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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. Interhemispheric correlation of late pleistocene glacial events.

    PubMed

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

    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 >/=33,500 carbon-14 years before present ((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(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(14)C yr B.P., and at the beginning of the Younger Dryas at 11,050 (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. PMID:17789444

  3. Early Pleistocene Glacial Cycles and the Integrated Summer Insolation Forcing

    NASA Astrophysics Data System (ADS)

    Huybers, Peter

    2006-07-01

    Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But the intensity of summer insolation is primarily controlled by 20,000-year cycles in the precession of the equinoxes, whereas early Pleistocene glacial cycles occur at 40,000-year intervals, matching the period of changes in Earth's obliquity. The resolution of this 40,000-year problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the Sun.

  4. LATE PLEISTOCENE EVOLUTION OF GLACIAL LAKE PURCELL: A POTENTIAL FLOODWATER SOURCE TO

    E-print Network

    Brennand, Tracy

    LATE PLEISTOCENE EVOLUTION OF GLACIAL LAKE PURCELL: A POTENTIAL FLOODWATER SOURCE TO THE CHANNELED: Master of Science Title of Thesis: Late Pleistocene evolution of glacial Lake Purcell: a potential Professor Department of Geography, University of Victoria Date Defended/Approved: September 18, 2012 #12;iii

  5. Pleistocene glacial evolution of Fuentes Carrionas (Cantabrian Range, NW Spain)

    NASA Astrophysics Data System (ADS)

    Pellitero, Ramon

    2014-05-01

    Fuentes Carrionas is a massif situated at the N of Spain, between Castilla y Leon and Cantabria regions. It is the second highest mountain massif of the Cantabrian Range after Picos de Europa, with peaks over 2500 m.a.s.l. and valleys well over 1000 m.a.s.l. Fuentes Carrionas was glaciated during Quaternary, and even during the Holocene and as far as Little Ice Age the presence of glaciers, or at least permafrost is controversial. Results from glacial geomorphology analysis of Fuentes Carrionas Massif are presented. Based on the interpretation of glacial landforms, glacial evolution since the Last Glacial Maximum until Pleistocene deglaciation is described. Four different glacial equilibrium phases are identified, the last one divided into two pulsations. Deglaciation process took place between 36 ka BP and 11 ka BP. Local Last Glacial Maximum is dated back to 36-38 ka. BP, therefore earlier than LGM. Glaciers reached 15 km. long and occupied valleys down to 1250 m.a.s.l. during this phase. By European LGM (20-18 ka.BP) glaciers had substantially retreated to fronts about 1700 m.a.s.l. A final stage with two marked pulsations shows only small glaciers located at cirques above 2000 m.a.s.l. and, finally, only small cirque glaciers at North and Northeast orientation above 2200 m.a.s.l. Both these phases have been correlated to Oldest and Younger Dryas, although no dates have been done yet. A palaeoenvironmental reconstruction is proposed, based on ELA (Equilibrium Line Altitude) rise. ELA has been calculated with the AAR method and 0.67 ratio. This reconstruction shows that temperatures ranged between 9°C and 10°C lower than present ones at the end of Pleistocene, depending on a precipitations variation between 30% higher and 20% lower than current ones. Further research will focus on these retreat phases, especially on Younger Dryas identification and reconstruction for this site and the rest of Cantabrian Range.

  6. Intensified deep Pacific inflow and ventilation in Pleistocene glacial times.

    PubMed

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

    2001-08-23

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

  7. 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.

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

    E-print Network

    Schöne, Bernd R.

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

  9. "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?

  10. Combined obliquity and precession pacing of the late Pleistocene glacial cycles

    E-print Network

    Huybers, Peter

    have called on the precession of the equinoxes relative to Earth's eccentric orbit1­3 , changesCombined obliquity and precession pacing of the late Pleistocene glacial cycles Peter Huybers, and this general concept has been elaborated to show how precession, obliquity, or combinations of both could

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

    SciTech Connect

    Saltzman, B.; Verbitsky, M.Ya.

    1993-10-01

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

  12. Pleistocene glacial cycle effects on the phylogeography of the Chinese endemic bat species, Myotis davidii

    PubMed Central

    2010-01-01

    Background Global climatic oscillations, glaciation cycles and the unique geographic topology of China have profoundly influenced species population distributions. In most species, contemporary distributions of populations cannot be fully understood, except in a historical context. Complex patterns of Pleistocene glaciations, as well as other physiographic changes have influenced the distribution of bat species in China. Until this study, there had been no phylogeographical research on Myotis davidii, an endemic Chinese bat. We used a combination of nuclear and mitochondrial DNA markers to investigate genetic diversity, population structure, and the demographic history of M. davidii. In particular, we compared patterns of genetic variation to glacial oscillations, topography, and environmental variation during the Pleistocene in an effort to explain current distributions in light of these historical processes. Results M. davidii comprises three lineages (MEP, SWP and SH) based on the results of molecular variance analysis (AMOVA) and phylogenetic analyses. The results of a STRUCTURE analysis reveal multi-hierarchical population structure in M. davidii. Nuclear and mitochondrial genetic markers reveal different levels of gene flow among populations. In the case of mtDNA, populations adhere to an isolation-by-distance model, whereas the individual assignment test reveals considerable gene flow between populations. MDIV analysis indicate that the split of the MEP and SWP/SH lineages, and from the SWP and SH lineages were at 201 ka BP and 158 ka BP, respectively. The results of a mismatch distribution analysis and neutrality tests indicate a population expansion event at 79.17 ka BP and 69.12 ka BP in MEP and SWP, respectively. Conclusions The complex demographic history, discontinuous extant distribution of haplotypes, and multiple-hierarchy population structure of M. davidii appear associated with climatic oscillations, topography and eco-environmental variation of China. Additionally, the three regions are genetically differentiated from one another in the entire sample set. The degree of genetic differentiation, based on the analysis of mtDNA and nDNA, suggests a male-mediated gene flow among populations. Refuges were in the MEP, SH and the lower elevations of SWP regions. This study also provides insights for conservation management units (MEP, SWP and SH). PMID:20618977

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

    SciTech Connect

    Roof, S.R.; Brigham-Grette, J. )

    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.

  14. Burial Ages for Middle Pleistocene Glacial Deposits of the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Balco, G.; Stone, J. O.; Patterson, C. J.; Caffee, M.

    2001-12-01

    Subglacial erosion and sediment dynamics influence the size, stability, and climatic sensitivity of large ice sheets as well as the landscape they leave behind. In the regions surrounding the former Laurentide Ice Sheet (LIS) thick deposits of glacial sediment contain a rich record of a) the extent and dynamics of the ice sheet during many glacial cycles, and b) the rate and timing of Pleistocene glacial erosion of the Canadian Shield. This record is poorly accessible at present due to difficulties in determining the age of glacial deposits older than the limit of radiocarbon dating. In order to better interpret this record of long-term ice sheet erosion, we have attempted to determine the age of a series of glacial and interglacial sediments in Minnesota, USA, using a technique of "burial dating" based on the different rates of decay of the in-situ-produced cosmogenic isotopes 10Be and 26Al in sediments first exposed to cosmic rays at the earth's surface and then buried for an extended time. We measured 10Be and 26Al on eight samples of fluvial or glaciofluvial sediment interbedded between tills previously thought to be middle Pleistocene in age. 26Al/10Be ratios were lower in stratigraphically lower units, and ratios were indistinguishable in units previously correlated based on their position and lithology. Thus, this may be a viable method for determining the age of these othewise hard-to-date sediments and may result in significant progress toward correlating terrestrial and marine records of Pleistocene glaciation. Results for sandy sediments within one set of tills are consistent with 10,000-14,000 years of exposure followed by 0.8 +/- 0.1 Myr burial; those within another group of tills indicate similar exposure times followed by 1.1 +/- 0.1 Myr burial. Subject to several assumptions, these results give the age of overlying till units. If correct, they corroborate other evidence suggesting that the LIS achieved its maximum known extent prior to the large oxygen-isotope excursions of the late Pleistocene.

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

    E-print Network

    Takahito Mitsui; Michel Crucifix; Kazuyuki Aihara

    2015-06-15

    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 nonchaotic attractor.

  16. Sedimentary effects of cataclysmic late Pleistocene glacial outburst flooding, Altay Mountains, Siberia

    NASA Astrophysics Data System (ADS)

    Rudoy, A. N.; Baker, V. R.

    1993-05-01

    Pleistocene glacial outburst floods were released from ice-dammed lakes of the Altay Mountains, south-central Siberia. The Kuray-Chuja lake system yielded peak floods in excess of 1 × 106 m3 s-1 and as great as 18 × 106 m3 s-1. The phenomenally high bed shear stresses and stream powers generated in these flows produced a main-channel, coarse-grained facies of coarse gravel in (1) foreset-bedded bars as much as 200 m high and several kilometers long, and (2) degradational, boulder-capped river terraces. Giant current ripples, 50 to 150 m in spacing, composed of pebble and cobble gravel, are locally abundant. The whole sedimentary assemblage is very similar to that of the Channeled Scabland, produced by the Pleistocene Missoula Floods of western North America.

  17. 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.

  18. Early Pleistocene Glacial Lake Lesley, West Branch Susquehanna River valley, central Pennsylvania

    NASA Astrophysics Data System (ADS)

    Ramage, Joan M.; Gardner, Thomas W.; Sasowsky, Ira D.

    1998-02-01

    Laurentide glaciers extended into north central Pennsylvania repeatedly during at least the last 2 million years. Early Pleistocene glaciation extended farther south into central Pennsylvania than any subsequent glaciation, reaching the West Branch Susquehanna River (WBSR) valley. Early Pleistocene ice dammed the northeast-flowing West Branch Susquehanna River at Williamsport, forming Glacial Lake Lesley, a 100-km-long proglacial lake. In this paper, we present compelling evidence for the lake and its age. Maximum lake volume (˜ 100 km 3) was controlled by the elevation of the lowest drainage divide, ˜ 340 m above sea level at Dix, Pennsylvania. Stratified deposits at McElhattan and Linden are used to reconstruct depositional environments in Glacial Lake Lesley. A sedimentary section 40 m thick at McElhattan fines upward from crossbedded sand to fine, wavy to horizontally laminated clay, consistent with lake deepening and increasing distance from the sediment source with time. At Linden, isolated cobbles, interpreted as dropstones, locally deform glacio-lacustrine sediment. We use paleomagnetism as an age correlation tool in the WBSR valley to correlate contemporaneous glaciofluvial and proglacial lacustrine sediments. Reversed remanent polarity in finely-laminated lacustrine clay and silt at McElhattan ( I = 20.4°, D = 146.7°, ?95 = 17.7°) and in interbedded silt and sand at Linden ( I = 55.3°, D = 175.2°, ?95 = 74.6°) probably corresponds to the latter part of the Matuyama Reversed Polarity Chron, indicating an age between ˜ 770 and ˜ 970 ka. At McElhattan, a diamicton deformed the finely laminated silt and clay by loading and partial fluidization during or soon after lake drainage. As a result, the deformed clay at McElhattan lacks discrete bedding and records a different characteristic remanent magnetism from underlying, undeformed beds. This difference indicates that the characteristic remanent magnetism is detrital. An electrical resistivity survey and drill borings define a buried bedrock channel at Bald Eagle near the drainage divide that is the proposed spillway for Glacial Lake Lesley. The highest terrace at Bald Eagle (Qt1 be) was truncated by the spillway channel. Age of Qt1 be is estimated as at least middle Middle Pleistocene to Early Pleistocene by correlation of soil physical properties on Qt1 be to soil chronosequences developed for Susquehanna River alluvial terraces, further downstream. This age is generally consistent with the age estimated from paleomagnetism.

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

    SciTech Connect

    Lewis, Claudia J; Mcdonald, Eric; Sancho, Carlos; Pena, Jose- Luis

    2008-01-01

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

  20. Late Pleistocene oscillations of Lake Owens, eastern California

    SciTech Connect

    Orme, A.J. . Dept. of Geography); Orme, A.R. . 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.

  1. 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.

  2. 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).

  3. 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.

  4. Seismic characteristics of Pleistocene glacial cycles near shelf edge, offshore Louisiana, Gulf of Mexico

    SciTech Connect

    Watkins, J.S.; Schneider, L.; Hilterman, F.

    1987-05-01

    Seismic stratigraphic studies of the shelf edge and the upper slope basins in the southern parts of the South Marsh Island, Eugene Island, Ship Shoal, and Green Canyon areas of the Louisiana outer continental shelf reveal at least four Pleistocene seismic stratigraphic cycles. These apparently reflect cyclic depositional patterns associated with glacially driven highstands and lowstands of sea level during this time. In the upper slope basins, a strong continuous reflector probably of turbiditic origin marks the base of each cycle. This reflector is thought caused by initial slumping occurring as sea level begins to fall. Overlying this reflector is a zone of chaotic-to-hummocky reflectors thought caused by slumping associated with knick-point erosion and channel-cutting during falling sea level. The upper portion of the cycle is largely reflectorless or weakly reflective punctuated with occasional strong, continuous turbidite reflectors. The reflectorless portion of the cycles is thought to represent homogeneous hemipelagic sedimentation during highstands. Shelf reflectors are usually moderately strong and continuous. A strong reflection(s), identified in some instances with gas sands, marks several sea level lowstands. Erosion is locally evident during lowstands. Otherwise, shelf reflectors are relatively uniform and show few characteristics associated with rising, falling, or highstanding parts of the sea level cycle.

  5. 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.

  6. Glacial-interglacial sea-surface temperature (SST) variability in the eastern tropical Pacific: spatial patterns from the late Pleistocene to present

    NASA Astrophysics Data System (ADS)

    Dyck, K.; Ravelo, C.

    2009-12-01

    The equatorial Pacific is an important component of the modern climate system and is critical for understanding climatic and oceanographic changes on glacial-interglacial timescales. While many studies examine the vertical structure of temperature, the spatial variability of SST patterns in the tropical and subtropical Pacific also influence global climate variability. SSTs in the eastern tropical Pacific play a vital role in such climate oscillations as ENSO and the PDO. Iinsight into mechanisms that explain long-term changes in tropical Pacific climate requires and capitalizes on the many realizations of glacial-interglacial cycles preserved in deep-sea sediments. However, most studies are limited to the last 250 ky with the bulk of the research centered on the last glacial maximum. It is now feasible to generate longer records that can resolve many glacial-interglacial cycles. Yet only a handful of geochemical SST records longer than the last few glacial cycles exist for the tropical Pacific. We construct a long geochemical SST record from the Ecuador margin to test various ideas for the causes of tropical climate change (e.g. equatorial ocean currents). In the modern eastern equatorial Pacific, cool nutrient-rich water advects and forms a well-defined cold tongue. Additionally, strong equatorial easterlies drive divergence of surface waters causing cool, deeper water to upwell along the equator and intensify the cold tongue. During periods of strong atmospheric Walker (equatorial Pacific) circulation, the zonal surface temperature gradient is large, supporting a strong equatorial cold tongue. By creating new geochemical records and correlating a number of cores over glacial-interglacial timescales, we evaluate the spatial strength and extent of the equatorial cold tongue for multiple climate cycles through the late Pleistocene and Holocene. To determine past SST we measure the unsaturation index of long-chain lipid ketones (alkenones) found in organic-rich ocean sediments. Alkenones are produced by haptophyte algae, such as the coccolithophorid Emiliani huxleyi and quantified using the lipid unsaturation index (Uk’37). We compare existing Uk’37 records from the center of upwelling (using ODP Site 846) to a new alkenone-based SST record from ODP Site 1239 (120 km from the Ecuador margin) on the northeastern edge of upwelling. This continental margin site constrains the lateral extent of cold, nutrient-rich upwelling in the eastern equatorial Pacific. We develop a clear picture of spatial variability within the equatorial cold tongue on glacial-interglacial scales by comparing this new record to previously analyzed cores (Site 846, southwest of the Galápagos Islands). Specifically, we show the consistent 2°C temperature offset in Site 1239 represents a constant regional temperature gradient to at least MIS 11 (~450 kya).

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We use ˜7000 km2 of high-resolution swath bathymetry data to describe and map the submarine glacial geomorphology, and reconstruct Late Pleistocene ice sheet flow configurations and retreat dynamics within the Inner Hebrides, western Scotland. Frequently dominated by outcrops of structurally complex bedrock, the seabed also comprises numerous assemblages of well-preserved glacigenic landforms typical of grounded ice sheet flow and punctuated ice-margin retreat. The occurrence and character of the glacially streamlined landforms is controlled in part by the shallow geology and topography, however these factors alone cannot account for the location, orientation, and configuration of the observed landforms. We attribute the distribution of these elongate streamlined landforms to the onset zone of the former Hebrides Ice Stream (HIS) - part of a major ice stream system that drained 5-10% of the last British-Irish Ice Sheet (BIIS). We suggest this geomorphic signature represents the transition from slow 'sheet flow' to 'streaming flow' as ice accelerated out from an environment characterized by numerous bedrock obstacles (e.g. islands, headlands), towards the smooth, sediment dominated shelf. The majority of streamlined landforms associated with the HIS indicate ice sheet flow to the southwest, with regional-scale topography clearly playing a major role in governing the configuration of flow. During maximal glacial conditions (˜29-23 ka) we infer that the HIS merged with the North Channel-Malin Shelf Ice Stream to form a composite ice stream system that ultimately reached the continental shelf edge at the Barra-Donegal Trough-Mouth Fan. Taken collectively however, the pattern of landforms now preserved at seabed (e.g. convergent flow indicators, cross-cutting flow sets) is more indicative of a thinning ice mass, undergoing reorganization during overall ice sheet retreat (during latter stages of Late Weischselian glaciation). Suites of moraines overprinting the streamlined landforms suggest partial stabilization of the HIS prior to the ice sheet retreating to more isolated, topographically confined troughs and basins. Retreat from the shelf towards, and back into the Inner Hebrides may have been rapid due the prevalence of overdeepened troughs. Within the near-shore fjord-like troughs and deeps, basin-aligned streamlined landforms indicate the subsequent flow of thinner topographically partitioned ice masses, and overprinted moraines record further ice margin retreat, potentially along tide-water margins. This work provides the first geomorphological constraints for this large marine-influenced sector of the former BIIS. We also shed new light on the glacial geomorphic record found at the transition from terrestrial to marine continental-shelf settings, and examine the interplay between substrate geology, bed topography/bathymetry, and grounding-line positions - relationships which are important for characterizing contemporary marine ice sheet margins.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  11. 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.

  12. Sensitivity of Photosynthetic Gas Exchange and Growth of Lodgepole Pine to Climate Variability Depends on the Age of Pleistocene Glacial Surfaces

    NASA Astrophysics Data System (ADS)

    Osborn, B.; Chapple, W.; Ewers, B. E.; Williams, D. G.

    2014-12-01

    The interaction between soil conditions and climate variability plays a central role in the ecohydrological functions of montane conifer forests. Although soil moisture availability to trees is largely dependent on climate, the depth and texture of soil exerts a key secondary influence. Multiple Pleistocene glacial events have shaped the landscape of the central Rocky Mountains creating a patchwork of soils differing in age and textural classification. This mosaic of soil conditions impacts hydrological properties, and montane conifer forests potentially respond to climate variability quite differently depending on the age of glacial till and soil development. We hypothesized that the age of glacial till and associated soil textural changes exert strong control on growth and photosynthetic gas exchange of lodgepole pine. We examined physiological and growth responses of lodgepole pine to interannual variation in maximum annual snow water equivalence (SWEmax) of montane snowpack and growing season air temperature (Tair) and vapor pressure deficit (VPD) across a chronosequence of Pleistocene glacial tills ranging in age from 700k to 12k years. Soil textural differences across the glacial tills illustrate the varying degrees of weathering with the most well developed soils with highest clay content on the oldest till surfaces. We show that sensitivity of growth and carbon isotope discrimination, an integrated measure of canopy gas exchange properties, to interannual variation SWEmax , Tair and VPD is greatest on young till surfaces, whereas trees on old glacial tills with well-developed soils are mostly insensitive to these interannual climate fluctuations. Tree-ring widths were most sensitive to changes in SWEmax on young glacial tills (p < 0.01), and less sensitive on the oldest till (p < 0.05). Tair correlates strongly with ?13C values on the oldest and youngest tills sites, but shows no significant relationship on the middle aged glacial till. It is clear that growth and photosynthetic gas exchange parameters are sensitive to glacial till surfaces, which is evident by the different responses to SWEmax and Tair across sites.

  13. 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.

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

    E-print Network

    Gilli, Adrian

    and atmospheric CO2 concentrations. Here we present foraminiferal Mg/Ca and d18 O results for the subsurface with other mechanisms, to lower glacial atmospheric CO2 concentrations during the MPT. & 2012 Elsevier B dioxide concentrations (pCO2) as the driving mechanism (Raymo et al., 1997; Paillard, 1998; Berger et al

  15. THE EXTENT OF PLEISTOCENE ICE CAP, GLACIAL DEPOSITS AND GLACIOKARST IN THE ALADAGLAR

    E-print Network

    Zreda, Marek

    between 1100 m and 3756 m of altitudes. Many of the glacial landforms, such as moraines and ice deposits are above 1800 m; older moraines extend further down to 1400 m. The Hacer valley has the largest number of moraines. Outwash deposits at the mouth of this valley extend down to 1200 m. Apart from

  16. Late Pleistocene glacial history of central Marquette and northern Dickinson counties, Michigan

    NASA Astrophysics Data System (ADS)

    Regis, Robert Stephen

    New techniques for mapping glacial landscape units located in the central Upper Peninsula of Michigan were developed using image processing software. Digital Elevation Model (DEM), Side-Looking Airborne Radar (SLAR), Landsat Thematic Mapper (TM) and overburden thickness (OBT) datasets were used. Many combinations of the DEM, SLAR, and TM datasets using the Intensity-Hue-Saturation (IHS) and Principal Components Analysis (PCA) transformations were valuable for visual interpretation of glacial landscape units. Such combinations showed relative elevations of landscape units, relief variations, and surface cover types in a single image. Also in the study, relief images and three-dimensional perspective views derived from the DEM were used to map ice-marginal positions and interpret how glacial ice receded from the area. The stair-step appearance of glacial outwash terraces at progressively lower elevations toward the east became evident using the perspective view technique. Visualization of glaciated terrain using these datasets in an image processor proved to be more effective for interpreting glacial landscapes than traditional topographic map or aerial photograph analyses. Texture analysis of the DEM was used to provide a measure of terrain ruggedness (or roughness) as input to a supervised maximum likelihood classification algorithm. Standard deviation of the DEM was assessed as a measure of texture in four moving windows of the following sizes; 64 pixelssp2, 32 pixelssp2, 16 pixelssp2, and 3 pixelssp2. Windows of different sizes were used to match the frequency of natural variation in size and spacing of features that comprise each of the landscape units in the study area. Texture files were combined with the TM, DEM, and OBT datasets into a single multi-band file. The maximum likelihood classification algorithm was then applied to the multiple-dataset file. The algorithm was first applied only to the two principal components (PC1 and PC2) of the TM's six non-thermal bands, then each remaining dataset was added, one at a time, and the algorithm was re-applied until all eight datasets (PC1, PC2, DEM, OBT, and the four texture datasets) were used. When compared to ground truth data, classification accuracy utilizing all eight datasets reached a maximum of 68.6% correctly classified pixels. Without any textural measure included in the classification (only using PC's, DEM, and OBT), overall accuracy was 54.2%. The addition of each dataset significantly improved the overall performance, suggesting that when classifying glacial landscape units, land cover, topography, overburden thickness, and a measure of surface roughness improves the accuracy of glacial landscape classification.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Benthic oxygen isotope records of deep marine sedimentary archives have yielded a wealth of information regarding ice sheet dynamics and climate change during the Pleistocene. However, since they often lack independent age control, these records are generally bound by a fixed phase relationship between orbital forcing and the climate response, e.g. ice volume changes. We present the first long (?1.2 Ma) benthic oxygen isotope record from the eastern Mediterranean, based on ODP Sites 967 and 968, which clearly reflects the behavior of global climate on a glacial-interglacial scale throughout the late Pleistocene time period. The age model for our record is based on tuning the elemental ratio of titanium versus aluminum (Ti/Al) against insolation. The Ti/Al record is dominated by the precession-related changes in northern African climate, i.e. monsoonal forcing, and hence largely independent of glacial-interglacial variability. We found the largest offset between our chronology and that of the widely applied, open ocean stacked record LR04 (Lisiecki and Raymo, 2005) for TVII (?624 ka), which occurred ?9 kyr earlier according to our estimates, though in agreement with the AICC2012 ?Dice chronology of EPICA Dome C (Bazin et al., 2013). Spectral cross-correlation analysis between our benthic ?18O record and 65°N summer insolation reveals significant amounts of power in the obliquity and precession range, with an average lag of 5.5 ± 0.8 kyr for obliquity, and 6.0 ± 1.0 kyr for precession. In addition, our results show that the obliquity-related time lag was smaller (3.0 ± 3.3 kyr) prior to ?900 ka than after (5.7 ± 1.1 kyr), suggesting that on average the glacial response time to obliquity forcing increased during the mid-Pleistocene transition, much later than assumed by Lisiecki and Raymo (2005). Finally, we found that almost all glacial terminations have a consistent phase relationship of ?45 ± 45° with respect to the precession and obliquity-driven increases in 65°N summer insolation, consistent with the general consensus that both obliquity and precession are important for deglaciation during the Late Pleistocene. Exceptions are glacial terminations TIIIb, T36 and potentially T32 (and TVII T24 and T34), which show this consistent phase relationship only with precession (only with obliquity). Our findings point towards an early (>1200 ka) onset of the Mid Pleistocene Transition. Vice versa, the timing of TVII, which can only be explained as a response to obliquity forcing, indicates that the transition lasted until at least after MIS 15.

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

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  20. 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.

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

    PubMed Central

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

    2014-01-01

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

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    Vazquez, J. A.; Woolford, J. M.

    2015-09-01

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

  5. 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.

  6. 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

  7. The hierarchical structure of glacial climatic oscillations: interactions between ice-sheet dynamics and climate

    NASA Astrophysics Data System (ADS)

    Paillard, Didier

    1995-04-01

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

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

    SciTech Connect

    Paillard, D.

    1995-04-01

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  11. Pleistocene glacial morphology and timing of last glacial cycle in cantabrian mountains (Northern Spain): new chronological data from the Asón area

    NASA Astrophysics Data System (ADS)

    Frochoso, Manuel; González-Pellejero, Raquel; Allende, Fernando

    2013-03-01

    The timing of the local last glacial maximum in the mountains of the Northern Iberian Peninsula is not synchronous with the global Last Glacial Maximum (LGM) probably due to the marginal position of the Northern Iberian Peninsula within the European continent. The study of a Cantabrian massif, the Asón platform and summits, provides new data on the extent and timing of the local last glaciation. Here we can place the last maximal extent of glaciers during Early Würm, according to OSL dating on till samples. The main glaciers developed at least between 78-65 ka BP, well centred on MIS 4 and even the transition to MIS 5. The erosive efficacy of these glaciers decreased later, ca. 45-40 ka BP, until they abruptly disappeared from the edges of the massif. A new ice advance left well-defined moraines at the edges of the massif's internal depressions, indicating a tongue disjunction phase with two glacier sub-stages, probably one at the beginning of the cooling ca. 27-25 ka BP, followed by a retreat and another glacial advance ca. 21-18 ka BP. After these episodes the glaciers disappeared from the Asón Mountains and only some residual glaciers were formed that may be related to the LGM.

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

    PubMed Central

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

    2011-01-01

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

  13. 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

  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. Modeling evidence for enhanced El Niño-Southern Oscillation amplitude during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    An, S.-I.; Timmermann, A.; Bejarano, L.; Jin, F.-F.; Justino, F.; Liu, Z.; Tudhope, A. W.

    2004-12-01

    We present a numerical eigenmode analysis of an intermediate El Niño-Southern Oscillation (ENSO) model which is driven by present-day observed background conditions as well as by simulated background conditions for the Last Glacial Maximum (LGM) about 21,000 years ago. The background conditions are obtained from two LGM simulations which were performed with the National Center for Atmospheric Research climate system model (CSM1.4) and an Earth system model of intermediate complexity (ECBilt-CLIO). Our analysis clearly shows that the leading 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-sustained interannual ENSO variations in the tropical Pacific. Our analysis indicates that off-equatorial climate conditions as well as a shoaling of the thermocline play a crucial role in amplifying the LGM ENSO mode.

  16. 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. . 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.

