

    As the most “continental” of the ocean basins, the Mediterranean provides a unique climate archive for monitoring the history of the climate of southern Europe and northern Africa over time. It also lies in a strategic position to trace the evolution of the northern edge of the African monsoonal regime and the southward extent of glaciation during the Plio-Pleistocene ice ages. We report here results on sea surface temperature (SST) over the critical time of initial growth of the northern hemisphere ice sheets (3.3-2.7 Ma) and into the heart of the late Pliocene and early Pleistocene 41 kyr ice age regime. We present a continuous record of SST from 3.3-1.6 Ma, sampled at orbital resolution, from a composite of marine sections outcropping on land and from ODP Site 964, based on the alkenone unsaturation proxy. We find that SSTs are quite decoupled from the amount of alkenones in the sediment (“C37 total”). The C37 total record is paced throughout by the precessional cycle that determines the well-known episodes of sapropel formation in the eastern Mediterranean. In contrast, the SST record traces a larger-scale evolution in northern hemisphere climate. Prior to ~2.7 Ma, SST fluctuated predominantly at the precessional time scale. After the advent of northern hemisphere glaciation, SST followed a 41 kyr rhythm, in conjunction with the waxing and waning of northern hemisphere ice sheets during late Pliocene and early Pleistocene time. However, we detected a major increase in the amplitude of SST change at the Pliocene-Pleistocene boundary. Glacial coolings increase by 2-3oC at this time. As this change is not reflected in the marine oxygen isotope record, it seems to shed light on a regional increase in the influence of ice sheets on the glacial climate of the Mediterranean. We hypothesize that the extent of glaciation in northern and central Europe increased significantly at approximately the dawn of the Pleistocene.

  8. Glacial Evidence in the Andes Mountains, Peru

    NSDL National Science Digital Library

    Les Hasbargen

    This exercise brings the students to a landscape in the Peruvian Andes in Google Earth, where some alpine and niche glaciers still exist. Their task is to determine glacial extent in the past, and infer the kind of glacier(s) that had existed in the area. In order to answer the question, students need to identify the current ice extent, approximate the equilibrium line altitude based on dirty vs white ice (or the firn line, if visible) in summer time imagery, and document glacial landforms. They also need to recognize the correspondence between elevation and ice extent. Key words: glaciers, glacial landforms, Google Earth

  9. Evidence for minimal Pleistocene ice sheet elevation changes from the Shackleton Range, Weddell Sea Embayment, Antarctica

    NASA Astrophysics Data System (ADS)

    Hein, A.; Fogwill, C. J.; Sugden, D. E.; Bentley, M. J.; Stewart, F. M.; Kubik, P. W.; Kerr, A. R.; Foeken, J.

    2009-04-01

    Studies using cosmogenic nuclide analysis in Antarctica have the potential to provide unique insights into Pleistocene ice sheet fluctuations. Here we report combined geomorphological evidence and integrated cosmogenic isotope analysis (21Ne, 10Be and 26Al) from the Shackleton Range, part of the Transantarctic Mountains over looking the Weddell Sea. The Shackleton Range bounded to the north by the Slessor Glacier and to the south by the Recovery Glacier, provides the ideal locality to record the trajectory of long term ice sheet changes in this sector of Antarctica. These major outlet glaciers drain large areas of East Antarctica and occupy deep troughs extending well below current sea level. Which combine to contribute approximately one third of the total inflow to the Ronnie Filchner Ice Shelf. Past estimates of ice elevation at the Last Glacial Maximum in the Shackleton Range vary from <340 m to over 1000 m. The results of recent geomorphological mapping combined with the concentrations of cosmogenic isotopes from bedrock summits suggests minimal (<350m) ice sheet thickening at the Last Glacial Maximum in this sector of Antarctica. These results are important as they have direct implications for ice shelf / grounding line dynamics in the Weddell Sea Embayment.

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

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

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

  11. New evidence for mid-Pliocene-early Pleistocene glaciation in the northern Patagonian Andes Argentina

    SciTech Connect

    Stephens, G.C.; Evenson, E.B.; Rabassa, J.

    1985-01-01

    Mount Tronador is an extinct, glacially eroded strato-volcano located in the northern Patagonian Andes. With a summit elevation of 3556 m, Mount Tronador lies mostly above the present regional snowline (2000 m) and is largely covered by extensive snow fields and glaciers. The rocks of Mount Tronador comprise the Tronador Formation, a 2000 m thick sequence of interlayered basalts, andesites, ignimbrites, agglomerates, volcanic mudflows and lahars. This volcanic edifice is built on an erosional land surface of Tertiary age. Three K-Ar dates from the Tronador Formation yield radiometric ages of 3.2, 0.34 and 0.18 m.y. Striated clasts have been found included in several large glacial boulders derived from volcanic mudflows and lahars of the Tronador Fm. These boulders have been eroded by the Rio Manso Glacier and deposited in its Neoglacial moraines. The lahar boulders themselves contain pebbles and boulders of andesitic rocks in a vitroclastic matrix of pyroclastic origin. The striated clasts are well-rounded, shaped and polished, and the striations can be traced beneath the volcanic matrix. Thus these striated clasts represent a pre-Holocene cycle of glaciation. Mercer (1976) and Ciesielski (1982) document glaciations from southern Patagonia (2.1-3.5 m.y.) and from the southwestern Atlantic (2.1-3.9 m.y.) respectively. The discovery of striated clasts in lahars and mudflows of the Tronador Fm. indicates the existence of a heretofore undocumented Pliocene-Pleistocene glaciation in northern Patagonia.

  12. The Pleistocene archaeology and environments of the Wasiriya Beds, Rusinga Island, Kenya.

    PubMed

    Tryon, Christian A; Tyler Faith, J; Peppe, Daniel J; Fox, David L; McNulty, Kieran P; Jenkins, Kirsten; Dunsworth, Holly; Harcourt-Smith, Will

    2010-12-01

    Western Kenya is well known for abundant early Miocene hominoid fossils. However, the Wasiriya Beds of Rusinga Island, Kenya, preserve a Pleistocene sedimentary archive with radiocarbon age estimates of >33-45 ka that contains Middle Stone Age artifacts and abundant, well-preserved fossil fauna: a co-occurrence rare in eastern Africa, particularly in the region bounding Lake Victoria. Artifacts and fossils are associated with distal volcanic ash deposits that occur at multiple localities in the Wasiriya Beds, correlated on the basis of geochemical composition as determined by electron probe microanalysis. Sediment lithology and the fossil ungulates suggest a local fluvial system and associated riparian wooded habitat within a predominantly arid grassland setting that differs substantially from the modern environment, where local climate is strongly affected by moisture availability from Lake Victoria. In particular, the presence of oryx (Oryx gazella) and Grevy's zebra (Equus grevyi) suggest a pre-Last Glacial Maximum expansion of arid grasslands, an environmental reconstruction further supported by the presence of several extinct specialized grazers (Pelorovis antiquus, Megalotragus sp., and a small alcelaphine) that are unknown from Holocene deposits in eastern Africa. The combination of artifacts, a rich fossil fauna, and volcaniclastic sediments makes the Wasiriya Beds a key site for examining the Lake Victoria basin, a biogeographically important area for understanding the diversification and dispersal of Homo sapiens from Africa, whose pre-Last Glacial Maximum history remains poorly understood. PMID:20880570

  13. The Idea of Marine Exogenic Processes in Glacial and Contemporary Periods

    NASA Astrophysics Data System (ADS)

    Matishov, G. G.

    2009-04-01

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

  14. Pleistocene effects on North American songbird evolution

    PubMed Central

    Klicka, J.; Zink, R. M.

    1999-01-01

    Recent studies have used comparisons of mitochondrial DNA (mtDNA) sequence divergence among populations and species to test existing hypotheses about avian evolution during the Pleistocene epoch. In 1998, Avise and Walker concluded that the Pleistocene was an important time for avian evolution, including the initiation of phylogeographic separations and the completion of speciation events that began in the Pliocene. The study implied that these conclusions conflicted with the study, in 1997, by Klicka and Zink, which concluded that most species pairs previously thought to have originated in the past 250 000 years were much older. The two studies are complementary in the sense that Avise and Walker dealt primarily with phylogeographic (intraspecific) separations. Furthermore, Klicka and Zink concentrated on the inception of divergences whereas the Avise and Walker focused on the timing of the completion of speciation. To accomplish this, Avise and Walker analysed 'phylogroups', geographically coherent subsets of biological species in which mtDNA haplotypes exhibit reciprocal monophyly. The study used the average interphylogroup mtDNA distance (0.027), calibrated at 2% per million years, to conclude that speciation required on average one million years to complete. Hence, speciation events begun in the Late Pliocene would have been completed in the mid- to late Pleistocene. Although we appreciate the extended nature of the speciation process and Avise and Walker's insightful attempt to estimate its duration, we conclude that their value was an overestimate by a factor of two. In particular we question whether phylogroups can be used in the novel evolutionary role that Avise and Walker envisioned, because of the vagaries of taxonomic practices and lack of consensus regarding species concepts. To extend their analysis of intraspecific, phylogeographic separations, we compiled previously analysed and newly available data for divergence times for North American songbird (order Passeriformes) phylogroups. More than 80% were initiated at least one million years ago, which is inconsistent with the late Pleistocene origins model previously rejected by Klicka and Zink mentioned above. Although some divergence events can be traced to the late Pleistocene, the significance of the distribution must be judged with reference to a null model. Whether the Pleistocene was a profound time for avian phylogeographic differentiation is at present unknown.

  15. North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems.

    PubMed

    Luetscher, Marc; Boch, R; Sodemann, H; Spötl, C; Cheng, H; Edwards, R L; Frisia, S; Hof, F; Müller, W

    2015-01-01

    The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7?ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5-23.5?ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3?ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation. PMID:25724008

  16. North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems

    PubMed Central

    Luetscher, Marc; Boch, R.; Sodemann, H.; Spötl, C.; Cheng, H.; Edwards, R. L.; Frisia, S.; Hof, F.; Müller, W.

    2015-01-01

    The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7?ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5–23.5?ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3?ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation. PMID:25724008

  17. North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems

    NASA Astrophysics Data System (ADS)

    Luetscher, Marc; Boch, R.; Sodemann, H.; Spötl, C.; Cheng, H.; Edwards, R. L.; Frisia, S.; Hof, F.; Müller, W.

    2015-02-01

    The European Alps are an effective barrier for meridional moisture transport and are thus uniquely placed to record shifts in the North Atlantic storm track pattern associated with the waxing and waning of Late-Pleistocene Northern Hemisphere ice sheets. The lack of well-dated terrestrial proxy records spanning this time period, however, renders the reconstruction of past atmospheric patterns difficult. Here we present a precisely dated, continuous terrestrial record of meteoric precipitation in Europe between 30 and 14.7?ka. In contrast to present-day conditions, our speleothem data provide strong evidence for preferential advection of moisture from the South across the Alps supporting a southward shift of the storm track during the local Last Glacial Maximum (that is, 26.5–23.5?ka). Moreover, our age control indicates that this circulation pattern preceded the Northern Hemisphere precession maximum by ~3?ka, suggesting that obliquity may have played a considerable role in the Alpine ice aggradation.

  18. A fresh look at glacial foods

    USGS Publications Warehouse

    Colman, Steven M.

    2002-01-01

    Over the last 20 years, it has become clear that ice ages are characterized by glacial as well as climatic instability on millennial time scales. In his Perspective, Colman highlights two recent papers investigating the role of glacial meltwater and continental drainage in this instability. The results suggest a fundamental instability feedback between ocean circulation and ice sheet dynamics and provides an explanation for why instability was greatest at times of intermediate ice volume.

  19. Genetic Signals of Demographic Expansion in Downy Woodpecker (Picoides pubescens) after the Last North American Glacial Maximum

    PubMed Central

    Pulgarín-R, Paulo C.; Burg, Theresa M.

    2012-01-01

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

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

    PubMed

    Pulgarín-R, Paulo C; Burg, Theresa M

    2012-01-01

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

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

    USGS Publications Warehouse

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

    2013-01-01

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

  2. Late pleistocene passerine birds from Sonora, Mexico

    Microsoft Academic Search

    Jessica A. Oswald; David W. Steadman

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  4. Bahamian Pleistocene model for some Mississippian oolites

    SciTech Connect

    Bain, R.J. (Univ. of Akron, OH (USA))

    1989-08-01

    San Salvador Island, unlike most Bahamian islands, is a narrow isolated platform surrounded by deep ocean. Therefore, sedimentary deposits on San Salvador must be explained in terms of processes and settings on this narrow, isolated shelf. Pleistocene oolite occurs between Illinoian and Wisconsinan paleosols. Dune ridges of up to 120 ft are composed of Pleistocene cross-bedded oolitic grainstone, whereas interdunal deposits are bioclastic packstone and wackestone containing abundant Chione cancellata. In lower dunal deposits, bioclastic content increases and the degree of sorting decreases. A fenestral porosity zone occurs approximately 5 ft above present-day sea level. In several ridges, oolite drapes over older paleosol-capped bioclastic ridges. During the Sangamonian, sea water flooded the platform, however some remnant Aftonian ridges remained above sea level. As cold water from the surrounding deep ocean warmed on the shelf, ooids were generated and were washed onto beaches and blown into dunes. Remnant ridges restricted water movement and acted as nucleii for eolian ooid dunes. As sea level continued to rise, ooids were replaced by lagoonal bioclastic deposits. Ooid production was restricted to the swash zone along beaches resulting in the mixture of ooids and bioclastic sand in later Sangamonian deposits. Numerous Mississippian oolites display features similar to the Pleistocene oolite of San Salvador Island. Possible comparisons include thick lenses of Ste. Genevieve and Bangor limestones, paleosols in the Ste. Genevieve halo-shaped bodies of Greenbrier oolite, and the relationship of nearly all olites with bioclastic facies.

  5. Periodic floods from glacial Lake Missoula into the Sanpoil arm of glacial Lake Columbia, northeastern Washington.

    USGS Publications Warehouse

    Atwater, B.F.

    1984-01-01

    At least 15 floods ascended the Sanpoil arm of glacial Lake Columbia during a single glaciation. Varves between 14 of the flood beds indicate one backflooding every 35 to 55 yr. This regularity suggests that the floods came from an ice-dammed lake that was self-dumping, probably glacial Lake Missoula, Montana. -from Author

  6. Estimates of glacial Si and N dynamics in the Glacial Southern Ocean using Isotopic Mass balance

    Microsoft Academic Search

    C. P. Beucher; M. A. Brzezinski; X. Crosta; K. Matsumoto; J. Sarmiento

    2007-01-01

    Evaluating the role of the Southern Ocean in regulating glacial-interglacial atmospheric CO2 cycles remains a major issue in paleoceanography. The Silicic Acid Leakage Hypothesis purports that increases in the export of silicic acid from the Southern Ocean to low latitudes via Subantarctic Mode Water (SAMW) during glacial times enhanced diatom productivity over that of calcifying forms thus contributing to lower

  7. The middle Pleistocene Merced-2 and -3 sequences from Ocean Beach, San Francisco

    NASA Astrophysics Data System (ADS)

    Carter, R. M.; Abbott, S. T.; Graham, I. J.; Naish, T. R.; Gammon, P. R.

    2002-10-01

    The Merced Formation comprises a 2-km-thick shallow marine and non-marine succession that was deposited in a small transtensional basin along the San Andreas Fault during the late Pliocene to middle Pleistocene. The sediments dip between 10° and 80° to the northeast, and are locally disrupted by small faults. During tilting, the beds have been rotated into subparallelism with the San Andreas Fault zone, splays of which bound the outcrop belt of Merced sediments to both the southwest and northeast. The Merced Formation contains more than 20 transgressive-regressive sedimentary rhythms (cyclothems, or sequences) that are generally between 40 and 120 m thick, and which were deposited mostly during interglacial time, under the influence of rising, highstand and early falling sea levels. Sequences Merced-2 [units M1-N of Soc. Econ. Paleontol. Mineral., Field Guidebook 3 (1984) 1] and Merced-3 (units O-P), though in fault contact, comprise typical Plio-Pleistocene shallow water cyclothems. The Merced-2 Sequence is 22+ m thick, and comprises a sandy and shelly transgressive systems tract, including a basal Type A shellbed, an in situ Type B mid-cycle shellbed, and a highstand systems tract of massive siltstone. The Merced-3 Sequence is 47 m thick, and comprises a basal compound shellbed, a thin highstand systems tract siltstone, and a sand-rich regressive systems tract. The RST comprises distal shoreface sands with an abundant in situ molluscan fauna, and upper shoreface and back-beach trough cross-bedded sands and pebbly sands. The top of the Merced-3 cycle comprises a beach sand capped by a palaeosol and lignite (the "Beetle Bed"), which together mark the subaerial exposure of the site during the ensuing glacial sea-level lowstand. Analysis of 10Be across the Merced-3 Sequence shows major peaks, indicative of sedimentation starvation, in the basal transgressive systems tract shellbed and in the capping lignite of the Beetle Bed. Smaller 10Be peaks are associated with a shellbed that is inferred to represent winnowing at the foot of the shoreface, and with a minor exposure surface that delimits a small paracycle in the top of the sequence. Otherwise, 10Be abundances decline regularly across the Merced-3 Sequence, consistent with an increasing sedimentation rate as shoreface progradation, and regression, progressed. The character of cycles Merced-2 and Merced-3 respectively resembles the Seafield and Rangitikei sequence motifs described from similar Plio-Pleistocene sediments in New Zealand. The cycles are of mid-Pleistocene age, and were probably deposited during interglacial oxygen isotope stages 21 and 19, respectively.

  8. Glacial to Holocene dynamics of Indonesian precipitation - New insights from plant-wax dD off Northwest Sumatra

    NASA Astrophysics Data System (ADS)

    Niedermeyer, E. M.; Mohtadi, M.; Sessions, A. L.; Feakins, S. J.

