Sample records for pleistocene glacial oscillations

  1. Timing of Pleistocene glacial oscillations recorded in the Cantabrian Mountains (North Iberia): correlation of glacial and periglacial sequences from both sides of the range using a multiple-dating method approach

    NASA Astrophysics Data System (ADS)

    Rodriguez-Rodriguez, Laura; Jiménez-Sánchez, Montserrat; José Domínguez-Cuesta, María; Rinterknecht, Vincent; Pallàs, Raimón; Bourlès, Didier

    2015-04-01

    The Cantabrian Mountains is a coastal mountain range up to 2648 m altitude located at 43oN latitude and directly influenced by the North Atlantic climate oscillations. Although nowadays it is fully deglaciatied, glacial sediments and landforms are clearly preserved elsewhere above 1600 m. Particularly, glacial evidence in the central Cantabrian Mountains suggests the formation of an icefield in the headwaters of the Porma and Esla catchments drained by glaciers up to 1-6 km in length in the northern slope and 19 km-long in the southern slope, with their fronts at minimum altitudes of 900 and 1150 m asl respectively (Rodríguez-Rodríguez et al., 2014). Numerical ages obtained from the base of the Brañagallones ice-dammed deposit and one of the lateral moraines that are damming this deposit suggest that the local glacial maximum was prior to ca 33.5 cal ka BP in the Monasterio Valley (see data compiled in Rodriguez-Rodríguez et al., in press). Currently, our research is focused on developing a full chronology of glacial oscillations in both sides of the range and investigating their paleoclimate significance and relationship with glacial asymmetry through the combined use of surface exposure, OSL and radiocarbon dating methods. In this work, we present 47 10Be surface exposure ages obtained from boulders in moraines, glacial erratic boulders and rock glaciers in the Monasterio and Porma valleys. The glacial record of these valleys was chosen because of: (i) its good preservation state; (ii) the occurrence of a quartz-rich sandstone formation; and (iii) the availability of previous 14C and OSL numerical ages. Sampling sites were selected considering the relative age of glacial stages to cover as complete as possible the history of Pleistocene glaciations in the studied area, from the glacial maximum stage to the prevalence of periglacial conditions. Preliminary results suggest the occurrence of several glacial advances of similar extent at ca 150 - 50 ka followed by a deglaciation sequence that changed gradually to periglacial conditions during the Lateglacial (16 - 12 ka). Radiocarbon and OSL sampling campaigns have been recently developed to complement and cross-check these preliminary results, which are compared with other paleoclimate proxies in this contribution. Rodríguez-Rodríguez, L., Jiménez-Sánchez, M., Domínguez-Cuesta, M.J., 2014. Geophysical Research Abstracts 16, EGU2014-292. Rodríguez-Rodríguez, L., Jiménez-Sánchez, M., Domínguez-Cuesta, M.J., Aranburu, A., in press. Quaternary International, http://dx.doi.org/10.1016/j.quaint.2014.06.007 Research funded by MINECO-PGE-FEDER through the project CANDELA (MINECO-CGL2012-31938). Laura Rodríguez-Rodríguez developed her research granted by the Spanish FPU Program (Ministerio de Educación Cultura y Deporte).

  2. RESEARCH ARTICLE Open Access Polyploid evolution and Pleistocene glacial cycles

    E-print Network

    Zürich, Universität

    RESEARCH ARTICLE Open Access Polyploid evolution and Pleistocene glacial cycles: A case study from and Elena Conti2 Abstract Background: Recent studies highlighted the role of Pleistocene climatic cycles, Flow cytometry, Non-adaptive processes, Phylogeny, Primula marginata, Alps, Refugia, Pleistocene

  3. Multiple instabilities and modes of glacial rhythmicity in the plio-Pleistocene: a general theory of late Cenozoic climatic change

    Microsoft Academic Search

    Barry Saltzman; Mikhail Ya Verbitsky

    1993-01-01

    It has been noted that several distinct modes of glacial oscillation have existed during the past few million years, ranging from low-amplitude, high-frequency oscillations in the early Pliocene, through relatively high amplitude, predominantly near-40 ky period, oscillations in the late Pliocene and early Pleistocene, to the major near-100 ky period oscillations of the late Pleistocene. In addition to other plausible

  4. 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.

  5. Changing climatic response: a conceptual model for glacial cycles and the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Daruka, I.; Ditlevsen, P. D.

    2014-03-01

    Milankovitch's astronomical theory of glacial cycles, attributing ice age climate oscillations to orbital changes in Northern Northern-Hemisphere insolation, is challenged by the paleoclimatic record. The climatic response to the variations in insolation is far from trivial. In general the glacial cycles are highly asymmetric in time, with slow cooling from the interglacials to the glacials (inceptions) and very rapid warming from the glacials to the interglacials (terminations). We shall refer to this fast-slow dynamics as the "saw-tooth" shape of the paleoclimatic record. This is non-linearly related to the time-symmetric variations in the orbital forcing. However, the most pronounced challenge to the Milankovitch theory is the Mid-Pleistocene Transition (MPT) occurring about one million years ago. During that event, the prevailing 41 kyr glacial cycles, corresponding to the almost harmonic obliquity cycle were replaced by longer saw-tooth shaped cycles with a time scale around 100 kyr. The MPT must have been driven by internal changes in climate response, since it does not correspond to any apparent changes in the orbital forcing. In order to identify possible mechanisms causing the observed changes in glacial dynamics, it is relevant to study simplified models with the capability of generating temporal behavior similar to the observed records. We present a simple oscillator type model approach, with two variables, a temperature anomaly and an ice volume analogous, climatic memory term. The generalization of the ice albedo feedback is included in terms of an effective multiplicative coupling between this latter climatic memory term (representing the internal degrees of freedom) and the external drive. The simple model reproduces the temporal asymmetry of the late Pleistocene glacial cycles and suggests that the MPT can be explained as a regime shift, aided by climatic noise, from a period 1 frequency locking to the obliquity cycle to a period 2-3 frequency locking to the same obliquity cycle. The change in dynamics has been suggested to be a result of a slow gradual decrease in atmospheric greenhouse gas concentration. The presence of chaos in the (non-autonomous) glacial dynamics and a critical dependence on initial conditions raises fundamental questions about climate predictability.

  6. A conceptual model for glacial cycles and the middle Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Daruka, István; Ditlevsen, Peter D.

    2015-03-01

    Milankovitch's astronomical theory of glacial cycles, attributing ice age climate oscillations to orbital changes in Northern-Hemisphere insolation, is challenged by the paleoclimatic record. The climatic response to the variations in insolation is far from trivial. In general the glacial cycles are highly asymmetric in time, with slow cooling from the interglacials to the glacials (inceptions) and very rapid warming from the glacials to the interglacials (terminations). We shall refer to this fast-slow dynamics as the "saw-tooth" shape of the paleoclimatic record. This is non-linearly related to the time-symmetric variations in the orbital forcing. However, the most pronounced challenge to the Milankovitch theory is the middle Pleistocene transition (MPT) occurring about one million years ago. During that event, the prevailing 41 kyr glacial cycles, corresponding to the almost harmonic obliquity cycle were replaced by longer saw-tooth shaped cycles with a time-scale around 100 kyr. The MPT must have been driven by internal changes in climate response, since it does not correspond to any apparent changes in the orbital forcing. In order to identify possible mechanisms causing the observed changes in glacial dynamics, it is relevant to study simplified models with the capability of generating temporal behavior similar to the observed records. We present a simple oscillator type model approach, with two variables, a temperature anomaly and a climatic memory term. The generalization of the ice albedo feedback is included in terms of an effective multiplicative coupling between this latter climatic memory term (representing the internal degrees of freedom) and the external drive. The simple model reproduces the temporal asymmetry of the late Pleistocene glacial cycles and suggests that the MPT can be explained as a regime shift, aided by climatic noise, from a period 1 frequency locking to the obliquity cycle to a period 2-3 frequency locking to the same obliquity cycle. The change in dynamics has been suggested to be a result of a slow gradual decrease in atmospheric greenhouse gas concentration. The critical dependence on initial conditions in the (non-autonomous) glacial dynamics raises fundamental questions about climate predictability.

  7. Simulations of cataclysmic outburst floods from Pleistocene Glacial Lake Missoula

    USGS Publications Warehouse

    Denlinger, Roger P.; O'Connell, D. R. H.

    2009-01-01

    Using a flow domain that we constructed from 30 m digital-elevation model data of western United States and Canada and a two-dimensional numerical model for shallow-water flow over rugged terrain, we simulated outburst floods from Pleistocene Glacial Lake Missoula. We modeled a large, but not the largest, flood, using initial lake elevation at 1250 m instead of 1285 m. Rupture of the ice dam, centered on modern Lake Pend Oreille, catastrophically floods eastern Washington and rapidly fills the broad Pasco, Yakima, and Umatilla Basins. Maximum flood stage is reached in Pasco and Yakima Basins 38 h after the dam break, whereas maximum flood stage in Umatilla Basin occurs 17 h later. Drainage of these basins through narrow Columbia gorge takes an additional 445 h. For this modeled flood, peak discharges in eastern Washington range from 10 to 20 × 106 m3/s. However, constrictions in Columbia gorge limit peak discharges to 6 m3/s and greatly extend the duration of flooding. We compare these model results with field observations of scabland distribution and high-water indicators. Our model predictions of the locations of maximum scour (product of bed shear stress and average flow velocity) match the distribution of existing scablands. We compare model peak stages to high-water indicators from the Rathdrum-Spokane valley, Walulla Gap, and along Columbia gorge. Though peak stages from this less-than-maximal flood model attain or exceed peak-stage indicators along Rathdrum-Spokane valley and along Columbia gorge, simulated peak stages near Walulla Gap are 10–40 m below observed peak-stage indicators. Despite this discrepancy, our match to field observations in most of the region indicates that additional sources of water other than Glacial Lake Missoula are not required to explain the Missoula floods.

  8. "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?

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

    SciTech Connect

    Saltzman, B.; Verbitsky, M.Ya. [Yale Univ., New Haven, CT (United States)

    1993-10-01

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

  10. Arctic, Antarctic, and Alpine Research, Vol. 37, No. 4, 2005, pp. 416424 Late Pleistocene Glacial Geology of the Okpilak-Kongakut Rivers Region,

    E-print Network

    Briner, Jason P.

    Arctic, Antarctic, and Alpine Research, Vol. 37, No. 4, 2005, pp. 416­424 Late Pleistocene Glacial combined with cosmogenic exposure dating provides the first detailed assessment of the late Pleistocene of Pleistocene glaciation. Much of the Brooks Range exhibits well- expressed glacial features that have been

  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. Cataclysmic Late pleistocene flooding from glacial Lake Missoula: A review

    NASA Astrophysics Data System (ADS)

    Baker, Victor R.; Bunker, Russell C.

    Late Wisconsin floods from glacial Lake Missoula occurred between approximately 16 and 12 ka BP. Many floods occurred; some were demonstrably cataclysmic. Early studies of Missoula flooding centered on the anomalous physiography of the Channeled Scabland, which J. Harlen Bretz hypothesized in 1923 to have developed during a debacle that he named 'The Spokane Flood'. Among the ironies in the controversy over this hypothesis was a mistaken view of uniformitarianism held by Bretz's adversaries. After resolution of the scabland's origin by cataclysmic outburst flooding from glacial Lake Missoula, research since 1960 emphasized details of flood magnitudes, frequency, routing and number. Studies of flood hydraulics and other physical parameters need to utilize modern computerized procedures for flow modeling, lake-burst simulation, and sediment-transport analysis. Preliminary simulation models indicate the probability of multiple Late Wisconsin jökulhlaups from Lake Missoula, although these models predict a wide range of flood magnitudes. Major advances have been made in the study of low-energy, rhythmically bedded sediments that accumulated in flood slack-water areas. The 'forty floods' hypothesis postulates that each rhythmite represents the deposition in such slack-water areas of separate, distinct cataclysmic floods that can be traced from Lake Missoula to the vicinity of Portland, Oregon. However, the hypothesis has numerous unsubstantiated implications concerning flood magnitudes, sources, routing and sedimentation dynamics. There were multiple great Late Wisconsin floods in the Columbia River system of the northwestern United States. Studies of high-energy, high altitude flood deposits are necessary to evaluate the magnitudes of these floods. Improved geochronologic studies throughout the immense region impacted by the flooding will be required to properly evaluate flood frequency. The cataclysmic flood concept championed by J. Harlen Bretz continues to stimulate exciting and controversial research.

  13. Bifurcations and strange nonchaotic attractors in a phase oscillator model of glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Mitsui, Takahito; Crucifix, Michel; Aihara, Kazuyuki

    2015-06-01

    Glacial-interglacial cycles are large variations in continental ice mass and greenhouse gases, which have dominated climate variability over the Quaternary. The dominant periodicity of the cycles is ?40 kyr before the so-called middle Pleistocene transition between ?1.2 and ?0.7 Myr ago, and it is ?100 kyr after the transition. In this paper, the dynamics of glacial-interglacial cycles are investigated using a phase oscillator model forced by the time-varying incoming solar radiation (insolation). We analyze the bifurcations of the system and show that strange nonchaotic attractors appear through nonsmooth saddle-node bifurcations of tori. The bifurcation analysis indicates that mode-locking is likely to occur for the 41 kyr glacial cycles but not likely for the 100 kyr glacial cycles. The sequence of mode-locked 41 kyr cycles is robust to small parameter changes. However, the sequence of 100 kyr glacial cycles can be sensitive to parameter changes when the system has a strange nonchaotic attractor.

  14. Bifurcations and strange nonchaotic attractors in a phase oscillator model of glacial-interglacial cycles

    E-print Network

    Mitsui, Takahito; Aihara, Kazuyuki

    2015-01-01

    Glacial-interglacial cycles are large variations in continental ice mass and greenhouse gases, which have dominated climate variability over the Quaternary. The dominant periodicity of the cycles is $\\sim $40 kyr before the so-called middle Pleistocene transition between $\\sim$1.2 and $\\sim$0.7 Myr ago, and it is $\\sim $100 kyr after the transition. In this paper, the dynamics of glacial-interglacial cycles are investigated using a phase oscillator model forced by the time-varying incoming solar radiation (insolation). We analyze the bifurcations of the system and show that strange nonchaotic attractors appear through nonsmooth saddle-node bifurcations of tori. The bifurcation analysis indicates that mode-locking is likely to occur for the 41 kyr glacial cycles but not likely for the 100 kyr glacial cycles. The sequence of mode-locked 41 kyr cycles is robust to small parameter changes. However, the sequence of 100 kyr glacial cycles can be sensitive to parameter changes when the system has a strange nonchaoti...

  15. 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.

  16. The bifurcation structure and noise induced transitions in the Pleistocene glacial cycles

    E-print Network

    Peter D. Ditlevsen

    2009-02-10

    The glacial cycles are attributed to the climatic response of the orbital changes in the irradiance to the Earth. These changes in the forcing are to small to explain the observed climate variations as simple linear responses. Non-linear amplifications are necessary to account for the glacial cycles. Here an empirical model of the non-linear response is presented. From the model it is possible to assess the role of stochastic noise in comparison to the deterministic orbital forcing of the ice ages. The model is based on the bifurcation structure derived from the climate history. It indicates the dynamical origin of the Mid-Pleistocene transition (MPT) from the '41 kyr world' to the '100 kyr world'. The dominant forcing in the latter is still the 41 kyr obliquity cycle, but the bifurcation structure of the climate system is changed. The model indicates that transitions between glacial and interglacial climate are assisted by internal stochastic noise in the period prior to the last five glacial cycles, while the last five cycles are deterministic responses to the orbital forcing.

  17. The bifurcation structure and noise induced transitions in the Pleistocene glacial cycles

    E-print Network

    Ditlevsen, Peter D

    2009-01-01

    The glacial cycles are attributed to the climatic response of the orbital changes in the irradiance to the Earth. These changes in the forcing are to small to explain the observed climate variations as simple linear responses. Non-linear amplifications are necessary to account for the glacial cycles. Here an empirical model of the non-linear response is presented. From the model it is possible to assess the role of stochastic noise in comparison to the deterministic orbital forcing of the ice ages. The model is based on the bifurcation structure derived from the climate history. It indicates the dynamical origin of the Mid-Pleistocene transition (MPT) from the '41 kyr world' to the '100 kyr world'. The dominant forcing in the latter is still the 41 kyr obliquity cycle, but the bifurcation structure of the climate system is changed. The model indicates that transitions between glacial and interglacial climate are assisted by internal stochastic noise in the period prior to the last five glacial cycles, while t...

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

    NASA Astrophysics Data System (ADS)

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

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

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

    USGS Publications Warehouse

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

    2003-01-01

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

  20. Agulhas salt-leakage oscillations during abrupt climate changes of the Late Pleistocene

    NASA Astrophysics Data System (ADS)

    Marino, Gianluca; Zahn, Rainer; Ziegler, Martin; Purcell, Conor; Knorr, Gregor; Hall, Ian R.; Ziveri, Patrizia; Elderfield, Henry

    2013-09-01

    An ensemble of new, high-resolution records of surface ocean hydrography from the Indian-Atlantic oceanic gateway, south of Africa, demonstrates recurrent and high-amplitude salinity oscillations in the Agulhas Leakage area during the penultimate glacial-interglacial cycle. A series of millennial-scale salinification events, indicating strengthened salt leakage into the South Atlantic, appear to correlate with abrupt changes in the North Atlantic climate and Atlantic Meridional Overturning Circulation (AMOC). This interhemispheric coupling, which plausibly involved changes in the Hadley Cell and midlatitude westerlies that impacted the interocean transport at the tip of Africa, suggests that the Agulhas Leakage acted as a source of negative buoyancy for the perturbed AMOC, possibly aiding its return to full strength. Our finding points to the Indian-to-Atlantic salt transport as a potentially important modulator of the AMOC during the abrupt climate changes of the Late Pleistocene.

  1. Oscillators and relaxation phenomena in Pleistocene climate theory

    E-print Network

    Crucifix, Michel

    2011-01-01

    Ice sheets appeared in the northern hemisphere around 3 million years ago and glacial-interglacial cycles have paced Earth's climate since then. Superimposed on these long glacial cycles comes an intricate pattern of millennial and sub-millennial variability, including Dansgaard-Oeschger and Heinrich events. There are numerous theories about theses oscillations. Here, we review a number of them in order draw a parallel between climatic concepts and dynamical system concepts, including, in particular, the relaxation oscillator, excitability, slow-fast dynamics and homoclinic orbits. Namely, almost all theories of ice ages reviewed here feature a phenomenon of synchronisation between internal climate dynamics and the astronomical forcing. However, these theories differ in their bifurcation structure and this has an effect on the way the ice age phenomenon could grow 3 million years ago. All theories on rapid events reviewed here rely on the concept of a limit cycle in the ocean circulation, which may be excited...

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

    E-print Network

    Stochastic forcing of Pleistocene ice sheets: Implications for the origin of millennial in these events, stochastically forced changes in the mass balance of the Pleistocene ice sheets may have resulted of Pleistocene ice sheets: Implications for the origin of millennial-scale climate oscillations, Paleoceanography

  3. Pleistocene glaciations in the weatern Arctic Ocean: Tentative age model of marine glacial landforms

    NASA Astrophysics Data System (ADS)

    Niessen, Frank; Stein, Rüdiger; Matthiessen, Jens; Jensen, Laura; Nam, Seung-Il; Schreck, Michael

    2015-04-01

    Recently glacial landforms were presented and interpreted as complex pattern of Pleistocene glaciations in the western Arctic Ocean along the continental margin of the East Siberian and Chukchi seas, (Niessen et al. 2013, Dove et al. 2014). These landforms include moraines, drumlins, glacigenic debris flows, till wedges and mega-scale glacial lineations. Orientations of some of the landforms suggest the presence of former ice sheets on the Chukchi Borderland and the East Siberian shelf. Here we present a tentative age model for some of the younger glacial events by correlation of sediment cores with glacial landforms as seen in subbottom profiles. The database was obtained during 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. The stratigraphic correlation of sediment cores is based on physical properties (wet-bulk density and magnetic susceptibility), lithology and color. The chronology of the area has been proposed by Stein et al. (2010) for a core from the Chukchi Abyssal Plain (PS72/340-5) and includes brown layers B1 to B9 (marine isotope stages MIS 1 to MIS 7), which are used as marker horizons for lateral core correlation. Our tentative age model suggests that the youngest and shallowest (480 m below present water level; mbpwl) grounding event of an ice sheet on the Chukchi Borderland is younger than B2 (interpreted as Last Glacial Maximum; LGM). There is no clear evidence for a LGM glaciation along the East Siberian margin because intensive post LGM iceberg scouring occurred above 350 m present water level. On the slopes of the East Siberian Sea two northerly directed ice advances occurred, both of which are older and younger than B2 and B3, respectively. The younger advance grounded to about 700 m present water depth along the continental slope and the older to 900 m and 1100 m on the Arlis Plateau and the East Siberian continental margin, respectively. We interpret these advances as Middle Weichselian glaciations on the Beringian shelf (MIS 4 to 3). Two older glaciations can be dated as Early Weichselian (MIS 5b to 5d), of which the younger event is older and younger than B3 and B4, respectively. This glaciation can be traced by glacial wedges, streamlined lineations in up to 1200 mbpsl and subglacial diamicton along the East Siberian margin, the Arlis Plateau, and the Mendeleev Ridge. There are at least three older glaciation visible in acoustic images from the East Siberian continental margin, which probably predate the Weichselian. The available cores did not penetrate these events and the ages remain speculative. Dove, D, Polyak, L., Coakley, B. (2014) Widespread, multi-source glacial erosion on the Chukchi margin, Arctic Ocean, Quat. Sci. Rev. 92, 112-122. Niessen, F. et al. (2013) Repeated Pleistocene glaciation of the East Siberian continental margin, Nature Geoscience, 6 (10), 842-846. Stein, R. et al. (2010) Towards a better (litho-) stratigraphy and reconstruction of Quaternary paleoenvironment in the Amerasian Basin (Arctic Ocean), Polarforschung, 79(2), 97-121.

  4. 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

  5. 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.

  6. Late Pleistocene oscillations of Lake Owens, eastern California

    SciTech Connect

    Orme, A.J. (California State Univ., Northridge, CA (United States). Dept. of Geography); Orme, A.R. (Univ. of California, Los Angeles, CA (United States). Dept. of Geography)

    1993-04-01

    Just before diversion of the Owens River drainage to Los Angeles in 1912--13, Owens Lake had a maximum depth of 14m and covered 290 km[sup 2] at a water-surface elevation of 1,095m. Indeed throughout most of Holocene time, the lake formed the sump for the Owens River drainage, its level fluctuating in response to variable inflow and evaporation. In late Pleistocene time, however, Lake Owens' spilled south towards Lake Searles' on reaching an elevation of 1,145m, at which level the lake was 64m deep and covered 694 km[sup 2]. Aided by radiometric dating, stratigraphic and sedimentological analyses of beach ridges and associated deposits around its northeast margin reveal complex oscillations of Lake Owens between 13,000 and 9,000 years B.P.. Following an earlier high stand, lake level fell until around 13,000 B.P. it rose again to at least 1138m, probably linked to late Wisconsinan glacier melt in the Sierra Nevada. Across the Pleistocene/Holocene transition, lake level fell to around 1100m and then rose to about 1,120m around 9,600 B.P., before falling away during Holocene time. This pattern is consistent with fluctuations in glacier budgets and meltwater regimes, and with late Pleistocene-early Holocene climatic oscillations postulated elsewhere in the region. Correlation with lake-level fluctuations observed at other localities around Owens Lake is complicated by tectonism, but the above sequence invites comparison with the detailed record obtained from Searles Lake farther south.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Our knowledge on the timing of glacial advances in the Southern Carpathians is limited. Recently, some attempts have been made to develop an improved temporal framework for the glaciations of the region using cosmogenic 10Be exposure dating. However, glacial chronology of the Romanian Carpathians remains contradictory. E.g. the timing of the maximum ice advance appears to be asynchronous within the area and also with other dated glacial events in Europe. Main objective of our study is to utilize cosmogenic in situ produced 10Be dating to disentangle the contradictions of the Southern Carpathian Late Pleistocene glacial chronology. Firstly, previously published 10Be data are recalculated in accordance with the new half-life, standardization and production rate of 10Be. The recalculated 10Be exposure ages of the second largest (M2) moraines in the Retezat Mts. appear to be ca. 19-24% older than exposure ages calculated by Reuther et al. (2007, Quat. Int. 164-165, 151-169). This contradicts the earlier conclusions suggesting post LGM age of M2 glacial advance and suggests that M2 moraines can be connected to the end of the LGM with final stabilization possibly at the beginning of the Late Glacial. We emphasize that it is ambiguous to correlate directly the exposure-dated glacier chronologies with millennial scale climate changes due to uncertainties in sample collection and in computation of exposure ages from measured nuclide concentrations. New 10Be samples were collected in order to determine the 10Be exposure age of moraines outside the most prominent generation (M2) including the largest and oldest moraine (M1) and the landforms connected to the smallest ice advances (M4), which remained undated so far. The new exposure ages of M2 moraines are well in harmony with the recalculated ages of Reuther at al. (2007). 10Be exposure age of boulders on the smallest moraine suggest that the last glaciers disappeared in the area during the Late Glacial, indicating no glaciation during the Younger Dryas and Holocene. Previous works, based on geomorphologic analogies and pedological properties suggested that the M1 ice advance was older than LGM, and possibly occurred during the MIS4. Our 10Be exposure dating provided LGM ages for boulders on the M1 side moraine. It is question of further research whether these ages show the time when the glacier abandoned the moraine or they only indicate an LGM erosional event affecting an older moraine. If we accept the LGM age of maximum ice extent (M1), our 10Be exposure age data enables the calculation of a mean glacier retreat rate of 1.3 m/a for the period between M1 and M4 (21.4 to 13.6ka). Alternatively, considering only the oldest 10Be exposure age of the M2 moraine, the M2 to M4 (20.2-13.6ka) glacier retreat rate was slightly lower: 1.1 m/a. Our research was supported by the OTKA PD83610, by the MTA-CNRS cooperation (NKM-96/2014), by the Bolyai Scholarship, and by the 'Lendület' program of the HAS (LP2012-27/2012). The 10Be measurements were performed at the ASTER AMS national facility (CEREGE, Aix en Provence, France).

  8. 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.

  9. Oscillators and relaxation phenomena in Pleistocene climate theory

    PubMed Central

    Crucifix, Michel

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Sheng, Y.

    2014-12-01

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

  11. Two mid-Pleistocene Glacial Cycles (MIS 14 to 10) From Lacustrine Sediments in the Valles Caldera, New Mexico

    NASA Astrophysics Data System (ADS)

    Fawcett, P. J.; Heikoop, J.; Anderson, R.; Hurley, L.; Goff, F.; Geissman, J. W.; Johnson, C.; Woldegabriel, G.; Allen, C. D.; Fessenden, J.

    2006-12-01

    A long-lived middle Pleistocene lake formed in the Valle Grande, a large moat valley of the Valles Caldera in northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The deposits of this lake were cored in May 2004 (GLAD5 project, hole VC-3) and 81 m of mostly lacustrine silty mud was recovered. A tentative chronology has been established for VC-3 with a basal tephra Ar-Ar date of 552 +/- 3 kyr, a correlation of major climatic changes in the core with other long Pleistocene records (SPECMAP and long Antarctic ice core records) and the recognition of several geomagnetic field polarity events in the core which can be correlated with globally recognized events. This record spans a critical interval of the middle Pleistocene from MIS 14 (552 kyr B.P.) to MIS 10 (~380 kyr B.P.), at which time the lacustrine sediments filled the available accommodation space in the caldera moat. Multiple analyses including core sedimentology and stratigraphy, sediment density and rock magnetic properties, organic carbon content and carbon isotopic ratios, C/N ratios, and pollen content reveal two glacial/interglacial cycles in the core (MIS 14 to MIS 10). Glacial terminations V and VI and complete sections spanning interglacials MIS 13 and MIS 11 are captured at a high resolution. In the VC-3 record, both of these interglacials are relatively long compared with the intervening glacials (MIS 14 and MIS 12), and interglacial MIS 13 is significantly muted in amplitude compared with MIS 11. These features are similar to several other mid-Pleistocene records. Of particular interest is relatively large amplitude millennial-scale variability evident in several proxies through the interglacial MIS 11 section. The glacial terminations are quite abrupt in this record with notable changes in sedimentation, organic carbon content, C/N ratios and watershed vegetation type. Termination V is the largest climate change evident in this part of the middle Pleistocene. The glacial inceptions tend to be more gradual, on the order of a few thousand years.

  12. 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.

  13. Provenance of Palouse Loess and Relation to Late Pleistocene Glacial Outburst Flooding, Washington State

    NASA Astrophysics Data System (ADS)

    Sweeney, M. R.; Busacca, A. J.; Gaylord, D. R.; Zender, C. S.

    2002-12-01

    The eolian system of the Pacific Northwest is a product of long-term deflation of expansive sedimentary units by prevailing winds throughout the Quaternary. The Palouse loess is a deposit of wind-blown silt that covers approximately 10,000 sqare km up to 75 m thick. Late Quaternary units of the loess become finer texturally and thinner to the northeast, suggesting that they were derived from sedimentary basins south and west. The source of the loess has been inferred and hypothesized but never directly determined. A geochemical study of the late-Pleistocene to Holocene L1 unit of the Palouse loess and its possible sources was conducted to determine its provenance. There are two sedimentary units that lie upwind of the loess that may have contributed sediment via eolian deflation: 1) sand- and silt-rich slackwater sediment derived from late-Pleistocene outburst flooding of glacial Lake Missoula, and 2) sand- and silt-rich sediment from the Miocene-Pliocene Ringold Formation. Both are very similar in mineral composition, being derived from plutonic, metamorphic, and volcanic rocks of the western United States and southern British Columbia. Major and trace element data determined by x-ray fluorescence (XRF) of silt to very fine sand from loess and potential source sediments was used to pinpoint the exact source of the loess. A one-to-one relationship of major and trace elements exists between eolian and flood sediments, whereas Ringold Formation sediments have elevated Ti, P, Mg, and Ca oxides and lower K oxide values as well as scattered trace element values relative to Palouse loess. These trends may be due to the presence of basalt lithic grains in flood sediment that have been broken down and distributed throughout the loess. The Ringold Formation lacks appreciable amounts of basalt. The geochemical data from this study demonstrates that flood sediment is the dominant source of eolian material for the Palouse loess. The spatial distribution of the possible source sediments also suggests that flood slackwater sediment is the dominant source. Slackwater flood sediments rest in basins upwind of loess, where deflation is documented today. The Ringold Formation has limited exposure near the present day Columbia River and was eroded by outburst floods or covered by slackwater sediments. Its limited extent and exposure makes the Ringold Formation an less likely candidate for a source of the L1 loess. Study of the oldest units of Palouse loess will show whether or not the Ringold contributed a larger proportion of eolian material prior to the onset of glacial outburst flooding. This new provenance data will allow estimates to be made of the volume of dust ejected into the atmosphere from the Palouse eolian system since the last glacial maximum, which is essential to modeling of atmospheric dust fluxes that force climate fluctuations.

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

    E-print Network

    Ingólfsson, Ólafur

    2001-01-01

    Quaternary Science Reviews 20 (2001) 405}417 Geomorphological correlation of Late Pleistocene in comparing the chronology and correlation of Late Pleistocene glaciations between Western and Eastern clearly con"rm that in all regions the latest late Pleistocene glaciation (24.0}10.5 ka) was restricted

  15. 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.

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

    E-print Network

    Schöne, Bernd R.

    @em.uni-frankfurt.de) Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN U.K. Department of Earth Science, Rice University, Houston TX 77251, USA §Geocoastal Research Group, School of Geosciences of younger, post-glacial deposits, are rare in pre- last glacial maximum core sections, possibly due

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The focus of this study is on the geochronological and paleoclimatic characterization of Pleistocene glaciation in central (Khangai Mountains) and western (Turgen Mountains, Mongolian Altai) Mongolia. These two mountain ranges form a 700 km long SE-NW transect through Mongolia and allow assumptions of the temporal and causal dynamics of regional glaciation and their correlation to other mountain glacier records from Central and High Asia. In order to evaluate the Pleistocene glaciations in Mongolia we undertook geomorphological mapping and cosmogenic radionuclide (CRN) surface exposure dating (10Be) in four valley systems located in the Khangai Mountains and Turgen Mountains. In total 46 glacial boulders and roche moutonnées were sampled, prepared and AMS measured to determine their 10Be surface exposure ages. Of these, 26 samples were obtained from the Khangai Mountains (three separate moraine sequences) and 20 samples were taken from the Turgen Mountains (one moraine sequence). Our results give evidence of major ice advances during early MIS-4 (74?71 ka) and MIS-2 (25?20 and 18? 17 ka) in both mountain ranges. However, in the Khangai Mountains of central Mongolia very significant ice advances also occurred during MIS-3 (37?32 ka), which exceeded the ice limits set during the MIS-2 glaciation. These results show that climatic conditions during phases of insolation minima characterized by extremely cold and dry conditions (MIS-4 and MIS-2) produced a favorable setting for major ice expansion in Mongolia. Yet, glacial accumulation in the Khangai Mountains also increased substantially in response to the cool-wet conditions of MIS-3, associated with a possibly greater-than-today input from winter precipitation. These records indicate that in addition to the thermally induced glaciations of MIS-4 and MIS-2, variations in atmospheric moisture supply are also capable of triggering large ice advances as observed during MIS-3. Taken together, this suggests that the role of atmospheric circulation and its significance for controlling regional precipitation results in a more differentiated pattern of late Pleistocene glaciation in Mongolia than previously recognized. Compared to other glacial records from High Asia, the observed patterns of past glaciations in Mongolia show similar results (i.e. ice maxima during interstadial wet phases) compared to monsoon influenced regions in southern Central Asia and NE-Tibet, while major expansion during insolation minima (MIS-4 and MIS-2) are more in tune with glacier responses known from western Central Asia and Siberia.

  18. Flux and provenance of ice-rafted debris in the earliest Pleistocene sub-polar North Atlantic Ocean comparable to the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Bailey, Ian; Foster, Gavin L.; Wilson, Paul A.; Jovane, Luigi; Storey, Craig D.; Trueman, Clive N.; Becker, Julia

    2012-08-01

    Relatively little is known in detail about the locations of the early Pleistocene ice-sheets responsible for ice-rafted debris (IRD) inputs to the sub-polar North Atlantic Ocean during intensification of northern hemisphere glaciation (iNHG). To shed new light on this problem, we present the first combined in-depth analysis of IRD flux and geochemical provenance of individual sand-sized IRD deposited in the sub-polar North Atlantic Ocean during the earliest large amplitude Pleistocene glacial, marine isotope stage (MIS) 100 (?2.52 Ma), arguably the key glacial during iNHG. IRD provenance is assessed using laser ablation lead (Pb) isotope analyses of single feldspar grains. We find that the Pb-isotope composition (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) of individual ice-rafted (>150 ?m) feldspars deposited at DSDP Site 611A, ODP Site 981 and IODP Site U1308 during MIS 100 records a shift from predominantly Archaean-aged circum-North Atlantic Ocean continental sources during early glacial ice-rafting events to dominantly Palaeozoic and Proterozoic-aged sources during full glacial conditions. The distribution of feldspars in Pb-Pb space for full glacial MIS 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial IRD belt (at IODP/DSDP Site U1308/609) during ambient (non-Heinrich-event) ice-rafting episodes of MIS 2 (?23.8 ka) than that documented for MIS 5d (?106 ka). Comparison of our early Pleistocene and last glacial cycle datasets suggests that MIS 100 was characterised by abundant iceberg calving from large ice-sheets on multiple continents in the high northern latitudes (not just on Greenland).

  19. 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.

  20. Phylogeography of Rhinichthys cataractae (Teleostei: Cyprinidae): pre-glacial colonization across the Great Continental Divide and Pleistocene diversification within the Rio Grande drainage

    E-print Network

    Kim, Dae Min

    2013-09-16

    -genetic studies on fishes with a trans- continental distribution (e.g., Catostomus catostomus; McPhail and Taylor, 1999; Salvelinus confluentus; Taylor et al., 1999; Lota lota; Van Houdt et al., 2005) have provided evidence for post-glacial or late... and Wilson, 1998; Rempel and Smith, 1998) and predate the hypothesized post-glacial or late-Pleistocene dispersal of Catostomus catostomus (McPhail and Taylor, 1999), Salvelinus confluentus (Taylor et al., 1999) and Lota lota (Van Houdt et al., 2005) across...

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

    SciTech Connect

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

    1995-06-01

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    USGS Publications Warehouse

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

    1999-01-01

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

  5. Investigating Sea Ice Regimes and Glacial Cycles of the Early Pleistocene in a Sediment Record from the Northwind Ridge, Western Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Dipre, G.; Polyak, L. V.; Ortiz, J. D.; Cook, A.; Oti, E.

    2014-12-01

    We are conducting a comprehensive study of a sediment record from the Arctic Ocean in order to improve our understanding of paleoceanographic conditions during the early Pleistocene, a potential paleo-analog for the current and future states of the Arctic. The study deals with a sediment core raised on the HOTRAX 2005 expedition from the Northwind Ridge, western Arctic Ocean. By comparison with an earlier reported stratigraphy (Polyak et al., 2013), the core dates back to estimated ca. 1.5 Ma. A suite of paleobiological, lithological, and geochemical proxies will be utilized to reconstruct paleoceanographic environments in the early Pleistocene part of the record. In contrast to most Arctic Ocean sediment cores, calcareous microfossils occur in abundance to ca. 1.2 Ma. This enables the use of microfaunal assemblages as proxies for sea-ice conditions, which control the seasonal organic production. Physical properties such as sediment density, grain size, and sediment fabric (based on XCT imagery) will be employed to determine the impact of glaciations on sedimentation. By reconstructing sea-ice history and glacial cycles, we will gain insights into poorly understood controls on the Arctic environments during the early Pleistocene and Mid-Pleistocene Transition.

  6. 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.

  7. Pleistocene glacial refugia across the Appalachian Mountains and coastal plain in the millipede genus Narceus: Evidence from population genetic, phylogeographic, and paleoclimatic data

    PubMed Central

    Walker, Matt J; Stockman, Amy K; Marek, Paul E; Bond, Jason E

    2009-01-01

    Background Species that are widespread throughout historically glaciated and currently non-glaciated areas provide excellent opportunities to investigate the role of Pleistocene climatic change on the distribution of North American biodiversity. Many studies indicate that northern animal populations exhibit low levels of genetic diversity over geographically widespread areas whereas southern populations exhibit relatively high levels. Recently, paleoclimatic data have been combined with niche-based distribution modeling to locate possible refugia during the Last Glacial Maximum. Using phylogeographic, population, and paleoclimatic data, we show that the distribution and mitochondrial data for the millipede genus Narceus are consistent with classical examples of Pleistocene refugia and subsequent post-glacial population expansion seen in other organismal groups. Results The phylogeographic structure of Narceus reveals a complex evolutionary history with signatures of multiple refugia in southeastern North America followed by two major northern expansions. Evidence for refugial populations were found in the southern Appalachian Mountains and in the coastal plain. The northern expansions appear to have radiated from two separate refugia, one from the Gulf Coastal Plain area and the other from the mid-Atlantic coastal region. Distributional models of Narceus during the Last Glacial Maximum show a dramatic reduction from the current distribution, with suitable ecological zones concentrated along the Gulf and Atlantic coastal plain. We found a strong correlation between these zones of ecological suitability inferred from our paleo-model with levels of genetic diversity derived from phylogenetic and population estimates of genetic structuring. Conclusion The signature of climatic change, during and after the Pleistocene, on the distribution of the millipede genus Narceus is evident in the genetic data presented. Niche-based historical distribution modeling strengthens the conclusions drawn from the genetic data and proves useful in identifying probable refugia. Such interdisciplinary biogeographic studies provide a comprehensive approach to understanding these processes that generate and maintain biodiversity as well as the framework necessary to explore questions regarding evolutionary diversification of taxa. PMID:19183468

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    PubMed Central

    Rao, Dingqi; Yang, Junxing

    2013-01-01

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

  10. Gradual and small decrease of glacial sea surface temperatures in the eastern equatorial Indian ocean across the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Casse, Marie; Malaize, Bruno; Bassinot, Franck; Caillon, Nicolas; Degaridel-Thoron, Thibault; Rebaubier, Hélène; Charlier, Karine; Caley, Thibaut; Marieu, Vincent; Beaufort, Luc; Rojas, Virginia; Meynadier, Laure; Valet, Jean Pierre; Reaud, Yvan

    2015-04-01

    The Mid-Pleistocene Transition (MPT), between about 1.2 and 0.7 Ma, is characterized by the emergence of asymmetric, high-amplitude 100 ka cycles, which contrast with the low amplitude, 41 kyr cycles that dominate the early Pleistocene climate. Here, we study the sediment core MD12-3409, which spans the last ~ 1.75 Ma, to document hydrographic changes across the MPT in the Eastern Equatorial Indian Ocean. Stratigraphy is based on benthic foraminifera delta18O and we reconstruct Sea Surface Temperatures (SST) using the Mg/Ca ratio of Globigerinoides ruber, a surface dwelling planktonic foraminifera. Our results reveal a progressive cooling of glacial maxima across the MPT but no long-term trend in mean SST over the last 1.75 Ma. The main periodicity of the surface temperature signal shifts from 41 kyr before the MPT, to both 100 kyr and 41 kyr for the post MPT time period. Over the last 800 ka, the strong correlation between core MD12-3409 SST fluctuations and the atmospheric CO2 record suggests a global, greenhouse forcing for the tropical Indian SST over the post-MPT time period. Within the MPT, and for earlier time interval, changes in temperature gradients between our SST record and other temperature records in, or at the edge of, the Pacific Warm Pool, could suggest reorganizations of sea surface circulation and lateral heat exchanges. Since the MPT, the amplification of sea level lowering during glacial periods might have shoaled the Indonesian Through Flow (ITF) gateway, restricting hydrographic exchanges between Pacific and Indian oceans.

  11. Periodic jökulhlaups from Pleistocene glacial Lake Missoula—New evidence from varved sediment in northern Idaho and Washington

    NASA Astrophysics Data System (ADS)

    Waitt, Richard B.

    1984-07-01

    Newly examined exposures in northern Idaho and Washington show that catastrophic floods from glacial Lake Missoula during late Wisconsin time were repeated, brief jökulhlaups 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.