  17. On the mechanism of the Middle Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Bol'shakov, V. A.

    2015-09-01

    The phenomenon of the Middle Pleistocene Transition (MPT)—a change of 41 k.y. periodicity of Pleistocene glacial cycles to 100 k.y. ones at about 1.24 Ma—is studied. Some MPT mechanisms proposed earlier by different authors are considered. It is concluded that the resonant MPT mechanism, implying the change in eigen (resonant) frequency of glacial sheets in the Northern Hemisphere due to the change in size of these sheets, is the least contradicting and fits the best the relevant empirical data. With respect to this mechanism, climate variations in the Early Pleistocene, until 1.24 Ma, resonantly responded to 41 k.y. insolation oscillations, which were caused by variations in Earth's axial tilt. After 1.24 Ma, owing to the growth of the global ice sheet volume and the increase in the period of eigen oscillations of the ice sheets, the direct eccentricity insolation signal characterized by the 100 k.y. (not 400 k.y.) periodicity was resonantly strengthened first. Some problems that emerged in the basis of the proposed mechanism are discussed. This mechanism explains the MPT phenomenon, the unsolved "100 k.y. period problem," and the absence of the 400 k.y. periodicity in the Pleistocene climate oscillations from a common viewpoint.

  18. Late-glacial (Allerød/Younger Dryas) buried organic deposits, Nova Scotia, Canada. A contribution to the 'North Atlantic seaboard programme' of IGCP-253, 'Termination of the Pleistocene'

    NASA Astrophysics Data System (ADS)

    Mott, R. J.; Stea, R. R.

    Numerous deposits of organic, shallow-pond sediments and wetland peat accumulations buried by minerogenic sediments have been discovered throughout Nova Scotia. They are interpreted as representing a late-glacial climatic oscillation correlative with the Allerød/Younger Dryas event of Europe and the North Atlantic Ocean. The organic deposits began forming during the warm or warming interval following deglaciation and often record a transition to colder conditions. The climatic reversion recorded in many deposits began about 10.8 ka BP and continued or sustained cooling culminated in the burial of the organic deposits by minerogenic sediments indicative of solifluction and mass-wasting processes. Some deposits provide strong evidence for regeneration or rejuvenation of local glaciers. As the organic deposits are not as susceptible as lake sediments to contamination by old carbon, they provide a more reliable chronological framework for deglaciation and late-glacial vegetational history. Palynological evidence shows that pioneer herb tundra communities colonized some areas shortly after 13 ka BP. Willow and birch shrubs followed soon after. Spruce woodlands had migrated into the region prior to 10.8 ka BP but had not yet reached the northeast mainland and Cape Breton Island. Cooling after 10.8 ka BP decimated tree populations and favoured a return to shrub and herb communities. The record in the buried deposits was then truncated by deposition of minerogenic sediments, and lake sediment sequences from deeper basins with continuous sedimentation are required to complete the record.

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

    E-print Network

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  1. 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.

  2. 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.

    moraines analyzed for 10 Be, the exposure ages on two moraines are tightly clustered. The results indicate on relative-weathering features of moraines and comparisons to previously dated glacial sequences in the central Brooks Range. In addition, we analyzed cosmogenic 10 Be in surface boulders of four moraines

  3. Glacial/Interglacial Variability in Terrigenous Input and Paleoproductivity in the North Atlantic During the Middle Pleistocene (MIS 19 to MIS 31)

    NASA Astrophysics Data System (ADS)

    Almeida, I. H.; Sierro, F. J.; Filippelli, G. M.; Flores, J.

    2009-12-01

    A number of biogeochemical proxies, including nutrient/metal sedimentary ratios, can be used as tracers of past-productivity. Additionally, geochemical proxies of terrigenously-derived elements can also be used to reconstruct the source and flux of terrigenous sediments in the ocean. In order to evaluate differences in primary productivity and ice-dynamics at glacial/interglacial time scales in the North Atlantic, we present sediment geochemical data from Site IODP U1314 over the 778-1060 ky time-period. This Site is located on Gardar drift, southwest of Iceland at about 2800 m water depth. Sedimentation rates are 7-7,5 cm/ky. The sedimentary sequence recovered at this site consists of nannofossil oozes enriched in biogenic and terrigenous components. Our study reveals a different productivity record between glacial/interglacial periods, with increases occurring either at glacial/interglacial transitions or during interglacial intervals. To estimate this productivity changes, we have used the P/Ti ratio. Our record exhibits several abrupt increases in P/Ti, during interglacials and usually during glacial/interglacial terminations, in contrast with concentrations and fluxes of terrigenous elements (i.e., Fe, Al, and Ti) which are low during interglacials and increase during glacials. In addition, several prominent peaks of biogenic opal, carbonate, and TOC fluxes were observed and corresponded to warm events. Quantitative analyses of planktonic foraminifera and radiolarian performed in this core allow a better understanding of the oceanographic scenario during the studied period. We conclude that primary productivity in the North Atlantic is under the influence of global factors such as the migration of the polar front and iceberg discharge.

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

    NASA Technical Reports Server (NTRS)

    Saltzman, Barry; Maasch, Kirk A.

    1988-01-01

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

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

    PubMed Central

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  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

    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.

  8. Morphology and palaeoenvironmental interpretation of deformed soft-sediment clasts: examples from within Late Pleistocene glacial outwash, Tempo Valley, Northern Ireland

    NASA Astrophysics Data System (ADS)

    Knight, Jasper

    1999-10-01

    Glacial outwash, deposited during deglaciation of the late Devensian ice sheet, is present as a flat-topped valley fill in the Tempo Valley on the southern flanks of the Fintona Hills, Northern Ireland. Sedimentologically, the outwash comprises well-sorted and interbedded rippled to massive sands which record distal deposition within a proglacial water body. Beds of ripple-drift cross-laminated sands contain deformed (folded and contorted) soft-sediment clasts which are composed mainly of silt and clay. The soft-sediment clasts were deformed prior to final deposition because clast a- b planes lie conformable to sand laminae which are undeformed. Morphological characteristics of the soft-sediment clasts, and their facies context, provide evidence for transport mechanisms, depositional environment, and processes of clast deformation. The soft-sediment clasts were transported into a proglacial water body by unidirectional water currents (˜1.5-2.5 m s -1). Sediment transport processes include sediment bypassing within the water column, a low bedload component, and grain flow activity during waning flow stages. The overall morphology of soft-sediment clasts records between 1 and 3 distinct phases of hydroplastic deformation prior to emplacement. The deformation phases are recognised on the basis of morphologically `unrolling' the superimposed folds of the soft-sediment clasts. Deformation structures (i.e. fold style) and direction of the principal stress axis relative to clast axes suggest that clasts were reoriented with respect to water flow direction following each deformation phase. Processes of deformation include folding-over of the clast along its b axis into two or more components, crumpling and abrasion of the outer margins of the b plane, and squashing of the clast c axis (some of which may be post-depositional deformation). The presence of silt- and clay-rich soft-sediment clasts within the outwash succession suggests that they were ripped-up from shallow and irregular pools on the glacier forefield, into which fine sediments accumulated after flood or meltwater events, and transported distally into a proglacial water body. These inferences based on facies evidence and styles of hydroplastic deformation impact on reconstructions of local palaeogeography, and the wider interpretation of similar soft-sediment clasts in the geological record.

  9. Arctic ocean sediment texture and the Pleistocene climate cycle

    SciTech Connect

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

    1985-01-01

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

  10. 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

  11. Luminescence Chronology for the Formation of Glacial Lake Calgary, Southern Alberta, Canada: Age Constraints for the Initiation of the Late Pleistocene Retreat of the Laurentide Ice Sheet from its Western Margin

    NASA Astrophysics Data System (ADS)

    Munyikwa, K.; Rittenour, T. M.

    2014-12-01

    Glacial Lake Calgary in southern Alberta, Canada, was a Late Pleistocene proglacial lake that formed along the southwest margin of the Laurentide Ice Sheet (LIS), dammed by the retreating ice sheet margin. Attempts to constrain the age of the lake using radiocarbon methods have been hampered by the lack of datable organic material. In an effort to apply an alternative chronometer, this study uses two optically stimulated luminescence (OSL) dating approaches to date fine grained sand and silt that were deposited in the lake during its existence. OSL dating determines the depositional ages of sediments by measuring the energy from ionizing radiation that is stored in mineral grains such as quartz and feldspar. Dividing the stored energy, also referred to as the paleodose, by the rate at which the dose accumulated, allows an age to be ascertained. In one method applied in this study, the paleodose stored in the feldspar component of the sediment is determined using normalized infrared stimulated luminescence signals acquired using a portable OSL reader. In the second method, blue optically stimulated luminescence signals obtained from quartz separates from the sediment by employing a regular OSL reader and standard protocols are used to determine the paleodose. After correcting the feldspar data for anomalous fading, the age results from the two dating approaches are compared. The ages signify a time period by which the LIS had retreated from the study area and, hence, serve as constraints for the initiation of the retreat of the ice sheet from its western limit. Advantages and limitations of the dating methods are briefly discussed. Constraining the chronology of the retreat of the LIS from western Canada allows for a better understanding of the driving forces behind ice sheet retreat. Secondly, assigning a temporal scale to the postglacial evolution of the environment of the region permits a better insight into the dynamics of the physical and biological environments of the time. Thirdly, the region is at the heart of the ice-free corridor that was ostensibly used by early humans to migrate southwards to populate the Americas ca. 16 ka ago. Hence, an improved deglaciation chronology would allow a more comprehensive evaluation of this concept.

  12. What Drives Mediterranean Outflow Water Variability during the Mid-Pleistocene Transition and Early Pleistocene at IODP Site U1387 in the Gulf of Cadiz?

    NASA Astrophysics Data System (ADS)

    Voelker, A. H. L.; Jimenez-Espejo, F. J.; Bahr, A.; Acton, G.; Alberto, A.; Rebotim, A.; Salgueiro, E.; Roehl, U.

    2014-12-01

    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. 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, 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 dominant climate cyclicity 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. Planktonic and benthic ?18O records are tightly coupled highlighting the constant exchange between the (sub)surface waters and the MOW. Low benthic ?13C values during deglacial and peak interglacial periods, coinciding with insolation maxima, reveal a poorly ventilated upper MOW core and 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. During the warmer MIS 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.

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

    USGS Publications Warehouse

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

    1998-01-01

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

  14. Guatemalan forest synthesis after Pleistocene aridity

    PubMed Central

    Leyden, Barbara W.

    1984-01-01

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

  15. A ~180,000 years sedimentation history of a perialpine overdeepened glacial trough (Wehntal, N-Switzerland)

    E-print Network

    Gilli, Adrian

    into the past glacial history. Keywords Pleistocene Á Glacial erosion Á Proglacial sedimentation Á Alps Á- stantial bedrock erosion and re-deposition of unconsolidated sediment, forming a variety of glacialA ~180,000 years sedimentation history of a perialpine overdeepened glacial trough (Wehntal, N

  16. Diversification in subtropical mountains: phylogeography, Pleistocene demographic expansion, and evolution of polyphenic mandibles in Taiwanese stag beetle, Lucanus formosanus.

    PubMed

    Huang, Jen-Pan; Lin, Chung-Ping

    2010-12-01

    Pleistocene glacial oscillations have had profound impacts on the historical population dynamics of extant species. However, the genetic consequences of past climatic changes depend largely on the latitude and topography of the regions in question. This study investigates the effect of Pleistocene glacial periods and the Central Mountain Range on the phylogeography, historical demography, and phenotypic differentiation of a montane forest-dwelling stag beetle, Lucanus formosanus (Coleoptera: Lucanidae), which exhibits extensive mandible variations across mountain ranges in subtropical Taiwan. Analyses of mitochondrial (cox1) and nuclear (wg) loci reveal that L. formosanus originated nearly 1.6 million years ago (Mya) in the early Pleistocene period and consisted of geographically overlapping Alishan and Widespread clades. A drastic population expansion starting approximately 0.2 Mya in the Widespread clade likely resulted from altitudinal range shift of the temperate forests, which was closely tied to the arrival of the Riss glacial period in the late Middle Pleistocene. A ring-like pattern of historical gene flow among neighboring populations in the vicinity of the Central Mountain Range indicates that the mountains constitute a strong vicariant barrier to the east-west gene flow of L. formosanus populations. A geographic cline of decreasing mandible size from central to north and south, and onto southeast of Taiwan is inconsistent with the low overall phylogeographic structures. The degree of mandible variation does not correlate with the expected pattern of neutral evolution, indicating that the evolutionary diversification of this morphological weapon is most likely subject to sexual or natural selection. We hypothesize that the adaptive evolution of mandibles in L. formosanus is shaped largely by the habitat heterogeneity. PMID:20971199

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

    PubMed Central

    2012-01-01

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

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

    PubMed Central

    2014-01-01

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

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

    SciTech Connect

    Reasoner, M.A.; Rutter, N.W. ); Osborn, G. )

    1994-05-01

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

  20. 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.

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

    E-print Network

    Montgomery, David R.

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

  2. Ages and inferred causes of Late Pleistocene glaciations on Mauna Kea, Hawai'i

    E-print Network

    Zreda, Marek

    Ages and inferred causes of Late Pleistocene glaciations on Mauna Kea, Hawai'i JEFFREY S. PIGATI,1y., Elmore, D. and Sharp, W. D. 2008. Ages and inferred causes of Late Pleistocene glaciations on Mauna Kea April 2008; Accepted 17 April 2008 ABSTRACT: Glacial landforms on Mauna Kea, Hawai'i, show

  3. Obliquity and precession as pacemakers of Pleistocene deglaciations

    NASA Astrophysics Data System (ADS)

    Feng, Fabo; Bailer-Jones, C. A. L.

    2015-08-01

    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 (2.6-0.01 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 (the mid-Pleistocene transition). We also find that geomagnetic field and orbital inclination variations are unlikely to have paced the Pleistocene deglaciations. We estimate that the mid-Pleistocene transition took place over a 220 kyr interval centered on a time 715 kyr ago, although the data permit a range of 600-1000 kyr. This transition, occurring within just two 100 kyr cycles, indicates a relatively rapid change in the climate response to insolation.

  4. 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.

    2013-03-01

    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- 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 favourable 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), Guado 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 behaviours benefited from 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 MIS 13 and 9 (ca. 500 to 300 ka). In this basin the persistence of high edaphic humidity, even during the glacial phases, could have favoured 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 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.

  5. NO MORE ICE IN PARADISE: AGES OF PLEISTOCENE GLACIATIONS ON MAUNA KEA, HAWAI'I

    E-print Network

    Zreda, Marek

    NO MORE ICE IN PARADISE: AGES OF PLEISTOCENE GLACIATIONS ON MAUNA KEA, HAWAI'I PIGATI, Jeffrey S.1 Court, Prescott, AZ 86305 Glacial deposits on Mauna Kea, the only location in the interior tropical events on Mauna Kea using in-situ cosmogenic 36 Cl dating of boulders and glacially abraded bedrock

  6. 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.

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

    E-print Network

    Cooper, David Matthew

    2013-11-28

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

  8. Plio-Pleistocene African Climate

    NASA Astrophysics Data System (ADS)

    Demenocal, Peter B.

    1995-10-01

    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 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.

  9. Plio-pleistocene African climate

    SciTech Connect

    deMenocal, P.B.

    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.

  10. Paleoclimatic implications of fossil shoreline deposits in the southern basin and range province during the Pleistocene-Holocene transition

    NASA Astrophysics Data System (ADS)

    Kowler, A. L.

    2010-12-01

    Paleolake shoreline deposits throughout the southern Basin and Range (SBAR) signify past intervals of steady-state climatic conditions occuring during the late Pleistocene slightly before, as well as after the Last Glacial Maximum (LGM; ~23-19 Ka). Unfortunately, a lack of knowledge about the age of fossil shoreline deposits—due to C-14 related uncertainties and incomplete dating of shorelines—has resulted in a large gap in our knowledge about past climatic and surface hydrologic conditions in the SBAR. Several studies collectively reveal multiple lake level oscillations during the LGM and last part of the Pleistocene, with reasonably well dated shoreline deposits existing for only four paleolakes: one in central New Mexico (Estancia), two in southwestern New Mexico (Playas and Cloverdale), and one in southeastern Arizona (Cochise). In summary, there is evidence for a pre-LGM high-stand at Cochise (>26 Ka), LGM high-stands at Estancia and Cloverdale (>20-16 Ka), deglacial age high-stands at Playas and Cochise (16-13 Ka), and latest Pleistocene-early Holocene still stands of as yet undetermined elevation at Playas and Estancia (13-9K). Further, the absence of high-stands from 11-10 Ka suggests that the Younger Dryas climatic reversal—which is detected in the stable O isotopic composition of speleothems from Cave-of-the-Bells in southeastern Arizona—was marked there by a decrease in mean annual air temperature without a significant increase in precipitation. Alternatively, if a return to glacial precipitation levels did occur, then it was for an interval so short that sedimentological evidence was not preserved. This presentation will cover the afore mentioned chronologies, along with discussion about associated atmospheric circulation patterns in the SBAR and across western North America.

  11. Probability of moraine survival in a succession of glacial advances.

    USGS Publications Warehouse

    Gibbons, A.B.; Megeath, J.D.; Pierce, K.L.

    1984-01-01

    Emplacement of glacial moraines normally results in obliteration of older moraines deposited by less extensive glacial advances, a process we call 'obliterative overlap'. Assuming randomness and obliterative overlap, after 10 glacial episodes the most likely number of surviving moraines is only three. The record of the Pleistocene is in agreement with the probability analysis: the 10 glaciations during the past 0.9 Myr inferred from the deep-sea record resulted in moraine sequences in which only two or three different-aged moraine belts can generally be distinguished. -from Authors

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Amphibian DNA shows marked genetic structure and tracks pleistocene climate change in northeastern Brazil.

    PubMed

    Carnaval, Ana Carolina; Bates, John M

    2007-12-01

    The glacial refugia paradigm has been broadly applied to patterns of species dynamics and population diversification. However, recent geological studies have demonstrated striking Pleistocene climate changes in currently semiarid northeastern Brazil at time intervals much more frequent than the climatic oscillations associated with glacial and interglacial periods. These geomorphic data documented recurrent pulses of wet regimes in the past 210,000 years that correlate with climate anomalies affecting multiple continents. While analyzing DNA sequences of two mitochondrial genes (cytochrome b and NADH-dehydrogenase subunit 2) and one nuclear marker (cellular-myelocytomatosis proto-oncogene) in the forest-associated frogs Proceratophrys boiei and Ischnocnema gr. ramagii, we found evidence of biological responses consistent with these pluvial maxima events. Sampled areas included old, naturally isolated forest enclaves within the semiarid Caatinga, as well as recent man-made fragments of humid coastal Atlantic forest. Results show that mtDNA lineages in enclave populations are monophyletic or nearly so, whereas nonenclave populations are polyphyletic and more diverse. The studied taxa show evidence of demographic expansions at times that match phases of pluvial maxima inferred from geological data. Divergence times between several populations fall within comparatively drier intervals suggested by geomorphology. Mitochondrial and nuclear data show local populations to be genetically structured, with some high levels of differentiation that suggest the need of further taxonomic work. PMID:17941838

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

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

  18. Different orbital rhythms in the Asian summer monsoon records from North and South China during the Pleistocene

    NASA Astrophysics Data System (ADS)

    Ao, Hong; Dekkers, Mark J.; Xiao, Guoqiao; Yang, Xiaoqiang; Qin, Li; Liu, Xiaodong; Qiang, Xiaoke; Chang, Hong; Zhao, Hui

    2012-01-01

    Here we construct a Pleistocene astronomical timescale for the Nihewan fluvio-lacustrine sediments (North China), via tuning a stacked summer monsoon index generated from grain size and low-field magnetic susceptibility records to orbital obliquity and precession. Combining the summer monsoon records retrieved from the Nihewan and the Chinese loess deposits in North China on the one hand, and those from the stalagmites and the marine deposits in South China on the other, the Asian summer monsoon records from North and South China appear to show different orbital rhythms during the Pleistocene. The monsoon records from both the Nihewan Basin and Chinese Loess Plateau are equally characterized by dominant obliquity (41 kyr) before ~ 0.9 Ma and dominant eccentricity (100 kyr) after this time, closely following the marine ? 18O record. In contrast, the ? 18O record of stalagmites from South China (Wang et al., 2001, 2008b; Cheng et al., 2009) and the iron oxide proxy record from the South China Sea (Zhang et al., 2007, 2009; Ao et al., 2011), which are considered as a proxy indicator of the Asian summer monsoon intensity in South China, reveal a dominant cyclicity of precession (23 kyr) over the past 1.8 Myr, closely following the solar insolation curve instead. We further present a possible interpretation of the different orbital rhythms in the Asian summer monsoon records from North and South China. The orbital rhythm in the summer monsoon records from North China is mainly modulated by the migration of the Asian summer monsoon due to changes in sea level and Northern Hemisphere ice volume during glacial-interglacial cycles. Strong summer monsoon may have reached North China mainly during interglacial periods. During glacial periods when the sea level was low and Northern Hemisphere ice volume was large, the southeasterly migration of summer monsoon would make North China beyond the reach of the summer monsoon. Thus the summer monsoon records from North China primarily show a cyclic oscillation similar to the glacial-interglacial climate cycles as indicated by cycle-by-cycle correlation between monsoon and marine oxygen isotope records. However, the summer monsoon always prevailed over South China during both glacial and interglacial periods. Therefore, the orbital-scale variability of the summer monsoon in South China shows a direct response to the orbital variations in the low-latitude summer insolation, without significant influence from the migration of monsoon during glacial-interglacial cycles.

  19. 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

  20. 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

  1. 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.

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

    PubMed Central

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

    2015-01-01

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

  3. 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

  4. 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 ...

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

    NASA Astrophysics Data System (ADS)

    Ashwin, Peter; Ditlevsen, Peter

    2015-11-01

    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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  8. Sr-isotopic variation in the Quaternary: The record from glacial and interglacial marine terraces

    SciTech Connect

    Ludwig, K.R.; Muhs, D.R.; Simmons, K.R.; Szabo, B.J.; Moore, J.G. )

    1990-05-01

    The authors report high-precision Sr isotope of aragonitic fossils from Pleistocene marine terraces, which formed during both glacial and interglacial periods, to (1) constrain the marine Sr-isotope trend for the late Quaternary, and (2) test the long-term marine Sr-isotope trend for reversals related to glacial-interglacial transitions. Analyses of multiple samples of mollusks from each of 15 interglacial terraces on San Nicolas Island, San Clemente Island, and the Palos Verdes Hills (California) define a marine Sr-isotope trend (assigning terrace ages based on an assumption of constant long-term uplift rates calculated from the height of dated 120-Ka terraces) that is generally similar to the trend defined by the data of recent workers for DSDP samples. Data for three U-series dated interglacial terraces on the East Coast of the US plot close to the California trend, as do data for 14 coral samples of 0-750 Ka age (dated by mass-spectrometric {sup 234}U/{sup 238}U) from submerged, glacial-stage reefs off Hawaii. As a whole, their data indicate an approximately linear increase of approximately 0.05 % in {sup 87}Sr/{sup 86}Sr over the last 800 k.y., confirm the presence of a subtle ({approximately}0.01 %) reversal between approximately 900 and 600 Ka, and resolve a previously unrecognized reversal of approximately 0.02{per thousand} between approximately 1,400 and 1,200 Ka. In addition, the lack of obvious fine structure in samples younger than 800 ka indicates that the amplitude of any short-period oscillations (<100 ky.) in the marine {sup 87}Sr/{sup 86}Sr trend for the Late Quaternary is probably less than approximately 0.02{per thousand}.

  9. Small mammal diversity loss in response to late-Pleistocene climatic change

    E-print Network

    Hadly, Elizabeth

    shifted from the cold, arid Last Glacial Maximum to the warm, mesic Holocene interglacial, causing many insmallmammals in northern California during the last `natural' global warming event at the Pleistocene stressed as humans arrived on the continent4 . The resulting megafaunal extinction event, in which 70

  10. Consequences of pacing the Pleistocene 100 kyr ice ages by nonlinear phase locking to Milankovitch forcing

    E-print Network

    Huybers, Peter

    Consequences of pacing the Pleistocene 100 kyr ice ages by nonlinear phase locking to Milankovitch in the presence of noise in the climate system and can be effective at setting glacial termination times even when the precession and obliquity bands account only for a small portion of the total power of an ice volume record

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

    E-print Network

    Zürich, Universität

    at least some ITS clones of P. marginata and P. allionii. Conclusions: Our results suggest an initial. marginata and higher total nucleotide diversity of ITS clones in dodecaploid vs. hexaploid individuals in the copy number of the nuclear genome, has played a key role in plant evolution [1-7]. Indeed, recent

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

    NASA Astrophysics Data System (ADS)

    Pedersen, V. K.; Egholm, D.

    2012-12-01

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

  13. 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.

  14. Interglacial Climate from Deglaciation to Glacial Inception

    NASA Astrophysics Data System (ADS)

    McManus, J. F.; Raynaud, D.; Tzedakis, P. C.; Wolff, E. W.; Yin, Q.; Pol, K.; Skinner, L. C.; Crucifix, M.; Hodell, D. A.; Berger, A.; Ganopolski, A.; Otto-Bliesner, B. L.; Mangili, C.

    2014-12-01

    Interglacials are the warm, minimum ice, high sea level end-member of the glacial climate cycles of the Pleistocene, with the present Holocene period as the most recent example. We have identified 11 interglacial intervals in the last 800 ka and have reviewed their occurrence, intensity, shape and timing, including the processes that accompany deglaciation and glacial inception. Our compilation of evidence from marine, terrestrial and ice core climate archives suggests that, despite spatial inhomogeneity, marine isotope stages (MIS) 5 and 11 were globally strong (warm), while MIS 13 tended to be cool. A step change in strength of interglacials at ~450 ka (mid-Brunhes) is apparent only in CO2, and Antarctic and deep ocean temperature. The onset of interglacials (deglaciation or glacial "termination") is relatively rapid, and seems to require a combination of low orbital precession (high northern hemisphere summer insolation) and the existence of a large ice sheet. Terminations involve highly non-linear interactions of ocean and atmospheric dynamics, sea level, CO2 and temperature, along with the imposed external insolation forcing. The precise timing appears to be closely tied to the fall in precession but may be modulated by millennial scale climate variability that determines the pattern of change seen in temperature in each hemisphere. There is some organized variability and a range of climatic trends within interglacials, resulting in intensity maxima that may occur either early or late in different instances. The end of interglacials (glacial inception) is typically a slower process involving a global sequence of changes. Interglacials are typically 10-30 ka long. Proposed analogs do not easily inform us about the natural progression or length of the current interglacial, but due to a combination of reduced insolation variability and greenhouse gas concentrations the timing of the next glacial inception appears to be many tens of millennia in the future.

  15. Pleistocene Indian Monsoon Rainfall Variability

    NASA Astrophysics Data System (ADS)

    Yirgaw, D. G.; Hathorne, E. C.; Giosan, L.; Collett, T. S.; Sijingeo, A. V.; Nath, B. N.; Frank, M.

    2014-12-01

    The past variability of the Indian Monsoon is mostly known from records of wind strength over the Arabian Sea. Here we investigate proxies for fresh water input and runoff in a region of strong monsoon precipitation that is a major moisture source for the east Asian Monsoon. A sediment core obtained by the IODP vessel JOIDES Resolution and a gravity core from the Alcock Seamount complex in the Andaman Sea are used to examine the past monsoon variability on the Indian sub-continent and directly over the ocean. The current dataset covers the last glacial and deglacial but will eventually provide a Pleistocene record. We utilise the ecological habitats of G. sacculifer and N. dutertrei to investigate the freshwater-induced stratification with paired Mg/Ca and ?18O analyses to estimate seawater ?18O (?18Osw). During the last 60 kyrs, Ba/Ca ratios and ?18Osw values generally agree well between the two cores and suggest the weakest surface runoff and monsoon during the LGM and strongest monsoon during the Holocene. The difference in ?18O between the species, interpreted as a proxy for upper ocean stratification, implies stratification developed around 37 ka and remained relatively constant during the LGM, deglacial and Holocene. To investigate monsoon variability for intervals in the past, single shell Mg/Ca and ?18O analyses have been conducted. Mg/Ca ratios from individual shells of N. dutertrei suggest relatively small changes in temperature. However, individual N. dutertrei ?18O differ greatly between the mid-Holocene and samples from the LGM and a nearby core top. The mid-Holocene individuals have a greater range and large skew towards negative values indicating greater fresh water influence.

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

    SciTech Connect

    McCabe, A.M.; O`Cofaigh, C.

    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.

  17. 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

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  20. 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.

  1. U-series and oxygen isotope chronology of the mid-Pleistocene Lake Amora (Dead Sea basin)

    E-print Network

    Torfstein, Adi

    U-series and oxygen isotope chronology of the mid-Pleistocene Lake Amora (Dead Sea basin) Adi of Lake Amora (Dead Sea basin, Israel), whose deposits (the Amora Formation) comprise one of the longest (Marine Isotope Stages (MIS) 18 to 5). Taking the last glacial Lake Lisan and the Holocene Dead Sea

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

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  4. 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).