    2012-12-01

    We used the stable hydrogen and stable carbon isotopic composition (dD and d13C, respectively) of terrestrial plant leaf waxes as a proxy for past rainfall variations over northwestern Indonesia. Our study site lies within the western boundary of the Indo-Pacific Warm Pool (IPWP), a key evaporative site for the global hydrologic cycle. At present, rainfall intensity in tropical Indonesia is influenced by the Pacific Ocean El Nino Southern Oscillation (ENSO) (see Kirono et al., 1999), the Indian Ocean Dipole (IOD) mode (Saji et al., 1999), and to some extend by the position of the Intertropical Convergence Zone (ITCZ) (e.g. Koutavas and Lynch-Stieglitz, 2005). Paleoclimate studies show that these systems have varied in the past, however, the impact of these changes on regional paelo-hydrology of Indonesia is yet unknown. We worked on marine sediment core SO189-144KL (1°09,300 N; 98°03,960 E) retrieved at 480 m water depth off Northwest Sumatra from the eastern Indian Ocean. Sediments consist of material from marine and terrestrial sources, and radiocarbon dating indicates an age of ~300 years at the core top and of ~24,000 years at the base. We used d13C and dD values of the n-C30 alkanoic acid as proxies for changes in vegetation composition (C3 vs. C4 plants) and rainfall variability on land, respectively. Values of d13C show only little variation and suggest persistent dominance of tropical trees throughout the past 24,000 years. Values of dD display distinct variability throughout the record, however, mean rainfall intensities during the late Last Glacial compare to those during the Holocene. This is in agreement with rather consistent vegetation at the study site but in sharp contrast with reconstructions of contemporaneous rainfall patterns at the nearby islands Borneo (Partin et al., 2007) and Flores (Griffiths et al., 2009), indicating multiple controls on regional hydrology of Indonesia. In combination with previous studies of late Pleistocene to Holocene ENSO and IOD variability, we further address the complex controls on Indonesian climate with emphasis of Holocene rainfall variability. References Griffiths, M.L., Drysdale, R.N., Gagan, M.K., Zhao, J.x., Ayliffe, L.K., Hellstrom, J.C., Hantoro, W.S., Frisia, S., Feng, Y.x., Cartwright, I., Pierre, E.S., Fischer, M.J., Suwargadi, B.W., 2009. Increasing Australian-Indonesian monsoon rainfall linked to early Holocene sea-level rise. Nature Geoscience 2, 636-639. Kirono, D.G.C., Tapper, N.J., McBride, J.L., 1999. Documenting Indonesian rainfall in the 1997/1998 El Nino event. Physical Geography 20, 422-435. Koutavas, A., Lynch-Stieglitz, J., 2005. Variability of the marine ITCZ over the eastern Pacific during the past 30,000 years: Regional perspective and global context. In: Bradley, R.S., Diaz, H.F. (Eds.), The Hadley Circulation: Present Past and Future. Springer, pp. 347-369. Partin, J.W., Cobb, K.M., Adkins, J.F., Clark, B., Fernandez, D.P., 2007. Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum. Nature 449, 452-455. Saji, N.H., Goswami, B.N., Vinayachandran, P.N., Yamagata, T., 1999. A dipole mode in the tropical Indian Ocean. Nature 401, 360-363.

  9. Glacial refugia in a maritime temperate climate: cicada (Kikihia subalpina) mtDNA phylogeography in New Zealand.

    PubMed

    Marshall, David C; Hill, Kathy B R; Fontaine, Kathryn M; Buckley, Thomas R; Simon, Chris

    2009-05-01

    Understanding the biological significance of Pleistocene glaciations requires knowledge of the nature and extent of habitat refugia during glacial maxima. An opportunity to examine evidence of glacial forest refugia in a maritime, Southern Hemisphere setting is found in New Zealand, where the extent of Pleistocene forests remains controversial. We used the mitochondrial phylogeography of a forest-edge cicada (Kikihia subalpina) to test the hypothesis that populations of this species survived throughout South Island during the Last Glacial Maximum. We also compared mitochondrial DNA phylogeographic patterns with male song patterns that suggest allopatric divergence across Cook Strait. Cytochrome oxidase I and II sequences were analyzed using network analysis, maximum-likelihood phylogenetic estimation, Bayesian dating and Bayesian skyline plots. K. subalpina haplotypes from North Island and South Island form monophyletic clades that are concordant with song patterns. Song divergence corresponds to approximately 2% genetic divergence, and Bayesian dating suggests that the North Island and South Island population-lineages became isolated around 761,000 years BP. Almost all South Island genetic variation is found in the north of the island, consistent with refugia in Marlborough Sounds, central Nelson and northwest Nelson. All central and southern South Island and Stewart Island haplotypes are extremely similar to northern South Island haplotypes, a 'northern richness/southern purity' pattern that mirrors genetic patterns observed in many Northern Hemisphere taxa. Proposed southern South Island forest habitat fragments may have been too small to sustain populations of K. subalpina, and/or they may have harboured ecological communities with no modern-day analogues. PMID:19434813

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

    PubMed Central

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

    2012-01-01

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

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

    PubMed

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

    2012-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  13. Timing of glaciation and last glacial maximum paleoclimate estimates from the Fish Lake Plateau, Utah

    NASA Astrophysics Data System (ADS)

    Marchetti, David W.; Harris, M. Scott; Bailey, Christopher M.; Cerling, Thure E.; Bergman, Sarah

    2011-01-01

    The High Plateaus of Utah include seven separate mountain ranges that supported glaciers during the Pleistocene. The Fish Lake Plateau, located on the eastern edge of the High Plateaus, preserves evidence of at least two glacial advances. Four cosmogenic 3He exposure ages of boulders in an older moraine range from 79 to 159 ka with a mean age of 129 ± 39 ka and oldest ages of 152 ± 3 and 159 ± 5 ka. These ages suggest deposition during the type Bull Lake glaciation and Marine Oxygen Isotope Stage (MIS) 6. Twenty boulder exposure ages from four different younger moraines indicate a local last glacial maximum (LGM) of ~ 21.1 ka, coincident with the type Pinedale glaciation and MIS 2. Reconstructed Pinedale-age glaciers from the Fish Lake Plateau have equilibrium-line altitudes ranging from 2950 to 3190 m. LGM summer temperature depressions for the Fish Lake Plateau range from -10.7 to -8.2°C, assuming no change in precipitation. Comparison of the Fish Lake summer temperature depressions to a regional dataset suggests that the Fish Lake Plateau may have had a slight increase (~ 1.5× modern) in precipitation during the LGM. A series of submerged ridges in Fish Lake were identified during a bathymetric survey and are likely Bull Lake age moraines.

  14. Glacial cycles as an allopatric speciation pump in north-eastern American freshwater fishes.

    PubMed

    April, Julien; Hanner, Robert H; Dion-Côté, Anne-Marie; Bernatchez, Louis

    2013-01-01

    Allopatric speciation may be the principal mechanism generating new species. Yet, it remains difficult to judge the generality of this process because few studies have provided evidence that geographic isolation has triggered the development of reproductive isolation over multiple species of a regional fauna. Here, we first combine results from new empirical data sets (7 taxa) and published literature (9 taxa) to show that the eastern Great Lakes drainage represents a multispecies suture zone for glacial lineages of freshwater fishes with variable levels of genetic divergence. Second, we performed amplified fragment length polymorphism analyses among four pairs of lineages. Results indicate that lineages with relatively deep levels of mtDNA 5' COI (barcode) sequence divergence (>2%) developed strong reproductive barriers, while lineages with lower levels of divergence show weaker reproductive isolation when found in sympatry. This suggests that a threshold of 2% sequence divergence at mtDNA could be used as a first step to flag cryptic species in North American freshwater fishes. By describing different levels of divergence and reproductive isolation in different co-occurring fishes, we offer strong evidence that allopatric speciation has contributed significantly to the diversification of north-eastern American freshwater fishes and confirm that Pleistocene glacial cycles can be viewed as a 'speciation pump' that played a predominant role in generating biodiversity. PMID:23206322

  15. Last Glacial loess in the conterminous USA

    USGS Publications Warehouse

    Bettis, E. Arthur, III; Muhs, Daniel R.; Roberts, Helen M.; Wintle, Ann G.

    2003-01-01

    The conterminous United States contains an extensive and generally well-studied record of Last Glacial loess. The loess occurs in diverse physiographic provinces, and under a wide range of climatic and ecological conditions. Both glacial and non-glacia lloess sources are present, and many properties of the loess vary systematically with distance from loess sources. United States' mid-continent Last Glacial loess is probably the thickest in the world, and our calculated mass accumulation rates (MARs) are as high as 17,500 g/m2/yr at the Bignell Hill locality in Nebraska, and many near-source localities have MARs greater than 1500 g/m2/yr. These MARs are high relative to rates calculated in other loess provinces around the world. Recent models of LastGlacial dust sources fail to predict the extent and magnitude of dust flux from the mid-continent of the United States. A better understanding of linkages between climate, ice sheet behaviour, routing of glacial meltwater, land surface processes beyond the ice margin, and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region.

  16. Neurodynamic oscillators

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  17. Preliminary Results from a Late Pleistocene to Holocene Paleoclimate Study of the Lake Sediment Cores, Northern New Mexico

    NASA Astrophysics Data System (ADS)

    Cedillo, D. N.; Brister, A. R.; LoPresti, C. A.; Maldonado, M.; Pitrucha, R. M.; West, C.; Martinez, E.; Lineline, J.; Petronis, M. S.

    2011-12-01

    We present the preliminary results from an integrated, paleoclimatic study of sediment cores collected from the Las Vegas National Wildlife Refuge (LVNWR) and surrounding region that bear on the late Pleistocene to Holocene paleoclimatic variations in northeastern NM. We collected sedimentologic, midge fossil, and rock magnetic data from sediment cores to characterize the materials, identify stratigraphic changes, document shifting lake levels, assess temperature changes, and infer paleoclimate conditions. Data from McAllister and Wallace Lake are encouraging and reveal depth dependent changes in fossil assemblages, grain size, and rock magnetic properties that we interpret to reflect climatic driven variations impacting the depositional system. We recognize three different types of chironomid subfamilies (Chironomini, Tanypodinae, and Orthocladiinae). Based on the fossil results, the water has been warm in the most recent years. Grain size distribution from the lower to upper core levels reveal that the amount of fine sand-sized sediment (0.125 mm diameter) increases while the amount of medium (0.25) to coarse (0.50) sand-sized sediment decreases implying that there may have been a reduction in stream energy and hence precipitation over the time period represented by the core. Bulk low-field magnetic susceptibility decreases by an order of magnitude from the surface to the base of the measured core suggesting a change in detrital magnetic influx into the lacustrian system. Curie point estimates indicate that the dominant magnetic mineral in all samples is cubic, low-Ti titanomagnetite phase. We postulate that concurrent with alpine glacial activity during the Pleistocene, the LVNWR and the transitional Great Plains region to the northeast was an expansive single lake or interconnected lake system, analogous to the Pleistocene lakes of the Estancia Basin (Lake Estancia) and the Tularosa Basin (Lake Otero) of central and southern NM. Following the end of glacial activity, these lacustrian systems shrank to their current condition of minor low-volume isolated lakes and numerous playas and pluvial bodies. We hypothesize that sediments from the LVNWR and surrounding playas contain an invaluable and untapped record of late Pleistocene to Holocene climatic change.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  19. Evidence of ice-stream stability during glacial cycles in the Weddell Sea sector, Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Sugden, D. E.; Hein, A. S.; Fogwill, C. J.

    2010-12-01

    It is widely accepted that ice streams draining the Antarctic Ice Sheet have thinned in response to ocean warming and sea-level rise since the Last Glacial Maximum (LGM). Indeed, the loss of ice mass from the Ross and Weddell Sea embayments may have contributed to the rise in sea level associated with Meltwater Pulse 1a. Here we present the results of a detailed cosmogenic-nuclide survey of the flanks of Slessor Glacier, an ice stream draining the East Antarctic Ice sheet flanking the Shackleton Range and flowing via the Filchner Ice Shelf into the Weddell Sea. Contrary to expectations, Slessor Glacier was no thicker than today during the LGM and probably during several prior glacial periods. We suggest that the Pleistocene stability of Slessor Glacier results from glacial erosion leading to self limiting ice-stream behaviour. In other words the location of the grounding line is pinned by the flank of the deep Thiel trough cut immediately offshore during earlier Antarctic glaciations, perhaps in the Miocene. This finding is a powerful limitation on the volume of ice that accumulated in the Weddell Sea embayment during the LGM.

  20. Glacial Lake Agassiz: Its northwest maximum extent and outlet in Saskatchewan (Emerson Phase)

    NASA Astrophysics Data System (ADS)

    Fisher, Timothy G.; Smith, Derald G.

    Six different lines of evidence support the hypothesis that glacial Lake Agassiz expanded an additional 70,000 km2 over that previously mapped in northwestern Saskatchewan and that the lake discharged out the northwestern (Clearwater) outlet, then through glacial Lake McConnell and Mackenzie River to the Arctic Ocean. Elevations of formerly unmapped (1) strandlines and (2) glaciolacustrine sediments between the previously mapped northwest limit of Lake Agassiz and the Clearwater-lower Athabasca spillway indicate that water extended 170 km farther northwest. Recently, mapped strandlines at elevations up to 60 m above the previously mapped extent of Lake Agassiz can be traced along (3) isobases to the mouth of the spillway. Based upon (4) six radiocarbon dates recovered from spillway flood deposits in the Athabasca River valley and its late Pleistocene delta, the (5) Clearwater spillway was cut at 9.9 ka BP. This date is synchronous with the initiation of the Emerson Phase (9.9 ka BP) in the southern Lake Agassiz basin and (6) coincides with the position of the Laurentide Ice Sheet at the Cree Lake Moraine (10 ka BP) along the northern margin of the lake. Following closure of the eastern outlets at the onset of the Emerson Phase, Lake Agassiz transgressed toward the northwest into the deglaciated and isostatically depressed glacial foreland in the Churchill River valley to an elevation of 490 m, the pre-flood elevation of the Churchill-Mackenzie drainage divide at the head of the Clearwater-lower Athabasca spillway. The Beaver River Moraine (an earthen drainage divide) was breached, resulting in lowering Lake Agassiz 52 m to a stable elevation at 438 m. The lake discharged 21,000 km3 of water into the Arctic Ocean that raised global sea level by 6 cm.

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

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

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

    PubMed Central

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

    2013-01-01

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

  3. Galactic oscillations

    NASA Technical Reports Server (NTRS)

    Miller, R. H.

    1991-01-01

    Long-lived oscillations that act like normal modes are described. The total kinetic energy is found to vary with time by amounts far in excess of the fluctuations expected from the virial theorem, and the variation shows periodic patterns that suggest oscillations. Experimental results indicate that oscillation amplitudes depend on the nature of the model. It is noted that it is difficult to answer questions about likely amplitudes in real galaxies with any confidence at the present time.

  4. The last interglacial-glacial transition as recorded in sediments from the deep Dead Sea basin

    NASA Astrophysics Data System (ADS)

    Neugebauer, I.; Brauer, A.; Schwab, M. J.; Waldmann, N.; Hadzhiivanova, E.; Frank, U.; Dulski, P.

    2013-12-01

    The Dead Sea and its Pleistocene precursors act as amplifier lakes of climate change affecting the eastern Mediterranean region. The ~460 m long sediment core 5017-1, retrieved from the deepest part of the lake, ideally mirrors the climate variability of the last approximately 200-250 ka. In the current study, we focus on the upper part of the last interglacial Samra Formation (~135-70 ka BP; Waldmann et al., 2009) and the transition into the last glacial Lisan Formation (~70-14ka BP; e.g. Bartov et al., 2002). Overlying the ca 45 m thick main salt layered sequence deposited during the last interglacial, the analyzed ca 30 m thick interval in core 5017-1 is characterized by a lower ~20 m thick interval of predominant alternating aragonite and detrital marl (aad) with occasional intercalations of mass movement deposits, accumulated during temporary humid climatic conditions. The entire sequence is topped by an upper ~10 m thick interval of predominantly layered massive halite, reflecting a dryer climate. Micro-facies analysis on large-scale petrographic thin sections, XRF element scanning, grain size and magnetic susceptibility measurements have been carried out on this interval for detailed and high-resolution characterization of the sediments and interpretation in terms of depositional processes and their value as paleoclimate proxies. The finding of a most likely millennial-scale dry interval just before the beginning of the stratigraphically defined humid Lisan interval falls in agreement with a previously identified depositional hiatus and associated erosional unconformity in the shallower areas outcropping at the margins of the lake (Stein, 2001). However, the deposition of glacial-like aad sediments prior to this pronounced dry period stands in contrast to previous analyses on outcrops (Waldmann et al. 2009). Investigating sediments from the deep Dead Sea basin will hence allow understanding and better deciphering the depositional processes in relation with climatic change during the last interglacial-glacial transition on centennial and millennial time-scales. References: Bartov, Y., Stein, M., Enzel, Y., Agnon, A., and Reches, Z., 2002. Lake Levels and Sequence Stratigraphy of Lake Lisan, the Late Pleistocene Precursor of the Dead Sea: Quaternary Research, v. 57, p. 9-21. Stein, M., 2001. The sedimentary and geochemical record of Neogene-Quaternary water bodies in the Dead Sea Basin - inferences for the regional paleoclimatic history: Journal of Paleolimnology, v. 26, p. 271-282. Waldmann, N., Stein, M., Ariztegui, D., and Starinsky, A., 2009. Stratigraphy, depositional environments and level reconstruction of the last interglacial Lake Samra in the Dead Sea basin: Quaternary Research, v. 72, p. 1-15.

  5. Phytologia (April 2007) 89 (1) 8 PLEISTOCENE INFRASPECIFIC EVOLUTION IN

    E-print Network

    Adams, Robert P.