  12. Periodic jökulhlaups from Pleistocene glacial Lake Missoula-New evidence from varved sediment in northern Idaho and Washington

    USGS Publications Warehouse

    Waitt, Richard B.

    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 jökulhlaups 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.

  13. 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

  14. 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.

  15. 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

  16. 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

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

    NASA Astrophysics Data System (ADS)

    Guyard, Hervé; St-Onge, Guillaume; Pienitz, Reinhard; Francus, Pierre; Zolitschka, Bernd; Clarke, Garry K. C.; Hausmann, Sonja; Salonen, Veli-Pekka; Lajeunesse, Patrick; Ledoux, Grégoire; Lamothe, Michel

    2011-12-01

    The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS 14C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850-5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (˜4200-600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.

  18. Unusual configuration of the Devonian-Pleistocene unconformity in the Susquehanna Valley, Oneonta, New York: Evidence for a subglacial meltwater inlet to glacial Lake Otego

    SciTech Connect

    Kucewicz, J. Jr.; Ebert, J.; Rasquin, C.; Sherman, R.; Nethaway, R.; Gardner, J.; Milunich, K.; Weber, J.; Wohlford, T.; Franz, J.; Brillon, S. (State Univ. of New York Coll., Oneonta, NY (United States). Dept. of Earth Sciences)

    1993-03-01

    A recently drilled test well and nearby abandoned bore hole have revealed anomalously shallow bedrock in a portion of the Susquehanna Valley near Oneonta, New York. Gravimetric and seismic refraction studies were conducted in the area to better delineate the Devonian--Pleistocene unconformity. On the northern flank of the valley, geophysical surveys indicate the presence of a shallowly buried bedrock shelf that is rimmed by a bedrock ridge. South of the ridge, bedrock drops abruptly beneath the thickening valley fill. This configuration contradicts predictions based upon projection of the valley walls to a classic U shape. These unusual features coincide with an extremely narrow portion of the valley, a recessional moraine and other stagnant ice features. The bedrock shelf may represent the initial glaciated valley floor. Incision of the valley floor below this surface can be attributed to scour by subglacial meltwaters at a nick point. As such, the narrow, deepest part of the bedrock valley may represent a subglacial inlet to glacial Lake Otego.

  19. 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.

  20. Solar Activity Induced Pronounced Temperature Oscillations During the Late Pleistocene to the Early Holocene in the Northeastern North America

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Hou, J.

    2008-12-01

    Sensitivity of the Earth's climate to the solar activity has profound implications for modeling future climate changes, but is a subject of intense scientific debate. GCM modeling considering solar forcing can successfully simulate climatic variations in the past millennia such as the Little Ice Age (LIA), but volcanic forcing during the same time period can also yield similar climatic effect and confound interpretations. Here we present decadal to centennial resolution compound-specific hydrogen isotopic records from two lakes in the northeastern North America to investigate the relationship between solar activity and temperature changes during the late Pleistocene to early Holocene. Our temperature reconstructions from the two lakes 100 km apart in New England are highly consistent with each other and agree well with established general climatic scenarios. More importantly, our records contain centennial-scale cyclicities related to the solar cycles (88 and 232 yr), indicating strong links between the pronounced 1 to 2 degree temperature oscillations and solar activity during the late Pleistocene. Our results strongly support the presence of an internal amplification mechanism for the solar forcing that is capable of causing disproportionally large climatic responses with relative small changes in the incoming solar radiation.

  1. Sanders, J. E., and Merguerian, Charles, 1994c, Glacial geology of Staten Island. The fundamental question pertaining to the Pleistocene features of the New York City

    E-print Network

    Merguerian, Charles

    Sanders, J. E., and Merguerian, Charles, 1994c, Glacial geology of Staten Island. The fundamental-moraine ridge in southern Staten Island prove that ice flowed regionally across Staten Island from NW to SE that on Staten Island are products of at least 3, possibly 4, glacial advances. We regard their ages as

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

    NASA Astrophysics Data System (ADS)

    Montgelard, Claudine; Matthee, Conrad A.

    2012-07-01

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

  3. Modeling evidence for enhanced El Nin~oSouthern Oscillation amplitude during the Last Glacial Maximum

    E-print Network

    for the Last Glacial Maximum (LGM) about 21,000 years ago. The background conditions are obtained from two LGM present-day unstable recharge-discharge mode changes its stability as well as its frequency during LGM conditions. Simulated LGM background conditions were favorable to support large-amplitude self

  4. Post-last glacial alluvial fan and talus slope associations (Northern Calcareous Alps, Austria): A proxy for Late Pleistocene to Holocene climate change

    NASA Astrophysics Data System (ADS)

    Sanders, Diethard; Ostermann, Marc

    2011-08-01

    Near Innsbruck city (Austria, Eastern Alps), following the Last Glacial Maximum (LGM), an alluvial fan-to-talus slope succession was supplied from a carbonate-rock cliff more than 1000 m in height. 234U/ 230Th ages of 9.5 to 9.37 isotope kyrs of diagenetic cements in the alluvial-fan succession suggest that the fan/talus deposit accumulated mainly during late-glacial to, perhaps, early Holocene times. The deepest-exposed interval of the fan succession contains cracked lithoclasts probably fractured by overburden from late-glacial ice; this interval is topped by an intra-sequence unconformity. Following final glacial retreat, and rapid aggradation of the alluvial fan and talus slope, the geomorphic regime changed to erosion, as recorded by fanhead trenching and cutting of fluvial terraces, abandonment and vegetating of scree slopes, and excavation of 'talus flatirons'. The changeover from the accumulation of fan and talus to abandonment and dissection probably took place during the terminal late-glacial interval to perhaps the early Holocene. This erosional regime persists until present. A record of rapid late-glacial to early Holocene accumulation of an alluvial fan/talus deposit followed by: (i) abandonment and vegetation growth, combined with (ii) cutting of intra-sequence unconformities of limited lateral extent, is typical of Alpine mountain-flank deposystems situated at comparatively low altitudes. This record consists of (a) an autocyclic component, that is, progressive lowering of sediment input due to onlap and burial of freshly-deglaciated mountain flanks supplying alluvial fans and talus slopes, and (b) an allocyclic component, that is, deglacial climatic warming and upward rise of an altitudinal range with a maximum number of freeze-thaw cycles ('talus window'), also leading to progressive vegetation-induced hillslope stabilization and lowering of scree production.

  5. Plio-Pleistocene diversification and genetic population structure of an

    E-print Network

    Alvarez, Nadir

    ORIGINAL ARTICLE Plio-Pleistocene diversification and genetic population structure of an endangered-wide during the Pleistocene, the severity of glacial and drought events ­ and hence their influence on animal we can assemble a comprehensive view of the impact of Pleistocene climatic variation

  6. 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

  7. 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

    Microsoft Academic Search

    James L. Bischoff; Kirsten M. Menking; Jeffrey P. Fitts; John A. Fitzpatrick

    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

  8. 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.

  9. A High-Resolution Study of a Late Pleistocene Interglacial-Glacial Transition and its Variability in Owens Lake, California Core OL-92

    NASA Astrophysics Data System (ADS)

    Meyers, C.; Kennedy, M. J.

    2010-12-01

    Owens Lake, California core OL-92 was examined between 203.10 - 224.21 m (~443-500 ka1) at sub-millennial resolution to explore interglacial MIS 13 suborbital climate variability in western North America. Calcium carbonate abundance, ?18O and ?13C (PDB) of bulk sediment, total organic carbon and the Shultz ratio2 were measured. A transition at ~460 ka from high average calcium carbonate (>20 weight %) and enriched ?18O and ?13C values to low values from ~458 - 442 ka (<5 weight % calcium carbonate) is consistent with a transition from closed, productive lake conditions to vigorously overflowing lake conditions. This is interpreted as the transition between the interglacial MIS 13 to glacial MIS 12. Two short (< 2 kyr) periods of overflow, possibly indicative of regional cooling, occur at ~496 ka and ~493 ka that do not correlate with interpreted patterns of climate in other Northern Hemisphere records from MIS 133,4. 1. Bischoff et al. 1997, GSA Special Paper 317: 91-98. 2. Kennedy et al. 2002, Science, 295: 657-660. 3. Winograd et al. 1992, Science, 258: 255 - 260. 4. Oppo et al. 1998, Science, 279: 1335-1338.

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

    SciTech Connect

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

    1988-06-01

    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. 35 refs.

  11. 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

  12. Mathematics Colloquium Characteristics of the Mid-Pleistocene Transition as Revealed by Empirical

    E-print Network

    Sze, Lawrence

    Mathematics Colloquium Characteristics of the Mid-Pleistocene Transition as Revealed by Empirical. A consensus as to the characterization of Pleistocene climate with respect to Milankovitch theory (the forcing timing and character of the transition from the small, fast glacial cycles of the early Pleistocene

  13. Large Glacitectonic structures on the Dogger Bank, southern North Sea; Implications for glacial dynamics, glacial limits, and interplay between the British and Fennoscandinavian Ice Sheets

    NASA Astrophysics Data System (ADS)

    Dove, Dayton; Cotterill, Carol; Long, Dave; Ruiter, Astrid; Phillips, Emrys; James, Leo; Forsberg, Carl Fredrik

    2013-04-01

    Recently acquired 2D seismic data (sparker) acquired over the Dogger Bank (DB) reveal large glacitectonic structures associated with late-Pleistocene glacial incursion into the southern North Sea. The densely populated survey data (100m line spacing) collected for the purposes of offshore windfarm development on the DB, allow for pseudo-3D interpretation. The sparker data show discrete thrust faults extending from within ~5 m of the seabed to ~200 m depth, and consistently terminate at one of two décollement surfaces. Preliminary mapping and amplitude extraction maps reveal the thrusts to occur in a series of thrust blocks (5-8 faults), with each set encompassing an area of approximately 6 km along-strike and 2 km at right angles. The overall zone of thrusting is up to 16 x 6 km on the western edge of the DB. The strike of the faults indicates ice-flow from the west. Other deformation structures include: open, recumbent, and fault propagation folds, as well as back thrusts, and pop-up structures. The relief of the DB (dimensions) is entirely accounted for by what has historically been termed the 'DB Formation'. These new data reveal that this seismostratigraphic unit likely consists of deposits from a variety of glacially influenced depositional regimes. The observed thrusts penetrate through the 'DB formation', indicating this phase of intense deformation post-dated the initial construction of the bank. Less pronounced glacial deformation affects much of the rest of the DB, and the products of this deformation (push-moraine complexes?) were possibly integral to the construction of the bank itself. While the style and fabric (NS?) of this deformation is less clear, it is likely there were multiple incursions of glacial ice, from different directions (and sources?), into this area where late-Pleistocene glaciation limits are poorly understood. Several mechanisms for forming such glacitectonic features have been proposed, and the thrust blocks here may have been caused by sub-glacial (gravitational spreading), ice-marginal (push-moraine complex), or pro-glacial (ice-push) processes, or a combination of the three at an oscillating ice-margin. The thrusts appear to have no surface expression, suggesting the topography was removed either by late-stage glacial erosion or Holocene marine transgression. Work to date on the paleoenvironmental implications of the data has been preliminary. The exact style, pattern, and timing glacial deformation (and associated sedimentation) on the Dogger Bank and circum-southern North Sea, and glacial history of the region, will be the focus of a Ph.D studentship which commenced Sept. 2012.

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

    Microsoft Academic Search

    A. Duk-Rodkin; R. W. Barendregt

    2009-01-01

    In the late Pleistocene the southern Mackenzie region was glaciated by ice masses from a Cordilleran and continental source (Laurentide). Stratigraphic and geomorphologic evidence indicate that the two glaciers occupied this region at different times during the Late Pleistocene. The continental ice sheet advanced over the foothills and up major valleys reaching its maximum extent, ca. 30 ka. B. P.

  15. 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

  16. Orbital-scale El Niño\\/Southern Oscillation-Like Variability During the Last Glacial-Interglacial Cycle

    Microsoft Academic Search

    M. Yamamoto; T. Oba; J. Shimamune; T. Ueshima

    2003-01-01

    How have the changes in the Earth's orbit have driven glacial-interglacial climate changes? Recently, a new hypothesis has been proposed that the tropical Pacific ocean-atmosphere interactions have a strong influence on global climate changes on an orbital timescale (Cane, 1998; Clement et al., 1999; Lea et al., 2000). Nevertheless, the orbital-scale changes in the tropical interactions are less clear, and

  17. 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

  18. Pleistocene glaciations, demographic expansion and subsequent isolation promoted morphological heterogeneity: A phylogeographic study of the alpine Rosa sericea complex (Rosaceae).

    PubMed

    Gao, Yun-Dong; Zhang, Yu; Gao, Xin-Fen; Zhu, Zhang-Ming

    2015-01-01

    While most temperate plants probably underwent glacial constriction to refugia and interglacial expansion, another type of interglacial refugia might have existed to maintain alpine plants during warm periods. To test this hypothesis, we applied phylogeographic methods to 763 individuals (62 populations) which belong to 7 taxonomically difficult species of the Rosa sericea complex distributed in alpine regions of the temperate and subtropical zones in eastern Asia. We used three chloroplast (cp) DNA fragments (trnL-trnF, ndhF-rpl32 and ndhJ-trnF) approximately 3,100?bp and nuclear microsatellite (nSSR) on eight sites to determine whether cold tolerant plants experienced expansion during the Pleistocene. The neutral test and mismatch distribution analysis (MDA) indicated that whole populations and major lineages of the Qinghai-Tibet Plateau (QTP) underwent expansion during the middle to late Pleistocene. Environmental niche modeling (ENM) indicates more suitable habitats during the Last Glacial Maximum (LGM) than at present. We concluded that the demographic history of R. sericea, which diverged in the middle Pleistocene, was mostly affected by climatic oscillations instead of by geographical barriers. The low genetic divergence, as well as the weak phylogenetic structure in the R. sericea complex both support treating this complex as a single taxon. PMID:26123942

  19. 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.

  20. 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.

  1. The Mid-Pleistocene Transition In The Tropical Pacific

    NASA Astrophysics Data System (ADS)

    Medina-Elizalde, M. A.; Lea, D. W.

    2005-12-01

    During the mid-Pleistocene transition (MPT) at ~950 kyr B.P., the climate of the Earth underwent profound changes. As suggested by foraminiferal oxygen isotopic records, high latitude climate switched from 41,000 years (kyr) to ~100 kyr dominant cycles at this time. A number of hypotheses have been proposed to explain the MPT which involve high latitude northern hemisphere processes. Recent paleoclimate reconstructions, however, indicate that the tropics also experienced climate changes resembling those at high latitude but also with their own unique patterns, which cannot be fully explained by current hypotheses. A sea surface temperature (SST) record based on planktonic foraminiferal Mg/Ca from the western equatorial Pacific (WEP) warm pool ODP Hole 806B reveals that glacial-interglacial (G-I) oscillations in SST also shifted from a period of 41 kyr to 100 kyr during the MPT. This observation is in agreement with the SST records from core MD97-2140, a site to the northwest of Hole 806B, and from ODP Hole 846 in the eastern equatorial Pacific cold tongue, which also show a shift in the dominant periodicity. Hole 806B SST average (27.8°C) and range (3°C) remained the same over the MPT with typical glacial and interglacial SSTs of 26°C and 29°C, respectively. Hole 806B SST lead foraminiferal d18O by 4± 3 kyr over the MPT in agreement with paired records from core MD97-2140 and Hole 846. SST cycles across the MPT have similar magnitude and are synchronous in both the western and the eastern equatorial Pacific but preceded changes in continental ice volume. Today, eastern equatorial Pacific SSTs are strongly influenced by wind-driven thermocline depth changes. In contrast, in the WEP, where the thermocline is very deep, SSTs are less likely to be affected by thermocline depth changes. The nature of tropical SST variability over the mid-Pleistocene transition is remarkably similar to late Pleistocene climate observations and implicates atmospheric greenhouse forcing as the cause of the switch in climate periodicities at this time.

  2. Pleistocene Speciation in the Genus Populus (Salicaceae)

    PubMed Central

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

    2012-01-01

    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

  3. 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).

  4. 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.

  5. Hominin responses to environmental changes during the Middle Pleistocene in Central and Southern Italy

    NASA Astrophysics Data System (ADS)

    Orain, R.; Lebreton, V.; Russo Ermolli, E.; Sémah, A.-M.; Nomade, S.; Shao, Q.; Bahain, J.-J.; Thun Hohenstein, U.; Peretto, C.

    2012-10-01

    The palaeobotanical record of early Palaeolithic sites from Western Europe indicates that hominins settled in different kinds of environments. During the "Mid-Pleistocene Transition (MPT)", from about 1 to 0.6 Ma, the transition from 41-ka to 100-ka dominant climatic oscillations, occurring within a long-term cooling trend, was associated with an aridity crisis which strongly modified the ecosystems. Starting from the MPT the more favorable climate of central and southern Italy provided propitious environmental conditions for long-term human occupations even during the glacial times. In fact, the human strategy of territory occupation was certainly driven by the availabilities of resources. Prehistoric sites such as Notarchirico (ca. 680-600 ka), La Pineta (ca. 600-620 ka), Gaudo San Nicola (ca. 380-350 ka) or Ceprano (ca. 345-355 ka) testify to a preferential occupation of the central and southern Apennines valleys during interglacial phases, while later interglacial occupations were oriented towards the coastal plains, as attested by the numerous settlements of the Roma basin (ca. 300 ka). Faunal remains indicate that human subsistence behaviors benefited of a diversity of exploitable ecosystems, from semi-open to closed environments. In central and southern Italy, several palynological records have already illustrated the regional and local scale vegetation dynamic trends. During the Middle Pleistocene climate cycles, mixed mesophytic forests developed during the interglacial periods and withdrew in response to increasing aridity during the glacial episodes. New pollen data from the Boiano basin (Molise, Italy), attest to the evolution of vegetation and climate between OIS 13 and 9 (ca. 500 to 300 ka). In this basin, the persistence of high edaphic humidity, even during the glacial phases, could have favored the establishment of a refuge area for the arboreal flora and provided subsistence resources for the animal and hominin communities during the Middle Pleistocene. This could have constrained human groups to migrate into such a propitious area. Regarding to the local climate evolution during the glacial episodes, the supposed displacement from these sites could be linked to the environmental dynamics solely due to the aridity increase rather than directly to the global climate changes.

  6. The role of stochastic noise in the abrupt climatic transitions of the pleistocene

    SciTech Connect

    Matteucci, G.

    1991-01-01

    Analyses of marine [delta][sup 18]O records suggest that the variations of the Earth's orbital parameters have induced and provided the timing of the Pleistocene climatic oscillations. This dissertation analyses some statistical properties of the Pleistocene climate by estimating the Probability Density Function (PDF) of the [delta][sup 18]O record. The results allow to define statistically what were the [open quotes]typical conditions[close quotes] (in a probabilistic sense) of the Quaternary, to identify the modes of the PDF as the mean glacial and interglacial climatic states, and to clarify the meaning and the abruptness of the climatic transitions. A zero-dimensional Energy Balance Model is developed. The nonlinearity of the ice albedo-temperature feedback leads to multiple steady-state equilibria. The role of stochastic perturbations and their interaction with the orbital forcing in producing the periodic and abrupt climatic transitions of the late Pleistocene are illustrated. A stochastic sensitivity analysis is used to clarify the results, especially the selective amplification of the orbitally-induced 100 kyr cycle, and the predictability of the system on the time scales of the orbital cycles. From the analysis of GCM simulations and observational zonally- averaged data a one-dimensional EBM is then developed. The strong nonlinearity of this model and the occurrence of multiple equilibria is caused by the presence of the Thin Ice Cap Instability. A discussion of the features that stochastic perturbations would introduce, follows. Finally a GCM sensitivity study to atmospheric CO[sub 2] shows how the effects of varying CO[sub 2] concentrations can be included in simple EBMs. The role that stochastic perturbations, orbital forcing, and the known past concentrations of atmospheric CO[sub 2] have played in producing the abrupt climatic transitions of the late Pleistocene is discussed.

  7. Pliocene-Pleistocene Surface and Intermediate Water Hydrography of the South Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Elmore, A.; McClymont, E.; Elderfield, H.; Kender, S.

    2014-12-01

    The reconstruction of past sea surface (SST) and intermediate water temperatures (IWT) is critical for understanding feedbacks within the ocean-climate system. Pliocene Southern Ocean dynamics are largely ambiguous, especially at intermediate water depths. However, the intermediate water reconstructions are particularly important since intermediate waters, including Antarctic Intermediate Water (AAIW), may be an important driver in high-low latitude teleconnections. Herein, we present the first Pliocene SST and IWT records from a sediment core in the Southwest Pacific (DSDP 593; 1068m water depth), in the core of modern AAIW. Benthic paleotemperature proxies have caveats, including the 'Carbonate Ion Effect' on the magnesium to calcium ratio (Mg/Ca) of benthic foraminifera. However, recent studies demonstrated that the infaunal species, Uvigerina peregrina, is carbonate ion independent, affording the use of Mg/CaU.peregrina as a paleotemperature proxy (Elderfield et al., 2010). Our results suggest that Southern Ocean IWT was warmer during the Pliocene than during the Mid- to Late-Pleistocene. The range of IWT values during the Pliocene is nearly as large as the glacial-interglacial-scale IWT changes during the Pleistocene, despite smaller ice volume oscillations suggested by benthic ?18O time series (Lisiecki & Raymo, 2005). Alkenone-derived UK37' data show Pliocene SSTs are also, on average, warmer than those estimated for the Mid- to Late-Pleistocene. Orbital-scale SST changes are evident through the Pliocene, although the range is smaller than during the late Pleistocene. Our data are consistent with modeled SST and IWT reconstructions by Dowsett et al. (2009), but raise questions about the stability or dynamism of Pliocene climate relative to the modern. References:Dowsett et al. (2009) www.clim-past.net/5/769/2009. Elderfield et al. (2010) doi:10.1594/PANGAEA.817473. Lisiecki & Raymo (2005) doi:10.1029/2004PA001071.

  8. The End Pleistocene Extinction Event - What Caused It?

    Microsoft Academic Search

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

    2007-01-01

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

  9. Pleistocene deglaciation and the Earth's rotation: a new analysis

    Microsoft Academic Search

    Patrick Wu; W. R. Peltier

    1984-01-01

    The authors provide a new analysis of the influence of the Pleistocene glacial cycle upon the Earth's rotation. This analysis reveals important errors and inconsistencies in previous calculations of the polar motion produced by ice sheet forcing. The authors' conclusion is that it is not possible to fit the observed polar wander in the ILS path with a homogeneous viscoelastic

  10. Plio-pleistocene African climate

    SciTech Connect

    deMenocal, P.B. [Lamont-Doherty Earth Observatory, Palisades, NY (United States)

    1995-10-06

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated. 65 refs., 6 figs.

  11. Laurentia Glacial Isostatic Adjustment Observed From GRACE and Satellite Altimetry

    Microsoft Academic Search

    H. Lee; C. Shum; C. Kuo; M. Schmidt; P. Wu; A. Braun; W. van der Wal; H. Wang

    2007-01-01

    The use of satellite radar altimetry to detect solid Earth deformation signals such as the Glacial Isostatic Adjustment (GIA) has been demonstrated by Lee et al. (2007) observing the Laurentia GIA signals using TOPEX (1992-2002) over the Hudson Bay land region. GRACE gravimetry, despite of its short data record (2002-present), confirmed the presence of two Pleistocene ice domes near the

  12. Interior hydrography and circulation of the glacial Pacific Ocean

    Microsoft Academic Search

    Katsumi Matsumoto; Tadamichi Oba; Jean Lynch-Stieglitz; Hirofumi Yamamoto

    2002-01-01

    The deep water of the Pacific Ocean is a key component of the global climate system on the time scale of late-Pleistocene glaciation and deglaciation. Despite its importance, the deep Pacific during the last glacial maximum has received relatively little attention compared to the deep Atlantic, in part, because the Pacific poorly preserves carbonate sediments on the sea floor. Here,

  13. Late Pleistocene- Holocene transgressive sedimentation in deltaic and non-deltaic areas of the northeastern Bering epicontinental shelf.

    USGS Publications Warehouse

    Nelson, C.H.

    1982-01-01

    The distribution of late Pleistocene and Holocene surface sediments on the northern Bering Seafloor is patchy and dependent upon locations of seafloor bedrock and pre-late Pleistocene glacial debris, late Holocene river sediment influx, and modern strong bottom currents. Seafloor vibracores and high-resolution profiles record two different sedimentary environments in the northern Bering shelf: late Pleistocene-Holocene shoreline transgression in Chirikov Basin, and Holocene deposition from the Yukon River in Norton Sound.-from Author

  14. A phase-space model for Pleistocene ice volume

    E-print Network

    Imbrie, John Z; Lisiecki, Lorraine E

    2011-01-01

    We present a phase-space model that simulates Pleistocene ice volume changes based on Earth's orbital parameters. Terminations in the model are triggered by a combination of ice volume and orbital forcing and agree well with age estimates for Late Pleistocene terminations. The average phase at which model terminations begin is approximately 90 +/- 90 degrees before the maxima in all three orbital cycles. The large variability in phase is likely caused by interactions between the three cycles and ice volume. Unlike previous ice volume models, this model produces an orbitally driven increase in 100-kyr power during the mid-Pleistocene transition without any change in model parameters. This supports the hypothesis that Pleistocene variations in the 100-kyr power of glacial cycles could be caused, at least in part, by changes in Earth's orbital parameters, such as amplitude modulation of the 100-kyr eccentricity cycle, rather than changes within the climate system.

  15. Mid-Pleistocene environmental change in tropical Africa began as early as 1.05 Ma

    NASA Astrophysics Data System (ADS)

    Dupont, L. M.; Donner, B.; Schneider, R.; Wefer, G.

    2001-03-01

    Palynological records from the Congo fan reveal environmental change in equatorial Africa occurring 1.05 Ma ago, 100 k.y. before the mid-Pleistocene climatic shift at 0.9 Ma. Prior to 1.05 Ma, a glacial-interglacial rhythm is not obvious in the African vegetation variation. Afterwards, Podocarpus spread in the mountains of central Africa mainly during glacials and Congo River discharge decreased. The sequence of vegetation variation associated with the mid-Pleistocene glacials and interglacials differed from that observed during the late Pleistocene. Between 0.9 and 0.6 Ma, interglacials were characterized by warm dry conditions and glacials were characterized by cool humid conditions, while during the past 0.2 Ma glacials were cold and dry and interglacials warm and humid. Our data indicate that before the Northern Hemisphere ice caps dramatically increased in size (0.9 0.6 Ma), low-latitude climate forcing and response in the tropics played an important role in the initiation of 100 k.y. ice-age cycles. During the mid to late Pleistocene, however, the climate conditions in the tropics were increasingly influenced by the glacial-interglacial variations of continental ice sheets.

  16. 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.

  17. Surface Water and Mediterranean Outflow Water Variability During the Mid-Pleistocene Transition (Marine Isotope Stages 17-36) - the IODP Site U1387 record

    NASA Astrophysics Data System (ADS)

    Voelker, Antje; Salgueiro, Emilia; Rodrigues, Teresa; Padilha, Maria; Alberto, Ana; Loureiro, Isabel; Rebotim, Andreia; Jimenez-Espejo, Francisco J.; Bahr, Andre; Röhl, Ulla

    2015-04-01

    The Mediterranean Outflow Water (MOW) forms extensive contourite drift deposits along the Iberian margin, especially in the Gulf of Cadiz, and injects heat and salt into the intermediate depths of the North Atlantic that affect the overturning circulation. The sediments recovered during IODP Expedition 339 allow studying MOW's history throughout the Pleistocene and Pliocene and thus under varying climate forcing. Here we present centennial-to-millennial scale proxy records for surface water and MOW variations as recorded at IODP Site U1387 (558 m water depth), drilled into the Faro Drift, which is formed by the upper MOW core. We focus our study on the early to middle Pleistocene with special attention on the Mid-Pleistocene Transition (MPT) when the period of the dominant climate cycle changed from 41 kyr to 100 kyr. Surface water and MOW proxy records show millennial-scale stadial/ interstadial oscillations on top of the glacial/ interglacial cycles. Changes in the planktonic and benthic oxygen isotope records are tightly coupled highlighting the constant exchange (entrainment) between the (sub)surface waters and the MOW. Alkenone-derived sea-surface temperatures (SST) increased abruptly at the beginning of an interglacial stage (with the exception of MIS 35) and reached maxima of 21-23°C. During the glacial stages, the SST record reveals abrupt drops down to 10-11°C that lasted approximately 1 kyr, respectively, and remind of the SST minima recorded on the western Iberian margin during Heinrich and Heinrich-type ice-rafting events of the middle to late Pleistocene (e.g., Rodrigues et al., 2011 in Paleoceanography). Low benthic carbon isotope values during deglacial and peak interglacial periods, coinciding with insolation maxima, reveal a poorly ventilated upper MOW core and point to a causal link between MOW ventilation and sapropel formation in the Mediterranean Sea. Better ventilation was recorded during glacial and stadial intervals, often in association with the formation of contourites (higher sand content; larger mean grain size) and thus higher bottom current velocity. During the warmer Marine Isotope Stages contourites, often more pronounced than their glacial counterparts, were formed during the stadial(s) following the peak interglacial period when northern hemisphere summer insolation was low. Thus, changes in the upper MOW core are tightly coupled to summer insolation with poor ventilation occurring during insolation maxima and higher current velocity marking insolation minima. This insolation forcing reveals a close link between MOW and Mediterranean Sea climate conditions, whereas the SST record reveals a tight link to surface water conditions in the open North Atlantic.

  18. Upper Middle Pleistocene climate and landscape development of Northern Germany

    NASA Astrophysics Data System (ADS)

    Urban, B.

    2009-04-01

    The Pleistocene sequence of the Schöningen lignite mine contains a number of interglacial and interstadial limnic and peat deposits, travertine tuff, soils, tills and fluvioglacial sediments as well as loess deposits. The complex Quaternary sequence contains six major cycles with evidence of four interglacials younger than the Elsterian glaciation and preceding the Holocene. The sequence begins with Late Elsterian glacial and three interstadial deposits formed in shallow basins. Cycle I is assigned to late parts of the Holsteinian interglacial. A strong cooling is recorded by a significant increase of Artemisia and grasses during the following Buschhaus A Stadial, which is considered to mark the onset of the Saalian Complex sensu lato (penultimate glacial-complex). The lacustrine sediments of Cycle II, Reinsdorf interglacial sequence (Urban, 1995), have been found to occur at archaeological sites Schöningen 12 and 13 (Thieme,1997). Recent investigations give evidence for at least 13 Local Pollen Assemblage Zones showing a five-fold division of the interglacial and a sequence of five climatic oscillations following the interglacial (Urban, 2006). From the relative high values for grasses and herbs in the inferred forested periods of the interglacial, a warm dry forest steppe climate can be deduced. The stratigraphic position of throwing spears (Thieme, 1997), can clearly be allocated to Reinsdorf Interstadial B (level II-4) characterized by an open pine-birch forest. Uppermost parts (level II-5) represent the transition into a periglacial environment indicating the definite end of cycle II. The Schöningen Interglacial (Cycle III) represents the youngest of the pre-Drenthe (Early Saalian Stadial) interglacials (Urban, 1995). In summary, it can be concluded that the Middle Pleistocene terrestrial pollen record of the Schöningen sequence represents tentative correlatives of MIS 7, 9 and 11. North of Leck (North Friesland, Schleswig-Holstein) sediments of the centre and the margin of a 286 m deep channel, subglacially eroded during the Elsterian, have recently been investigated by 9 counter flash or cored drillings (Stephan et al., in press). Studies focussed on the uppermost 50 m, made up of a series of approximately 9 m thick fluviatile sediments ("Leck-Folge") with intercalations of organic sand layers and a gyttja band, up to 1.5 m thick. This sequence is overlain by several metres of mainly decalcified groundmoraine, that, itself, is overlain by glaciofluvial and periglacial sediments. The palynological investigations of the gyttja reveal a floral development of interglacial character ("Leck-Thermomer"). Compared to other Middle Pleistocene warm periods in North Germany, correlations of the Leck-Thermomer with the Holsteinian and with the warm periods of the Reinsdorf and Wacken (Dömnitz) interglacials are precluded or appear rather implausible. The Leck-Thermomer is most likely a correlative of the marine oxigen isotope stage 7 c (MIS 7). Stephan, H.-J., Urban, B., Lüttig, G., Menke, B. und M. Sierralta: Palynologische, petrographische und geochronologische Untersuchungen der Leck-Warmzeit (spätes Mittelpleistozän) und ihrer begleitenden Sedimente.- [Palynological, petrographical, and geochronological investigations of deposits of the "Leck-Thermomer" and accompanying sediments].- Geologisches Jahrbuch, in press. Thieme, H., 1997. Lower Paleolithic hunting spears from Germany. Nature 385, 807-810. Urban, B. 1995. Palynological evidence of younger Middle Pleistocene Interglacials (Holsteinian, Reinsdorf, Schöningen) in the Schöningen open cast lignite mine (eastern Lower Saxony/Germany). Mededelingen Rijks Geologische Dienst 52, 175-186. Urban, B. 2006. Interglacial pollen records from Schöningen, north Germany.- In: THE CLIMATE OF PAST INTERGLACIALS. Sirocko, F., Litt, T., Claussen, M., Sanchez-Goni, M.F. (eds.), Springer Verlag; in press.

  19. Late Pleistocene lithostratigraphy and sequences in the southwestern Mesopotamia (Argentina): Evidences of the last interglacial stage

    NASA Astrophysics Data System (ADS)

    Ernesto, Brunetto; Soledad, Ferrero Brenda; Ignacio, Noriega Jorge

    2015-03-01

    The aim of this paper is to show the stratigraphic record of the Late Pleistocene corresponding to the distal region of the Paraná River basin. It displays sedimentological, paleontological and geochronological evidences that characterise the last interglacial-glacial cycle. In particular, strong environmental records are shown for the Last Interglacial Stage (LIS). Salto Ander Egg Formation (SAEF) is defined as a new lithostratigraphic unit representative of the Late Pleistocene in southwestern Mesopotamia. This unit is formed of complex fluvial deposits, which contains a heterogeneous collection of sub-environments, of ages ranging from 120 to 60 ky BP. The clast-supported gravel facies containing sparse boulders indicate high flow during a humid climate. The large and middle-scale architectures of fluvial sedimentary bodies evidence the relationship between the sediment accommodation and the sea level oscillations. Three sub-sequences identified in the succession suggest a transgressive trend during the MIS5e, a highstand stage in MIS5c, and a minor transgressive cycle during MIS3. A Brazilian faunal association collected at the bottom of the sequence and sedimentological interpretations display wet and warm climatic conditions, typical of tropical or subtropical environments. Such environmental conditions are characteristic of the maximum of the last interglacial stage (MIS5e) and show a signal stronger than the signal of the current interglacial stage. All these data show a direct correlation between the increases of paleodischarges and the elevation of the sea level. The whole sequence is completed with transitional swampy deposits, accumulated probably during the MIS3/MIS2 transition, and the typical loess of the Tezanos Pinto Formation, mantled during the Last Maximum Glacial.

  20. Molecular evidence of Pleistocene bidirectional faunal exchange between Europe and the Near East: the case of the bicoloured

    E-print Network

    Alvarez, Nadir

    Molecular evidence of Pleistocene bidirectional faunal exchange between Europe and the Near East Introduction The impact of Pleistocene climatic fluctuations on Euro- pean biota is well documented. Studies the impact of Pleistocene climatic oscillations, e.g. the dating of population expansions and identifying

  1. Late Pleistocene dune activity in the central Great Plains, USA

    USGS Publications Warehouse

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

    2011-01-01

    Stabilized dunes of the central Great Plains, especially the megabarchans and large barchanoid ridges of the Nebraska Sand Hills, provide dramatic evidence of late Quaternary environmental change. Episodic Holocene dune activity in this region is now well-documented, but Late Pleistocene dune mobility has remained poorly documented, despite early interpretations of the Sand Hills dunes as Pleistocene relicts. New optically stimulated luminescence (OSL) ages from drill cores and outcrops provide evidence of Late Pleistocene dune activity at sites distributed across the central Great Plains. In addition, Late Pleistocene eolian sands deposited at 20-25 ka are interbedded with loess south of the Sand Hills. Several of the large dunes sampled in the Sand Hills clearly contain a substantial core of Late Pleistocene sand; thus, they had developed by the Late Pleistocene and were fully mobile at that time, although substantial sand deposition and extensive longitudinal dune construction occurred during the Holocene. Many of the Late Pleistocene OSL ages fall between 17 and 14 ka, but it is likely that these ages represent only the later part of a longer period of dune construction and migration. At several sites, significant Late Pleistocene or Holocene large-dune migration also probably occurred after the time represented by the Pleistocene OSL ages. Sedimentary structures in Late Pleistocene eolian sand and the forms of large dunes potentially constructed in the Late Pleistocene both indicate sand transport dominated by northerly to westerly winds, consistent with Late Pleistocene loess transport directions. Numerical modeling of the climate of the Last Glacial Maximum has often yielded mean monthly surface winds southwest of the Laurentide Ice Sheet that are consistent with this geologic evidence, despite strengthened anticyclonic circulation over the ice sheet. Mobility of large dunes during the Late Pleistocene on the central Great Plains may have been the result of cold, short growing seasons with relatively low precipitation and low atmospheric CO2 that increased plant moisture stress, limiting the ability of vegetation to stabilize active dune sand. The apparent coexistence of large mobile dunes with boreal forest taxa suggests a Late Pleistocene environment with few modern analogs. ?? 2011 Elsevier Ltd.

  2. 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

  3. The Middle Pleistocene transition as a generic bifurcation on a slow manifold

    NASA Astrophysics Data System (ADS)

    Ditlevsen, Peter; Ashwin, Peter

    2015-04-01

    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 (BP) 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 (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 we propose that the synchrony of the climate oscillations with the astronomical forcing is through the mechanism of phase-resetting oscillation in which the internal frequency of oscillation is increased to match the frequency of the forcing, while the opposite possibility of a faster internal oscillation cannot be slowed down to match a longer period forcing. In spite of its simplicity as a forced ODE, the model is able to reproduce 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.

  4. 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.

  5. 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

  6. 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

  7. Scales of climatic variability and time averaging in Pleistocene biotas: implications for ecology and evolution

    Microsoft Academic Search

    Kaustuv Roy; James W. Valentine; David Jablonski; Susan M. Kidwell

    1996-01-01

    Biotic responses to Pleistocene climatic fluctuations have traditionally been analyzed in the context of glacial-interglacial cycles on the scale of 10000–100 000 years. However, emerging evidence indicates that short-term, high-amplitude, climatic ‘flickers’, close to the limits of the resolving power of the fossil record, occurred within the glacial and interglacial substages. Because species shift geographically in response to the climate

  8. Outburst floods from glacial Lake Missoula

    NASA Astrophysics Data System (ADS)

    Clarke, G. K. C.; Mathews, W. H.; Pack, R. T.

    1984-11-01

    The Pleistocene outburst floods from glacial Lake Missoula, known as the "Spokane Floods", released as much as 2184 km 3 of water and produced the greatest known floods of the geologic past. A computer simulation model for these floods that is based on physical equations governing the enlargement by water flow of the tunnel penetrating the ice dam is described. The predicted maximum flood discharge lies in the range 2.74 × 10 6-13.7 × 10 6 m 3 sec -1, lending independent glaciological support to paleohydrologic estimates of maximum discharge.

  9. 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

  10. Obliquity and precession as pacemakers of Pleistocene deglaciations

    E-print Network

    Feng, Fabo

    2015-01-01

    The Milankovitch theory states that the orbital eccentricity, precession, and obliquity of the Earth influence our climate by modulating the summer insolation at high latitudes in the northern hemisphere. Despite considerable success of this theory in explaining climate change over the Pleistocene epoch (2.6 to 0.01 Myr ago), it is inconclusive with regard to which combination of orbital elements paced the 100 kyr glacial-interglacial cycles over the late Pleistocene. Here we explore the role of the orbital elements in pacing the Pleistocene deglaciations by modeling ice-volume variations in a Bayesian approach. When comparing models, this approach takes into account the uncertainties in the data as well as the different degrees of model complexity. We find that the Earth's obliquity (axial tilt) plays a dominant role in pacing the glacial cycles over the whole Pleistocene, while precession only becomes important in pacing major deglaciations after the transition of the dominant period from 41 kyr to 100 kyr ...

  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. Glacial refugia and the phylogeography of Steller's sea lion (Eumatopias jubatus) in the North Pacific.

    PubMed

    Harlin-Cognato, A; Bickham, J W; Loughlin, T R; Honeycutt, R L

    2006-05-01

    Mitochondrial DNA sequence data were used to examine the phylogeographic history of Steller's sea lions (Eumetopias jubatus) in relation to the presence of Plio-Pleistocene insular refugia. Cytochrome b and control region sequences from 336 Steller's sea lions reveal phylogenetic lineages associated with continental refugia south of the ice sheets in North America and Eurasia. Phylogenetic analysis suggests the genetic structure of E. jubatus is the result of Pleistocene glacial geology, which caused the elimination and subsequent reappearance of suitable rookery habitat during glacial and interglacial periods. The cyclic nature of geological change produced a series of independent population expansions, contractions and isolations that had analogous results on Steller's sea lions and other marine and terrestrial species. Our data show evidence of four glacial refugia in which populations of Steller's sea lions diverged. These events occurred from approximately 60,000 to 180,000 years BP and thus preceded the last glacial maximum. PMID:16674591

  13. 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.

  14. Phylogeography of the Cape velvet worm (Onychophora: Peripatopsis capensis) reveals the impact of Pliocene/Pleistocene climatic oscillations on Afromontane forest in the Western Cape, South Africa.