  5. Earth's glacial record and its tectonic setting

    NASA Astrophysics Data System (ADS)

    Eyles, N.

    1993-09-01

    Glaciations have occurred episodically at different time intervals and for different durations in Earth's history. Ice covers have formed in a wide range of plate tectonic and structural settings but the bulk of Earth's glacial record can be shown to have been deposited and preserved in basins within extensional settings. In such basins, source area uplift and basin subsidence fulfill the tectonic preconditions for the initiation of glaciation and the accomodation and preservation of glaciclastic sediments. Tectonic setting, in particular subsidence rates, also dictates the type of glaciclastic facies and facies successions that are deposited. Many pre-Pleistocene glaciated basins commonly contain well-defined tectonostratigraphic successions recording the interplay of tectonics and sedimentation; traditional climatostratigraphic approaches involving interpretation in terms of either ice advance/retreat cycles or glacio-eustatic sea-level change require revision. The direct record of continental glaciation in Earth history, in the form of classically-recognised continental glacial landforms and "tillites", is meagre; it is probable that more than 95% of the volume of preserved "glacial" strata are glacially-influenced marine deposits that record delivery of large amounts of glaciclastic sediment to offshore basins. This flux has been partially or completely reworked by "normal" sedimentary processes such that the record of glaciation and climate change is recorded in marine successions and is difficult to decipher. The dominant "glacial" facies in the rock record are subaqueous debris flow diamictites and turbidites recording the selective preservation of poorly-sorted glaciclastic sediment deposited in deep water basins by sediment gravity flows. However, these facies are also typical of many non-glacial settings, especially volcanically-influenced environments; numerous Archean and Proterozoic diamictites, described in the older literature as tillites, have no clearly established glacial parentage. The same remarks apply to many successions of laminated and thin-bedded facies interpreted as "varvites". Despite suggestions of much lower values of solar luminosity (the weak young sun hypothesis), the stratigraphic record of Archean glaciations is not extensive and may be the result of non-preservation. However, the effects of very different Archean global tectonic regimes and much higher geothermal heat flows, combined with a Venus-like atmosphere warmed by elevated levels of CO 2, cannot be ruled out. The oldest unambiguous glacial succession in Earth history appears to be the Early Proterozoic Gowganda Formation of the Huronian Supergroup in Ontario; the age of this event is not well-constrained but glaciation coincided with regional rifting, and may be causally related to, oxygenation of Earth's atmosphere just after 2300 Ma. New evidence that oxygenation is tectonically, not biologically driven, stresses the intimate relationship between plate tectonics, evolution of the atmosphere and glaciation. Global geochemical controls, such as elevated atmospheric CO 2 levels, may be responsible for a long mid-Proterozoic non-glacial interval after 2000 Ma that was terminated by the Late Proterozoic glaciations just after 800 Ma. A persistent theme in both Late Proterozoic and Phanerozoic glaciations is the adiabatic effect of tectonic uplift, either along collisional margins or as a result of passive margin uplifts in areas of extended crust, as the trigger for glaciation; the process is reinforced by global geochemical feedback, principally the drawdown of atmospheric CO 2 and Milankovitch "astronomical" forcing but these are unlikely, by themselves, to inititiate glaciation. The same remarks apply to late Cenozoic glaciations. Late Proterozoic glacially-influenced strata occur on all seven continents and fall into two tectonostratigraphic types. In the first category are thick sucessions of turbidites and mass flows deposited along active, compressional plate margi

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

    PubMed Central

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

    2006-01-01

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

  7. 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.

  8. A first 10Be cosmogenic glacial chronology from the High Atlas, Morocco, during the last glacial cycle.

    NASA Astrophysics Data System (ADS)

    Fink, David; Hughes, Philip; Fenton, Cassie

    2014-05-01

    Glacial geomorphological mapping, 10Be cosmogenic exposure ages of 21 erratics from cirque-valley systems and paleo-glacier climate modelling in the High Atlas Mountains, Morocco (31.1° N, 7.9° W), provides new and novel insights as to the history and evolution of the largest desert region on Earth. The Atlas Mountains display evidence of extensive and multiple Late Pleistocene glaciations whose extent is significantly larger than that recognised by previous workers. The largest glaciers formed in the Toubkal massif where we find 3 distinct phases of glacial advances within the last glacial cycle. The oldest moraines occurring at the lowest elevations have yielded eight 10Be ages ranging from 30 to 88 ka. Six of eight samples from moraines at intermediate elevations gave ages of 19 to 25 ka (2 outliers) which correlates well with the global Last Glacial Maximum (ca. 26-21 ka) and the last termination during marine isotope stage 2. Five erratics from the youngest and most elevated moraines yielded a suite of normally distributed exposure ages from 11 to 13 ka which supports a correlation with the northern hemisphere Younger Dryas (12.9-11.7 ka). The glacial record of the High Atlas effectively reflects moisture supply to the north-western Sahara Desert and can provide an indication of shifts between arid and pluvial conditions. The plaeo equilibrium line altitudes (ELA) of these three glacier phases was more than 1000 m lower than the predicted ELA based on today's temperatures. Glacier-climate modelling indicates that for each of these glacier phases climate was not only significantly cooler than today, but also much wetter. The new evidence on the extent, timing and palaeoclimatic significance of glaciations in this region has major implications for understanding moisture transfer between the North Atlantic Ocean and the Sahara Desert during Pleistocene cold stages.

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

  10. Aspects of conducting site investigations in glacial terrain

    SciTech Connect

    Schilling, K.E. )

    1993-03-01

    Much of northern US is mantled by Pleistocene glacial drift consisting of heterogeneous deposits of fine to coarse-textured sediments. Hazardous waste site investigations in glacial settings can often present unique design and implementation considerations. Complex glacial stratigraphy encountered during drilling activities demands flexibility built into work plans to allow for field decisions based on field conditions. Continuous cores should be collected from boreholes on a routine basis for stratigraphic purposes with particular importance assigned to field identification of relative permeabilities of stratigraphic units. Selection of appropriate field screening methodology should be based on site conditions. Utilization of open borehole groundwater sampling is recommended for fine-textured glacial settings where soil gas and well point sampling are ineffective. Installation of boreholes allows for collection of stratigraphic information and enables more surface area exposed beneath the water table for groundwater recharge and sampling. Water level determinations can be made on open boreholes for an initial assessment of the horizontal direction of groundwater flow. Placement of screens for monitoring wells should be based on field determination of likely groundwater flow paths. Nested wells are necessary to define the vertical groundwater flow system at most sites. Evaluation of the vertical flow system can often dominate site investigations in fine-textured glacial terrain. Two case studies from Iowa illustrate the usefulness of incorporating the above considerations in planning and implementing in fine-textured glacial sediments. Field investigations utilizing open borehole groundwater sampling successfully delineated site glacial geology and hydrogeology for determination of the nature and extent of groundwater contamination and better located the horizontal and vertical placement of monitoring wells.

  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. An early to mid-Pleistocene deep Arctic Ocean ostracode fauna with North Atlantic affinities

    USGS Publications Warehouse

    DeNinno, Lauren H.; Cronin, Thomas M.; Rodriquez-Lazaro, J.; Brenner, Alec R.

    2015-01-01

    An early to middle Pleistocene ostracode fauna was discovered in sediment core P1-93-AR-23 (P23, 76.95°N, 155.07°W) from 951 meter water depth from the Northwind Ridge, western Arctic Ocean. Piston core P23 yielded more than 30,000 specimens and a total of about 30 species. Several early to mid-Pleistocene species in the genera Krithe,Echinocythereis, Pterygocythereis, and Arcacythere are now extinct in the Arctic and show taxonomic affinities to North Atlantic Ocean species. Our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the Mid-Pleistocene Transition (MPT, ~ 1.2 to 0.7 Ma) and the Mid-Brunhes Event (MBE, ~ 400 ka) reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400,000 years.

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

    NASA Astrophysics Data System (ADS)

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

    1986-11-01

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

  14. New data on the pleistocene of Mallorca

    NASA Astrophysics Data System (ADS)

    Hearty, P. J.

    Stratigraphic, geomorphologic and isoleucine epimerization studies at 15 sites in Mallorca define four aminozones (A, C, E and F-G) of increasing age that are related to transgressive-regressive marine cycles from the Holocene to the mid Pleistocene. Calibration of aminozone E ( Glycymeris aIle/Ile mean from all sites = 0.41 ± 0.03 ( n=38)) is provided by a 129 ± 7 ka U-series coral age on Cladocora caespitosa from Son Grauet. Of the younger aminozones, A relates to the Holocene transgression and aminozone C to a mid to late isotopic stage 5 event (90 ± 15 ka) revealed only by supralittoral eolianites. Assigning an age to the older, poorly resolved aminozones F and G (called F-G in this case) is uncertain without supporting radiometric data. But an age of > 180 ka can be assigned to these aminozone (s) F-G based on a kinetic model and other examples in the Mediterranean. Several deposits, previously dated (U-series, molluscs) between 75 and > 300 ka appear to belong to the last interglacial complex (Stage 5) and aminozone E. A proposed revision of the positive sea level history of Mallorca shows multiple minor oscillations during the major last interglacial cycle (Stage 5) and two mid Pleistocene sea levels, one lower than present and the other at about 14 m a.s.l.

  15. Glacial integrative modelling.

    PubMed

    Ganopolski, Andrey

    2003-09-15

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

  16. Evidence for Obliquity Forcing of Glacial Termination II

    NASA Astrophysics Data System (ADS)

    Drysdale, R. N.; Hellstrom, J. C.; Zanchetta, G.; Fallick, A. E.; Sánchez Goñi, M. F.; Couchoud, I.; McDonald, J.; Maas, R.; Lohmann, G.; Isola, I.

    2009-09-01

    Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth’s obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 ± 2500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth’s obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2014-01-01

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

  1. A Late Pleistocene sea level stack

    NASA Astrophysics Data System (ADS)

    Spratt, R. M.; Lisiecki, L. E.

    2015-08-01

    Late Pleistocene sea level has been reconstructed from ocean sediment core data using a wide variety of proxies and models. However, the accuracy of individual reconstructions is limited by measurement error, local variations in salinity and temperature, and assumptions particular to each technique. Here we present a sea level stack (average) which increases the signal-to-noise ratio of individual reconstructions. Specifically, we perform principal component analysis (PCA) on seven records from 0-430 ka and five records from 0-798 ka. The first principal component, which we use as the stack, describes ~80 % of the variance in the data and is similar using either five or seven records. After scaling the stack based on Holocene and Last Glacial Maximum (LGM) sea level estimates, the stack agrees to within 5 m with isostatically adjusted coral sea level estimates for Marine Isotope Stages 5e and 11 (125 and 400 ka, respectively). When we compare the sea level stack with the ?18O of benthic foraminifera, we find that sea level change accounts for about ~40 % of the total orbital-band variance in benthic ?18O, compared to a 65 % contribution during the LGM-to-Holocene transition. Additionally, the second and third principal components of our analyses reflect differences between proxy records associated with spatial variations in the ?18O of seawater.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    SciTech Connect

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

    1985-01-01

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

  4. Giant glacial cirques of non-mountainous terrains

    NASA Astrophysics Data System (ADS)

    Amantov, A.; Amantova, M.

    2012-04-01

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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, ?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.

  7. 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

  8. 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

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  10. 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…

  11. 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.

  12. 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

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

    SciTech Connect

    De Oliveira, P.E.; Colinvaux, P.A. )

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

    NASA Astrophysics Data System (ADS)

    Helmens, Karin F.

    2014-02-01

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

  15. Constraining Middle Pleistocene Glaciations in Birmingham, England; Using Optical Stimulated Luminescence (OSL) Dating.

    NASA Astrophysics Data System (ADS)

    Gibson, S. M.; Gibbard, P. L.; Bateman, M. D.; Boreham, S.

    2014-12-01

    Birmingham is built on a complex sequence of Middle Pleistocene sediments, representing at least three lowland glaciations (MIS12, MIS6, and MIS2). British Geological Survey mapping accounts 75% of the land mass as Quaternary deposits; predominantly glacial-sandy tills, glacial-fluvial sands, clays and organic silts and peats. Understanding the age of fluvial-glacial outwash, related to specific glaciations, is critical in establishing a Geochronology of Birmingham. Shotton (1953) found a series of Middle Pleistocene glacial sediments, termed the Wolstonian, intermediate in age between MIS11 and MIS5e Interglacial's. Uncertainty surrounding the relation to East Anglian sequences developed by Rose (1987) implies Birmingham sequences should be referred to MIS12. Despite this, younger Middle Pleistocene glacial sequences occur in Birmingham, yet uncertainty has deepened over our understanding of the complex, inaccessible sediments, especially as deposits have similar extent with MIS2 sequences. Five Optical Stimulated Luminescence (OSL) dates from three sites around Birmingham have been sampled. East of Birmingham, ice advanced from the Irish Sea and later the North East. In Wolston, a sample of outwash sand, associated with the Thurssington Till, is dated. In Meriden, two samples of outwash sands, associated with a distal Oadby Till, are dated. West of Birmingham, ice advanced from the Welsh Ice Sheet. In Seisdon, two samples of an Esker and outwash sand, associated with a Ridgeacre Till, are dated. Correlation of OSL dates provide an important constraint on understanding the history of Birmingham. Using GSI3D modeling to correlate geochronology and sedimentology, the significance of OSL dating can be understood within the complex sequences (and regional stratigraphy), complimented by Cosmogenic and Palynology dates taken in South West and North East. OSL dating on Birmingham's outwash sands, deposited by extensive repeated Middle Pleistocene glaciations, asserts the Wolstonian Glaciation was present in Birmingham during MIS6, this contributes hugely to debate surrounding the timing of glaciations in East Anglia and across the UK. This has a wider significance due to East Anglia sequences being associated with sequences in the Netherlands, Denmark and Germany (Rose, 2009; Lee et al, 2012).

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    PubMed

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

    2009-03-01

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

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

    USGS Publications Warehouse

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

    2008-01-01

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

  19. Simulating the mid-Pleistocene transition through regolith removal

    NASA Astrophysics Data System (ADS)

    Tabor, Clay R.; Poulsen, Christopher J.

    2016-01-01

    Quaternary ?18O ice-volume proxy records show a transition from high frequency, small-amplitude glacial cycles to low frequency, large-amplitude glacial cycles. This reorganization of the climate system, termed the mid-Pleistocene transition (MPT), is thought to reflect a change in land-ice response to orbital forcing, despite no significant change in orbital cycles during this period. One potential explanation for the MPT proposes that gradual erosion of high-latitude northern hemisphere regolith by multiple cycles of glaciation caused a transition in ice sheet response to external forcing. Here, we explore this "regolith hypothesis" using a complex Earth system model. We show that simulating a transition from deformable sediment to crystalline bedrock produces an evolution in ice-volume response similar to proxy reconstructions of the MPT. The simulated change in ice-volume response is due to a combination of climate and ice-flow changes, with crystalline bedrock producing thicker, colder ice sheets that accumulate more snowfall and have a smaller ablation zone. Further, experiments that include transient eccentricity-amplifying CO2 forcing show only small differences in ice response compared to those with orbital forcing only, suggesting that cycles of CO2 were not the primary cause of the MPT.

  20. 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.

  1. 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.

  2. Small mammal diversity loss in response to late-Pleistocene climatic change.

    PubMed

    Blois, Jessica L; McGuire, Jenny L; Hadly, Elizabeth A

    2010-06-10

    Communities have been shaped in numerous ways by past climatic change; this process continues today. At the end of the Pleistocene epoch about 11,700 years ago, North American communities were substantially altered by the interplay of two events. The climate shifted from the cold, arid Last Glacial Maximum to the warm, mesic Holocene interglacial, causing many mammal species to shift their geographic distributions substantially. Populations were further stressed as humans arrived on the continent. The resulting megafaunal extinction event, in which 70 of the roughly 220 largest mammals in North America (32%) became extinct, has received much attention. However, responses of small mammals to events at the end of the Pleistocene have been much less studied, despite the sensitivity of these animals to current and future environmental change. Here we examine community changes in small mammals in northern California during the last 'natural' global warming event at the Pleistocene-Holocene transition and show that even though no small mammals in the local community became extinct, species losses and gains, combined with changes in abundance, caused declines in both the evenness and richness of communities. Modern mammalian communities are thus depauperate not only as a result of megafaunal extinctions at the end of the Pleistocene but also because of diversity loss among small mammals. Our results suggest that across future landscapes there will be some unanticipated effects of global change on diversity: restructuring of small mammal communities, significant loss of richness, and perhaps the rising dominance of native 'weedy' species. PMID:20495547

  3. A morphometric analysis of the Late Pleistocene Human Skeleton from the Moh Khiew Cave in Thailand.

    PubMed

    Matsumura, Hirofumi; Pookajorn, Surin

    2005-01-01

    Few Late Pleistocene human remains have been found in Southeast Asia and the morphological features of the people of that age are still largely unknown due to the virtual lack of human remains in the area. Recent excavations at the Moh Khiew Cave in Thailand resulted in the discovery of a Late Pleistocene human skeleton in a relatively good state of preservation. An AMS radiocarbon date on the charcoal sample gathered from the burial gave a result of 25,800 +/- 600 BP, implying that the inhabitants of Moh Khiew Cave resided in a part of Sundaland during the last glacial age. In debates on the population history of Southeast Asia, it has been repeatedly advocated that Southeast Asia was occupied by indigenous people akin to present-day Australo-Melanesians prior to an expansion of migrants from Northeast Asia into this area. Morphometric analyses were undertaken to test the validity of this hypothesis. In the present study, cranial and dental measurements recorded from the Moh Khiew remains are compared with those of early and modern samples from Southeast Asia and Australia. These comparisons demonstrate that the Moh Khiew specimen resembles the Late Pleistocene series from Coobool Creek, Australia in both cranial and dental measurements. These results suggest that the Moh Khiew skeleton, as well as other fossil remains from the Tabon, Niah and Gua Gunung sites, represents a member of the Sundaland population during the Late Pleistocene, who may share common ancestry with the present-day Australian Aborigines and Melanesians. PMID:16130834

  4. Somma-Vesuvius ground deformation over the last glacial cycle

    NASA Astrophysics Data System (ADS)

    Marturano, Aldo; Aiello, Giuseppe; Barra, Diana

    2013-04-01

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

  5. Pleistocene aridification cycles shaped the contemporary genetic architecture of Southern African baboons.

    PubMed

    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

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

    PubMed

    Pena, Leopoldo D; Goldstein, Steven L

    2014-07-18

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

  8. What drives glacial cycles

    SciTech Connect

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

    1990-01-01

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

  9. 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

  10. 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

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

    PubMed

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

    2002-08-01

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

  12. Glacial and periglacial geomorphology and its paleoclimatological significance in three North Ethiopian Mountains, including a detailed geomorphological map

    NASA Astrophysics Data System (ADS)

    Hendrickx, Hanne; Jacob, Miro; Frankl, Amaury; Nyssen, Jan

    2015-10-01

    Geomorphological investigations and detailed mapping of past and present (peri)glacial landforms are required in order to understand the impact of climatic anomalies. The Ethiopian Highlands show a great variety in past and contemporary climate, and therefore, in the occurrence of glacial and periglacial landforms. However, only a few mountain areas have been studied, and detailed geomorphological understanding is lacking. In order to allow a fine reconstruction of the impact of the past glacial cycle on the geomorphology, vegetation complexes, and temperature anomalies, a detailed geomorphological map of three mountain areas (Mt. Ferrah Amba, 12°51?N 39°29?E; Mt. Lib Amba, 12°04?N 39°22?; and Mt. Abuna Yosef, 12°08?N 39°11?E) was produced. In all three study areas, inactive solifluction lobes, presumably from the Last Glacial Maximum (LGM), were found. In the highest study area of Abuna Yosef, three sites were discovered bearing morainic material from small late Pleistocene glaciers. These marginal glaciers occurred below the modeled snowline and existed because of local topo-climatic conditions. Evidence of such Pleistocene avalanche-fed glaciers in Ethiopia (and Africa) has not been produced earlier. Current frost action is limited to frost cracks and small-scale patterned ground phenomena. The depression of the altitudinal belts of periglacial and glacial processes during the last cold period was assessed through periglacial and glacial landform mapping and comparisons with data from other mountain areas taking latitude into account. The depression of glacial and periglacial belts of approximately 600 m implies a temperature drop around 6 °C in the last cold period. This cooling is in line with temperature depressions elsewhere in East Africa during the LGM. This study serves as a case study for all the intermediate mountains (3500-4200 m) of the North Ethiopian highlands.

  13. Unstable AMOC during glacial intervals and millennial variability: The role of mean sea ice extent

    NASA Astrophysics Data System (ADS)

    Sévellec, Florian; Fedorov, Alexey V.

    2015-11-01

    A striking feature of paleoclimate records is the greater stability of the Holocene epoch relative to the preceding glacial interval, especially apparent in the North Atlantic region. In particular, strong irregular variability with an approximately 1500 yr period, known as the Dansgaard-Oeschger (D-O) events, punctuates the last glaciation, but is absent during the interglacial. Prevailing 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 that reproduces a realistic power spectrum of millennial variability, we explore differences in the AMOC stability between glacial and interglacial intervals of the 100 kyr glacial cycle of the Late Pleistocene (1 kyr = 1000 yr). 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 AMOC also southward. Here we demonstrate that, by shifting the AMOC with respect to the mean atmospheric precipitation field, such a displacement makes the system unstable, which explains chaotic millennial variability during the glacials and the persistence of stable ocean conditions during the interglacials.

  14. Glacial terminations and the global water budget

    SciTech Connect

    Broecker, W.S. . Lamont-Doherty Geological Observatory)

    1992-01-01

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

  15. 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.

  16. 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

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

    NASA Astrophysics Data System (ADS)

    Dube-Loubert, Hugo; Roy, Martin

    2014-05-01

    The Laurentide ice sheet played an important role in the late Pleistocene climate, notably through discharges of icebergs and meltwater. In this context, the Ungava Bay region in northern Quebec-Labrador appears particularly important, especially during the last deglaciation when the retreating ice margin dammed major river valleys, creating large proglacial lakes (e.g., McLean, aux Feuilles). The history of these lakes is closely related to the temporal evolution of the Labrador-Quebec ice dome. There are, however, large uncertainties regarding the position of its ice divide system through time, thereby limiting our understanding of the history of these glacial lakes. Here we focus on glacial and deglacial landforms present in the George River valley, south of Ungava Bay, in order to bring additional constraints on the late-glacial ice dynamics of this region, which also comprised glacial Lake Naskaupi. This work is based on surficial mapping using aerial photos and satellite imagery, combined with extensive fieldwork and sediment sampling. Our investigation showed significant differences in the distribution of glacial landforms across the region. The area east of the George River is characterized by well-developed Naskaupi shorelines while the elevated terrains show a succession of geomorphological features indicative of cold-based ice or ice with low basal velocities. In the easternmost part of this sector, ice flow directional data indicate that the ice was flowing towards ENE, against the regional slope. Eskers show paleocurrent directions indicating a general ice retreat from east to west. In the western part of this sector, near the George River valley, eskers are absent and the region is covered by felsenmeer and ground moraine that likely reflect the presence of a residual ice mass that was no longer dynamic. The presence of a stagnant ice represents the best mechanism to explain the formation of glacial lakes in the George River valley and its main tributaries. In contrast, the area west of the George River valley shows very few shorelines, implying that Lake Naskaupi was mostly in contact with the decaying ice margin. The abundance ice-marginal meltwater channels allowed the reconstruction of the general ice retreat pattern. The area is also characterized by abundant WNW-trending drumlins and crag-and-tails indicating an important ice flow towards Ungava Bay. These glacial lineations may be linked with eskers further to west that terminated into the postglacial Iberville Sea, forming large ice-contact deltas. This setting suggests that this landform assemblage likely developed during the deglaciation. Our results thus underlie important differences in the subglacial regime across the ice divide of the Labrador sector during the late-glacial and early deglacial interval. The so-called horseshoe unconformity appear to delineate an inner area characterized by warm-based conditions that allowed a massive deglacial ice flow to developed in Ungava Bay, while the area under and proximal to the divide in the east appears to have evolved towards cold-based ice conditions, resulting with a stagnant ice mass that dammed the major proglacial lakes.

  18. 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.

  19. Middle Pleistocene age of the Nome River glaciation, northwestern Alaska

    NASA Astrophysics Data System (ADS)

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

    1991-11-01

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

  20. Early Pleistocene origin of reefs around Lanai, Hawaii

    USGS Publications Warehouse

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

    2010-01-01

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

  1. Tentative correlation of midcontinent glacial sequence with marine chronology

    SciTech Connect

    Dube, T.E.

    1985-01-01

    A tentative glacial-interglacial 3-million-year chronology is synthesized by regional correlation of Midcontinent tills and paleosols to marine paleotemperature/eustatic cycles and oxygen isotope stages. The paleotemperature curves of Beard et al. (1982), based on planktonic foraminiferal abundances, correspond directly with eustatic cycles during the last 3 Ma. These generalized curves are shown to correlate reasonably well with standard oxygen isotope stages at least for the past 900 ka. This indicates that paleotemperature and Vail-type eustatic cycles have been glacially induced during the last 3 Ma. The chronology developed here utilizes both paleotemperature and oxygen isotope stages; however, below the Jaramillo magnetic subchron, isotope curves are more variable and only paleotemperature stages are used. Tills and paleosols at type localities in the Midcontinent area of the US are correlated to the SPECMAP oxygen isotope time scale. Because mid-Brunhes events are poorly constrained by radiometric dates, alternative correlations are possible. The oldest known Midcontinent tills correlate to the first Plio-Pleistocene cold paleotemperature stage and drop in sea level at 2.4 Ma. This Late Pliocene event also corresponds to the first major isotopic enrichment and the onset of late Cenozoic ice-rafting in the North Atlantic region.

  2. Ice shelves in the Pleistocene Arctic Ocean inferred from glaciogenic deep-sea bedforms.

    PubMed

    Polyak, L; Edwards, M H; Coakley, B J; Jakobsson, M

    2001-03-22

    It has been proposed that during Pleistocene glaciations, an ice cap of 1 kilometre or greater thickness covered the Arctic Ocean. This notion contrasts with the prevailing view that the Arctic Ocean was covered only by perennial sea ice with scattered icebergs. Detailed mapping of the ocean floor is the best means to resolve this issue. Although sea-floor imagery has been used to reconstruct the glacial history of the Antarctic shelf, little data have been collected in the Arctic Ocean because of operational constraints. The use of a geophysical mapping system during the submarine SCICEX expedition in 1999 provided the opportunity to perform such an investigation over a large portion of the Arctic Ocean. Here we analyse backscatter images and sub-bottom profiler records obtained during this expedition from depths as great as 1 kilometre. These records show multiple bedforms indicative of glacial scouring and moulding of sea floor, combined with large-scale erosion of submarine ridge crests. These distinct glaciogenic features demonstrate that immense, Antarctic-type ice shelves up to 1 kilometre thick and hundreds of kilometres long existed in the Arctic Ocean during Pleistocene glaciations. PMID:11260709

  3. 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

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

    NASA Astrophysics Data System (ADS)

    Mange, Maria A.; Otvos, Ervin G.

    2005-12-01

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

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

    PubMed Central

    2013-01-01

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

  6. 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.

  7. 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

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

    NASA Astrophysics Data System (ADS)

    Tormey, Daniel

    2010-11-01

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

  9. 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

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

    SciTech Connect

    Pietraszek, S.R. . 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.

  11. 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

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

    PubMed

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

    2014-08-12

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

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

    PubMed

    Neiman, Maurine; Lively, Curtis M

    2004-10-01

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

  14. 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, Prakash

    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.

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

    SciTech Connect

    Phillips, F.M.; Zreda, M.G.; Plummer, M.A.

    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.

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

    SciTech Connect

    Otvos, E.G. . Geology Section)

    1993-03-01

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

  17. Lake core record of Grinnell Glacier dynamics during the latest Pleistocene deglaciation and the Younger Dryas, Glacier National Park, Montana, USA

    NASA Astrophysics Data System (ADS)

    Schachtman, Nathan S.; MacGregor, Kelly R.; Myrbo, Amy; Hencir, Nora Rose; Riihimaki, Catherine A.; Thole, Jeffrey T.; Bradtmiller, Louisa I.