    Phytologia (April 2007) 89 (1) 8 PLEISTOCENE INFRASPECIFIC EVOLUTION IN JUNIPERUS ASHEI BUCH. A new variety of Juniperus ashei, J. ashei Buch. var. ovata R. P. Adams is recognized from west Texas. KEY WORDS: Juniperus, J. ashei var. ovata, RAPDs, essential oils, Pleistocene distributions

  6. Principles of pleistocene stratigraphy, applied to the Gulf of Mexico

    Microsoft Academic Search

    R. H. Fillon; N. Healy-Williams; M. T. Ledbetter; R. C. Thunell; D. F. Williams

    1984-01-01

    This study of one of the world's major oil provinces is an examination of advances made in the past decade in high resolution stratigraphy of Pleistocene marine sediments. Topics covered include magnetostratigraphy, planktonic foraminiferal biostratigraphy, oxygen isotope stratigraphy, tephrochronology and a review and updating of terrestrial-marine correlations during the Pleistocene. The emphasis is on the Gulf of Mexico, but the

  7. Andrew S. Hein Chapter 4 Middle Pleistocene glaciation in

    E-print Network

    Andrew S. Hein 89 Chapter 4 Middle Pleistocene glaciation in Patagonia dated by cosmogenic in Patagonia dated by cosmogenic-nuclide measurements on outwash gravels. Earth and Planetary Science Letters measurements. #12;Middle Pleistocene glaciation in Patagonia dated by cosmogenic-nuclide measurements... 90

  8. Late Pleistocene braided rivers of the Atlantic Coastal Plain, USA

    Microsoft Academic Search

    David S Leigh; Pradeep Srivastava; George A Brook

    2004-01-01

    Infrared Landsat imagery (band 4) clearly reveals braided river patterns on late Pleistocene terraces of unglaciated rivers in the Atlantic Coastal Plain of the southeastern United States, a region that presently exhibits meandering patterns that have existed throughout the Holocene. These Pleistocene braided patterns provide a unique global example of river responses to late Quaternary climate changes in an unglaciated

  9. Ethological inferences on Pleistocene rhinoceroses of Europe

    Microsoft Academic Search

    Paul Mazza; A. Azzaroli

    1993-01-01

    The skulls of the five living species,Diceros bicornis (L.),Ceratotherium simum (Burchell),Rhinoceros unicornis L., R.sondaicus Desmarest andDicerorhinus sumatrensis (Fischer) are carefully examined to recognize the characters which may give evidence on specific life habits. The state of\\u000a these characters is analysed in the skulls of Pleistocene rhinocerotids of Europe, namelyStephanorhinus etruscus (Falconer),S. hundsheimensis (Toula),S. kirchbergensis (Jäger),S. hemitoechus (Falconer),Coelodonta antiquitatis (Blumenbach) andElasmotherium

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

    USGS Publications Warehouse

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

    2008-01-01

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

  11. Exploring hypsometry in glacial and fluvial environments

    NSDL National Science Digital Library

    Karen Gran

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

  12. Tracing glacial refugia of Triturus newts based on mitochondrial DNA phylogeography and species distribution modeling

    PubMed Central

    2013-01-01

    Introduction The major climatic oscillations during the Quaternary Ice Age heavily influenced the distribution of species and left their mark on intraspecific genetic diversity. Past range shifts can be reconstructed with the aid of species distribution modeling and phylogeographical analyses. We test the responses of the different members of the genus Triturus (i.e. the marbled and crested newts) as the climate shifted from the previous glacial period (the Last Glacial Maximum, ~21 Ka) to the current interglacial. Results We present the results of a dense mitochondrial DNA phylogeography (visualizing genetic diversity within and divergence among populations) and species distribution modeling (using two different climate simulations) for the nine Triturus species on composite maps. Conclusions The combined use of species distribution modeling and mitochondrial phylogeography provides insight in the glacial contraction and postglacial expansion of Triturus. The combined use of the two independent techniques yields a more complete understanding of the historical biogeography of Triturus than both approaches would on their own. Triturus newts generally conform to the ‘southern richness and northern purity’ paradigm, but we also find more intricate patterns, such as the absence of genetic variation and suitable area at the Last Glacial Maximum (T. dobrogicus), an ‘extra-Mediterranean’ refugium in the Carpathian Basin (T. cristatus), and areas where species displaced one another postglacially (e.g. T. macedonicus and western T. karelinii). We provide a biogeographical scenario for Triturus, showing the positions of glacial refugia, the regions that were postglacially colonized and the areas where species displaced one another as they shifted their ranges. PMID:23514662

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

    Microsoft Academic Search

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

    2004-01-01

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

  14. Glacial Tree Physiology: Using Stable Isotopes to Reconstruct Plant Responses to Environmental Change Since the Last Glacial Period

    E-print Network

    Gerhart Barley, Laci Manette

    2013-05-31

    years of low CO2 conditions. Oxygen isotope analysis was performed on glacial and modern Juniperus to reconstruct El Niño impacts in southern California over the last glacial period using a Bayesian model developed on low-elevation southern California...

  15. Glacial isostatic stress shadowing by the Antarctic ice sheet

    Microsoft Academic Search

    Erik R. Ivins; Thomas S. James; Volker Klemann

    2003-01-01

    Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to

  16. Glacial Meltwater Contirbutions to the Bow River, Alberta, Canada

    Microsoft Academic Search

    E. A. Bash; S. J. Marshall; E. C. White

    2009-01-01

    Assessment of glacial melt is critical for water resource management in areas which rely on glacier-fed rivers for agricultural and municipal uses. Changes in precipitation patterns coupled with current glacial retreat are altering the glacial contribution to river flow in areas such as the Andes of South America and the high ranges of Asia, as well as the Rockies of

  17. Central Michigan University's Glacial Park: Instruction through Landscaping.

    ERIC Educational Resources Information Center

    Pape, Bruce; Francek, Mark A.

    1992-01-01

    Describes the creation of a glacial park on a university campus. Suggests that the park is a useful instructional resource that helps students relate classroom material to outdoor phenomena by visualizing and identifying glacial landforms, recognizing their spatial relationships, and understanding how glacial features originated. Offers advice for…

  18. Inferring Glacial Dynamics From Temperate Glacimarine Grounding-Line Deposits

    Microsoft Academic Search

    B. A. Willems; R. D. Powell; E. A. Cowan; S. P. Gulick; L. D. Trusel

    2009-01-01

    Reconstruction of glacial dynamics from the glacimarine sediment record is dependent on our understanding of sedimentary and glacigenic processes. Development of positive relief grounding-line deposits in the marine record is a product of the rate of glacial retreat and the net sediment flux to the grounding-line deposystem. These deposits are consequently key for reconstructing past glacial dynamics. In temperate glacimarine

  19. The Middle Pleistocene human tibia from Boxgrove.

    PubMed

    Stringer, C B; Trinkaus, E; Roberts, M B; Parfitt, S A; Macphail, R I

    1998-05-01

    The Boxgrove tibia was discovered in 1993, associated with Middle Pleistocene fauna, and Lower Palaeolithic archaeology. The sediments at Boxgrove were deposited during a temperate interglacial episode and ensuing cold stage. They thus represent a wide range of modes and environments of deposition. Archaeological remains have been excavated from all the major stratigraphic units, giving a continuity of occupation for this part of southern England over a 10(4) year timescale, through markedly changing climatic regimes. The stratigraphic, archaeological and sedimentological contexts of the tibia are described, as well as its preservation and morphology. Measurements are given, with discussion of reconstructed bone length, and stature estimates. Comparative measurements are provided for fossil and recent human samples: the large dimensions of its diaphysis place the Boxgrove tibia near or beyond the upper size limits of the comparative samples, but its reconstructed length and estimated stature are less exceptional. The elevated robusticity of the specimen indicates exceptional diaphyseal strength and/or cold adapted body proportions paralleling those of the Neanderthals. Disagreement about the taxonomy of Middle Pleistocene hominids and lack of comparable fossil material make a specific assignment for the Boxgrove tibia problematic. The tibia can only definitely be assigned to non-modern Homo sp., with possible further reference to Homo cf. heidelbergensis (Schoetensack, 1908) on temporal and geographic grounds, if the validity of that species is accepted. PMID:9614636

  20. Impact of external forcing on the timing of MIS 7 glacial inception

    NASA Astrophysics Data System (ADS)

    Colleoni, Florence; Masina, Simona; Cherchi, Annalisa; Iovino, Dorotea

    2014-05-01

    MIS 7 glacial inception is characterised by particularly low GHG values (up to 224 ppm) and low sea-level (-10 to -20 mSLE). On the contrary, MIS 5 glacial inception has larger GHGs values (260 ppm) and a high sea-level (+1-5 m SLE). To understand what are the climate implication of MIS 7 low GHGs on inception processes, we use a coupled Atmosphere-Ocean General Circulation Model (AOGCM) to simulate the mean climate state of four time-slices at 115 kyrs BP, 125 kyrs BP, 229 kyrs BP and 236 kyrs BP, indicative of MIS 5 and MIS 7 pre-inceptions (K236 and K125, perihelion occurring during late summer) and glacial inceptions (K229 and K115, perihelion occurring during late winter). Our results show that in both Northern high and low latitudes, the structure of large scale circulation features is determined by the orbital configuration of the simulated time period while GHGs influence their intensity but only in the high latitudes. The simulated perennial snow cover, classical indicator of glacial inception, is more extended in K115 than in K125, which is in agreement with the orbital forcing of both experiments. However, for MIS 7, the perennial snow cover appears to be more extended in K236 than in K229 as a result of the particularly low GHGs values of this period, which is not what is expected from the orbital forcing. The climate teleconnections, ie. Arctic Oscillation, the ITCZ, the Hadley cell and the Walker circulation, reflecting the orbital configuration of each time slice, indicate K115 and K229 as glacial inception climates and K125 and K236 as pre-inception climates in both high and low latitudes. However, the large perennial snow cover accumulating in K236 contradicts these facts. We conclude that in our experiments, the impact of external forcing, and especially low GHGs values, on MIS 7 glacial inception is to anticipate the real glacial inception time to 236 kyrs BP instead of 229 kyrs BP.

  1. Investigation of glacial dynamics in lambert glacial basin using satellite remote sensing techniques

    E-print Network

    Yu, Jaehyung

    2006-04-12

    The Antarctic ice sheet mass budget is a very important factor for global sea level. An understanding of the glacial dynamics of the Antarctic ice sheet are essential for mass budget estimation. Utilizing a surface velocity field derived from...

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

    PubMed Central

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Hardy, Bruce L.

    2010-03-01

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

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

    PubMed Central

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

    2007-01-01

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

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

    PubMed

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

    2013-07-01

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

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

    PubMed Central

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

    2013-01-01

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

  7. Phylogeographic insights into cryptic glacial refugia

    E-print Network

    Provan, Jim

    recovered from fossilised material such as bones and wood. Problems with ancient DNA technology include low most notably in the Ice Ages [1]. The advance and retreat of the ice sheets through multiple glacial by standardising values to represent a single sample size, usually the smallest used. Ancient DNA (aDNA): DNA

  8. Gifts of the Glaciers Glacial Landforms

    E-print Network

    Cochran-Stafira, D. Liane

    Gifts of the Glaciers Glacial Landforms Gifts of the Glaciers Moving ice of glacier was responsible. Glaciers perform, in many ways, like an excavator. Although they can push weak material, like gravel, like it in place, like a ripper. And, like a bulldozer, glaciers are poor at eroding rock unless it is already

  9. Glacial Retreat The Great Lakes are Born

    E-print Network

    Cochran-Stafira, D. Liane

    Michigan by the retreating ice margin Carried water northward from the Erie basin. Formed Glacial Lake Most, if not all, of the basins of Lakes Michigan and Huron were deglaciated One large body of water for process come from the end moraines left behind The Saginaw lobe was thinner than the Lake Michigan

  10. Illustrated Glossary of Alpine Glacial Landforms

    NSDL National Science Digital Library

    Karen A Lemke

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

  11. Climate Change Affects Glacial Water Source

    NSDL National Science Digital Library

    ThinkTV

    This video discusses how the populous areas west of the Andes are largely desert and rely on glacial meltwater as an important source of fresh water. Because the Peruvian glaciers high in the Andes are in rapid retreat, scientists are monitoring the steadily shrinking glaciers and the impact of their reduction on local populations.

  12. Late glacial aridity in southern Rocky Mountains

    SciTech Connect

    Davis, O.K.; Pitblado, B.L. [Univ. of Arizona, Tucson, AZ (United States)

    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.

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

    PubMed

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

    2010-01-01

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

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

    SciTech Connect

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

    1993-03-01

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

  15. Glaciers, glacial lakes and glacial lake outburst floods in the Mount Everest region, Nepal

    Microsoft Academic Search

    Samjwal Ratna BAJRACHARYA; Pradeep MOOL

    2009-01-01

    Recent climate changes have had a significant impact on the high-mountain glacial environment. Rapid melting of glaciers has resulted in the formation and expansion of moraine-dammed lakes, creating a potential danger from glacial lake outburst floods (GLOFs). Most lakes have formed during the second half of the 20th century. Glaciers in the Mount Everest (Sagamartha) region, Nepal, are retreating at

  16. Antarctic Science 10 (3): 326-344 (7998) Antarctic glacial history since the Last Glacial Maximum: an

    E-print Network

    Ingólfsson, �lafur

    Antarctic Science 10 (3): 326-344 (7998) Antarctic glacial history since the Last Glacial Maximum, Universiq ofNewcastle, Callaghan, Newcastle, NSW 2308, Australia 6AntarcticCRC and SCAR Global Change: This overview examines available circum-Antarctic glacial history archives on land, related to developments

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

    USGS Publications Warehouse

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

    1999-01-01

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

  18. Potential flood volume of Himalayan glacial lakes

    NASA Astrophysics Data System (ADS)

    Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

    2013-07-01

    Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

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

    USGS Publications Warehouse

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

    2009-01-01

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

  20. Identification of Late Pleistocene Ice-Rafted Debris (IRD) on the New Jersey Shelf

    NASA Astrophysics Data System (ADS)

    Turner, R. J.; Christensen, B. A.; Wampler, J.; Uptegrove, J.; Goff, J.

    2004-12-01

    The purpose of this study is to evaluate the potential for ice-rafted debris (IRD) on the New Jersey shelf and develop procedures for IRD identification on a shelf environment using a variety of techniques to assess texture and age of the sediments. Pleistocene New Jersey shelf sedimentology is strongly defined by glacially driven sea level changes. IRD and its provenance may be identified on a shelf environment through analysis of grain size distribution, heavy mineral content (higher % suggests non-fluvial processes), mineralogical point counts (anomalous mineralogy indicates distal source), isotopic dating methods (age value determination to narrow down potential source rocks), and surface texture analysis (specific glacial transport features). IRD must be differentiated from sediment derived from the NJ bedrock. Likely sources for IRD include the bedrock of Maine and of the southeastern Canadian Shield. Duncan and Goff (2001) reported iceberg grounding along the NJ shelf. IRD is typically identified in the deep sea through anomalously large grain size within pelagic mud, but different methods are needed for the shelf, where regressive shoreline processes, subaerial exposure, fluvial downcutting, and deposition and reworking during transgression have influenced the sediment composition found today. We analyzed grab samples in or near the features believed to be iceberg scour marks and downcore samples from recent Geoclutter drilling in the same area. The coarse grain size fractions of shelf samples were separated by phi classes before heavy mineral separation methods were employed. Initial analyses show high percentages of heavy minerals in the 2 phi and 3 phi size fractions, consistent with past NJ shelf studies. Hornblende grains were hand-picked from select samples for K-Ar dating, providing age values of about 0.96 ± 0.03 Ga for three sites within iceberg scours. Mineral content of each size fraction is determined by point count. Qualitative assessment of surface textures of select grains as seen with a Hitachi S-2500 SEM is useful in interpretation of source and transport.

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

    PubMed Central

    Pfenninger, Markus; Posada, David; Magnin, Frédéric

    2003-01-01

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

  2. Pleistocene isolation in the Northwestern Pacific marginal seas and limited dispersal in a marine fish, Chelon haematocheilus (Temminck & Schlegel, 1845).

    PubMed

    Liu, Jin-Xian; Gao, Tian-Xiang; Wu, Shi-Fang; Zhang, Ya-Ping

    2007-01-01

    The Northwestern Pacific has a unique tectonic and geographical history with several marginal seas separating Asia from the Pacific Ocean. During low sea level periods of Pleistocene glaciations, populations might have been isolated in three marginal seas: the Sea of Japan, East China Sea and South China Sea. Following postglacial sea level rise, we would expect the populations isolated in the three regions to have been homogenized by high dispersal potential. To assess these hypotheses, we explore the intraspecific phylogeographical patterns in redlip mullet, Chelon haematocheilus. Fragments of 435 bp at the 5' end of mitochondrial DNA control region were sequenced for 272 individuals from nine localities over most of the species' range. Three distinct lineages were detected, which might have diverged in the three marginal seas during Pleistocene low sea levels. Contrary to homogenization expectation, there were strong differences in the geographical distribution of the three lineages. Analyses of molecular variance and the population statistic Phi(ST) also revealed significant genetic structure among populations of the three marginal seas. These results indicate that gene flow in Chelon haematocheilus is far more restricted spatially than predicted by the potential dispersal capabilities of this species. The lack of phylogeographical structure in East China Sea may reflect a recent range expansion after the last glacial maximum and insufficient time to attain migration-drift equilibrium. PMID:17217344

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

    USGS Publications Warehouse

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

    2008-01-01

    Various lines of evidence support conflicting interpretations of the timing, abruptness, and nature of climate change in the Great Plains during the Pleistocene-Holocene transition. Loess deposits and paleosols on both the central and northern Great Plains provide a valuable record that can help address these issues. A synthesis of new and previously reported optical and radiocarbon ages indicates that the Brady Soil, which marks the boundary between late Pleistocene Peoria Loess and Holocene Bignell Loess, began forming after a reduction in the rate of Peoria Loess accumulation that most likely occurred between 13.5 and 15 cal ka. Brady Soil formation spanned all or part of the B??lling-Aller??d episode (approximately 14.7-12.9 cal ka) and all of the Younger Dryas episode (12.9-11.5 cal ka) and extended at least 1000 years beyond the end of the Younger Dryas. The Brady Soil was buried by Bignell Loess sedimentation beginning around 10.5-9 cal ka, and continuing episodically through the Holocene. Evidence for a brief increase in loess influx during the Younger Dryas is noteworthy but very limited. Most late Quaternary loess accumulation in the central Great Plains was nonglacigenic and was under relatively direct climatic control. Thus, Brady Soil formation records climatic conditions that minimized eolian activity and allowed effective pedogenesis, probably through relatively high effective moisture. Optical dating of loess in North Dakota supports correlation of the Leonard Paleosol on the northern Great Plains with the Brady Soil. Thick loess in North Dakota was primarily derived from the Missouri River floodplain; thus, its stratigraphy may in part reflect glacial influence on the Missouri River. Nonetheless, the persistence of minimal loess accumulation and soil formation until 10 cal ka at our North Dakota study site is best explained by a prolonged interval of high effective moisture correlative with the conditions that favored Brady Soil formation. Burial of both the Brady Soil and the Leonard Paleosol by renewed loess influx probably represents eolian system response that occurred when gradual change toward a drier climate eventually crossed the threshold for eolian activity. Overall, the loess-paleosol sequences of the central and northern Great Plains record a broad peak of high effective moisture across the late Pleistocene to Holocene boundary, rather than well-defined climatic episodes corresponding to the B??lling-Aller??d and Younger Dryas episodes in the North Atlantic region. ?? 2008 Elsevier Ltd. All rights reserved.