    PubMed

    McDonald, D E; Daniels, S R

    2012-05-01

    Habitat specialists such as soft-bodied invertebrates characterized by low dispersal capability and sensitivity to dehydration can be employed to examine biome histories. In this study, the Cape velvet worm (Peripatopsis capensis) was used to examine the impacts of climatic oscillations on historical Afromontane forest in the Western Cape, South Africa. Divergence time estimates suggest that the P. capensis species complex diverged during the Pliocene epoch. This period was characterized by dramatic climatic and topographical change. Subsequently, forest expansion and contraction cycles led to diversification within P. capensis. Increased levels of genetic differentiation were observed along a west-to-south-easterly trajectory because the south-eastern parts of the Cape Fold Mountain chain harbour larger, more stable fragments of forest patches, have more pronounced habitat heterogeneity and have historically received higher levels of rainfall. These results suggest the presence of three putative species within P. capensis, which are geographically discreet and genetically distinct. PMID:22409213

  15. The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO 2

    Microsoft Academic Search

    Peter U. Clark; David Archer; David Pollard; Joel D. Blum; Jose A. Rial; Victor Brovkin; Alan C. Mix; Nicklas G. Pisias; Martin Roy

    2006-01-01

    The emergence of low-frequency, high-amplitude, quasi-periodic (?100-kyr) glacial variability during the middle Pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system. This middle Pleistocene transition (MPT) began 1250ka and was complete by 700ka. Its onset was accompanied by decreases in sea surface temperatures (SSTs) in the North Atlantic and

  16. Provenance and glacial history of very fine quartz sand from the Weddell Sea, Antarctica 

    E-print Network

    Smith, Caryn Hallett

    1988-01-01

    (central Weddell Basin) was to determine continental erosion during glacial and pre-glacial periods and obtain a record of bottom-water production. The major lithologies that were recovered include (1) Pliocene to Pleistocene clay and clayey mud...PROVENANCE AND GLACIAL Hl S1ORY OF VERY FINE QUARTZ SA;Kl FR(Ivi 1HE ~ SEA, ANfARCTICA A Thesis by Submitted to the Office of Graduate Studies Texas A%M University in partial fulfillment of the requirements for the degree of STER OF SCIENCE...

  17. 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.

  18. 2, 9791000, 2006 Pleistocene climate

    E-print Network

    Paris-Sud XI, Université de

    CPD 2, 979­1000, 2006 Predicting Pleistocene climate C. Loehle Title Page Abstract Introduction Discussions is the access reviewed discussion forum of Climate of the Past Predicting Pleistocene climate from Pleistocene climate C. Loehle Title Page Abstract Introduction Conclusions References Tables Figures Back

  19. Pleistocene drainage incision in the upper Mississippi Valley Driftless Area

    SciTech Connect

    Knox, J.C.

    1985-01-01

    The deep dissection of the Wisconsin Driftless Area and topographically similar, but glaciated areas in adjacent states is generally acknowledged to have occurred during the Pleistocene, but the precise chronology has been poorly understood. The distribution of pre-Illinoian glacial outwash gravels on uplands and valley side benches near the Mississippi River, on the western margin of the Wisconsin Driftless Area, indicates that the major incision (50-60 m) of drainage had occurred during the very early Pleistocene. Deposits in cut-off valley meanders, a common feature in the lower reaches of Driftless Area rivers, provide a basis for relative dating of the valley incision. The cut-offs appear to have evolved episodically when, at various times during the Pleistocene, glacial debris blocked the drainages of the Mississippi and Wisconsin Rivers causing massive alluviation of side valley tributaries. A radiocarbon date of 21,910 +/- 350 year B.P., representing a buried soil horizon at 22 m depth and about 9 m above the bedrock floor of a cut-off valley meander and 18 m above the bedrock floor of the adjacent present-day valley, supports stratigraphic interpretations that suggest modest valley incision into bedrock probably occurred during the Illinoian and may have also occurred during the early Wisconsinan.

  20. Modern and last local glacial maximum snowlines in the Central Andes of Peru, Bolivia, and Northern Chile

    Microsoft Academic Search

    Andrew G. Klein; Geoffrey O. Seltzer; Bryan L. Isacks

    1999-01-01

    Late Pleistocene snowlines in the central Andes were 500–1200m lower than at present. Radiocarbon dates imply that the late-Pleistocene glacial maximum in the region occurred prior to 20 14Cka, but lack of maximum limiting ages adds considerable uncertainty to the exact timing. Snowline modeling demonstrates that snowlines in the eastern and western cordilleras of the central Andes respond differently to

  1. 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.

  2. Upper Pleistocene facies sequences and relative sea-level trends along the south coast of Ireland

    SciTech Connect

    McCabe, A.M. [Univ. of Ulster, Londonderry (Ireland). Dept. of Environmental Studies; O`Cofaigh, C. [Univ. of Alberta, Edmonton, Alberta (Canada). Dept. of Geography

    1996-03-01

    Upper Pleistocene sequences, deposited around 20 ka provide a record of sedimentation during the last glacial/deglacial cycle along the south coast of Ireland. A stratigraphy based on eight lithofacies associations is recognized. Typically, the facies sequences overlie a glaciated shore platform furrowed by subglacial meltwaters. Elements within the stratigraphy comprise: (1) ice advance southwards onto the continental shelf; (2) stagnation-zone retreat triggered by rising sea level related to isostatic depression coupled with subglacial meltwater events that furrowed the platform; (3) progressive rise in relative sea level recorded by a submergent facies sequence on an isostatically depressed slope (beach gravels {yields} subaqueous jet efflux sediments {yields} wave-influenced sands {yields} glaciomarine mud drape); ice-marginal oscillation is recorded by glaciotectonically deformed gravels, sands, and foliated diamict; (4) terrestrial emergence is marked by angular breccias derived from local slopes by periglacial weathering. There is a clear facies transition between the breccias and underlying wave-influenced sands. Facies sequences suggest that the local deglacial cycle was out of phase with the global eustatic cycle along the south coast of Ireland. Stagnation-zone retreat was largely dependent on magnitudes of isostatic depression, high relative sea level, and meltwater events, and not on climatic forcing.

  3. Pleistocene Lake Bonneville and Eberswalde Crater of Mars: Quantitative Methods for Recognizing Poorly Developed Lacustrine Shorelines

    NASA Astrophysics Data System (ADS)

    Jewell, P. W.

    2014-12-01

    The ability to quantify shoreline features on Earth has been aided by advances in acquisition of high-resolution topography through laser imaging and photogrammetry. Well-defined and well-documented features such as the Bonneville, Provo, and Stansbury shorelines of Late Pleistocene Lake Bonneville are recognizable to the untrained eye and easily mappable on aerial photos. The continuity and correlation of lesser shorelines must rely quantitative algorithms for processing high-resolution data in order to gain widespread scientific acceptance. Using Savitsky-Golay filters and the geomorphic methods and criteria described by Hare et al. [2001], minor, transgressive, erosional shorelines of Lake Bonneville have been identified and correlated across the basin with varying degrees of statistical confidence. Results solve one of the key paradoxes of Lake Bonneville first described by G. K. Gilbert in the late 19th century and point the way for understanding climatically driven oscillations of the Last Glacial Maximum in the Great Basin of the United States. Similar techniques have been applied to the Eberswalde Crater area of Mars using HRiSE DEMs (1 m horizontal resolution) where a paleolake is hypothesized to have existed. Results illustrate the challenges of identifying shorelines where long term aeolian processes have degraded the shorelines and field validation is not possible. The work illustrates the promises and challenges of indentifying remnants of a global ocean elsewhere on the red planet.

  4. 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

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

    PubMed

    Spellman, Garth M; Klicka, John

    2006-12-22

    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

  6. Sources and distribution of upper Pleistocene sand, Eastern United States Atlantic Shelf

    SciTech Connect

    Leschak, P.; Prusak, D.; Mazzullo, J.

    1985-02-01

    A 2-yr study of the sources and distribution of upper Pleistocene and Holocene sand on the eastern US shelf between the Bay of Fundy and Cape Hatteras reveals that 3 sand types are found on this shelf: (1) glacially transported, very angular sands, (2) fluvially transported, well-rounded sands derived from unlithified coastal plan deposits, and (3) fluvially transported, moderately angular sands derived from lithified sedimentary and crystalline rocks of the Appalachian and New England areas. For the most part, the distribution of these sand types reflects the late Pleistocene paleogeography of this shelf. Glacial sands are found in the areas of upper Pleistocene till, moraine, and outwash-plain deposits east and northeast of the Hudson Canyon; the 2 fluvial sands are found in coast-normal stripes that correspond to the ancestral paths of the many rivers that traversed this shelf during the late Pleistocene. The preservation of relict paleogeographic patterns of these sorts are an indication of diffusive transport of sand through most of this shelf. The exceptions to this are found in the shallow waters of Nantucket Shoals and Geoges Bank, where glacial sands are presently being advected to the southwest by the strong tidal currents that prevail.

  7. Speciation of Iberian diving beetles in Pleistocene refugia (Coleoptera, Dytiscidae).

    PubMed

    Ribera, Ignacio; Vogler, Alfried P

    2004-01-01

    The Mediterranean basin is an area of high diversity and endemicity, but the age and origin of its fauna are still largely unknown. Here we use species-level phylogenies based on approximately 1300 base pairs of the genes 16S rRNA and cytochrome oxidase I to establish the relationships of 27 of the 34 endemic Iberian species of diving beetles in the family Dytiscidae, and to investigate their level of divergence. Using a molecular clock approach, 18-19 of these species were estimated to be of Pleistocene origin, with four to six of them from the Late Pleistocene ( approximately 100 000 years). A second, lower speciation frequency peak was assigned to Late Miocene or Early Pliocene. Analysis of the distributional ranges showed that endemic species placed in the tip nodes of the trees are significantly more likely to be allopatric with their sisters than endemic species at lower node levels. Allopatric sister species are also significantly younger than sympatric clades, in agreement with an allopatric mode of speciation and limited subsequent range movement. These results strongly suggest that for some taxa Iberian populations were isolated during the Pleistocene long enough to speciate, and apparently did not expand their ranges to recolonize areas north of the Pyrenees. This is in contradiction to observations from fossil beetles in areas further north, which document large range movements associated with the Pleistocene glacial cycles hypothesized to suppress population isolation and allopatric speciation. PMID:14653798

  8. Ecological change, range fluctuations and population dynamics during the Pleistocene.

    PubMed

    Hofreiter, Michael; Stewart, John

    2009-07-28

    Apart from the current human-induced climate change, the Holocene is notable for its stable climate. In contrast, the preceding age, the Pleistocene, was a time of intensive climatic fluctuations, with temperature changes of up to 15 degrees C occurring within a few decades. These climatic changes have substantially influenced both animal and plant populations. Until recently, the prevailing opinion about the effect of these climatic fluctuations on species in Europe was that populations survived glacial maxima in southern refugia and that populations died out outside these refugia. However, some of the latest studies of modern population genetics, the fossil record and especially ancient DNA reveal a more complex picture. There is now strong evidence for additional local northern refugia for a large number of species, including both plants and animals. Furthermore, population genetic analyses using ancient DNA have shown that genetic diversity and its geographical structure changed more often and in more unpredictable ways during the Pleistocene than had been inferred. Taken together, the Pleistocene is now seen as an extremely dynamic era, with rapid and large climatic fluctuations and correspondingly variable ecology. These changes were accompanied by similarly fast and sometimes dramatic changes in population size and extensive gene flow mediated by population movements. Thus, the Pleistocene is an excellent model case for the effects of rapid climate change, as we experience at the moment, on the ecology of plants and animals. PMID:19640497

  9. The role of meltwater in glacial processes

    NASA Astrophysics Data System (ADS)

    Eyles, Nick

    2006-08-01

    Water plays a dominant role in many glacial processes and the erosional, depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized. At its maximum extent c. 20,000 years ago, the volume of the Laurentide ice sheet was 33 × 10 6 km 3 (about the same as the volume of all ice present today on planet Earth). The bulk of this was released as water in little more than 10,000 years. Pulses of meltwater flowing to the Atlantic Ocean from large ice dammed lakes altered thermohaline circulation of the world's oceans and global climate. One such discharge event via Hudson Bay at 8200 years BP released 160,000 km 3 of water in 12 months. Global sea levels recovered from glacial maximum low stands reached at about 20,000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods, rates as high as 4 m per hundred years. Meltwaters played a key role in lubricating ice sheet motion (and thus areal abrasion) across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the Canadian Shield. The recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments (till) by sliding-induced shearing and deformation of overpressured sediment and soft rock. The transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates. Some workers credit catastrophic subglacial 'megafloods' with the formation of drumlins and flutes on till surfaces. Subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins; it has been estimated that less than 6% of the total volume of glaciclastic sediment produced during the Pleistocene remains on land. Fluvioglacial and glaciolacustrine sediments and landforms dominate large tracts of the 'glacial' landscape in North America. The recharge of subglacial meltwater into underlying bedrock and sediment aquifers created transient reversals in the long-term equilibrium flow directions of basinal fluids. With regard to pre-Pleistocene glacial record, meltwaters moved enormous volumes of terrestrial 'glaciclastic' sediment to marine basins and thus played a key role in preserving a record of glaciation, a record otherwise almost entirely lost on land.

  10. HEINRICH EVENTS: MASSIVE LATE PLEISTOCENE DETRITUS LAYERS OF THE NORTH ATLANTIC

    E-print Network

    Jellinek, Mark

    ; accepted 30 September 2003; published 18 March 2004. [1] Millennial climate oscillations of the glacial as their precursory intervals. Studies of previous glacial intervals may also provide important constraints. INDEX.g., Schulz et al., 1998], and stronger north- erly winds in the western Mediterranean [e.g., Cacho et al

  11. New exposure ages for the Last Glacial Cycle in the Sanabria Lake region (northwestern Spain)

    NASA Astrophysics Data System (ADS)

    Rodríguez-Rodríguez, Laura; Jiménez-Sánchez, Montserrat; Domínguez-Cuesta, María Jose; Rinterknecht, Vincent; Pallàs, Raimon; Braucher, Régis; Bourlès, Didier; Valero-Garcés, Blas

    2013-04-01

    The Sanabria Lake region is located in the Trevinca Massif, a mid-latitude mountain area up to 2128 m asl in the northwest corner of the Iberian Peninsula (42oN 6oW). An ice cap glaciation took place during the Last Glacial Cycle in this massif, with an equilibrium line altitude of 1687 m for the Tera glacial outlet at its local maximum (Cowton et al., 2009). A well preserved glacial sequence occurs on an area of 45 km2 around the present Sanabria Lake (1000 m asl) and is composed by lateral and end moraines in close relationship with glaciolacustrine deposits. This sequence shows the ice snout oscillations of the former Tera glacier during the Last Glacial Cycle and offers a good opportunity to compare radiocarbon and OSL- based chronological models with new cosmogenic isotope dates. The new dataset of 10Be exposure ages presented here for the Sanabria Lake moraines is based on measurements conducted on 23 boulders and is compared with previous radiocarbon and OSL data conducted on ice related deposits (Pérez-Alberti et al., 2011; Rodríguez-Rodríguez et al., 2011). Our results are coherent with the available deglaciation radiocarbon chronology, and support a last deglaciation origin for the whole set of end moraines that are downstream the Sanabria Lake (19.2 - 15.7 10Be ka). Discrepancies between results of the different dating methods concern the timing of the local glacial maximum, with the cosmogenic exposure method always yielding the youngest minimum ages. As proposed to explain similar observations made elsewhere (Palacios et al., 2012), reconciling the ages from different dating methods would imply the occurrence of two glacial advances close enough in extent to generate an overlapping polygenic moraine. Cowton, T., Hughes, P.D., Gibbard, P.L., 2009. Palaeoglaciation of Parque Natural Lago de Sanabria, northwest Spain. Geomorphology 108, 282-291. Rodríguez-Rodríguez, L., Jiménez-Sánchez, M., Domínguez-Cuesta, M.J., Rico, M.T., Valero-Garcés, B., 2011. Last deglaciation in northwestern Spain: New chronological and geomorphologic evidence from the Sanabria region. Geomorphology 135, 48-65. Palacios, D., Andrés, N., Úbeda, J., Alcalá, J., Marcos, J., Vázquez-Selem, L., 2012. The importance of poligenic moraines in the paleoclimatic interpretation from cosmogenic dating. Geophysical Research Abstracts 14, EGU2012-3759-1. Pérez-Alberti, A., Valcárcel-Díaz, M., Martini, I.P., Pascucci, V., Andrucci, S., 2011. Upper Pleistocene glacial valley-junction sediments at Pias, Trevinca Mountains, NW Spain. In: Martini, I.P., French, H.M., Pérez-Alberti, A. (Eds.), Ice-Marginal and Periglacial Processes and Sediments. Geological Society (London) Special Publication 354, pp. 93-110. Research funded by the projects LIMNOCLIBER (REN2003-09130-C02-02), IBERLIMNO (CGL2005-20236-E/CLI), LIMNOCAL (CGL2006-13327-C04-01) and GRACCIE (CSD2007-00067) of the Spanish Inter-Ministry Commission of Science and Technology (CICYT). Additional funding was provided by the Fundación Patrimonio Natural de Castilla y León through the project "La investigacion en el Lago de Sanabria dentro del proyecto CALIBRE: perspectivas y posibilidades", and by the projects Consolider Ingenio 2006 (CSD2006-0041, Topo-Iberia), 2003 PIRA 00256, HF02.4, and RISKNAT (2009SGR520). L. Rodríguez-Rodríguez has developed her research under a Severo Ochoa Programme fellowship (FICYT- Asturias).

  12. Differentiation of pleistocene deposits in northeastern Kansas by clay minerals

    USGS Publications Warehouse

    Tien, P.-L.

    1968-01-01

    Seventy-four samples from eight stratigraphic sections of lower Pleistocene glacial and glaciofluvial deposits in Doniphan County, extreme northeastern Kansas, were analyzed using X-ray diffraction techniques. Clay-mineral assemblages of the <2 ?? fraction of these deposits are nearly identical, consisting of a mixed-layer clay mineral associated with minor amounts of kaolinite and illite. An attempt was made to differentiate units of till and nontill deposits by using the relative intensities of 001 reflections of "mixed-layer mineral," kaolinite, and illite. At least two tills were recognizable. Associated nontill deposits, could not be differentiated from one another, although the nontills are easily distinguished from tills. ?? 1968.

  13. How long do U-shaped valleys last? The lifespan of glacial topography set by tectonics.

    NASA Astrophysics Data System (ADS)

    Prasicek, Günther; Larsen, Isaac; Montgomery, David

    2015-04-01

    More than 10 kyr after the last major glaciation the topography of mountain ranges world-wide remains dominated by characteristic glacial landforms such as U-shaped valleys, but the transition from a glacial to a fluvial landscape is poorly constrained and it remains unclear how long glacial morphology persists following deglaciation. The longevity of glacial topography influences glacial extent and erosion in subsequent glaciations and hence the cumulative impact of Pleistocene glacial cycles on the evolution of mountain ranges. We tested whether tectonic forcing and erosional response control the timescale over which glacial topography persists into inter-glacial periods in the western Southern Alps of New Zealand and other mountain ranges worldwide, including the syntaxes of the Himalaya and Taiwan. We quantified the degree of glacial imprint by exploiting the conventional interpretation of V-shaped fluvial and U-shaped glacial valleys. Valley cross sections were automatically extracted from digital terrain models and power-laws were fitted to each cross section to quantify the shape of the valley flanks. A power-law exponent of 1 characterizes the straight valley flanks of a V-shaped cross section and greater exponents are indicative of progressively more U-shaped valleys. Our results show that tectonic forcing is a first-order control on landscape evolution and on the persistence of glacial morphology worldwide. In Earth's most rapidly uplifting mountain ranges the lifespan of glacial topography is on the order of one interglacial period, preventing the development of a cumulative glacial signal. In contrast, in most alpine landscapes more than 100 kyr are required for the transformation from glacial back to fluvial topography and glacial landforms have not or have only partially been erased during the current interglacial. Thus we suggest, emphasizing the influence of glacially preconditioned topography on glacial extent and erosion, that tectonic forcing governs the impact of climate depressions on active orogens beyond controlling their vertical extent, by also altering the spatial and temporal pattern of erosion during subsequent glacial periods via a link between rock uplift and valley cross-sectional shape.

  14. Origin of the epeirogenic uplift of Pliocene-Pleistocene beach ridges in Florida and development of the Florida karst

    Microsoft Academic Search

    N. D. Opdyke; D. P. Spangler; D. L. Smith; D. S. Jones; R. C. Lindquist

    1984-01-01

    Marine fossils of Pleistocene age are known to occur in beach ridges near the border of northern Florida and southern Georgia at elevations of between 42 and 49 m above mean sea level. No evidence exists for a massive melt-off of glacial ice, which would be required to raise sea level to these elevations. Florida, therefore, must have been uplifted

  15. 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.

  16. 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

  17. Glacial Lake Hides Bacteria

    NSDL National Science Digital Library

    Peplow, Mark

    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.

  18. Geographic variation in the mitochondrial DNA of the red shiner (Cyprinella lutrensis): the influence of Pleistocene glaciation on population dispersal and divergence 

    E-print Network

    Richardson, Linda Rose

    1994-01-01

    after the glaciers receded, or whether it occurred in these regions prior to glaciation and persisted throughout the Pleistocene in glacial refugia. Gibbs (1957) and Metcalf (1966) hypothesized that C. lutrensis originated preglacially... in the northern and central portions of its range (i. e. , in areas directly or indirectly affected by Pleistocene glaciation), or did C. lutrensis colonize these areas after the glaciers receded; and ii) do patterns of geographic diversity in mtDNA of C...

  19. Early onset and origin of 100-kyr cycles in Pleistocene tropical SST records

    NASA Astrophysics Data System (ADS)

    Liu, Zhonghui; Cleaveland, Laura C.; Herbert, Timothy D.

    2008-01-01

    The large 100-kyr cycles evident in most late-Pleistocene (0-0.6 Ma) paleoclimatic records still lack a satisfactory explanation. Previous studies of the nature of the transition from the early Pleistocene (1.2-1.8 Ma) 41-kyr-dominated climate regime to the 100-kyr world have been based almost exclusively on benthic foraminiferal oxygen isotopic ( ?18O) data. It is generally accepted that the late Pleistocene 100-kyr cycles represent a newly evolved sensitivity to eccentricity/precession, superimposed on an earlier, and largely constant, response to obliquity and precession forcing. However, orbitally-resolved Pleistocene sea surface temperature (SST) records from a variety of oceanic regions paint a rather different picture of the global climate transition across the mid-Pleistocene transition (MPT, 0.6-1.2 Ma). Reanalysis of these SST records shows that: (1) an early onset of strong 100-kyr-like cycles in two low-frequency bands (˜ 120-145 kyr and ˜ 60-80 kyr), derived from the bundling of two/three obliquity cycles into grand cycles (obliquity subharmonics), occurred in tropical SST records during the early Pleistocene, (2) these two early Pleistocene periods converge into the late-Pleistocene 100-kyr period in tropical SST records, (3) the dominance of 100-kyr SST power in the late Pleistocene coincides with a dramatic decline in the 41-kyr SST power, and (4) the correlation of timing of glacial terminations with eccentricity/precession variation could well extend back into the early Pleistocene. We demonstrate that most of these features also occur in ?18O records, but in a much more subtle manner. These features could be explained in two plausible ways: a shift in climate sensitivity from obliquity to eccentricity/precession (a modified version of the conventional view) or an increasingly nonlinear response to orbital obliquity across the MPT. However, our examination of the development of ˜100-kyr cycles favors an obliquity bundling mechanism to form late Pleistocene 100-kyr cycles. We therefore suggest that the late Pleistocene 100-kyr climatic cycles are likely a nonlinear response to orbital obliquity, although the timing of late Pleistocene 100-kyr climatic cycles and their early forms appears to be paced by eccentricity/precession.

  20. Sedimentary and Paleoclimatic Controls on Caddisfly (Insecta: Trichoptera) Assemblages during the Last Interglacial-to-Glacial Transition in Southern Ontario

    Microsoft Academic Search

    Nancy E. Williams; Nicholas Eyles

    1995-01-01

    Southern Ontario, Canada, has late Pleistocene deposits that contain evidence for climatic cooling during the last interglacial\\/glacial transition and much of the succeeding Wisconsin glaciation. Fossils of lacustrine and riverine caddisflies (Insecta: Trichoptera) are abundant and well-preserved in these deposits. We examined 26 samples from the interglacial section exposed in the Don Valley Brickyard and compared their caddisfly assemblages with

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

    Microsoft Academic Search

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

    2000-01-01

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

  2. Biological consequences of a cold, stratified, high latitude, glacial ocean

    NASA Astrophysics Data System (ADS)

    Hays, J. D.

    2010-12-01

    Increasing oceanic organic carbon export by improving the efficiency of the oceans biological pump has been invoked as a means to transfer CO2 between atmosphere and ocean during glacial cycles. Although this mechanism is supported by evidence of higher late Pleistocene than Holocene redox-sensitive metal concentrations in deep-sea sediments, evidence of higher glacial primary productivity, to generate greater export, is lacking (Jaccard et al., 2009). This study proposes that glacial cold ocean stratification has profound biological consequences that can resolve this paradox, evidenced by the changing flux of radiolarians from different levels within the water column. Mesopelagic (200-1000m) radiolarians, which are beneficiaries of carbon export, have higher glacial than Holocene flux to northwest Pacific sediments, indicating increased glacial export, in agreement with the redox-sensitive metal data, but glacial epipelagic (0-200m) radiolarian flux is lower than Holocene flux indicating an inhibition of epipelagic production. Modern radiolarian flux patterns, similar to the glacial northwest Pacific, occur only in the strongly stratified Sea of Okhotsk, where a thin (10-20m), summer, nutrient depleted mixed layer is underlain (20 to 150m) by perennially cold (-1 to 0° C) remnant winter water. Radiolarian and zooplankton concentrations in the cold winter layer are low relative to warmer water below (200 and 1000m) (Nimmergut and Abelmann, 2002; Gorbatenko, 1996). This physical and biological stratification generates greater mesopelagic radiolarian flux, dominated by C. davisiana, than epipelagic flux. The similar radiolarian flux pattern in glacial northwest Pacific sediments suggests a similar overlying physical and biological stratification and its greater implied export is probably caused by reduced epipelagic consumption in the cold winter water, rather than increased primary production. High C. davisiana percentages, in glacial high latitude (above 45°) sediments of both hemispheres, indicate the presence of an Okhotsk-like physical and biological stratification. This glacial stratification would have stripped nutrients from a thin sun-drenched mixed layer, reduced epipelagic heterotrophic consumption increasing biological pump efficiency and enhancing mesopelagic heterotrophic consumption, inspite of no increase and possibly a decease of high latitude primary productivity.

  3. On the Interpretation of Late Pleistocene 100-kyr Phases

    NASA Astrophysics Data System (ADS)

    Lisiecki, L. E.

    2013-12-01

    Phase calculations are often used to measure leads and lags in paleoclimate records and then make inferences about the causal mechanisms associated with orbitally forced glacial cycles. Fourier and wavelet spectral analyses work well for near-sinusoidal cycles, but Late Pleistocene 100-kyr glacial cycles are typically sawtooth shaped (e.g., 10 kyr of warming followed by 90 kyr of cooling) and are thus extremely non-sinusoidal. Here I present phase calculations for a variety of 100-kyr sawtooth shapes similar to those observed in paleoclimate records. These calculations demonstrate that variations in cycle shape can produce apparent differences in 100-kyr phase even when records experience synchronous warming and cooling. For example, changing the amplitude of MIS 5e in otherwise identical records can shift the 100-kyr wavelet phase by 13° (3.6 kyr). Therefore, spectral phase calculations are not well-suited for characterizing leads, lags, or response times of 100-kyr cyclicity in paleoclimate records. Direct comparison of the timing of distinctive features (e.g., termination onset or the onset of cooling at the end of an interglacial) is more appropriate for evaluating possible causal sequences in Late Pleistocene 100-kyr cycles.

  4. The identity of the Pleistocene mosses Drepanocladus minnesotensis and Neocalliergon integrifolium (Amblystegiaceae)

    Microsoft Academic Search

    Norton G. Miller

    1983-01-01

    The type specimens ofDrepanocladus minnesotensis Williams andNeocalliergon integrifolium Williams are shown to beD. aduncus var.kneiffii (B.S.G.) Monk. andScorpidium scorpioides (Hedw.) Limpr., respectively. These fossils, which were originally obtained from late glacial sediments in Minneapolis, Minnesota,\\u000a together with other mosses identified from the deposit, indicate that deposition probably took place in a shallow depression\\u000a filled with calcareous water. Pleistocene mosses from

  5. Biogeochemical Characteristics of Lacustrine Sediments Reflecting a Changing Alpine Neotropical Ecosystem during the Pleistocene

    Microsoft Academic Search

    Germán Mora; Lisa M. Pratt; Arnoud Boom; Henry Hooghiemstra

    2002-01-01

    Continuous lacustrine deposits of the Funza-II core from the Bogotá basin, Colombia (5°N74°W) record late Pleistocene climatic variations, providing an opportunity to assess the influence of glacial–interglacial climate changes on alpine ecosystems in equatorial South America. Biogeochemical response of this tropical alpine system to climate change was inferred from changes in elemental concentrations and ratios and isotopic signatures in the

  6. Main Geologic-Paleoecological Events of the Late Pleistocene in the North of Western Siberia

    Microsoft Academic Search

    M. Levitan; Yu Lavrushin

    The major geological and paleoecological events of the Late Pleistocene in the north of West Siberia are two glaciations {Yermak\\u000a (Zyryan) and Sartan} and three transgressions (Kazantsev, Kargin and post-glacial) (Arkhipov, 2000) (Fig. 3.1). As stated\\u000a above, the Kazantsev transgression is correlated with the Eemian transgression of West Europe and MIS 5e (Troitsky, 1966;\\u000a Gudina, 1976; Arkhipov, 1997, 2000). The

  7. Fluvial development of major Alpine valleys since the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Leith, Kerry; Fox, Matthew; Moore, Jeffrey R.

    2015-04-01

    The effects of both fluvial and glacial processes are evident in the morphology of bedrock hillslopes and river channels throughout the European Alps. While steep rock slopes in upper, U-shaped reaches of valleys provide clear evidence for a Pleistocene history that includes at least one period of major glacial erosion, river channels near the toe of blocky rock slopes in lower, V-shaped reaches suggest fluvial incision has played an important role in Alpine evolution. In order to differentiate the impact of these two process regimes on the development of the orogen, we use a combination of integral analysis and forward streampower models to identify a series of corresponding steepened channel reaches across a relatively homogeneous tectonic block of the southern Swiss Alps. We consider these steepened channel sections represent up to seven knickpoints that extend 800 m above the elevation of the present-day Rhone Valley. The uppermost (oldest) knickpoint is currently located approximately half-way into each valley, and effectively defines the front of fluvial erosion into a relict glacial landscape preserved in the upper reaches of each catchment. We expect that these knickpoints form near the outlet of tributary valleys as a result of bedrock uplift during major glacial cycles. The knickpoints are exposed during deglaciation, and propagate upstream as in response to increased streampower during major Pleistocene interglacials. By employing a forward streampower incision model regulated by the timing of global marine isotope stages we are able to reproduce both the form, and location of knickpoints across our study region, and correlate distinct breaks in cross-sectional valley slope to discrete glacial - interglacial transitions. Our results indicate that Alpine landscape evolution has been driven by a combination of tectonic uplift and fluvial incision since an initial period of enhanced glacial erosion prior to 0.7 Ma. We find that rates of tectonic uplift have been relatively consistent since this time, while transitional landscape forms have been largely preserved throughout each glacial cycle.

  8. Progressive shoaling of the equatorial Pacific thermocline over the last eight glacial periods

    NASA Astrophysics Data System (ADS)

    Regoli, Fabienne; Garidel-Thoron, Thibault; Tachikawa, Kazuyo; Jian, Zhiming; Ye, Liming; Droxler, André W.; Lenoir, Guillaume; Crucifix, Michel; Barbarin, Nicolas; Beaufort, Luc

    2015-05-01

    The depth of equatorial Pacific thermocline is diagnostic of the main modes of tropical climates. Past estimates of Pacific thermocline dynamics have been reconstructed either for the Last Glacial Maximum or on longer timescales at low resolution. Here we document a new high-resolution set of reconstructed past sea surface and subsurface waters temperatures from the southwestern subequatorial Pacific, core MD05-2930, in the Gulf of Papua, over the last 800 ka. We used two morphotypes of Globigerinoides ruber known to live at different water depths to reconstruct past stratification. We estimated calcification temperature of each morphotypes by Mg/Ca paleothermometry. Our subequatorial Pacific thermocline paleotemperature record indicates a response of the thermocline to both direct orbital forcing and glacial-interglacial changes. Our stratification record shows a systematic shallower glacial thermocline, whereas sea surface temperatures are characterized by precessional forcing. The record is indicative of a progressive long-term shoaling of the thermocline during the glacial stages during the late Pleistocene. The shoaling of the subequatorial Pacific thermocline is consistent with regional estimates. An enhanced South Pacific shallow overturning wind-driven circulation could have driven this progressive shoaling. We speculate that this late Pleistocene glacial shoaling of the thermocline could be related to an increase in the amplitude of the obliquity.

  9. Pleistocene Speciation and the Mitochondrial DNA Clock

    E-print Network

    Arbogast, Brian

    Pleistocene Speciation and the Mitochondrial DNA Clock John Klicka and Robert M. Zink (1) used whether Late Pleistocene ( 250,000 years ago) glaciations may have been an important mechanism in the Late Pliocene or Early Pleistocene, which would suggest that Pleistocene glaciation, in general, did

  10. Glacial Legacies of New York State

    NSDL National Science Digital Library

    2001-04-09

    Glacial Legacies of New York State is a presentation of digital images illustrating the origins of the glacial record in New York. Designed for classroom use, Glacial Legacies has a complementing narrative for each slide, images of glacial features in New York, classic examples of glacial features from around the country, and diagrams of glacial processes.

  11. Recurring middle Pleistocene outburst floods in east-central Alaska

    USGS Publications Warehouse

    Froese, D.G.; Smith, D.G.; Westgate, J.A.; Ager, T.A.; Preece, S.J.; Sandhu, A.; Enkin, R.J.; Weber, F.

    2003-01-01

    Recurring glacial outburst floods from the Yukon-Tanana Upland are inferred from sediments exposed along the Yukon River near the mouth of Charley River in east-central Alaska. Deposits range from imbricate gravel and granules indicating flow locally extending up the Yukon valley, to more distal sediments consisting of at least 10 couplets of planar sands, granules, and climbing ripples with up-valley paleocurrent indicators overlain by massive silt. An interglacial organic silt, occurring within the sequence, indicates at least two flood events are associated with an earlier glaciation, and at least three flood events are associated with a later glaciation which postdates the organic silt. A minimum age for the floods is provided by a glass fission track age of 560,000 ?? 80,000 yr on the GI tephra, which occurs 8 m above the flood beds. A maximum age of 780,000 yr for the floods is based on normal magnetic polarity of the sediments. These age constraints allow us to correlate the flood events to the early-middle Pleistocene. And further, the outburst floods indicate extensive glaciation of the Yukon-Tanana Upland during the early-middle Pleistocene, likely representing the most extensive Pleistocene glaciation of the area. ?? 2003 University of Washington. Published by Elsevier Inc. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Lake Ohrid (Macedonia/Albania) is one of the world's oldest lakes and is renowned for its high degree of biological diversity. It is the target site for the ICDP SCOPSCO (Scientific Collaboration on Past Speciation Conditions in Lake Ohrid) project, an international research initiative to study the links between geology, environment and the evolution of endemic taxa. In 2011 a 10-meter core was recovered from the western shore of Lake Ohrid adjacent to the Lini Peninsula. Here we present high-resolution stable isotope and geochemical data from this core through the Late Glacial to Holocene to reconstruct past climate and hydrology (TIC, ?18Ocalcite, ?13Ccalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, ?13Corganic, Rock-Eval pyrolysis). The data identify 3 main zones: (1) the Late Glacial-Holocene transition represented by low TIC, TOC and higher isotope values, (2) the early to mid-Holocene characterised by higher TOC, TOC/N and lower ?18Ocalcite, and (3) the late Holocene which shows a marked decrease in TIC and TOC. In general there is an overall trend of increasing ?18Ocalcite from 9 ka to present, suggesting progressive aridification through the Holocene, which is consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the SCOPSCO project cores recovered in spring-summer 2013 dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.

  13. 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.

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

    PubMed Central

    Newman, Catherine E.; Austin, Christopher C.

    2015-01-01

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

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

    PubMed

    Newman, Catherine E; Austin, Christopher C

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  17. Last Glacial Maximum

    NSDL National Science Digital Library

    Kristine DeLong

    In this activity for undergraduates, students explore the CLIMAP (Climate: Long-Range Investigation, Mapping and Prediction) model results for differences between the modern and the Last Glacial Maximum (LGM) and discover the how climate and vegetation may have changed in different regions of the Earth based on scientific data.

  18. 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…

  19. 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.

  20. Latest Pleistocene Deposition and Erosion on the New Jersey Shelf

    NASA Astrophysics Data System (ADS)

    Christensen, B. A.; Alexander, C.; Stackhouse, S.; Turner, R.; Nordfjord, S.; Austin, J.; Goff, J.; Gulick, S.; Fulthorpe, C.

    2007-12-01

    The New Jersey margin is an ideal location for the study of sedimentary response to glacioeustatic forcing because this passive continental edge is both wide and stable. Although the region has been intensively imaged and mapped geophysically, it is still far from being understood stratigraphically because of a lack of samples to constrain timing and paleo-depositional environment. This study examines the timing and nature of latest Pleistocene erosion and deposition on the shelf, using grab samples and core recovered using the AHC-800 (Active Heave Compensation - 800 m) drilling system. The latest Pleistocene shelf is characterized by (1) downcutting and erosion by rivers associated with subaerial exposure during glacial retreat of sea level; (2) deposition at the shelf edge during sea level fall associated with formation of an outer shelf wedge; and (3) deposition in estuarine environments as sea level rose. Foraminiferal and sediment textural analyses of cores samples ground truth previous seismic reflection-based interpretations of incision and paleochannel formation. Grab samples analyzed for foraminiferal content and grain size identify environment of deposition within three main bathymetric features: sand ridges, sand ribbons, and glacial scours. Radiometric dating (14C) further constrains the timing of intervals of erosion and deposition. We relate our results to other studies and suggest a complex, spatially variable shelf response to glacial advance and retreat. K-Ar analyses of hornblende crystals provide constraints on sediment sources. Two assemblages exist: one consistent with ages of Proterozoic age plutons in the New Jersey area, and another, younger, indicating mixing. K-Ar dates show a clear difference between and Holocene (930- 970 +/- 20 Ma) sedimentary assemblages and sediments older than 30 k.y, (850-880 Ma +/- 20-30 Ma). Holocene hornblend crystal ages are consistent with Grenvillian aged plutons common to the source region (e.g., northwestern New Jersey) and were likely delivered to the depositional region by glacial erosion during the last glacial stage. The 40 - 30 Ka aged hornblende crystals are likely a mixture of Grenville and Paleozoic source rocks such as the Cortland complex (55 km north of NYC on the Hudson River), and implies a different source for sediment delivery during stages 4 and 3.

  1. Contribution of glacial-isostatic adjustment to the geocenter motion

    NASA Astrophysics Data System (ADS)

    Klemann, Volker; Martinec, Zden?k

    2011-11-01

    The geocenter motion describes the surface net-displacement of the entire solid Earth with respect to the center-of-mass of the entire Earth including surface masses. Therefore, it resembles an integrative quantity of surface displacement and mass redistribution inside the Earth as well as at its surface. Seasonal variations of this quantity are understood to originate mainly from mass redistribution in the water cycle. In contrast, a secular trend of the geocenter motion is possible to result also from the dynamics of the Earth's interior. One mechanism inducing a secular geocenter motion is the glacial-isostatic adjustment, describing the deformation and mass redistribution in the Earth's interior due to glaciations during the Pleistocene. Focusing on this contribution, we compute the geocenter motion from the displacement and gravity-potential fields calculated for a spherical, self-gravitating, incompressible and viscoelastic Earth model loaded by the last Pleistocene glacial cycle. We discuss the fluid-core approximation usually adopted and assess the influence of a list of modelling parameters which are the upper- and lower-mantle viscosity, lithosphere thickness, and glaciation history. We find a rather robust geocenter motion with respect to parameter variations, which is directed towards Northeast Canada and shows velocities that vary between 0.1 and 1 mm/yr depending on the adopted Earth-model and glaciation-history parameterizations.

  2. 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

  3. 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.

  4. Last glacial aeolian dynamics at the Titel loess plateau (Vojvodina, Serbia)

    NASA Astrophysics Data System (ADS)

    Markovi?, S. B.; Bokhorst, M. P.; Machalett, B.; Štrbac, D.; Hambach, U.; Basarin, B.; Svir?ev, Z.; Stevens, T.; Frechen, M.; Vandenberghe, J.