    2015-07-01

    Few records in the alpine landscape of western North America document the geomorphic and glaciologic response to climate change during the Pleistocene-Holocene transition. While moraines can provide snapshots of glacier extent, high-resolution records of environmental response to the end of the Last Glacial Maximum, Younger Dryas cooling, and subsequent warming into the stable Holocene are rare. We describe the transition from the late Pleistocene to the Holocene using a ~ 17,000-yr sediment record from Swiftcurrent Lake in eastern Glacier National Park, MT, with a focus on the period from ~ 17 to 11 ka. Total organic and inorganic carbon, grain size, and carbon/nitrogen data provide evidence for glacial retreat from the late Pleistocene into the Holocene, with the exception of a well-constrained advance during the Younger Dryas from 12.75 to 11.5 ka. Increased detrital carbonate concentration in Swiftcurrent Lake sediment reflects enhanced glacial erosion and sediment transport, likely a result of a more proximal ice terminus position and a reduction in the number of alpine lakes acting as sediment sinks in the valley.

  18. Global and Regional Controls on Alkenone Sea Surface Temperature and Productivity Records for the Pleistocene From the Arabian Sea

    NASA Astrophysics Data System (ADS)

    Alpert, A. E.; Cleaveland, L. C.; Herbert, T. D.

    2007-12-01

    The Arabian Sea is home to one of the modern ocean's largest upwelling zones and represents a region that is sensitive to the dynamics of the Asian monsoon system as well as glacial-interglacial climate changes. High sedimentation rates in this region enable highly resolved climate reconstructions, which provide the opportunity to evaluate the impacts of both local and global forcing of oceanographic conditions in the Arabian Sea. We present high-resolution (1.5 kyr) alkenone SST and alkenone abundance data for the last 1.8 Myr from Ocean Drilling Program Site 722 in the northwest Arabian Sea. Over the course of the Pleistocene, SST at this site ranges from 23.3°C to 27.8°C with a long term decrease of 0.7°C/Myr. Like the well-known benthic oxygen isotope record, the SST record contains a long-term increase in amplitude and a switch from 41 kyr cyclicity to 100 kyr cyclicity across the mid-Pleistocene transition. Because of the strong similarity between our Arabian Sea SST record, ice volume, carbon dioxide (where data are available), and an additional SST record from the Eastern Equatorial Pacific upwelling zone, we conclude that SST at Site 722 is strongly linked to global glacial-interglacial climate variability throughout the Pleistocene, with warmest water temperatures occurring during interglacial periods and vice versa. Our data indicate that Site 722 SST was decoupled from the monsoon system on orbital timescales and was likely driven by variations in subsurface mode water temperatures, ultimately linked to high latitude climate. Alkenone abundance, which we relate to productivity, is highly variable over the last 1.8 Myr, ranging over two orders of magnitude. Average productivity and productivity variability both decreased during the early Pleistocene and remained low through the mid-Pleistocene transition. During the late Pleistocene both average productivity and productivity variability increased. Throughout the Pleistocene, inferred productivity at Site 722 appears to be related to monsoon-driven upwelling based on the similarity between our alkenone abundance record and a grain size record from Site 722, which responds to variations in wind speed.

  19. Ice-Sheet Dynamics and Millennial-Scale Climate Variability in the North Atlantic across the Middle Pleistocene Transition (Invited)

    NASA Astrophysics Data System (ADS)

    Hodell, D. A.; Nicholl, J.

    2013-12-01

    During the Middle Pleistocene Transition (MPT), the climate system evolved from a more linear response to insolation forcing in the '41-kyr world' to one that was decidedly non-linear in the '100-kyr world'. Smaller ice sheets in the early Pleistocene gave way to larger ice sheets in the late Pleistocene with an accompanying change in ice sheet dynamics. We studied Sites U1308 (49° 52.7'N, 24° 14.3'W; 3871 m) and U1304 (53° 3.4'N, 33° 31.8'W; 3024 m) in the North Atlantic to determine how ice sheet dynamics and millennial-scale climate variability evolved as glacial boundary conditions changed across the MPT. The frequency of ice-rafted detritus (IRD) in the North Atlantic was greater during glacial stages prior to 650 ka (MIS 16), reflecting more frequent crossing of an ice volume threshold when the climate system spent more time in the 'intermediate ice volume' window, resulting in persistent millennial scale variability. The rarity of Heinrich Events containing detrital carbonate and more frequent occurrence of IRD events prior to 650 ka may indicate the presence of 'low-slung, slippery ice sheets' that flowed more readily than their post-MPT counterparts (Bailey et al., 2010). Ice volume surpassed a critical threshold across the MPT that permitted ice sheets to survive boreal summer insolation maxima, thereby increasing ice volume and thickness, lengthening glacial cycles, and activating the dynamical processes responsible for Laurentide Ice Sheet instability in the region of Hudson Strait (i.e., Heinrich events). The excess ice volume during post-MPT glacial maxima provided a large, unstable reservoir of freshwater to be released to the North Atlantic during glacial terminations with the potential to perturb Atlantic Meridional Overtunring Circulation. We speculate that orbital- and millennial-scale variability co-evolved across the MPT and the interaction of processes on orbital and suborbital time scales gave rise to the changing patterns of glacial-interglacial cycles through the Quaternary. Bailey, I., Bolton, C.T., DeConto, R.M., Pollard, D., Schiebel, R. and Wilson, P.A. (2010) A low threshold for North Atlantic ice rafting from "low-slung slippery" late Pliocene ice sheets. Paleoceanography, 25, PA1212-[14pp]. (doi:10.1029/2009PA001736).

  20. A phylogeographic, demographic and historical analysis of the short-tailed pit viper (Gloydius brevicaudus): evidence for early divergence and late expansion during the Pleistocene.

    PubMed

    Ding, Li; Gan, Xiao-Ni; He, Shun-Ping; Zhao, Er-Mi

    2011-05-01

    The impact of quaternary glaciation in eastern China on local fanua and flora has been a topic of considerable interest. We used mitochondrial DNA (mtDNA) sequence data and coalescent simulations to test two general biogeographic hypothesis related to the effects of Pleistocene climatic fluctuations for a widespread ophidian species (Gloydius brevicaudus) in eastern China and Korean Peninsula. The phylogenetic analysis revealed three major lineages, the southeast Coastal, Yangtze and North Lineages. The latter two are closely related and jointly form a continental lineage. Divergence dating and coalescent simulations indicate a Late Pliocene to Early Pleistocene divergence between lineages from the southeast coast and continental interior, followed by a mid-to-late Pleistocene divergence between lineages from the north and the middle-lower Yangtze Valley across East China, suggesting that all these lineages predated the last glacial maximum. An overlapping range between the two lineages within the continental lineage and a secondary contact associated with ecological transition zones on the margins of the North China Plain were also observed. These results show that vicariance patterns dominated the history of G. brevicaudus. Though the climatic events of the Pleistocene have had a marked effect on the historical distribution and intra-specific divergence of reptiles in China, coalescent and non-coalescent demographic analyses indicate that all lineages of G. brevicaudus seem not to have been adversely affected by glacial cycles during the Late Pleistocene, presumably because of an increase in the amount of climatically mild habitat in East Asia due to a decline in elevation and the development of monsoons since the Mid-End Pleistocene. PMID:21438932

  1. 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)

  2. Sub-glacial volcanic eruptions

    USGS Publications Warehouse

    White, Donald Edward

    1956-01-01

    The literature on sub-glacial volcanic eruptions and the related flood phenomena has been reviewed as a minor part of the larger problem of convective and conductive heat transfer from intrusive magma. (See Lovering, 1955, for a review of the extensive literature on this subject.) This summary of data on sub-glacial eruptions is part of a program that the U.S. Geological Survey is conducting in connection with its Investigations of Geologic Processes project on behalf of the Division of Research, U.S. Atomic Energy Commission.

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

    PubMed

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

    2014-03-01

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

  4. Post-Glacial and Paleo-Environmental History of the West Coast of Vancouver Island

    NASA Astrophysics Data System (ADS)

    Dallimore, A.; Enkin, R. J.

    2005-12-01

    Annually laminated sediments in anoxic fjords are potentially ideal paleoclimate recorders, particularly once proxy measurements for atmospheric, oceanographic and sedimentological conditions have been calibrated. On the west coast of Canada, these sediments also record the changing environment as glaciers retreated from this area about 12 ka y BP. In Effingham Inlet, a 40 m core taken from the French ship the Marion Dufresne as part of the international IMAGES/PAGES program, gives evidence of an isolation basin at maximum glacial isostatic rebound and lowest paleo-sea level followed by eustatic sea level rise about 10 ka y BP. The Late Pleistocene record also marks dramatic changes in glacial sedimentary source and transport. Excellent chronological control is provided by complementary yet independent dating methods including radiocarbon dates on both plants and shells, identification of the Mazama Ash, varve counting and paleomagnetic, paleosecular variation correlations in the lower, pro-glacial section of the core which does not contain organic material. Paleoenvironmental evidence from this core provides information on immediate post-glacial conditions along the coast and rapid climatic changes throughout the Holocene, with implications for the possibility of early human migration routes and refugia.

  5. Rapid Changes in North Atlantic Deep Ocean Circulation During the MIS 5a/4 Glacial Inception

    NASA Astrophysics Data System (ADS)

    Barker, S.; Thornalley, D. J.; Hall, I. R.; Knorr, G.

    2009-12-01

    Understanding the role of ocean ventilation in late Pleistocene atmospheric CO2 variability requires high resolution reconstructions of ocean circulation changes during intervals of varying CO2. Recent studies have provided valuable insights into the mechanism of CO2 release during glacial termination, in response to abrupt changes in the mode of overturning circulation within the Atlantic Ocean (e.g. Anderson et al., 2009; Barker et al., 2009). Here we focus in turn on the severe decrease in CO2 that occurred during the development of full glacial conditions across the boundary from Marine Isotope Stage (MIS) 5a to 4. We present very high resolution (150-200 year) multi-core, multi-proxy reconstructions of the depth and vigour of the deep western boundary current (DWBC) in the North Atlantic, during MIS 5a / 4 and throughout MIS 4. We show that large and abrupt shifts in the position of the DWBC occurred in parallel with high latitude climate variability. Using the position of the DWBC as an indicator of the vertical extent of Atlantic Meridional Overturning Circulation (AMOC) we investigate the role of AMOC variability in CO2 drawdown during glacial inception. In particular we focus on the changes associated with the rapid temperature fluctuations of Dansgaard-Oeschgar events 19 and 20 in contrast with the transition to full glacial conditions entering MIS 4. We discuss these differences in terms of their potential impact on ocean ventilation and atmospheric CO2.

  6. 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

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

    USGS Publications Warehouse

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

    2010-01-01

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

  8. Quaternary glacial and post-glacial depositional history associated with the Green Bay lobe, east-central Wisconsin

    SciTech Connect

    Thieme, L.D.; Smith, G.L. . Dept. of Geology)

    1993-03-01

    Multiple layers of peat and wood fragments indicate that Quaternary glaciation of the east-central region of Wisconsin was punctuated by at least two interglacial periods. Till, outwash, and glaciolacustrine deposits suggest that deposition took place in alternating glacial and non-glacial environments due to oscillations in the position of the Green Bay Lobe terminus. The data for this study consists of 36 auger borings, 70 geologic logs and 100 well-construction reports from water wells. Nine vibracores were taken at the northern margin of Lake Winnebago in order to document in detail the post-glacial history of Glacial Lake Oshkosh/Lake Winnebago. Local bedrock consists of limestones and dolomites of the Middle Ordovician Sinnipee Group. Bedrock elevations range from 211--237 m; bedding dips regionally to the southeast at 1--2 degrees. Bedrock is overlain by a 3--13 m-thick layer of alternating red clay and gray silty-clay (basal Kewaunee Formation ) perhaps deposited in a proglacial lake. These sediments are overlain by apeat/wood layer indicating marsh deposition. This peat/wood layer is overlain by more proglacial lake sediment, 3--10 m of gray brown clay to silty-clay. A second peat/wood layer overlies the gray/brown sediment and may correlate with the Two Creeks buried forest bed. The uppermost unit consists of 2--3 m red silty-clay till (Middle Inlet Member of the Kewaunee Formation). Along the northern margin of present-day Lake Winnebago, red silty-clay is overlain by silty-sand deposited by Glacial Lake Oshkosh. Future work includes obtaining radiocarbon dates from buried peat/wood layers to verify these tentative correlations between east-central Wisconsin and the Lake Michigan Basin.

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

    NASA Astrophysics Data System (ADS)

    Hamilton, Thomas D.; Ashley, Gall M.; Reed, Katherine M.; Schweger, Charles E.

    1993-05-01

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

  10. 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.

  11. Increased late Pleistocene erosion rates during fluvial aggradation in the Garhwal Himalaya, northern India

    NASA Astrophysics Data System (ADS)

    Scherler, Dirk; Bookhagen, Bodo; Wulf, Hendrik; Preusser, Frank; Strecker, Manfred R.

    2015-10-01

    The response of surface processes to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Himalaya, most large rivers feature prominent fill terraces that record an imbalance between sediment supply and transport capacity, presumably due to past fluctuations in monsoon precipitation and/or effects of glaciation at high elevation. Here, we present volume estimates, chronological constraints, and 10Be-derived paleo-erosion rates from a prominent valley fill in the Yamuna catchment, Garhwal Himalaya, to elucidate the coupled response of rivers and hillslopes to Pleistocene climate change. Although precise age control is complicated due to methodological problems, the new data support formation of the valley fill during the late Pleistocene and its incision during the Holocene. We interpret this timing to indicate that changes in discharge and river-transport capacity were major controls. Compared to the present day, late Pleistocene hillslope erosion rates were higher by a factor of ?2-4, but appear to have decreased during valley aggradation. The higher late Pleistocene erosion rates are largely unrelated to glacial erosion and could be explained by enhanced sediment production on steep hillslopes due to increased periglacial activity that declined as temperatures increased. Alternatively, erosion rates that decrease during valley aggradation are also consistent with reduced landsliding from threshold hillslopes as a result of rising base levels. In that case, the similarity of paleo-erosion rates near the end of the aggradation period with modern erosion rates might imply that channels and hillslopes are not yet fully coupled everywhere and that present-day hillslope erosion rates may underrepresent long-term incision rates.

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

    PubMed

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

    2011-09-01

    Batadomba-lena, a rockshelter in the rainforest of southwestern Sri Lanka, has yielded some of the earliest evidence of Homo sapiens in South Asia. H. sapiens foragers were present at Batadomba-lena from ca. 36,000 cal BP to the terminal Pleistocene and Holocene. Human occupation was sporadic before the global Last Glacial Maximum (LGM). Batadomba-lena's Late Pleistocene inhabitants foraged for a broad spectrum of plant and mainly arboreal animal resources (monkeys, squirrels and abundant rainforest snails), derived from a landscape that retained equatorial rainforest cover through periods of pronounced regional aridity during the LGM. Juxtaposed hearths, palaeofloors with habitation debris, postholes, excavated pits, and animal and plant remains, including abundant Canarium nutshells, reflect intensive habitation of the rockshelter in times of monsoon intensification and biome reorganisation after ca. 16,000 cal BP. This period corresponds with further broadening of the economic spectrum, evidenced though increased contribution of squirrels, freshwater snails and Canarium nuts in the diet of the rockshelter occupants. Microliths are more abundant and morphologically diverse in the earliest, pre-LGM layer and decline markedly during intensified rockshelter use on the wane of the LGM. We propose that changing toolkits and subsistence base reflect changing foraging practices, from shorter-lived visits of highly mobile foraging bands in the period before the LGM, to intensified use of Batadomba-lena and intense foraging for diverse resources around the site during and, especially, following the LGM. Traces of ochre, marine shell beads and other objects from an 80 km-distant shore, and, possibly burials reflect symbolic practices from the outset of human presence at the rockshelter. Evidence for differentiated use of space (individual hearths, possible habitation structures) is present in LGM and terminal Pleistocene layers. The record of Batadomba-lena demonstrates that Late Pleistocene pathways to (aspects of) behavioural 'modernity' (composite tools, practice of symbolism and ritual, broad spectrum economy) were diverse and ecologically contingent. PMID:21777951

  13. Constraints on the Pleistocene chronology of sediments from the Lomonosov Ridge

    USGS Publications Warehouse

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

    Goyanes, Gabriel; Massabie, Armando

    2015-01-01

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

  17. 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

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

    NASA Astrophysics Data System (ADS)

    Deschamps, Rémy; Eschard, Rémi; Roussé, Stéphane

    2013-05-01

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

  19. Pleistocene glacial terminations triggered by synchronous changes in Southern and Northern Hemisphere insolation

    E-print Network

    Zeebe, Richard E.

    between the two orbital parameters obliquity and precession, explaining why terminations occur at integer parameters [3,7­9] predicts quasi- periodic variations of eccentricity, obliquity and precession of the equinoxes with dominant frequencies centered around 100, 41 and 23/19 kyr, respectively. While the 19/ 23

  20. 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.

  1. 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.

  2. An interhemispheric mechanism for glacial abrupt climate change

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  4. Glacial geomorphology of the Torres del Paine region (southern Patagonia): Implications for glaciation, deglaciation and paleolake history

    NASA Astrophysics Data System (ADS)

    García, Juan-Luis; Hall, Brenda L.; Kaplan, Michael R.; Vega, Rodrigo M.; Strelin, Jorge A.

    2014-01-01

    The processes affecting paleoclimate variability and Pleistocene glacial landscape development in the southern mid-latitudes remain poorly understood, in part because of the scarcity of comprehensive, well-studied records. Glacial landforms are invaluable for reconstructing past ice-sheet, climate, and associated environmental changes along the southern Andes, but there are significant spatial and temporal gaps in existing data. In this paper, we present new geomorphic and sedimentologic analyses, including surficial maps, for the Torres del Paine region (51°S, 73°W), southern South America. Our findings provide a new framework for understanding changes in the regional glacier history and Pleistocene landscape development. Glacial extent during the local last glacial maximum (LGM) remains unknown but new chronological data supported by geomorphic evidence afford evidence for a larger ice sheet at Torres del Paine than previously assumed. Deglaciation from the local LGM was underway by 17,400 ± 200 (1?) cal. yr. BP. As opposed to previous suggestions, we have found that most of the moraines fringing the lakes in the Torres del Paine national park were deposited during a late-glacial expansion that occurred between 14,100 and 12,500 cal. yr. BP. Late-glacial advances also have been documented recently for the Última Esperanza and Lago Argentino basins to the south and north of Torres del Paine, respectively, suggesting an overall regional ice response to a climate signal. The Tehuelche paleolake accompanied each of the ice-sheet fluctuations in Torres del Paine. New data document at least three main phases of this paleolake, which drained eastward to the Atlantic Ocean, while the Andes gaps were blocked with ice. During the late phase of glacial lake formation, when water levels reached 125-155 m a.s.l., the lake likely merged with paleolake Consuelo in the Última Esperanza area at the end of the last glaciation. Lake Tehuelche in Torres del Paine had drained into the Pacific Ocean by the late-glacial period, suggesting that ice southwest of Torres del Paine may have retreated back into the mountains by this time.

  5. Interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles

    NASA Astrophysics Data System (ADS)

    Wilson, David J.; Piotrowski, Alexander M.; Galy, Albert; Banakar, Virupaxa K.

    2015-06-01

    Changes in ocean circulation structure, together with biological cycling, have been proposed for trapping carbon in the deep ocean during glacial periods of the Late Pleistocene, but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles. In this study, we use neodymium (Nd) and carbon isotopes from a deep Indian Ocean sediment core to reconstruct water mass mixing and carbon cycling in Circumpolar Deep Water over the past 250 thousand years, a period encompassing two full glacial cycles and including a range of orbital forcing. Building on recent studies, we use reductive sediment leaching supported by measurements on isolated phases (foraminifera and fish teeth) in order to obtain a robust seawater Nd isotope reconstruction. Neodymium isotopes record a changing North Atlantic Deep Water (NADW) component in the deep Indian Ocean that bears a striking resemblance to Northern Hemisphere climate records. In particular, we identify both an approximately in-phase link to Northern Hemisphere summer insolation in the precession band and a longer-term reduction of NADW contributions over the course of glacial cycles. The orbital timescale changes may record the influence of insolation forcing, for example via NADW temperature and/or Antarctic sea ice extent, on deep stratification and mixing in the Southern Ocean, leading to isolation of the global deep oceans from an NADW source during times of low Northern Hemisphere summer insolation. That evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions. However, mid-depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods, and a return to an interglacial-like circulation state during marine isotope stage (MIS) 6.5 was accompanied by only minor changes in atmospheric CO2. Although a gradual reduction of NADW export through glacial periods may have produced slow climate feedbacks linked to the growth of Northern Hemisphere ice sheets, carbon cycling in the glacial ocean was instead more strongly linked to Southern Ocean processes.

  6. Ice-rafting from the British-Irish ice sheet since the earliest Pleistocene (2.6 million years ago): implications for long-term mid-latitudinal ice-sheet growth in the North Atlantic region

    NASA Astrophysics Data System (ADS)

    Thierens, M.; Pirlet, H.; Colin, C.; Latruwe, K.; Vanhaecke, F.; Lee, J. R.; Stuut, J.-B.; Titschack, J.; Huvenne, V. A. I.; Dorschel, B.; Wheeler, A. J.; Henriet, J.-P.

    2012-06-01

    The Plio-Pleistocene intensification of Northern Hemisphere continental ice-sheet development is known to have profoundly affected the global climate system. Evidence for early continental glaciation is preserved in sediments throughout the North Atlantic Ocean, where ice-rafted detritus (IRD) layers attest to the calving of sediment-loaded icebergs from circum-Atlantic ice sheets. So far, Early-Pleistocene IRD deposition has been attributed to the presence of high-latitudinal ice sheets, whereas the existence and extent of ice accumulation in more temperate, mid-latitudinal regions remains enigmatic. Here we present results from the multiproxy provenance analysis of a unique, Pleistocene-Holocene IRD sequence from the Irish NE Atlantic continental margin. There, the Challenger coral carbonate mound (IODP Expedition 307 site U1317) preserved an Early-Pleistocene record of 16 distinctive IRD events, deposited between ca 2.6 and 1.7 Ma. Strong and complex IRD signals are also identified during the mid-Pleistocene climate transition (ca 1.2 to 0.65 Ma) and throughout the Middle-Late Pleistocene interval. Radiogenic isotope source-fingerprinting, in combination with coarse lithic component analysis, indicates a dominant sediment source in the nearby British-Irish Isles, even for the oldest, Early-Pleistocene IRD deposits. Hence, our findings demonstrate, for the first time, repeated and substantial (i.e. marine-terminating) ice accumulation on the British-Irish Isles since the beginning of the Pleistocene. Contemporaneous expansion of both high- and mid-latitudinal ice sheets in the North Atlantic region is therefore implied at the onset of the Pleistocene. Moreover, it suggests the recurrent establishment of (climatically) favourable conditions for ice sheet inception, growth and instability in mid-latitudinal regions, even in the earliest stages of Northern Hemisphere glacial expansion and in an obliquity-driven climate system.

  7. 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

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

    NASA Astrophysics Data System (ADS)

    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 231Pa/230Th and 143Nd/144Nd), which are not directly affected by changes in the global cycle, reveal consistent responses of the AMOC during the last two glacial terminations. Any significant deviations from this configuration, resulting in slowdowns of the AMOC, were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials. Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage, probably as a result of increased fresh-water input. In contrast, the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states, and an active AMOC prevailed during Dansgaard-Oeschger interstadials (Greenland warm periods).

  9. 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.

  10. Synchronous extinction of North America's Pleistocene mammals

    PubMed Central

    Faith, J. Tyler; Surovell, Todd A.

    2009-01-01

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

  11. Glacially driven formation of high-elevation, low-relief landscapes in eastern Tibet

    NASA Astrophysics Data System (ADS)

    Oskin, M. E.; Zhang, H.; Liu-Zeng, J.; Zhang, P.; Reiners, P. W.; Xiao, P.

    2014-12-01

    Low-relief landscapes in central and eastern Tibet have been interpreted as relicts formed by lowland fluvial erosion before being uplifted to elevations exceeding 4 km a.s.l. The timing and amount of surface uplift indicated by these surfaces in Tibet and other orogens provide important constraints on geodynamic processes of crustal thickening and plateau formation. Low-temperature thermochronology and catchment-average 10Be concentrations indicate limited and low rates of long- and short-term erosion of these landscapes. But it is their morphology, dominated by gentle stream gradients, that drives the interpretation that these landscapes formed at much lower elevations than at present. Here we show for the plateau landscape of eastern Tibet that glacial erosion is ubiquitous along drainage divides that separate low-relief areas from deeply incised river gorges. The extent of late Pleistocene glaciation increases along a gradient of late Cenozoic exhumation from ~1 to >4 km indicated by apatite- and zircon-helium cooling ages. We interpret that glacial erosion effectively limits ridgeline elevations and promotes formation of low-relief landscapes in arid plateau interiors undergoing modest (<50 m Myr-1) exhumation rates. More intensive glacial erosion, associated with higher (>200 m Myr-1) exhumation rates nearer to plateau margins, produces bimodal topography, with low-relief cirques at high elevation and gentle, U-shape valleys below the equilibrium line altitudes (ELA). This yields similar mean elevations as nearby plateau surfaces, but with more rugged local relief. As rock uplift rate declines, these nascent plateau surfaces inherit low-gradient glaciated valley networks pinned by glacial erosion at their headwaters and smoothed by periglacial hillslope processes and transport-limited streams. Glacially driven formation of low-relief plateau landscapes within high-elevation eastern Tibet occurs in tandem with external drainage, and does not require uplift of a low-elevation peneplain.

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

    NASA Astrophysics Data System (ADS)

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

    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 use pollen data to reconstruct the vegetation of the Amazon basin in oxygen isotope stages 3 and 2 of the last glaciation in order to measure how the plant populations of the Amazon responded to the global warming at the onset of the Holocene. We find that plant communities of the neotropics vent copious pollen to lake sediments and that this pollen yields powerful signals for community composition. Three continuous sedimentary records reaching through oxygen isotope stage 2 are available from the Amazon lowlands, those from Carajas, Lake Pata and marine deposits off the mouth of the Amazon River. All three records yield pollen histories of remarkable constancy and stability. By comparing them with deposits of equal antiquity from the cerrado (savanna) of central Brazil, we show that most of the Amazon lowlands remained under forest throughout a glacial cycle. This forest was never fragmented by open vegetation as postulated by the refugia hypothesis. Instead the intact forest of glacial times included significant populations of plants that are now montane, suggesting that the global warming of the early Holocene resulted in the expulsion of heat intolerant plants from the lowland forest. Pollen data from the Amazonian flank of the Andes and from Pacific Panama provide evidence that populations of these heat intolerant plants survive the heat of interglacials in part by maintaining large populations at cooler montane altitudes. Our conclusion that the Amazon lowlands were forested in glacial times specifically refutes the hypothesis of Amazonian glacial aridity. Accordingly we examine the geomorphological evidence for glacial aridity and find it wanting. Of the three paleodune systems reported for tropical South America, that of NE Brazil was active in the Holocene as well as the Pleistocene. Parts of NE Brazil were actually moister than now in late-glacial times. Paleodunes in the Pantanal have never been seen on the ground, and those in the Orinoco Llanos are undated and may be of any age since the Tertiary. Arkosic sands in the Amazon fan deposits came from the Andean foothills or from down cutting by rivers and cannot be evidence of a former arid land surface. White sands of Amazonia formed as podzols, not by aeolian activity. Such Amazonian stone lines as have received critical scrutiny are concretionary pisolites in stratigraphic formations that are more than ten million years old. Although the Amazon was never arid, modeling cooler glacial tropics gives plausibility to a somewhat drier Amazon in glacial times, a concept given substance by pollen data for the movement of ecotones in Rondonia, by stream histories in the Bolivian Andes, and by evidence for lowered lake levels at Carajas and Lake Pata. But this reduced precipitation was never enough to fragment the forest in the Amazon lowlands themselves. Pleistocene mammals of the Napo river valley in Ecuador were able to live along the river system in a forested landscape. Our data suggest that the Amazon forests have been stable since the start of the Pleistocene, a fact that has contributed to the storage of vast diversity. The coming anthropogenic global warming and CO 2 enrichment will add to the global warming already endured by Amazon biota in the Holocene. We think it possible that the expulsion from the lowland forests of heat intolerant species is already complete and that the forest property of maintaining its own microhabitat will allow the high species richness to survive more global warming, provided large enough tracts of forest are preserved.