  4. Relations between of the Pleistocene glaciations and karstification processes on Velebit Mt. (Croatia)

    NASA Astrophysics Data System (ADS)

    Bocic, Neven

    2014-05-01

    Velebit is the Dinaric karst mountain. It is located in Croatia and extends to a length of 145 km along the northern part of the eastern coast of the Adriatic Sea. The highest peak is 1757 m high. It is mostly made of well karstified carbonate rocks (limestone, dolomite and carbonate clastic rocks). Glaciation of this region has long attracted researchers. Studies have shown that a large part of the area was affected by the Pleistocene glaciation. These results have prompted questions about the impact of glaciation on the development of karst, especially underground karst formations - caves in this area. This work explores the impact of Pleistocene glaciations on karst development in the northern and central Velebit. Special emphasis is given to the research on the impact of glaciation on the development and morphology of caves, which is analyzed in few examples. The main methods used are geomorphological mapping and speleological research. Also, some sedimentological methods were used and 14C dating of the flowstone crust was provided. Studies on some sites are already well advanced while in some localities are only just begun. In the area of Jezera (Lakes in Croatian, northern part of the mountain) we noticed that the moraine material affects the appearance of the small occasional streams with cutting small torrents and surface erosion processes. In areas where the moraine cover is thinner or missing rekarstification of bedrock is visible, and occasional short streams sinking at contact zone of the moraine material and bedrock. In glacial valley Lomska duliba is the Ledena jama (Ice cave), 536 meters deep characterized by ice accumulation thicker than 50 m. During this study we have been mapped moraine forms along the valley and found that the same material plugs parts of the pit which led to its further dynamics. Great influence on the development of glaciation surface and underground karst forms was studied in Štirova?a (middle Velebit area). Here is the 351 m long cave with lot of erosional remnants of the fluvioglacial deposits that were fully filed much of the known part of the cave. It is concluded that the Pleistocene glaciation had multiple effects on the development of karst in this area. Moraine deposits, relatively impermeable, promote local development of surface runoff and erosion. In this way, they temporarily slowing the process of karstification below, but because of the contact process they accelerated karstification along their edges. This material can also be accumulated in the caves, directly or after resedimentation as fluvioglacial material. In this way fills the underground channels and then reduce and hinder drainage function of these channels.

  5. The Last Glacial Maximum and Termination in the Torres del Paine Region, Southern South America

    NASA Astrophysics Data System (ADS)

    Garcia, J.; Hall, B. L.; Kaplan, M. R.; Vega, R. M.; Binnie, S.; Gómez, G.; Santana, F.

    2012-12-01

    Deciphering the timing, structure and termination of the local last glacial maximum (LGM) throughout Patagonia (42-55 S) remains one of the key unsolved paleoclimate questions in Quaternary sciences. During the last glaciation, the Patagonian ice sheet formed one ice body along the Patagonian Andes (42-55 S) in southern South America, but previous work has revealed different spatiotemporal ice dynamics along the eastern and western ice margins. The Patagonian Andes is the only landmass that exists at this latitude confronting the southern westerly wind belt, which seems to have played a key role in past glacial and climate changes. Therefore, reconstructing southern Andes glacier history constitutes a key element for understanding the causes of glaciations in the Southern Hemisphere. Major progress has been made to document the local Late-Pleistocene glacier history, particularly in response to recent application of exposure-cosmogenic dating technique in the region, although only sparse well-dated paleoclimate records exist in this vast area. LGM moraine-based records in south Patagonia (~48-55 S) have been developed for the Strait of Magellan area, where full glacial conditions seems to have occurred between ~28.0 - 17.5 ka. Despite that these data seem to confirm previous glacial chronologies developed in north Patagonia and the Chilean Lake District (40-42 S), recent works in Torres del Paine and Última Esperanza basins (50-51 S), suggest that glacial maximum conditions may have occurred earlier (i.e., during Marine Isotope Stage 3) and that ice extent could have been twice the size of previously thought. Here, we discuss paleoclimatological implications from our 10Be and 26Al-dating program of moraines in the Torres del Paine region in southern Patagonia. We focused our efforts in the previously undated Río de las Viscachas (RV) I and II moraines, which occur distal to the late-glacial TDP II, III and IV moraines that enclose present lake bodies at the Torres del Paine National Park (e.g., Lagos del Toro, Sarmiento and Azul). RV moraines parallel each other and can be tracked continuously for several km along the southern slope of Sierra Contreras in Chile. To the east, in present day Argentina, they constitute concentric wide moraine arcs that include tens of frontal moraine ridges. We collected boulders embedded in the relatively sharp RV I and II moraines for 10Be and 26Al cosmogenic-exposure dating to reconstruct the last glacial period. We also sampled and dated cobbles from the main glaciofluvial plain grading to the outer RV I landforms, to crosscheck with the cosmogenic ages obtained from boulders embedded at moraine tops. Additionally, we present new 10Be cosmogenic ages from boulders in TDP I and TDP IV moraines at Lago del Toro basin, which help us to define the structure of the local termination.

  6. Evolutionary history of the Maltese wall lizard Podarcis filfolensis: insights on the ‘Expansion–Contraction’ model of Pleistocene biogeography.

    PubMed

    Salvi, Daniele; Schembri, Patrick J; Sciberras, Arnold; Harris, D James

    2014-03-01

    The expansion–contraction (EC) model predicts demographic and range contraction of temperate species during Pleistocene glaciations as a consequence of climate-related habitat changes, and provides a paradigm for explaining the high intraspecific diversity found in refugia in terms of long-term demographic stability. However, recent evidence has revealed a weak predictive power of this model for terrestrial species in insular and coastal settings. We investigated the Pleistocene EC dynamics and their evolutionary consequences on temperate species using the Maltese archipelago and its endemic lizard Podarcis filfolensis as a model system. The evolutionary and demographic history of P. filfolensis as inferred from mitochondrial and nuclear sequences data does not conform to the EC model predictions, supporting (i) demographic and spatial stability or expansion, rather than contraction, of the northern and southern lineages during the last glacial period; and (ii) a major role for allopatric differentiation primed by sea-level dynamics, rather than prolonged demographic stability, in the formation of the observed genetic diversity. When combined with evidence from other Mediterranean refugia, this study shows how the incorporation of Pleistocene sea-level variations in the EC model accounts for a reverse demographic and range response of insular and coastal temperate biotas relative to continental ones. Furthermore, this cross-archipelago pattern in which allopatric diversity is formed and shaped by EC cycles resembles that seen between isolated populations within mainland refugia and suggests that the EC model, originally developed to explain population fluctuations into and out-of refugia, may be appropriate for describing the demographic and evolutionary dynamics driving the high genetic diversity observed in these areas. PMID:24716210

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

    NASA Astrophysics Data System (ADS)

    Buckley, Francis

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-08-01

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

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

    PubMed Central

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

    2013-01-01

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

  10. Post-glacial coast development and human settling of the North European Ice Marginal Landscape (IML)

    NASA Astrophysics Data System (ADS)

    Bregman, I. Kant Baltic Federal State University, Kaliningrad, Russia, E. P. H.; Netherlands, Utrecht University, the; Druzhinina, I. Kant Baltic Federal State University, Kaliningrad, Russia, O. A.

    2012-04-01

    In North Europe, in the Ice Marginal Landscapes (IML) from the Netherlands to Estonia, human settling is in the Late-Pleistocene - Holocene strongly influenced by post-glacial relative coast development(MESO, 2010; SINCOS, 2002-2009; Machu, 2006-2009, IGCP project 346, CoPaF, 2009-2012) and glacio-isostasy. Geological processes like updoming and tectonic block displacements not only influenced sedimentation of river systems in delta's (e.g. Cohen, 2003), but influenced coastal development and human settling too in the North Sea area (e.g. Peeters, 2009; Hijma e.a., 2011) the Wadden areas (e.g. de Langen, 2011) and lagoons (e.g. Druzhinina, 2010). An overview of shoreline development at the distal side of the Late Glacial forbulge related to glaciological and geophysical processes however does not exist and coastal development models are also not correlated with human settling. Our project( 2012 - 2018) has the aim to describe the influence of shifting coast on the way of settling and living of ancient man in the IML. The main questions to be answered are as follow: (i) Is coast development influenced by glaciations a result of interaction between endo- and exogenic (glaciological-, geological-, and geophysical) forces in general and at the local scale of morphological elements? (ii) Did ancient man adept to changes in natural circumstances and what did that mean for his social behavior and economy? (iii) Were forms of human society and economy in the IML primarily dependent on the natural environment with regard to geophysical and geological differences and related to post-glacial response of the earth crust? Detailed integrated studying of "key-areas", with attention to deep geology, will allow to get new insight of the impact of post-glacial shoreline changes and history of man on the coast in the IML with focus on his past (history of relations) and future (impact of climate change. The project is an international project, with participation of institutes all over the IML.

  11. Variability of Quaternary glacial erosion rates - A global perspective with special reference to the Eastern Pyrenees

    NASA Astrophysics Data System (ADS)

    Delmas, Magali; Calvet, Marc; Gunnell, Yanni

    2009-03-01

    Glaciers erode bedrock but are also efficient conveyors of debris supplied during a cycle of glaciation by processes other than basal erosion. In this dual capacity as both an eroding and a transporting agent lies the ambiguity of 'glacial erosion' as a geomorphic process, with implications for methods of measuring the removal of rock mass by glaciers in the geological past, and for interpreting what exactly the consequences have been on topography and elevation change. A global review of ˜400 Quaternary glacial denudation rates estimated from five different measurement techniques provides values ranging between 10 -4 and 10 mm yr -1. We investigate the causes of such wide variability by examining the respective influences of environmental setting and methodological bias. A reference frame chosen for assessing these issues is the Massif du Carlit (Pyrenees, France), where a quantified mass balance of the well preserved glacial, periglacial and paraglacial deposits was made possible by detailed geomorphological mapping and terrestrial cosmogenic nuclide dating of extant erosional and depositional landform sequences. Resulting age brackets helped to define three main episodes of ice-cap growth and decline, each characterized by a volume of debris and a mappable source area. Erosion rates were expressed in two ways: (i) as spatially averaged denudation rates ( D) during the successive stages of glacial advance to the line of maximum ice extent (MIE), post-MIE ice recession, and Lateglacial cirque readvance, respectively; and (ii) as cirque-wall recession rates ( R) where moraine facies criteria indicated a supraglacial provenance of debris. Results indicate low erosion ( D ? 0.05 mm yr -1) during the ice advance phase, probably because of thin or passive ice covering the low-gradient subglacial topography that occurs just above the late Pleistocene equilibrium line altitude (2.2-2.4 km). Erosion rates peaked ( D ? 0.6 mm yr -1 and R ? 2.4-4.5 mm yr -1) during the main transition to ice-free conditions, when deglacial debuttressing promoted the rapid response of freshly exposed slope systems to new equilibrium conditions in the steep crest zone. Lateglacial D- and R-values declined to 0.2-0.3 mm yr -1, with indications of spatially variable R controlled by lithology. In this environment glaciers overall behaved more as conveyors of debris supplied by supraglacial rock exposures in the mountain crest zone than as powerful modifiers of subglacial topography. This explains the widespread preservation of deep, in situ preglacial weathering profiles on relict Cenozoic land surfaces in the deglacierized part of the Eastern Pyrenees. When plotted on the global data set analyzed and discussed in the review, the East Pyrenean erosion rates stand out as being amongst the lowest on record.

  12. Power oscillator

    DOEpatents

    Gitsevich, Aleksandr (Montgomery Village, MD)

    2001-01-01

    An oscillator includes an amplifier having an input and an output, and an impedance transformation network connected between the input of the amplifier and the output of the amplifier, wherein the impedance transformation network is configured to provide suitable positive feedback from the output of the amplifier to the input of the amplifier to initiate and sustain an oscillating condition, and wherein the impedance transformation network is configured to protect the input of the amplifier from a destructive feedback signal. One example of the oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to match the driving frequency of the oscillator to a plurality of tuning states of the lamp.

  13. Pleistocene Homo sapiens from Middle Awash, Ethiopia.

    PubMed

    White, Tim D; Asfaw, Berhane; DeGusta, David; Gilbert, Henry; Richards, Gary D; Suwa, Gen; Howell, F Clark

    2003-06-12

    The origin of anatomically modern Homo sapiens and the fate of Neanderthals have been fundamental questions in human evolutionary studies for over a century. A key barrier to the resolution of these questions has been the lack of substantial and accurately dated African hominid fossils from between 100,000 and 300,000 years ago. Here we describe fossilized hominid crania from Herto, Middle Awash, Ethiopia, that fill this gap and provide crucial evidence on the location, timing and contextual circumstances of the emergence of Homo sapiens. Radioisotopically dated to between 160,000 and 154,000 years ago, these new fossils predate classic Neanderthals and lack their derived features. The Herto hominids are morphologically and chronologically intermediate between archaic African fossils and later anatomically modern Late Pleistocene humans. They therefore represent the probable immediate ancestors of anatomically modern humans. Their anatomy and antiquity constitute strong evidence of modern-human emergence in Africa. PMID:12802332

  14. Ice flow models and glacial erosion over multiple glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological timescales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model yields erosion rates that vary spatially and by almost an order of magnitude from those of the SIA model. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered area that are greater than 30% those of the SIA model, again with larger differences for temperate ice. Over multiple glaciations and long timescales, these results suggest that higher-order glacial physics should be considered, particularly in temperate, mountainous settings.

  15. Ice flow models and glacial erosion over multiple glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological time scales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes-flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model has a larger impact on the erosion rate, with variations of almost an order of magnitude. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered that are greater than 30%, again with larger differences for temperate ice. Over multiple glaciations and long-time scales, these results suggest that consideration of higher-order glacial physics may be necessary, particularly in temperate, mountainous settings.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  18. Pollen analysis of a late pliocene and early pleistocene section from the Gubik Formation of Arctic Alaska

    USGS Publications Warehouse

    Nelson, R.E.; Carter, L.D.

    1985-01-01

    A 14-m-thick section of marine and nonmarine sediments of the Gubik Formation of northern Alaska, exposed in bluffs near Ocean Point on the Colville River, has been studied by means of pollen analysis. Pollen from the marine sediments, of probable late Pliocene age, records a boreal forest of spruce and birch with minor amounts of alder in the adjacent terrestrial vegetation. Pine and perhaps true fir were probably at or near their northern limit here, but hemlocks and hardwoods were absent. The suggested environment for the Arctic Slope during the time represented by the marine sediments is similar to that of present-day Anchorage. Pollen floras from the overlying fluvial strata, of early or middle Pleistocene age, record predominantly herbaceous taxa indicating tundra conditions probably more severe than those of the present day. These deposits were most likely contemporaneous with glacial conditions in the Brooks Range to the south. Pollen of woody taxa (spruce, alder, birch, heaths) is rare through most of the section, although birch and alder percentages similar to those found in modern river sediments indicate an interstadial or interglacial warming in midsection. Inland climates during glacial episodes may have been similar to those of the present Arctic coast. ?? 1985.

  19. late Pleistocene and Holocene pollen record from Laguna de las Trancas, northern coastal Santa Cruz County, California

    USGS Publications Warehouse

    Adam, David P.; Byrne, Roger; Luther, Edgar

    1981-01-01

    A 2.1-m core from Laguna de las Trancas, a marsh atop a landslide in northern Santa Cruz County, California, has yielded a pollen record for the period between about 30,000 B. P. and roughly 5000 B. P. Three pollen zones are recognized. The earliest is characterized by high frequencies of pine pollen and is correlated with a mid-Wisconsinan interstade of the mid-continent. The middle zone contains high frequencies of both pine and fir (Abies, probably A. grandis) pollen and is correlated with the last full glacial interval (upper Wisconsinan). The upper zone is dominated by redwood (Sequoia) pollen and represents latest Pleistocene to middle Holocene. The past few thousand years are not represented in the core. The pollen evidence indicates that during the full glacial period the mean annual temperature at the site was about 2°C to 3°C lower than it is today. We attribute this small difference to the stabilizing effect of marine upwelling on the temperature regime in the immediate vicinity of the coast. Precipitation may have been about 20 percent higher as a result of longer winter wet seasons.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  1. The circumboreal tundra-taiga interface: late Pleistocene and Holocene changes.

    PubMed

    Payette, S; Eronen, M; Jasinski, J J P

    2002-08-01

    Creating a global perspective on past treeline changes is problematic due to the varying methods and definitions used. A general lack of a detailed description of the modern treeline position and vegetation complicates any comparative analysis of the magnitude of the most important changes. However, one seemingly common factor in most regions was an extremely rapid dispersal of trees when climate warmed drastically from full glacial conditions. Most Arctic treelines reached their northernmost positions in the early Holocene and receded to present positions starting at about 5.8 ka. The early occupation of the northernmost sites in ice-free and early deglaciated areas was possible because of the close proximity of invading trees in nearby glacial refugia, particularly in Fennoscandia and northern Russia. In Canada, the Northwest Territories and Quebec-Labrador were out of phase with this general trend due to their late deglaciation. However, even here colonization was rapid, indicating that the tree species were present adjacent to the glaciers. Following this trend and based on the present evidence, we propose a scenario of a continuous but modest occupation of eastern Beringia by spruce during the late-Pleistocene instead of an exceptionally rapid spread of conifers from the glacial refugium south of the Laurentide ice sheet (2000 to 3000 km in about 200 years), which typically has been assumed. Macrofossil evidence of scattered occurrences of "exotic species" (for instance Siberian larch in central Sweden) far from their natural range limits in the early Holocene highlight the disparity between pollen and macrofossil analyses. It questions the validity of assigned pollen percentages to indicate the presence of a species within a region as these species were not observed in the pollen record. Thus, it is likely that trees were present at any given site well before the rise in pollen abundance. There is still a large potential to improve our knowledge about the environmental history of the circumboreal treeline areas. In particular, future research should concentrate not only on patterns of species displacement, but on finding the factors, apart from climate, which cause treeline shifts. PMID:12374054

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  3. Post-glacial expansion into the Paleozoic Plateau: evidence of an Ozarkian refugium for the Ozark minnow Notropis nubilus (Teleostei: Cypriniformes).

    PubMed

    Berendzen, P B; Dugan, J F; Gamble, T

    2010-10-01

    Genetic variation was examined within the Ozark minnow Notropis nubilus using complete mtDNA cytochrome b gene sequences from 160 individuals representing 30 localities to test hypotheses on the origin of the distribution. Phylogenetic analyses revealed three strongly supported clades of haplotypes consistent with geographic distributions: a clade from the Western Ozarks, a clade from the Southern Ozarks and a clade from the Northern Ozarks and upper Mississippi River basin. The estimated mean ages of these clades indicated that they diverged during pre-Illinoian glacial cycles extending from the late Pliocene into the early Pleistocene. Results of demographic analyses based on coalescent approaches supported the hypothesis that the Paleozoic Plateau was not a refugium for N. nubilus during periodic glacial advances. There is evidence of a genetic signature of northern expansion into the Paleozoic Plateau from a Southern Ozarkian refugium. Populations expanded out of drainages in the Northern Ozarks into the Paleozoic Plateau during the late Pleistocene. Subsequently, the two regions were isolated due to the recent extirpation of intervening populations caused by the loss of suitable habitat. PMID:21039494

  4. Glacial Isostatic Adjustment in the static gravity field of Fennoscandia

    NASA Astrophysics Data System (ADS)

    Root, B. C.; van der Wal, W.; Gradmann, S.; Novak, P.; Vermeersen, B. L.