    2009-04-01

    The Titel loess plateau (Vojvodina, Serbia) is situated at the confluence of the rivers Danube and Tisa, in the southeastern part of the Ba?ka subregion. Various phases of fluvial erosion have shaped the ellipsoid form of the plateau, which is characterized by steep slopes on the margins. The Titel loess plateau is a unique geomorphologic feature, further emphasising the wide diversity of the loess landforms. The plateau is an island of loess with a maximum length of about 16 km and a maximum width of 7.2 km. Thick loess deposits of between 35 and 55 m are intercalated by 5 main pedocomplexes likely deposited thought the last 5 glacial/interglacial cycles. Steep loess cliffs expose several important sections for understanding climatic and environmental change during the middle and late Pleistocene in the region. The succession of palaeosols through the sequence strongly suggests a transition from humid interglacial climates in the middle Pleistocene, to drier interglacial climates in the late Pleistocene. Past aeolian dynamics have been reconstructed using magnetic susceptibility, grain size, geochemical and malacological investigations by depth in the thick last glacial unit. Luminescence dating and magnetic susceptibility inter-profile correlation provide the chronological framework. Lower last glacial loess unit V-L1L2 is loosely cemented porous sandy loess, with occasional fine laminations and thin, fine sand beds. Identified malacofauna indicates very dry climatic conditions and poor steppic vegetation. It is hypothesized that while the last glacial vegetation cover is extremely sparse, significant sedimentation rates during the lower last glacial can be explained by the presence of a cyanobacterial crust. Protection of loess sediments from deflation by the presence of a cyanobacterial crust is observed at present in loess quarries (Ruma, Crvenka, Petrovaradin). The middle glacial was warmer and relatively moist, as indicated by an increase in clay content and magnetic susceptibility values in a weakly developed pedocomplex, V-L1S1. Loess sub-layers intercalated into V-L1S1 preserve evidence of episodes of abrupt cooling and aridification. In contrast with other European loess sites, the middle glacial pedocomplex is weakly developed at exposures on the Titel loess plateau. The uppermost late glacial loess stratum V-L1L1 shows low values of magnetic susceptibility and clay content, plus high values of carbonate content and the presence of a few frigophilous and cold resistant snails, preserved in sediments laid down during the coldest palaeoclimatic interval of the last glacial period. Composite mollusc associations in loess unit V-L1L1 suggest a higher diversity of environments in comparison to those preserved in the V-L1L2 and V-L1S1 units. In addition to climatic changes over interglacial-glacial and interstadial-stadial timescales, climate proxies (especially grain size) in the last glacial loess exhibit many abrupt fluctuations. Evidence of similar abrupt high frequency fluctuations during the last glacial period appear in loess through out much of Eurasia. Without a detailed and precise chronological framework, provided by independent dating, as yet it is not possible to determine whether the variations recorded in the Titel plateau loess are related to widely documented events in the North Atlantic or independent regional or local depositional/environmental variations. The intensity of deposition of coarser material during the relatively cold early last glacial exceeds that during the coldest last glacial maximum. This may be explainable via changes in general atmospheric circulation, as well as changes in the transportation and depositio regime of the Danube fluvial system. During the last glacial maximum, extension of the ice sheets in northern Europe was greatest and may have redirected the penetration of Atlantic air masses to the east (e.g. Dodonov and Baiguzina, 1995). Model results presented in van Huissteden and Pollard (2003) indicate strong anticyclonal circulation over the Fennoscandian ice sheet

  5. Abrupt glacial climate shifts controlled by ice sheet changes.

    PubMed

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

    2014-08-21

    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. PMID:25119027

  6. Plio-Pleistocene stratigraphy and relative sea level estimates: an emerging global perspective

    NASA Astrophysics Data System (ADS)

    Hearty, Paul; O'Leary, Michael; Rovere, Alessio; Raymo, Maureen; Sandstrom, Michael

    2015-04-01

    The historical rise of atmospheric CO2 to over 400 ppmv amplifies the need to better understand natural systems during past warmer interglacials. This change over the past 150 years approximates the CO2 range of full glacial-interglacial cycles. Resulting future global impacts are likely, and accurate geological field data would help us better understand the past behavior of sea level (SL) and ice sheets. The middle Pliocene warm period (MPWP) offers an approximate analogue for a 400-ppmv world. Before PLIOMAX (www.pliomax.org), only a handful of estimates of relative sea levels (RSL) along with considerable uncertainties were available for the MPWP. Precise elevations of Plio-Pleistocene RSL indicators were measured with decimeter accuracy using an OmniStar dGPS at sites in Australia, South Africa, Argentina, and other seemingly stable locations. High-resolution SL indicators include wave abrasion surfaces, sub- and intertidal sedimentary structures, and in situ marine invertebrates such as shallow water oysters and barnacles. In addition, thousands of km of terraced coastline was surveyed with dGPS between study sites. The coastal geomorphic expression of Pliocene SL is profound. From ~5 to 3 Ma, high frequency orbitally-paced, low amplitude SL oscillations acted as a shoreline "buzz saw" on hard bedrock, forming extensive high terraces. In high sediment environments such as that of the southeast US Atlantic Coastal Plain, relatively stable Pliocene ocean levels trapped huge volumes of fluvial sediments in the coastal zone, resulting in broad sandy terraces and extensive dune fields. However, glacio-isostatic adjustment (GIA), dynamic topography (DT), and other post-depositional processes have warped these marine terraces by tens of meters since the Pliocene (Raymo et al. 2011, Rovere et al 2014). The PLIOMAX team has documented precise RSLs from numerous global sites that clearly indicate that global ice volume was significantly reduced during intervals of the Pliocene. Modeling of tectonic, GIA, and DT effects, combined with a renewed Sr dating effort will greatly clarify the SL history evident from the geology of these sites. Raymo, M.E., Mitrovica, J.X., O'Leary, M.J., DeConto, R. M., and Hearty, P.J., 2011. Departures from eustasy in Pliocene sea-level records. Nature Geoscience, doi: 10.1038/NGEO1118. Rovere, A., Raymo, M.E., Mitrovica, J.X., Hearty, P.J., O'Leary, M.J., Inglis, J.D., 2013. The Mid-Pliocene sea-level conundrum: Glacial isostasy, eustasy and dynamic topography. Earth and Planetary Science Letters 387 (2014) 27-33, doi.org/10.1016/j.epsl.2013.10.030.

  7. 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.

  8. Conditional Instability of the Glacial Deep Ocean

    NASA Astrophysics Data System (ADS)

    Adkins, J. F.; Pasquero, C.

    2005-12-01

    Deep-sea sediment pore fluid results indicate that the Last Glacial Maximum (LGM) deep ocean was at or near the freezing point and very salty. In contrast to the modern, these salty waters were formed in the Southern Ocean and they show how salt, not heat, dominated abyssal density gradients at the LGM. To the degree that these data are representative of the glacial period as a whole, the salty waters allow for heat storage in the abyss. Starting from a stably stratified water column, continuous heat flux to the deep (either from geothermal or advective sources) will initially remain statically stable, but will eventually trigger instability and convective mixing. The accumulated heat is then rapidly released in the upper part of the ocean and eventually into the atmosphere. In this scenario, climate variability is associated with phases of heat accumulation at depth followed by periods of rapid heat release from the ocean into the atmosphere. With the aid of different simplified interhemispheric models, conditional instability in the deep ocean is investigated and time dependent solutions are studied. Deep convection is found to occur periodically in one hemisphere, releasing large quantities of heat into the overlying atmosphere, followed by times where the whole ocean heat content increases. In the opposite hemisphere, a much smaller air-sea heat flux oscillation is found, in phase with the global ocean heat content variability. These oscillations have several features in common with the "bi-polar seesaw" observation and might help explain climate variability during the last glacial period.

  9. 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.

  10. Late Pleistocene Environments of the Central Ukraine

    Microsoft Academic Search

    Denis-Didier Rousseau; Natalia Gerasimenko; Zhanna Matviischina; George Kukla

    2001-01-01

    The Vyazivok loess sequence from the Dnieper Plain, Ukraine, documents regional environmental changes during the late Pleistocene and Holocene. Pedological and palynological analyses and low-field magnetic susceptibility document changes from dense temperate forest during the last interglacial maximum to open, harsh, loess–steppe during the latest Pleistocene. The Vyazivok section overlies hillwash derived from a lower Pleistocene terrace and consists of

  11. ORIGINAL ARTICLE Pleistocene genetic legacy suggests incipient

    E-print Network

    Bernatchez, Louis

    ORIGINAL ARTICLE Pleistocene genetic legacy suggests incipient species of Sebastes mentella the Pleistocene glaciations followed by secondary contact. Although hybridization was observed between groups; Knowlton, 1993). The Pleistocene period is known as a period of intense speciation for a number of biota

  12. Transient nature of late Pleistocene climate variability

    E-print Network

    LETTERS Transient nature of late Pleistocene climate variability Thomas J. Crowley1 & William T. Hyde2 Climate in the early Pleistocene1 varied with a period of 41 kyr and was related to variations. There is an increase in variability after the Pliocene/Pleistocene boundary (,1.8 Myr ago), with clear evidence

  13. The consequences of pleistocene climate change on lowland neotropical vegetation

    SciTech Connect

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

    1994-06-01

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

  14. 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.

  15. 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

  16. Co-operation between Gda?sk and Vilnius Universities in Pleistocene geochronology investigations

    NASA Astrophysics Data System (ADS)

    Gaigalas, Algirdas; Fedorowicz, Stanis?aw

    2009-10-01

    The thermoluminescence (TL) dating of aquatic sand'y sediments, carried out as a co-operation between Gda?sk and Vilnius Universities, provided a more accurate chronology of the Middle-Upper Pleistocene in Lithuania. Based on TL dating, Middle and Upper Pleistocene fine-grained sands of aquatic origin have been attributed to the But?nai (Holsteinian) Interglacial (Tartokai outcrop), Snaigup?l? (Drenthe-Wartha) Interglacial (Tartokai and Valakampiai (Valakupiai) outcrops), Merkin? (Eemian) Interglacial (Tartokai and Netiesos outcrops) and Nemunas (Vistulian) Glacial (Tartokai, Netiesos and Rokai outcrops). The dating of samples from the outcrops studied show the age of the But?nai Interglacial to be 430.2 to 280.3 ka years BP, of the Snaigup?l? Interglacial 239.4 to 179.3 ka years BP and the Merkin? Interglacial 135.9 to 103.2 ka years BP. The Early Nemunas and the Middle Nemunas non-glacial sediments accumulated between 67.2-30.6 ka years BP. Tills in the upper part of the Tartokai and Rokai outcrops are younger than 30,000 BP and belong to the Late Nemunas glacial maximum in Lithuania. Different dosimetric (TL, OSL) ages of granular fractions of the same sample indicate different parametres predetermined by the distribution of grain size fractions during aquatic sedimentation of quartz sand. The granulometry of sand or the grain size distribution of quartz particles in samples reflect the state of the hydrodynamic sedimentation space.

  17. Dynamics of Pleistocene population extinctions in Beringian brown bears.

    PubMed

    Barnes, I; Matheus, P; Shapiro, B; Jensen, D; Cooper, A

    2002-03-22

    The climatic and environmental changes associated with the last glaciation (90,000 to 10,000 years before the present; 90 to 10 ka B.P.) are an important example of the effects of global climate change on biological diversity. These effects were particularly marked in Beringia (northeastern Siberia, northwestern North America, and the exposed Bering Strait) during the late Pleistocene. To investigate the evolutionary impact of these events, we studied genetic change in the brown bear, Ursus arctos, in eastern Beringia over the past 60,000 years using DNA preserved in permafrost remains. A marked degree of genetic structure is observed in populations throughout this period despite local extinctions, reinvasions, and potential interspecies competition with the short-faced bear, Arctodus simus. The major phylogeographic changes occurred 35 to 21 ka B.P., before the glacial maximum, and little change is observed after this time. Late Pleistocene histories of mammalian taxa may be more complex than those that might be inferred from the fossil record or contemporary DNA sequences alone. PMID:11910112

  18. 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.

  19. Late Pleistocene deglaciation in the upper Gállego Valley, central Pyrenees

    NASA Astrophysics Data System (ADS)

    Palacios, David; de Andrés, Nuria; López-Moreno, Juan I.; García-Ruiz, José M.

    2015-05-01

    Deglaciation processes in the upper Gállego Valley, central-southern Pyrenees, were studied using geomorphological mapping and 36Cl cosmogenic dating of moraine and rock glacier boulders, as well as polished bedrock. Although the precise position of the Gállego Glacier during the global last glacial maximum is not known, there is evidence that ice tongues retreated to the headwaters, which caused subdivision of the main glacier into a number of individual glaciers prior to 17 ka. A range of ages (16 to 11 ka) was found among three tributary valleys within the general trend of deglaciation. The retreat rate to cirque was estimated to be relatively rapid (approximately 5 km per ka). The mapped glacial sedimentology and geomorphology appears to support the occurrence of multiple minor advances and retreats, or periods of stasis during the late deglaciation. Geomorphological and geological differences among the tributary valleys, and error estimates associated with the results obtained, prevented unambiguous correlations of the advances with the late Pleistocene cold periods. During the latter advances, small glaciers and rock glaciers developed close to the cirque headwalls, and co-occurred under the same climatic conditions. No evidence for Holocene re-advance was found for any of the three tributary valleys.

  20. 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

  1. Glacial Legacies of New York State

    NSDL National Science Digital Library

    Tom McGuire

    This presentation of digital images illustrates the origins of the glacial record in New York. It is designed for classroom use, and contains narrative for each slide, images of glacial features in New York, classic examples of glacial features from around the country, and diagrams of glacial processes.

  2. 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

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

    PubMed Central

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

    2013-01-01

    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

  4. 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

  5. Early Pleistocene sea level and millennial-scale climate fluctuations: a view from the tropical Pacific

    NASA Astrophysics Data System (ADS)

    Alix Jakob, Kim; Friedrich, Oliver; Pross, Jörg

    2015-04-01

    This project aims at deciphering the rate of sea level variability and its effect on millennial-scale climate fluctuations during the final phase of the intensification of northern hemisphere glaciation (NHG). Millennial-scale climate fluctuations appear to have changed significantly at glacial-interglacial time scales during the late Pliocene and Pleistocene. Thereby, millennial-scale climate fluctuations under a warmer climate during late Pliocene and early Pleistocene show markedly lower ampitudes compared to the fluctuations of the late Pleistocene. Numerous Pleistocene proxy records (e.g. McManus et al., 1999) suggest that this difference can be explained by an ice-volume/sea-level threshold that amplifies millennial-scale climate fluctuations and was not reached prior to the Mid-Pleistocene Transition (MPT). However, new records question the existence of this threshold (Bolton et al., 2010) and indicate that either the amplification of millennial-scale climate fluctuations before the MPT required a higher ice-volume threshold than in the late Pleistocene, that ice-volume had no significant effect on the amplitude of climate fluctuations, and/or the available sea level estimates for the early Pleistocene are inaccurate. For identifying the mechanisms underlying the dynamics of early Pleistocene ice sheets, material from the tropical Pacific Ocean (ODP Site 849) is studied over a time interval from 2.6 to 2.4 Ma (marine isotope stages 104 to 96). In summary, the main deliverables are (1) the establishment of a precise ?18O chemostratigraphy using the benthic foraminifera Cibicidoides wuellerstorfi by tuning the ?18O dataset to the LR04 benthic isotope stack (Lisiecki & Raymo, 2005), and (2) providing high-resolution (˜700 years) Mg/Ca and ?18O datasets using the benthic foraminifera Oridorsalis umbonatus and the planktonic foraminifera Globigerinoides ruber. This combined geochemical approach will be used to address the following research questions: (1) Quantification of sea level change from 2.6 to 2.4 Ma; (2) Critically assess the hypothesis of an ice-volume threshold for millennial-scale climate amplification during the early Pleistocene (and if it exists, what its value was); (3) Detailed comparison with late Pleistocene glacials; (4) Model-data comparison to assess the fidelity of model-based sea level estimates; and (5) reconstruction of sea surface temperature fluctuations of the tropical Pacific. References Bolton, C.T., Wilson, P.A., Bailey, I., Friedrich, O., Beer, C.J., Becker, J., Baranwal, S., Schiebel, R. (2010): Millennial-scale climate variability in the subpolar North Atlantic Ocean during the late Pliocene. Paleoceanography 25, doi:10.1029/2010PA001951. Lisiecki, L.E. & Raymo, M.E. (2005): A Pliocene-Pleistocene stack of 57 globally distributed benthic ?18O records. Paleoceanography 20, doi:10.1029/2004PA 001071. McManus, J., Oppo, D.W., Cullen, J.L. (1999): A 0.5-Million-Year Record of Millenial-Scale Climate Variability in the North Atlantic. Science 283, 971-975.

  6. Pleistocene Aridification Cycles Shaped the Contemporary Genetic Architecture of Southern African Baboons

    PubMed Central

    Sithaldeen, Riashna; Ackermann, Rebecca Rogers; Bishop, Jacqueline M.

    2015-01-01

    Plio-Pleistocene environmental change influenced the evolutionary history of many animal lineages in Africa, highlighting key roles for both climate and tectonics in the evolution of Africa’s faunal diversity. Here, we explore diversification in the southern African chacma baboon Papio ursinus sensu lato and reveal a dominant role for increasingly arid landscapes during past glacial cycles in shaping contemporary genetic structure. Recent work on baboons (Papio spp.) supports complex lineage structuring with a dominant pulse of diversification occurring 1-2Ma, and yet the link to palaeoenvironmental change remains largely untested. Phylogeographic reconstruction based on mitochondrial DNA sequence data supports a scenario where chacma baboon populations were likely restricted to refugia during periods of regional cooling and drying through the Late Pleistocene. The two lineages of chacma baboon, ursinus and griseipes, are strongly geographically structured, and demographic reconstruction together with spatial analysis of genetic variation point to possible climate-driven isolating events where baboons may have retreated to more optimum conditions during cooler, drier periods. Our analysis highlights a period of continuous population growth beginning in the Middle to Late Pleistocene in both the ursinus and the PG2 griseipes lineages. All three clades identified in the study then enter a state of declining population size (Nef) through to the Holocene; this is particularly marked in the last 20,000 years, most likely coincident with the Last Glacial Maximum. The pattern recovered here conforms to expectations based on the dynamic regional climate trends in southern Africa through the Pleistocene and provides further support for complex patterns of diversification in the region’s biodiversity. PMID:25970269

  7. 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.

  8. Revisiting the late Pleistocene mammal extinction record at Tight Entrance Cave, southwestern Australia

    NASA Astrophysics Data System (ADS)

    Faith, J. Tyler; O'Connell, James F.

    2011-11-01

    Tight Entrance Cave (TEC) in southwestern Australia provides a Pleistocene sequence documenting the extinction of 14 large mammal species. This record has been interpreted as indicating that extinctions did not occur during or before the penultimate glacial maximum (PGM) and that humans played a primary role in the extinctions. However, it remains possible that the majority of extinct megafauna persisted no later than the PGM. The TEC extinctions correspond with vegetation change, a cooling/drying trend, increased biomass burning, and increasingly unstable small mammal communities. The initiation of these trends predates human arrival on the continent and implies environmentally mediated extinctions.

  9. 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

  10. Shorelines of Glacial Lake Hitchcock

    NSDL National Science Digital Library

    Bob Newton

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

  11. 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.

  12. Predicting Pleistocene climate from vegetation

    Microsoft Academic Search

    C. Loehle

    2006-01-01

    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

  13. Phylogeographic patterns of mtDNA variation revealed multiple glacial refugia for the frog species Feirana taihangnica endemic to the Qinling Mountains.

    PubMed

    Wang, Bin; Jiang, Jianping; Xie, Feng; Li, Cheng

    2013-03-01

    Diversification patterns and demography of montane species are affected by Pleistocene climate fluctuations. Empirical cases from the Qinling Mountains (QM) region, which is a major biogeographic divider of East Asia, are few. We used DNA sequence data of the complete mitochondrial ND2 gene to detect effects of the Pleistocene glaciations on phylogeographic profiles of a frog species, Feirana taihangnica, which is endemic to the QM. Four distinct lineages consisting of seven sublineages were revealed. The strongest signal of biogeographical structure (F(ct) = 0.971, P < 0.01) was found when populations were grouped according to these seven sublineages. One narrow secondary contact zone was detected in the middle QM between the lineage from middle QM and the lineage from eastern QM. Coalescent simulations indicated that this species colonized the QM region by a stepping-stone model. Divergences among lineages had likely been influenced by the uplift of the Tibetan Plateau during the late Miocene-to-late Pleistocene, as well as by the Pleistocene climatic cycles. Coalescent simulations also suggested that F. taihangnica populations have persisted through the Pleistocene glacial periods in multiple refugia across the QM region. Demographic analyses indicated that all lineages, except the lineage in the Funiu Mountains, have been experienced postglacial expansion of population size and distribution range. In conclusion, Pleistocene climate fluctuations and tectonic changes during the late Miocene-late Pleistocene have profoundly influenced the phylogeography and historical demography of F. taihangnica. PMID:23381112

  14. 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.

  15. Speciation durations and Pleistocene effects on vertebrate phylogeography

    E-print Network

    Avise, John

    Speciation durations and Pleistocene effects on vertebrate phylogeography John C. Avise* , De to evaluate Pleistocene phylogeographic e¡ects and to estimate temporal spans of the speciation process and birds, Pleistocene conditions played an important role in initiating phylogeographic di

  16. 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.

  17. Millennial climate oscillation spied

    SciTech Connect

    Kerr, R.A.

    1996-01-12

    Although evaluating the effects of greenhouse gases on climatic warming has been a major growth industry, greenhouse gases are not the only effect on the global climate. Analysing climate records stored in sediments and glacial ice, researchers have detected a slow climate oscillation that has alternately warmed and cooled the world very couple of thousand years for the past hundred thousand years, perhaps millions of years. This article gives an overview of the evidence.

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

    NASA Astrophysics Data System (ADS)

    Visser, Katherine; Thunell, Robert; Goñi, Miguel 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.

  19. 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.

  20. 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

  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 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

  3. 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

  4. SEM microfabric analysis of glacial varves, Geneseo, N. Y

    SciTech Connect

    Pietraszek, S.R. (Potsdam Coll., State Univ. of New York, Potsdam, NY (United States). Geology Dept.)

    1993-03-01

    A detailed study of the microfabric of Pleistocene varved silty-clay from Geneseo Valley (Geneseo, N.Y.) indicates rapid deposition of sediment in a flocculated state into a glacial lake. Ten varve couplets of a 10 cm thick sample were studied using the Scanning Electron Microscope to determine their microfabric. Each varve ranges from 0.5 cm to 2.0 cm and represents an annual ( ) deposit. Varves consists of a lower light colored, coarse zone of silt and clay, and an upper darker colored, organic fine clayey zone. Graded bedding is observed in each couplet, and random clay particle orientation is dominant throughout a varve, with the exception of the top 0.5 mm of the fine layer. The upper and lower contacts are sharp. Fabric features are instrumental in reconstructing a depositional environment. Microfabric results of the glacial unit indicate that an initial heavy concentration of clay and silt was introduced into the basin in a single pulse during spring runoff. The majority of silt settled together with clay in a flocculated or aggregated state, forming the lower coarse zone of random orientation. As the silt concentration diminished, the clay continued to flocculate and settled as a fine clay aggregate. It is proposed that the settling took place during the spring and summer months. Finally, during the winter months, the sediment surface of the varve was disturbed by nemotode burrows, which reoriented the clay flakes into a zone of preferred fabric. Microfabric analysis of these glacial varves, thus suggests that sediment was rapidly deposited in a flocculated state.

  5. Plio-pleistocene African climate

    Microsoft Academic Search

    P. B. deMenocal

    1995-01-01

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps

  6. Pleistocene vertebrates of the Yukon Territory

    Microsoft Academic Search

    C. R. Harington

    2011-01-01

    Unglaciated parts of the Yukon constitute one of the most important areas in North America for yielding Pleistocene vertebrate fossils. Nearly 30 vertebrate faunal localities are reviewed spanning a period of about 1.6 Ma (million years ago) to the close of the Pleistocene some 10 000 BP (radiocarbon years before present, taken as 1950). The vertebrate fossils represent at least

  7. Perchlorate in Pleistocene and Holocene Groundwater in

    E-print Network

    Perchlorate in Pleistocene and Holocene Groundwater in North-Central New Mexico L . N I E L P L U M with evapotranspiration (ET) factors of about 7-40. Most of the ET values for Pleistocene recharge were nearly twice

  8. 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.

  9. Mapping Glacial Erratics with GPS and GIS

    NSDL National Science Digital Library

    Katherine McCarville

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

  10. Late to middle Pleistocene climate variability recorded in stalagmites from Sofular Cave, Northern Turkey

    NASA Astrophysics Data System (ADS)

    Fleitmann, D.; Cheng, H.; Edwards, R. L.; Badertscher, S.; Tüysüz, O.

    2012-04-01

    The modern climate in Turkey and the eastern Mediterranean is strongly affected by two major climate systems; the North Atlantic/Siberian pressure system in winter and the Indian monsoon in summer. Turkey is thus ideally situated to study how and to what extent both systems were dynamically linked during the Holocene and Pleistocene. Our current knowledge of continental climate variability in Turkey relies almost entirely on lake records with only a few extending back to the Last Glacial Maximum and beyond. Another source of information on Pleistocene and Holocene climate variability is speleothems, which can be found in caves throughout Turkey. Here we present composite stalagmite oxygen and carbon isotope records from Sofular Cave located at the Black Sea coast in north-western Turkey, which cover the last 670.000 discontinuously. Uranium-series dates with unprecedented small age uncertainties of only 0.25-2% and highly resolved isotope profiles allow us to (1) identify the climatic impacts of Dansgaard-Oeschger and Heinrich events, (2) compare climatic and environmental conditions during different interglacial and glacial periods (Marine Isotope Stages 1-7, 9, 13 and 15) and (3) reveal changes in the hydrological state of the Black Sea in unprecedented detail.

  11. 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

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

    PubMed Central

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

    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 some species to boreal forest. This, in turn, facilitated the development of transcontinental range expansions during interglacials. Subsequent glacial advances repeatedly fragmented the ranges of these species into eastern and western populations; western isolates speciated to form the multispecies groups observed among various North American birds. We used mtDNA restriction site data to reconstruct the phylogeny of the black-throated green warbler complex-the group that Mengel considered the best fit to his model. Contrary to Mengel's model, the phylogeny indicates that not all western endemics were derived from an eastern ancestor. Instead, our results imply a mix, wherein some western endemics were budded off an eastern source, as Mengel posits, while others probably resulted from intermontane isolations in the west. PMID:11607307

  13. Cyclicity in Pleistocene upper-slope cool-water carbonates: Unravelling sedimentary dynamics in deep-water sediments, Great Australian Bight, Odp Leg 182, Site 1131A

    Microsoft Academic Search

    Ángel Puga-Bernabéu; Christian Betzler

    2008-01-01

    Ocean Drilling Program Site 1131, located in the central Great Australian Bight, recovered an expanded series of Pleistocene cool-water carbonates. Three distinct facies are arranged in repeating sedimentary cycles. Omission intervals form the base of the cycles and are overlain by laminated deposits. The upper part of the cycles consists of bioturbated sediments. Facies cyclicity parallels glacial–interglacial sea-level changes. Firmground\\/hardground

  14. Cosmogenic Be10 ages of Angel Lake and Lamoille moraines and late Pleistocene slip rate of the rangefront normal fault, Ruby Mountains, Basin and Range, Nevada

    Microsoft Academic Search

    R. W. Briggs; S. G. Wesnousky; F. J. Ryerson; R. C. Finkel; A. Meriaux

    2004-01-01

    We use Be-10 cosmogenic radionuclide (CRN) exposure dating to quantify the timing of late Pleistocene glacial advances and to estimate the rangefront normal fault slip rate along the Ruby Mountains in the Basin and Range, Nevada. Ten Be-10 CRN exposure ages from the Angel Lake terminal moraine in Hennen Canyon limit deposition to between 15.4-23.1 ka (average = 18.2 ka;

  15. Arsenic geochemistry and hydrostratigraphy in midwestern U.S. glacial deposits.

    PubMed

    Root, Tara L; Gotkowitz, Madeline B; Bahr, Jean M; Attig, John 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. PMID:19840125

  16. Did the West Antarctic Ice Sheet collapse during late Pleistocene interglacials: A reassessment

    NASA Astrophysics Data System (ADS)

    Scherer, R. P.

    2009-04-01

    Ever since John Mercer's provocative paper, "West Antarctic ice sheet and CO2 Greenhouse effect: a threat of disaster" (Nature 271:321-325; 1978), researchers have grappled with questions regarding whether, when, how frequently, and, especially, how quickly the West Antarctic Ice Sheet has disintegrated and reformed during the Pliocene and Pleistocene (and whether and when it may again in the future). Oxygen isotope records, being global averages, are insufficient to answer these questions, because (1) the WAIS signal is relatively small, and (2) antiphased behavior between the poles of the precession cycle will tend to cancel part of the signal, as outlined by Raymo et. al. (Science 313, 492-495, 2006). Previously, Antarctica lacked proximal, well-dated Pleistocene and Pliocene marine geologic records, so eustatic, mostly tropical sea-level records were used to infer past WAIS collapses. The first direct evidence of past Pleistocene WAIS collapse came from diatoms recovered from beneath the WAIS on the Whillans Ice Stream (UpB). Scherer (GPC, 4, 395-412, 1991) and Scherer et al. (Science, 281, 82-85, 1998) interpreted these results as most likely reflecting WAIS retreat during MIS-11, but could not rule out other interglacials, including MIS-5e, the penultimate interglacial discussed by Mercer. More recently, proximal evidence of WAIS retreat (or collapse) during early Pleistocene MIS-31 came from drilling at Cape Roberts (CRP-1) and the ANDRILL McMurdo Ice Shelf project (AND-1B) (Scherer et al., GRL, 35, doi:10.1029/2007GL032254, 2008). These diatom results provide evidence of ice sheet retreat events, but no constraint on the rate of ice sheet "collapse," which is critical to assessing the threat of future collapse. These results provided impetus and constraints for new coupled climate/ice sheet models, which are yielding significant insights (Pollard and DeConto, Nature, in press). The ANDRILL-MIS site contains no clear evidence of WAIS collapse events subsequent to MIS-31, but there is poor age control in the recovered diamictons. Furthermore, evidence of significant interglacials may have been lost in glacial erosion. A reassessment of diatom data from UpB indicates that the Pleistocene diatoms identified from beneath the WAIS are compatible with MIS-31 deposition as well as late Pleistocene marine deposition. This, once again, leaves the question of the configuration of the WAIS during MIS-11, MIS-5e and other late Pleistocene interglacials open for discussion.

  17. Similar glacial and Holocene Southern Ocean hydrography

    Microsoft Academic Search

    Katsumi Matsumoto; Jean Lynch-Stieglitz; Robert F. Anderson

    2001-01-01

    We present new Holocene and glacial delta18O data measured on planktonic foraminifera Neogloboquadrina pachyderma and benthic foraminifera Cibicidoides species from the Atlantic and Pacific sectors of the Southern Ocean in order to better understand its glacial hydrography. Combined with previously published data, the latitudinal delta18O distributions of these foraminifera show no appreciable difference during the Holocene and the Last Glacial

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

    PubMed

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

    2014-01-01

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

  19. Eccentricity cycles shown by early Pleistocene planktonic foraminifers of the Omma Formation, Sea of Japan

    NASA Astrophysics Data System (ADS)

    Kitamura, Akihisa; Kimoto, Katsunori

    2007-02-01

    There is a continuous record of planktonic foraminifers for oxygen isotope stages 50 to 26 (ca. 1.5-1.0 Ma) in the early Pleistocene Omma Formation near Kanazawa City, Central Japan, on the Sea of Japan coast. The warm-water species Globigerinoides ruber entered the Sea of Japan with the Tsushima Current during all interglacial periods and went locally extinct in the succeeding glacial periods. This implies that the marine climate of the Sea of Japan varied predominantly with the 41,000-year period of Earth's orbital obliquity. However, the relative abundances of G. ruber in marine isotope stages 47, 43 and 31 are significantly higher than those in other interglacial stages. These stages correspond to periods when eccentricity-modulated precession extremes were aligned with obliquity maxima. The Tsushima Current is a branch of the warm Kuroshio Current which is the strong northwestern component of the subtropical North Pacific Ocean gyre. Our data imply that the early Pleistocene climate in the northwestern Pacific was influenced not only by obliquity cycles but also by eccentricity cycles. This study also supports the climate model regarding eccentricity's role in the origin of low-frequency climate changes before the late Pleistocene ice ages.

  20. 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

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

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

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

  2. 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.

  3. 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.

  4. Composite sedimentary record of falling stages of Pleistocene glacio-eustatic cycles in a shelf setting (Crotone basin, south Italy)

    NASA Astrophysics Data System (ADS)

    Massari, F.; Sgavetti, M.; Rio, D.; D'Alessandro, A.; Prosser, G.

    1999-08-01

    A thick Pleistocene shelf and nearshore cyclical succession was deposited in the S. Mauro sub-basin of the Crotone basin (southern Italy). The regressive units of the cycles are mostly represented by coastal siliciclastic and bioclastic prograding wedges showing a clinoform geometry. These are separated by blanket-like deposits of high lateral persistence recording major transgressive episodes. The aim of this paper is (1) to describe facies patterns and depositional setting of two prograding wedges, particularly focussing on their polycyclic internal architecture, (2) to analyze these units within a sequence-stratigraphic framework, and (3) to speculate on the possible origin of the small-scale cyclicity. The two wedges analyzed in this paper consist of a number of shingles. Individual shingles consist of two physically connected units: (1) a relatively thin package of sigmoid clinoforms, grading into (2) a volumetrically dominant package of oblique-tangential clinoforms with toplap terminations. The shingles are bounded by seaward-dipping surfaces with sigmoid clinoform geometry, which are ravinement surfaces updip, passing into conformable flooding surfaces downdip. The wedges are thus organized into high-frequency, small-scale sequences, each comprising transgressive, highstand and falling-stage systems tracts. As a whole, individual prograding wedges are interpreted as forced-regressive units, as the shoreline was subject to an overall shift basinwards and downwards along a low-angle trajectory, in spite of the repeated minor relative sea-level rises. Tectonic subsidence, and particularly the syndepositional growth of gentle synclines, are thought to have been the key factors allowing the preservation of these forced-regressive units. Progradation of the wedges took place in a high-energy wave climate characterized by high frequency of storms and very efficient alongshore redistribution of sediments. Recurrent, storm-driven, offshore currents led to intense reworking of sediments on the topset platform and gravity spreading on the foreset slope of the prograding wedges. Well-oxygenated conditions over the shelf due to intensified storm activity during glacial periods may have enhanced the rate of production of skeletal, foramol-type carbonates. It can reasonably be assumed that progradation took place from a line source and that the sand bodies are to be regarded as coastal prograding bodies. In spite of active syndepositional tectonics, the cycles can be correlated to Pleistocene high-amplitude sea-level oscillations. The older of the two wedges can be correlated, through bio-magnetostratigraphy, to the major climatic transition which occurred from the marine oxygen-isotope stage 25 to 24-22 ( Rio et al., 1996). The younger probably developed during the sea-level fall that ended with substage 18.2, as suggested by sequence- and bio-stratigraphic data. The prograding wedges are thus interpreted to record long-lived sea-level falls of fourth-order cycles. Due to the particular depositional setting, we are inclined to exclude authigenic mechanisms in the origin of small-scale cyclicity. Although the concomitance and interaction of different controlling factors may be taken into account, it is tempting to ascribe this cyclicity to minor eustatic changes punctuating long-lived, erratic falling stages, possibly accompanied by climate-driven fluctuations of sediment supply. Shelf-perched and shelf-edge prograding units consisting of foramol-type carbonates are apparently a common falling-stage to lowstand depositional feature in the Mediterranean area during the Late Pliocene and Pleistocene.

  5. Unstable Atlantic Meridional Overturning Circulation during Glacial Intervals and Millennial Variability: The Role of Mean Sea Ice Extent

    NASA Astrophysics Data System (ADS)

    Fedorov, A. V.; Sevellec, F.

    2014-12-01

    A striking feature of paleoclimate records is the strong irregular variability with an approximately 1500 yr period, known as the Dansgaard-Oeschger (D-O) events, which punctuate the last glacial interval but disappear during the Holocene. Many theories, modeling and data suggest that these events, seen as abrupt warming episodes in Greenland ice cores and sea surface temperature records in the North Atlantic, are linked to reorganizations of the Atlantic Meridional Overturning Circulation (AMOC). In this study, using a new low-order ocean model, we are able to reproduce a realistic power spectrum of this millennial variability, which emerges in the model as a result of unstable AMOC dynamics rather than due to external freshwater forcing. Within this model we explore differences in the AMOC stability between glacial and interglacial intervals of the 100 kyr glacial cycle of the Late Pleistocene. Previous modeling studies show that the edge of sea ice in the North Atlantic shifts southward during glacial intervals, moving the region of the North Atlantic Deep Water formation and the entire AMOC also southward. Here we demonstrate that, by altering the precipitation structure that the AMOC feels, such an expansion of sea ice cover makes the system unstable, which explains chaotic millennial variability during the glacials and the persistence of stable ocean conditions during the interglacials.

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

    PubMed

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

    2004-02-29

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

  7. 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

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

    PubMed

    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

    2010-08-24

    Our new data address the paradox of Late Ordovician glaciation under supposedly high pCO(2) (8 to 22x 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 degrees -70 degrees S to approximately 40 degrees 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 pCO(2) from a modeled Sandbian level of approximately 8x PAL to approximately 5x 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

  9. Using glacial morphology to constrain the impact of the Chile active spreading ridge subduction in Central Patagonia

    NASA Astrophysics Data System (ADS)

    Scalabrino, B.; Ritz, J. F.; Lagabrielle, Y.

    2009-04-01

    The Central Patagonian Cordillera is a unique laboratory to study interaction between oceanic and continental lithospheres during the subduction of an active spreading ridge beneath a continent. The subduction of the South Chile spreading Ridge, which separates the Nazca plate from the Antarctic plate, started ca. 15-14 Ma at the southern tip of Patagonia (55°S latitude). The northwards migration of the Chile Triple Junction induces the subduction of several segments especially around 46°S latitude. There, three segments subducted at ca. 6, 3 and 0.3 Ma, leading to the formation of a large asthenospheric slab-window beneath Central Patagonia. Contemporaneously, the Central Patagonia reliefs are undergoing major glacial events since at least 7 Ma. These events are evidenced to the east of the Central Patagonian morphotectonic front within perched relict surfaces. Inset in these perched glacial surfaces are found mid-Pleistocene glacial valleys, as the Lake General Carrera-Buenos Aires amphitheatre (LGCBA), which formed between 1.1 Ma and 16 ka. We used the relationships between the glacial valleys and the volcanism associated with the asthenospheric slab-window to better constraints the structural evolution of the Patagonian Cordillera related to the subduction of the Chili active spreading Ridge. The present work focused within two well-preserved perched flat surfaces named Meseta del Lago Buenos Aires and Meseta del Cerro Galera: (i) The meseta del Lago Buenos Aires defines a plateau made of interbedded units of tills and lavas dated between 12 Ma and 3 Ma. The top surface of the meseta, ˜2000 meters high is dated at 3 Ma, and is shaped by four NE-SW trending glacial lobes characterized with kettles, lineations and moraines. The glacial valleys are beheaded westwards and define perched valleys 200 to 400 meters higher than the western Cordillera. This suggests recent vertical movement along N160 extensive/transtensive corridor located between the morphotectonic front and the western side of the meseta del Lago Buenos Aires. (ii) Further north, the meseta del Cerro Galera exhibits a sequence of more than 200 m thick tills and fluvio-glacial deposits which top of is at 1500 m. This perched sequence shows accumulation of polygenic material, which sources are situated 100 to 150 km westwards. The glacial sequence of Cerro Galera is situated more than 1000 meters above the tectonic-controlled depression of Coihaique where younger (Pleistocene) glacial deposits have been identified. As observed along the western margin of the Meseta del Lago Buenos Aires, the till is presently disconnected from any former glacial morphology to the west. This feature can be attribute to a major fault zone west to the meseta del Cerro Galera. In summary, we demonstrate that the location of pre-Quaternary glacial markers found as preserved on perched relict surfaces at around 1500-2000 meters whereas the location of Quaternary glacial deposits are 1000 meters below within the present-day glacial valleys suggest a drastic change in the glacial drainage network of the Central Patagonia. This change can be attributed to the extensional/transtensional tectonics responsible for the formation of transverse depressions and oblique tectonic corridors, which occurred between 3 Ma and 1 Ma. Geodynamically, this recent phase has been closely related with the subduction of the South Chile Ridge. The development of a large slab window beneath the Central Patagonian Cordillera since 3 Ma allowed hot mantle to reach sub-lithospheric regions, producing a weakening of the crust triggering in turn localized collapse.

  10. Late-Pleistocene paleowinds and aeolian sand mobilization in north-central Lower Michigan

    NASA Astrophysics Data System (ADS)

    Arbogast, Alan F.; Luehmann, Michael D.; Miller, Bradley A.; Wernette, Phillipe A.; Adams, Kristin M.; Waha, Jaimen D.; O'Neil, Glenn A.; Tang, Ying; Boothroyd, Jeremy J.; Babcock, Chad R.; Hanson, Paul R.; Young, Aaron R.

    2015-03-01

    Simulation of late glacial atmospheric conditions with atmospheric general circulation models suggest a strong anticyclone over the Laurentide Ice Sheet and associated easterly winds along the glacial margin. In the upper Midwest of North America, evidence supporting this modeled air flow exists in the orientation of paleospits in northeastern Lower Michigan that formed ?13 ka in association with glacial Lake Algonquin. Conversely, parabolic dunes that developed between 15 and 10 ka in central Wisconsin, northwestern Indiana, and northwestern Ohio resulted from westerly winds, suggesting that the wind gradient was indeed tight. Study results refine our understanding of late-Pleistocene wind conditions even closer to the ice margin in the upper Midwest by focusing on the timing of aeolian sand mobilization in north-central Lower Michigan at the Rosco dune field. The area was deglaciated ?16 ka, and parabolic dunes have westerly orientations, indicating that they resulted from westerly winds. Optical ages suggest that mobilization last occurred between about 13 ka and 10 ka. The close proximity (?150 km) of this dune field to more northerly paleolacustrine landforms resulting from easterly winds suggests that anticyclonic circulation indeed extended only a very short distance south of the ice sheet, which is consistent with modeled airflow and the orientation of dunes in central Canada. This study also presents evidence suggesting that, in addition to prevailing winds, dunes likely formed because the sparsely-vegetated local outwash plain was deflated.

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

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    We report new mapping, soils, survey, and geochronologic (luminescence, U-series, and cosmogenic-nuclide) data from Pleistocene deposits in the arid setting of eastern Grand Canyon. The result is a stratigraphic framework of inset fill gravels and associated terraces that provide a record of the responses of hillslopes, tributary streams, and the Colorado River to the last ˜400 kyr of glacial-interglacial climate change. The best-preserved last 80 kyr of this record indicates a stratigraphic-chronologic disconnect between both deposition and incision along the Colorado River versus along the trunks of local tributaries. For example, the Colorado River finished aggrading and had already begun incising before the main pulse of aggradation in the trunks of local catchments during Marine Isotope Stage 3, and then tributary incision followed during the millennial-scale fluctuations of the last glacial epoch, potentially concurrent with mainstem aggradation. The mainstem record appears to broadly correlate with regional paleoclimate and upstream geomorphic records and thus may be responding to climatic-hydrologic changes in its mountain headwaters, with aggradation beginning during full-glacial times and continuing into subsequent interglacials. The contrasting lag time in responses of the dryland catchments within Grand Canyon may be largely a function of the weathering-limited nature of hillslope sediment supply.

  12. Environmental Influences on Pleistocene Hominid Dental Evolution

    ERIC Educational Resources Information Center

    Greene, David L.

    1970-01-01

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

  13. 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.

  14. Evidence for Early Pleistocene Glaciation obtained from borecores collected in East-Central Alberta, Canada

    NASA Astrophysics Data System (ADS)

    Barendregt, R. W.; Andriashek, L. D.; Jackson, L. E.