  13. Mediterranean Outflow and surface water variability off southern Portugal during the early Pleistocene: A snapshot at Marine Isotope Stages 29 to 34 (1020-1135 ka)

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    Centennial-to-millennial scale records from IODP Site U1387, drilled during IODP Expedition 339 into the Faro Drift at 558 m water depth, now allow evaluating the climatic history of the upper core of the Mediterranean Outflow (MOW) and of the surface waters in the northern Gulf of Cadiz during the early Pleistocene. This study focuses on the period from Marine Isotope Stages (MIS) 29 to 34, i.e. the interval surrounding extreme interglacial MIS 31. Conditions in the upper MOW reflect obliquity, precession and millennial-scale variations. The benthic ?18O signal follows obliquity with the exception of an additional, smaller ?18O peak that marks the MIS 32/31 transition. Insolation maxima (precession minima) led to poor ventilation and a sluggish upper MOW core, whereas insolation minima were associated with enhanced ventilation and often also increased bottom current velocity. Millennial-scale periods of colder sea-surface temperatures (SST) were associated with short-term maxima in flow velocity and better ventilation, reminiscent of conditions known from MIS 3. A prominent contourite layer, coinciding with insolation cycle 100, was formed during MIS 31 and represents one of the few contourites developing within an interglacial period. MIS 31 surface water conditions were characterized by an extended period (1065-1091 ka) of warm SST, but SST were not much warmer than during MIS 33. Interglacial to glacial transitions experienced 2 to 3 stadial/interstadial cycles, just like their mid-to-late Pleistocene counterparts. Glacial MIS 30 and 32 recorded periods of extremely cold (< 12 °C) SST that in their climatic impact were comparable with the Heinrich events of the mid and late Pleistocene. Glacial MIS 34, on the other hand, was a relative warm glacial period off southern Portugal. Overall, surface water and MOW conditions at Site U1387 show a strong congruence with Mediterranean climate, whereas millennial-scale variations are closely linked to North Atlantic circulation changes.

  14. 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.

  15. Glaciers and Late Quaternary glacial deposits of Turkey

    NASA Astrophysics Data System (ADS)

    Çiner, A.

    2003-04-01

    Turkish glaciers and Late Quaternary glacial deposits are observed in 3 regions: 1. The Taurus Mountain Range (Mediterranean coast and SE Turkey): Two thirds of the present day glaciers are concentrated in the SE part. Among these mountains, Mount Cilo (4168 m) alone supports more than ten glaciers, couple of them 4 km long. In the central part, Aladag (3756 m) and Bolkardag (3524 m) Mountains contain few small glaciers. Small ice caps developed on top of both mountains in Pleistocene. Several U-shaped valleys were carved by glaciers that formed different types of moraines. Even though there are signs of past glacial activity in Beydag (3086 m), Akdag (3016 m) and Sandiras Mountains (2295 m) no glaciers are present in the W Taurus Mountains today. 2. The Pontic Mountain Range (E Black Sea coast): The highest peak is Mount Kaçkar (3932 m) where five glaciers are developed. Several other mountains such as Verçenik (3710 m), Bulut (3562 m), Altiparmak (3353 m), Karagöl (3107 m) and Karadag (3331 m) also support various glaciers. Large U-shaped valleys containing terminal, lateral and ground moraines are observed although the present humid climatic conditions altered most of them. 3. Volcanoes and independent mountain chains scattered in the Anatolian Plateau: The volcanoes in the interior of the country support active glaciers and show signs of past glacial activity. Among them, Mount Agri (Ararat) (5165 m) is the only mountain on which a 10 km2 recent ice cap is developed. Eleven glaciers emerged from the summit, descending down to 3900 m on the N-facing slope and 4200 m on the S facing slope. The near absence of moraines can be explained by the lack of confining ridges to control valley glaciers, by insufficient debris load in the ice to form moraines and by volcanic eruptions that later covered the pre-existing moraines. Other important volcanoes, Mount Süphan (4058 m) and Mount Erciyes (3916 m) also contain active glaciers and well preserved moraines. Apart from the volcanoes, few other mountains in Central Anatolia, such as Uludag (2543 m), Mercan (3368 m) and Mescid (3239 m) bear signs of past glacial activity. The absence of dating of the morainic landforms makes it difficult to assign a precise age to the past glacial periods. However a project that aims to establish glacial chronlogies for the above mentioned mountains by using in situ cosmogenic 36Cl in the moraines, is recently developed. The data available on glaciers indicate that the most recent glacier retreat probably started at the beginning of the 20th century, becoming faster since the 1930's. This shrinkage trend is yet to be quantified by additional field observations in order to understand the glacier evolution of Turkey.

  16. Comparison of glacial periods reveals systematic cold climate variability

    NASA Astrophysics Data System (ADS)

    Bauch, Henning

    2013-04-01

    On a global scale, major variations in Pleistocene temperatures correlate well with glacial-interglacial changes of northern hemisphere ice sheet sizes. While a discharge of icebergs from the ice sheets surrounding the polar North Atlantic region directly reflects the rates of growth and decay of the ice sheet margins at sea level, it is also the result of a rapidly changing climate which affected both the meridional overturning in the ocean and the pattern in ocean-atmosphere circulation. Ice cores and many deep-sea sediment records from this region have demonstrated such complex interrelations between these main environmental processes for the last glaciation (Weichselian). In ice cores, the millennial-scale climate variabilities of the Weichselian are recognized in both hemispheres, albeit with apparently a significant time lag between the southern and northern pole regions. Comparing records of iceberg discharge from the polar and subpolar North Atlantic now reveals a very similar millennial-scale variability between the Weichselian and the penultimate glaciation (Saalian) during which warmer, interstadial times alternated with rather cold polar conditions. Because cold conditions in the polar North were also time-coeval with enhanced aridity and atmospheric dust content (e.g. at least over northern Africa due to changes in the monsoon system), the glacial dust records of Antarctica, which extend back in time much farther than Greenland ice records, could be used to also make an interhemispheric climate comparison. For the last two glaciations such a comparison would indeed indicate a strong linkage between iceberg discharge events in the polar North and increased dust content in the atmosphere.

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

    Goldstein, S. L.; Pena, L.

    2013-12-01

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

  20. Ice Age Reboot: Thermohaline Circulation Crisis during the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Pena, L.; Goldstein, S. L.

    2014-12-01

    The mid-Pleistocene transition (MPT) marked a fundamental change in glacial-interglacial periodicity, when it increased from ~41- to 100-kyr cycles and developed higher amplitude climate variability. Because it took place without significant changes in the Milankovitch forcing, this fundamental change must reflect either non-linear responses of the climate system to these external forcings, or internal changes in the ocean-atmosphere-cryosphere system that led to longer periodicities and more intense glacial periods. We document using Nd isotopes a major disruption of the ocean thermohaline circulation (THC) system during the MPT between MIS 25-21 at ~950-860 ka, which effectively marks the first 100-kyr cycle, including an exceptional weakening through critical interglacial MIS 23 at ~900 ka. The data are from ODP Sites 1088 (41°8.163'S, 13°33.77'E, 2082m) and 1090 (42°54.82'S, 8°53.98E', 3702m) in the SE Atlantic Subantarctic Zone, near the upper and lower boundaries of NADW and Circumpolar Deep Water (CDW). Given evidence for nearly stable NADW and North Pacific Water (NPW) ?Nd-values over the last 2 Ma, we interpret the ?Nd variations to reflect changes in the NADW:NPW mixing fractions. During the studied pre-MPT 41-kyr world (MIS 31-25, 1,100-950 ka), at both sites the differences in glacial and interglacial ?Nd-values are small, indicating strong glacial as well as interglacial export of NADW. A major weakening of NADW export occurred during MIS 24-22, including MIS 23, which is unique as the only known interglacial in which the THC did not strengthen, and thus can be considered as a 'trans-glacial' period. The recovery into the post-MPT 100-kyr world is characterized by continued weak glacial THC. We conclude that the MPT ocean circulation crisis 'rebooted' the pacing and intensity of ice ages and facilitated the coeval drawdown of atmospheric CO2 and high latitude ice sheet growth, generating the conditions that stabilized 100-kyr cycles.

  1. Paleotopography of glacial-age ice sheets

    SciTech Connect

    Edwards, R.L.

    1995-01-27

    This is technical comment and response to the subject of paleotophography of glacial age ice sheets. The model presented by Peltier reconstructing the paleotopography of glacial age ice sheets has implications for atmospheric general circulation models of ice age climate. In addition, the model suggests that the glacial-age Antarctic Ice Sheet was significantly larger than today`s. The commentor, Edwards, suggests there is a discrepancy between data from Papua New Guinea and the model results.

  2. {13C }/{12C } ratios of pleistocene mummified remains from beringia

    NASA Astrophysics Data System (ADS)

    Bombin, Miguel; Muehlenbachs, Karlis

    1985-01-01

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

  3. 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.

  4. Maximum glacial advance and deglaciation of the Pinar Valley (Sierra de Gredos, Central Spain) and its significance in the Mediterranean context

    NASA Astrophysics Data System (ADS)

    Palacios, David; Andrés, Nuria; Marcos, Javier; Vázquez-Selem, Lorenzo

    2012-12-01

    Pinar Valley is located on the north side of Galana Peak (40° 15? 21? N; 5° 18? 00? W; 2564 m a.s.l.), Sierra de Gredos, in the center of the Iberian Peninsula. Surface exposure ages based on the in situ accumulation of 36Cl were obtained from six moraine boulders and from three bedrock outcrops to investigate the timing of both the last local glacial maximum and the deglaciation. The oldest moraines, which probably overrode older glacial deposits, are coeval to the global Last Glacial Maximum. Subsequently the Pinar glacier underwent minor pulsations close to its maximum position, followed by general glacier retreat after ~ 17-16 ka. Small cirque glaciers probably remained during the terminal Pleistocene but they had completely disappeared by 10 ka.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    USGS Publications Warehouse

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

    2011-01-01

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

  8. 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.

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

    PubMed

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

    2014-12-30

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

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

    PubMed Central

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

    2014-01-01

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

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

    PubMed

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

    2006-10-01

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

  12. Temporal labyrinths of eastern Eurasian Pleistocene humans

    PubMed Central

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

    2014-01-01

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

  13. Early Pleistocene British-Irish ice rafting: Was the onset of Northern Hemisphere glaciation more widespread than previously assumed?

    NASA Astrophysics Data System (ADS)

    Thierens, M. M.; Tyrrell, S.; Wheeler, A. J.

    2011-12-01

    The late Pliocene - early Pleistocene onset and intensification of Northern Hemisphere glaciation marks an important threshold in Earth's climate system. Unravelling the extent and dynamics of early ice-sheet development is crucial to our understanding of the processes driving Quaternary glaciations and hence, affecting global climate and its variability[1]. In the North Atlantic Ocean, ice-rafted detritus (IRD) layers attest to the development of marine-terminating ice sheets, discharging sediment-loaded icebergs into the ocean. So far, Early-Pleistocene IRD deposition has been predominantly linked to the intensified glaciation of high-latitudinal regions surrounding the North Atlantic (Canada, Greenland, Iceland and Scandinavia), while the extent and role of early ice build-up in more temperate mid-latitudinal regions is still poorly understood. Here we present results from a multiproxy provenance analysis of the unique, Pleistocene IRD record that has been preserved in the Challenger Mound sequence (IODP Expedition 307; Irish NE Atlantic continental margin). This archive has, recently, revealed the first evidence supporting substantial and repeated ice build-up on the British-Irish Isles (57° - 52°N) since the earliest Pleistocene (ca 2.6 Ma) [2]. Nd-Sr isotopic analysis of multiple IRD intervals throughout the sequence show a dominant sediment input from the adjacent British-Irish Isles, even for the early Pleistocene IRD deposits. Furthermore, the Pb isotopic composition of detrital, and apparently ice-rafted, K-feldspar grains shows excellent correspondence to a NW Irish Mainland source, definitively ruling out more far-travelled, northern sources for these grains. The long-term development of an ice sheet on NW Ireland, even in the early stages of Northern Hemisphere glacial expansion, is evidenced and discussed in this study. Overall, widespread circum-Atlantic ice-sheet development at more temperate, mid-latitudes appears to be a persistent feature of the Pleistocene climate system and, hence, should be accounted for. References [1] e.g. Raymo, M.E., Huybers, P., 2008. Unlocking the mysteries of the ice ages. Nature 451, 284-285. [2] Thierens, M., Pirlet, H., Colin, C., et al. 2011. Ice-rafting from the British-Irish ice sheet since the earliest Pleistocene (2.6 million years ago): implications for long-term mid-latitudinal ice-sheet growth in the North Atlantic region. Quaternary Science Reviews, 10.1016/j.quascirev.2010.12.020.

  14. Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance

    NASA Astrophysics Data System (ADS)

    Rother, Henrik; Shulmeister, James; Fink, David; Alexander, David; Bell, David

    2015-11-01

    During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ?26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM, challenges the conventional geomorphic model of glaciation in New Zealand where the vertical arrangement of glacial landform-associations is used to assign successively older glaciation ages.

  15. Aeolian dust in East Antarctica (EPICA-Dome C and Vostok): Provenance during glacial ages over the last 800 kyr

    NASA Astrophysics Data System (ADS)

    Delmonte, B.; Andersson, P. S.; Hansson, M.; Schöberg, H.; Petit, J. R.; Basile-Doelsch, I.; Maggi, V.

    2008-04-01

    Aeolian mineral dust archived in Antarctic ice cores represents a key proxy for Quaternary climate evolution. The longest and most detailed dust and climate sequences from polar ice are provided today by the Vostok and by the EPICA-Dome C (EDC) ice cores. Here we investigate the geographic provenance of dust windborne to East Antarctica during Early and Middle Pleistocene glacial ages using strontium and neodymium isotopes as tracers. The isotopic signature of Antarctic dust points towards a dominant South American origin during Marine Isotopic Stage (MIS) 8, 10, 12, and back to MIS 16 and 20 as deduced from EDC core. Data provide evidence for a persistent overall westerly circulation pattern allowing efficient transfer of dust from South America to the interior of Antarctica over the last 800 kyr. Some small but significant dissimilarity between old and recent glacial ages suggests a slightly reduced Patagonian contribution during ancient glaciations.

  16. 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.

  17. Revision of the late Pleistocene stratigraphy of Bermuda

    NASA Astrophysics Data System (ADS)

    Hearty, Paul J.

    2002-10-01

    The Quaternary stratigraphy of Bermuda is one of the world's most complete sedimentary records of interglacial highstands, representing at least the past million years. Yet in terms of the last interglacial (Rocky Bay Formation), marine isotope substage (MIS) 5e, only scanty deposits are preserved. In contrast, MIS 7, generally regarded as a diminutive interglaciation, exposes widespread emergent subtidal deposits of the Belmont Formation indicating a prolonged sea level highstand at ca. +2.5±0.3 m. This "Belmont paradox" has prompted a reexamination of the geology of key sites along the South Shore of Bermuda. This revision of the late Quaternary stratigraphy of Bermuda is based on geological field observations; primarily the questionable origin of red soil-like deposits. It is concluded here that there is no physical evidence of the exposure of the upper Belmont surface for a full glacial cycle (˜70-100 ka), and that interbedded, reddish soil-like, lenticular deposits are the result of colluvial activity during mid-MIS 5e. Reexamination of previously published uranium-series (U/Th) ages indicates that several "+3-m notches" contain a mix of ca. 125 ka and older coral ages. Contrary to previous works, this study favors an early MIS 5e interpretation of the coral ages from the +2.5-m Belmont shoreline, which is further supported by amino acid racemization (AAR) ratios on whole-rock, Poecilozonites, Glycymeris, and Brachiodontes samples from shore and notch deposits. An updated AAR kinetic model demonstrates that the bulk of epimerization occurred during warm interglacial intervals between 130 and 80 ka and the last 10 ka of the Holocene. This revised stratigraphy of Bermuda now falls into accordance with a more general view of middle and late Pleistocene sea level history.

  18. 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.

  19. Forcing of tropical Atlantic sea surface temperatures during the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Schefuß, Enno; Sinninghe Damsté, Jaap S.; Jansen, J. H. Fred

    2004-12-01

    We compare a new mid-Pleistocene sea surface temperature (SST) record from the eastern tropical Atlantic to changes in continental ice volume, orbital insolation, Atlantic deepwater ventilation, and Southern Ocean front positions to resolve forcing mechanisms of tropical Atlantic SST during the mid-Pleistocene transition (MPT). At the onset of the MPT, a strong tropical cooling occurred. The change from a obliquity- to a eccentricity-dominated cyclicity in the tropical SST took place at about 650 kyr BP. In orbital cycles, tropical SST changes significantly preceded continental ice-volume changes but were in phase with movements of Southern Ocean fronts. After the onset of large-amplitude 100-kyr variations, additional late glacial warming in the eastern tropical Atlantic was caused by enhanced return flow of warm waters from the western Atlantic driven by strong trade winds. Pronounced 80-kyr variations in tropical SST occurred during the MPT, in phase with and likely directly forced by transitional continental ice-volume variations. During the MPT, a prominent anomalous long-term tropical warming occurred, likely generated by extremely northward displaced Southern Ocean fronts. While the overall pattern of global climate variability during the MPT was determined by changes in mean state and frequency of continental ice volume variations, tropical Atlantic SST variations were primarily driven by early changes in Subantarctic sea-ice extent and coupled Southern Ocean frontal positions.

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

    SciTech Connect

    Sydow, J.; Roberts, H.H. )

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

    NASA Astrophysics Data System (ADS)

    Hooghiemstra, H.

    2013-05-01

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

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

    PubMed Central

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

    2015-01-01

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

  3. 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.

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

    PubMed

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

    2015-03-01

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

  5. Catastrophic middle Pleistocene jökulhlaups in the upper Susquehanna River: Distinctive landforms from breakout floods in the central Appalachians

    NASA Astrophysics Data System (ADS)

    Kochel, R. Craig; Nickelsen, Richard P.; Eaton, L. Scott

    2009-09-01

    Widespread till and moraines record excursions of middle-Pleistocene ice that flowed up-slope into several watersheds of the Valley and Ridge Province along the West Branch of the Susquehanna River. A unique landform assemblage was created by ice-damming and jökulhlaups emanating from high gradient mountain watersheds. This combination of topography formed by multiple eastward-plunging anticlinal ridges, and the upvalley advance of glaciers resulted in an ideal geomorphic condition for the formation of temporary ice-dammed lakes. Extensive low gradient (1°-2° slope) gravel surfaces dominate the mountain front geomorphology in this region and defy simple explanation. The geomorphic circumstances that occurred in tributaries to the West Branch Susquehanna River during middle Pleistocene glaciation are extremely rare and may be unique in the world. Failure of ice dams released sediment-rich water from lakes, entraining cobbles and boulders, and depositing them in elongated debris fans extending up to 9 km downstream from their mountain-front breakout points. Poorly developed imbrication is rare, but occasionally present in matrix-supported sediments resembling debris flow deposits. Clast weathering and soils are consistent with a middle Pleistocene age for the most recent flows, circa the 880-ka paleomagnetic date for glacial lake sediments north of the region on the West Branch Susquehanna River. Post-glacial stream incision has focused along the margins of fan surfaces, resulting in topographic inversion, leaving bouldery jökulhlaup surfaces up to 15 m above Holocene channels. Because of their coarse nature and high water tables, jökulhlaup surfaces are generally forested in contrast to agricultural land use in the valleys and, thus, are readily apparent from orbital imagery.

  6. DATING GLACIAL LANDFORMS Jason P. Briner

    E-print Network

    Briner, Jason P.

    - and absolute-dating methods, etc.) to glacial landforms (e.g., moraines) to yield the timing of past glaciation (Moraine and Glacial Geomorphology and Landforms Evolution). Introduction Ever since scientists first on moraine boulders to elucidate their exposure age (hence the timing of moraine deposition), using the pat

  7. On the potential role of marine calcifiers in glacial-interglacial dynamics

    NASA Astrophysics Data System (ADS)

    Omta, A.; van Voorn, G.; Rickaby, R. E.; Follows, M. J.

    2013-12-01

    Ice-core measurements have revealed a highly asymmetric cycle in Antarctic temperature and atmospheric CO2 over the last 800,000 years. Both CO2 and temperature decrease over 100,000 years going into a glacial period, then rise steeply over less than 10,000 years at the end of a glacial. There does not yet exist wide agreement about the causes of this cycle or about the ori- gin of its shape. Here, we explore the possibility that an ecologically driven oscillator plays a role in the dynamics. A conceptual model describing the in- teraction between calcifying plankton and ocean alkalinity shows interesting features: (i) it generates an oscillation in atmospheric CO2 with the charac- teristic asymmetric shape observed in the ice-core record, (ii) the system can transform a sinusoidal Milankovitch forcing into a sawtooth-shaped output, and (iii) there are spikes of enhanced calcifier productivity at the glacial- interglacial transitions, consistent with several sedimentary records. This suggests that ecological processes might play an active role in the observed glacial-interglacial cycles.

  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. 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. )

    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.

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

    PubMed Central

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

    2013-01-01

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

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

    SciTech Connect

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

    1985-01-01

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

  12. 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

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

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Ganopolski, A.

    2014-01-01

    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 variables and dust deposits 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 factors 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 factors are varied within uncertainty ranges known from available data and detailed model studies. Although the parameters are reasonably constrained by use of these studies, the simulated dust DRF spans a wide uncertainty range related to nonlinear dependencies. In our simulations, the dust DRF is highly localized. Medium-range parameters result in negative DRF of several W m-2 in regions close to major dust sources and negligible values elsewhere. In case of high absorption efficiency, the local dust DRF can reach positive values and the global mean DRF can be insignificantly small. In 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 the DRF has the potential to either damp or reinforce glacial-interglacial climate changes.

  16. 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.

  17. Late Pleistocene piedmont glaciations in the Eastern Mediterranean; insights from cosmogenic 36Cl dating of hummocky moraines in southern Turkey

    NASA Astrophysics Data System (ADS)

    Çiner, Attila; Sar?kaya, Mehmet Akif; Y?ld?r?m, Cengiz

    2015-05-01

    We report the presence of Late Pleistocene piedmont glaciers represented by the largest hummocky moraine field observed in the Eastern Mediterranean. The piedmont glaciers originated from the Geyikda? ice cap (?40 km2), situated between 2350 and 2650 m above sea level (a.s.l.) (Central Tauride Mountains of Turkey), and deeply carved the north-facing hillslopes before reaching the Namaras Valley (2000-2050 m a.s.l). The hummocky moraines resulted from in-situ deposition of stagnant glacier ice where debris cover was heterogeneously distributed on the glacier surface. Thirty-four boulders from hummocky, disintegration, lateral and terminal moraines from the Namaras Valley and the tributary Susam Valley (2100-2200 m a.s.l.) were dated by cosmogenic 36Cl surface exposure dating. The moraine ages indicate three phases of deglaciation during the Late Pleistocene. The oldest deglaciation occurred in the Namaras Valley at 18.0 ± 1.1 ka (ka: thousand years ago) towards the end of the Last Glacial Maximum (LGM) and is recorded entirely by hummocky moraines. We speculate that hummocky moraine forming processes with cycles of relief inversion gave rise to boulder apparent ages up to a few thousand years younger in our study area. Therefore, 18.0 ± 1.1 ka should be regarded as a minimum age with a probable true age much closer to the local-LGM values (?20 ka) as observed in the surrounding mountains. Paleo-piedmont glaciers also deposited several lateral moraines that are ?50 m higher than the hummocky moraines. Although the lateral moraines probably represent the build-up and the hummocky moraines the final phase of the same local-LGM-pulse, both lateral moraines started to retreat from the Late-glacial (14.0 ± 2.7 ka) and gradually disappeared by mid-Holocene (5.2 ± 1.0 ka), encompassing the Younger Dryas (YD) stadial. In the Susam Valley, the Late-glacial is represented by a terminal moraine (13.4 ± 1.5 ka). The glacier retreat was very fast as indicated by an almost instantaneous disappearance of 5 km long Susam Valley glacier, represented by disintegration and hummocky moraines (14.0 ± 1.3 ka). Alternatively, in case the oldest boulder age is taken into account, the Susam Valley glacier can be also attributed to the late LGM (?17 ka) to Late-glacial (?14 ka) transition. Near the exit of the Susam Valley a right lateral moraine was deposited 11.6 ± 1.3 ka ago, confirming the presence of the YD in Geyikda?. Comparable glacial chronologies were obtained from other Turkish and Mediterranean mountains.

  18. Peripatric speciation of an endemic species driven by Pleistocene climate change: The case of the Mexican prairie dog (Cynomys mexicanus).

    PubMed

    Castellanos-Morales, Gabriela; Gámez, Niza; Castillo-Gámez, Reyna A; Eguiarte, Luis E

    2016-01-01

    The hypothesis that endemic species could have originated by the isolation and divergence of peripheral populations of widespread species can be tested through the use of ecological niche models (ENMs) and statistical phylogeography. The joint use of these tools provides complementary perspectives on historical dynamics and allows testing hypotheses regarding the origin of endemic taxa. We used this approach to infer the historical processes that have influenced the origin of a species endemic to the Mexican Plateau (Cynomys mexicanus) and its divergence from a widespread ancestor (Cynomys ludovicianus), and to test whether this endemic species originated through peripatric speciation. We obtained genetic data for 295 individuals for two species of black-tailed prairie dogs (C. ludovicianus and C. mexicanus). Genetic data consisted of mitochondrial DNA sequences (cytochrome b and control region), and 10 nuclear microsatellite loci. We estimated dates of divergence between species and between lineages within each species and performed ecological niche modelling (Present, Last Glacial Maximum and Last Interglacial) to determine changes in the distribution range of both species during the Pleistocene. Finally, we used Bayesian inference methods (DIYABC) to test different hypotheses regarding the divergence and demographic history of these species. Data supported the hypothesis of the origin of C. mexicanus from a peripheral population isolated during the Pleistocene [?230,000years ago (0.1-0.43Ma 95% HPD)], with a Pleistocene-Holocene (?9000-11,000years ago) population expansion (?10-fold increase in population size). We identified the presence of two possible refugia in the southern area of the distribution range of C. ludovicianus and another, consistent with the distribution range of C. mexicanus. Our analyses suggest that Pleistocene climate change had a strong impact in the distribution of these species, promoting peripatric speciation for the origin of C. mexicanus and lineage divergence within C. ludovicianus. PMID:26343460

  19. 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.

  20. Tracing the Mid-Pleistocene Transition using SST and Sea Ice Proxies in the Sub-Arctic Pacific.

    NASA Astrophysics Data System (ADS)

    Stroynowski, Z. N.; Rodrigues, T.; Cardoso, R.; Bruno, E.

    2014-12-01

    The Middle Pleistocene Transition (MPT) is defined as a dramatic change in the Earth's climate when glacial/interglacial cyclicity switched from a 41-kyr orbital obliquity to 100-kyr precessional forcing. The cause of the 100-kyr cycle emergence in the absence of any change in orbital forcing remains unknown. High latitude sites, such as the Bering Sea, can provide important data as the timing and mechanisms behind this major climatic shift. This work will present high resolution alkenone-derived SST and diatom data from core U1340A collected during IODP Expedition 323. Preliminary results reveal a broad intensification of cold surface water conditions averaging 2-4oC and increased sea ice duration at ca. 0.8-1.1 Ma. Diatom assemblages reveal a marked downturn in Alaskan Stream water masses and greater influence of western basin waters after this period. These results suggest both an intensification of glacial/interglacial cycles and increased isolation of the basin during glacial periods

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

    USGS Publications Warehouse

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

    2013-01-01

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

  2. 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.

  3. 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

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1996-01-01

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

  6. Glacial greenhouse-gas fluctuations controlled by ocean circulation changes.

    PubMed

    Schmittner, Andreas; Galbraith, Eric D

    2008-11-20

    Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO(2)) and nitrous oxide (N(2)O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N(2)O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO(2). Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature, as well as CO(2) and N(2)O fluctuations. Despite significant changes in the land carbon inventory, CO(2) variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N(2)O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO(2) and N(2)O fluctuations on millennial timescales. PMID:19020618

  7. 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.

  8. Glacial Isostatic Adjustment in Antarctica

    NASA Astrophysics Data System (ADS)

    Whitehouse, P. L.

    2014-12-01

    In order to determine the distribution of present-day ice mass change across the Antarctic Ice Sheet it is first necessary to remove the geodetic signal of past ice mass change. This signal arises due to the ongoing process of Glacial Isostatic Adjustment (GIA), which has traditionally been estimated by modelling the response of the Earth system to ice-sheet changes during a glacial cycle. Reconstructions of ice-sheet change are typically based on field observations relating to past ice extent and thickness, although a more recent approach has involved the use of ice-sheet models, and even coupled ice-sheet - GIA models, to reconstruct the ice-sheet history in areas where field constraints are sparse. Both methods have their limitations and in this presentation I will highlight the advantages of each and compare recently-published models to assess our current state of knowledge in the field of Antarctic GIA. I will also briefly discuss the motivation behind active areas of model development, which include the consideration of lateral variations in Earth structure and feedbacks between solid Earth, ice sheet and ocean processes. Finally, I will assess the suitability of the various data sets that are used to constrain or test Antarctic GIA models, and I will explain how combinations of data are being used to isolate the GIA signal independently of traditional modelling assumptions. Despite the clear benefits of this approach for the purposes of quantifying present-day ice mass change, it is still crucial to be able to model how GIA processes will evolve in the future. The motivation for this goal is provided by recent modelling studies, which suggest that GIA processes will be modified by, and are capable of influencing, the future dynamics of the Antarctic Ice Sheet.