    2013-12-01

    In Fennoscandia the crust is currently rising due to the negative mass anomaly created by the melting of the late-Pleistocene ice sheet. From this motion it can be concluded that there is no isostatic equilibrium in the area. Therefore it should be possible to see a negative gravity anomaly in the static gravity field. Its size and magnitude could be used as a constraint in GIA modeling, but only if the gravity anomaly can be corrected for crustal and upper mantle density variations. In this study it is examined if Glacial Isostatic Adjustment can be made visible in the static gravity field. Another goal of this study is to see what the effects are in geophysical modeling if the static gravity field is corrected for GIA using results from numerical GIA models. The forward gravity modeling is based on a spherical harmonic approach. Density layers are converted from seismic wave velocities or computed from global crustal models. The GIA model is based on the normal mode method and ice loading history ICE-5Gv1.2. The viscosities of the two mantle layers are fitted to relative sea-level observations, GPS uplift rates and temporal gravity observations from GRACE. The best fitted model is used in the process, which gives a negative gravity anomaly of -35 mGal (peak value) in Fennoscandia and a deflection of the lithosphere of -250 meter. Density models based on seismic wave velocity observations are still too uncertain to be used in the correction of the gravity field, as the uncertainty is around 200 mGal, much larger than the model-based GIA gravity signal. Different methods introduce an uncertainty in the computation of the isostatic gravity anomaly. This uncertainty, but also the uncertainty of other non-isostatic gravity effects it can be concluded that the GIA signal can not be distinguished in gravity field observations. Correcting gravity observations and topography for the remaining GIA effect, results in changes of several km in the structural layers of the modeled lithosphere using the corrected observations.

  5. Zonation of uplifted pleistocene coral reefs on barbados, west indies.

    PubMed

    Mesolella, K J

    1967-05-01

    The coral species composition of uplifted Pleistocene reefs on Barbados is very similar to Recent West Indian reefs. Acropora palmata, Acropora cervicornis, and Montastrea annularis are qtuantitatively the most important of the coral species. PMID:17837159

  6. The Role of Topography in Glacial Inception

    NASA Astrophysics Data System (ADS)

    Vavrus, S. J.; Philippon-Berthier, G.; Kutzbach, J. E.; Ruddiman, W. F.

    2009-12-01

    We test the influence of model topography on glacial inception using a coupled atmosphere-slab ocean version of NCAR’s Community Climate System Model (CCSM3). Simulations employ a modern orbital configuration and greenhouse gas concentrations representing both recent (year 1990) and hypothetically lower present-day values in accordance with Ruddiman’s Early Anthropogenic Hypothesis (240 ppm CO2 and 450 ppb CH4). The model is run at two different resolutions: a relatively coarse horizontal configuration (T42, approximately 2.8 degrees) and comparatively fine resolution (T85, approximately 1.4 degrees). Although under contemporary greenhouse forcing the extent of permanent boreal snow cover in the two model configurations is similar, imposing lower concentrations of CO2 and CH4 generates much more extensive glacial inception in the T85 experiment (150% increase) than in the T42 version (80% increase). Furthermore, the spatial patterns of glacial inception differ considerably. Only the T85 resolution produces widespread permanent snow cover over the Rocky Mountains and on Baffin Island, consistent with geologic evidence for ice sheet nucleation in northeastern Canada. Although much of the enhanced sensitivity in the higher-resolution simulations is directly attributable to the colder and wetter conditions around elevated topography, some of the response also appears to be driven dynamically and remotely as a function of the simulated elevation of Greenland. The colder conditions over and downstream of the Greenland Ice Sheet in the modern T85 simulation promote a smaller cooling locally under lowered greenhouse forcing that seems to activate a wave-1 dynamical response in the atmospheric pressure field. The resulting circulation anomalies favor stronger upslope wind flow from the Pacific Ocean over the northern Rocky Mountains, enhancing the regional development of a permanent snow pack. Although these experiments are driven by greenhouse forcing rather than historical orbital variations, we believe that our findings apply to the general mechanisms of glacial inception.

  7. Illustrated Glossary of Alpine Glacial Landforms

    NSDL National Science Digital Library

    Karen Lemke

    This glossary provides definitions and examples of common alpine glacial landforms. The landforms are divided into three categories: erosional landforms, depositional landforms, and ice features. Each definition is accompanied by a photo of the feature, and many also include a topographic map showing the same feature with the camera position marked to indicate where the photo was taken from. An online exercise is also included to allow students to test their knowledge.

  8. Illustrated Glossary of Alpine Glacial Landforms

    NSDL National Science Digital Library

    The Illustrated Glossary of Alpine Glacial Landforms is maintained by the University of Wisconsin Stevens Point's Department of Geology and Geography. This simple but well done site lists over twenty landforms as either an erosional landform, depositional landform, or an ice feature -- each including a brief description. Clicking on the corresponding link brings up a page with a photograph, a topographical map, a more in-depth description, and links to additional examples.

  9. A regional geochronological study of late pleistocene permafrost

    SciTech Connect

    Kostyukevich, V.V. (Russian Academy of Sciences, Yakutsk (Russian Federation). Geochemistry Lab.)

    1993-01-01

    The use of radiocarbon dating in geocryological investigations makes it possible to establish a chronology for permafrost-geological development during the Late Pleistocene. Both global and regional time scales for the formation of Late Pleistocene permafrost have been worked out over the past 15--20 years at the Permafrost Institute of the Siberian Branch of Russian Academy of Sciences. He presents here results from study areas of northwestern Siberia and of North, Central and West Yakutia.

  10. Coral associations of the Pleistocene Ironshore Formation, Grand Cayman

    NASA Astrophysics Data System (ADS)

    Hunter, I. G.; Jones, B.

    1996-11-01

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

  11. New evidence concerning the Plio-Pleistocene landscape evolution of southern Santa Cruz region

    NASA Astrophysics Data System (ADS)

    Strelin, J. A.; Re, G.; Keller, R.; Malagnino, E.

    1999-11-01

    Remnants of an old aggradational landscape, Cerro Cuadrado Proglacial, are preserved on top of the high mesetas Pampa Alta and La Meseta on both sides of the upper Santa Cruz river valley, South Patagonia. A first dissection of the mesetas, attributable to extended river erosion, predates the expansion of glacier lobes down the piedmontane area. The glacial advance is represented by the moraines of Pampa Alta Glaciation displayed on the top of Meseta Pampa Alta. Glacifluvial outlets contribute to the proglacial plain, Pampa Alta Proglacial, which is widespread to the southeast. Strong and persistent fluvial erosion followed the retreat of the ice masses leading to the formation of several terrace levels in the main upper valley, La Australasia Terraces and San Fernando Terraces, and a step, Cordón Alto, that truncates the Meseta Pampa Alta. These foreland features and the relief covered by the basalts at Cerro Fraile in the cordillera, are probably a consequence of a diastrophic phase that affected both areas during this stage. Late Pliocene basaltic lavas draining into the main and tributary valleys overran this landscape. The evidence indicates that during the eruption of the basalts the glaciation was active in the cordillera and that coeval fluvial and lacustrine aggradation took place in the extra-andean valleys. During the Middle Pleistocene subsequent lava flows covered the high pampas and partially occupied the fluvial valleys again. After this last volcanic episode the glaciers reached their maximum expansion to the east.

  12. Skeletal and isotopic composition and paleoclimatic significance of late Pleistocene carbonates, Ross Sea, Antarctica

    SciTech Connect

    Taviani, M. (Ist. per la Geologia Marina, Bologna (Italy)); Reid, D.E.; Anderson, J.B. (Rice Univ., Houston, TX (United States))

    1993-01-01

    Carbonates cover an extensive area of the northwestern Ross Sea continental shelf. Radiocarbon dates yield late Pleistocene (stage 3) ages for these deposits, hence the carbonates appear to be correlative with widespread tills and glacial marine deposits in the region. Four carbonate facies are recognized on the basis of skeletal composition: a barnacle/foraminifer facies, a muddy bryozoan facies, a bryozoan/barnacle/pelecypod/foraminifer facies, and a planktonic foraminiferal facies. These deposits occur on the shelf and upper slope, while carbonate turbidities derived from them occur on the adjacent continental slope and rise. Compositional analyses of Ross Sea carbonates lend support to previously recognized criteria for identifying cold water carbonates. These include: (1) the presence of an associated ice-rafted component (including dropstones); (2) a dominance of calcite relative to other carbonate minerals (the remaining fraction consists solely of aragonite); (3) allochems that are entirely skeletal; and (4) heavy oxygen isotopic compositions (in the range of +3.0 to +5.1% PDB).

  13. Malacological and palynological evidence of the Lower Pleistocene cold phase at the Carpathian Foothills (Southern Poland)

    NASA Astrophysics Data System (ADS)

    Stworzewicz, Ewa; Granoszewski, Wojciech; Wójcik, Antoni

    2012-05-01

    Early Pleistocene sediments bearing gastropod shells and pollen flora were found during coring at Jawornik (South Poland) at a depth interval of 54.30-39.00 m, beneath the oldest till of the Carpathians. Thirteen land-snail taxa identified in 55 samples of the core formed two molluscan assemblages. In the bottom part, typical cold-loving snails were found (e.g. Vallonia tenuilabris, Pupilla loessica, Vertigo genesii, Columella columella), whereas in the upper part only Semilimax kotulae was present. The succession of molluscan assemblages may suggest that at the site of deposition, after a phase of tundra, steppe-tundra or forest-steppe landscape with patches of wet habitats in cold climate, the climate became slightly milder but still cool, favourable to the spreading of boreal (coniferous) woodlands. Pollen analysis was performed only for the upper part of the profile. The pollen spectra, besides the Tertiary (Miocene) elements, contained sporomorphs common to the Tertiary and Quaternary floras. Among them, the highest percentages were noted for Pinus haploxylon t., P. diploxylon t., Picea, Quercus, Ericaceae, Betula, and Ulmus. The fact that the sediments with organic remains underlie the oldest Scandinavian till suggests that they are older than the oldest glacial unit of the South-Polish Complex (Narevian = Menapian, ~ 1.2 Ma).

  14. The nature of the Pleistocene-Holocene palaeosols in the Gaza Strip, Palestine

    NASA Astrophysics Data System (ADS)

    Ubeid, Khalid F.

    2011-09-01

    The Pleistocene to Holocene succession in the Gaza Strip, Palestine, consists of an alternation of calcareous sandstones and reddish fine-grained deposits (palaeosols). The palaeosols can be subdivided into two main groups based on the sand-sized versus clay- to silt-sized grains: (1) the sandy hamra palaeosols, and (2) the loess and loess-derived palaeosols. The hamra palaeosols can, in turn, also be subdivided into two main types according to their colour and grain size: (1) light brown loamy to sandy hamra palaeosols, and (2) dark brown sandy clay hamra palaeosols. The hamra palaeosols are polygenetic and originated in humid environments. Their red colour results from ferric oxides coating the sand grains, but also by illuviation. The various pedogenitic units and their gradual transition to loess palaeosols are due to different phases of dust accretion. Both groups of palaeosols developed during the last glacial. They are considered to represent different climate environments: hamra palaeosols represent humid climates, whereas the loess and loess-derived palaeosols represent dry and semi-dry climates.

  15. A link between global climate variability in the Pleistocene and variations in the Earth's orbital parameters

    NASA Astrophysics Data System (ADS)

    Bol'shakov, V. A.

    2014-09-01

    The study demonstrates that the orbital climatic diagram (OCD) built on the basis of the simplified and general concepts of mechanisms for climatic response to orbital forcing can be a reasonable alternative to Milankovitch's and his followers' discrete insolation curves, which are widely used in paleoclimate interpretations. Comparison of the OCD and the oxygen isotope record LR04 indicates a fairly good match (considering the simplicity of the OCD construction and interpretation) in 0-1240 ka. The study discusses some discrepancies in the chronology and structure of the LR04 and OCD. It was shown that climate response may differ from that predicted by orbital insolation forcing on the basis of the generally accepted mechanisms causing transformation of orbital signals. It was shown that a shift from a dominant glacial periodicity of 41 to 100 k.y. (Middle Pleistocene transition) took place at ˜1240 ka. Since then, the 100-k.y. eccentricity cycle has not been interrupted. Therefore, strictly speaking, the revised numbering of marine isotope stages (MIS) should be adopted for the interval of 1240-900 ka to reflect realistic 100-k.y. cycles instead of 41-k.y. cycles, similar to the interval of 900-100 ka.

  16. 3D hydro-mechanically coupled groundwater flow modelling of Pleistocene glaciation effects

    NASA Astrophysics Data System (ADS)

    Rühaak, Wolfram; Bense, Victor F.; Sass, Ingo

    2014-06-01

    Pleistocene glaciation led to temporal and spatial variations of sub-surface pore fluid pressure. In basins covered by ice sheets, fluid flow and recharge rates are strongly elevated during glaciations as compared to inter-glacial periods. Present-day hydrogeological conditions across formerly glaciated areas are likely to still reflect the impact of glaciations that ended locally more than 10 thousand years before present. 3D hydro-mechanical coupled modelling of glaciation can help to improve the management of groundwater resources in formerly glaciated basins. An open source numerical code for solving linear elasticity, which is based on the finite element method (FEM) in 3D, has been developed. By coupling this code with existing 3D flow codes it is possible to enable hydro-mechanical coupled modelling. Results of two benchmark simulations are compared to existing analytical solutions to demonstrate the performance of the newly developed code. While the result for a fluid-structure coupled case is in reasonable agreement with the analytical model, the result for a classical structure-fluid coupled benchmark showed that the analytical solution only matches the numerical result when the relevant coupling parameter (loading efficiency) is known in advance. This indicates that the applicability of widely applied approaches using an extra term in the groundwater flow equation for vertical stress to simulate hydro-mechanical coupling might have to be re-evaluated. A case study with the commercial groundwater simulator FEFLOW demonstrates the newly developed solution.

  17. Late Pleistocene human occupation of the hyperarid core in the Atacama Desert, northern Chile

    NASA Astrophysics Data System (ADS)

    Latorre, Claudio; Santoro, Calogero M.; Ugalde, Paula C.; Gayo, Eugenia M.; Osorio, Daniela; Salas-Egaña, Carolina; De Pol-Holz, Ricardo; Joly, Delphine; Rech, Jason A.

    2013-10-01

    Few archeological sites in South America contain uncontroversial evidence for when the first peopling of the continent occurred. Largely ignored in this debate, extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability. Here, we report on a rare 12-13 ka human occupation from Quebrada Maní (site QM12), a plantless, near rainless landscape (1240 m asl and 85 km from the Pacific Ocean) located in the hyperarid core of the Atacama Desert. This location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central Andes during the latest Pleistocene. Excavations at QM12 yielded a diverse cultural assemblage of lithics, burned and cut bones, marine gastropods, pigments, plant fibers, and wooden artifacts alongside a prepared fireplace. Sixteen radiocarbon dates from site QM12 on charcoal, marine shells, animal dung, plant remains and wood reveal that the occupation took place between 12.8 and 11.7 ka. These results demonstrate that the Atacama Desert was not a barrier to early American settlement and dispersal, and provide new clues for understanding the cultural complexity and diversity of the peopling of South America during the Last Glacial-interglacial transition.

  18. A new model linking atmospheric methane sources to Pleistocene glaciation via methanogenesis in sedimentary basins

    NASA Astrophysics Data System (ADS)

    Formolo, M. J.; Salacup, J. M.; Petsch, S. T.; Martini, A. M.; Nüsslein, K.

    2008-02-01

    Methane (CH4) is an important greenhouse gas and amplifier ofclimate change. However, the causes of atmospheric CH4 variationsover glacial-interglacial cycles remain unresolved. We proposethat microbial methanogenesis along the shallow margins of sedimentarybasins provides a source of atmospheric CH4 temporally connectedwith both advance and retreat of continental ice sheets. Extensivebiodegradation of hydrocarbons in the Antrim Shale Formation,Michigan, United States, is associated with an active subsurfaceconsortium of fermentative and methanogenic microorganisms.This activity was initially stimulated when saline formationwaters were diluted by meltwater derived from overriding Pleistoceneice sheets. During glaciation, CH4 produced by this communityaccumulated in the shale at a rate of 1 Tg CH4 per 1000 yr asa result of ice coverage and increased hydrostatic pressure.We estimate that at present the Antrim Shale contains only 12%-25%of the cumulative mass of CH4 generated in the shale over thePleistocene, indicating that CH4 that had accumulated duringglaciation was subsequently released following ice-sheet retreat.While release from the Antrim Shale represents only a smallpart of the global CH4 budget, when extended to other glaciatedsedimentary basins, subsurface methanogenesis may generate asubstantial, previously unrecognized source of atmospheric CH4during deglaciation.

  19. The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe.

    PubMed

    Yeakel, Justin D; Guimarães, Paulo R; Bocherens, Hervé; Koch, Paul L

    2013-07-01

    Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before--and possibly after--the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities. PMID:23658198

  20. Limited hydrologic response to Pleistocene climate change in deep vadose zones — Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Paces, James B.; Neymark, Leonid A.; Whelan, Joseph F.; Wooden, Joseph L.; Lund, Steven P.; Marshall, Brian D.

    2010-12-01

    Understanding the movement of water through thick vadose zones, especially on time scales encompassing long-term climate change, is increasingly important as societies utilize semi-arid environments for both water resources and sites viewed as favorable for long-term disposal or storage of hazardous waste. Hydrologic responses to Pleistocene climate change within a deep vadose zone in the eastern Mojave Desert at Yucca Mountain, Nevada, were evaluated by uranium-series dating of finely layered hyalitic opal using secondary ion mass spectrometry. Opal is present within cm-thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface. Uranium concentrations in opal fluctuate systematically between 5 and 550 ?g/g. Age-calibrated profiles of uranium concentration correlate with regional climate records over the last 300,000 years and produce time-series spectral peaks that have distinct periodicities of 100- and 41-ka, consistent with planetary orbital parameters. These results indicate that the chemical compositions of percolating solutions varied in response to near-surface, climate-driven processes. However, slow (micrometers per thousand years), relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial-interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates.