    2014-12-01

    Borecores collected from the east-central region of Alberta, Canada have recently been sub-sampled and studied for paleomagnetic remanence characteristics. A preliminary magnetostratigraphy has been established for sediments previously assumed to represent multiple continental (Laurentide) glaciations, but for which no geochronology was available for the pre-late Wisconsin units. Comprised primarily of tills and lesser thicknesses of interbedded glacio-lacustrine and outwash sediments, the record is extensive, reaching to thicknesses of 300 metres within buried valleys. Most of the sampled units are not accessible from outcrop, and their sedimentology and stratigraphy is derived from core data only. The lowermost tills are reversely magnetized in the majority of borecores sampled to date. These tills are underlain by Empress Formation sediments and/or Colorado Group shales, and overlain by normally magnetized sediments. Both tills contain substantial weathering horizons at their surface, suggesting that interglacial or nonglacial conditions persisted for some time after each period of till deposition. Whether these tills represent a single Early Pleistocene glaciation, or perhaps two, will require additional borecore measurements. This new record of Early Pleistocene glaciation(s) in east-central Alberta places the westernmost extent of earliest Laurentide ice some 300 km farther westward from its previously established limit in the Saskatoon to Regina region of the western Canadian prairies, but still well short of the all-time limit and elevation reached during the Late Wisconsin (Late Pleistocene) in the foothills of the Alberta and Montana Rocky Mountains. Key Words: East-Central Alberta glacial history, Early Pleistocene (Laurentide) glaciation, till magnetostratigraphy, Quaternary history of Western Canadian Prairies, continental glaciations of North America.

  15. Pleistocene vegetation change in central Africa recorded off the Congo River

    NASA Astrophysics Data System (ADS)

    Dupont, L. M.

    2003-04-01

    Marine sediments from the Congo Canyon accumulate material and information from one of Africa's large inland basins that is covered, at present, mainly with lowland rain forest and swamp forests. The sediments provide a record of monsoon related hydrological and vegetation change. Multiproxy studies were carried out on ODP Site 1075 located north of the undersea canyon, and GeoB Site 1008 located south of the canyon. Pollen records are compared with other terrestrial signals (iron, clay minerals, biomarkers). The differentiated responses of mangroves, grasslands and swamps, lowland rain forest, and Afromontane forest to environmental fluctuations give insight in several aspects of Pleistocene climate cycles. The record of Rhizophora (mangrove tree) pollen is consolidated by biomarker data and shows maxima during interglacial periods and during periods of rapid sea-level rise. While the latter might be the effect of increased erosion of mangrove peat, the first indicates extension of mangrove swamps during periods with increased run-off. The record of lowland forest pollen indicates extension of the rain forest as a response to increased precipitation in periods of strong monsoons of the past 150 ka which is corroborated by clay mineral fluctuations. During the humid periods, Poaceae (grasses) and Cyperaceae pollen percentages are low indicating a closed canopy in large areas of the basin. During interglacial stages of the early Pleistocene, maxima of tropical forest elements combine with maxima of grass and cyperaceous pollen indicating that the warm periods might have been drier than those of the late Pleistocene. Podocarpus pollen percent maxima register extension of the Afromontane forest during cool periods from 1.05 to 0.6 Ma. Restricted distribution of mountainous forest during the late Pleistocene glacial stages (MIS 6, 4-2) is concurrent with extension of open vegetation types indicating more arid conditions in equatorial areas.

  16. Extending the Chatham Rise (ODP Site 1123) Deep Ocean Temperature Record into the Plio-Pleistocene: Inception of Northern Hemisphere Glaciation

    NASA Astrophysics Data System (ADS)

    Weidle, I.; Elderfield, H.

    2014-12-01

    The Plio-Pleistocene was a time of global climate cooling: a transition from a state of significant and prolonged climate warmth (Mid Pliocene) to a state of bi-polar glacials (Pleistocene), marked by the onset and intensification of continental ice sheets in the Northern hemisphere (Late Pliocene) and the reorganization of glacial cycle amplitude and frequencies (Mid Pleistocene Transition). This is an interesting and important chapter of climate history for understanding the sensitivity of large ice sheets to perturbations in the climate system on glacial-interglacial and much longer timescales. Of possible priming mechanisms (incl. closure of Panama seaway, orographic uplift), the decline of atmospheric carbon dioxide is considered to have a strong connection with the late Pliocene cooling and ice sheet inception, although the causal mechanism for its decline remains relatively unknown. High-resolution, long term climate records are necessary to further constrain the timings of ice volume evolution and the associated driving factors during the Plio-Pleistocene, however such records are presently limited. ODP Site 1123 (Chatham Rise, southwest Pacific, 3290m) records the evolution of the deep western boundary current of the southwest Pacific, a primary feeder of Antarctic Bottom Water to the global deep ocean. By calculating the oxygen stable isotope composition of past seawater, a proxy calculation combining Mg/Ca-palaeothermometry and ?18O from benthic foraminifera, we present a high-resolution record of global ice volume as a measure of climate change, extending the existing 0-1.5 Ma record (Elderfield et al., 2012) at ODP 1123 to the Plio-Pleistocene (1.5-3.0 Ma). We use this measure of global ice volume evolution to assess the relative timing and magnitude of northern hemisphere glaciation and concomitant deep ocean temperature decline, which aids to infer temperatures around Antarctica during this time. Deep ocean temperature results show high frequency glacial-cycles, approaching near-freezing temperatures at peak glacials. Reference Elderfield, H., Ferretti, P., Greaves, M., Crowhurst, S., McCave, I.N., Hodell, D., Piotrowski, A.M. (2012), Science, 337, 704-709.

  17. Pleistocene vertebrates of the Yukon Territory

    Microsoft Academic Search

    C. R. Harington

    2011-01-01

    Unglaciated parts of the Yukon constitute one of the most important areas in North America for yielding Pleistocene vertebrate fossils. Nearly 30 vertebrate faunal localities are reviewed spanning a period of about 1.6 Ma (million years ago) to the close of the Pleistocene some 10 000 BP (radiocarbon years before present, taken as 1950). The vertebrate fossils represent at least 8 species

  18. 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

  19. Society for American Archaeology Was Agriculture Impossible during the Pleistocene but Mandatory during the Holocene? A

    E-print Network

    Richerson, Peter J.

    Society for American Archaeology Was Agriculture Impossible during the Pleistocene but Mandatory://www.jstor.org #12;WASAGRICULTUREIMPOSSIBLE DURING THE PLEISTOCENE BUT MANDATORYDURING THE HOLOCENE? A CLIMATE CHANGE knownfrom the Pleistocene, evenfrom the late Pleistocene whenhumanpopulations were oth- erwise

  20. Cryptic lineages and Pleistocene population expansion in a Brazilian Cerrado frog

    E-print Network

    Zamudio, Kelly R.

    Cryptic lineages and Pleistocene population expansion in a Brazilian Cerrado frog CYNTHIA P. A Tertiary events and Pleistocene climatic fluctuations. Nonetheless, phylogeo- graphical studies of taxa during the mid-Pleistocene. Thus, both Tertiary geological events and Pleistocene climatic fluctuations

  1. 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.

  2. 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.

  3. The INTIMATE event stratigraphy of the last glacial period

    NASA Astrophysics Data System (ADS)

    Olander Rasmussen, Sune; Svensson, Anders

    2015-04-01

    The North Atlantic INTIMATE (INtegration of Ice-core, MArine and TErrestrial records) group has previously recommended an Event Stratigraphy approach for the synchronisation of records of the Last Termination using the Greenland ice core records as the regional stratotypes. A key element of these protocols has been the formal definition of numbered Greenland Stadials (GS) and Greenland Interstadials (GI) within the past glacial period as the Greenland expressions of the characteristic Dansgaard-Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. Using a recent synchronization of the NGRIP, GRIP, and GISP2 ice cores that allows the parallel analysis of all three records on a common time scale, we here present an extension of the GS/GI stratigraphic template to the entire glacial period. In addition to the well-known sequence of Dansgaard-Oeschger events that were first defined and numbered in the ice core records more than two decades ago, a number of short-lived climatic oscillations have been identified in the three synchronized records. Some of these events have been observed in other studies, but we here propose a consistent scheme for discriminating and naming all the significant climatic events of the last glacial period that are represented in the Greenland ice cores. In addition to presenting the updated event stratigraphy, we make a series of recommendations on how to refer to these periods in a way that promotes unambiguous comparison and correlation between different proxy records, providing a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations. The work presented is a part of a newly published paper in an INTIMATE special issue of Quaternary Science Reviews: Rasmussen et al., 'A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy', Quaternary Science Reviews, vol. 106, p. 14-24, 2014.

  4. Optical properties of deep glacial ice at the South Pole

    NASA Astrophysics Data System (ADS)

    Ackermann, M.; Ahrens, J.; Bai, X.; Bartelt, M.; Barwick, S. W.; Bay, R. C.; Becka, T.; Becker, J. K.; Becker, K.-H.; Berghaus, P.; Bernardini, E.; Bertrand, D.; Boersma, D. J.; Böser, S.; Botner, O.; Bouchta, A.; Bouhali, O.; Burgess, C.; Burgess, T.; Castermans, T.; Chirkin, D.; Collin, B.; Conrad, J.; Cooley, J.; Cowen, D. F.; Davour, A.; De Clercq, C.; de los Heros, C. P.; Desiati, P.; De Young, T.; Ekström, P.; Feser, T.; Gaisser, T. K.; Ganugapati, R.; Geenen, H.; Gerhardt, L.; Goldschmidt, A.; Groß, A.; Hallgren, A.; Halzen, F.; Hanson, K.; Hardtke, D. H.; Harenberg, T.; Hauschildt, T.; Helbing, K.; Hellwig, M.; Herquet, P.; Hill, G. C.; Hodges, J.; Hubert, D.; Hughey, B.; Hulth, P. O.; Hultqvist, K.; Hundertmark, S.; Jacobsen, J.; Kampert, K. H.; Karle, A.; Kestel, M.; Kohnen, G.; Köpke, L.; Kowalski, M.; Kuehn, K.; Lang, R.; Leich, H.; Leuthold, M.; Liubarsky, I.; Lundberg, J.; Madsen, J.; Marciniewski, P.; Matis, H. S.; McParland, C. P.; Messarius, T.; Minaeva, Y.; Mio?inovi?, P.; Morse, R.; Münich, K.; Nahnhauer, R.; Nam, J. W.; Neunhöffer, T.; Niessen, P.; Nygren, D. R.; Olbrechts, P.; Pohl, A. C.; Porrata, R.; Price, P. B.; Przybylski, G. T.; Rawlins, K.; Resconi, E.; Rhode, W.; Ribordy, M.; Richter, S.; Rodríguez Martino, J.; Sander, H.-G.; Schlenstedt, S.; Schneider, D.; Schwarz, R.; Silvestri, A.; Solarz, M.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Steele, D.; Steffen, P.; Stokstad, R. G.; Sulanke, K.-H.; Taboada, I.; Tarasova, O.; Thollander, L.; Tilav, S.; Wagner, W.; Walck, C.; Walter, M.; Wang, Y.-R.; Wiebusch, C. H.; Wischnewski, R.; Wissing, H.; Woschnagg, K.

    2006-07-01

    We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity (for wavelengths less than ~450 nm) varies by a factor of three in the depth range between 1300 and 2300 m, where four dust peaks due to stadials in the late Pleistocene have been identified. In our absorption data, we also identify a broad peak due to the Last Glacial Maximum around 1300 m. In the scattering data, this peak is partially masked by scattering on residual air bubbles, whose contribution dominates the scattering coefficient in shallower ice but vanishes at ~1350 m where all bubbles have converted to nonscattering air hydrates. The wavelength dependence of scattering by dust is described by a power law with exponent -0.90 +/- 0.03, independent of depth. The wavelength dependence of absorptivity in the studied wavelength range is described by the sum of two components: a power law due to absorption by dust, with exponent -1.08 +/- 0.01 and a normalization proportional to dust concentration that varies with depth; and a rising exponential due to intrinsic ice absorption which dominates at wavelengths greater than ~500 nm.

  5. Glacial climate in the tropics

    SciTech Connect

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

    1996-06-28

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

  6. Orbital- to Sub-Orbital-Scale Cyclicity in Seismic Reflections and Sediment Character in Early to Middle Pleistocene Mudstone, Santa Barbara Basin, California

    NASA Astrophysics Data System (ADS)

    Peterson, C. D.; Behl, R. J.; Nicholson, C.; Lisiecki, L. E.; Sorlien, C. C.

    2009-12-01

    High-resolution seismic reflection records and well logs from the Santa Barbara Channel suggest that large parts of the Pleistocene succession records climate variability on orbital to sub-orbital scales with remarkable sensitivity, much like the well-studied sediments of the last glacial cycle (ODP Site 893). Spectral analysis of seismic reflection data and gamma ray logs from stratigraphically similar Pleistocene sections finds similar cyclic character and shifts through the section. This correlation suggests that acoustic impedance and physical properties of sediment are linked by basin-scale, likely climatically-driven, oscillations in lithologic composition and fabric during deposition, and that seismic profiling can provide a method for remote identification and correlation of orbital- and sub-orbital-scale sedimentary cyclicity. Where it crops out along the northern shelf of the central Santa Barbara Channel, the early to middle Pleistocene succession (~1.8-1.2 Ma) is a bathyal hemipelagic mudstone with remarkably rhythmic planar bedding, finely laminated fabric, and well-preserved foraminifera, none of which have been significantly altered, or obscured by post-depositional diagenesis or tectonic deformation. Unlike the coarser, turbiditic successions in the central Ventura and Los Angeles basins, this sequence has the potential to record Quaternary global climate change at high resolution. Seismic reflection data (towed chirp) collected on the R/V Melville 2008 Cruise (MV08) penetrate 10's of meters below seafloor into a ~1 km-long sequence of south-dipping seismic reflectors. Sampling parallel to the seafloor permits acquisition of consistent signal amplitude for similar reflectors without spreading loss. Based on established age ranges for this section, sedimentation rates may range from 0.4 to 1.4 meters/kyr, therefore suggesting that the most powerful cycles are orbital- to sub-orbital-scale. Discrete sets of cycles with high power show an abrupt shift to shorter wavelengths midway through the section. Deep in the section, the strongest cycles indicated by spectral analysis are 50 and 16 meters thick, whereas up section, the strongest cycles are 20 and 12 meters thick. Nearby industry boreholes that penetrate a stratigraphically similar, 1500-meter-thick mudstone section, provide logs of natural gamma ray intensity with a higher sample interval (15 cm), allowing resolution and analysis of even higher frequency lithologic cycles. The strongest cycle deep in the section is 100 meters thick, and up section, the strongest cycle is 12 meters thick. This abrupt decrease in dominant cycle thickness midway through both the seismic and gamma ray records perhaps indicates a basin-wide shift in sedimentation. With improved chronostratigraphy based on Sr-isotope ratios and biostratigraphy, and comparison with paleoclimate proxy data, we will test if seismically resolved lithologic oscillations can be reliably interpreted as representing climatically driven Milankovitch cycles. This method may be used to evaluate the age and paleoceanographic potential of sedimentary strata before a coring vessel is deployed.

  7. Glacial cycles and the growth and destruction of Alaska volcanoes

    NASA Astrophysics Data System (ADS)

    Coombs, M. L.; Calvert, A. T.; Bacon, C. R.

    2014-12-01

    Glaciers have affected profoundly the growth, collapse, preservation, and possibly, eruptive behavior of Quaternary stratovolcanoes in Alaska. Holocene alpine glaciers have acted as effective agents of erosion on volcanoes north of ~55 °N and especially north of 60 °N. Cook Inlet volcanoes are particularly vulnerable as they sit atop rugged intrusive basement as high as 3000 m asl. Holocene glaciers have swept away or covered most of the deposits and dome lavas of frequently active Redoubt (60.5 °N); carved through the flanks of Spurr's active vent, Crater Peak (61.3 °N); and all but obscured the edifice of Hayes (61.6 °N), whose Holocene eruptive history is known almost exclusively though far-traveled tephra and flowage deposits. Relationships between Pleistocene eruptive histories, determined by high-precision Ar-Ar dating of lava flows, and marine oxygen isotope stages (MIS) 2-8 (Bassinot et al., 1994, EPSL, v. 126, p. 91­-108) vary with a volcano's latitude, size, and elevation. At Spurr, 26 ages cluster in interglacial periods. At Redoubt, 28 ages show a more continual eruptive pattern from the end of MIS 8 to the present, with a slight apparent increase in output following MIS 6, and almost no preservation before 220 ka. Veniaminof (56.2 °N) and Emmons (55.5°N), large, broad volcanoes with bases near sea level, had voluminous eruptive episodes during the profound deglaciations after MIS 8 and MIS 6. At Akutan (54.1 °N), many late Pleistocene lavas show evidence for ice contact; ongoing dating will be able to pinpoint ice thicknesses. Furthest south and west, away from thick Pleistocene ice on the Alaska Peninsula and mainland, the Tanaga volcanic cluster (51.9 °N) has a relatively continuous eruptive record for the last 200 k.y. that shows no clear-cut correlation with glacial cycles, except a possible hiatus during MIS 6. Finally, significant edifice collapse features have been temporally linked with deglaciations. A ~10-km3 debris-avalanche deposit from Spurr directly overlies bedrock, suggesting that edifice collapse closely followed MIS 2. The geologic history of Veniaminof suggests possible massive edifice collapse following MIS 6. A stack of westward-dipping lavas and breccias on the east flank of Redoubt Volcano erupted during MIS 6, and may have also failed during the major deglaciation of MIS 5.5.

  8. Siphateles (Gila) sp. and Catostomus sp. from the Pleistocene OIS-6 Lake Gale, Panamint Valley, Owens River system, California

    NASA Astrophysics Data System (ADS)

    Jayko, A. S.; Forester, R. M.; Smith, G. R.

    2014-12-01

    Panamint Valley lies within the Owens River system which linked southeastern Sierra Nevada basins between Mono Lake and Death Valley during glacial-pluvial times. Previous work indicates that late Pleistocene glacial-pluvial Lake Gale, Panamint Valley was an open system during OIS-6, a closed ground water supported shallow lake during OIS-4, and the terminal lake basin for the Owens River system during OIS-2. We here report the first occurrence of fossil fish from the Plio-Pleistocene Panamint basin. Fish remains are present in late Pleistocene OIS-6 nearshore deposits associated with a highstand that was spillway limited at Wingate Wash. The deposits contain small minnow-sized remains from both Siphateles or Gila sp. (chubs) and Catostomus sp. (suckers) from at least four locations widely dispersed in the basin. Siphateles or Gila sp. and Catostomus are indigenous to the Pleistocene and modern Owens River system, in particular to the historic Owens Lake area. Cyprinodon (pupfish) and Rhinichthys (dace) are known from the modern Amargosa River and from Plio-Pleistocene deposits in Death Valley to the east. The late Pleistocene OIS-6 to OIS-2 lacustrine and paleohydrologic record in Panamint basin is interpreted from ostracod assemblages, relative abundance of Artemia sp. pellets, shallow water indicators including tufa fragments, ruppia sp. fragments and the relative abundance of charophyte gyrogonites obtained from archived core, as well as faunal assemblages from paleoshoreline and nearshore deposits. The OIS-4 groundwater supported shallow saline lake had sufficiently low ratios of alkalinity to calcium (alk/Ca) to support the occurrence of exotic Elphidium sp. (?) foraminfera which are not observed in either OIS-2 or OIS-6 lacustrine deposits. The arrival of Owens River surface water into Panamint Basin during OIS-2 is recorded by the first appearance of the ostracod Limnocythere sappaensis at ~27 m depth in an ~100 m archived core (Smith and Pratt, 1957) which extends between OIS-5 and post OIS-2 based on based on proxy correlation with the marine oxygen isotope record.

  9. 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.

  10. 36Cl dating of the classic Pleistocene glacial record in the northeastern Cascade Range, Washington

    Microsoft Academic Search

    STEPHEN C. PORTER; TERRY W. SWANSON

    2008-01-01

    and are more degraded. Seventy-six 36Cl dates for the moraines cluster in groups having mean ages ( 1) of 12,500 500, 13,300 800, 16,100 1100, 19,100 3000, 70,900 1500, 93,100 2600, and 105,400 2200 years; a still-older, highly weathered and eroded moraine is undated, but likely is at least 165,000 years old. The moraine ages and relative extent of the

  11. Two Middle Pleistocene Glacial-Interglacial Cycles from the Valle Grande, Jemez Mountains, northern New Mexico

    E-print Network

    Anderson, R. Scott

    valley of the Valles Caldera in northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The deposits of this lake were cored in May 2004 (GLAD5 sediments filled the available accommodation space in the caldera moat. Multiple analyses, including core

  12. Provenance of Palouse Loess and Relation to Late Pleistocene Glacial Outburst Flooding, Washington State

    Microsoft Academic Search

    M. R. Sweeney; A. J. Busacca; D. R. Gaylord; C. S. Zender

    2002-01-01

    The eolian system of the Pacific Northwest is a product of long-term deflation of expansive sedimentary units by prevailing winds throughout the Quaternary. The Palouse loess is a deposit of wind-blown silt that covers approximately 10,000 sqare km up to 75 m thick. Late Quaternary units of the loess become finer texturally and thinner to the northeast, suggesting that they

  13. Precipitation Isotopes Reveal Intensified Indonesian Monsoon Circulation During the Dry Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Konecky, B. L.; Russell, J. M.; Vogel, H.; Bijaksana, S.; Huang, Y.

    2014-12-01

    The Indo-Pacific Warm Pool (IPWP) invigorates the oceanic-atmospheric circulation in the tropics, with far-reaching climate impacts that extend into the high latitudes. A growing number of deglacial proxy reconstructions from the region have revealed the importance of both high- and low-latitude climate processes to IPWP rainfall during the late Pleistocene. Many of these proxies reconstruct the oxygen and hydrogen isotopic composition of rainfall (?18Oprecip, ?Dprecip), a powerful tool for understanding changes in climate. However, an increasing number of studies from the region have highlighted the tendency for ?18Oprecip and ?Dprecip to reflect regional and/or remote circulation processes rather than local rainfall amounts, complicating the reconstruction of IPWP hydroclimate. To better understand high- and low-latitude drivers of late Pleistocene hydroclimate in the IPWP, precipitation isotopic reconstructions must be constrained with both modern observations and independent proxies for rainfall amount. We present a reconstruction of ?Dprecip using leaf wax compounds preserved in the sediments of Lake Towuti, Sulawesi, from 60,000 years before present to today. We interpret our proxy record with the aid of a new precipitation isotopic dataset from our study site, with daily rainfall isotope measurements to constrain the processes controlling ?Dprecip. Our Lake Towuti ?Dwax record is strikingly similar to a speleothem ?18O record from southern Indonesia (Ayliffe et al., 2013) and shares features with other nearby records spanning the Last Glacial Maximum to present. Together, these records indicate that monsoon circulation was intensified in central and southern Indonesia during the glacial period. However, other independent rainfall proxies from Lake Towuti indicate that dry conditions accompanied the intensified monsoon. Regional-scale isotopic depletion during the dry glacial period may have arisen from dynamical and other fractionating processes that are evident in our modern precipitation isotopic data during the monsoon season. We use these findings to reconcile some key differences among proxy reconstructions from the region, and to examine the influence of high-latitude and glacial processes on IPWP glacial climate.

  14. 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.

  15. 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).

  16. 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

  17. 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.

  18. Molecular phylogeography of Dryas integrifolia: glacial refugia and postglacial recolonization.

    PubMed

    1999-07-01

    Chloroplast DNA variation in the Arctic plant species Dryas integrifolia (Rosaceae) was analysed in relation to both the present-day geographical distribution of populations and to Pleistocene fossil records of this species. The phylogeographical structure was weak but the analysis of haplotype diversity revealed several groups of haplotypes having present-day geographical ranges that overlap locations postulated from geographical and fossil evidence to have been glacial refugia. Based on this information we infer that two important refugial sources of Arctic recolonization by this species were Beringia and the High Arctic. Two other putative refugia, located southeast of the ice sheet and along coastal regions of the eastern Arctic may have served as sources for recolonization of smaller portions of the Arctic. The genetic substructure in the species is mostly due to variation among populations regardless of the ecogeographical region in which they are found. Spatial autocorrelation at the regional scale was also detected. High levels of diversity both within populations and ecogeographical regions are probably indicative of population establishment from several sources possibly combined with recent gene flow. PMID:10447859

  19. 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.

  20. Connecting Soils and Glacial Geology

    NSDL National Science Digital Library

    Holly Dolliver

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

  1. Pleistocene phylogeographic effects on avian populations and the speciation process

    E-print Network

    Avise, John

    Pleistocene phylogeographic effects on avian populations and the speciation process John C. Avise* and DeEtte Walker Department of Genetics, University of Georgia, Athens, GA 30602-7223, USA Pleistocene in birds and reinterpret the molecular evidence bearing on Pleistocene in£u- ences. At least 37 of the 63

  2. Research Focus The Pleistocene re-wilding gambit

    E-print Network

    Wolverton, Steve

    Research Focus The Pleistocene re-wilding gambit Tim Caro Department of Wildlife, Fish Pleistocene re-wild- ing and edge debate from hazy conceptual arguments to empirical questions that can plug extinct during the Pleistocene, or morphologically similar species, if no descendants exist. For example

  3. Research paper Pleistocene magnetochronology of the fauna and Paleolithic sites

    E-print Network

    Utrecht, Universiteit

    Research paper Pleistocene magnetochronology of the fauna and Paleolithic sites in the Nihewan: Magnetostratigraphy Nihewan Fauna Human evolution Paleoenvironment Nihewan Basin Pleistocene a b s t r a c sources of Early Pleistocene Paleolithic sites and mammalian fossils (known as the Nihewan Fauna sensu

  4. Southern crossroads of the Western Palaearctic during the Late Pleistocene

    E-print Network

    Binford, Michael W.

    ORIGINAL ARTICLE Southern crossroads of the Western Palaearctic during the Late Pleistocene Pleistocene. For animals, most studies so far have focused on species having low to moderate dispersal of contributing to filling this gap, we here investigate the Late Pleistocene evolutionary history of one

  5. 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.

  6. 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.

  7. Age constraints on Pleistocene megafauna at Tight Entrance Cave in southwestern Australia

    NASA Astrophysics Data System (ADS)

    Ayliffe, Linda K.; Prideaux, Gavin J.; Bird, Michael I.; Grün, Rainer; Roberts, Richard G.; Gully, Grant A.; Jones, Rhys; Fifield, L. Keith; Cresswell, Richard G.

    2008-09-01

    A well-stratified succession of fossiliferous sediments occurs in Tight Entrance Cave, southwestern Australia. These infill deposits contain the remains of megafauna and have accumulated intermittently since the Middle Pleistocene: >137, 137-119 and 50-29 ka, according to the results of 14C, U-Th, ESR and OSL dating techniques. Megafaunal species richness was highest in the latest part of the penultimate glacial maximum and during the subsequent last interglacial (137-119 ka), but remains are less abundant following an apparent ˜70 ka depositional hiatus in the sequence. Most megafaunal specimens from the upper (<44 ka) units are fragmentary, and reworking from older strata cannot yet be ruled out. However, one specimen of Simosthenurus occidentalis (a large extinct kangaroo), a pair of articulated dentaries showing no signs of secondary transportation, was found within a sedimentary layer deposited between 48 and 50 ka. This represents one of the youngest demonstrably in situ occurrences of an Australian megafaunal taxon.

  8. Glacial effects limiting mountain height.

    PubMed

    Egholm, D L; Nielsen, S B; Pedersen, V K; Lesemann, J-E

    2009-08-13

    The height of mountain ranges reflects the balance between tectonic rock uplift, crustal strength and surface denudation. Tectonic deformation and surface denudation are interdependent, however, and feedback mechanisms-in particular, the potential link to climate-are subjects of intense debate. Spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first-order controls on mountain range width, crustal deformation rates and rock uplift. Moreover, limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus, such as those in Tibet and the central Andes. There are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw. Here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate-controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles. With the aid of a numerical model, we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier-sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline. The model thereby self-consistently produces the hypsometric signature of the glacial buzzsaw, and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces. PMID:19675651

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

    NASA Astrophysics Data System (ADS)

    Poirier, Robert K.; Billups, Katharina

    2014-11-01

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

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

    Microsoft Academic Search

    Heinrich Zoller; Nikolaos Athanasiadis; Annekäthi Heitz-Weniger

    1998-01-01

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

  11. Variability in Sediment Supply to the Pleistocene Eastern Arctic Ocean: A Mineralogical Perspective

    NASA Astrophysics Data System (ADS)

    Mildner, T.; Matthiessen, J.; Vogt, C.

    2007-12-01

    ODP Leg 151 Hole 910A is located on the Yermak Plateau which is a crucial area for monitoring the Pleistocene variability of Atlantic Water inflow to the Arctic Ocean and the history of glaciations at the Eurasian continental margin. In contrast to other Arctic Ocean records, a well-constrained chronostratigraphy based on stable isotopes, biostratigraphy and magnetostratigraphy allows the identification of glacial-interglacial cycles and a detailed reconstruction of paleoenvironmental conditions in the past 800,000 years. Thus, stable isotope studies revealed that the glacial-interglacial cycles are superimposed by short-term freshwater supply to the Eastern Arctic Ocean on sub-Milankovitch time-scales (Knies et al. in press, Effects of Arctic freshwater forcing on thermohaline circulation during the Pleistocene, Geology). The sources of freshwater and the history of glaciations in the Brunhes Chron prior to the late Pleistocene are virtually unknown. Previous studies on clay mineral assemblages revealed a pronounced variability on various time-scales in the past 150,000 years, reflecting shifts in sediment input between different source areas in response to freshwater input and waxing and waning of ice sheets. Based on these results, the middle to late Pleistocene of Hole 910A has been studied at sub-Milankovitch time-scales to decipher a possible relationship between climate cycles and input of fine sediments from various source areas during the Brunhes Chron. Despite of a strong imprint of local sources on clay mineral sedimentation on the southern Yermak Plateau, a distinct variability has been recognized in the past 800,000 years. The strongest supply from northern Spitsbergen occurred only during the LGM associated with a maximum input of coarse sediments. Previous reconstructions that suggest a pronounced advance of the northern Barents Sea Ice Sheet across the southern Yermak Plateau are refuted since sediments of Hole 910A are normally consolidated in the Middle and Late Pleistocene. The supply of coarse sediments prior to the LGM is moderate indicating that the location was somewhat protected from massive deposition of ice-rafted debris from melting icebergs. Therefore, the clay mineral record of Hole 910A reflects not only supply from local sources but also long-distance transport of fine sediments from source regions located at the Eurasian continental margin. There is apparently a distinct link between climate cycles and the supply from specific source areas. Sequences of sedimentological and clay mineral events are recurrently recorded in Hole 910A indicating that cryosphere variability followed a characteristic pattern at the Northern Barents Sea margin, in particular during deglaciations. Pleistocene clay mineral records are compared along a transect from Yermak Plateau to Lomonosov Ridge to identify events that were of basinwide significance in the Eurasian Arctic.

  12. Sensitivity simulations with direct shortwave radiative forcing by aeolian dust during glacial cycles

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Ganopolski, A.

    2014-07-01

    Possible feedback effects between aeolian dust, climate and ice sheets are studied for the first time with an Earth system model of intermediate complexity over the late Pleistocene period. Correlations between climate and dust deposition records suggest that aeolian dust potentially plays an important role for the evolution of glacial cycles. Here climatic effects from the dust direct radiative forcing (DRF) caused by absorption and scattering of solar radiation are investigated. Key elements controlling the dust DRF are the atmospheric dust distribution and the absorption-scattering efficiency of dust aerosols. Effective physical parameters in the description of these elements are varied within uncertainty ranges known from available data and detailed model studies. Although the parameters can be reasonably constrained, the simulated dust DRF spans a~wide uncertainty range related to the strong nonlinearity of the Earth system. In our simulations, the dust DRF is highly localized. Medium-range parameters result in negative DRF of several watts per square metre in regions close to major dust sources and negligible values elsewhere. In the case of high absorption efficiency, the local dust DRF can reach positive values and the global mean DRF can be insignificantly small. In the case of low absorption efficiency, the dust DRF can produce a significant global cooling in glacial periods, which leads to a doubling of the maximum glacial ice volume relative to the case with small dust DRF. DRF-induced temperature and precipitation changes can either be attenuated or amplified through a feedback loop involving the dust cycle. The sensitivity experiments suggest that depending on dust optical parameters, dust DRF has the potential to either damp or reinforce glacial-interglacial climate changes.

  13. Pleistocene glaciations and polyphyletic origins of polyploidy in an arctic cladoceran

    PubMed Central

    Dufresne, F.; Hebert, P. D. N.

    1997-01-01

    RFLP analysis of the ND4-ND5 genes of the mtDNA genome in Daphnia middendorffiana and three closely allied species was used to investigate its origin and age. Populations of D. middendorffiana from arctic Canada were found to possess three distinct mtDNA lineages, only one of which appears unique to this species. The other two mtDNA lineages are either closely allied or identical to haplotypes in D. pulicaria, suggesting that it is the maternal parent of many clones of D. middendorffiana. Within D. pulicaria, mtDNA lineages have largely disjunct distributions, suggesting that populations of this species persisted in three glacial refugia (arctic, western, eastern) during the Pleistocene. Hybridizations between these refugial stocks and other species such as D. melanica and D. pulex likely generated many of the polyploid lineages of D. middendorffiana following the Wisconsinan glaciation. The presence of one unique mtDNA lineage in D. middendorffiana suggests that at least some of its clones are more ancient, but further studies are needed to rule out the possibility of their recent derivation from an as yet undetected sexual species. As a general result, this study suggests that polyploid cladocerans are unlikely to predate the Pleistocene.

  14. 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.

  15. 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

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

    SciTech Connect

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  18. Late Pleistocene Southeast Amazonia Paleoenvironmental reconstruction inferred by bulk, isotopic and molecular organic matter. Saci lake-Para-Brazil

    NASA Astrophysics Data System (ADS)

    Martins, G. S.; Cordeiro, R. C.; Turcq, B.; Moreira, L. S.; Bouloubassi, I.; Sifeddine, A.

    2014-12-01

    Bulk, Isotope and biolomecular analysis supported by 22 14C AMS dates, allowed the reconstruction of environmental changes during the last 35 000 years BP in the Southeast Amazonian basin. A terrestrial origin has been inferred for the odd carbon-numbered long-chain (>C27) n-alkanes. The entire n-alkane ?13C range between -31.7‰ and -36.8‰, which is the isotopic range occupied by C3 vegetation. The C29:C31 ratio shows that a gramineae contribution is higher during the Pleistocene than in Holocene. The n-alkanes concentration decrease between 32 000 - 18 000, suggesting a increase in arid conditions. The ACL index confirm this interpretation showing high values due the Pleistocene linked to more hydrological stress. A shift in the abundance of n-alkane and isotopic values are observed across the late Pleistocene glacial-Holocene interglacial climate change, suggesting a climate-induced vegetational change. During the middle Holocene the n-alcanes values decreases indicating rain forest regression accompanied by increase in the ACL values confirming the dry climate conditions. Comparison with other South American records, our record indicates regression/expansion of the rain forest linked to the South American System monsoon activity since 35 kyrs.

  19. Geochronological reconstruction of the Pleistocene evolution of the Sarre valley (France and Germany) using OSL and ESR dating techniques

    NASA Astrophysics Data System (ADS)

    Cordier, Stéphane; Harmand, Dominique; Lauer, Tobias; Voinchet, Pierre; Bahain, Jean-Jacques; Frechen, Manfred

    2012-09-01

    This paper focuses upon the Pleistocene terraces of the Sarre River, a right bank tributary of the Moselle River (NE France and SW Germany) flowing through the Vosges Massif, the eastern Paris Basin and the Rhenish Massif. Recent research has allowed the recognition of 12 well preserved alluvial terraces (Sa1 youngest to Sa12 oldest) between the present floodplain Sa0 and + 120 m relative height. The youngest terraces were dated using Optically Stimulated Luminescence (OSL). A first chronological framework was also provided for older terraces by Electron-Spin-Resonance (ESR) dating. The ages range between the end of the Early Pleistocene and the last glacial-interglacial cycle of the Late Pleistocene (ca. 1.1 Ma to 50 ka). Age ranges are consistent with the terrace elevation and stratigraphy, allowing correlation of the youngest terraces with established global climate cycles and with the younger terraces in the Moselle valley. In particular, an erosional period was recognised at the end of the Saalian, (end of MIS 6) suggesting that the terrace incision occurred at the cold-to-warm transition. This result contrasts with those obtained for the Moselle and Meurthe Rivers, where previous studies suggest that major incision took place at the beginning of the cold periods. The differences are attributed to a variable fluvial response to climate change which could relate to the presence or absence of glaciers in the upper catchment.

  20. Stratigraphic framework of a late pleistocene shelf-edge delta, northeast Gulf of Mexico

    SciTech Connect

    Sydow, J.; Roberts, H.H. (Louisiana State Univ., Baton Rouge, LA (United States))

    1994-08-01

    Lithologic, biostratrigraphic, and chronostratigraphic data from a 92-m continuous surface boring, in the Main Pass area of the outer Mississippi-Alabama shelf, were used to calibrate high-resolution seismic profiles in a study of a late Pleistocene shelf-edge delta. The boring is the first of its kind through a shelf-edge clinoform wedge and the first [open quotes]ground-truth[close quotes] confirmation that the clinoforms in the study area are deltaic in origin. Chronologic control for the late Pleistocene outer shelf stratigraphy is based on the identification of Ericson Zones X, Y, and Z (alternating warm and cold water planktonic foraminifera zones) in the boring, representing at least the last 130 k.y. During sea level lowering related to the previous glacial maximum, the delta system prograded onto a carbonate-rich outer shelf and upper slope starved of terrigenous sediments. The ancestral Mobile River, possibly joined by the Pascagoula River, was the fluvial feeder of the shelf-edge delta. The upper portion of the delta wedge is extensively eroded, primarily by a broad swath of significant fluvial scour centered along the northeast- to southwest-oriented dip axis of the delta, and to a lesser extent by subsequent transgressive truncation. Fluvial scour resulted in a broad erosional trough filled with fluvial and estuarine facies. Thin estuarine and overlying marine units reflect transgression of the Lagniappe delta during the late Pleistocene-early Holocene transgression. According to standard sequence stratigraphic definitions, the extent of the sequence boundary, identified as the erosional base of the fluvial facies, places the majority of the outer shelf delta in the highstand systems tract. The portion of the delta thus categorized as highstand was built during the falling to lowstand minimum part of the relative sea level curve. 64 refs., 18 figs.

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

    USGS Publications Warehouse

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

    1981-01-01

    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. ?? 1981.

  2. Ecological consequences of early Late Pleistocene megadroughts in tropical Africa.

    PubMed

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

    2007-10-16

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

  3. Late Pleistocene glaciers and climate in the Mediterranean

    NASA Astrophysics Data System (ADS)

    Hughes, P. D.; Woodward, J. C.; Gibbard, P. L.

    2006-02-01

    Evidence for Late Pleistocene glaciers and rock glaciers in the Pindus Mountains, Greece, is used to reconstruct palaeoclimate for this part of the Mediterranean during the last cold stage (Tymphian/ Würmian). Mean annual precipitation was c. 2300 ± 200 mm and the mean summer temperature (June/July/August) was c. 4.9 °C at 2174 m a.s.l., the equilibrium line altitude of the former glaciers, at the last local glacier maximum. The glacier-climate relationship in the northern Pindus Mountains during the local glacier maximum of the Tymphian Stage closely resembled that found today at the equilibrium line altitude of Norwegian glaciers. The local glacier maximum on Mount Tymphi is likely to have preceded both the most severe phase of climate indicated in the pollen record at nearby Ioannina and also the global last glacial maximum. Major stadials, including the most severe phase of the last cold stage, were characterised by cold sea surfaces temperatures, which inhibited atmospheric moisture supply creating unfavourable conditions for glacier formation. Such stadial conditions are likely to have favoured periglacial conditions and the formation of features such as rock glaciers. Conversely, warm summer temperatures during major interstadials would have promoted glacier ablation, offsetting increased precipitation enabled by warmer sea surface temperatures. Thus, the most favourable conditions for glacier formation would have occurred during intermediate conditions between major stadials and interstadials. It is clear that former glacier behaviour in the mountains of this region is best understood with reference to temporally dynamic glacier-climate models, which take into account millennial-scale changes in both precipitation and temperature.

  4. 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).

  5. Mid-Pleistocene Lacustrine Records of Carbon and Nitrogen Elemental and Isotopic data from Valles Caldera, New Mexico, USA

    NASA Astrophysics Data System (ADS)

    Cisneros-Dozal, L.; Heikoop, J.; Fessenden, J.; Fawcett, P.; Kawka, O.; Sachs, J.

    2007-12-01

    Lacustrine deposits dating back to the middle Pleistocene were recovered from Valles Caldera, located in Northern New Mexico. The core (82 m long) contained ~75 meters of lacustrine sediments. The age of the sediments was constrained by Ar-Ar dating of a primary tephra layer from the base of the core, in combination with correlation to the deep-sea marine isotope stage record along the length of the core. The lacustrine sediments span from ~350 k YBP to 552 k YBP covering two glacial-interglacial stages, from MIS 11 to MIS 14 and part of MIS 10. Total organic carbon (TOC) in the siderite free fraction (i.e. diagenetic siderite was chemically removed) ranged from <1% to 7% with the lowest values predominantly observed during glacial times and marked increases at the onset of interglacials. Particularly high TOC is observed during the long interglacial MIS 11. C/N ratios ranged from values of <2 to ~11 with lowest values in general observed during glacial times indicating increased input from aquatic sources and suggesting deepening of the lake as a result of wetter glacial climate. ?13C values measured in the siderite free fraction, ranged from -28‰ to -20‰ and remained more negative overall during glacial times. We are currently working on D/H analyses of leaf lipid biomarkers which may provide insight into the delivery of meteoric water to the region during these climatic stages, i.e. relative contributions of summer monsoonal (from the Gulfs of Mexico and California) vs. winter frontal precipitation (from the North Pacific).

  6. New Pleistocene vertebrate fauna from El Salvador

    Microsoft Academic Search

    Juan Carlos Cisneros

    2005-01-01

    The discovery of an Early-Middle Pleistocene continental vertebrate fauna from El Salvador is here reported. These fossils provide information about a poorly studied geographic area that played an important role during the Great American Faunal Interchange. The fauna is dominated by numerous remains of the proboscidean Cuvieronius tropicus and probably represents the largest known concentration of this genus in America.