  9. 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.

  10. 3D seismic interpretations of the Pliocene-Pleistocene stratigraphy and tunnel valleys of the North Sea Plateau-Fladen area, northern North Sea

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  11. The Punta Lucero Quarry site (Zierbena, Bizkaia): a window into the Middle Pleistocene in the Northern Iberian Peninsula

    NASA Astrophysics Data System (ADS)

    Gómez-Olivencia, Asier; Sala, Nohemi; Arceredillo, Diego; García, Nuria; Martínez-Pillado, Virginia; Rios-Garaizar, Joseba; Garate, Diego; Solar, Gonzalo; Libano, Iñaki

    2015-08-01

    The period between the end of the Early Pleistocene and the mid-Middle Pleistocene (roughly between 1.0 and 0.4 Ma BP) is of great interest in Western Europe. It witnessed several climatic oscillations and changes in the fauna, the demise of a hominin species and the appearance of another, along with important cultural and technological changes. Thus, the few available sites with these chronologies is vital to the understanding of the tempo and mode of these changes. Middle Pleistocene sites in the Northern Iberian Peninsula are very rare. Here we present the study of the site found at the Punta Lucero Quarry (Biscay province, Northern Iberian Peninsula), which includes for the first time the complete collection from the site. The fossil association from this site includes several ungulates, such as a Megacerine deer, Cervus elaphus, large bovids (likely both Bos primigenius and Bison sp. are present), Stephanorhinus sp., and carnivores, such as Homotherium latidens, Panthera gombaszoegensis, Canis mosbachensis and Vulpes sp. This association is typical of a middle Middle Pleistocene chronology and would be the oldest macro-mammal site in the Eastern Cantabrian region. This site would likely correspond to a chronology after Mode 1 technological complex and before the arrival of Mode 2 technology in this region. Thus, it offers a glimpse into the paleoecological conditions slightly prior to or contemporaneous with the first Acheulian makers in the northern fringe of the Iberian Peninsula.

  12. 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.

  13. 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.

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

    PubMed Central

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

    2012-01-01

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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2001-01-01

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

  17. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  19. 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.

  20. Paleoecology of central Kentucky since the last glacial maximum

    NASA Astrophysics Data System (ADS)

    Wilkins, Gary R.; Delcourt, Paul A.; Delcourt, Hazel R.; Harrison, Frederick W.; Turner, Manson R.

    1991-09-01

    Pollen grains and spores, plant macrofossils, and sponge spicules from a 7.2-m sediment core from Jackson Pond dating back to 20,000 yr B.P. are the basis for new interpretations of vegetational, limnological, and climatic changes in central Kentucky. During the full-glacial interval (20,400 to 16,800 yr B.P.) upland vegetation was closed spruce forest with jack pine as a subdominant. Aquatic macrophyte and sponge assemblages indicate that the site was a relatively deep, open pond with low organic productivity. During late-glacial time (16,800 to 11,300 yr B.P.) spruce populations continued to dominate while jack pine declined and sedge increased as the vegetation became a more open, taiga-like boreal woodland. Between 11,300 and 10,000 yr B.P., abundances of spruce and oak pollen oscillated reciprocally, possibly reflecting the Younger Dryas oscillation as boreal taxa underwent a series of declines and increases at the southern limit of their ranges before becoming extirpated and replaced by deciduous forest. In the early Holocene (10,000 to 7300 yr B.P.) a mesic deciduous woodland developed; it was replaced by xeric oak-hickory forest during the middle Holocene between 7300 and 3900 yr B.P. Grass increased after 3900 yr B.P., indicating that the presettlement vegetation mosaic of mixed deciduous forest and prairie (the "Kentucky Barrens") became established in central Kentucky after the Hypsithermal interval. Sponge spicules increased in number during the Holocene, reflecting reduced water depths in the pond. Sediment infilling, as well as climatic warming and the expansion of fringing shrub thickets, increased nutrient and habitat availability for freshwater sponges.

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  4. Glacial tunnel valleys and Quaternary history of the outer Scotian shelf

    NASA Astrophysics Data System (ADS)

    Boyd, Ron; Scott, D. B.; Douma, M.

    1988-05-01

    High-resolution seismic reflection data indicate the presence of huge sub-surface channel networks on the outer Nova Scotian continental shelf. Channel axes extend to over 450 m below present sea level (b.s.l.). Channel walls average 2-3 km in width. Mechanisms capable of producing such channels include fluvial, submarine canyon or glacial erosion. Considerable debate has focused on the positions of the Tertiary/Quaternary (T/Q) and Pleistocene/ Holocene (P/H) boundaries1-4 in this region and the relationship of the T/Q boundary to the unconformity at the base of the channel networks. Uncertainty also surrounds the extent of Pleistocene ice sheets on the south-east Canadian continental margin4-7. Here we present a new stratigraphy for the Sable Island region (Fig. 1) based on seismic profiles, with lithologic and biostratigraphic control provided by two strategically placed boreholes. This strati-graphic analysis establishes the positions of the T/Q and P/H boundaries outside the valleys at 51 m and 220 m b.s.l. respectively. Our analysis also implies that the large channel systems are tunnel valleys, cut by a sub-ice meltwater process under a pre- to early Wisconsinan ice sheet which extended close to the shelf edge.

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

    PubMed Central

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

    2012-01-01

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

  6. 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

  7. Culture, population structure, and low genetic diversity in Pleistocene hominins

    E-print Network

    Kohler, Tim A.

    Culture, population structure, and low genetic diversity in Pleistocene hominins L. S. Premo1 diversity than living great apes. The traditional interpre- tation that low levels of genetic diversity levels of genetic diversity in Middle Pleistocene hominins. A more parsimonious hypothesis proposes

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

    E-print Network

    Nekola, Jeffrey C.

    locations suggest that changes in groundwater levels during the late Pleistocene in desert wet- lands2224 ABSTRACT During the late Pleistocene, emergent groundwater supported persistent and long in the geologic record by groundwater discharge deposits, which are also called spring or wetland deposits

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

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

    PubMed

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

    2009-05-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. Modelled glacial and non-glacial HCO3 , Si and Ge fluxes since

    E-print Network

    Huybrechts, Philippe

    Modelled glacial and non-glacial HCO3 À , Si and Ge fluxes since the LGM: little potential for impact on atmospheric CO2 concentrations and a potential proxy of continental chemical erosion À , Si and Ge that arise from chemical erosion in non-glaciated terrain, are modelled at six time

  15. 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.

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

    PubMed

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

    2013-01-01

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

  17. 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

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

  19. 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.

  20. 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.

  1. 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.

  2. 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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  4. Abrupt Climate Oscillations During the Last Deglaciation in

    E-print Network

    Yu, Zicheng

    , such as the Gerzensee-Killarney Oscillation (also known as the Intra-Allerød Cold Period), Younger Dryas, and Preboreal state to another. The most detailed records of this transition--the late glacial period--are from as the cause of observed changes. The basins are predom- inately situated in Ordovician and Silurian dolomites

  5. Last Glacial loess in the conterminous USA

    USGS Publications Warehouse

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

    2003-01-01

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

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

    PubMed Central

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

    2007-01-01

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

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

    PubMed Central

    2012-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Hardy, Bruce L.

    2010-03-01

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

  9. West Antarctic Ice Sheet dynamics recorded in Plio-Pleistocene strata of the Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Loth, A. S.; Bartek, L. R.; Luyendyk, B. P.; Wilson, D. S.

    2008-12-01

    Within the 100,000 square kilometer Eastern Basin of the Ross Sea, a 290 km section, oriented parallel to depostional dip along with 10 intersecting seismic sections that are oriented parallel to depositional strike were analyzed. Using Single-Channel Seismic (SCS) data from three different seismic surveys (NBP 0306, PD9022, and NBP 9308) 36 Plio-Pleistocene sequences were correlated across the basin from the modern ice shelf edge to the contemporary shelf break. Few of the sequences are continuous across the shelf, the majority of the sequences are of limited lateral extent. The facies within the sequences were analyzed to determine ice sheet behavior at the time of deposition. Three distinct depositional environments were interpreted based upon variations in the reflection attributes within the seismic data. Subglacial facies have a spectrum of reflection attributes from reflection-free to parallel, low-amplitude, discontinuous facies. The Grounding Line Zone facies are characterized by high amplitude, mildly discontinuous reflections. Proglacial environments are distinguished by parallel, high amplitude, continuous reflection packages. The facies distribution within many of the sequences consists of Subglacial facies in updip locales, Grounding Line Zone facies widely distributed across the shelf, and Proglacial facies present at downdip sites. The facies distribution within the sequences provides a record of the variation of the extent of the West Antarctic Ice Sheet (WAIS) throughout the Plio-Pleistocene. Not all sequences have a consecutive facies relationship, which may have resulted from several causes: 1) changes in the flow of the WAIS, 2) interplay between the East Antarctic Ice Sheet (EAIS) with the WAIS, or 3) additional grounding of the WAIS on paleobasin highs. Understanding the short-lived glacial events, whether they are a function of non-deposition or cannibalization of previous deposits, provides insight into the dynamics of marine based ice sheets.

  10. 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

  11. 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

  12. Response of fluvial, aeolian, and lacustrine systems to late Pleistocene to Holocene climate change, Lower Moravian Basin, Czech Republic

    NASA Astrophysics Data System (ADS)

    Kadlec, Jaroslav; Kocurek, Gary; Mohrig, David; Shinde, Dattatreya P.; Murari, Madhav K.; Varma, Vaidehi; Stehlík, Filip; Beneš, Vojt?ch; Singhvi, Ashok K.

    2015-03-01

    Late Pleistocene to Holocene Morava River valley-fill of the eastern Czech Republic reflects the geomorphic evolution of the valley as forced by climate change. Valley-fill stratigraphy was studied through measured sections, optically stimulated luminescence (OSL) and radiocarbon dating, ground-penetrating radar surveys of relict sand dunes, archived drill-hole data, and a comparison of elevations and ages of stratigraphic units. Fluvial systems evolved from meandering with floodplains to braided during MIS 3. Braided fluvio-aeolian systems dominated through MIS 2 and the Last Glacial Maximum (LGM). Valley aggradation occurred during arid glacial times of a low water-to-sediment discharge ratio. Most valley-fill was removed at 13 ka with incision by a large-bend meandering river with an estimated bankful paleodischarge 3 × larger than the modern Morava River. The Holocene Morava River has varied from meandering to anabranching with low rates of floodplain aggradation. The Bzenec sand body, up to 36 m thick, represents an erosional remnant bypassed during late Pleistocene incision and consists of interpreted lacustrine turbidites overlain by braided stream and aeolian dune strata. The turbidites consist of laterally continuous, thin, normally graded beds of rounded and frosted sand grains of aeolian origin. Dates and elevation data argue that the valley lake formed during the LGM through downstream damming by a braided terminal fan and sand dune complex. The turbidites are interpreted to have formed through fluvial undercutting and slumping of dune accumulations as lake level rose. This process forced an erosional unroofing of aeolian accumulations, reflected in inverted OSL dates for the turbidites.

  13. Red Sea isolation history suggested by Plio-Pleistocene seismic reflection sequences

    NASA Astrophysics Data System (ADS)

    Mitchell, Neil C.; Ligi, Marco; Rohling, Eelco J.

    2015-11-01

    High evaporation rates in the desert climate of the Red Sea ensure that, during glacial sea level lowstands when water exchange with the Indian Ocean was more restricted, water salinity and ?18 O became unusually extreme. Modeling of the effect on Red Sea sedimentary ?18 O has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea-level model could be extended if continuous core material of older sediment became available. We attempt to address this question here by examining seismic reflection data. The upper Pleistocene hemipelagic sediments in the Red Sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea-level lowstands. Seismic impedance changes associated with boundaries to those aragonite-rich layers appear to explain seismic reflection sequences. A segment of Chirp sediment profiler data from the central Red Sea reveals prominent reflections at ?1, ?5, ?23, ?26 and ?36 ms two-way travel time (TWT) from the seabed. Based on depths to the glacial marine isotope stages (MIS) in cores, we relate the upper three reflections to the tops of aragonite-rich layers and hence the sea level rises immediately following MIS 2, 6 and 12. The reflection at 26 ms is related to an unusually rapid fall into MIS 12 predicted by one sea level reconstruction, which may have created an abrupt lower boundary to the MIS 12 aragonite-rich layer. With the aid of seismogram modeling, we tentatively associate the ?36 ms reflection with the top of an aragonite-rich layer formed during MIS 16. Furthermore, some segments of lower frequency (airgun and sparker) seismic data from the central and southern Red Sea show a lower (earlier) Plio-Pleistocene (PP) interval that is less reflective than the upper (late) PP interval. This implies less variability in sediment impedance and that extreme variability in water salinity did not develop; water exchange with the Indian Ocean likely continued throughout this interval. These results suggest that viable relative sea level reconstructions may be recovered from Red Sea sediment ?18 O data to at least MIS 16 and perhaps even as far back as the early Pliocene.

  14. Reprint of "Pleistocene and Holocene glacier fluctuations upon the Kamchatka Peninsula"

    NASA Astrophysics Data System (ADS)

    Barr, Iestyn D.; Solomina, Olga

    2015-11-01

    This review summarises landform records and published age-estimates (largely based upon tephrochronology) to provide an overview of glacier fluctuations upon the Kamchatka Peninsula during the Holocene and, to a lesser degree, earlier phases of glaciation. The evidence suggests that following deglaciation from the Last Glacial Maximum (LGM), the peninsula experienced numerous phases of small-scale glacial advance. During the Late Glacial, moraine sequences appear to reflect the former presence of extensive glaciers in some parts of the peninsula, though little chronological control is available for deposits of this period. During the Holocene, the earliest and most extensive phase of advance likely occurred sometime prior to c. 6.8 ka, when glaciers extended up to 8 km beyond their current margins. However, these deposits lack maximum age constrains, and pre-Holocene ages cannot be discounted. Between c. 6.8 ka and the onset of 'Neoglaciation' c. 4.5 ka, there is little evidence of glacial advance upon the peninsula, and this period likely coincides with the Holocene climatic optimum (or 'hypsithermal'). Since c. 4.5 ka, numerous moraines have been deposited, likely reflecting a series of progressively less extensive phases of ice advance during the Late Holocene. The final stage of notable ice advance occurred during the Little Ice Age (LIA), between c. 1350 and 1850 C.E., when reduced summer insolation in the Northern Hemisphere likely coincided with solar activity minima and several strong tropical volcanic eruptions to induce widespread cooling. Following the LIA, glaciers upon the peninsula have generally shown a pattern of retreat, with accelerated mass loss in recent decades. However, a number of prominent climatically and non-climatically controlled glacial advances have also occurred during this period. In general, there is evidence to suggest that millennial scale patterns in the extent and timing of glaciation upon the peninsula (encompassing much of the last glacial period) are governed by the extent of ice sheets in North America. Millennial-to-centennial scale fluctuations of Kamchatkan glaciers (encompassing much of the Holocene) are governed by the location and relative intensity of the Aleutian Low and Siberian High pressure systems. Decadal scale variations in glacier extent and mass balance (particularly since the LIA) are governed by inter-decadal climatic variability over the North Pacific (as reflected by the Pacific Decadal Oscillation), alongside a broader trend of hemispheric warming.

  15. 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.

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

    PubMed

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

    2013-10-01

    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. 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

  18. 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.

  19. 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.

  20. The Pleistocene glaciations and the evolutionary history of the polytypic snail species Arianta arbustorum (Gastropoda, Pulmonata, Helicidae).

    PubMed

    Gittenberger, E; Piel, W H; Groenenberg, D S J

    2004-01-01

    The evolutionary history of the snail Arianta arbustorum is controversial. This diverse, polytypic species has two distinct forms: one, with a globular shell and closed umbilicus, is found from lowland to high altitudes; the other, with a depressed shell and open umbilicus, is found at a few scattered, high altitude localities. What is the origin of these two forms? Some believe that the depressed shell is a recent, local, ecotypic adaptation to alpine environments. Others believe that this form is a relic of an ancestral condition that may have survived the Pleistocene glaciations on nunatak-like montane refugia, while the globular shell is a derived condition and its presence at high altitudes follows post-Pleistocene recolonisation. We analysed a portion of the mitochondrial gene cytochrome oxidase I for 100 snails of the species A. arbustorum, three additional Arianta species, and nine outgroup taxa from five genera, in order to understand the phylogeographic history of the species. Despite some confounding artefacts that are likely due to introgression among the morphological forms, the resulting phylogeny shows that the depressed shell is plesiomorphic, while the globular shell is derived. Moreover, their disparate histories suggest that the depressed shell variety survived the glaciations in pockets of alpine refugia, while the globular shell variety recolonised the alpine environment post-glacially. PMID:15022758

  1. Phylogeography of the land snail genus Circassina (Gastropoda: Hygromiidae) implies multiple Pleistocene refugia in the western Caucasus region.

    PubMed

    Neiber, Marco T; Hausdorf, Bernhard

    2015-12-01

    The phylogeny and historical biogeography of the Caucasian land snail genus Circassina was reconstructed using multilocus amplified fragment length polymorphism (AFLP) data and mitochondrial DNA sequences. Diversification within the group started with a divergence of populations from the western Lesser Caucasus from those of the Greater Caucasus during the late Miocene. Distinct AFLP clusters and major mitochondrial clades separated by long internal branches lend evidence to the hypothesis of separate glacial refuges in the Lesser and Greater Caucasus during the Pleistocene. High genetic distances across low geographic distances and admixture analysis revealed a phylogeographic boundary running through the Colchis lowlands, which may have been established and maintained in part by repeated transgressions of the Black Sea during the Pleistocene and Holocene. Localities in Ciscaucasia were probably colonised through long-distance dispersal across the main ridge of the Greater Caucasus. The phylogeny implies multiple independent losses of accessory genital organs, i.e. dart sac and mucus glands, within Circassina. None of the anatomically defined (sub-) species distinguished so far is monophyletic and there is gene flow between the two main population groups across the Colchis lowlands. Thus, we propose to classify these population groups as subspecies of a single species. PMID:26220841

  2. Dancing to the rhythms of the Pleistocene? Early Middle Paleolithic population dynamics in NW Iberia (Duero Basin and Cantabrian Region)

    NASA Astrophysics Data System (ADS)

    Sánchez Yustos, Policarpo; Diez Martín, Fernando

    2015-08-01

    The Northwest of Iberia has yielded one of the most complete European Middle Paleolithic records. Despite this wealth of information, very little is known about population dynamics during this period. For that reason, the main concern of this paper is to provide socio-environmental models that may help explain Early Middle Paleolithic (EMP) population dynamics in NW Iberia, assessing to what extent they were shaped by climate forces. The archaeological record is analyzed on the basis of the heuristics of ecological models, already employed in the European Pleistocene record but never at a regional scale, in order to detect long-term changes in the composition of EMP populations, and the environmental, biological and sociocultural process influencing those changes. According to the models proposed, we have detected a long-term population dynamic between MIS 11 and MIS 6, characterized by low environmental stress, high biological productivity, interaction among populations and sociocultural complexity. Eventually, this population dynamic was broken due to an extreme climate phase in late MIS 6 that had a profound impact on populations and sociocultural structures. As a result, the Upper Pleistocene population of NW Iberia was concentrated in the Cantabrian region. This area became an isolated Neanderthal glacial refugium that hosted a population with different origins and fragile long-term demographic stability.

  3. 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.

  4. Investigating the Benthic Foraminiferal Stilostomellid Extinction and Mid Pleistocene Phytoplankton Evolution

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    As global climate cooled during the Mid Pleistocene Transition (MPT, ~1.1-0.6 Ma), the last great extinction of benthic foraminifera occurred. The so-called 'Stilostomella Extinction' saw the disappearance of almost two families of elongated uniserial species with distinctive apertural architecture. The stepwise extinction consisted of a gradual disappearance at different water depths and ocean basins over successive glacials. Understanding the causes of this extinction has proven difficult, in part because ecological preferences are not well known, and because their extinction has not been documented in high resolution along with other paleoenvironmental proxies. For instance, one hypothesis for the extinction is lowering bottom water temperature. We present new high-resolution (~5 ka time step) benthic foraminiferal data from ODP Site 593 in the Tasman Sea (~1068 m water depth) through the MPT, and compare with new intermediate water temperature (benthic Mg/Ca) and surface water productivity proxies (nannofossil assemblages and sediment pigment analyses). Extinction group occurrences do not correlate with intermediate water temperature. There are, however, clear changes in surface water productivity associated with the final phase of the extinction, at ~0.85 Ma. Pigments increase in abundance, indicating elevated glacial productivity across the MPT. Coccolith assemblages shift towards small Gephyrocapsa spp., and extinction occurs within the Reticulofenestra, both of which are global events. Comparisons with the Pacific and Atlantic Ocean extinction data indicates 0.85 Ma as a critical time interval in the global Stilostomella Extinction. This evidence strengthens the hypothesis that changes in the type of organic carbon reaching the sea floor, driven by reorganization within marine phytoplankton communities, may have been linked to the disappearance of the extinction group.

  5. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

    PubMed

    Gulick, Sean P S; Jaeger, John M; Mix, Alan C; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L; Berbel, Glaucia B B; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Kioka, Arata; Konno, Susumu; LeVay, Leah J; März, Christian; Matsuzaki, Kenji M; McClymont, Erin L; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R; Ridgway, Kenneth D; Romero, Oscar E; Slagle, Angela L; Stoner, Joseph S; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D; Worthington, Lindsay L; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M

    2015-12-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (?2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (?100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

  6. Late Miocene-Pleistocene Stability of upper Ferrar Glacier, Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Staiger, J. W.; Marchant, D. R.; Schaefer, J. M.; Johnson, J. V.; Oberholzer, P.

    2005-12-01

    Vernier Valley (78o S, 161o E) opens onto a peripheral lobe of upper Ferrar glacier in the Dry Valleys of southern Victoria Land, Antarctica. The areal distribution of Ferrar drifts, along with a relative and numerical chronology afforded by surface-weathering characteristics and 3He - 21Ne exposure-age data, are used to reconstruct the Late Miocene-to-Pleistocene history of upper Ferrar Glacier. Applying a modest erosion rate correction of 10 cm Ma-1, our results show that the glacial record provided by Ferrar (1, 2, 3, and 4) drifts in Vernier Valley extends back into late Miocene time. Cosmogenic ages for clasts on the modern, ice-cored Ferrar 1 moraine suggest that nuclide inheritance is negligible. The development of weathering pits and desert varnish on surface cobbles varies linearly with cosmogenic age. Ice-surface profiles reconstructed from the moraine distribution and exposure-ages of boulders atop the moraines indicate that the ice-surface elevation of upper Ferrar Glacier has lowered roughly 50 m throughout the Quaternary Period and roughly 125 m since late Miocene time. Conversely, during MIS 2, the ice-surface elevation of upper Ferrar Glacier was likely no higher than today and may have been below modern levels. The moraine now forming through ice sublimation and debris accumulation at the modern, cold-based Ferrar Glacier margin is texturally similar to older drifts up-valley. The slow recession of cold-based glacier ice (and without surface melting ablation zones) in lower Vernier Valley implies enduring cold-desert conditions, much like those of today, for at least the last ~6.5 Ma. Results from a 2-D glacier flow-band model also demonstrate that upper Ferrar Glacier lacked basal-melting zones even during the Pliocene optimum. The overall stability of this glacial system has implications for the response of ice in this sector of Antarctica to future polar warming.

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

    USGS Publications Warehouse

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

    2008-01-01

    Various lines of evidence support conflicting interpretations of the timing, abruptness, and nature of climate change in the Great Plains during the Pleistocene-Holocene transition. Loess deposits and paleosols on both the central and northern Great Plains provide a valuable record that can help address these issues. A synthesis of new and previously reported optical and radiocarbon ages indicates that the Brady Soil, which marks the boundary between late Pleistocene Peoria Loess and Holocene Bignell Loess, began forming after a reduction in the rate of Peoria Loess accumulation that most likely occurred between 13.5 and 15 cal ka. Brady Soil formation spanned all or part of the B??lling-Aller??d episode (approximately 14.7-12.9 cal ka) and all of the Younger Dryas episode (12.9-11.5 cal ka) and extended at least 1000 years beyond the end of the Younger Dryas. The Brady Soil was buried by Bignell Loess sedimentation beginning around 10.5-9 cal ka, and continuing episodically through the Holocene. Evidence for a brief increase in loess influx during the Younger Dryas is noteworthy but very limited. Most late Quaternary loess accumulation in the central Great Plains was nonglacigenic and was under relatively direct climatic control. Thus, Brady Soil formation records climatic conditions that minimized eolian activity and allowed effective pedogenesis, probably through relatively high effective moisture. Optical dating of loess in North Dakota supports correlation of the Leonard Paleosol on the northern Great Plains with the Brady Soil. Thick loess in North Dakota was primarily derived from the Missouri River floodplain; thus, its stratigraphy may in part reflect glacial influence on the Missouri River. Nonetheless, the persistence of minimal loess accumulation and soil formation until 10 cal ka at our North Dakota study site is best explained by a prolonged interval of high effective moisture correlative with the conditions that favored Brady Soil formation. Burial of both the Brady Soil and the Leonard Paleosol by renewed loess influx probably represents eolian system response that occurred when gradual change toward a drier climate eventually crossed the threshold for eolian activity. Overall, the loess-paleosol sequences of the central and northern Great Plains record a broad peak of high effective moisture across the late Pleistocene to Holocene boundary, rather than well-defined climatic episodes corresponding to the B??lling-Aller??d and Younger Dryas episodes in the North Atlantic region. ?? 2008 Elsevier Ltd. All rights reserved.

  8. Relations between of the Pleistocene glaciations and karstification processes on Velebit Mt. (Croatia)

    NASA Astrophysics Data System (ADS)

    Bocic, Neven

    2014-05-01

    Velebit is the Dinaric karst mountain. It is located in Croatia and extends to a length of 145 km along the northern part of the eastern coast of the Adriatic Sea. The highest peak is 1757 m high. It is mostly made of well karstified carbonate rocks (limestone, dolomite and carbonate clastic rocks). Glaciation of this region has long attracted researchers. Studies have shown that a large part of the area was affected by the Pleistocene glaciation. These results have prompted questions about the impact of glaciation on the development of karst, especially underground karst formations - caves in this area. This work explores the impact of Pleistocene glaciations on karst development in the northern and central Velebit. Special emphasis is given to the research on the impact of glaciation on the development and morphology of caves, which is analyzed in few examples. The main methods used are geomorphological mapping and speleological research. Also, some sedimentological methods were used and 14C dating of the flowstone crust was provided. Studies on some sites are already well advanced while in some localities are only just begun. In the area of Jezera (Lakes in Croatian, northern part of the mountain) we noticed that the moraine material affects the appearance of the small occasional streams with cutting small torrents and surface erosion processes. In areas where the moraine cover is thinner or missing rekarstification of bedrock is visible, and occasional short streams sinking at contact zone of the moraine material and bedrock. In glacial valley Lomska duliba is the Ledena jama (Ice cave), 536 meters deep characterized by ice accumulation thicker than 50 m. During this study we have been mapped moraine forms along the valley and found that the same material plugs parts of the pit which led to its further dynamics. Great influence on the development of glaciation surface and underground karst forms was studied in Štirova?a (middle Velebit area). Here is the 351 m long cave with lot of erosional remnants of the fluvioglacial deposits that were fully filed much of the known part of the cave. It is concluded that the Pleistocene glaciation had multiple effects on the development of karst in this area. Moraine deposits, relatively impermeable, promote local development of surface runoff and erosion. In this way, they temporarily slowing the process of karstification below, but because of the contact process they accelerated karstification along their edges. This material can also be accumulated in the caves, directly or after resedimentation as fluvioglacial material. In this way fills the underground channels and then reduce and hinder drainage function of these channels.

  9. 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.

  10. 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.