  1. Limited hydrologic response to Pleistocene climate change in deep vadose zones - Yucca Mountain, Nevada

    USGS Publications Warehouse

    Paces, J.B.; Neymark, L.A.; Whelan, J.F.; Wooden, J.L.; Lund, S.P.; Marshall, B.D.

    2010-01-01

    Understanding the movement of water through thick vadose zones, especially on time scales encompassing long-term climate change, is increasingly important as societies utilize semi-arid environments for both water resources and sites viewed as favorable for long-term disposal or storage of hazardous waste. Hydrologic responses to Pleistocene climate change within a deep vadose zone in the eastern Mojave Desert at Yucca Mountain, Nevada, were evaluated by uranium-series dating of finely layered hyalitic opal using secondary ion mass spectrometry. Opal is present within cm-thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface. Uranium concentrations in opal fluctuate systematically between 5 and 550 ?g/g. Age-calibrated profiles of uranium concentration correlate with regional climate records over the last 300,000 years and produce time-series spectral peaks that have distinct periodicities of 100- and 41-ka, consistent with planetary orbital parameters. These results indicate that the chemical compositions of percolating solutions varied in response to near-surface, climate-driven processes. However, slow (micrometers per thousand years), relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial–interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates.

  2. The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe

    PubMed Central

    Yeakel, Justin D.; Guimarães, Paulo R.; Bocherens, Hervé; Koch, Paul L.

    2013-01-01

    Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before—and possibly after—the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities. PMID:23658198

  3. Hot spots of genetic diversity descended from multiple Pleistocene refugia in an alpine ungulate.

    PubMed

    Shafer, Aaron B A; Côté, Steeve D; Coltman, David W

    2011-01-01

    Species that inhabit naturally fragmented environments are expected to be spatially structured and exhibit reduced genetic diversity at the periphery of their range. Patterns of differentiation may also reflect historical processes such as recolonization from glacial refugia. We examined the relative importance of these factors in shaping the spatial patterns of genetic differentiation across the range of an alpine specialist, the North American mountain goat (Oreamnos americanus). Contrary to fossil evidence that suggests a single southern refugium, we detected evidence for additional refugia in northern British Columbia and the Alaskan coast using both mitochondrial and microsatellite DNA. A core area of elevated genetic diversity characterized both regions, and molecular dating suggested a recent Pleistocene split was followed by demographic expansion. Across their range, mountain goats were highly genetically structured and displayed the expected pattern of declining diversity toward the periphery. Gene flow was high within contiguous mountain ranges, but cross-assignments paradoxically suggest that long-distance contemporary dispersal movements are not uncommon. These results improve our understanding of how historical vicariance and contemporary fragmentation influence population differentiation, and have implications for conserving the adaptive potential of alpine populations and habitat. PMID:20731714

  4. Relation of heavy mineral suites to Pleistocene to Holocene shoreline sequences in Georgia

    SciTech Connect

    Cocker, M.D. (Georgia Geologic Survey, Atlanta, GA (United States))

    1993-03-01

    The major Pleistocene paleobarrier island complexes recognized on the Georgia coastal plain may represent two distinct shoreline sequences. This is suggested by differences in geomorphology and in heavy mineral suites. The higher and older Talbot, Penholoway, Wicomico, Okefenokee and Waycross complexes are characterized by large, linear, undissected sand bodies. The younger Pamlico, Princess Anne and Silver Bluff complexes consist of small, stubby and complexly dissected sand bodies and are similar to those developed on the Holocene shoreline. The average labile (1.88), ilmenite/leucoxene (1.28), and ZTR (22.07) indices of the three older complexes indicate distinctly more mature heavy mineral suites than the average labile, (8.88) ilmenite/leucoxene (4.54), and ZTR (18.42) indices in the younger complexes. The heavy mineral suites of the older shoreline sequence exhibit little variation in mineralogy. The heavy mineral suites in the younger sequence exhibit a greater range in mineralogy, and the suites change progressively from the Pamlico through the Silver Bluff complexes. Continuation of these trends is evident in the heavy mineral suite of the Holocene deposits. The increasing range in composition also indicates the relatively immaturity of the younger complexes. The difference in heavy mineral content between the older (0.53 wt. %) and the younger (1.33 wt. %) shoreline sequences may result from increased weathering and removal of the labile components during a warm inter-glacial period.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  6. Constraint envelope analyses of macroecological patterns reveal climatic effects on Pleistocene mammal extinctions

    NASA Astrophysics Data System (ADS)

    Lima-Ribeiro, Matheus S.; Hortal, Joaquín; Varela, Sara; Diniz-Filho, José Alexandre F.

    2014-07-01

    Quantitative analysis of macroecological patterns for late Pleistocene assemblages can be useful for disentangling the causes of late Quaternary extinctions (LQE). However, previous analyses have usually assumed linear relationships between macroecological traits, such as body size and range size/range shift, that may have led to erroneous interpretations. Here, we analyzed mammalian datasets to show how macroecological patterns support climate change as an important driver of the LQE, which is contrary to previous analyses that did not account for more complex relationships among traits. We employed quantile regression methods that allow a detailed and fine-tuned quantitative analysis of complex macroecological patterns revealed as polygonal relationships (i.e., constraint envelopes). We showed that these triangular-shaped envelopes that describe the macroecological relationship between body size and geographical range shift reflect nonrandom extinction processes under which the large-bodied species are more prone to extinction during events of severe habitat loss, such as glacial/interglacial transitions. Hence, we provide both a theoretical background and methodological framework to better understand how climate change induces body size-biased species sorting and shapes complex macroecological patterns.

  7. The role of an Arctic ice shelf in the climate of the MIS 6 glacial maximum (140 ka)

    NASA Astrophysics Data System (ADS)

    Colleoni, F.; Krinner, G.; Jakobsson, M.

    2010-12-01

    During the last decade, Arctic icebreaker and nuclear submarine expeditions have revealed large-scale Pleistocene glacial erosion on the Lomonosov Ridge, Chukchi Borderland and along the Northern Alaskan margin indicating that the glacial Arctic Ocean hosted large Antarctic-style ice shelves. Dating of sediment cores indicates that the most extensive and deepest ice grounding occurred during Marine Isotope Stage (MIS) 6. The precise extents of Pleistocene ice shelves in the Arctic Ocean are unknown but seem comparable to present existing Antarctic ice shelves. How would an Antarctic-style ice shelf in the MIS 6 Arctic Ocean influence the Northern Hemisphere climate? Could it have impacted on the surface mass balance (SMB) of the MIS 6 Eurasian ice sheet and contributed to its large southward extent? We use an Atmospheric General Circulation Model (AGCM) to investigate the climatic impacts of both a limited MIS 6 ice shelf covering portions of the Canada Basin and a fully ice shelf covered Arctic Ocean. The AGCM results show that both ice shelves cause a temperature cooling of about 3 °C over the Arctic Ocean mainly due to the combined effect of ice elevation and isolation from the underlying ocean heat fluxes stopping the snow cover from melting during summer. The calculated SMB of the ice shelves are positive. The ice front horizontal velocity of the Canada Basin ice shelf is estimated to ? 1 km yr -1 which is comparable to the recent measurements of the Ross ice shelf, Antarctica. The existence of a large continuous ice shelf covering the entire Arctic Ocean would imply a mean annual velocity of icebergs of ?12 km yr -1 through the Fram Strait. Our modeling results show that both ice shelf configurations could be viable under the MIS 6 climatic conditions. However, the cooling caused by these ice shelves only affects the Arctic margins of the continental ice sheets and is not strong enough to significantly influence the surface mass balance of the entire MIS 6 Eurasian ice sheet.

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

    NASA Astrophysics Data System (ADS)

    Mehl, A. E.; Zárate, M. A.

    2013-10-01

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

  9. Sea Surface Temperatures and Stratification of the Subpolar North Atlantic during the Mid-Pleistocene (ca. 800-400 ka)

    NASA Astrophysics Data System (ADS)

    Alonso-Garcia, M.; Sierro, F. J.; Cacho Lascorz, I.; Villarejo, J.; Kucera, M.

    2012-12-01

    The onset of 100-kyr glacial-interglacial cyclicity occurred during the Mid-Pleistocene transition (ca. 1.2-0.5 ka), and is linked to important climatic changes, including: intensification of glacial periods, expansion of Northern Hemisphere ice sheets, enhancement of Asian and African aridity, and reorganization of deep ocean circulation. Although multiple hypotheses exist to explain these climatic changes, the detailed forcing mechanisms are not fully understood. To adequately assess these hypotheses, high-resolution multi-proxy reconstructions of high latitude sea surface conditions are required. Here we present a high-resolution study of subpolar North Atlantic sediments from IODP Site U1314 (56 N, 27 W, 2820 m water depth) across four climatic cycles (ca. 800 to 400 ka). We use paired Neogloboquadrina pachyderma sinistral (s) ?18O and Mg/Ca, N. pachyderma dextral (d) ?18O, and planktonic foraminifer assemblage records to improve understanding of subpolar North Atlantic sea surface temperature (SST) and upper water column stratification during the Mid-Pleistocene. Planktic foraminifer Mg/Ca paleothermometry has been used successfully to reconstruct SSTs at low to mid-latitudes. However, the cold temperatures at high-latitudes reduce the sensitivity of Mg incorporation into foraminiferal calcite. Several calibration datasets involving N. pachyderma (s) indicate anomalously high Mg/Ca in Arctic and Polar waters that may not reflect temperature but other factors like salinity, alkalinity or calcification depth. Thus, a multi-proxy approach is essential to study past subpolar SSTs. However, we can infer the presence of Arctic waters at Site U1314 tracking the abundance of N. pachyderma (s), which provides a unique opportunity to evaluate the influence of Arctic waters in N. pachyderma (s) Mg/Ca paleothermometry due to the southward migration of the Arctic front across glacial-interglacial cycles. To examine upper water column stratification, we generated N. pachyderma (s) and (d) ?18O records and planktic foraminifer assemblages. N. pachyderma (s) lives at the pycnocline, where the waters are usually close to winter temperatures, whereas N. pachyderma (d) lives in the upper 50-100 m of the water column during summer and autumn periods of stratification. Thus, the offset between the ?18O records may reflect variations in regional thermal stratification, particularly during interglacial periods. Planktic foraminifer assemblages support our ?18O-based interpretations of the upper water column.

  10. Coupled Warming and Drought in the American Southwest During Long mid-Pleistocene Interglacials (MIS 11 and 13)

    NASA Astrophysics Data System (ADS)

    Fawcett, P. J.; Werne, J.; Anderson, R.; Heikoop, J.; Brown, E.; Hurley, L.; Smith, S.; Berke, M.; Soltow, H.; Goff, F.; Geissman, J.; Woldegabriel, G.; Fessenden, J.; Cisneros-Dozal, M.; Allen, C. D.

    2008-12-01

    An 82-m deep lacustrine sediment core from the Valles Caldera, northern New Mexico reveals details of climate change over two glacial cycles in the middle Pleistocene. Core VC-3, taken from the Valle Grande, has a basal 40Ar/39Ar date of 552 kyr from a tephra associated with the eruption of the South Mountain rhyolite which formed the lake. A variety of proxies including core sedimentology, organic carbon and carbon isotopic ratios, pollen, scanning XRF analysis and a new paleotemperature proxy, MBT (methylated branched tetraether) content of soil bacteria reveal two major warm periods above the basal tephra which we correlate with interglacials MIS 13 and MIS 11. This chronology is corroborated by the identification of two geomagnetic field "events" which are correlated with globally recognized events (14? and 11?). The lacustrine record terminates at ~350 ka when the lake filled its available accommodation space behind the dam of rhyolite lava. MBT temperature estimates show average glacial temperatures in core VC-3 of ~ -4°C, and average interglacial temperatures of ~ +4°C, and the general trends are well corroborated by multiple proxies including pollen and lacustrine organic productivity estimates. A temperature increase of ~9°C occurs during Termination V, the largest glacial termination in the Pleistocene. Multiple proxies from VC-3 show significant structure during the two interglacials present in the core (MIS 13 and 11). Three warm substages (~ 2°C warmer) are recognized within MIS 11 based on organic productivity (Corg, Si/Ti ratios), pollen taxa, elevated charcoal from fires, and the MBT temperature estimates. These warm substages appear to be a strong response to precessional forcing in the SW continental interior even though the amplitude of eccentricity-modulated precession was at a minimum during MIS 11. These results suggest that future climate change in the SW may be characterized by similar natural temperature variability on precessional timescales, superimposed on future anthropogenic warming. Intervals of mudcrack facies representing significant drought conditions occur during or just after the warmest phases of the two interglacials. This past coupling between warm temperatures and extended drought in the SW as a natural feature of long interglacials is consistent with recent predictions of extended Dust-Bowl-like conditions in the SW as a response to global warming.

  11. Did debris-covered glaciers serve as pleistocene refugia for plants? A new hypothesis derived from observations of recent plant growth on glacier surfaces

    USGS Publications Warehouse

    Fickert, T.; Friend, D.; Gruninger, F.; Molnia, B.; Richter, M.

    2007-01-01

    This study proposes a new hypothesis: Debris-covered glaciers served as Pleistocene biological refugia. This is based on detailed studies of vascular plant growth on six debris-mantled glaciers, literally around the world, as well as many casual observations also across the globe. We find that such glaciers are quite common and are distributed globally. Using Carbon Glacier, Mount Rainier, U.S.A., as a type locality and case study, we show aspects of the floristic and structural diversity as well as spatial patterns of plant growth on the glacier surface. Migration strategies, root characteristics, and origin and dispersal strategies for vascular plant species are documented. Also reported are special microclimatic conditions in these areas allowing for this remarkable plant ecology. We find that alpine taxa can grow considerably below their usual altitudinal niche due to the cooler subsurface soil temperatures found on glacial debris with ice underneath, and that may have significantly altered the spatial distribution of such flora during full glacial conditions. This in turn creates previously undocumented areas from which alpine, and perhaps arctic, plant species reestablished in post-glacial time. This hypothesis is complementary to both the nunatak hypothesis and tabula rasa theory and possibly helps solve the ongoing controversy between them. ?? 2007 Regents of the University of Colorado.

  12. Pleistocene phylogeographic effects on avian populations and the speciation process.

    PubMed Central

    Avise, J C; Walker, D

    1998-01-01

    Pleistocene biogeographic events have traditionally been ascribed a major role in promoting speciations and in sculpting the present-day diversity and distributions of vertebrate taxa. However, this paradigm has recently come under challenge from a review of interspecific mtDNA genetic distances in birds: most sister-species separations dated to the Pliocene. Here we summarize the literature on intraspecific mtDNA phylogeographic patterns in birds and reinterpret the molecular evidence bearing on Pleistocene influences. At least 37 of the 63 avian species surveyed (59%) are sundered into recognizable phylogeographic units, and 28 of these separations (76%) trace to the Pleistocene. Furthermore, use of phylogroup separation times within species as minimum estimates of 'speciation durations' also indicates that many protracted speciations, considered individually, probably extended through time from Pliocene origins to Pleistocene completions. When avian speciation is viewed properly as an extended temporal process rather than as a point event, Pleistocene conditions appear to have played an active role both in initiating major phylogeographic separations within species, and in completing speciations that had been inaugurated earlier. Whether the Pleistocene was exceptional in these regards compared with other geological times remains to be determined. PMID:9569664

  13. Glacial Retreat and Associated Glacial Lake Hazards in the High Tien Shan

    NASA Astrophysics Data System (ADS)

    Smith, T. T.

    2013-12-01

    A number of studies have identified glacial retreat throughout the greater Himalayan region over the past few decades, but the Karakorum region remains an anomaly with large stagnating or advancing glaciers. The glacial behavior in the Tien Shan is still unclear, as few studies have investigated mass balances in the region. This study focuses on the highest peaks of the Tien Shan mountain range, in the region of Jengish Chokusu along the Kyrgyzstan-China-Kazakhstan border. In a first step, a 30-year time series of Landsat imagery (n=27) and ASTER imagery (n=10) was developed to track glacial growth and retreat in the region. Using a combination of spectral and topographic information, glacial outlines are automatically delineated. As several important glaciers in the study region contain medium to high levels of debris cover, our algorithm also improves upon current methods of detecting debris-covered glaciers by using topography, distance weighting methods, river networks, and additional spectral data. Linked to glacial retreat are glacial lake outburst floods (GLOFs) that have become increasingly common in High Mountain Asia over the last few decades. As glaciers retreat, their melt water is often trapped by weakly bonded moraines. These moraines have been known to fail due to overtopping caused by surge waves created by avalanches, rockslides, or glacial calving. A suite of studies throughout High Mountain Asia have used remotely-sensed data to monitor the formation and growth of glacial lakes. In a second step of the work, lake-area changes over the past 15 years were tracked monthly and seasonally using dense Landsat/ASTER coverage (n=30) with an automatic procedure based on spectral and topographic information. Previous work has identified GLOFs as a significant process for infrastructural damage in the southern Tien Shan/northern Pamir, as well as in the better studied Himalaya region. Lake identification and quantification of lake-growth rates is a valuable first step to identifying potential flooding hazards in the region. In a third step, ASTER imagery is used for mass balance estimates from stereogrammetry over the last 10 years (n=10). These mass balance estimates are some of the first in the region, and provide valuable context on the rate of retreat identified using Landsat imagery. By combining glacial retreat rates with lake-change rates, a preliminary hydrological budget was derived for the region. This budget provides a basis for estimating GLOF risk in the region, by combining risk factors such as lake-growth rate and glacial retreat rate with glacier slope and other near-lake risk factors, such as propensity for landslides, likely to cause overtopping in lakes and downstream flooding. Following the identification of dangerous lakes, elevation models were used for flow routing, to assess total downstream area that would be affected by a GLOF. In combination with infrastructure and demographic information, the algorithm can estimate potential downstream impacts on local communities. This work provides an integrated picture of glacial lake hazards in a previously unstudied region of the Tien Shan, as well as valuable mass balance and glacial retreat rate estimates.

  14. Paleowaters in Silurian-Devonian carbonate aquifers: Geochemical evolution of groundwater in the Great Lakes region since the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    McIntosh, J. C.; Walter, L. M.

    2006-05-01

    Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying glacial drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater-saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from -10 to -2‰, 87Sr/ 86Sr ratios range from 0.7080 to 0.7090, and ?34S-SO4 values range from +10 to 30‰. A few waters have elevated ?13C DIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and ?18O and ?D values of confined groundwaters indicate they originated as subglacial recharge beneath the Laurentide Ice Sheet (14-50 ka BP, -15 to -13‰ ?18O). These paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined glacial drift aquifers. Recharge waters in Silurian-Devonian and unconfined drift aquifers have ?18O values within the range of Holocene precipitation: -11 to -8‰ and -7 to -4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions ( ?13C DIC = -14.7 to-11.1‰ and 87Sr/ 86Sr = 0.7080-0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins.