  7. Vegetation and climate changes in western Amazonia during a previous Interglacial- Glacial transition

    NASA Astrophysics Data System (ADS)

    Cardenas, M. L.; Gosling, W. D.; Sherlock, S. C.; Poole, I.; Pennington, R. T.

    2009-12-01

    Amazonia is one of the most biodiverse areas of the world and its vegetation plays a crucial role in controlling the global climate through the regulation of the levels of atmospheric CO2. However, Amazonian ecosystems and their role in the climate system are threatened by ongoing the human impact (already estimated loss of 60% of the species in western Amazonia) and predicted climate change (+1.1-6.4oC by 2100). Unfortunately, there is absence of data relating to the ecological baseline function and response to global climate change of western Amazonian ecosystems in the absence of humans. To help anticipate the impact of future climate change predictions an improved understanding of the natural responses of tropical vegetation to known past climate change is required. Here we present the first study that shows the response of pristine tropical ecosystems in western Amazonia biodiversity hotspot to a major global climate change event (a Quaternary Interglacial-Glacial transition). Pleistocene lake/swamp sediments preserved at the Erazo study site (Lat. 00o 33’S, Long. 077o 52’W, 1927m alt.) today within tropical cloud forest vegetation provide a unique opportunity to examine the impact of past climate shifts. The sediment are >40,000 years old (radiocarbon infinite) and younger than 1 million years (presence of Alder biomarker) and consist of organic layers interbedded with volcanic ash (tephra). This study presents data from multiple proxies (fossil pollen, wood macrofossils and charcoal) to establish a comprehensive picture of regional and local vegetation change prior to human arrival. Our data show a change of vegetation from palm-dominated forest indicative of warm and wet conditions similar to the present at the base of this record, to a forest dominated by Podocarpus sp. suggesting cold and wet conditions at the top of the record. The transition between these two vegetation communities appears to be progressive with small sharp changes along the ecological succession. Fire activity appears to be minor through the record associated only with volcanic events (tephra layers). We conclude that western Amazonian vegetation was effected by Pleistocene global climate change. The Erazo record shows the progression of the vegetation from warm/wet Interglacial-like period similar to the present, to a colder and wetter Glacial-like period. This magnitude of change agrees with similar magnitude changes inferred for the last glacial-interglacial transition at 14,700-9,000 calendar years BP. We also establish for the first time that no natural fire occurred in western Amazonia in the absence of humans, under interglacial or glacial conditions, without volcanic eruptions acting as a source of ignition.

  8. Obsidian hydration dates glacial loading?

    USGS Publications Warehouse

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

    1973-01-01

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

  9. Obsidian hydration dates glacial loading?

    PubMed

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

    1973-05-18

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

  10. Robustness of Quaternary glacial cycles

    NASA Astrophysics Data System (ADS)

    Ganopolski, Andrei; Brovkin, Victor; Calov, Reinhard

    2015-04-01

    In spite of significant progress in paleoclimate reconstructions and modeling some aspects of Quaternary climate cycles are still poorly understood. Among them is the question of whether glacial cycles are deterministic and solely externally forced or, at least partially, they are stochastic. The answer to this question can only be obtained using a comprehensive Earth system models which incorporates all major components of the Earth system - atmosphere, ocean, land surface, northern hemisphere ice sheets, terrestrial biota and soil carbon, aeolian dust and marine biogeochemistry. Here, we used the Earth system model of intermediate complexity CLIMBER-2. The model was optimally tuned to reproduce climate, ice volume and CO2 variability for the last 0.8 million years. Using the same model version, we performed a large set of simulations covering the entire Quaternary (3 million years). By starting the model at different times (with the time step of 100,000 years) and using identical initial conditions we run the model for 500,000 years using the Earth's orbital variations as the only prescribed radiative forcing. We show that within less than 100,000 years after the beginning of each experiment the modeling results converge to the same solution which depends only on the orbital forcing and boundary conditions, such as topography and terrestrial sediment thickness for the ice sheets or volcanic CO2 outgassing for the carbon cycle. By using only several sets of the Northern Hemisphere orography and sediment thickness which represent different stages of landscape evolution during Quaternary, we are able to reproduce all major regimes of Quaternary long-term climate variability. Our results thus strongly support the notion that Quaternary glacial cycles are deterministic and externally forced.

  11. 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.

  12. Late Quaternary Glacial / Interglacial Cyclicity Models of the Red Sea

    NASA Astrophysics Data System (ADS)

    Badawi, Amani

    2015-04-01

    Four distinct glacial / interglacial cycle during the last 380 Kyr have been recognized in the Red Sea. The identified four cycles reveal deviation in deep-sea ecosystem between the northern and southern Red Sea. In the northern Red Sea salinity fluctuations, productivity and deep-water ventilation and formation had the major impact on benthic foraminiferal pattern corresponding to glacial/interglacial cycles and glacio-eustatic sea level changes coupled with the impact of Mediterranean climate regime. While in the southern Red Sea region the oscillation trend of benthic foraminiferal pattern within the glacials and interglacials stages, indicating a high frequency environmental alternation. This alternation is consistent with the extent of NE monsoonal wind that controls the intensity and extension of the productivity, which in turn determine organic matter fluxes and oxygen level at the sea floor. The benthic foraminiferal faunas from samples of two piston cores retrieved along a North-South transect in the Red Sea were studied. The northern core was collected during Meteor cruise M 31/2, while the southern one was collected during the Sonne cruise 121. Benthic foraminiferal faunas from both sites exhibit large variability with respect to density, diversity, species composition and assemblages combined with stable oxygen and carbon isotope records of planktic and benthic foraminifera. One hundered thirty benthic foraminiferal species were identified in the investigated cores. The faunal data set of the northern core was reduced to five assemblages (factors) while the southern one was reduced to four assemblages. All assemblages were ranked according to their ecological significance. Besides, Relative abundance of major benthic foraminiferal suborders (Textulariina (agglutinating foraminifera), Miliolina, and Rotaliina), in addition to infaunal/epifaunal relative abundance were used as paleoenvironmental proxies allowing the reconstruction of past changes in deep-water salinity, ventilation, and organic carbon fluxes at the sea-floor.

  13. Climate-Ice Sheet Interactions through the Pliocene-Pleistocene: Preliminary Results from IODP Expedition 341 (Gulf of Alaska)

    NASA Astrophysics Data System (ADS)

    Müller, J.; McClymont, E.; Sanchez Montes, M. L.; Moy, C. M.; Romero, O. E.; Lloyd, J. M.

    2014-12-01

    Since the Pliocene, global climate history is distinguished by the transition into a colder world, dominated by the onset and intensification of major Northern Hemisphere glaciations which have also changed in their duration and intensity. Potential drivers for these events include falling atmospheric CO2, progressive sub-glacial erosion, tectonic uplift, and associated feedbacks. At present, isolating climate as the driver of evolving continental ice volume since the Pliocene is hindered by the limited long term data sets which directly link climate changes to evidence for ice-sheet advance/retreat, erosion, and tectonic evolution over million year timescales. IODP Expedition 341 drilled a cross-margin transect in the Gulf of Alaska from ice-proximal sites on the continental shelf to distal sites in the deep Pacific. This study focuses on the distal site (Site U1417, c.4190 m water depth) which contains variable biogenic and terrigenous contributions, and evidence for deposition through pelagic, mass movement and glacial processes. Our aim is to investigate links between north-east Pacific paleoceanography and the history of the north-west Cordilleran ice sheet, neither of which are fully understood given limited data pre-dating the Last Glacial Maximum. We reconstruct SSTs during the mid-Pliocene, Plio-Pleistocene Transition (PPT) and mid-Pleistocene transition (MPT) using the UK37' index. We consider the interaction between SSTs and primary production by examining the absolute and relative abundances of plankton biomarkers (e.g. for haptophytes, diatoms and dinoflagellates), carbon/nitrogen ratios, stable isotopes (?13C, ?15N) and diatom assemblages. Links between these climatic events and the north-west Cordilleran ice-sheet advance/retreat history are initially made using shipboard stratigraphy; emerging data sets on ice-rafting from members of the Expedition 341 Scientific Party will refine these relationships.

  14. Glacial erosion and expected permafrost thickness of Fennoscandia and adjacent regions

    NASA Astrophysics Data System (ADS)

    Amantov, Aleksey

    2013-04-01

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

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

    PubMed

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

    2007-05-01

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

  16. Evidence of two glacial-interglacial climatic shifts from lacustrine records of TOC, ?13C and C/N ratios in the southwestern USA

    NASA Astrophysics Data System (ADS)

    Heikoop, J.; Cisneros-Dozal, L.; Fessenden-Rahn, J.; Fawcett, P.

    2007-05-01

    Valles Caldera, located in Northern New Mexico, contains lacustrine deposits dating back to the middle Pleistocene. An 82 m long core containing ~75 meters of lacustrine sediments was recovered from Valles Caldera in 2004. The age of the sediments was constrained by Ar-Ar dating of a primary tephra layer from the base of the core, in combination with correlation to the deep-sea marine isotope stage record along the length of the core. The lacustrine sediments span from ~350 k YBP to 552 k YBP covering two glacial-interglacial stages, from MIS 11 to MIS 14 and part of MIS 10. Total organic carbon (TOC) in the siderite free fraction (i.e. diagenetic siderite was chemically removed) ranged from <1% to 7% with the lowest values predominantly observed during glacial times and marked increases at the onset of interglacials. Particularly high TOC is observed during the long interglacial MIS 11. C/N ratios ranged from values of <2 to ~11 with lowest values in general observed during glacial times indicating increased input from aquatic sources and suggesting deepening of the lake as a result of wetter glacial climate. ?13C values measured in the siderite free fraction, ranged from - 28‰ to -20‰ and remained more negative overall during glacial times. Further isotopic analyses including ?D values of n-alkanes will be performed to reconstruct the delivery of meteoric water to the region and thus contribute to understand the history of climate change.

  17. Parallel responses of bees to Pleistocene climate change in three isolated archipelagos of the southwestern Pacific

    PubMed Central

    Groom, Scott V. C.; Stevens, Mark I.; Schwarz, Michael P.

    2014-01-01

    The impacts of glacial cycles on the geographical distribution and size of populations have been explored for numerous terrestrial and marine taxa. However, most studies have focused on high latitudes, with only a few focused on the response of biota to the last glacial maximum (LGM) in equatorial regions. Here, we examine how population sizes of key bee fauna in the southwest Pacific archipelagos of Fiji, Vanuatu and Samoa have fluctuated over the Quaternary. We show that all three island faunas suffered massive population declines, roughly corresponding in time to the LGM, followed by rapid expansion post-LGM. Our data therefore suggest that Pleistocene climate change has had major impacts across a very broad tropical region. While other studies indicate widespread Holarctic effects of the LGM, our data suggest a much wider range of latitudes, extending to the tropics, where these climate change repercussions were important. As key pollinators, the inferred changes in these bee faunas may have been critical in the development of the diverse Pacific island flora. The magnitude of these responses indicates future climate change scenarios may have alarming consequences for Pacific island systems involving pollinator-dependent plant communities and agricultural crops. PMID:24807250

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

    SciTech Connect

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

    1994-12-23

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

  19. Diagenesis in coastal carbonates related to Pleistocene sea level, Bermuda Platform

    SciTech Connect

    Vollbrecht, R.; Meischner, D. [Inst. fuer Geologie und Palaeontologie, Goettingen (Germany)

    1996-01-01

    Pleistocene glacioeustatic sea-level oscillation on the stable Bermuda Platform is expressed in a succession of shallow-water carbonates interrupted by lowstand unconformities. In Bermuda, the maximum highstands of the last 400,000 yr ranged within 10 m around the present level. Coastal carbonates of various highstands are exposed along the present shoreline. These carbonates were penetrated by meteoric and marine pore waters during lowstands and highstands following on deposition. Two representative Pleistocene shoreline sections were studied to see whether early diagenesis has recorded these pore-water changes. The sediments of both sections show multiple generations of cement. Optical and scanning electron microscopy, cathodoluminescence microscopy, X-ray diffraction, microprobe studies and stable-isotope analyses were used to determine the diagenetic environments involved. Regardless of the degree of substrate cementation, freshwater alteration was mainly vadose whereas marine cementation was either phreatic or vadose or both. Early diagenetic oscillation is easier recorded in coastal successions than in lagoonal sediments, mainly because marine cementation is more active nearshore.Because the coastal environment is prone to wave destruction, the potential for preserving these diagenetic features is usually low. Data published on tectonically unstable areas suggest that early diagenetic oscillation may characterize stable coastlines.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  1. 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

  2. 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

  3. Genetic consequences of Pleistocene glaciations for the tundra vole (Microtus oeconomus) in Beringia.

    PubMed

    Galbreath, Kurt E; Cook, Joseph A

    2004-01-01

    Repeated glacial events during the Pleistocene fragmented and displaced populations throughout the northern continents. Different models of the effects of these climate-driven events predict distinct phylogeographic and population genetic outcomes for high-latitude faunas. The role of glaciations in (i) promoting intraspecific genetic differentiation and (ii) influencing genetic diversity was tested within a phylogeographic framework using the rodent Microtus oeconomus. The spatial focus for the study was Beringia, which spans eastern Siberia and northwestern North America, and was a continental crossroads and potential high arctic refugium during glaciations. Variation in mitochondrial DNA (cytochrome b and control region; 214 individuals) and nuclear DNA (ALDH1 intron; 63 individuals) was investigated across the Beringian region. Close genetic relationships among populations on either side of the Bering Strait are consistent with a history of periodic land connections between North America and Asia. A genetic discontinuity observed in western Beringia between members of a Central Asian clade and a Beringian clade is geographically congruent with glacial advances and with phylogeographic discontinuities identified in other organisms. Divergent island populations in southern Alaska were probably initially isolated by glacial vicariance, but subsequent differentiation has resulted from insularity. Tests of the genetic effects of postglacial colonization were largely consistent with expansion accompanied by founder effect bottlenecking, which yields reduced diversity in populations from recently deglaciated areas. Evidence that populations in the Beringian clade share a history of expansion from a low-diversity ancestral population suggests that Beringia was colonized by a small founder population from central Asia, which subsequently expanded in isolation. PMID:14653795

  4. The Influence of True Polar Wander on Climate and Glacial Inception in North America

    NASA Astrophysics Data System (ADS)

    Daradich, A.; Huybers, P. J.; Mitrovica, J. X.; Chan, N. H.

    2014-12-01

    While plate tectonic motions and dynamic topography of continents each reflect an active mantle convective regime, excursions of the Earth's rotation axis relative to a fixed hotspot reference frame are remarkably muted. Early studies of paleomagnetically inferred pole positions suggested excursions of less than a few degrees [Jurdy and Van Der Voo, 1975]. For this reason, long-term changes in Earth's rotation, or true polar wander (TPW), were thought to have a negligible role in the observed long-term secular cooling of Earth's climate through the Tertiary [Donn and Shaw, 1977]. This gradual cooling over the past 65 million years began at a time when much of Earth's climate was relatively warm and quiescent and culminated in dramatic glacial cycles of the Pleistocene. In contrast to earlier studies, recent reanalyses of paleomagnetic pole positions suggest a secular drift in Earth's rotation axis of greater than ten degrees in the last 40 million years [Torsvik et al., 2012; Doubrovine et al., 2012]. The direction of this drift brings North America, a site of advancing and retreating ice sheets throughout the Pleistocene, to increasingly higher latitudes. Using an orbital solution valid for the last 50 million years [Laskar et al., 2004], we compute the effect of TPW on insolation quantities for sites in Greenland and the Canadian Arctic Archipelago. Our results indicate that a three degree shift in latitude driven by TPW is comparable to a two degree change in obliquity in terms of its impact on summer energy (i.e. the total energy for the year on days surpassing a given insolation threshold; Huybers, 2006). In addition, we explore climatological gradients using modern climatological data and employ simple climate models to characterize reductions in positive degree days for the North American Arctic over the last 40 million years. We find that TPW and continental drift that moved arctic North America poleward could have driven cooling that contributed to glacial inception ~3 Ma.

  5. Late Middle Pleistocene climate in southwestern China: inferences from the stratigraphic record of Panxian Dadong Cave, Guizhou

    NASA Astrophysics Data System (ADS)

    Karkanas, Panagiotis; Schepartz, Lynne A.; Miller-Antonio, Sari; Wang, Wei; Huang, Weiwen

    2008-08-01

    Panxian Dadong Cave, situated in the subtropical zone of southwestern China, preserves a fan-like sedimentary sequence close to its entrance that spans the period between MIS 8 and 5 (300-130 ka). The frequent alternation of flowstone formation, cementation, clastic deposition, and frost activity in the depositional sequence makes it ideal for reconstructing the environmental conditions prevailing during the later Middle Pleistocene on the Guizhou Plateau. Macroscopic and microscopic sedimentary analyses determine that clastic deposits were entering the cave in the form of intermittent cohesive debris flows and sheetflows during cold and relatively dry climatic conditions when vegetation cover was reduced. Interlayered impure flowstones were forming during wetter phases but still under glacial conditions. Seasonally freezing temperatures are deduced from the frequent occurrence of cycles of well-developed freeze-thaw features affecting both the clastic parts of the sequence and the flowstones as they were deposited. The described depositional processes were responsible for lateral redistribution on the fan surface of bone remains and lithic artifacts that were accumulating on the surface as a result of hominid activities. During the intervening interglacial stages (MIS 7 and possibly MIS 5) clastic deposition was considerably reduced and only thin flowstone caps and weathering manganese-iron crusts were forming. It is suggested that precipitation was much higher during glacial intervals than interglacials under a predominantly cold climate. Dadong Cave provides a good example of very cold and wet climatic conditions during glacials in the subtropics of East Asia.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  8. Mass wasting deposits in the upper Sehonghong valley, eastern Lesotho: Late Pleistocene climate implications

    NASA Astrophysics Data System (ADS)

    Mills, S. C.; Grab, S. W.

    2009-04-01

    Despite considerable research attention on apparent periglacial, glacial and sedimentary phenomena in the Maluti-Drakensberg alpine environment, knowledge on the Quaternary environmental history of this important watershed and climate-divide is still rather rudimentary. The dearth of Quaternary environmental indicators (proxy data) in the high Drakensberg is partly owing to the harsh climate (e.g. high wind speeds and high seasonal precipitation), which offers a poor preservation of past biological remains (e.g. bones, dung, middens, pollen). Possibly the best opportunity to reconstruct high Drakensberg palaeoenvironments is from sedimentary sequences exposed along fluvially-incised valley fills. The upper Sehonghong River (3000 to 3200 m a.s.l.) flows in a westerly direction and is flanked by north- and south-facing slopes reaching 3465 m a.s.l. Sediment is exposed on both the north- and south-facing slopes along the river. Despite uniform regional environmental conditions (geology, topography, climate, vegetation), there is a notable absence of similar north-facing deposits in adjacent upper valley catchments to the north and south of Sehonghong Valley. The upper Sehonghong Valley thus presents somewhat ‘unique' evidence for palaeo-slope mass movement in this alpine region. Thick colluvial deposits are most prominent on the south-facing slopes along the Sehonghong River and occur at altitudes between 3100 m a.s.l. and 3150 m a.s.l. The colluvial mantles are approximately 7 m in thickness, however reach up to 13 m in some areas. Although the north-facing lower valley side-slopes are generally absent of deposits, the notable exception is the thick stratified deposit located a few kilometres upstream. Whilst the south-facing deposits are relatively uniform in nature, the north-facing deposits consist of alternating units of gravel and organic sediment, dated to 36 600 ± 1400 14C yrs BP, and reflecting environmental changes during the Late Pleistocene. Mass wasting deposits support enhanced periglacial activity during the Late Pleistocene, particularly on south-facing slopes, and also where conditions were conducive to enhanced sediment transport on the adjacent north-facing slope of the Sehonghong River. Recent published work has suggested evidence for marginal glaciation in the high Drakensberg within 10 km of the Sehonghong Valley, suggesting that whilst particular environmental settings host deposits classified as glacial moraine, adjacent valleys are occupied by deep (~8 m) valley deposits flanking south-facing slopes. We demonstrate that the variable nature of adjacent valley slope deposits at similar altitudes is a product of a past climate that was within the glacial/periglacial equilibrium zone, and influenced by specific topographic and associated micro-climatic thresholds.

  9. Late Pleistocene biogenic sedimentation in the Gulf of Alaska: A biogeochemical perspective from IODP Expedition 341

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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. Here, we present sedimentologic, physical property, stable isotope, and biogenic opal concentration data from IODP Expedition 341 Sites U1417 and U1419 and identify intervals where diatom ooze lithofacies and geochemical evidence for increased algal productivity are prevalent during the Pleistocene. Sites U1417 and U1419 are located in the center and the margin of the Fe-limited GoA, respectively, and they offer the potential to characterize past changes in biogeochemical cycling during different Pleistocene time intervals. Site U1419 cores were collected from a small slope basin at the edge of the continental shelf. Sediment cores reveal two prominent ~6-m-thick intervals of diatomaceous ooze. Between these intervals are numerous 20-cm-thick sections of biogenic-rich sediment, interbedded with gray mud that commonly contains lonestones. Based on preliminary age models, the two diatom ooze intervals likely correspond to the Holocene and MIS 3, while the intervening interbedded glacigenic and biogenic sediment can broadly be ascribed to MIS 2. Diatomaceous ooze and diatom-rich sediments are generally characterized by lower magnetic susceptibility, natural gamma ray, bulk density, and higher b* color reflectance. Initial C & N concentration and stable isotopic data show elevated concentrations and more positive stable isotope values during the Holocene and MIS 3, which approximate the isotopic signature of modern phytoplankton measured in the GoA. Within the glacial period, the biogenic-rich intervals are also characterized by more positive C and N isotopic values. When combined with the shipboard physical property data, the stable isotopic results are indicative of millennial-scale variations in productivity and/or changes in glacial ice extent in the GoA during the last glacial period. We will discuss these results in the context of an improved isotope stratigraphy and ongoing work examining multiple interglacial productivity variations at Site U1417.

  10. Pleistocene evolutionary history of the Clouded Apollo (Parnassius mnemosyne): genetic signatures of climate cycles and a 'time-dependent' mitochondrial substitution rate.

    PubMed

    Gratton, P; Konopi?ski, M K; Sbordoni, V

    2008-10-01

    Genetic data are currently providing a large amount of new information on past distribution of species and are contributing to a new vision of Pleistocene ice ages. Nonetheless, an increasing number of studies on the 'time dependency' of mutation rates suggest that date assessments for evolutionary events of the Pleistocene might be overestimated. We analysed mitochondrial (mt) DNA (COI) sequence variation in 225 Parnassius mnemosyne individuals sampled across central and eastern Europe in order to assess (i) the existence of genetic signatures of Pleistocene climate shifts; and (ii) the timescale of demographic and evolutionary events. Our analyses reveal a phylogeographical pattern markedly influenced by the Pleistocene/Holocene climate shifts. Eastern Alpine and Balkan populations display comparatively high mtDNA diversity, suggesting multiple glacial refugia. On the other hand, three widely distributed and spatially segregated lineages occupy most of northern and eastern Europe, indicating postglacial recolonization from different refugial areas. We show that a conventional 'phylogenetic' substitution rate cannot account for the present distribution of genetic variation in this species, and we combine phylogeographical pattern and palaeoecological information in order to determine a suitable intraspecific rate through a Bayesian coalescent approach. We argue that our calibrated 'time-dependent' rate (0.096 substitutions/ million years), offers the most convincing time frame for the evolutionary events inferred from sequence data. When scaled by the new rate, estimates of divergence between Balkan and Alpine lineages point to c. 19 000 years before present (last glacial maximum), and parameters of demographic expansion for northern lineages are consistent with postglacial warming (5-11 000 years before present). PMID:18986502

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  12. 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.

  13. Last glacial vegetation of northern Eurasia

    NASA Astrophysics Data System (ADS)

    Allen, Judy R. M.; Hickler, Thomas; Singarayer, Joy S.; Sykes, Martin T.; Valdes, Paul J.; Huntley, Brian

    2010-09-01

    In order to investigate the potential role of vegetation changes in megafaunal extinctions during the later part of the last glacial stage and early Holocene (42-10 ka BP), the palaeovegetation of northern Eurasia and Alaska was simulated using the LPJ-GUESS dynamic vegetation model. Palaeoclimatic driving data were derived from simulations made for 22 time slices using the Hadley Centre Unified Model. Modelled annual net primary productivity (aNPP) of a series of plant functional types (PFTs) is mapped for selected time slices and summarised for major geographical regions for all time slices. Strong canonical correlations are demonstrated between model outputs and pollen data compiled for the same period and region. Simulated aNPP values, especially for tree PFTs and for a mesophilous herb PFT, provide evidence of the structure and productivity of last glacial vegetation. The mesophilous herb PFT aNPP is higher in many areas during the glacial than at present or during the early Holocene. Glacial stage vegetation, whilst open and largely treeless in much of Europe, thus had a higher capacity to support large vertebrate herbivore populations than did early Holocene vegetation. A marked and rapid decrease in aNPP of mesophilous herbs began shortly after the Last Glacial Maximum, especially in western Eurasia. This is likely implicated in extinction of several large herbivorous mammals during the latter part of the glacial stage and the transition to the Holocene.

  14. Sea surface temperatures from the southern Benguela region from the Pliocene and Pleistocene: tracking Agulhas Current input into the SE Atlantic

    NASA Astrophysics Data System (ADS)

    Petrick, B. F.; McClymont, E.; Felder, S.; Lloyd, J. M.; Leng, M. J.

    2011-12-01

    The Pliocene and-Pleistocene epochs provide a way to understand the effect of past climate changes on key ocean currents. Here, we show results from ODP Site1087 (31.28'S, 15.19'E, 1374m water depth) to investigate changes in ocean circulation over the period of the mid-Pliocene warm period 3.0-3.5 Ma and compare these to the time of the 100 kyr Pleistocene glacial cycles. ODP 1087 is located in the South-eastern Atlantic Ocean, outside of the Benguela upwelling region; reconstructing the temperature history of the site will therefore provide an important data set from a part of the ocean that has few orbital-scale and continuous Pliocene temperature reconstructions. ODP 1087 can be used to investigate the history of the heat and salt transfer to the Atlantic Ocean from the Indian Ocean via the Agulhas Retroflection, which plays an important part in the global thermohaline circulation (Lutjeharms, 2007). Climate models and reconstructions for the most recent glacial-interglacial cycles have shown that changes to the strength of the heat transfer may cause major climatic changes and may play a role in transitions from glacial to interglacial events (Knorr & Lohmann, 2003). It is unknown how this transfer reacted to generally warmer global temperatures during the mid-Pliocene. Because the mid-Pliocene is seen as a model for future climate change it might provide a model for ocean circulations in a warmer world. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the history of ODP 1087. The UK37' index records differences in the unsaturated bonds in the C37 alkenones to reconstruct sea surface temperatures (Brassell et al., 1986). We present SSTs generated for the mid-Pliocene Warm period with a resolution of 4000 years. We compare this data to the time of the 100 kyr glacial cycles during the late Pleistocene. Even though ODP 1087 is located outside the Benguela upwelling system, it has lower Pliocene temperatures than sites to the north which are thought to be affected by the upwelling. However, our combination of alkenone and chlorin data indicates a potentially different productivity regime at this site in the Pliocene than exists in the late Pleistocene. To investigate the controls over these results we also present evidence from planktonic foraminifera assemblages to indicate the presence of warm salty Indian Ocean waters to the Atlantic (and thus active Agulhas Leakage in the Pliocene) and/or the presence of nutrient-rich upwelling waters.

  15. Modeling glacial inception with GENIE

    NASA Astrophysics Data System (ADS)

    Rutt, I. C.; Payne, A. J.; Lunt, D. J.; Valdes, P. J.

    2004-12-01

    Glacial inception is difficult to capture accurately in Earth-system models. It has been suggested that inception can occur either when a wide area gains snow cover which persists from year to year, enhanced by the albedo feedback effect, or when mountain glaciers merge to form larger volumes of ice (the mass balance-elevation effect). Insufficient horizontal resolution may explain the difficulty of simulating the latter process, though it is unclear how it would impact on the former. In this study, we consider the problem in the context of a new, modular Earth-system model (GENIE). In the present configuration, GENIE is run with an intermediate-complexity, fully-dynamical atmosphere (T21, seven levels), a high-resolution thermo-mechanical ice-sheet model, a slab ocean and sea-ice model. A novel feature of the ice-sheet model is that it may be configured to run on any number of arbitrary domains simultaneously, and at different resolutions. This enables small-scale topography to be captured within the ice model over particular regions of the Earth's surface, without compromising performance unduly. Because of these difficulties, and specifically because it requires an accurate calculation of mass-balance, the modelling of glacial inception is a stringent test of the model. It also exploits its particular strengths, namely the flexible coupling of a high-resolution ice sheet model with a dynamical atmosphere. The coupling is achieved via a degree-day method mass-balance scheme, forced by daily temperatures and precipitation from the atmospheric model. The ice model performs a lapse-rate correction to account for the high-resolution topography, and returns albedo and topography to the global model annually. The study considers the effects on modelled inception of orbital parameters and CO2 levels, with conditions 115kyr ago serving as a starting-point. A range of sensitivity studies are performed; these results are presented and interpreted in the light of the characteristics of the model.

  16. 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.

  17. Multiple Pleistocene refugia and Holocene range expansion of an abundant southwestern American desert plant species (Melampodium leucanthum, Asteraceae).

    PubMed

    Rebernig, Carolin A; Schneeweiss, Gerald M; Bardy, Katharina E; Schönswetter, Peter; Villaseñor, Jose L; Obermayer, Renate; Stuessy, Tod F; Weiss-Schneeweiss, Hanna

    2010-08-01

    Pleistocene climatic fluctuations had major impacts on desert biota in southwestern North America. During cooler and wetter periods, drought-adapted species were isolated into refugia, in contrast to expansion of their ranges during the massive aridification in the Holocene. Here, we use Melampodium leucanthum (Asteraceae), a species of the North American desert and semi-desert regions, to investigate the impact of major aridification in southwestern North America on phylogeography and evolution in a widespread and abundant drought-adapted plant species. The evidence for three separate Pleistocene refugia at different time levels suggests that this species responded to the Quaternary climatic oscillations in a cyclic manner. In the Holocene, once differentiated lineages came into secondary contact and intermixed, but these range expansions did not follow the eastwardly progressing aridification, but instead occurred independently out of separate Pleistocene refugia. As found in other desert biota, the Continental Divide has acted as a major migration barrier for M. leucanthum since the Pleistocene. Despite being geographically restricted to the eastern part of the species' distribution, autotetraploids in M. leucanthum originated multiple times and do not form a genetically cohesive group. PMID:20670366

  18. Mitochondrial differentiation in a polymorphic land snail: evidence for Pleistocene survival within the boundaries of permafrost

    E-print Network

    Wirth, Thierry

    Mitochondrial differentiation in a polymorphic land snail: evidence for Pleistocene survival within arbustorum; dispersal; mitochondrial DNA; phylogeography; Pleistocene; polymorphism; refugia. Abstract the Pleistocene glaciations depends to a great extent on the speed of expansion. Slow dispersers maintain

  19. Magnetic mineral dissolution in Pleistocene fluvio-lacustrine sediments, Nihewan Basin (North China)

    E-print Network

    Utrecht, Universiteit

    Magnetic mineral dissolution in Pleistocene fluvio-lacustrine sediments, Nihewan Basin (North China magnetism dissolution Nihewan Basin Pleistocene fluvio-lacustrine sediment The Nihewan fluvio-lacustrine sequence (North China) has recorded late Pliocene­Pleistocene climatic and environmental changes

  20. 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

  1. 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.

  2. Pleistocene vertebrates of the Yukon Territory

    NASA Astrophysics Data System (ADS)

    Harington, C. R.

    2011-08-01

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

  3. The significance of ice-rafted debris in Sturtian glacial successions

    NASA Astrophysics Data System (ADS)

    Le Heron, D. P.

    2015-06-01

    Globally, Sturtian (early Cryogenian) glacial deposits are well expressed, and belong to the oldest Neoproterozoic icehouse Earth event. The evidence for glaciation typically includes the phenomena such as striated pavements, striated clasts in diamictites, and abundant dropstones. More problematic, and potentially more significant, are intercalated deposits that exhibit no apparent evidence of a glacial influence on deposition. These apparently non-glacially-influenced intervals may represent deposition during interglacial periods, or at times when ice sheets transitioned to cold-based ice masses where sediment advection into basins was suppressed. Here, using three case studies from South Australia, northern Namibia, and Death Valley (USA), we show that many IRD-free intervals occur at the top of backstepping successions, where they are best interpreted as glacial minima deposits. In other cases, the volume of IRD in a succession shows less distinct increases and decreases upsection. Rhythmic intercalation of IRD-bearing and IRD-free intervals with glaciomarine turbidites can also be observed. These latter examples may be interpreted to record variations in debris content of ice margins, switch on/switch off of ice streams, or simply dynamic oscillation of a hinterland ice margin.

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

    PubMed

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

    2013-05-01

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

  5. Mite dispersal among the Southern Ocean Islands and Antarctica before the last glacial maximum

    PubMed Central

    Mortimer, E.; Jansen van Vuuren, B.; Lee, J. E.; Marshall, D. J.; Convey, P.; Chown, S. L.

    2011-01-01

    It has long been maintained that the majority of terrestrial Antarctic species are relatively recent, post last glacial maximum, arrivals with perhaps a few microbial or protozoan taxa being substantially older. Recent studies have questioned this ‘recolonization hypothesis’, though the range of taxa examined has been limited. Here, we present the first large-scale study for mites, one of two dominant terrestrial arthropod groups in the region. Specifically, we provide a broad-scale molecular phylogeny of a biologically significant group of ameronothroid mites from across the maritime and sub-Antarctic regions. Applying different dating approaches, we show that divergences among the ameronothroid mite genera Podacarus, Alaskozetes and Halozetes significantly predate the Pleistocene and provide evidence of independent dispersals across the Antarctic Polar Front. Our data add to a growing body of evidence demonstrating that many taxa have survived glaciation of the Antarctic continent and the sub-Antarctic islands. Moreover, they also provide evidence of a relatively uncommon trend of dispersals from islands to continental mainlands. Within the ameronothroid mites, two distinct clades with specific habitat preferences (marine intertidal versus terrestrial/supralittoral) exist, supporting a model of within-habitat speciation rather than colonization from marine refugia to terrestrial habitats. The present results provide additional impetus for a search for terrestrial refugia in an area previously thought to have lacked ice-free ground during glacial maxima. PMID:20943685

  6. 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.

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  9. Astronomical forcing, insolation and millennial-scale climate variability: evidence from the North Atlantic Ocean (IODP Expedition 306, Site U1313) during the Early-Middle Pleistocene

    NASA Astrophysics Data System (ADS)

    Ferretti, Patrizia; Crowhurst, Simon; Naafs, David; Barbante, Carlo

    2015-04-01

    Since the seminal work by Hays, Imbrie and Shackleton (1976), a plethora of studies mostly based on marine sediments collected during DSDP-ODP-IODP Expeditions has demonstrated a correlation between orbital variations and climatic change. However, information on how changes in orbital boundary conditions affected the frequency and amplitude of millennial-scale climate variability is still fragmentary. Here we examine the record of climatic conditions from MIS 23 to 17 (c. 920-670 ka) using high-resolution stable isotope records from benthic and planktonic foraminifera from a sedimentary sequence in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313) in order to evaluate the climate system's response in the millennial band to known orbitally induced insolation changes. Special emphasis is placed on Marine Isotope Stage (MIS) 19, an interglacial centred at around 785 ka during which the insolation appears comparable to the current orbital geometry: MIS 19 is characterised by a minimum of the 400-kyr eccentricity cycle, subdued amplitude of precessional changes, and small amplitude variations in insolation making this marine isotopic stage a potential astronomical analogue for the Holocene and its future evolution, if this remains governed by natural forcing (Loutre and Berger 2000). Benthic and planktonic foraminiferal oxygen isotope values indicate relatively stable conditions during the peak warmth of MIS 19, but sea-surface and deep-water reconstructions start diverging during the transition towards the glacial MIS 18, when large, cold excursions disrupt the surface waters whereas low amplitude millennial scale fluctuations persist in the deep waters as recorded by the oxygen isotope signal (Ferretti et al., 2015). The glacial inception occurred at ˜779 ka, in agreement with an increased abundance of tetra-unsaturated alkenones, reflecting the influence of icebergs and associated meltwater pulses and high-latitude waters at the study site. Using a variety of time series analysis techniques, we evaluate the evolution of millennial climate variability in response to changing orbital boundary conditions during the early-middle Pleistocene. Suborbital variability in both surface- and deep-water records is mainly concentrated at a period of ˜11 kyr and, additionally, at ˜5.8 and ˜3.9 kyr in the deep ocean; these periods are equal to harmonics of precession band oscillations. The fact that the response at the 11 kyr period increased over the same interval during which the amplitude of the response to the precessional cycle increased supports the notion that most of the variance in the 11 kyr band in the sedimentary record is nonlinearly transferred from precession band oscillations. Considering that these periodicities are important features in the equatorial and intertropical insolation, these observations are in line with the view that the low-latitude regions play an important role in the response of the climate system to the astronomical forcing. We conclude that the effect of the orbitally induced insolation is of fundamental importance in regulating the timing and amplitude of millennial scale climate variability. Ferretti P., Crowhurst S.J., Naafs B.D.A., Barbante C., 2015. Quaternary Science Reviews 108, 95-110. Hays J.D., Imbrie J., Shackleton N.J., 1976. Science 194, 1121-1132. Loutre M.F., Berger A., 2000. Climatic Change 46, 61-90.

  10. Nearly synchronous climate change in the Northern Hemisphere during the last glacial termination

    USGS Publications Warehouse

    Benson, L.; Burdett, J.; Lund, S.; Kashgarian, Michaele; Mensing, S.

    1997-01-01

    The climate of the North Atlantic region underwent a series of abrupt cold/warm oscillations when the ice sheets of the Northern Hemisphere retreated during the last glacial termination (17.711.5 kyr ago). Evidence for these oscillations, which are recorded in European terrestrial sediments as the Oldest Dryas/Bolling/Older Dryas/Allerod/Younger Dryas vegetational sequence, has been found in Greenland ice cores. The geographical extent of many of these oscillations is not well known, but the last major cold event (the Younger Dryas) seems to have been global in extent. Here we present evidence of four major oscillations in the hydrological balance of the Owens basin, California, that occurred during the last glacial termination. Dry events in western North America occurred at approximately the same time as cold events recorded in Greenland ice, with transitions between climate regimes in the two regions taking place within a few hundred years of each other. Our observations thus support recent climate simulations which indicate that cooling of the North Atlantic Ocean results in cooling of the North Pacific Ocean which, in turn, leads to a drier climate in western North America.

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  12. Geodesy: Modeling Earth's Post-Glacial Rebound

    NASA Astrophysics Data System (ADS)

    Spada, Giorgio; Antonioli, Andrea; Boschi, Lapo; Brandi, Valter; Cianetti, Spina; Galvani, Gabriele; Giunchi, Carlo; Perniola, Bruna; Agostinetti, Nicola Piana; Piersanti, Antonio; Stocchi, Paolo

    2004-02-01

    Efforts to mathematically model the Earth's post-glacial rebound, or, in general, long-term planetary-scale viscoelastic deformations, have been ongoing for several decades. Unfortunately, research in the post-glacial rebound community has not been characterized by much exchange of knowledge. Groups around the world have developed their code independently, sometimes with profoundly different approaches, occasionally leading to inconsistent results [e.g., Boschi et al., 1999]. Postglacial Rebound Calculator (TABOO) is a post-glacial rebound software that is being made freely available (through Samizdat Press at http://samizdat.mines.edu/taboo/)in the hope that it might become a common reference for all post-glacial rebound researchers. TABOO is portable and has been tested on Unix, Linux, and Windows systems; all it requires is a Fortran90 compiler supporting quadruple precision. The software is easy to use. It comes with a detailed guide that can work as a quick reference cookbook, and it is also accompanied by a textbook, The Theory Behind TABOO, collecting the most significant theoretical results from post-glacial rebound literature. TABOO is not a ``black-box,'' although it may easily be used as such. The entire source code is provided and should be easy to understand for intermediate-level Fortran programmers.

  13. 26Al/10Be burial ages for a Pleistocene terrace in the Vienna Basin, Austria

    NASA Astrophysics Data System (ADS)

    Braumann, S.; Fiebig, M.; Neuhuber, S.; Schaefer, J. M.; Haeuselmann, P.; Schwartz, R.; Finkel, R. C.

    2014-12-01

    The Vienna Basin in the northeastern part of Austria between the Eastern Alps and the West Carpathians is a pull-apart basin crossed by the Danube river. The structure is filled with marine and terrestrial sediments showing thicknesses of up to 6 km. An increase in glacial melt water discharges, typically linked to high productivity of Alpine glaciers, had an essential impact on the formation of the investigated terrace. The scale of erosion and sediment transport translates to deposition rates in the foreland and is influenced by the magnitude of melt water discharges in Alpine catchment areas. Variations in layer characteristics (i.e. grain size, sorting, thickness) are an indicator for glacial pulses. Burial dates of ten quartz pebbles originating from the Gaenserndorfer terrace, situated in the northeastern part of the basin, set time dependent constraints on the required hydrological regime for mobilization, transport and sedimentation of bedloads and allow relating the deposition of glacial sediments to past glacial periods. But the geomorphic evolution of the Vienna Basin was not only determined by sedimentation processes. A number of irregularities manifest that tectonics affected the area as well: Terrace tilts are dipping against the slope of the Danube and offsets of some decameters between sediment layers showing the same facies, but located several kilometers apart from each other, could be identified. An extensive Miocene fault system was partly reactivated during the Middle Pleistocene and could have caused the formation of these discontinuities. It is of great interest to discriminate impacts on the area due to deposition from morphological elements formed by seismic events. The preliminary burial ages afford for putting the sampled terrace segment into a coherent geochronological context and provide a dataset to compare ages of the Gaenserndofer terrace to ages of sediment layers at other locations within the basin in order to either validate or reject the hypothesis that they belong to the same stratigraphical unit. The dating of the terrace helps to analyze the processes dominating this complex area and can contribute to a better understanding of the prevalent climate conditions in the Alps, the Alpine foreland and the inner Alpine basins during the Quaternary.

  14. The End Pleistocene Extinction Event - What Caused It?

    NASA Astrophysics Data System (ADS)

    Becker, L.; Poreda, R.; Kennett, J.; West, A.; Wolbach, W.