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

    PubMed

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

    2015-01-01

    The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45-63 ?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

  13. The Plio-Pleistocene development of Atlantic deep-water circulation and its influence on climate trends

    NASA Astrophysics Data System (ADS)

    Bell, David B.; Jung, Simon J. A.; Kroon, Dick

    2015-09-01

    Using benthic stable isotope records from 10 sites in the Atlantic Ocean, including two new records from Walvis Ridge in the Southeast Atlantic (Sites 1264 and 1267), we review changes in Atlantic deep-water circulation in the context of Plio-Pleistocene climate. Overall, we find non-linear responses of Atlantic deep-water circulation to a cooling climate, with differently evolving glacial and interglacial states. Our main conclusion is that peak North Atlantic Deep Water (NADW) production was reached between ˜2.0 and 1.5 Ma, most prominently seen by a maximum in ventilated (high ?13C) conditions in the mid-depth Southeast Atlantic (Site 1264). We infer that a major source of NADW at this time was the export of dense overflow water from the Nordic Seas into the abyssal East Atlantic. Sea surface temperature records from the North and South Atlantic support this notion and indicate that the peak NADW production between ˜2.0 and 1.5 Ma was compensated by a stronger warm surface-water return flow (i.e. Atlantic Meridional Overturning Circulation (AMOC) was enhanced), causing long-term (>105 year) heat piracy from the South to the North Atlantic. In the wider picture of Plio-Pleistocene climate evolution, we find that a long-term enhancement in the average state of AMOC (˜2.4-1.3 Ma) coincides with the "41-kyr world". Hence, we speculate that the transitory negative feedback response of enhanced AMOC to a cooling climate supplied heat to key areas of ice-sheet growth, acting to limit their size and maintain the "41-kyr world". Once a threshold in global cooling was reached, the strength of AMOC lessened, providing a positive feedback for the Early-Middle Pleistocene Transition and the associated build-up of northern hemisphere ice-sheets.

  14. 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

  15. 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.

  16. Neurodynamic oscillators

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    ERIC Educational Resources Information Center

    Pape, Bruce; Francek, Mark A.

    1992-01-01

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

  18. Impact of glacial erosion on 10 Be concentrations in fluvial

    E-print Network

    Bookhagen, Bodo

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

  19. 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.

  20. 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.

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

    SciTech Connect

    Saltzman, B.; Verbitsky, M.Ya.

    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. 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.

  3. A Paleoclimatic and Paleohydrologic Reconstruction of Pleistocene Fossil Lake, Oregon

    E-print Network

    Retrum, Julie Beth

    2010-09-30

    Fossil Lake, Oregon, is a Pleistocene lacustrine basin (~ 650-13 ka) in the northwestern part of the Great Basin best known for its abundant and diverse vertebrate assemblage. Multi-proxy studies using lithostratigraphy, ...

  4. Seismic stratigraphy of the Antarctic Peninsula pacific margin: A record of Pliocene-Pleistocene ice volume and paleoclimate

    SciTech Connect

    Larter, R.D.; Barker, P.F. )

    1989-08-01

    Multichannel seismic profiles across the Pacific margin of the Antarctic Peninsula show a series of oblique progradational sequences. These sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum. Reflection events from deeper stratigraphic levels, followed down the continental slope and onto the rise, overlie ocean crust of known age, showing that at least eight such glacial sequences have been deposited within the past 6 m.y. Similar groundings have probably occurred on most Antarctic margins, but the depositional record is particularly well preserved at this margin because of Pliocene-Pleistocene thermal subsidence. Neogene global sea-level fluctuations have been attributed to changes in volume of continental ice sheets. The depositional sequences on the Pacific margin of the Antarctic Peninsula are thought to record West Antarctic ice-sheet fluctuations directly. Further investigation of these sequences would assess the relation between fluctuations in ice volume and the low-latitude record of global sea-level change.

  5. Pollen analysis of a late pliocene and early pleistocene section from the Gubik Formation of Arctic Alaska

    USGS Publications Warehouse

    Nelson, R.E.; Carter, L.D.

    1985-01-01

    A 14-m-thick section of marine and nonmarine sediments of the Gubik Formation of northern Alaska, exposed in bluffs near Ocean Point on the Colville River, has been studied by means of pollen analysis. Pollen from the marine sediments, of probable late Pliocene age, records a boreal forest of spruce and birch with minor amounts of alder in the adjacent terrestrial vegetation. Pine and perhaps true fir were probably at or near their northern limit here, but hemlocks and hardwoods were absent. The suggested environment for the Arctic Slope during the time represented by the marine sediments is similar to that of present-day Anchorage. Pollen floras from the overlying fluvial strata, of early or middle Pleistocene age, record predominantly herbaceous taxa indicating tundra conditions probably more severe than those of the present day. These deposits were most likely contemporaneous with glacial conditions in the Brooks Range to the south. Pollen of woody taxa (spruce, alder, birch, heaths) is rare through most of the section, although birch and alder percentages similar to those found in modern river sediments indicate an interstadial or interglacial warming in midsection. Inland climates during glacial episodes may have been similar to those of the present Arctic coast. ?? 1985.

  6. late Pleistocene and Holocene pollen record from Laguna de las Trancas, northern coastal Santa Cruz County, California

    USGS Publications Warehouse

    Adam, David P.; Byrne, Roger; Luther, Edgar

    1981-01-01

    A 2.1-m core from Laguna de las Trancas, a marsh atop a landslide in northern Santa Cruz County, California, has yielded a pollen record for the period between about 30,000 B. P. and roughly 5000 B. P. Three pollen zones are recognized. The earliest is characterized by high frequencies of pine pollen and is correlated with a mid-Wisconsinan interstade of the mid-continent. The middle zone contains high frequencies of both pine and fir (Abies, probably A. grandis) pollen and is correlated with the last full glacial interval (upper Wisconsinan). The upper zone is dominated by redwood (Sequoia) pollen and represents latest Pleistocene to middle Holocene. The past few thousand years are not represented in the core. The pollen evidence indicates that during the full glacial period the mean annual temperature at the site was about 2°C to 3°C lower than it is today. We attribute this small difference to the stabilizing effect of marine upwelling on the temperature regime in the immediate vicinity of the coast. Precipitation may have been about 20 percent higher as a result of longer winter wet seasons.

  7. Late glacial aridity in southern Rocky Mountains

    SciTech Connect

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

    1995-09-01

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

  8. INTRODUCTION Terminal Proterozoic glacial intervals are

    E-print Network

    Kennedy, Martin J.

    , their association with marine carbon iso- tope excursions, and paleomagnetic evidence for low-latitude glaciation nega- tive carbon isotope ratios (13C ­4 relative to the PDB [Peedee belemnite] standard; Knoll et al m) of platformal and slope carbonates includes two Neoproterozoic glacial horizons (Hoffmann

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

    SciTech Connect

    Johnston, R.A.; Kelley, J.T. ); Belknap, D. . Dept. of Geological Sciences)

    1993-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  11. A regional geochronological study of late pleistocene permafrost

    SciTech Connect

    Kostyukevich, V.V. . Geochemistry Lab.)

    1993-01-01

    The use of radiocarbon dating in geocryological investigations makes it possible to establish a chronology for permafrost-geological development during the Late Pleistocene. Both global and regional time scales for the formation of Late Pleistocene permafrost have been worked out over the past 15--20 years at the Permafrost Institute of the Siberian Branch of Russian Academy of Sciences. He presents here results from study areas of northwestern Siberia and of North, Central and West Yakutia.

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

    NASA Astrophysics Data System (ADS)

    Buckley, Francis

    2013-04-01

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

  13. 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.

  14. Pleistocene megafaunal interaction networks became more vulnerable after human arrival.

    PubMed

    Pires, Mathias M; Koch, Paul L; Fariña, Richard A; de Aguiar, Marcus A M; dos Reis, Sérgio F; Guimarães, Paulo R

    2015-09-01

    The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics, which may favour extinction cascades in communities facing extrinsic perturbations. Our findings suggest that the basic aspects of the organization of ecological communities may have played an important role in major extinction events in the past. Knowledge of community-level properties and their consequences to dynamics may be critical to understand past and future extinctions. PMID:26336175

  15. 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

  16. 3D hydro-mechanically coupled groundwater flow modelling of Pleistocene glaciation effects

    NASA Astrophysics Data System (ADS)

    Rühaak, Wolfram; Bense, Victor F.; Sass, Ingo

    2014-06-01

    Pleistocene glaciation led to temporal and spatial variations of sub-surface pore fluid pressure. In basins covered by ice sheets, fluid flow and recharge rates are strongly elevated during glaciations as compared to inter-glacial periods. Present-day hydrogeological conditions across formerly glaciated areas are likely to still reflect the impact of glaciations that ended locally more than 10 thousand years before present. 3D hydro-mechanical coupled modelling of glaciation can help to improve the management of groundwater resources in formerly glaciated basins. An open source numerical code for solving linear elasticity, which is based on the finite element method (FEM) in 3D, has been developed. By coupling this code with existing 3D flow codes it is possible to enable hydro-mechanical coupled modelling. Results of two benchmark simulations are compared to existing analytical solutions to demonstrate the performance of the newly developed code. While the result for a fluid-structure coupled case is in reasonable agreement with the analytical model, the result for a classical structure-fluid coupled benchmark showed that the analytical solution only matches the numerical result when the relevant coupling parameter (loading efficiency) is known in advance. This indicates that the applicability of widely applied approaches using an extra term in the groundwater flow equation for vertical stress to simulate hydro-mechanical coupling might have to be re-evaluated. A case study with the commercial groundwater simulator FEFLOW demonstrates the newly developed solution.

  17. Lacustrine chronology links late Pleistocene climate change and mass movements in northern New Mexico

    SciTech Connect

    Dethier, D.P.; Reneau, S.L.

    1996-06-01

    Well-dated lacustrine deposits in northern White Rock Canyon, New Mexico, record damming of the Rio Grande by at least four separate failures of a slump complex between about 17.5 and 12.4 ka ({sup 14}C), linking mass movements to a period of rapid climate change in the western United States. Failure of metastable slumps probably resulted from removal of lateral support during down-cutting and erosion by the Rio Grande and from a decrease in resisting forces due to increased pore pressures. Our chronology suggests that the lake that formed between 17.5 and 15.0 ka may record effects of both glacial melt and pluvial activity (mainly enhanced rainfall); the youngest lake (neary 12.4 ka) may record pluvial runoff; and the intermediate lakes (13.7 to 13.1 ka) may record pluvial and minor melt-water activity. We have not found lacustrine deposits younger than about 12.4 ka. The record of geomorphic response along the Rio Grande suggests that late Pleistocene climatic changes may have triggered similar mass movements elsewhere in the southwest. 27 refs., 4 figs.

  18. Pleistocene survival on central Alpine nunataks: genetic evidence from the jumping bristletail Machilis pallida.

    PubMed

    Wachter, Gregor A; Arthofer, Wolfgang; Dejaco, Thomas; Rinnhofer, Lukas J; Steiner, Florian M; Schlick-Steiner, Birgit C

    2012-10-01

    Mechanisms of survival during the Pleistocene glaciation periods have been studied for more than a century. Until now, molecular studies that confirmed animal survival on Alpine nunataks, that is, ice-free summits surrounded by glaciers, were restricted to peripheral areas. Here, we search for molecular signatures of inner-Alpine survival of the narrow endemic and putatively parthenogenetic Alpine jumping bristletail Machilis pallida combining mitochondrial and AFLP data from its three known populations. The mitochondrial data indicate survival on both peripheral and central nunataks, the latter suggesting that refugia in the centre of the Alpine main ridge were more widespread than previously recognized. Incongruences between mitochondrial and AFLP patterns suggest a complex evolutionary history of the species and may be explained via parallel fixation of parthenogenesis of different origins during the last glacial maximum. We suggest that the inferred parthenogenesis may have been essential for central nunatak survival, but may pose a serious threat for M. pallida in consideration of the present climatic changes. PMID:22994297

  19. Limited hydrologic response to Pleistocene climate change in deep vadose zones - Yucca Mountain, Nevada

    USGS Publications Warehouse

    Paces, J.B.; Neymark, L.A.; Whelan, J.F.; Wooden, J.L.; Lund, S.P.; Marshall, B.D.

    2010-01-01

    Understanding the movement of water through thick vadose zones, especially on time scales encompassing long-term climate change, is increasingly important as societies utilize semi-arid environments for both water resources and sites viewed as favorable for long-term disposal or storage of hazardous waste. Hydrologic responses to Pleistocene climate change within a deep vadose zone in the eastern Mojave Desert at Yucca Mountain, Nevada, were evaluated by uranium-series dating of finely layered hyalitic opal using secondary ion mass spectrometry. Opal is present within cm-thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface. Uranium concentrations in opal fluctuate systematically between 5 and 550 ?g/g. Age-calibrated profiles of uranium concentration correlate with regional climate records over the last 300,000 years and produce time-series spectral peaks that have distinct periodicities of 100- and 41-ka, consistent with planetary orbital parameters. These results indicate that the chemical compositions of percolating solutions varied in response to near-surface, climate-driven processes. However, slow (micrometers per thousand years), relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial–interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates.

  20. The Potential Role of Regolith in the Mid-Pleistocene Transition

    NASA Astrophysics Data System (ADS)

    Tabor, C. R.; Poulsen, C. J.; Pollard, D.

    2014-12-01

    The mid-Pleistocene transition (MPT) occurred between 1.2 and 0.7 Ma with a shift to ~100-kyr glacial cycles and ~50 m greater sea level variability. This transition appears to suggest an increased ice-volume response to the 100-kyr-1 frequency periodicity of eccentricity; however, insolation forcing from eccentricity decreased during this period. Further, proxy records show no significant corresponding decrease in mean CO2. A possible explanation for the MPT invokes removal of North American regolith. In theory, the gradual exposure of crystalline bedrock by multiple cycles of ice advance and retreat provides a higher friction substrate, which leads to thicker ice sheets. These thicker ice sheets then require greater insolation forcing, potentially produced by a combination of high obliquity and eccentricity / precession, to retreat. Here we test this hypothesis using an Earth system model with dynamic atmosphere, vegetation, and ice components. Using idealized, transient orbits of obliquity and precession, we compare the ice-volume responses under several basal sliding scenarios. Our preliminary results show increased ice-volume spectral power at the frequency of precession relative to obliquity and a larger ice-volume response when basal sliding is low, lending support to the reduced regolith hypothesis. These differences in ice response are due, in part, to changes in the temperature and circulation feedbacks as the ice sheets become bigger and thicker.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  2. Paleoecological and climatic implications of stable isotope results from late Pleistocene bone collagen, Ziegeleigrube Coenen, Germany

    NASA Astrophysics Data System (ADS)

    Wißing, Christoph; Matzerath, Simon; Turner, Elaine; Bocherens, Hervé

    2015-07-01

    Climatic and ecological conditions during Marine Oxygen Isotope Stage (MIS) 3 are complex and the impact of cold spells on the ecosystems in Central Europe still needs to be investigated thoroughly. Ziegeleigrube Coenen (ZC) is a late Pleistocene MIS 3 locality in the Lower Rhine Embayment of Germany, radiocarbon-dated to > 34 14C ka BP. The site yielded a broad spectrum of mammal species. We investigated the carbon (?13C), nitrogen (?15N) and sulfur (?34S) isotope signatures of bone collagen, since these are valuable tools in characterizing ecological niches, environmental conditions and aspects of climate and mobility. By comparison with pre- and post-Last Glacial Maximum (LGM) sites in Central Europe we show that ZC belongs in a cold event of MIS 3 and was climatically more similar to post-LGM sites than to pre-LGM sites. However, the trophic structure resembled that of typical pre-LGM sites in Belgium. This cold event in MIS 3 changed the bottom of the foodweb, but do not seem to have had a direct impact on the occurrence of the mammalian species and their ecological distribution. Apparently the (mega-) faunal community could adapt also to harsher environmental conditions during MIS 3.

  3. Late Pleistocene human occupation of the hyperarid core in the Atacama Desert, northern Chile

    NASA Astrophysics Data System (ADS)

    Latorre, Claudio; Santoro, Calogero M.; Ugalde, Paula C.; Gayo, Eugenia M.; Osorio, Daniela; Salas-Egaña, Carolina; De Pol-Holz, Ricardo; Joly, Delphine; Rech, Jason A.

    2013-10-01

    Few archeological sites in South America contain uncontroversial evidence for when the first peopling of the continent occurred. Largely ignored in this debate, extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability. Here, we report on a rare 12-13 ka human occupation from Quebrada Maní (site QM12), a plantless, near rainless landscape (1240 m asl and 85 km from the Pacific Ocean) located in the hyperarid core of the Atacama Desert. This location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central Andes during the latest Pleistocene. Excavations at QM12 yielded a diverse cultural assemblage of lithics, burned and cut bones, marine gastropods, pigments, plant fibers, and wooden artifacts alongside a prepared fireplace. Sixteen radiocarbon dates from site QM12 on charcoal, marine shells, animal dung, plant remains and wood reveal that the occupation took place between 12.8 and 11.7 ka. These results demonstrate that the Atacama Desert was not a barrier to early American settlement and dispersal, and provide new clues for understanding the cultural complexity and diversity of the peopling of South America during the Last Glacial-interglacial transition.

  4. 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).

  5. Limited hydrologic response to Pleistocene climate change in deep vadose zones — Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Paces, James B.; Neymark, Leonid A.; Whelan, Joseph F.; Wooden, Joseph L.; Lund, Steven P.; Marshall, Brian D.

    2010-12-01

    Understanding the movement of water through thick vadose zones, especially on time scales encompassing long-term climate change, is increasingly important as societies utilize semi-arid environments for both water resources and sites viewed as favorable for long-term disposal or storage of hazardous waste. Hydrologic responses to Pleistocene climate change within a deep vadose zone in the eastern Mojave Desert at Yucca Mountain, Nevada, were evaluated by uranium-series dating of finely layered hyalitic opal using secondary ion mass spectrometry. Opal is present within cm-thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface. Uranium concentrations in opal fluctuate systematically between 5 and 550 ?g/g. Age-calibrated profiles of uranium concentration correlate with regional climate records over the last 300,000 years and produce time-series spectral peaks that have distinct periodicities of 100- and 41-ka, consistent with planetary orbital parameters. These results indicate that the chemical compositions of percolating solutions varied in response to near-surface, climate-driven processes. However, slow (micrometers per thousand years), relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial-interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates.

  6. Skeletal and isotopic composition and paleoclimatic significance of late Pleistocene carbonates, Ross Sea, Antarctica

    SciTech Connect

    Taviani, M. ); Reid, D.E.; Anderson, J.B. )

    1993-01-01

    Carbonates cover an extensive area of the northwestern Ross Sea continental shelf. Radiocarbon dates yield late Pleistocene (stage 3) ages for these deposits, hence the carbonates appear to be correlative with widespread tills and glacial marine deposits in the region. Four carbonate facies are recognized on the basis of skeletal composition: a barnacle/foraminifer facies, a muddy bryozoan facies, a bryozoan/barnacle/pelecypod/foraminifer facies, and a planktonic foraminiferal facies. These deposits occur on the shelf and upper slope, while carbonate turbidities derived from them occur on the adjacent continental slope and rise. Compositional analyses of Ross Sea carbonates lend support to previously recognized criteria for identifying cold water carbonates. These include: (1) the presence of an associated ice-rafted component (including dropstones); (2) a dominance of calcite relative to other carbonate minerals (the remaining fraction consists solely of aragonite); (3) allochems that are entirely skeletal; and (4) heavy oxygen isotopic compositions (in the range of +3.0 to +5.1% PDB).

  7. Relation of heavy mineral suites to Pleistocene to Holocene shoreline sequences in Georgia

    SciTech Connect

    Cocker, M.D. )

    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.

  8. The nature of the Pleistocene-Holocene palaeosols in the Gaza Strip, Palestine

    NASA Astrophysics Data System (ADS)

    Ubeid, Khalid F.

    2011-09-01

    The Pleistocene to Holocene succession in the Gaza Strip, Palestine, consists of an alternation of calcareous sandstones and reddish fine-grained deposits (palaeosols). The palaeosols can be subdivided into two main groups based on the sand-sized versus clay- to silt-sized grains: (1) the sandy hamra palaeosols, and (2) the loess and loess-derived palaeosols. The hamra palaeosols can, in turn, also be subdivided into two main types according to their colour and grain size: (1) light brown loamy to sandy hamra palaeosols, and (2) dark brown sandy clay hamra palaeosols. The hamra palaeosols are polygenetic and originated in humid environments. Their red colour results from ferric oxides coating the sand grains, but also by illuviation. The various pedogenitic units and their gradual transition to loess palaeosols are due to different phases of dust accretion. Both groups of palaeosols developed during the last glacial. They are considered to represent different climate environments: hamra palaeosols represent humid climates, whereas the loess and loess-derived palaeosols represent dry and semi-dry climates.

  9. Variability of Quaternary glacial erosion rates - A global perspective with special reference to the Eastern Pyrenees

    NASA Astrophysics Data System (ADS)

    Delmas, Magali; Calvet, Marc; Gunnell, Yanni

    2009-03-01

    Glaciers erode bedrock but are also efficient conveyors of debris supplied during a cycle of glaciation by processes other than basal erosion. In this dual capacity as both an eroding and a transporting agent lies the ambiguity of 'glacial erosion' as a geomorphic process, with implications for methods of measuring the removal of rock mass by glaciers in the geological past, and for interpreting what exactly the consequences have been on topography and elevation change. A global review of ˜400 Quaternary glacial denudation rates estimated from five different measurement techniques provides values ranging between 10 -4 and 10 mm yr -1. We investigate the causes of such wide variability by examining the respective influences of environmental setting and methodological bias. A reference frame chosen for assessing these issues is the Massif du Carlit (Pyrenees, France), where a quantified mass balance of the well preserved glacial, periglacial and paraglacial deposits was made possible by detailed geomorphological mapping and terrestrial cosmogenic nuclide dating of extant erosional and depositional landform sequences. Resulting age brackets helped to define three main episodes of ice-cap growth and decline, each characterized by a volume of debris and a mappable source area. Erosion rates were expressed in two ways: (i) as spatially averaged denudation rates ( D) during the successive stages of glacial advance to the line of maximum ice extent (MIE), post-MIE ice recession, and Lateglacial cirque readvance, respectively; and (ii) as cirque-wall recession rates ( R) where moraine facies criteria indicated a supraglacial provenance of debris. Results indicate low erosion ( D ? 0.05 mm yr -1) during the ice advance phase, probably because of thin or passive ice covering the low-gradient subglacial topography that occurs just above the late Pleistocene equilibrium line altitude (2.2-2.4 km). Erosion rates peaked ( D ? 0.6 mm yr -1 and R ? 2.4-4.5 mm yr -1) during the main transition to ice-free conditions, when deglacial debuttressing promoted the rapid response of freshly exposed slope systems to new equilibrium conditions in the steep crest zone. Lateglacial D- and R-values declined to 0.2-0.3 mm yr -1, with indications of spatially variable R controlled by lithology. In this environment glaciers overall behaved more as conveyors of debris supplied by supraglacial rock exposures in the mountain crest zone than as powerful modifiers of subglacial topography. This explains the widespread preservation of deep, in situ preglacial weathering profiles on relict Cenozoic land surfaces in the deglacierized part of the Eastern Pyrenees. When plotted on the global data set analyzed and discussed in the review, the East Pyrenean erosion rates stand out as being amongst the lowest on record.

  10. Post-glacial coast development and human settling of the North European Ice Marginal Landscape (IML)

    NASA Astrophysics Data System (ADS)

    Bregman, I. Kant Baltic Federal State University, Kaliningrad, Russia, E. P. H.; Netherlands, Utrecht University, the; Druzhinina, I. Kant Baltic Federal State University, Kaliningrad, Russia, O. A.

    2012-04-01

    In North Europe, in the Ice Marginal Landscapes (IML) from the Netherlands to Estonia, human settling is in the Late-Pleistocene - Holocene strongly influenced by post-glacial relative coast development(MESO, 2010; SINCOS, 2002-2009; Machu, 2006-2009, IGCP project 346, CoPaF, 2009-2012) and glacio-isostasy. Geological processes like updoming and tectonic block displacements not only influenced sedimentation of river systems in delta's (e.g. Cohen, 2003), but influenced coastal development and human settling too in the North Sea area (e.g. Peeters, 2009; Hijma e.a., 2011) the Wadden areas (e.g. de Langen, 2011) and lagoons (e.g. Druzhinina, 2010). An overview of shoreline development at the distal side of the Late Glacial forbulge related to glaciological and geophysical processes however does not exist and coastal development models are also not correlated with human settling. Our project( 2012 - 2018) has the aim to describe the influence of shifting coast on the way of settling and living of ancient man in the IML. The main questions to be answered are as follow: (i) Is coast development influenced by glaciations a result of interaction between endo- and exogenic (glaciological-, geological-, and geophysical) forces in general and at the local scale of morphological elements? (ii) Did ancient man adept to changes in natural circumstances and what did that mean for his social behavior and economy? (iii) Were forms of human society and economy in the IML primarily dependent on the natural environment with regard to geophysical and geological differences and related to post-glacial response of the earth crust? Detailed integrated studying of "key-areas", with attention to deep geology, will allow to get new insight of the impact of post-glacial shoreline changes and history of man on the coast in the IML with focus on his past (history of relations) and future (impact of climate change. The project is an international project, with participation of institutes all over the IML.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

    An 82-m deep lacustrine sediment core from the Valles Caldera, northern New Mexico reveals details of climate change over two glacial cycles in the middle Pleistocene. Core VC-3, taken from the Valle Grande, has a basal 40Ar/39Ar date of 552 kyr from a tephra associated with the eruption of the South Mountain rhyolite which formed the lake. A variety of proxies including core sedimentology, organic carbon and carbon isotopic ratios, pollen, scanning XRF analysis and a new paleotemperature proxy, MBT (methylated branched tetraether) content of soil bacteria reveal two major warm periods above the basal tephra which we correlate with interglacials MIS 13 and MIS 11. This chronology is corroborated by the identification of two geomagnetic field "events" which are correlated with globally recognized events (14? and 11?). The lacustrine record terminates at ~350 ka when the lake filled its available accommodation space behind the dam of rhyolite lava. MBT temperature estimates show average glacial temperatures in core VC-3 of ~ -4°C, and average interglacial temperatures of ~ +4°C, and the general trends are well corroborated by multiple proxies including pollen and lacustrine organic productivity estimates. A temperature increase of ~9°C occurs during Termination V, the largest glacial termination in the Pleistocene. Multiple proxies from VC-3 show significant structure during the two interglacials present in the core (MIS 13 and 11). Three warm substages (~ 2°C warmer) are recognized within MIS 11 based on organic productivity (Corg, Si/Ti ratios), pollen taxa, elevated charcoal from fires, and the MBT temperature estimates. These warm substages appear to be a strong response to precessional forcing in the SW continental interior even though the amplitude of eccentricity-modulated precession was at a minimum during MIS 11. These results suggest that future climate change in the SW may be characterized by similar natural temperature variability on precessional timescales, superimposed on future anthropogenic warming. Intervals of mudcrack facies representing significant drought conditions occur during or just after the warmest phases of the two interglacials. This past coupling between warm temperatures and extended drought in the SW as a natural feature of long interglacials is consistent with recent predictions of extended Dust-Bowl-like conditions in the SW as a response to global warming.

  12. 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)

  13. Did debris-covered glaciers serve as pleistocene refugia for plants? A new hypothesis derived from observations of recent plant growth on glacier surfaces

    USGS Publications Warehouse

    Fickert, T.; Friend, D.; Gruninger, F.; Molnia, B.; Richter, M.

    2007-01-01

    This study proposes a new hypothesis: Debris-covered glaciers served as Pleistocene biological refugia. This is based on detailed studies of vascular plant growth on six debris-mantled glaciers, literally around the world, as well as many casual observations also across the globe. We find that such glaciers are quite common and are distributed globally. Using Carbon Glacier, Mount Rainier, U.S.A., as a type locality and case study, we show aspects of the floristic and structural diversity as well as spatial patterns of plant growth on the glacier surface. Migration strategies, root characteristics, and origin and dispersal strategies for vascular plant species are documented. Also reported are special microclimatic conditions in these areas allowing for this remarkable plant ecology. We find that alpine taxa can grow considerably below their usual altitudinal niche due to the cooler subsurface soil temperatures found on glacial debris with ice underneath, and that may have significantly altered the spatial distribution of such flora during full glacial conditions. This in turn creates previously undocumented areas from which alpine, and perhaps arctic, plant species reestablished in post-glacial time. This hypothesis is complementary to both the nunatak hypothesis and tabula rasa theory and possibly helps solve the ongoing controversy between them. ?? 2007 Regents of the University of Colorado.

  14. Genetic variation of Ginkgo biloba L. (Ginkgoaceae) based on cpDNA PCR-RFLPs: inference of glacial refugia.

    PubMed

    Shen, L; Chen, X-Y; Zhang, X; Li, Y-Y; Fu, C-X; Qiu, Y-X

    2005-04-01

    Ginkgo biloba, a famous living fossil, is the sole survivor of the genus Ginkgo. To make inferences about the glacial refugia that harbored G. biloba, we examined the genetic structure of eight potential refugial populations and plantations using chloroplast DNA (cpDNA) with eight size variants in the trnK1-trnK2 fragment. The data consist of haplotypes from 158 trees collected from eight localities. The majority of the cpDNA haplotypes are restricted to minor portions of the geographical range. Our results suggest that refugia of G. biloba were located in southwestern China. This area is a current biodiversity hotspot of global importance, and may have been protected from the extremes of climatic fluctuations during the Pleistocene. The Ginkgos on West Tianmu Mountain, which were previously considered to be wild by many researchers, may, instead, have been introduced by Buddhist monks. PMID:15536482

  15. Mitochondrial phylogeny shows multiple independent ecological transitions and northern dispersion despite of Pleistocene glaciations in meadow and steppe vipers (Vipera ursinii and Vipera renardi).