  15. New Tooth Enamel Isotopic Data from the West Coast of South Africa and a Comparison of Terrestrial and Marine Records of Plio-Pleistocene Climate Change

    NASA Astrophysics Data System (ADS)

    Lehmann, S. B.; Levin, N. E.; Stynder, D. D.; Bishop, L. C.; Forrest, F.; Braun, D. R.

    2012-12-01

    The Plio-Pleistocene transition marks a change in the Earth's climate from relative global warmth to colder temperatures with the initiation of glacial-interglacial cycles. Proxy records from marine cores off SW Africa archive changes in ocean upwelling and terrestrial vegetation that suggest increased aridity across the Plio-Pleistocene transition. Today, the SW African coast has a Winter Rainfall Zone (WRZ) and is dominated by C3 vegetation, which results from the regional high-pressure system and upwelling in the Benguela Current. While marine records provide an integrated perspective on regional responses to global climate change, terrestrial paleoclimate records are needed to assess the effects of these changes in a heterogeneous environment like southern Africa. Archeological and paleontological sites can provide useful proxies of paleoclimate, but many southern African sites are poorly dated or postdate the Plio-Pleistocene transition. Langebaanweg (LBW, ~5 Ma) and Elandsfontein (EFT, ~1.0-0.6 Ma) are sites on the SW coast of South Africa that are rich in fossil mammals and represent landscapes where surface water was more prevalent than it is in today's dry coastal environment. Fossil teeth of large herbivores (e.g. hippopotamids, giraffids, bovids, rhinocerotids, suids and equids) are preserved at both sites and enable isotopic studies of vegetation and climate across the Plio-Pleistocene transition. In this study, carbon and oxygen isotopic data are reported for 100 fossil teeth (11 herbivore taxa) at EFT and are compared to published isotopic data from early Pliocene teeth from LBW for many of the same genera. ?13C values of the EFT tooth enamel range from 13 to 8‰ (VPDB) and ?18O values range from -2 to +3‰ (VPDB). Among the EFT data, there are consistent differences in the distribution of both ?13C and ?18O values among the sampled taxa. When the EFT and LBW isotopic results are compared, ?13C values from the two sites are similar within each taxonomic group. However, ?18O values of the EFT teeth are more than 2‰ higher than ?18O values of LBW teeth for each herbivore family that was sampled. Enamel ?13C values from LBW and EFT indicate herbivore diets that were dominated by C3 vegetation during the Pliocene and Pleistocene. Mesowear studies of teeth suggest that the West Coast of South Africa was a forested environment with seasonal grasses during the Pliocene but that it supported trees, fynbos and grasses in the mid-Pleistocene. The isotopic indications of C3 diets among grazers from both sites suggest that a WRZ must have existed across the Plio-Pleistocene transition. The positive shift in ?18O values of fossil tooth enamel between the early Pliocene and the mid-Pleistocene on the West Coast of South Africa might suggest a change in the oxygen isotopic composition of rainfall and a decrease in the amount of rainfall across the Plio-Pleistocene transition. Excluding diagenesis, these conclusions are consistent with marine records. This study indicates the potential for using the stable isotope records from fossil teeth from the West Coast of South Africa to evaluate how the intensification of the Benguela Upwelling System, which is well documented in the marine records, affected terrestrial ecosystems across the Plio-Pleistocene transition.

  16. Paleohydrology of the southern Great Basin, with special reference to water table fluctuations beneath the Nevada Test Site during the late(?) Pleistocene

    USGS Publications Warehouse

    Winograd, Isaac Judah; Doty, Gene C.

    1980-01-01

    Knowledge of the magnitude of water-table rise during Pleistocene pluvial climates, and of the resultant shortening of groundwater flow path and reduction in unsaturated zone thickness, is mandatory for a technical evaluation of the Nevada Test Site (NTS) or other arid zone sites as repositories for high-level or transuranic radioactive wastes. The distribution of calcitic veins filling fractures in alluvium, and of tufa deposits between the Ash Meadows spring discharge area and the Nevada Test Site indicates that discharge from the regional Paleozoic carbonate aquifer during the Late( ) Pleistocene pluvial periods may have occurred at an altitude about 50 meters higher than at present and 14 kilometers northeast of Ash Meadows. Use of the underflow equation (relating discharge to transmissivity, aquifer width, and hydraulic gradient), and various assumptions regarding pluvial recharge, transmissivity, and altitude of groundwater base level, suggest possible rises in potentiometric level in the carbonate aquifer of about -90 meters beneath central Frenchman Flat. During Wisconsin time the rise probably did not exceed 30 meters. Water-level rises beneath Frenchman Flat during future pluvials are unlikely to exceed 30 meters and might even be 10 meters lower than modern levels. Neither the cited rise in potentiometric level in the regional carbonate aquifer, nor the shortened flow path during the Late( ) Pleistocene preclude utilization of the NTS as a repository for high-level or transuranic-element radioactive wastes provided other requisite conditions are met as this site. Deep water tables, attendant thick (up to several hundred meter) unsaturated zones, and long groundwater flow paths characterized the region during the Wisconsin Stage and probably throughout the Pleistocene Epoch and are likely to so characterize it during future glacial periods. (USGS)

  17. Late Pleistocene Glacial-Interglacial related shell size isotope variability in planktonic foraminifera as a function of local hydrology

    NASA Astrophysics Data System (ADS)

    Metcalfe, B.; Feldmeijer, W.; de Vringer-Picon, M.; Brummer, G.-J. A.; Peeters, F. J. C.; Ganssen, G. M.

    2015-01-01

    So called "vital effects", a collective noun for a suite of physiological and metabolic induced variability, in oxygen (?18O) and carbon (?13C) isotope ratios of planktonic foraminifer shells hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from the equilibrium or the expected value is paramount, as too is the ability to define a comparable life-stage for each species that allows for direct comparison. Past research has focused upon finding a specific size range for individual species in lieu of other identifiable features, that allow ocean parameters from a particular constant (i.e. a specific depth or season) to be reconstructed. Single shell isotope analysis of fossil shells from a mid-latitude North Atlantic Ocean piston-core covering Termination III (200 to 250 kyr) highlight the advantage of using a dynamic size range in studies of palaeoclimate. Using this methodology, we show that isotopic offsets between specimens in successive size fractions of G. inflata and G. truncatulinoides are not constant over time, contrary to previous findings. For ?18O in smaller sized globorotalids it is suggested that the offset from other size fractions may reflect a shallower habitat in an early ontogenetic stage. A reduction in the difference between small and large specimens of G. inflata between insolation minima and maxima is interpreted to relate to a prolonged period of reduced water column stratification. For the shallow dwelling species G. bulloides no size isotope difference between size fractions is observed, and the variability in the oxygen isotopic values are shown to correlate well with the seasonal insolation patterns. As such, patterns in oxygen isotope variability of fossil populations may be used successfully for reconstruction of past seasonality changes.

  18. Possible Asynchronous Glacial Expansion During Climatic Warming in the Holocene, Glacier Bay Region, Alaska

    NASA Astrophysics Data System (ADS)

    Lawson, D. E.; Finnegan, D. C.; Bigl, S. R.; Kopczynski, S. E.; Magilligan, F. J.

    2003-12-01

    Glacial expansion is commonly thought to occur during cold climatic periods whereas thinning and recession follow as the climate warms. However, data from Glacier Bay, Alaska, on the location and timing of ice margin positions suggest that ice growth of the terrestrial and tidewater systems continued long after warming began. Radiocarbon dating of trees overridden by glacial advance provide rates and positions of ice margins over the last 9500 years BP. Major periods of ice advance were initiated prior to 9500 yrs BP and continued through at least 6000 yrs BP. Similarly ice returned to the region around 4900 yrs BP and continued to expand apparently without interruption through 3200 yrs BP. Data from more recent periods of ice advance are not as well constrained but appear to suggest ice filled much of the bay, perhaps including parts of the ice mass remaining from the 4.9 K advance, during three separate periods including the Little Ice age. Current investigations are evaluating signals in the tree ring record for causes, including signals developed by external forcings such as El Nino, the Pacific Decadal Oscillation (PDO) and Arctic Oscillation(AO).

  19. Holocene environmental change resets lichen surface dates on Recess Peak glacial deposits in the Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Scuderi, Louis A.; Fawcett, Peter J.

    2013-09-01

    Development of an accurate chronology for glacial deposits in the Sierra Nevada has long been problematic given the lack of suitable organic material for radiocarbon dating. Lichenometry initially appeared promising as ages showed an increase from cirque headwalls to down-canyon moraines. However, while Recess Peak lichen age estimates range from 2 to 3 ka, recent work shows these deposits to be at least 10 ka older. Here, we present evidence for a late Holocene reset of Recess Peak lichen ages by significant post-depositional climate change. Following late-Pleistocene deposition of Recess Peak moraines, warming through the mid-Holocene allowed forests to advance into shallow basins eliminating local inverted tree lines. This produced a partial canopy where shading killed the original post-Pleistocene crustose lichen colonies. Late-Holocene cooling resulted in forest retreat from these basins as alpine tree line fell. Lichens then recolonized the re-exposed Recess Peak deposits. We conclude that while Recess Peak lichen ages are accurate to within the dating uncertainty of the technique, existing lichen ages actually date the timing of post-mid-Holocene cooling and recolonization, and not the original emplacement of these deposits. Thus, applications of Lichenometry should consider post-depositional environmental change when interpreting the meaning of these dates.

  20. Mitochondrial phylogeny shows multiple independent ecological transitions and northern dispersion despite of Pleistocene glaciations in meadow and steppe vipers (Vipera ursinii and Vipera renardi).

    PubMed

    Zinenko, Oleksandr; Stümpel, Nikolaus; Mazanaeva, Lyudmila; Bakiev, Andrey; Shiryaev, Konstantin; Pavlov, Aleksey; Kotenko, Tatiana; Kukushkin, Oleg; Chikin, Yury; Duisebayeva, Tatiana; Nilson, Göran; Orlov, Nikolai L; Tuniyev, Sako; Ananjeva, Natalia B; Murphy, Robert W; Joger, Ulrich

    2015-03-01

    The phylogeny and historical demography of small Eurasian vipers of the Vipera ursinii and V. renardi complexes were studied using mitochondrial DNA sequences analysed with Bayesian inference, Maximum Likelihood and Maximum Parsimony approaches, and mismatch distributions. Diversification in the group resulted from an initial dispersion in the later Pliocene - Pleistocene in two directions: north-westwards via the Balkans (V. ursinii complex) and north-eastwards from Asia Minor via the Caucasus (V. renardi complex). An independent, comparatively recent transition occurred from montane habitats to lowland grasslands in different mitochondrial lineages during the Late Pleistocene, when representatives of the both complexes had reached lowland steppes to the north. Effective population size showed clear signs of rapid growth in eastern V. renardi, triggered by colonization of vast lowland steppes, but in western V. ursinii complex grew during the Last Glaciation and experienced stabilization in Holocene. Expansion and population growth in lowland lineages of V. renardi was not strongly affected by Pleistocene climatic oscillations, when cold, dry conditions could have favoured species living in open grasslands. The high diversity of closely related haplotypes in the Caucasus and Tien-Shan could have resulted from repetitive expansion-constriction-isolation events in montane regions during Pleistocene climate fluctuations. The mitochondrial phylogeny pattern conflicts with the current taxonomy. PMID:25527984

  1. Latest Pleistocene and Holocene glacier variations in the European Alps

    NASA Astrophysics Data System (ADS)

    Ivy-Ochs, Susan; Kerschner, Hanns; Maisch, Max; Christl, Marcus; Kubik, Peter W.; Schlüchter, Christian

    2009-10-01

    In the Alps, climatic conditions reflected in glacier and rock glacier activity in the earliest Holocene show a strong affinity to conditions in the latest Pleistocene (Younger Dryas). Glacier advances in the Alps related to Younger Dryas cooling led to the deposition of Egesen stadial moraines. Egesen stadial moraines can be divided into three or in some cases even more phases (sub-stadials). Moraines of the earliest and most extended advance, the Egesen maximum, stabilized at 12.2 ± 1.0 ka based on 10Be exposure dating at the Schönferwall (Tyrol, Austria) and the Julier Pass-outer moraine (Switzerland). Final stabilization of moraines at the end of the Egesen stadial was at 11.3 ± 0.9 ka as shown by 10Be data from four sites across the Alps. From west to east the sites are Piano del Praiet (northwestern Italy), Grosser Aletschgletscher (central Switzerland), Julier Pass-inner moraine (eastern Switzerland), and Val Viola (northeastern Italy). There is excellent agreement of the 10Be ages from the four sites. In the earliest Holocene, glaciers in the northernmost mountain ranges advanced at around 10.8 ± 1.1 ka as shown by 10Be data from the Kartell site (northern Tyrol, Austria). In more sheltered, drier regions rock glacier activity dominated as shown, for example, at Julier Pass and Larstig valley (Tyrol, Austria). New 10Be dates presented here for two rock glaciers in Larstig valley indicate final stabilization no later than 10.5 ± 0.8 ka. Based on this data, we conclude the earliest Holocene (between 11.6 and about 10.5 ka) was still strongly affected by the cold climatic conditions of the Younger Dryas and the Preboreal oscillation, with the intervening warming phase having had the effect of rapid downwasting of Egesen glaciers. At or slightly before 10.5 ka rapid shrinkage of glaciers to a size smaller than their late 20th century size reflects markedly warmer and possibly also drier climate. Between about 10.5 ka and 3.3 ka conditions in the Alps were not conducive to significant glacier expansion except possibly during rare brief intervals. Past tree-line data from Kaunertal (Tyrol, Austria) in concert with radiocarbon and dendrochronologically dated wood fragments found recently in the glacier forefields in both the Swiss and Austrian Alps points to long periods during the Holocene when glaciers were smaller than they were during the late 20th century. Equilibrium line altitudes (ELA) were about 200 m higher than they are today and about 300 m higher in comparison to Little Ice Age (LIA) ELAs. The Larstig rock glacier site we dated with 10Be is the type area for a postulated mid-Holocene cold period called the Larstig oscillation (presumed age about 7.0 ka). Our data point to final stabilization of those rock glaciers in the earliest Holocene and not in the middle Holocene. The combined data indicate there was no time window in the middle Holocene long enough for rock glaciers of the size and at the elevation of the Larstig site to have formed. During the short infrequent cold oscillations between 10.5 and 3.3 ka small glaciers (less than several km 2) may have advanced to close to their LIA dimensions. Overall, the cold periods were just too short for large glaciers to advance. After 3.3 ka, climate conditions became generally colder and warm periods were brief and less frequent. Large glaciers (for example Grosser Aletschgletscher) advanced markedly at 3.0-2.6 ka, around 600 AD and during the LIA. Glaciers in the Alps attained their LIA maximum extents in the 14th, 17th, and 19th centuries, with most reaching their greatest LIA extent in the final 1850/1860 AD advance.

  2. The Pleistocene of Schöningen, Germany: a complex tunnel valley fill revealed from 3D subsurface modelling and shear wave seismics

    NASA Astrophysics Data System (ADS)

    Lang, Jörg; Winsemann, Jutta; Steinmetz, Dominik; Polom, Ulrich; Pollok, Lukas; Böhner, Utz; Serangeli, Jordi; Brandes, Christian; Hampel, Andrea; Winghart, Stefan

    2012-04-01

    The Pleistocene deposits of Schöningen represent an outstanding geological and archaeological archive, where an up to 45 m thick Middle to Late Pleistocene succession has been preserved and unique artefacts from the Lower Palaeolithic have been discovered. The preservation of such a thick and complete glacial/interglacial succession is very rare in the geological record and requires a specific depositional setting. We will present a new depositional model for the Pleistocene succession of Schöningen, integrating outcrop data, borehole data and high-resolution shear wave seismics. A total of four outcrop sections and 744 borehole logs were examined to document the complex facies architecture. All collected sedimentological and geophysical data sets were integrated into a high-resolution 3D geological model (GOCAD®) for reconstructing the spatial distribution of facies associations and the large-scale depositional architecture. The spatial distribution of the artefacts will be discussed with respect to the depositional environment. The Elsterian and Holsteinian deposits are restricted to a NNW-SSE trending, elongated trough, which is deeply incised into unconsolidated lignite-bearing Palaeogene deposits. The geometry of this erosional structure points to a tunnel valley origin that was incised below the Elsterian ice sheet. The basal tunnel valley fill consists of cross-stratified pebbly sand and gravel overlain by till. After deglaciation the tunnel valley remained underfilled and acted as a depocentre for interglacial deposition. During the subsequent Holsteinian interglacial (MIS 9) a lake formed within this depocentre and lacustrine sediments accumulated. This interglacial succession consists of peat, organic-rich silt and fine-grained sand interpreted as lake-bottom and deltaic sediments fed by surface run-off shed from the Elm ridge. The lacustrine deposition was controlled by repeated lake-level fluctuations in the range of 1-6 m leading to the formation of laterally stacked delta systems. These lake-level changes were probably triggered by climate, causing variations of precipitation and surface run-off. During the late Saalian glaciation the remnant tunnel valley was completely filled with meltwater deposits. The sedimentary facies and depositional architecture point to a shallow-water delta. Subsequently the meltwater deposits were overlain by till. The deposition of the Middle Pleistocene sediments within an Elsterian tunnel valley explains the unique preservation of the sedimentary succession of Schöningen. The long-lived interglacial lake provided an attractive site for animals and early humans ambushing them. Artefacts mainly became embedded on the delta plain, which rapidly was transgressed during lake-level rise and artefacts were thus preserved.

  3. Late Pliocene and Early Pleistocene vegetation history of northeastern Russian Arctic inferred from the Lake El'gygytgyn pollen record

    NASA Astrophysics Data System (ADS)

    Andreev, A. A.; Tarasov, P. E.; Wennrich, V.; Raschke, E.; Herzschuh, U.; Nowaczyk, N. R.; Brigham-Grette, J.; Melles, M.