    2007-05-01

    It is well established that the last catastrophic faunal extinction in the geologic past coincided with the end of the Pleistocene during the deglaciation between the last glacial episode and the present Holocene interglacial. The cause of this extinction has been debated for many years but remains highly controversial in part because of limitations of available data, but also because the two major hypotheses that have been long invoked, climate change and human overhunting, have continued to present significant problems. Recently, Firestone et al. [1] have reported strong evidence for an extraterrestrial (ET) impact including peak abundances of metallic microspherules and magnetic grains with elevated iridium, glass-like carbon, carbon microspherules, soot and charcoal in a carbon-rich black layer dating close to ~12.9 ka (referred to as Younger Dryas Black Layer or YDB) in numerous terminal Clovis-age sites across North America. To assess the YDB impact hypothesis and its potential effects on the megafauna and humans in North America [2-4], we have analyzed several well-dated suites of samples in search of fullerenes with ET noble gases and other impact debris (e.g. microspherules). These sites include Daisy Cave (DC) on California's San Miguel Island, Murray Springs (MS) in Arizona and Blackwater Draw (BWD) in New Mexico, all well known previously described archaeological and paleontological sites, with established chronologies spanning the YDB (~12.9 k) [5-7]. To further assess the environmental effects of the impact on the Pleistocene fauna and human activity, we examined the YDB layer at each of these locations for evidence of wildfires triggered by the ET event. If there were wildfires, a group of high molecular weight aromatic compounds or polycyclic aromatic hydrocarbons (PAHs) should be present in the associated soot and charcoal material within the YDB. By examining the distributions of the PAHs, the source of these compounds, wildfire or human activity, can be determined. The recognition of global wildfires at the time of the K/T impact event was first proposed based on the presence of elemental carbon (mainly soot) associated with ET tracers in the boundary layer [8-10]. Soot produced by severe wildfires at the YDB would have severely affected the ecological niches, reduced primary productivity, eliminated food sources and added to the effects of the ejecta cloud [8]. Here, we present our evidence in support of an ET impact and its effects on the environment at the YDB and compare these results to other well-known impact events in the geologic record. [1] Firestone et al. (2006) Proceeding of the National Academies of Science (submitted). [2] Martin, P.S. Twilight of the Mammoths Ice Age Extinctions and the Rewilding of America. University of California Press, Berkeley 250 pp. (2005). [3] Haynes, C.V. (2002) World Archeology 33,391-416. [4] Grayson, D. K. and Meltzer, D.J. (2002) Journal of World Prehistory 16, 313-359. [5] Erlandson, J.M. et al. (1996) Radiocarbon 38,355-373. [6] Haynes, C.V.et al., (1999) Geoarcheology: An International Journal, 14, 455-470.[7] Tayler, R.E., Haynes, C.V. and Stuvier, M. (1996) Antiquity 70, 515-525. [8] Wolbach, W.S., Lewis, R.S. and Anders, L.E. (1985) Science 230,167-170. [9] Wolbach et al. (1988) Nature 334,57-669. [10] Venkatesan, M.I. and Dahl, J. (1989) Nature 338,57-60.

  15. 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.

  16. 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

  17. Chronostratigraphical investigations on Pleistocene fluvioglacial terraces of NW-Austria

    NASA Astrophysics Data System (ADS)

    Terhorst, B.

    2009-04-01

    Investigations on paleopedology and Quaternary stratigraphy were carried out in the area of fluvioglacial terraces of the rivers Inn and Traun/Enns. Research projects have been financed by the German Research Foundation (DFG) and the ICSU Grant Programme. Detailed studies were carried out on paleosols and loess sequences of different ages. The investigations of the research group were focused on loess/paleosol sequences located on top of Riss terraces (OIS 6 and older) as well as in areas with Mindel and Günz terraces. Loess records of the last glacial/interglacial cycle can be well observed in the study areas. Generally, the Eemian soil (O/S 5e) is developed as a reddish Bt-horizon in fluvioglacial gravels. U/Th-datings of calcites in the fluvioglacial sediments are indicating that soil formation took place in the catchment area about 113.000 ± 4.400 ka (Terhorst et al., 2002). The interglacial paleosol was truncated and a redeposited colluvial layer was deposited on top of the Bt-horizons containing charcaol with characteristic relicts of coniferous trees. After this land surface destabilisation phase, sedimentation of loess became the predominant process. Pedogenesis in form of a brown paleosol occurred, which partly has been redeposited. The pedocomplex is characterized by intense bioturbation of steppe animals. OSL-datings show that this part of the sequence belong to the Middle Würmian stage. The pedocomplex is overlain by a Cambisol corresponding to the youngest Middle Würmian interstadial. The paleosol is covered by thick loess deposits of the Upper Pleniglacial. Well-developed Tundragleysols subdivide the loess deposits. The uppermost soil corresponds to the Holocene Luvisol that includes hydromorphic properties. Older fluvioglacial terraces of Mindel and Günz age (in the classical stratigraphy) show a completely different structure of the covering layers (c.f. Kohl, 1999). In this case, several thick interglacial paleosols are embedded within records of loess loam and redeposited material. However, four to five interglacial paleosols are developed inside the studied sequences. Paleomagnetical investigations are leading to the assumption that different Middle Pleistocene excursions could provide chronological data in the future. Terhorst, B., 2007. Korrelation von mittelpleistozänen Löß-/Paläobodensequenzen in Oberösterreich mit einer marinen Sauerstoffisotopenkurve. E & G, Quaternary Science Journal, 56/3: 172 - 185. Terhorst, B., Frechen, M. and Reitner, J., 2002 Chronostratigraphische Ergebnisse aus Lößprofilen der Inn- und Traun-Hochterrassen in Oberösterreich. - Z. Geomorph. N.F., Suppl.-Bd., 127: 213 -232, Berlin, Stuttgart (Gebr. Bornträger).

  18. Pleistocene climate change promoted rapid diversification of aquatic invertebrates in

    E-print Network

    : The Pleistocene Ice Ages were the most recent geohistorical event of major global impact, but their consequences was the Pleistocene glaciations, or Ice Ages, which represent the largest expansion of cold climates since the Permian by the processes of speci- ation and extinction, whose rates vary depending on re- gion, environment, taxonomic

  19. Amazon Fan biomarker evidence against the Pleistocene rainforest refuge hypothesis?

    E-print Network

    Jones, Peter JS

    Amazon Fan biomarker evidence against the Pleistocene rainforest refuge hypothesis? MARK A. MASLIN; biomarker; Pleistocene; rainforest. Introduction Tropical rainforests display a level of biodiversity rainforest refuge hypothesis' (e.g. Haffer, 1969; Haffer and Prance, 2001). It has been suggested that

  20. Simulating the climate of the last glacial cycle Steve Phipps

    E-print Network

    Phipps, Steven J.

    Simulating the climate of the last glacial cycle Steve Phipps 3 December 2003 PhD seminar Simulating the climate of the last glacial cycle Steve Phipps, 3 December 2003 #12;Supervisors: · A the climate of the last glacial cycle Steve Phipps, 3 December 2003 #12;Overview · Background · Aims

  1. 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

  2. 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

  3. 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

  4. High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): O correlation between a Gerzensee-stack and NGRIP

    E-print Network

    Bern, Universität

    High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): 18 O-water lake marl from Gerzensee, Switzerland, in order to evaluate major and minor climatic oscillations changes. The oxygen- isotopic composition of inorganic lake carbonate is mainly in uenced by (1) the 18 O

  5. High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): O correlation between a Gerzensee-stack and NGRIP

    E-print Network

    Gilli, Adrian

    High-resolution late-glacial chronology for the Gerzensee lake record (Switzerland): 18 O-water lake marl from Gerzensee, Switzerland, in order to evaluate major and minor climatic oscillations changes. The oxygen- isotopic composition of inorganic lake carbonate is mainly influenced by (1) the 18 O

  6. 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

  7. 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.

  8. First Global Climate Model Simulations of the M2 Pliocene Glacial

    NASA Astrophysics Data System (ADS)

    Dolan, A.; Haywood, A.; Hunter, S. J.; Tindall, J.; Valdes, P. J.

    2013-12-01

    The Pliocene Epoch (5.2 to 2.6 Ma) and specifically the PRISM interval (3.0 to 3.3 Ma) have frequently been targeted to investigate warm intervals in Earth history (e.g. Haywood et al., 2013). However, climate variability within the Pliocene is often overlooked. Although not as dramatic as the glacial and interglacial cycles that typified the Pleistocene, the Pliocene also exhibited climate variability and periods which were apparently cooler than modern (Lisiecki and Raymo, 2005). Of particular interest is the major cooling event that occurred around 3.3 Ma during Marine Isotope Stage (MIS) M2. This 'Pliocene glacial' punctuates an otherwise relatively warm background climate and has been referred to as a failed attempt of the climate to reach a full glacial state (De Schepper et al., 2009; Haug and Tiedemann, 1998). The onset of full Northern Hemisphere (NH) glaciation finally occurred at the end of the Pliocene (~ 2.75 Ma). Although numerous temperature reconstructions from around the world's oceans tend to capture the MIS M2 cooling event, the exact nature of M2 remains enigmatic. Sea level records vary but suggest a maximum sea level drop of ~65 m compared to modern, which in itself is significant enough to necessitate the growth of a NH ice sheet (Dwyer and Chandler, 2009). Previous ice sheet modelling suggests that ~8 m sea level equivalent (SLE) ice could be stored on Antarctica (Pollard and DeConto, 2009) and this larger ice sheet (compared to modern) is potentially supported by the increase in ice-rafted debris (IRD) found offshore of East Antarctica during this time (Passchier, 2011). IRD in the North Atlantic would suggest the presence of an ice sheet on Greenland (e.g. Kleiven et al., 2002), but the locations of other ice caps in the NH are not determined due to the destructive nature of subsequent Pleistocene ice sheet advances. Moreover, recent evidence questions whether the climate in the NH was favourable at all for the initiation of ice sheets over North America at the M2 glacial (Brigham-Grette et al., 2013). We present the first fully coupled atmosphere-ocean climate model simulations of the M2 glacial event in order to investigate the climate effect of potential ice sheet scenarios during this time. Our climate model, HadCM3 is run with dynamic vegetation, altered CO2 and orbital configurations. Possible ice sheet configurations are based on Quaternary analogues and represent large, medium and small (i.e. restricted to Greenland) M2 ice sheet scenarios in the NH. We compare our simulations with available terrestrial (e.g. biomes, precipitation and warm month temperatures from Brigham-Grette et al., 2013) and marine reconstructions (DeSchepper et al., 2009) to provide guidance as to which experimental set-up might offer the most compatible reconstruction of global climate during the M2 glaciation.

  9. 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 ...

  10. Short Communication Plio-pleistocene diversification and connectivity between mainland and

    E-print Network

    Keogh, Scott

    Short Communication Plio-pleistocene diversification and connectivity between mainland, are congruent with Plio-pleistocene climatic variations. Two highly divergent genetic lineages within Drysdalia in the Pleistocene. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Pliocene and Pleistocene climatic

  11. Built for Speed: Pleistocene Climate Variation and the Origin of Human Culture

    E-print Network

    Richerson, Peter J.

    Built for Speed: Pleistocene Climate Variation and the Origin of Human Culture Peter J. Richerson that the Pleistocene climatic fluctuations are responsible for the evolution of human anatomy and cognition is satisfactory. The "Pleistocene hypothesis", as proposed, does not explain how Pleistocene fluctuations favor

  12. Migration of the Antarctic Polar Front through the mid-Pleistocene transition: evidence and climatic implications

    E-print Network

    Naveira Garabato, Alberto

    Migration of the Antarctic Polar Front through the mid-Pleistocene transition: evidence degrees of latitude in the early/mid Pleistocene. The mid-Pleistocene transition marks a stepwise minimum southward return to a locus similar to its modern position and further south than any mid-Pleistocene locus

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  14. Late glacial to post glacial sea levels in the Western Indian Ocean

    Microsoft Academic Search

    G. F. Camoin; L. F. Montaggioni; C. J. R. Braithwaite

    2004-01-01

    Late glacial to post glacial sea-level changes provide direct evidence of the progress of melting of large ice sheets during the last deglaciation but, although the correlation between ice and ocean volumes is incontrovertible, the causal link is commonly obscured. Local effects including tectonics, isostatic and hydroisostatic responses and equatorial ocean-syphoning impose additional signals that hide the true picture.A detailed

  15. A late-glacial and post-glacial history of amsoldingersee and vicinity, Switzerland

    Microsoft Academic Search

    André Lotter; Mary M. Boucherle

    1984-01-01

    A multidisciplinary approach was used to study the Late-Glacial and Post-Glacial history of a Swiss Plateau lake. Pollen analysis\\u000a revealed thirteen major changes in vegetation. A series of coordinated fluctuations in vegetation and lacustrine trophic status\\u000a were found, which were partially interpreted as the result of climatic changes. Oxygen isotope ratios revealed three major\\u000a shifts in temperature which correspond with

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

    Microsoft Academic Search

    Brian F. Atwater

    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 the self-dumping lake was glacial Lake Missoula, Montana, because the floods accord with inferred

  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, Robert 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. Conditional Instability of the Glacial Deep Ocean

    Microsoft Academic Search

    J. F. Adkins; C. Pasquero

    2005-01-01

    Deep-sea sediment pore fluid results indicate that the Last Glacial Maximum (LGM) deep ocean was at or near the freezing point and very salty. In contrast to the modern, these salty waters were formed in the Southern Ocean and they show how salt, not heat, dominated abyssal density gradients at the LGM. To the degree that these data are representative

  19. Bacterial recovery from ancient glacial ice

    Microsoft Academic Search

    Brent C. Christner; Ellen Mosley-Thompson; Lonnie G. Thompson; John N. Reeve

    2003-01-01

    Summary Ice that forms the bottom 18 m of a 308 m ice core drilled from the Guliya ice cap on the Qinghan-Tibetan plateau in Western China is over 750 000 years old and is the oldest glacial ice known to date. Fourteen bacterial isolates have been recovered from samples of this ice from ~ ~ ~ ~ 296 m

  20. Time reversal location of glacial earthquakes

    Microsoft Academic Search

    Carène Larmat; Jeroen Tromp; Qinya Liu; Jean-Paul Montagner

    2008-01-01

    In 2003, Ekström et al. reported the detection and location of a new class of earthquakes occurring in the polar regions of the Earth. The proposed source mechanism involves large and sudden sliding motions of glaciers, which gave the name ``glacial earthquakes'' to these events. In this study we localize some of these earthquakes with a time reversal mirror (TRM)

  1. Time reversal location of glacial earthquakes

    Microsoft Academic Search

    Carène Larmat; Jeroen Tromp; Qinya Liu; Jean-Paul Montagner

    2008-01-01

    In 2003, Ekström et al. reported the detection and location of a new class of earthquakes occurring in the polar regions of the Earth. The proposed source mechanism involves large and sudden sliding motions of glaciers, which gave the name “glacial earthquakes” to these events. In this study we localize some of these earthquakes with a time reversal mirror (TRM)

  2. Lethal interpersonal violence in the middle pleistocene.

    PubMed

    Sala, Nohemi; Arsuaga, Juan Luis; Pantoja-Pérez, Ana; Pablos, Adrián; Martínez, Ignacio; Quam, Rolf M; Gómez-Olivencia, Asier; Bermúdez de Castro, José María; Carbonell, Eudald

    2015-01-01

    Evidence of interpersonal violence has been documented previously in Pleistocene members of the genus Homo, but only very rarely has this been posited as the possible manner of death. Here we report the earliest evidence of lethal interpersonal violence in the hominin fossil record. Cranium 17 recovered from the Sima de los Huesos Middle Pleistocene site shows two clear perimortem depression fractures on the frontal bone, interpreted as being produced by two episodes of localized blunt force trauma. The type of injuries, their location, the strong similarity of the fractures in shape and size, and the different orientations and implied trajectories of the two fractures suggest they were produced with the same object in face-to-face interpersonal conflict. Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill. This finding shows that the lethal interpersonal violence is an ancient human behavior and has important implications for the accumulation of bodies at the site, supporting an anthropic origin. PMID:26018668

  3. Lethal Interpersonal Violence in the Middle Pleistocene

    PubMed Central

    Sala, Nohemi; Arsuaga, Juan Luis; Pantoja-Pérez, Ana; Pablos, Adrián; Martínez, Ignacio; Quam, Rolf M.; Gómez-Olivencia, Asier; Bermúdez de Castro, José María; Carbonell, Eudald

    2015-01-01

    Evidence of interpersonal violence has been documented previously in Pleistocene members of the genus Homo, but only very rarely has this been posited as the possible manner of death. Here we report the earliest evidence of lethal interpersonal violence in the hominin fossil record. Cranium 17 recovered from the Sima de los Huesos Middle Pleistocene site shows two clear perimortem depression fractures on the frontal bone, interpreted as being produced by two episodes of localized blunt force trauma. The type of injuries, their location, the strong similarity of the fractures in shape and size, and the different orientations and implied trajectories of the two fractures suggest they were produced with the same object in face-to-face interpersonal conflict. Given that either of the two traumatic events was likely lethal, the presence of multiple blows implies an intention to kill. This finding shows that the lethal interpersonal violence is an ancient human behavior and has important implications for the accumulation of bodies at the site, supporting an anthropic origin. PMID:26018668

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

    USGS Publications Warehouse

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

    2008-01-01

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

  5. 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

  6. Evidence for prolonged El Nino-like conditions in the Pacific during the Late Pleistocene: a 43 ka noble gas record from California groundwaters

    USGS Publications Warehouse

    Kulongoski, J.T.; Hilton, David R.; Izbicki, J.A.; Belitz, K.

    2009-01-01

    Information on the ocean/atmosphere state over the period spanning the Last Glacial Maximum - from the Late Pleistocene to the Holocene - provides crucial constraints on the relationship between orbital forcing and global climate change. The Pacific Ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes. Through targeting groundwaters in the Mojave Desert, California, we show that noble gas derived temperatures in California averaged 4.2 ?? 1.1 ??C cooler in the Late Pleistocene (from ???43 to ???12 ka) compared to the Holocene (from ???10 to ???5 ka). Furthermore, the older groundwaters contain higher concentrations of excess air (entrained air bubbles) and have elevated oxygen-18/oxygen-16 ratios (??18O) - indicators of vigorous aquifer recharge, and greater rainfall amounts and/or more intense precipitation events, respectively. Together, these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the Mojave Desert from ???43 to ???12 ka. We suggest that during the Late Pleistocene, the Pacific ocean/atmosphere state was similar to present-day El Nino-like patterns, and was characterized by prolonged periods of weak trade winds, weak upwelling along the eastern Pacific margin, and increased precipitation in the southwestern U.S.

  7. 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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Chao, Luo; Zicheng, Peng; Dong, Yang; Weiguo, Liu; Zhaofeng, Zhang; Jianfeng, He; Chenlin, Chou

    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.

  10. 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.

  11. Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition

    PubMed Central

    Dong, Yajie; Wu, Naiqin; Li, Fengjiang; Huang, Linpei; Wen, Wenwen

    2015-01-01

    The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45–63 ?m quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL) samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3–4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast. PMID:26186443

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

    USGS Publications Warehouse

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

    2004-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  14. 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.

  15. Neutrino oscillations

    SciTech Connect

    Simkovic, Fedor [Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska dolina, SK-84248 Bratislava (Slovakia)

    2007-11-26

    The field of neutrino oscillations is introduced. The basic elements of the theory of neutrino oscillations in vacuum and matter are presented. The history, current status of neutrino oscillations as well as the prospects for the next generation of neutrino experiments are briefly reviewed.

  16. 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

  17. Vegetation responses to climate changes during the penultimate glacial period (marine isotope stage 6) in southern Europe

    NASA Astrophysics Data System (ADS)

    Roucoux, Katy; Margari, V.; Lawson, I. T.; Tzedakis, P. C.

    2010-05-01

    Like the last glacial, the penultimate glacial interval (MIS 6, 185,000 to 132,000 years before present) was characterised by increasing continental ice volume and decreasing concentrations of atmospheric greenhouse gases. However, greater orbital eccentricity during MIS 6 resulted in precessional-scale insolation changes of higher amplitude. This led to some unexpected combinations of climatic boundary conditions such as the high northern hemisphere summer insolation but relatively large ice volume and low atmospheric carbon dioxide concentrations of marine isotopic event 6.5. Records of regional climatic responses to different combinations of climatic forcing factors, in the form of pollen records of vegetation change, can contribute to our understanding of which factors determine conditions at the Earth's surface. Few palaeoecological records cover the penultimate glacial in detail and hence environmental and climatic responses during this interval are not yet well known. At Lake Ioannina, NW Greece, records of the last two glacial intervals are preserved at the same site enabling comparisons of vegetation responses to be made between periods with differing orbital configurations while keeping site variables constant. Our new palynological record spans the penultimate glacial interval at centennial scale resolution and represents the most detailed terrestrial record of this interval to date. Vegetation development throughout the glacial period indicates long-term cooling and drying reflecting the overall decline of northern hemisphere summer insolation and accumulation of large-northern hemisphere ice sheets, as expected. Conditions in NW Greece at the penultimate glacial maximum (PGM) appear to have been colder and drier than during the Last Glacial Maximum, consistent with records of lower Mediterranean sea surface temperature and greater extent of the European ice sheet at the PGM. During the early part of MIS 6, however, it appears that the high amplitude changes in insolation are not translated into high amplitude changes in vegetation and climate at Ioannina. Millennial-scale expansions and contractions of tree populations indicative of oscillations in temperature and moisture availability are recorded but they appear to have been more subdued than their counterparts during the last glacial. This supports the presence of non-linearity in the link between orbital-scale insolation forcing and regional climate.

  18. Multiple glacial refugia in the North American Arctic: inference from phylogeography of the collared lemming (Dicrostonyx groenlandicus).

    PubMed Central

    Fedorov, Vadim B; Stenseth, Nils Chr

    2002-01-01

    Cryptic northern refugia beyond the ice limit of the Pleistocene glaciations may have had significant influence on the current pattern of biodiversity in Arctic regions. In order to evaluate whether northern glacial refugia existed in the Canadian Arctic, we examined mitochondrial DNA phylogeography in the northernmost species of rodents, the collared lemming (Dicrostonyx groenlandicus) sampled across its range of distribution in the North American Arctic and Greenland. The division of the collared lemming into the Canadian Arctic and eastern Beringia phylogroups does not support postglacial colonization of the North American Arctic from a single eastern Beringia refugium. Rather, the phylogeographical structure and sparse fossil records indicate that, during the last glaciation, some biologically significant refugia and important sources of postglacial colonization were located to the northwest of the main ice sheet in the Canadian Arctic. PMID:12396480

  19. 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.

  20. North Atlantic Bottom Water Temperature and Ice Volume Records during the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Ford, H. L.; Raymo, M. E.

    2014-12-01

    During the Mid-Pleistocene Transition (MPT), climate cyclicity changed from dominantly 41 thousand year cycles to 100 thousand year cycles in the absence of any obvious orbital forcing. Currently, only two high-resolution bottom water temperature records based on the Mg/Ca values of benthic foraminifera exist and these data record fundamentally different trends across the MPT. These Mg/Ca records have been coupled with oxygen stable isotope records to separate out the effects of temperature and ice volume signals. The DSDP Site 607 record from the North Atlantic suggests bottom water temperature cooled prior to and during the MPT and that global ice volume gradually increased across this interval (Sosdian and Rosenthal, 2009). In contrast, the Elderfield et al. (2012) IODP Site 1123 record from the South Pacific suggests near freezing bottom water temperatures occurred during glacial intervals over the entire length of the 1.5 Myr record and that an abrupt increase in ice volume occurred at ~0.9 Ma (MIS22). Here we present Mg/Ca records from the North Atlantic DSDP Site 607 and ODP Site 664 based on Uvigerina spp. and use this data to construct a comprehensive view of bottom water temperature and deep ocean ventilation from the North Atlantic across the MPT. Our Uvigerina spp. record from site 607 is similar to the Sosdian and Rosenthal (2009) record and also suggests a long-term cooling trend in glacial and interglacial bottom water temperature prior to the MPT. Before 900 ka and after 600 ka, sites 607 and 664 vary from ?13C-enriched, warm northern-component-type water to ?13C-depleted, cold southern-component water which suggests strong glacial-interglacial water mass variability. However preliminary analyses indicate from 600-900 ka, ?13C-depleted, cold southern-component water flooded the N. Atlantic suggesting weaker North Atlantic Deep Water formation during the MPT. This suggests changes in the character and strength of bottom water circulation may have contributed and/or responded to the MPT.

  1. Asthenospheric ice-load effects in a global dynamical-system model of the Pleistocene climate

    SciTech Connect

    Saltzman, B.; Verbitsky, M.Ya. [Yale Univ., New Haven, CT (United States)

    1992-10-01

    In a previous dynamical model the late Cenozoic climate variations were simulated, taking into account free and forced variations of atmospheric carbon dioxide acting in concert with changes in global ice mass and the deep ocean thermal state, all under the influence of the known earth-orbital radiative changes. This model is now extended by adding another relevant variable, bedrock/asthenosphere depression, including its associated ice-calving effects. Within the context of this extended model we (1) demonstrate the main results of previous bedrock/ice sheet models in what we believe is the simplest possible manner, (2) show how these previous models can exhibit the mid-Pleistocene transition with the inclusion of CO{sub 2} effects, (3) discuss the limitations of these previous bedrock models, and (4) illustrate the possibility of removing some of these limitations and accounting for further aspects of the paleoclimate record by using the full dynamical system that includes forced and free effects of CO{sub 2}, as well as effects of bedrock depression and Milankovitch forcing. As one example of a new possibility, with bedrock effects included in the full system we can obtain a solution characterized by irregularly spaced, intermittent episodes in which the behavior is dominated either by near-40 kyr period oscillations or by near-100 kyr periods (such as prevailed over the Pleistocene). 27 refs., 15 figs., 1 tab.

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

    PubMed

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

    2003-12-01

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

  3. Male strategies and Plio-Pleistocene archaeology.

    PubMed

    O'Connell, J F; Hawkes, K; Lupo, K D; Blurton Jones, N G

    2002-12-01

    Archaeological data are frequently cited in support of the idea that big game hunting drove the evolution of early Homo, mainly through its role in offspring provisioning. This argument has been disputed on two grounds: (1) ethnographic observations on modern foragers show that although hunting may contribute a large fraction of the overall diet, it is an unreliable day-to-day food source, pursued more for status than subsistence; (2) archaeological evidence from the Plio-Pleistocene, coincident with the emergence of Homo can be read to reflect low-yield scavenging, not hunting. Our review of the archaeology yields results consistent with these critiques: (1) early humans acquired large-bodied ungulates primarily by aggressive scavenging, not hunting; (2) meat was consumed at or near the point of acquisition, not at home bases, as the hunting hypothesis requires; (3) carcasses were taken at highly variable rates and in varying degrees of completeness, making meat from big game an even less reliable food source than it is among modern foragers. Collectively, Plio-Pleistocene site location and assemblage composition are consistent with the hypothesis that large carcasses were taken not for purposes of provisioning, but in the context of competitive male displays. Even if meat were acquired more reliably than the archaeology indicates, its consumption cannot account for the significant changes in life history now seen to distinguish early humans from ancestral australopiths. The coincidence between the earliest dates for Homo ergaster and an increase in the archaeological visibility of meat eating that many find so provocative instead reflects: (1) changes in the structure of the environment that concentrated scavenging opportunities in space, making evidence of their pursuit more obvious to archaeologists; (2) H. ergaster's larger body size (itself a consequence of other factors), which improved its ability at interference competition. PMID:12473486

  4. Phylogeny and biogeography of Philippine bent-toed geckos (Gekkonidae: Cyrtodactylus) contradict a prevailing model of Pleistocene diversification.

    PubMed

    Siler, Cameron D; Oaks, Jamie R; Esselstyn, Jacob A; Diesmos, Arvin C; Brown, Rafe M

    2010-05-01

    In the Philippines, Pleistocene sea level oscillations repeatedly connected and isolated neighboring islands. Hence, an understanding of the island platforms adjoined during periods of low sea level has led biologists to a suite of expectations that, taken together, represent a paradigm for the process of recent diversification in southeast Asia. We employ statistical tests of phylogenetic topology and population genetic analyses of widespread species of bent-toed geckos (Cyrtodactylus) to ascertain whether patterns of inter- and intra-specific diversity can be explained by a Pleistocene aggregate island model of diversification. Contrary to many classic studies of Philippine vertebrates, we find complex patterns that are only partially explained by past island connectivity. In particular, we determine that some populations inhabiting previously united island groups show substantial genetic divergence and are inferred to be polyphyletic. Additionally, greater genetic diversity is found within islands, than between them. Among the topological patterns inconsistent with the Pleistocene model, we note some similarities with other lineages, but no obviously shared causal mechanisms are apparent. Finally, we infer well-supported discordance between the gene trees inferred from mitochondrial and nuclear DNA sequences of two species, which we suspect is the result of incomplete lineage sorting. This study contributes to a nascent body of literature suggesting that the current paradigm for Philippine biogeography is an oversimplification requiring revision. PMID:20132898

  5. Late Pleistocene glaciation in the Central Andes: Temperature versus humidity control — A case study from the eastern Bolivian Andes (17°S) and regional synthesis

    NASA Astrophysics Data System (ADS)

    Kull, C.; Imhof, S.; Grosjean, M.; Zech, R.; Veit, H.

    2008-01-01

    A glacier-climate model was used to calculate climatic conditions in a test site on the east Andean slope around Cochabamba (17°S, Bolivia) for the time of the maximum Late Pleistocene glaciation. Results suggest a massive temperature reduction of about - 6.4 °C (+ 1.4/- 1.3 °C), combined with annual precipitation rates of about 1100 mm (+ 570 mm/- 280 mm). This implies no major change in annual precipitation compared with today. Summer precipitation was the source for the humidity in the past, as is the case today. This climate scenario argues for a maximum advance of the paleo-glaciers in the eastern cordillera during the global Last Glacial Maximum (LGM, 20 ka BP), which is confirmed by exposure age dates. In a synthesized view over the central Andes, the results point to an increased summer precipitation-driven Late Glacial (15-10 ka BP) maximum advance in the western part of the Altiplano (18°S-23°S), a temperature-driven maximum advance during full glacial times (LGM) in the eastern cordillera, and a pre- and post-LGM (32 ka BP/14 ka BP) maximum advance around 30°S related to increased precipitation and reduced temperature on the western slope of the Andes. The results indicate the importance of understanding the seasonality and details of the mass balance-climate interaction in order to disentangle drivers for the observed regionally asynchronous past glaciations in the central Andes.

  6. A new Pleistocene vertebrate fauna from Austin, Texas

    E-print Network

    Young, Ker Shun

    2011-08-04

    is differentiated from Synaptomys borealis in that Synaptomys borealis molars are only made of lingual triangles and completely lack labial triangles (Semkem and Wallace, 2002). Fossils of Synaptomys cooperi has been recovered from several other Pleistocene caves...

  7. During the late Pleistocene, emergent groundwater supported persistent and

    E-print Network

    Nekola, Jeffrey C.

    present in many areas of the Mojave Desert during the late Pleistocene (Jefferson, 2003; Wells et al of square kilometers of broad valleys and basins along the Owens River drainage system were occupied

  8. Time reversal location of glacial earthquakes

    NASA Astrophysics Data System (ADS)

    Larmat, CarèNe; Tromp, Jeroen; Liu, Qinya; Montagner, Jean-Paul

    2008-09-01

    In 2003, Ekström et al. reported the detection and location of a new class of earthquakes occurring in the polar regions of the Earth. The proposed source mechanism involves large and sudden sliding motions of glaciers, which gave the name "glacial earthquakes" to these events. In this study we localize some of these earthquakes with a time reversal mirror (TRM) algorithm, which, contrary to ordinary back projection methods, does not involve testing each possible source location. In TRM localization, an earthquake is located on the basis of only one 3-D spectral element simulation of seismic wave propagation by using the full complexity of recorded data as simultaneous time-reversed sources. We show that on the basis of this approach, even glacial earthquakes with a faint signal can be correctly localized and that the pattern of the time-reversed wavefield is coherent with the motion of glaciers down their valley.

  9. 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.

  10. 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.

  11. 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

  12. Population genetic structure in migratory sandhill cranes and the role of Pleistocene glaciations

    USGS Publications Warehouse

    Jones, K.L.; Krapu, G.L.; Brandt, D.A.; Ashley, M.V.

    2005-01-01

    Previous studies of migratory sandhill cranes (Grus canadensis) have made significant progress explaining evolution of this group at the species scale, but have been unsuccessful in explaining the geographically partitioned variation in morphology seen on the population scale. The objectives of this study were to assess the population structure and gene flow patterns among migratory sandhill cranes using microsatellite DNA genotypes and mitochondrial DNA haplotypes of a large sample of individuals across three populations. In particular, we were interested in evaluating the roles of Pleistocene glaciation events and postglaciation gene flow in shaping the present-day population structure. Our results indicate substantial gene flow across regions of the Midcontinental population that are geographically adjacent, suggesting that gene flow for most of the region follows an isolation-by-distance model. Male mediated gene flow and strong female philopatry may explain the differing patterns of nuclear and mitochondrial variation. Taken in context with precise geographical information on breeding locations gained from satellite telemetry, the morphologic and microsatellite DNA variation shows a gradation from the Arctic-nesting subspecies G.c. canadensis to non Arctic subspecies G. c. tabida. Analogous to other Arctic-nesting birds, it is probable that the population structure seen in the Midcontinental sandhill cranes reflects the result of post-glacial secondary contact. Our data suggest that subspecies of migratory sandhills experience significant gene flow and therefore do not represent distinct and independent genetic entities.

  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. 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.

  15. Southern Ocean giant diatom mat deposits: markers of Pleistocene Antarctic Polar Front migration.

    NASA Astrophysics Data System (ADS)

    Kemp, A. E.; Grigorov, I.; Pearce, R. B.

    2006-12-01

    The Southern Ocean is a critical location for the biogeochemical cycling of silica and beneath its waters a sedimentary biogenic silica belt has formed. This sediment lies under and to the south of the present location of the Antarctic Polar Front which acts as a critical biogeochemical divider. The sediments recovered from ODP Sites 1091, 1093 and 1094 represent the only deep piston-cored record from this important zone. Within these sequences, that were deposited at the highest sustained pelagic accumulation rates ever recorded, giant Thalassiothrix diatom mat deposits occur intermittently. Following evidence from analogous diatom concentrations and recent oceanographic surveys in the Southern Ocean, the peak fluxes of Thalassiothrix diatoms are thought to have occurred beneath frontal zones such that these distinctive sediments may be used as a paleo-front indicators. Analysis of the occurrence of laminated diatom mat deposits from the above sites shows that a major southward migration in frontal position was associated with the Mid Pleistocene Transition. Higher frequency changes track the migration of the frontal region through glacial-interglacial cycles. Periods lacking diatom mat deposits at any site may represent periods of prolonged frontal instability.

  16. 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.

  17. 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)

  18. Pleistocene seismic sequences may result from eustatic change but can they be used for global correlations? New Insights from the Canterbury Basin, New Zealand

    NASA Astrophysics Data System (ADS)

    McHugh, C. M.; Fulthorpe, C.; Hoyanagi, K.; Blum, P.

    2013-12-01

    To understand the influence of eustasy on continental margin sedimentation and test the concepts of sequence stratigraphy, Integrated Ocean Drilling Program Expedition 317 drilled four sites on the continental shelf and upper slope of the Canterbury Basin, eastern South Island, New Zealand. We present results from upper slope Site U1352 (320 m water depth). A high-resolution multiproxy approach involving geochemical elemental analyses, lithostratigraphy and biostratigraphy, calibrated to an oxygen isotope scale, was applied to understand sedimentation over the past ~1.8 million years. Multichannel seismic data (EW00-01 survey) provided a seismic sequence stratigraphic framework against which to interpret the data. Seismic sequence boundaries are represented by a unique geochemical signature and arrangement of overlying sedimentary facies. However, several such geochemical-lithologic units are commonly contained within each seismic sequence. These higher frequency, intrasequence geochemical units generally correlate with100 ky glacial-interglacial Milankovic variability in the late Pleistocene, revealing that it took several glacio-eustatic cycles to build each seismic sequence. These findings support prior results obtained from Pleistocene sediments recovered by Ocean Drilling Program Leg 174A that drilled on the New Jersey margin with similar objectives to those of Expedition 317. In both northern and southern hemisphere siliciclastic settings there is a strong correlation between seismic sequences and glacio-eustasy, but the correlation between isotopic cycles and sequence boundaries is not one-to-one: only a subset of the glacioeustatic cycles result in a preserved seismic sequence boundary. Furthermore, late Pleistocene sequence boundaries on the two margins are not synchronous. Local conditions cause different isotopic peaks to be preferentially preserved as sequence boundaries in each location and preserved seismic sequences contain different groupings of marine isotope stages. Therefore, high-frequency Pleistocene seismic sequences may not correlate globally even though they are driven by glacio-eustasy.

  19. 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.

  20. 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.

  1. Extent of Pleistocene lakes in the western Great Basin

    USGS Publications Warehouse

    Reheis, Marith C.

    1999-01-01

    During the Pliocene to middle Pleistocene, pluvial lakes in the western Great Basin repeatedly rose to levels much higher than those of the well-documented late Pleistocene pluvial lakes, and some presently isolated basins were connected. Sedimentologic, geomorphic, and chronologic evidence at sites shown on the map indicates that Lakes Lahontan and Columbus-Rennie were as much as 70 m higher in the early-middle Pleistocene than during their late Pleistocene high stands. Lake Lahontan at its 1400-m shoreline level would submerge present-day Reno, Carson City, and Battle Mountain, and would flood other now-dry basins. To the east, Lakes Jonathan (new name), Diamond, Newark, and Hubbs also reached high stands during the early-middle(?) Pleistocene that were 25-40 m above their late Pleistocene shorelines; at these very high levels, the lakes became temporarily or permanently tributary to the Humboldt River and hence to Lake Lahontan. Such a temporary connection could have permitted fish to migrate from the Humboldt River southward into the presently isolated Newark Valley and from Lake Lahontan into Fairview Valley. The timing of drainage integration also provides suggested maximum ages for fish to populate the basins of Lake Diamond and Lake Jonathan. Reconstructing and dating these lake levels also has important implications for paleoclimate, tectonics, and drainage evolution in the western Great Basin. For example, shorelines in several basins form a stair-step sequence downward with time from the highest levels, thought to have formed at about 650 ka, to the lowest, formed during the late Pleistocene. This descending sequence indicates progressive drying of pluvial periods, possibly caused by uplift of the Sierra Nevada and other western ranges relative to the western Great Basin. However, these effects cannot account for the extremely high lake levels during the early middle Pleistocene; rather, these high levels were probably due to a combination of increased effective moisture and changes in the size of the Lahontan drainage basin.

  2. Late Glacial ice advances in southeast Tibet

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

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

  3. 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.

  4. 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

  5. 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.

  6. Effects of Pleistocene environmental changes on the distribution and community structure of the mammalian fauna of Mexico

    E-print Network

    Dever, Jennifer A.

    Effects of Pleistocene environmental changes on the distribution and community structure Article history: Received 22 June 2008 Available online 7 April 2010 Keywords: Pleistocene mammals Mexico Extinctions Extralimital distributions Biogeographic corridors Pleistocene refugia Biological communities

  7. 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.

  8. New Benthic ?18o Stacks and Age Models for the Last Glacial Cycle (0-150 kyr ago)

    NASA Astrophysics Data System (ADS)

    Lisiecki, L. E.; Stern, J. V.

    2014-12-01

    The ?18O of formainiferal calcite is a common paleoceanographic proxy, which measures ice volume and deep water temperature change. Foraminiferal ?18O is also often used to create marine sediment core age models by aligning down-core variations in ?18O to a global stack, or average. However, the most commonly used stack, known as "LR04," has an outdated age model, assumes global benthic ?18O synchrony, and is biased to the Atlantic [Lisiecki and Raymo, 2005]. Here we present six regional benthic ?18O stacks of the last glacial cycle (0-150 kyr) that are combined to form a volume-weighted global stack with data from 263 sites. We develop new benthic ?18O age models using regional radiocarbon dates from 0-40 ka and correlations to the GICC05 layer-counted Greenland age model from 40-56 ka [Svensson et al., 2008] and U-Th-dated Chinese speleothems from 56-150 kyr [Wang et al., 2001; Cheng et al., 2009; Barker et al, 2011]. Additional features of the new stacks are diachronous benthic ?18O changes during the last two glacial terminations and explicit age uncertainty estimates throughout. Our new global stack indicates that some portions of the LR04 stack are up to 4 kyr too young. We estimate corrections to the LR04 age model throughout the Pleistocene that imply faster climate responses to orbital forcing than previously estimated.

  9. 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.

  10. 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

  11. 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.

  12. Pliocene-pleistocene evolution of tropical aridity

    SciTech Connect

    Menocal, P.B. de.

    1992-01-01

    This research tries 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 wholecore 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 and 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 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 sensitivity tests were used to examine physical linkages between high and low latitude climate, demonstrating 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.