    PubMed

    Zinenko, Oleksandr; Stümpel, Nikolaus; Mazanaeva, Lyudmila; Bakiev, Andrey; Shiryaev, Konstantin; Pavlov, Aleksey; Kotenko, Tatiana; Kukushkin, Oleg; Chikin, Yury; Duisebayeva, Tatiana; Nilson, Göran; Orlov, Nikolai L; Tuniyev, Sako; Ananjeva, Natalia B; Murphy, Robert W; Joger, Ulrich

    2015-03-01

    The phylogeny and historical demography of small Eurasian vipers of the Vipera ursinii and V. renardi complexes were studied using mitochondrial DNA sequences analysed with Bayesian inference, Maximum Likelihood and Maximum Parsimony approaches, and mismatch distributions. Diversification in the group resulted from an initial dispersion in the later Pliocene - Pleistocene in two directions: north-westwards via the Balkans (V. ursinii complex) and north-eastwards from Asia Minor via the Caucasus (V. renardi complex). An independent, comparatively recent transition occurred from montane habitats to lowland grasslands in different mitochondrial lineages during the Late Pleistocene, when representatives of the both complexes had reached lowland steppes to the north. Effective population size showed clear signs of rapid growth in eastern V. renardi, triggered by colonization of vast lowland steppes, but in western V. ursinii complex grew during the Last Glaciation and experienced stabilization in Holocene. Expansion and population growth in lowland lineages of V. renardi was not strongly affected by Pleistocene climatic oscillations, when cold, dry conditions could have favoured species living in open grasslands. The high diversity of closely related haplotypes in the Caucasus and Tien-Shan could have resulted from repetitive expansion-constriction-isolation events in montane regions during Pleistocene climate fluctuations. The mitochondrial phylogeny pattern conflicts with the current taxonomy. PMID:25527984

  16. Ice flow models and glacial erosion over multiple glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological time scales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes-flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model has a larger impact on the erosion rate, with variations of almost an order of magnitude. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered that are greater than 30%, again with larger differences for temperate ice. Over multiple glaciations and long-time scales, these results suggest that consideration of higher-order glacial physics may be necessary, particularly in temperate, mountainous settings.

  17. Ice flow models and glacial erosion over multiple glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Mountain topography is constructed through a variety of interacting processes. Over glaciological timescales, even simple representations of glacial-flow physics can reproduce many of the distinctive features formed through glacial erosion. However, detailed comparisons at orogen time and length scales hold potential for quantifying the influence of glacial physics in landscape evolution models. We present a comparison using two different numerical models for glacial flow over single and multiple glaciations, within a modified version of the ICE-Cascade landscape evolution model. This model calculates not only glaciological processes but also hillslope and fluvial erosion and sediment transport, isostasy, and temporally and spatially variable orographic precipitation. We compare the predicted erosion patterns using a modified SIA as well as a nested, 3-D Stokes flow model calculated using COMSOL Multiphysics. Both glacial-flow models predict different patterns in time-averaged erosion rates. However, these results are sensitive to the climate and the ice temperature. For warmer climates with more sliding, the higher-order model yields erosion rates that vary spatially and by almost an order of magnitude from those of the SIA model. As the erosion influences the basal topography and the ice deformation affects the ice thickness and extent, the higher-order glacial model can lead to variations in total ice-covered area that are greater than 30% those of the SIA model, again with larger differences for temperate ice. Over multiple glaciations and long timescales, these results suggest that higher-order glacial physics should be considered, particularly in temperate, mountainous settings.

  18. 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.

  19. Periglacial process and Pleistocene environment in northern China

    SciTech Connect

    Guo Xudong; Liu Dongsheng ); Yan Fuhua )

    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.

  20. Pleistocene cave art from Sulawesi, Indonesia.

    PubMed

    Aubert, M; Brumm, A; Ramli, M; Sutikna, T; Saptomo, E W; Hakim, B; Morwood, M J; van den Bergh, G D; Kinsley, L; Dosseto, A

    2014-10-01

    Archaeologists have long been puzzled by the appearance in Europe ?40-35 thousand years (kyr) ago of a rich corpus of sophisticated artworks, including parietal art (that is, paintings, drawings and engravings on immobile rock surfaces) and portable art (for example, carved figurines), and the absence or scarcity of equivalent, well-dated evidence elsewhere, especially along early human migration routes in South Asia and the Far East, including Wallacea and Australia, where modern humans (Homo sapiens) were established by 50 kyr ago. Here, using uranium-series dating of coralloid speleothems directly associated with 12 human hand stencils and two figurative animal depictions from seven cave sites in the Maros karsts of Sulawesi, we show that rock art traditions on this Indonesian island are at least compatible in age with the oldest European art. The earliest dated image from Maros, with a minimum age of 39.9 kyr, is now the oldest known hand stencil in the world. In addition, a painting of a babirusa ('pig-deer') made at least 35.4 kyr ago is among the earliest dated figurative depictions worldwide, if not the earliest one. Among the implications, it can now be demonstrated that humans were producing rock art by ?40 kyr ago at opposite ends of the Pleistocene Eurasian world. PMID:25297435

  1. Late Pleistocene glacial-interglacial shell-size-isotope variability in planktonic foraminifera as a function of local hydrography

    NASA Astrophysics Data System (ADS)

    Metcalfe, B.; Feldmeijer, W.; de Vringer-Picon, M.; Brummer, G.-J. A.; Peeters, F. J. C.; Ganssen, G. M.

    2015-08-01

    So-called "vital effects" are a collective term for a suite of physiologically and metabolically induced variability in oxygen (?18O) and carbon (?13C) isotope ratios of planktonic foraminifer shells that hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from equilibrium or the expected value is paramount, as too is the ability to define a comparable life stage for each species that allows for direct comparison. Past research has focused upon finding a specific size range for individual species in lieu of other identifiable features, thus allowing ocean parameters from a particular constant (i.e. a specific depth or season) to be reconstructed. Single-shell isotope analysis of fossil shells from a mid-latitude North Atlantic Ocean piston core covering Termination III (200 to 250 ka) highlight the advantage of using a dynamic size range, i.e. utilising measurements from multiple narrow sieve size fractions spanning a large range of total body sizes, in studies of palaeoclimate. Using this methodology, we show that isotopic offsets between specimens in successive size fractions of Globorotalia inflata and Globorotalia truncatulinoides are not constant over time, contrary to previous findings. For ?18O in smaller-sized globorotalids (212-250 ?m) it is suggested that the offset from other size fractions may reflect a shallower habitat in an early ontogenetic stage. A reduction in the difference between small and large specimens of G. inflata between insolation minima and maxima is interpreted to relate to a prolonged period of reduced water column stratification. For the shallow-dwelling species Globigerina bulloides, no size-isotope difference between size fractions is observed, and the variability in the oxygen isotopic values is shown to correlate well with the seasonal insolation patterns. As such, patterns in oxygen isotope variability of fossil populations may be used to reconstruct past seasonality changes.

  2. Late Pleistocene Glacial-Interglacial related shell size isotope variability in planktonic foraminifera as a function of local hydrology

    NASA Astrophysics Data System (ADS)

    Metcalfe, B.; Feldmeijer, W.; de Vringer-Picon, M.; Brummer, G.-J. A.; Peeters, F. J. C.; Ganssen, G. M.

    2015-01-01

    So called "vital effects", a collective noun for a suite of physiological and metabolic induced variability, in oxygen (?18O) and carbon (?13C) isotope ratios of planktonic foraminifer shells hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from the equilibrium or the expected value is paramount, as too is the ability to define a comparable life-stage for each species that allows for direct comparison. Past research has focused upon finding a specific size range for individual species in lieu of other identifiable features, that allow ocean parameters from a particular constant (i.e. a specific depth or season) to be reconstructed. Single shell isotope analysis of fossil shells from a mid-latitude North Atlantic Ocean piston-core covering Termination III (200 to 250 kyr) highlight the advantage of using a dynamic size range in studies of palaeoclimate. Using this methodology, we show that isotopic offsets between specimens in successive size fractions of G. inflata and G. truncatulinoides are not constant over time, contrary to previous findings. For ?18O in smaller sized globorotalids it is suggested that the offset from other size fractions may reflect a shallower habitat in an early ontogenetic stage. A reduction in the difference between small and large specimens of G. inflata between insolation minima and maxima is interpreted to relate to a prolonged period of reduced water column stratification. For the shallow dwelling species G. bulloides no size isotope difference between size fractions is observed, and the variability in the oxygen isotopic values are shown to correlate well with the seasonal insolation patterns. As such, patterns in oxygen isotope variability of fossil populations may be used successfully for reconstruction of past seasonality changes.

  3. Ventilation of the glacial deep Pacific Ocean.

    PubMed

    Broecker, Wallace; Barker, Stephen; Clark, Elizabeth; Hajdas, Irka; Bonani, Georges; Stott, Lowell

    2004-11-12

    Measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial Pacific deep-sea cores suggest that during peak glacial time the radiocarbon age of water at 2-kilometers depth was no greater than that of today. These results make unlikely suggestions that a slowdown in deep-ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon-14 (14C) to carbon in the atmosphere and surface ocean during glacial time. Comparison of 14C ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14C to C ratio difference was not substantially different from today's. PMID:15539598

  4. 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.

  5. Holocene environmental change resets lichen surface dates on Recess Peak glacial deposits in the Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Scuderi, Louis A.; Fawcett, Peter J.

    2013-09-01

    Development of an accurate chronology for glacial deposits in the Sierra Nevada has long been problematic given the lack of suitable organic material for radiocarbon dating. Lichenometry initially appeared promising as ages showed an increase from cirque headwalls to down-canyon moraines. However, while Recess Peak lichen age estimates range from 2 to 3 ka, recent work shows these deposits to be at least 10 ka older. Here, we present evidence for a late Holocene reset of Recess Peak lichen ages by significant post-depositional climate change. Following late-Pleistocene deposition of Recess Peak moraines, warming through the mid-Holocene allowed forests to advance into shallow basins eliminating local inverted tree lines. This produced a partial canopy where shading killed the original post-Pleistocene crustose lichen colonies. Late-Holocene cooling resulted in forest retreat from these basins as alpine tree line fell. Lichens then recolonized the re-exposed Recess Peak deposits. We conclude that while Recess Peak lichen ages are accurate to within the dating uncertainty of the technique, existing lichen ages actually date the timing of post-mid-Holocene cooling and recolonization, and not the original emplacement of these deposits. Thus, applications of Lichenometry should consider post-depositional environmental change when interpreting the meaning of these dates.

  6. Glacial bed forms at Findelengletscher, Zermatt, Switzerland

    NASA Astrophysics Data System (ADS)

    Madella, Andrea; Nyffenegger, Franziska; Schlüchter, Christian

    2013-04-01

    The current glacier meltdown is increasingly unveiling the glacial bed forms produced by the most recent glacial advance of the 1980ies, such as flutes, mega-flutes and drumlins. This is a challenging opportunity to study these morphologies and the processes involved in their formation; in addition, our observation suggests a new question to be answered: why can't any of these features in units belonging to previous glacial advances be recognised? Similar forms could either have been washed away already, or never been built during LGM and since. The most beautiful and evident of the forms under investigation are the flutes and mega-flutes: elongated streamlined ridges of sediments either starting from an obstacle or just sticking out of the basal lodgement till. The way flutes have been initiated and then evolve is still partially unknown, due to their variety in shape, size and material. The glacial forefield at Findelengletscher under investigation deglaciated over the past two years, offers a well-preserved variety of such forms at all scales. Their material (basal lodgement till) is homogeneous and consistent all over the site, as well as their fabric. In addition, this silty sand shows a low plasticity index. These preliminary results support the idea that flutes build up very quickly during repeated seasonal advances in thin ice conditions with retreating trend (Coray, 2007), and that they could be equally easily and rapidly washed away. References: Coray Sandro (2007): Genesis and significance of flutes at Findelengletscher, Valais, Switzerland, Institute of Geological Sciences, University of Bern.

  7. Flat-slab subduction, orogenesis, intraplate deformation, and glacial erosion in southern Alaska: A tectonic-glacial progression from STEEP

    NASA Astrophysics Data System (ADS)

    Pavlis, T. L.; Gulick, S. S.; Bruhn, R. L.; Christeson, G. L.; Enkelmann, E.; Freymueller, J. T.; Hallet, B.; Horton, B. K.; Hansen, R. A.; Koons, P. O.; Pavlis, G. L.; Ridgway, K. D.; Spotila, J. A.; Van Avendonk, H. J.

    2012-12-01

    The ST. Elias Erosion and tectonics Project (STEEP) is a Continental Dynamics multidisciplinary collaboration involving offshore and onshore studies of a modern example of an oceanic plateau collision with a continental margin in southern Alaska. These studies constrain erosion-tectonic interactions and clarify the timeline of northern Cordilleran orogenesis. At ~55 Ma an oceanic plateau formed on either the Kula-Farallon or Farallon-Resurrection spreading center. From 50-46 Ma, this plateau attempted to subduct beneath an accretionary complex, the Yakutat Group (YG), near offshore British Columbia. The YG was thrust onto the plateau to form what is now the Yakutat Terrane. From ~40 to as late as 33 Ma the Yakutat Terrane was part of North America and the proto-Transition Fault was active moving the remnant Kula Plate towards the Aleutian Trench, slicing off the southern edge of the Yakutat Terrane, and emplacing Pacific crust adjacent to the Terrane. From ~33 to 6 Ma the Yakutat Terrane moved northward with the Pacific Plate. There is some Oligocene paleogeographic uncertainly, but upper plate deformation and basin development starting ~ 20-25 Ma may be Yakutat related. At ~6 Ma the Pacific Plate underwent a clockwise shift in motion reactivating the Transition Fault, albeit at a slow rate, and this motion drove a component of oblique convergence along the Fairweather Fault and orogenesis in the St. Elias. Rejuvenation of the Transition Fault formed a stable triple junction with the Aleutian Trench and the Yakutat-North American subduction front. Uplift in the orogen seeded glacial systems that reached tidewater by ~5.5 Ma and the sediments produced were the glaciomarine, syn-orogenic Yakataga Formation. The eastern syntaxis of the St. Elias orogen began to focus exhumation as thickened crust generated along the transpressive Fairweather system was fed into the fully contractional core of the orogen. Between 4 and 3 Ma, the thicker portions of the Yakutat Terrane (25-35 km thick crust) entered the orogen. From 6 to 1 Ma, the Yakutat Fold and Thrust Belt advanced east due to the influx of Yakataga sediments extending the Yakutat-North America megathrust and causing triple junction instability; the current deformation front trending from the eastern Pamplona Zone to the Malaspina Fault to the Esker Creek Fault has been active since ~1 Ma while near the Trench the Transition Fault stepped southward and became increasingly transpressive in an attempt to re-attain stability. Climatically at ~1 Ma, the Mid-Pleistocene Transition enhanced the magnitude of the glacial-interglacial cycles resulting in a significant increase in exhumation along the windward side of the orogen. The sedimentary products from this Transition dominate the deep-sea Surveyor Fan on the Pacific Plate and fill the proximal Trench. Currently, the strong feedback between exhumation and tectonic shortening continues with activation of faults both on and offshore atop a geodetically observed transition from flat slab subduction in the western portion of the orogen to collision in the eastern portion culminating in the syntaxis that forms Mt. St. Elias and Mt. Logan. The Yakutat subduction/collision has produced far-field deformation throughout Alaska, the Yukon, and the proximal Pacific Plate.

  8. Power oscillator

    DOEpatents

    Gitsevich, Aleksandr (Montgomery Village, MD)

    2001-01-01

    An oscillator includes an amplifier having an input and an output, and an impedance transformation network connected between the input of the amplifier and the output of the amplifier, wherein the impedance transformation network is configured to provide suitable positive feedback from the output of the amplifier to the input of the amplifier to initiate and sustain an oscillating condition, and wherein the impedance transformation network is configured to protect the input of the amplifier from a destructive feedback signal. One example of the oscillator is a single active element device capable of providing over 70 watts of power at over 70% efficiency. Various control circuits may be employed to match the driving frequency of the oscillator to a plurality of tuning states of the lamp.

  9. Pleistocene sediments of Lake Baikal: Lithology and stratigraphic correlation

    NASA Astrophysics Data System (ADS)

    Akulov, N. I.; Mashchuk, I. M.; Akulova, V. V.

    2015-01-01

    The Cenozoic sediments of Lake Baikal penetrated by boreholes and investigated by the manned submersible Pisces, as well as coeval deposits cropping out in beach scarps, recovered by mine workings, and drilled in the coastal zone were the object of this investigation. The main attention was paid to Pleistocene bottom sediments penetrated by Borehole BDP-99-2. The investigations included the detailed analysis of the lithology (grain-size composition, immersion mineralogy of light and heavy fractions, X-ray structural analysis of clayey fraction) and palynological assemblages to specify facies features of Cenozoic sediments, correlate all their known stratigraphic units constituting the sedimentary section of the lake with their analogs in the onshore part of the Baikal rift zone, and compile the composite Cenozoic section. The following features of these sediments are noted: (1) as a whole, Pleistocene sediments are characterized by the hydromica-smectite composition of their clayey fraction with an insignificant share of kaoline; (2) the heavy fraction is dominated by the terrigenous epidote-amphibole association poorly resistant to weathering; (3) Pleistocene sediments of the lake contain siderite, vivianite, pyrite, and goethite concretions and micrometeorites, in addition to well-known ferromanganese nodules; (4) the presence of relict palynomorphs in Pleistocene sediments of Baikal is determined by their erosion from Miocene and Pliocene cavernous clays cropping out on underwater slopes of the Posol'skaya Bank and subsequent reburial along with Pleistocene palynological assemblages.

  10. Retardation of arsenic transport through a Pleistocene aquifer

    PubMed Central

    van Geen, Alexander; Bostick, Benjamín C.; Trang, Pham Thi Kim; Lan, Vi Mai; Mai, Nguyen-Ngoc; Manh, Phu Dao; Viet, Pham Hung; Radloff, Kathleen; Aziz, Zahid; Mey, Jacob L.; Stahl, Mason O.; Harvey, Charles F.; Oates, Peter; Weinman, Beth; Stengel, Caroline; Frei, Felix; Kipfer, Rolf; Berg, Michael

    2013-01-01

    Groundwater drawn daily from shallow alluvial sands by millions of wells over large areas of South and Southeast Asia exposes an estimated population of over 100 million to toxic levels of arsenic (1). Holocene aquifers are the source of widespread arsenic poisoning across the region (2, 3). In contrast, Pleistocene sands deposited in this region more than ~12,000 years ago mostly do not host groundwater with high levels of arsenic. Pleistocene aquifers are increasingly used as a safe source of drinking water (4) and it is therefore important to understand under what conditions low levels of arsenic can be maintained. Here we reconstruct the initial phase of contamination of a Pleistocene aquifer near Hanoi, Vietnam. We demonstrate that changes in groundwater flow conditions and the redox state of the aquifer sands induced by groundwater pumping caused the lateral intrusion of arsenic contamination over 120 m from Holocene aquifer into a previously uncontaminated Pleistocene aquifer. We also find that arsenic adsorbs onto the aquifer sands and that there is a 16–20 fold retardation in the extent of the contamination relative to the reconstructed lateral movement of groundwater over the same period. Our findings suggest that arsenic contamination of Pleistocene aquifers in South and Southeast Asia as a consequence of increasing levels of groundwater pumping have been delayed by the retardation of arsenic transport. PMID:24025840

  11. Abrupt climate variability of eastern Anatolia vegetation during the last glacial

    NASA Astrophysics Data System (ADS)

    Pickarski, N.; Kwiecien, O.; Langgut, D.; Litt, T.

    2015-07-01

    Detailed analyses of the Lake Van pollen and stable oxygen isotope record allow the identification of millennial-scale vegetation and environmental changes in eastern Anatolia throughout the last glacial. The climate within the last glacial period (∼75-15 ka BP) was cold and dry, with low arboreal pollen (AP) levels. The driest and coldest period corresponds to Marine Isotope Stage (MIS) 2 (∼28-14.5 ka BP) dominated by the highest values of xerophytic steppe vegetation. Our high-resolution multi proxy record shows rapid expansions and contractions that mimic the stadial-interstadial pattern of the Dansgaard-Oeschger (DO) events as recorded in the Greenland ice cores, and thus, provide a linkage to North Atlantic climate oscillations. Periods of reduced moisture availability characterized at Lake Van by enhanced xerophytic species correlates well with increase in ice-rafted debris (IRD) and a decrease of sea surface temperature (SST) in the North Atlantic. Furthermore, comparison with the marine realm reveals that the complex atmosphere-ocean interaction can be recognized by the strength and position of the westerlies in eastern Anatolia. Influenced by rough topography at Lake Van, the expansion of temperate species (e.g. deciduous Quercus) was stronger during interstadials DO 19, 17-16, 14, 12 and 8. However, Heinrich events (HE), characterized by highest concentrations of ice-rafted debris in marine sediments, are identified in eastern Anatolia by AP values not lower and high steppe components not more abundant than during DO stadials. In addition, this work is a first attempt to establish a continuous microscopic charcoal record over the last glacial in the Near East, which documents an initial immediate response to millennial-scale climate and environmental variability and enables the shed light on the history of fire activity during the last glacial.

  12. The role of Southern Ocean winds and CO2 in glacial abrupt climate change

    NASA Astrophysics Data System (ADS)

    Banderas, R.; Alvarez-Solas, J.; Montoya, M.

    2011-12-01

    The last glacial period (ca. 110-10 kyr before present, hereafter kyr BP) is characterized by substantial climate instability, manifested as climatic variability on millennial timescales. Two types of events dominate this variability: Dansgaard-Oeschger (DO) events, which involve decadal-scale warming by more than 10K, and Heinrich events, massive iceberg discharges from the Laurentide Ice Sheet at intervals of ca. 10 kyr during peak glacial conditions. Both DO and Heinrich events are associated with widespread centennial to millennial scale climatic changes, including a synchronous temperature response over the North Atlantic and an anti-phase temperature relationship over Antarctica and most of the Southern Ocean, as revealed by a wealth of deep sea sediments and terrestrial record. Recent studies indicate CO2 changes during deglaciation and, possibly, during glacial abrupt climate changes were preceded by significant increases of Southern Ocean upwelling caused by an enhancement and/or a shift of surface winds over that region. The proposed hypothesis is that periods of halted or reduced North Atlantic deep water (NADW) formation resulted in warming of the Southern Ocean through the bipolar see-saw effect leading to a reorganization of Southern Hemisphere (SH) surface winds, and thereby enhanced upwelling and atmospheric CO2 concentrations. Here, the role of SH surface wind and CO2 changes in the Atlantic meridional overturning circulation (MOC) is analyzed in a coupled climate model of intermediate complexity. We investigate whether changes in the former could eventually trigger an intensification of the Atlantic overturning circulation and a northward shift of NADW formation, which would allow to explain glacial abrupt climate changes as the result of an oscillation which involves the MOC, CO2 and the winds.

  13. Variable water column structure of the South Atlantic on glacial-interglacial time scales

    NASA Astrophysics Data System (ADS)

    Martínez-Méndez, Gema; Molyneux, Elizabeth G.; Hall, Ian R.; Zahn, Rainer

    2009-12-01

    The structure of the glacial ocean was significantly different to that of the present day with intermediate to mid-depth waters being notably more ? 13C enriched than deep waters. This contrast was especially pronounced in the South Atlantic suggesting the development of a sharp chemical divide, or 'chemocline', at around 2500 m water depth between upper and lower layers, with implications for deep-ocean carbon storage [ Hodell et al., 2003. Pleistocene vertical carbon isotope and carbonate gradients in the South Atlantic sector of the Southern Ocean. Geochemistry, Geophysics, Geosystems, 4(1): doi: 1004 10.1029/2002GC000367.]. We evaluate existing benthic foraminiferal ? 13C, Cd/Ca and derived carbon isotope air-sea exchange signature (? 13C as) data sets for the Atlantic during the Last Glacial Maximum (LGM), and Marine Isotope Stages (MIS) 6 and 8 in order to examine the regional extent of the chemocline in the South Atlantic. Benthic ? 13C data north of the approximate latitude of the LGM Subantarctic Front (LGM-SAF, 43°S) linearly decrease with water depth, indicative of mixing between upper 'well' and lower 'poorly' ventilated water masses, with little evidence of the sharp chemical divide. Conversely, benthic ? 13C data south of the LGM-SAF below 2500 m water depth are uniformly around -0.8‰. The apparent ? 13C gradient across the LGM-SAF suggests enhanced mid-depth ventilation north of the SAF and reduced ventilation to the south. From this pattern we conclude that the regional chemocline in the South Atlantic constituted a dominantly meridional, rather than a vertical gradient, and was developed during at least the past three glacial periods. Benthic Cd/Ca data indicate that the gradient was not nutrient related, although further data from the South Atlantic are needed for a better assessment of this suggestion. The combined benthic ? 13C and Cd/Ca data indicate the source of well-ventilated upper waters in the South Atlantic changed from Northern Component Water (NCW) during early glacial phases to Upper Southern Component Water (USCW) during mid-to-late glacial phases when the Southern Ocean may have become isolated. USCW maintained a positive ? 13C and ? 13C as signature simulating a North Atlantic origin that has been implicated in previous studies. The data demonstrate that secular imprints on ? 13C must be taken into consideration when assessing the implications of the vertical ? 13C gradient. This data also supports a variable water column architecture and modes of water mass formation as primary means to draw down atmospheric CO 2 and storage in the abyssal ocean by involving processes occurring on either side of the SAF in the glacial Southern Ocean.

  14. Mineral and grain-size partitioning in a glacial to marine transect, western Baffin Bay, Canada

    SciTech Connect

    Geirsdottir, A.; Jennings, A.E.; Andrews, J.T.

    1985-01-01

    Pleistocene and neoglacial tills on the Precambrian shield of Baffin Island are sandy gravels with <10% in the silt/clay fraction. Observations indicate that large amounts of sediments are being carried in suspension by glacial melt water streams. Silts and clays are transported into the proximal marine environment largely as overflows where they flocculate and settle. Mineralogical analysis of the clay and silt-size fraction of one fiord core (SU5) and one shelf core (HU78-37) from western Baffin Bay were completed to investigate mineral partitioning of transport from land to sea. Such studies are commonly conducted on the clay-sized particles, but there are few investigations of the silt-sized fraction, even though silts often make up more than 50% of these marine sediments. X-ray diffraction analyses of two cores show significant differences in mineralogy. Relative to the average composition of the Precambrian shield rocks of Baffin Island the clay-size mineralogy reflects a significant enhancement in mica and depletions in quartz and feldspar. The same trend is observed in the silt-sized mineralogy, where enrichment in mica is still significant, however, the mineralogy of the two size fractions differs markedly. The overall change in mineralogy from the clay-sized to silt-sized particles shows a decrease in mica, kaolinite and chlorite and a significant increase in dolomite and calcite, which are foreign to the area. These results, combined with ongoing studies on sand-sized mineralogy will enable a sediment budget approach to glacial erosion/deposition.

  15. Long-Term Glacial Erosion Rates and Pre-Glacial Topography in Southwest British Columbia

    NASA Astrophysics Data System (ADS)

    Ehlers, T. A.; Farley, K. A.; Rusmore, M. E.; Woodsworth, G. J.

    2004-12-01

    The hypothesis that Late Cenozoic climate change increased the topographic relief of mountain ranges relies on the assumption that alpine glaciers are more efficient at eroding valley bottoms than ridge crests. Although theoretical and field studies have made advances in quantifying glacial erosion processes, rigorous tests of this hypothesis have been limited by uncertainties in long-term glacial erosion rates and pre-glacial topographic relief. Here we interpret long-term (>106 yr) glacial erosion rates and pre-glacial topographic relief in the southern Coast Mountains, British Columbia, using apatite (U-Th)/He and apatite fission track cooling ages and a thermal-kinematic numerical model. Twenty-six new apatite (U-Th)/He samples were collected along two 60 km long transects that cross the glacially sculpted topography of Mount Waddington. Samples were collected between elevations of 0 and 4000 m, with a subset of samples along each transect collected at a constant elevation of 1600 m. Apatite (U-Th)/He ages range between 1.5 and 14.1 Myr. Two patterns are present in the spatial distribution of ages. First, ages generally increase in el