    2014-05-01

    The 318 m thick lacustrine sediment record from Lake El'gygytgyn, northeastern Russian Arctic cored by the international El'gygytgyn Drilling Project provides unique opportunities for the time-continuous reconstruction of the regional paleoenvironmental history for the past 3.6 Myr. Pollen studies of the lower 216 m of the lacustrine sediments demonstrate their value as an excellent archive of vegetation and climate changes during the Late Pliocene and Early Pleistocene. About 3.5-3.35 Myr BP, the vegetation at Lake El'gygytgyn, now an area of tundra was dominated by spruce-larch-fir-hemlock forests. After ca. 3.35 Myr BP dark coniferous taxa gradually disappeared. A very pronounced environmental change took place ca. 3.31-3.28 Myr BP, corresponding to the Marine Isotope Stage (MIS) M2, when treeless tundra- and steppe-like habitats became dominant in the regional vegetation. Climate conditions were similar to those of Late Pleistocene cold intervals. Numerous coprophilous fungi spores identified in the pollen samples suggest the presence of grazing animals around the lake. Following the MIS M2 event, larch-pine forests with some spruce mostly dominated the area until ca. 2.6 Myr BP, interrupted by colder and drier intervals ca. 3.043-3.025, 2.935-2.912, and 2.719-2.698 Myr BP. At the beginning of the Pleistocene, ca. 2.6 Myr BP, noticeable climatic deterioration occurred. Forested habitats changed to predominantly treeless and shrubby environments, which reflect a relatively cold and dry climate. Peaks in observed green algae colonies (Botryococcus) around 2.53, 2.45, 2.32-2.305, 2.20 and 2.16-2.15 Myr BP suggest a spread of shallow water environments. A few intervals (i.e., 2.55-2.53, ca. 2.37, and 2.35-2.32 Myr BP) with a higher presence of coniferous taxa (mostly pine and larch) document some relatively short-term climate ameliorations during Early Pleistocene glacial periods.

  4. Transient simulations of the last Glacial Cycle with an AOGCM

    NASA Astrophysics Data System (ADS)

    Smith, R. S.; Gregory, J. M.

    2010-12-01

    Using FAMOUS, a fast atmosphere-ocean general circulation model (AOGCM), a number of transient climate runs simulating the last 120kyr have been carried out. This is the first time such experiments have been done with an AOGCM, providing a three-dimensional simulation of both atmosphere and ocean over this period, including internally generated temporal variability over periods from days to millennia and physically detailed representations of important processes such as clouds and precipitation. Although the model is fast, computational restrictions mean that the rate of change of the forcings has been increased by a factor of 10, making each experiment 12kyr long. Atmospheric greenhouse gases (GHGs), northern hemisphere ice sheets and variations in solar radiation arising from changes in the Earth's orbit are treated as forcing factors, and are applied both separately and combined in different experiments. The long-term temperature changes on Antarctica match well with reconstructions derived from ice-core data, as does variability on timescales longer than 10kyr. Last Glacial Maximum (LGM) cooling on Greenland is reasonably well simulated, although our simulations do not reproduce the abrupt, millennial scale climate shifts seen in northern hemisphere climate proxies or their slower southern hemisphere counterparts. The spatial pattern of sea surface cooling at the LGM matches reasonably proxy reconstructions reasonably well. There is significant anti-correlated variability in the strengths of the Atlantic Meridional Overturning Circulation (AMOC) and the Antarctic Circumpolar Current (ACC) on timescales greater than 10kyr in our experiments. GHG forcing weakens the AMOC and strengths the ACC, whilst the presence of northern hemisphere icesheets strengthens the AMOC and weakens the ACC. The structure of the AMOC at the LGM is found to be sensitive to the details of the ice-sheet reconstruction used. The precessional component of the orbital forcing induces ~20kyr oscillations in the AMOC and ACC, whose amplitude is mediated by changes in the eccentricity of the Earth's orbit. These forcing influences combine, to first order, in a linear fashion to produce the ocean variability seen in the run with all forcings and set the deep-water properties of the global ocean, which is key to determining the carbon inventory of the glacial ocean.

  5. Pleistocene cave art from Sulawesi, Indonesia.

    PubMed

    Aubert, M; Brumm, A; Ramli, M; Sutikna, T; Saptomo, E W; Hakim, B; Morwood, M J; van den Bergh, G D; Kinsley, L; Dosseto, A

    2014-10-01

    Archaeologists have long been puzzled by the appearance in Europe ?40-35 thousand years (kyr) ago of a rich corpus of sophisticated artworks, including parietal art (that is, paintings, drawings and engravings on immobile rock surfaces) and portable art (for example, carved figurines), and the absence or scarcity of equivalent, well-dated evidence elsewhere, especially along early human migration routes in South Asia and the Far East, including Wallacea and Australia, where modern humans (Homo sapiens) were established by 50 kyr ago. Here, using uranium-series dating of coralloid speleothems directly associated with 12 human hand stencils and two figurative animal depictions from seven cave sites in the Maros karsts of Sulawesi, we show that rock art traditions on this Indonesian island are at least compatible in age with the oldest European art. The earliest dated image from Maros, with a minimum age of 39.9 kyr, is now the oldest known hand stencil in the world. In addition, a painting of a babirusa ('pig-deer') made at least 35.4 kyr ago is among the earliest dated figurative depictions worldwide, if not the earliest one. Among the implications, it can now be demonstrated that humans were producing rock art by ?40 kyr ago at opposite ends of the Pleistocene Eurasian world. PMID:25297435

  6. Studies of the PostGlacial History of British Vegetation. XIV. Late-Glacial Deposits at Moss Lake, Liverpool

    Microsoft Academic Search

    H. Godwin

    1959-01-01

    Investigations of deposits at a built-over site near the centre of Liverpool disclose a basal stratigraphic sequence characteristic of the west-European Late-glacial period. Detailed pollen analyses confirm that the deposits extended from the Late-glacial (Zone I) to the Post-glacial thermal maximum (Zone VIIa). The lake was overgrown in Zone VI by floating Sphagna, and in Zone VII a typical raised

  7. Glacial History of the North Atlantic Marine Snail, Littorina saxatilis, Inferred from Distribution of Mitochondrial DNA Lineages

    PubMed Central

    Panova, Marina; Blakeslee, April M. H.; Miller, A. Whitman; Mäkinen, Tuuli; Ruiz, Gregory M.; Johannesson, Kerstin; André, Carl

    2011-01-01

    The North Atlantic intertidal gastropod, Littorina saxatilis (Olivi, 1792), exhibits extreme morphological variation between and within geographic regions and has become a model for studies of local adaptation; yet a comprehensive analysis of the species' phylogeography is lacking. Here, we examine phylogeographic patterns of the species' populations in the North Atlantic and one remote Mediterranean population using sequence variation in a fragment of the mitochondrial cytochrome b gene (607 bp). We found that, as opposed to many other rocky intertidal species, L. saxatilis has likely had a long and continuous history in the Northwest Atlantic, including survival during the last glacial maximum (LGM), possibly in two refugia. In the Northeast Atlantic, several areas likely harboured refugial populations that recolonized different parts of this region after glacial retreat, resulting in strong population structure. However, the outlying monomorphic Venetian population is likely a recent anthropogenic introduction from northern Europe and not a remnant of an earlier wider distribution in the Mediterranean Sea. Overall, our detailed phylogeography of L. saxatilis adds an important piece to the understanding of Pleistocene history in North Atlantic marine biota as well as being the first study to describe the species' evolutionary history in its natural range. The latter contribution is noteworthy because the snail has recently become an important model species for understanding evolutionary processes of speciation; thus our work provides integral information for such endeavours. PMID:21412417

  8. Milankovitch insulation forcing and cyclic formation of large-scale glacial, fluvial, and eolian landforms in central Alaska

    NASA Technical Reports Server (NTRS)

    Beget, J. E.

    1993-01-01

    Continuous marine and ice-core proxy climate records indicate that the Earth's orbital geometry modulates long-term changes. Until recently, little direct evidence has been available to demonstrate correlations between Milankovitch cycles and large-scale terrestrial landforms produced during worldwide glaciations. In central Alaska large areas of loess and sand fill valleys and basins near major outwash streams. The streams themselves are bordered by sets of outwash terraces, and the terraces grade up valley into sets of moraines. The discovery of the Stampede tephra (approximately 175,000 yr ago) reworked within push moraines of the Lignite Creek glaciation suggests that this event correlates with the glaciation of marine isotope stage 6. A new occurrence of the Old Crow tephra (approximately 140,000 yr ago) on the surface of the oldest outwash terrace of the Tanana River, correlated with Delta glaciation, suggests this event also occurred at this time. The penultimate Healy glaciation apparently correlates with marine isotope stage 4, while radiocarbon dates indicate the latest Pleistocene moraines correlate with marine isotope stage 2. Recognition of the importance of orbital forcing to the cyclical formation of glacial landforms and landscapes can help in interpretations of remotely sensed glacial and proglacial land forms.

  9. Fluvial and glacial implications of tephra localities in the western Wind River basin, Wyoming, U. S. A

    SciTech Connect

    Jaworowski, C. (Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology)

    1993-04-01

    Examination of Quaternary fluvial and glacial deposits in the western Wind River Basin allows a new understanding of the Quaternary Wind River fluvial system. Interbedded fluvial sediments and volcanic ashes provide important temporal information for correlation of Quaternary deposits. In the western Wind River Basin, six mid-Pleistocene localities of tephra, the Muddy Creek, Red Creek, Lander, Kinnear, Morton and Yellow Calf ashes are known. Geochronologic studies confirm the Muddy Creek, Red Creek, Kinnear and Lander ashes as the 620--650ka Lava Creek tephra from the Yellowstone region in northwestern Wyoming. The stratigraphic position and index of refraction of volcanic glass from the Morton and Yellow Calf ashes are consistent with identification as Lava Creek tephra. Approximately 350 feet (106 meters) above the Wind River and 13 miles downstream from Bull Lake, interbedded Wind River fluvial gravels, volcanic glass and pumice at the Morton locality correlate to late (upper) Sacajawea Ridge gravels mapped by Richmond and Murphy. Associated with the oxygen isotope 16--15 boundary, the ash-bearing terrace deposits reveal the nature of the Wind River fluvial system during late glacial-early interglacial times. The Lander and Yellow Calf ashes, are found in terrace deposits along tributaries of the Wind River. Differences in timing and rates of incision between the Wind River and its tributary, the Little Wind River, results in complex terrace development near their junction.

  10. Post-glacial Paleo-oceanographic and Paleo-climatic Conditions and Linkages Along the West Coast of Canada

    NASA Astrophysics Data System (ADS)

    Dallimore, A.; Enkin, R. J.; McKechnie, I.

    2006-12-01

    Along the west coast of Canada, our continuing studies of annually laminated marine sediments in anoxic fjords illustrate the changing environment as glaciers retreated from this area about 12 ka y BP. New data from mid-coastal British Columbia expands our knowledge of the interplay between climate and ocean dynamics in the northeastern Pacific Ocean, and defines the evolution of modern climate conditions as ice receded from the coast, followed by the establishment of modern oceanographic and climatic conditions about 6,000 ky BP. The Late Pleistocene and Holocene record also marks dramatic changes in sea level, climate, coastal oceanographic dynamics and glacial sedimentary source and transport, with implications for the possibility of early human migration routes and glacial refugia. Changes in pre-historical aboriginal settlement sites and food sources also give indications of a dynamic Holocene land and seascape as modern conditions became established. Excellent chronological control is provided by complementary yet independent dating methods including radiocarbon dates on both plants and shells, identification of the Mazama Ash, varve counting and paleomagnetic/paleosecular variation correlations.

  11. Killer Whale Nuclear Genome and mtDNA Reveal Widespread Population Bottleneck during the Last Glacial Maximum

    PubMed Central

    Moura, Andre E.; Janse van Rensburg, Charlene; Pilot, Malgorzata; Tehrani, Arman; Best, Peter B.; Thornton, Meredith; Plön, Stephanie; de Bruyn, P.J. Nico; Worley, Kim C.; Gibbs, Richard A.; Dahlheim, Marilyn E.; Hoelzel, Alan Rus

    2014-01-01

    Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline. PMID:24497033

  12. Responses of high-elevation herbaceous plant assemblages to low glacial CO? concentrations revealed by fossil marmot (Marmota) teeth.

    PubMed

    McLean, Bryan S; Ward, Joy K; Polito, Michael J; Emslie, Steven D

    2014-08-01

    Atmospheric CO2 cycles of the Quaternary likely imposed major constraints on the physiology and growth of C3 plants worldwide. However, the measured record of this remains both geographically and taxonomically sparse. We present the first reconstruction of physiological responses in a late Quaternary high-elevation herbaceous plant community from the Southern Rocky Mountains, USA. We used a novel proxy-fossilized tooth enamel of yellow-bellied marmots (Marmota flaviventris)-which we developed using detailed isotopic analysis of modern individuals. Calculated C isotopic discrimination (?) of alpine plants was nearly 2 ‰ lower prior to the Last Glacial Maximum than at present, a response almost identical to that of nonherbaceous taxa from lower elevations. However, initial shifts in ? aligned most closely with the onset of the late Pleistocene bipolar temperature "seesaw" rather than CO2 increase, indicating unique limitations on glacial-age high-elevation plants may have existed due to both low temperatures and low CO2. Further development of system-specific faunal proxies can help to clarify this and other plant- and ecosystem-level responses to past environmental change. PMID:24916834

  13. Killer whale nuclear genome and mtDNA reveal widespread population bottleneck during the last glacial maximum.

    PubMed

    Moura, Andre E; Janse van Rensburg, Charlene; Pilot, Malgorzata; Tehrani, Arman; Best, Peter B; Thornton, Meredith; Plön, Stephanie; de Bruyn, P J Nico; Worley, Kim C; Gibbs, Richard A; Dahlheim, Marilyn E; Hoelzel, Alan Rus

    2014-05-01

    Ecosystem function and resilience is determined by the interactions and independent contributions of individual species. Apex predators play a disproportionately determinant role through their influence and dependence on the dynamics of prey species. Their demographic fluctuations are thus likely to reflect changes in their respective ecological communities and habitat. Here, we investigate the historical population dynamics of the killer whale based on draft nuclear genome data for the Northern Hemisphere and mtDNA data worldwide. We infer a relatively stable population size throughout most of the Pleistocene, followed by an order of magnitude decline and bottleneck during the Weichselian glacial period. Global mtDNA data indicate that while most populations declined, at least one population retained diversity in a stable, productive ecosystem off southern Africa. We conclude that environmental changes during the last glacial period promoted the decline of a top ocean predator, that these events contributed to the pattern of diversity among extant populations, and that the relatively high diversity of a population currently in productive, stable habitat off South Africa suggests a role for ocean productivity in the widespread decline. PMID:24497033

  14. Millennial-scale climate variability through the Mid to Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Barker, S.; Chen, J.; McManus, J. F.; Mokeddem, Z.; Theobald, M.; Thornalley, D. J.

    2013-12-01

    Millennial-scale climate variability has been pervasive throughout the last 800kyr at least. The global expression of such variability is epitomised by ice core temperature records from Greenland and Antarctica, with northern records revealing abrupt changes while southern records generally display more gradual changes that are approximately out of phase with their northern counterparts. One of the most intuitive mechanisms invoked to explain these opposing signals involves varying the northward heat transport associated with the Atlantic Meridional Overturning Circulation (AMOC). Additional evidence from a range of locations also highlights the importance of atmospheric shifts (e.g. rainfall and winds) in the global transmission of abrupt climate change. The (thermal) bipolar seesaw provides a simple means for transposing between the Antarctic and Greenland temperature records and has recently been exploited to produce a prediction of what Greenland records might look like if they extended back to 800ka. This exercise allowed an initial assessment of the potential interplay between millennial-scale variability and glacial-interglacial climate change (for example by confirming a link between seesaw oscillations and glacial terminations). However, the synthetic record is only a prediction and it is only 800kyr long. In order to place tighter constraints on the nature of millennial-scale variability through time and its relationship with the glacial cycles, we need to test and extend the prediction. Here we present the results from the first phase of a major effort to provide such a test. We present continuous high resolution (mean <200year) proxy SST records from ODP site 983 in the NE Atlantic spanning the last 400kyr (>2,200 samples - the final records will reach back to 1.7Ma and involve approximately 10,000 samples). Our results provide a vivid and revealing account of high latitude climate variability that can be compared directly with records from other sites and archives.

  15. Is There Evidence for Impact-Triggered Fires at the End Pleistocene?

    NASA Astrophysics Data System (ADS)

    Wolbach, W. S.; Stich, A.; Kloosterman, J. B.; Becker, L.; Kennett, J.; Firestone, R.; West, A.

    2007-05-01

    Recent evidence suggests an extraterrestrial contribution to the End Pleistocene extinctions. Sediments at the base of a carbon-rich, dark layer dating to ~12.9 ka contain magnetic grains, microspherules, elevated Ir, fullerenes with abundant 3He, and other evidence consistent with extraterrestrial impact [1]. To test the possibility that combustion of the impactor, carbon-bearing rocks, or biomass could have been triggered by the impact (as hypothesized at the End Cretaceous 65 Ma ago [2]), we searched for soot in a variety of Clovis-age sites marked by this dark layer in North America, Germany, and Belgium. Thirty-eight samples from the following North American sites were studied: Carolina Bays at Blackville and Myrtle Beach, SC; Murray Springs, AZ; Chobot Site, Alberta, Canada; Blackwater Draw, Clovis, NM; Glacial Lake Hind, Manitoba, Canada; Daisy Cave, San Miguel Channel Island, Santa Barbara. Four samples from the Usselo Horizon in Schleswig-Holstein and one sample from Lommel, Belgium were also analyzed. Dissolution and analysis procedures were based on those used successfully for detecting soot from impact- produced wildfires at the Cretaceous-Tertiary (K/T) boundary [3, 4, 5]. Reduced carbon was isolated from sediments using HCl and HCl/HF. Elemental carbon was separated from organic carbon by acidic dichromate oxidation. Any remaining minerals were removed from carbonaceous residues using sodium metatungstate density separation. The elemental carbon of interest (soot) was identified and characterized using SEM imaging and quantified by weighing and particle size analysis. Two of the samples contained significant quantities of soot: Murray Springs, AZ, with a soot content of 21 ± 5 ppm; and Carolina Bay, Blackville, SC, with a soot content of 1969 ± 167 ppm. None of the remaining End Pleistocene samples studied showed significant soot contents. Negative results do establish that surface contamination by soot was not a problem, even though some sample locations were undoubtedly close to automobile traffic or possible natural biomass fires. The magnitude and location of the End Pleistocene bolide is unknown and so it is impossible to predict the magnitude of any fires triggered by the impact. The presence of significant soot, however, especially the large amount at the Carolina Bay, suggests that significant burning at the very least occurred near that location ~12.9 ka ago. The fire that produced the observed soot might have been regional, or perhaps soot was initially deposited at additional sites but simply not preserved. These questions will be addressed by analyzing more End Pleistocene samples. [1] Firestone R.B., West A., Kennett J.P., Becker L., Bunch T.E., et al.