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

    NASA Astrophysics Data System (ADS)

    Pope, Richard; Hughes, Philip

    2014-05-01

    Compared to the mountainous areas of northern Greece (e.g. Woodward et al., 2008), the influence of deglaciation cycles on sedimentation in mountainous catchments in southern Greece remains poorly understood due to the poor preservation of small moraines and limited opportunities to date glacial and fluvial sediment dynamics fluvial sediments (Pope, unpublished data). Nevertheless, intriguing new insight into links between glacial cycles and sediment transfer/deposition phases in upland catchments have emerged by applying multiple dating techniques to well-preserved multiple generations of moraines and extensive glacio-fluvial fan systems on Mount Chelmos (2355 m a.s.l.). U-series dating of calcites within proximal fan sediments constrain the earliest phase of glacio-fluvial sedimentation to 490 (±21.0)(ka (MIS 12), while OSL dating of fine sands constrains the deposition of extensive medial glacio-fluvial gravels in (valley we walked down through trees) to between 250.99 (±20.67) and 160.82 (±11.08) ka. By comparison, cosmogenic dating of moraine boulders indicates that three generations of well-preserved moraines in the highest cirque areas date to 31-23 ka, 17-16 ka and 12-11.5 ka. OSL dating also provides ages of 18 and 17 (±11.08) for an extensive glacio-fluvial terrace in a major valley draining the southern flanksof Mount Chelmos. The initial Mount Chelmos geochronology suggests that the earliest and middle phases of glacio-fluvial sedimentation are coincident with the Middle Pleistocene glacial stages stages recorded in the Pindus range (Hughes et al, 2006). These include the Skamnellian (MIS 12) and the Vlasian (MIS 6) Stages as well as other cold stage between these (e.g. MIS 8).Evidence of glacio-fluvial outwash in MIS 8 is interesting since evidence for this in the moraine records has remained elusive although is suggested further north in the Balkans (Hughes et al., 2011). The valley moraines and glacio-fluvial terraces (late MIS 2) post-date the local last glacial maximum and are coeval with the later part of the Tymphian stage in the Pindus range. Refs: Hughes, P.D., Woodward, J.C., Gibbard, P.L., Macklin, M.G., Gilmour, M.A. & Smith G.R. (2006) The glacial history of the Pindus Mountains, Greece. Journal of Geology 114, 413-434. Hughes, P.D., Woodward, J.C., van Calsteren, P.C. and Thomas, L.E. (2011) The Glacial History of The Dinaric Alps, Montenegro. Quaternary Science Reviews 30, 3393-3412. Woodward, J.C., Hamlin, R.H.B., Macklin, M.G., Hughes, P.D. & Lewin, J. (2008) Pleistocene catchment dynamics in the Mediterranean: glaciation, fluvial geomorphology and the slackwater sediment record. Geomorphology 101, 44-67.

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

    E-print Network

    Long, Bernard

    Institut für Geographie, University of Bremen, Germany f Department of Earth and Ocean Sciences, University from a digital elevation model. These results support the hypothesis that the bottom sediments-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio

  15. Modern CaCO3 preservation in equatorial Pacific sediments in the context of late-Pleistocene glacial cycles

    E-print Network

    Winckler, Gisela

    Modern CaCO3 preservation in equatorial Pacific sediments in the context of late cycles. Both biological productivity and carbonate preservation have been proposed to be the master variable regulating this variability. We have evaluated the preserved flux of CaCO3 in cores from

  16. Glacial sea surface and subsurface temperature reconstructions off northern Chile (27.5°S) from 970 ka to present

    NASA Astrophysics Data System (ADS)

    Martinez-Mendez, G.; Groeneveld, J.; Hebbeln, D.; Lamy, F.; Mohtadi, M.

    2014-12-01

    Subantarctic surface and intermediate waters flow equatorwards along the Chilean continental margin within the Peru-Chile Current system while Subtropical Surface and Equatorial Subsurface Waters flow poleward. Pacific Deep water also flows poleward here. Thus, there is an interplay of high versus low latitude sourced waters throughout the water column. The degree of north/southward advection of upper column subantarctic/subtropical waters varies on glacial-interglacial time scales, global cooling favours northwards advection of subantarctic waters, global warming can promote southwards advection of subtropical waters. We investigate the nature of this interaction for the past 970 kyr using a splice of gravity core GeoB3375-1 and MeBo Site GeoB15016 from off northern Chile (27.5°S, 70°W). We measured stable isotopes and Mg/Ca in Globigerina bulloides (surface dweller) and Globorotalia inflata (sub-surface dweller). The number of foraminifera available for Mg/Ca analyses varied significantly and we used the annotated number of individuals per sample to generate pseudo-abundance records of both species. During interglacial periods, they are both scarce indicating conditions non-favorable for their proliferation, potentially due to stronger advection of nutrient-poor subtropical waters. Exceptions are Marine Isotope Stages (MIS) 23 and 25 during the Mid-Pleistocene Transition, which show, similarly to glacial periods, high abundances. Because of the scarcity in foraminifera, our Mg/Ca-derived surface and subsurface temperature (SST, subSST) records are discontinuous and represent mostly glacial periods (see Caniupán´s et al. contribution for alkenone-based interglacial SST estimations). Through the past 970 kyr, glacial Mg/Ca-derived SST and subSST (upper thermocline) became progressively colder towards present. This is in line with equatorial Pacific records pointing to a low latitude Pacific-wide signal. The difference between surface and subsurface temperatures does not show a clearly defined pattern. The largest difference occurs from MIS 4 to 1 (6-8°C) suggesting strong water column stratification, while during glacial MIS 8, 10, and 16 both records are nearly similar, which we interpret as well mixed conditions in the upper water column.

  17. Phylogeography of a widespread terrestrial vertebrate in a barely-studied Palearctic region: green toads (Bufo viridis subgroup) indicate glacial refugia in Eastern Central Asia.

    PubMed

    Zhang, Yi-Jun; Stöck, Matthias; Zhang, Peng; Wang, Xiu-Ling; Zhou, Hui; Qu, Liang-Hu

    2008-11-01

    The phylogeography of western Palearctic species is relatively well studied, but data on Eastern Central Asia are scarce. We present one of the first data sets from a widespread terrestrial vertebrate (Bufo pewzowi) inhabiting Eastern Central Asian mountains and deserts to gain knowledge on its phylogeography in this region. We applied combined phylogenetic and demographic analyses to understand the evolutionary history using mitochondrial DNA D-loop variation of toads from 37 locations. Genetic structure of Bufo pewzowi is strongly affected by landscape: we found three haplotype groups in eastern Kazakhstan, Dzungaria and Tarim Basin, divided by the Tian Shan and Dzungarian Alatau ranges. A vicariant hypothesis may explain divergence among groups. The divergence time of the three major clades was estimated about 0.9 million years ago (confidence interval 0.5-1.4), and is discussed with respect to Quaternary uplifting and glaciation in the Tian Shan. Demographic analyses provided evidence for both historical bottlenecks and population expansions and suggested Pleistocene signatures. Glacial refugia were inferred in the Tarim Basin (around the Turpan depression), in southern Dzungaria (Urumqui region), at the northern foot of the Tian Shan (Gongnaisi) and perhaps at the Altai range (Terekti). Regional Post-Last Glacial Maximum dispersal patterns are proposed. A taxonomic hypothesis is presented. This study provides a detailed history of how a widespread terrestrial vertebrate responded to geological change and Quaternary glacial events in Eastern Central Asia and may have significance for future phylogeographic research in this understudied region. PMID:18301990

  18. 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., Proceedings of the National Academy of Sciences, submitted. [2] Wolbach W. S., Lewis R. S., and Anders E. (1985) Science 230, 167-170. [3] Wolbach W.S., Gilmour I., Anders E., Orth C.J., and Brooks R.R. (1988) Nature 334, 665-669. [4] Wolbach W.S. and Anders E. (1989) Geochimica et Cosmochimica Acta 53, 1637-1647. [5] Wolbach W.S., Gilmour I., and Anders E. (1990) In: Global Catastrophes in Earth History (eds. V.L. Sharpton and P. Ward). Geological Society of America Special Paper 247, 391-400.

  19. Submerged Tioga and Tahoe age Moraines at Meeks Bay, Lake Tahoe, Calif. Implications to Late Pleistocene Lake Levels

    NASA Astrophysics Data System (ADS)

    Howle, J. F.; Schweickert, R. A.; Finkel, R. C.; Kitts, C. A.; Ota, J.

    2005-12-01

    At Meeks Bay, a well-preserved right-lateral morainal complex is constructed of till from the Tioga (>20.4 +/- 0.7 ka B.P.) and Tahoe (>62.0 +/- 1.3 ka B.P.; Howle et al., 2005) glacial advances. High-resolution digital bathymetry merged with the terrestrial DEM reveals that the onshore Tioga and Tahoe moraines extend offshore below the modern lake level of 1,899m. Longitudinal profiles show that the sub-aerial moraine crests grade evenly with the submerged crests and that the slopes of the sub-aqueous crests match the profile of the adjacent submarine canyon. In the digital bathymetry, the Tioga and Tahoe moraines are recognizable to 1,844 and 1,768m respectively. In May of 2004 and 2005 the moraines were imaged with the remotely operated submersible Triton deployed from the UC Davis research vessel, John LeConte. The Tioga moraine goes down to 1,817m, and rests upon Pliocene (?) lacustrine sediments. Above 1,817m the moraine is comprised of unsorted gravel, cobbles, and angular granitic boulders up to 3m across, typical of the Tioga age till on land. The moraine crest is continuous from 1,817m up to the shoreline promontory where the Tioga till on land enters the lake. Between 1,868m and 1,838m, the submerged Tahoe moraine contains well-rounded granitic boulders up to 2m across. The degree of rounding is consistent with the Tahoe boulders on land. The lowest occurrence of the Tahoe moraine was not imaged, but the glacial origin of the crest was confirmed. The submerged Tioga and Tahoe lateral moraines place upper limiting constraints on lake elevation, because lateral moraines do not form in water deeper than the ice thickness. Instead, when the relatively thin terminal ice cliff of an ablating alpine glacier interacts with water the glacier either melts, disintegrates by calving, or detaches along crevasses and floats when submerged to about 0.9 of the ice thickness. Reconstructions of ice thickness at the lower limits of the Tioga and Tahoe moraines here yield estimates of the maximum lake elevations at the glacial maxima. During the Tioga and Tahoe glacial maxima (>20 and >62 ka B.P., respectively) the lake elevation was <1,810m and <1,765m. These data indicate that in the Tahoe basin, late Pleistocene lake low-stands occurred during the glacial maxima. Asynchrony between glacial and lacustrine maxima has also been documented at Pleistocene lakes Russell and Lahonton (Lajoie and Robinson, 1982). Evidence at Meeks Bay for a post-Tahoe and pre-Tioga high-stand between 1,914 and 1,920m is provided by a gently sloping bench cut into the Tahoe moraine. This correlates well with reports of a Tahoe age high-stand at 1,926m. Birkeland (1963) proposed a Tahoe age ice dam at that may have raised lake levels to about 1950m. However, there is no evidence of this at 1950m in the Tahoe moraine at Meeks Bay, and therefore any such high-stand must have predated the Tahoe maximum. Available data suggests that large fluctuations in lake elevation have occurred from a mid Pleistocene (?) high-stand of about 2073m (Birkeland, 1963) to <1,765m at the Tahoe glacial maximum, up to about 1,920m after the Tahoe advance, down to <1,810m at the Tioga glacial maximum, and finally up to elevations between 1876 and 1899m during the Holocene (Schweickert et al., 2000). We thank the IEEE Oceanic Engineering Society for partial funding and commend the engineering students of Santa Clara University for designing, building, and deploying the Triton. Special thanks to Bob Richards and Brant Allen, captains of the LeConte.

  20. Growth, Uplift and Truncation of Indo-Burman Anticlines Paced By Glacial-Interglacial Sea Level Change

    NASA Astrophysics Data System (ADS)

    Gale, J.; Steckler, M. S.; Sousa, D.; Seeber, L.; Goodbred, S. L., Jr.; Ferguson, E. K.

    2014-12-01

    The Ganges-Brahmaputra Delta abuts the Indo-Burman Arc on the east. Subduction of the thick delta strata has generated a large subaerial accretionary prism, up to 250 km wide, with multiple ranges of anticlines composed of the folded and faulted delta sediments. As the wedge has grown, the exposed anticlines have become subject to erosion by the rivers draining the Himalaya, a local Indo-Burman drainage network, and coastal processes. Multiple lines of geophysical, geologic, and geomorphologic evidence indicate anticline truncation as a result of interaction with the rivers of the delta and sea level. Seismic lines, geologic mapping, and geomorphology reveal truncated anticlines with angular unconformities that have been arched due to continued growth of the anticline. Buried, truncated anticlines have been identified by seismic lines, tube well logs, and resistivity measurements. The truncation of these anticlines also appears to provide a pathway for high-As Holocene groundwater into the generally low-As Pleistocene groundwater. Overall, the distribution of anticline erosion and elevation in the fold belt appears to be consistent with glacial-interglacial changes in river behavior in the delta. The anticline crests are eroded during sea level highstands as rivers and the coastline sweep across the region, and excavated by local drainage during lowstands. With continued growth, the anticlines are uplifted above the delta and "survive" as topographic features. As a result, the maximum elevations of the anticlines are clustered in a pattern suggesting continued growth since their last glacial highstand truncation. An uplift rate is calculated from this paced truncation and growth that is consistent with other measurements of Indo-Burman wedge advance. This rate, combined with the proposed method of truncation, give further evidence of dynamic fluvial changes in the delta between glacial and interglacial times.

  1. Pollen- and diatom based environmental history since the Last Glacial Maximum from the Andean core Fúquene-7, Colombia

    NASA Astrophysics Data System (ADS)

    Vélez, Maria Isabel; Hooghiemstra, Henry; Metcalfe, Sarah; Martínez, Ignacio; Mommersteeg, Herman

    2003-01-01

    The late Pleistocene-Holocene ecological and limnological history of Lake Fúquene (2580 m a.s.l.), in the Colombian Andes, is reconstructed on the basis of diatom, pollen and sediment analyses of the upper 7 m of the core Fúquene-7. Time control is provided by 11 accelerator mass spectrometry (AMS) 14C dates ranging from 19 670 +/- 240 to 6040 +/- 60 yr BP. In this paper we present the evolution of the lake and its surroundings. Glacial times were cold and dry, lake-levels were low and the area was surrounded by paramo and subparamo vegetation. Late-glacial conditions were warm and humid. The El Abra Stadial, a Younger Dryas equivalent, is reflected by a gap in the sedimentary record, a consequence of the cessation of deposition owing to a drop in lake-level. The early Holocene was warm and humid; at this time the lake reached its maximum extension and was surrounded by Andean forest. The onset of the drier climate prevailing today took place in the middle Holocene, a process that is reflected earlier in the diatom and sediment records than in the pollen records. In the late Holocene human activity reduced the forest and transformed the landscape.Climate patterns from the Late-glacial and throughout the Holocene, as represented in our record, are similar to other records from Colombia and northern South America (the Caribbean, Venezuela and Panama) and suggest that the changes in lake-level were the result of precipitation variations driven by latitudinal shifts of the Intertropical Convergence Zone.

  2. Synchronous signatures of time-irreversibility in Northern and Southern Hemisphere records of last glacial climate and the Holocene

    NASA Astrophysics Data System (ADS)

    Donges, Jonathan; Vogel, Ralf; Donner, Reik; Kurths, Jürgen

    2015-04-01

    The time-reversibility structure of climate time series provides relevant information on the nature of the underlying processes. A novel statistical test for time-reversibility is employed that is based on the study of time-directed properties of visibility graphs constructed from time series and is particularly suitable for the study of irregularly sampled paleoclimate proxy records. Several ice core, speleothem and lacustrine records of paleoclimate during the late Pleistocene and Holocene from both Northern and Southern hemispheres are investigated. We find a consistent and robust signature of time-irreversibility and, hence, nonlinear processes driving climate dynamics, in the time-interval between approx. 40 and 60 kyr BP (before present). This signature is most pronounced in ice core records from Greenland and Antarctica, but also partially apparent in selected speleothem and lacustrine records from the mid-latitudes and tropics. In contrast, time-reversible climatic dynamics is detected consistently during the following last glacial maximum period and the Holocene. These findings suggest that strongly nonlinear (irreversible) climate dynamics (probably related to the asymmetric saw-tooth-like profile of particularly pronounced Dansgaard-Oeschger and Heinrich events) between 40-60 kyr BP were followed by reversible more Holocene-like dynamics appearing well before the actual beginning of the Holocene. These globally detectable changes in time-reversibility structure may provide novel insights into climatic dynamics, particularly considering the mechanisms underlying Dansgaard-Oeschger events during the last glacial and Bond events during the Holocene, as well as those behind the switch between glacial and interglacial conditions.

  3. Periglacial process and Pleistocene environment in northern China

    SciTech Connect

    Guo Xudong; Liu Dongsheng (Academia Sinica, Beijing (China)); Yan Fuhua (State Seismological Bureau, Beijing (China))

    1991-03-01

    In the present time, five kinds of periglacial phenomena have been defined: ice wedges, periglacial involutions, congelifolds, congeliturbations, and loess dunes. From the stratigraphical and geochronological data, the periglacial process is divided into six stages. (1) Guanting periglacial stage, characterized by the congeliturbative deposits that have developed in early Pleistocene Guanting loess-like formation. Paleomagnetic dating gives 2.43 Ma B.P. (2) Yanchi periglacial stage, characterized by the congelifold that has developed in middle Pleistocene Yanchi Lishi loess formation. Paleomagnetic dating gives 0.50 Ma B.P. (3) Zhaitang periglacial stage (II), characterized by the periglacial involutions that have developed in lower middle Pleistocene Lishi loess formation. Paleomagnetic dating gives 0.30 Ma B.P. (4) Zhaitang periglacial state (I), characterized by the ice (soil) wedge that has developed in upper-middle Pleistocene Lishi loess formation. Paleomagnetic dating gives 0.20 Ma B.P. (5) Qiansangyu periglacial stage (II), characterized by the ice (sand) wedges that has developed in late Pleistocene Malan loess formation. Paleomagnetic dating gives 0.13 Ma B.P. (6) Qiansangyu periglacial stage (I), characterized by the ice (soil) wedge that has developed in late Pleistocene Malan loess-like formation. Thermoluminescent dating gives 0.018 Ma B.P. Spore-pollen composition analysis shows that the savannah steppe environment prevailed in northern China during Pleistocene periglacial periods. These fossilized periglacial phenomena indicate a rather arid and windy periglacial environment with a mean annual temperature estimated some 12-15C colder than that in the present.

  4. Plankton Functional Group Variability and Global Change: The Eastern Equatorial Pacific on the Glacial-Interglacial Timescale

    NASA Astrophysics Data System (ADS)

    Loubere, P.

    2005-12-01

    Ice core records show a clear variation of atmospheric CO2 with late Pleistocene glaciations, and a timing that indicates a climate forcing role for the gas concentration changes. We lack an explanation for the variations, but a candidate is changes in plankton functional group production in such a way as to change the organic carbon to calcite flux ratio in the deep ocean. This rain ratio reflects the balance of biogeochemical exchange of CO2 between ocean and atmosphere, and it has the potential to change carbon storage in the deep ocean. We take a bottom up view and attempt reconstruction of organic carbon and calcite fluxes to infer changes in rain ratio, and hence production of the different functional groups. Since diatoms are the major non-carbonate producing group which can impact the rain ratio, we also report opal accumulation and preservation data. We examine the eastern equatorial Pacific in particular because this region has the highest efflux of CO2 to the atmosphere of any part of the oceans. We reconstruct conditions over the late Pleistocene as this time period has seen important variations in climate and atmospheric CO2. We use a benthic foraminiferal transfer function to estimate flux of labile (reactive) organic carbon to the seabed. We couple this with a proxy of calcite flux which we have developed using 230-Th normalized calcite accumulation rates corrected with a transfer function for fraction of calcite preserved. These are compared to one another and to opal accumulation rates and proxies for thermocline nutrient concentrations. We find that organic carbon flux decreases with each full glacial, in concert with decreases in thermocline nutrients. This appears to reflect reductions in overall nutrient supply to the tropics coming from the Southern Ocean. The record of calcite flux is different, with decreases at full glacials, but lower values broadly except at full inter-glacials. The evidence suggests a higher organic carbon to calcite rain ratio at all but the warmest time periods. This would provide positive feedback on climate change. The cause may be changes in nutrient ratios (especially SiO2 to NO3) that accompanied the changes in overall nutrient supply.

  5. Inverted Oscillator

    E-print Network

    C. Yuce; A. Kilic; A. Coruh

    2007-03-25

    The inverted harmonic oscillator problem is investigated quantum mechanically. The exact wave function for the confined inverted oscillator is obtained and it is shown that the associated energy eigenvalues are discrete and it is given as a linear function of the quantum number $n$.

  6. From accumulation to discharge: modification of stable isotopes during glacial and post-glacial processes

    Microsoft Academic Search

    W. Stichler; U. Schotterer

    2000-01-01

    The isotopes of the water molecule (tritium, deuterium and oxygen-18) are considered to be ideal tracers of the water cycle, an isobalance of accumulation and discharge from glaciated areas is therefore challenging. In this article we review data from the Alps concerning both the isotopic information of accumulated snow and ice and the relevant information of glacial discharge on a

  7. Dating Middle Pleistocene loess using IRSL luminescence

    NASA Astrophysics Data System (ADS)

    Michel, L.

    2008-12-01

    Loess is a unique palaeoclimate proxy that has a relatively global distribution. A major issue in loess studies is their age, as most terrestrial sediments are outside the realm of isotopic dating methods. Luminescence dating of loess has been attempted with limited success as Optically Stimulated Luminescence (OSL) from the two common dosimeters used in luminescence, quartz and feldspar minerals, both yielded age underestimates. Quartz is limited by dose saturation and feldspar suffers from anomalous fading. Over the last decade, we have developed methods to deal with anomalous fading and hence correct Infrared Stimulated Luminescence (IRSL) ages from feldspar dominated samples. A method known as Dose Rate Correction (DRC) has been successfully applied to loess from the Western European Belt, for ages as old as the Middle Pleistocene. Ages using the same method have been obtained for loess in Alaska and the technique is now being extended to loess from Illinois and China. IRSL can also be used as a reliable telecorrelation tool as luminescence properties of loess are broadly similar, whatever the geological provenance. DRC corrected IRSL extends the applicability of luminescence to dating loess up to at least 500 ka. The limiting factor in the specific case of loess is dose saturation due to relatively high dose rate compared to the average terrestrial sediment radioactivity.

  8. Post-glacial sea-level changes around the Australian margin: a review

    NASA Astrophysics Data System (ADS)

    Lewis, Stephen E.; Sloss, Craig R.; Murray-Wallace, Colin V.; Woodroffe, Colin D.; Smithers, Scott G.

    2013-08-01

    It has been known since Rhodes Fairbridge's first attempt to establish a global pattern of Holocene sea-level change by combining evidence from Western Australia and from sites in the northern hemisphere that the details of sea-level history since the Last Glacial Maximum vary considerably across the globe. The Australian region is relatively stable tectonically and is situated in the 'far-field' of former ice sheets. It therefore preserves important records of post-glacial sea levels that are less complicated by neotectonics or glacio-isostatic adjustments. Accordingly, the relative sea-level record of this region is dominantly one of glacio-eustatic (ice equivalent) sea-level changes. The broader Australasian region has provided critical information on the nature of post-glacial sea level, including the termination of the Last Glacial Maximum when sea level was approximately 125 m lower than present around 21,000-19,000 years BP, and insights into meltwater pulse 1A between 14,600 and 14,300 cal. yr BP. Although most parts of the Australian continent reveals a high degree of tectonic stability, research conducted since the 1970s has shown that the timing and elevation of a Holocene highstand varies systematically around its margin. This is attributed primarily to variations in the timing of the response of the ocean basins and shallow continental shelves to the increased ocean volumes following ice-melt, including a process known as ocean siphoning (i.e. glacio-hydro-isostatic adjustment processes). Several seminal studies in the early 1980s produced important data sets from the Australasian region that have provided a solid foundation for more recent palaeo-sea-level research. This review revisits these key studies emphasising their continuing influence on Quaternary research and incorporates relatively recent investigations to interpret the nature of post-glacial sea-level change around Australia. These include a synthesis of research from the Northern Territory, Queensland, New South Wales, South Australia and Western Australia. A focus of these more recent studies has been the re-examination of: (1) the accuracy and reliability of different proxy sea-level indicators; (2) the rate and nature of post-glacial sea-level rise; (3) the evidence for timing, elevation, and duration of mid-Holocene highstands; and, (4) the notion of mid- to late Holocene sea-level oscillations, and their basis. Based on this synthesis of previous research, it is clear that estimates of past sea-surface elevation are a function of eustatic factors as well as morphodynamics of individual sites, the wide variety of proxy sea-level indicators used, their wide geographical range, and their indicative meaning. Some progress has been made in understanding the variability of the accuracy of proxy indicators in relation to their contemporary sea level, the inter-comparison of the variety of dating techniques used and the nuances of calibration of radiocarbon ages to sidereal years. These issues need to be thoroughly understood before proxy sea-level indicators can be incorporated into credible reconstructions of relative sea-level change at individual locations. Many of the issues, which challenged sea-level researchers in the latter part of the twentieth century, remain contentious today. Divergent opinions remain about: (1) exactly when sea level attained present levels following the most recent post-glacial marine transgression (PMT); (2) the elevation that sea-level reached during the Holocene sea-level highstand; (3) whether sea-level fell smoothly from a metre or more above its present level following the PMT; (4) whether sea level remained at these highstand levels for a considerable period before falling to its present position; or (5) whether it underwent a series of moderate oscillations during the Holocene highstand.

  9. Late-glacial of southern South America

    NASA Astrophysics Data System (ADS)

    Heusser, C. J.

    Overall trends in late-glacial paleoenvironments of southern South America are interpretable from the pollen stratigraphy of radiocarbon dated sections of mires in Tierra del Fuego (55°S), the Chilotan archipelago (42-43°S), and the Chilean Lake District (39-41°S). In Tierra del Fuego, southern beech ( Nothofagus) and shrub and herb taxa (Gramineae, Empetrum, Acaena, Gunnera, Compositae and Cyperaceae) serve as indicators of the changing climate; in the Chilotan archipelago and in the Chilean Lake District, southern beech and other trees (species of Myrtaceae, Podocarpus, Prumnopitys, Pseudopanax and Weinmannia) suffice as indices of climatic change. Pollen records from each of these regions, although in need of greater dating control, indicate climatic sequences that are broadly similar. The records, however, are not regionally consistent in all aspects and differ in their indicator value with the implication of fossil beetle evidence. Attempts at correlation can be unsatisfactory at times and can stem inter alia from the different ecophysiological responses of both plants and beetles to environmental pressures. These differences, which affect the timing of reproduction and migration, may result in the variable occurrence of different species in the records. The broad implication of the pollen data is that following a glacial readvance culminating at about 15,000-14,500 BP, late-glacial climate was generally warmer during intervals before 13,000 and between 12,000 and 11,000 BP, and was cooler between 13,000 and 12,000 and from 11,000 to 10,000 BP.

  10. Resolving Large Pre-glacial Valleys Buried by Glacial Sediment Using Electric Resistivity Imaging (ERI)

    NASA Astrophysics Data System (ADS)

    Schmitt, D. R.; Welz, M.; Rokosh, C. D.; Pontbriand, M.-C.; Smith, D. G.

    2004-05-01

    Two-dimensional electric resistivity imaging (ERI) is the most exciting and promising geological tool in geomorphology and stratigraphy since development of ground-penetrating radar. Recent innovations in 2-D ERI provides a non-intrusive mean of efficiently resolving complex shallow subsurface structures under a number of different geological scenarios. In this paper, we test the capacity of ERI to image two large pre-late Wisconsinan-aged valley-fills in central Alberta and north-central Montana. Valley-fills record the history of pre-glacial and glacial sedimentary deposits. These fills are of considerable economical value as groundwater aquifers, aggregate resources (sand and gravel), placers (gold, diamond) and sometime gas reservoirs in Alberta. Although the approximate locations of pre-glacial valley-fills have been mapped, the scarcity of borehole (well log) information and sediment exposures make accurate reconstruction of their stratigraphy and cross-section profiles difficult. When coupled with borehole information, ERI successfully imaged three large pre-glacial valley-fills representing three contrasting geological settings. The Sand Coulee segment of the ancestral Missouri River, which has never been glaciated, is filled by electrically conductive pro-glacial lacustrine deposits over resistive sandstone bedrock. By comparison, the Big Sandy segment of the ancestral Missouri River valley has a complex valley-fill composed of till units interbedded with glaciofluvial gravel and varved clays over conductive shale. The fill is capped by floodplain, paludal and low alluvial fan deposits. The pre-glacial Onoway Valley (the ancestral North Saskatchewan River valley) is filled with thick, resistive fluvial gravel over conductive shale and capped with conductive till. The cross-sectional profile of each surveyed pre-glacial valley exhibits discrete benches (terraces) connected by steep drops, features that are hard to map using only boreholes. Best quality ERI results were obtained along the Sand Coulee and Onoway transects where the contrast between the bedrock and valley-fill was large and the surficial sediment was homogeneous. The effects of decreasing reliability with depth, 3-D anomalies, principles of equivalence and suppression, and surface inhomogeneity on the image quality are discussed.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  12. Paleolithic human exploitation of plant foods during the last glacial maximum in North China

    PubMed Central

    Liu, Li; Bestel, Sheahan; Shi, Jinming; Song, Yanhua; Chen, Xingcan

    2013-01-01

    Three grinding stones from Shizitan Locality 14 (ca. 23,000–19,500 calendar years before present) in the middle Yellow River region were subjected to usewear and residue analyses to investigate human adaptation during the last glacial maximum (LGM) period, when resources were generally scarce and plant foods may have become increasingly important in the human diet. The results show that these tools were used to process various plants, including Triticeae and Paniceae grasses, Vigna beans, Dioscorea opposita yam, and Trichosanthes kirilowii snakegourd roots. Tubers were important food resources for Paleolithic hunter–gatherers, and Paniceae grasses were exploited about 12,000 y before their domestication. The long tradition of intensive exploitation of certain types of flora helped Paleolithic people understand the properties of these plants, including their medicinal uses, and eventually led to the plants' domestication. This study sheds light on the deep history of the broad spectrum subsistence strategy characteristic of late Pleistocene north China before the origins of agriculture in this region. PMID:23509257

  13. Late-Glacial Cooling in Amazonia Inferred from Pollen at Lagoa do Caçó, Northern Brazil

    NASA Astrophysics Data System (ADS)

    Ledru, Marie-Pierre; Cordeiro, Renato Campello; Dominguez, José Maria Landim; Martin, Louis; Mourguiart, Philippe; Sifeddine, Abdelfetah; Turcq, Bruno

    2001-01-01

    New pollen data from a core at Lagoa do Caçó, Maranhão state, Brazil (2°58?S 43°25?W; 120 m elevation), show higher frequencies of Podocarpus at the end of the Pleistocene than today. The increase in Podocarpus, which follows the successive increase of various pioneer species such as Didymopanax, Melastomataceae/Combretaceae, and Cecropia, implies a progressive late-glacial increase of moist and cool climatic conditions. A comparable increase in Podocarpus is found in other lowland records in Amazonia. A review of published pollen data from Amazonia suggests that the moisture source was from the southeast. By contrast, present-day moisture comes from the tropical Atlantic and from the Amazon basin, with its convective precipitation. The likely cause for the southeastern moisture source between ca. 15,000 and 14,500 cal yr B.P. was enhanced polar (Antarctic) advection that reached low latitudes and maintained year-round the meteorological equator in its austral-winter position at northern latitudes or reduced drastically its southward summer displacement. This hypothesis is consistent with marine and ice core records.

  14. 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. Ya.; Francke, A.; Ritter, B.; Nowaczyk, N.; Sauerbrey, M. A.; Brigham-Grette, J.; Melles, M.

    2013-10-01

    The 3.6 Ma sediment record of Lake El'gygytgyn, Far East Russian Arctic, represents the longest continuous climate archive of the terrestrial Arctic. Its elemental composition monitored by X-ray fluorescence scanning exhibits significant changes since the Mid-Pliocene caused by climate driven variations in the primary production, postsedimentary diagenetic processes, and current activity in the lake 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 highly masked by intensified detrital input from the catchment, visible in maxima of clastic-related proxies such as the K concentration. In addition, calcite formation in the early lake history points to enhanced nutrient flux into the lake caused by intensified weathering in its catchment. Its termination at ca. 3.3 Ma is supposed to be linked to the development of permafrost in the region triggered by a first cooling in the Mid-Pliocene. After ca. 3.0 Ma the elemental data suggest a gradual transition to Quaternary-style glacial / interglacial cyclicity. In the early Pleistocene, the cyclicity was first dominated by variations on the 41 ka obliquity band but experienced a change to a 100 ka eccentricity dominance after the Middle Pleistocene Transition at ca. 1.2 to 0.7 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 to 1.8 Ma reflects an overall change in the bottom water oxygenation due to an intensified occurrence of pervasive glacial episodes in the early Quaternary. 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 regional cooling and/or changes in the ocean-land moisture transport. Further rising TOC and TN values after ca. 1.6 Ma are attributed to a progressive intensification of the glacial intensity. In the course of the Quaternary glacial/interglacial sequence eight so-called "super-interglacials" occur. Their exceptional warm conditions are reflected by extreme Si / Ti peaks accompanied by lows in Ti, K, and Fe, thus indicating an extraordinary high lake productivity.

  15. Quaternary Glacial Mapping in Western Wisconsin Using Soil Survey Information

    ERIC Educational Resources Information Center

    Oehlke, Betsy M.; Dolliver, Holly A. S.

    2011-01-01

    The majority of soils in the western Wisconsin have developed from glacial sediments deposited during the Quaternary Period (2.6 million years before present). In many regions, multiple advances and retreats have left a complex landscape of diverse glacial sediments and landforms. The soils that have developed on these deposits reflect the nature…

  16. EPICA Dome C record of glacial and interglacial intensities

    Microsoft Academic Search

    V. Masson-Delmotte; B. Stenni; K. Pol; P. Braconnot; O. Cattani; S. Falourd; M. Kageyama; J. Jouzel; A. Landais; B. Minster; J. M. Barnola; J. Chappellaz; G. Krinner; S. Johnsen; R. Röthlisberger; J. Hansen; U. Mikolajewicz; B. Otto-Bliesner

    2010-01-01

    Climate models show strong links between Antarctic and global temperature both in future and in glacial climate simulations. Past Antarctic temperatures can be estimated from measurements of water stable isotopes along the EPICA Dome C ice core over the past 800?000 years. Here we focus on the reliability of the relative intensities of glacial and interglacial periods derived from the

  17. Late Pleistocene and Holocene paleoenvironments of the North Pacific coast

    Microsoft Academic Search

    Daniel H. Mann; Thomas D. Hamilton

    1995-01-01

    Unlike the North Atlantic, the North Pacific Ocean probably remained free of sea ice during the last glacial maximum (LGM), 22,000 to 17,000 BP. Following a eustatic low in sea level of ca. ?120 m at 19,000 BP, a marine transgression had flooded the Bering and Chukchi shelves by 10,000 BP. Post-glacial sea-level history varied widely in other parts of

  18. Glacial-age deep sea carbonate ion concentrations

    NASA Astrophysics Data System (ADS)

    Broecker, W. S.; Clark, Elizabeth

    2003-06-01

    A second stab is taken at the reconstruction of the distribution of carbonate ion concentration in the deep tropical Pacific and Atlantic Oceans. It takes into account glacial to Holocene changes in size-normalized initial shell weights; it adopts a more rigorous relationship between measured core-top shell weights and pressure-normalized CO3= concentrations; and it employs an expanded glacial data set. While the conclusion that the effective glacial CO3= ion concentration decreased with water depth, when greater initial shell weights for glacial-age shells are adopted, the conclusion is that dissolution during glacial time exceeded that during the late Holocene. This conclusion is seemingly at odds with previous studies of deep Pacific sediments, all of which suggest that more extensive dissolution occurred during periods of interglaciation than during periods of glaciation.

  19. Geothermal activity helps life survive glacial cycles

    PubMed Central

    Fraser, Ceridwen I.; Terauds, Aleks; Smellie, John; Convey, Peter; Chown, Steven L.

    2014-01-01

    Climate change has played a critical role in the evolution and structure of Earth’s biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this “geothermal glacial refugia” hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species. PMID:24616489

  20. Glacial geology of Barron County, Wisconsin

    NASA Astrophysics Data System (ADS)

    Johnson, M. D.

    The glacial geology of Barron County consists of deposits and landforms associated with at least seven glacial advances. The Des Moines Lobe advanced into Barron County (the Reeve advance) probably several hundred thousand years ago and deposited olive-black loam till (till of the Pierce Formation) in the western third of the county. Following a period of weathering, ice of the Superior Lobe advanced (the Baldwin advance) and deposited yellowish-red sandy-loam till (till of an unnamed member of the River Falls Formation) concurrently with the Chippewa Lobe that advanced (the Dallas advance) and deposited yellowish-red sandy-loam till (till of the Prairie Farm Member of the River Falls Formation). These advances occurred after the Reeve advance and probably before the Wisconsin Glaciation. Weathered magnetite and clay minerals indicate that these till units were weathered for a long time following these advances. The remaining four advances into Barron County Occurred during the last part of the Wisconsin Glaciation. Each advance deposited yellowish-red sandy-loam till.

  1. Glacial isostasy - possible tilting of petroleum reservoirs

    NASA Astrophysics Data System (ADS)

    Fjeldskaar, Willy; Amantov, Aleksey

    2015-04-01

    Scandinavia has experienced major uplift after the last ice age. The rate of uplift along the coasts is so high that its effects have been observed within one generation. Glaciers, sediments and erosion act as loads on the Earth's surface - positive or negative. When a load is applied to the lithosphere covering the asthenosphere, part of the applied load will be supported by the elastic stiffness of the lithosphere, and part by the buoyant forces of the asthenosphere. This process is called isostasy, and the rebound over the last thousands of years has revealed how the Earth reacts to loads. Prior to the last glaciation, northern Europe has experienced more than 30 glaciations. Glacial erosion and repeated ice loading over the last millions of years has significantly influenced the temperature history of sedimentary basins, and associated hydrocarbon maturation in potential source rocks. In addition, repeated loading of glaciers leads to an isostatic response of the lithosphere, which may cause tilting of potential reservoirs, and possible remigration of hydrocarbons. The effects of glaciations are assumed to have caused parts of the accumulation in the Johan Sverdrup field (Utsira High) due to changed migration pathways. Glacial isostasy will lead to tilting of potential reservoirs on the entire Norwegian Continental Shelf. In the western Barents Sea and offshore mid Norway the tilts could exceed 4 m/km, dipping towards east during the glaciations.

  2. Fault activation due to glacially induced stresses

    NASA Astrophysics Data System (ADS)

    Steffen, Rebekka; Lund, Björn

    2014-05-01

    Melting glaciers worldwide have an effect on sea level, but also on the stability of pre-existing faults. The load due to continental ice sheets or glaciers depresses the surface below, leading to changes in the lithospheric stresses. The accumulation of ice mass increases the vertical stress, and the horizontal stresses increase due to the accompanying flexure of the lithosphere. During deglaciation, ice-mass loss causes a simultaneous decrease in vertical stress; however, horizontal stresses decrease only slowly due to the slow readjusting of the Earth. After the end of deglaciation, only the induced horizontal stresses remain as the process of glacial isostatic adjustment (GIA) proceeds visco-elastically. The modelling of this process and the estimation of fault slip is enabled by a new GIA-fault model. However, this finite-element model is only available in two dimensions, and the extension to three dimensions is a necessary step further to allow the comparison of obtained fault slips to observations of glacially induced faults in Europe and North America. The model has several input parameters, which affect the activation time of faults and their resulting slip (e.g. ice history, rheology of the Earth, frictional properties, pore-fluid pressure). We will present the results of the new 3D model and show the sensitivity of faults with respect to modelling parameters. Furthermore, a comparison to observations will be presented.

  3. Fault activation due to glacially induced stresses

    NASA Astrophysics Data System (ADS)

    Steffen, R.; Lund, B.; Wu, P. P.

    2013-12-01

    Melting glaciers worldwide have an effect on sea level, but also on the stability of pre-existing faults. The load due to continental ice sheets or glaciers depresses the surface below, leading to changes in the lithospheric stresses. The accumulation of ice mass increases the vertical stress, and the horizontal stresses increase due to the accompanying flexure of the lithosphere. During deglaciation, ice-mass loss causes a simultaneous decrease in vertical stress; however, horizontal stresses decrease only slowly due to the slow readjusting of the Earth. After the end of deglaciation, only the induced horizontal stresses remain as the process of glacial isostatic adjustment (GIA) proceeds visco-elastically. The modelling of this process and the estimation of fault slip is enabled by a new GIA-fault model. However, this finite-element model is only available in two dimensions, and the extension to three dimensions is a necessary step further to allow the comparison of obtained fault slips to observations of glacially induced faults in Europe and North America. The model has several input parameters, which affect the activation time of faults and their resulting slip (e.g. ice history, rheology of the Earth, frictional properties, pore-fluid pressure). We will present the results of the new 3D model and show the sensitivity of faults with respect to modelling parameters. Furthermore, a comparison to observations will be presented.

  4. Southward Pleistocene migration of Douglas-fir into Mexico: phylogeography, ecological niche modeling,

    E-print Network

    Gugger, Paul F.

    Southward Pleistocene migration of Douglas-fir into Mexico: phylogeography, ecological niche modeling, Mexico, mtDNA, phylogeography, Pseudotsuga menziesii, rear edge. Summary · Poleward Pleistocene or Pleistocene origin for temperate `sky island' plant taxa in Mexico. These `rear edge' populations situated

  5. Contrasted morphosedimentary activity of the lower Kert River (northeastern Morocco) during the Late Pleistocene and the

    E-print Network

    Paris-Sud XI, Université de

    the Late Pleistocene and the Holocene. Possible impact of bioclimatic variations and human action Mohamed). While the Late Pleistocene is mainly marked by sedimentary accretion (UF1 forming part of T1 bioclimatic trends that did not appear during the Late Pleistocene. Human activities modified the earth

  6. PLEISTOCENE HYDROLOGY OF NORTH AMERICA: THE ROLE OF ICE SHEETS IN REORGANIZING

    E-print Network

    Jellinek, Mark

    PLEISTOCENE HYDROLOGY OF NORTH AMERICA: THE ROLE OF ICE SHEETS IN REORGANIZING GROUNDWATER FLOW consequences of Pleistocene megafloods have been known for some time, it has been only in the past 2 decades are controlled primarily by the water table configuration during the Pleistocene. Rather, groundwater flow

  7. Late Pleistocene Human Subsistence in Northern Africa: The State of our Knowledge and Placement

    E-print Network

    Chapter 8 Late Pleistocene Human Subsistence in Northern Africa: The State of our Knowledge- inently in the debate of the mode and tempo of modern human origins during the Late Pleistocene of Africa the zooarchae- ological record for Late Pleistocene human subsistence in northwestern Africa. This region

  8. Late Pleistocene and Holocene glaciation of the Fish Lake valley, northeastern Alaska Range,

    E-print Network

    Briner, Jason P.

    Late Pleistocene and Holocene glaciation of the Fish Lake valley, northeastern Alaska Range, Alaska, N. E., Briner, J. P. and Kaufman, D. S. 2009. Late Pleistocene and Holocene glaciation of the Fish a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley

  9. JournalofHuman Evolution(1988) 17, 643-645 STUDIES OF THE NORTHERN PLEISTOCENE