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1

Late Pleistocene Glacial Chronology of Northcentral Brooks Range, Alaska.  

National Technical Information Service (NTIS)

End moraines and exposed stratigraphic sections of glacial sediments along the Anaktuvuk and Chandler Rivers represent four substages of the late Pleistocene Itkillik glaciation in the north-central Brooks Range, Alaska. Ice of the maximum advance, the Ba...

S. C. Porter

1964-01-01

2

Interhemispheric correlation of late pleistocene glacial events  

SciTech Connect

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

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

1995-09-15

3

Interhemispheric correlation of late pleistocene glacial events.  

PubMed

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

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

4

Early Pleistocene glacial cycles and the integrated summer insolation forcing.  

PubMed

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. PMID:16794041

Huybers, Peter

2006-06-22

5

Intensified deep Pacific inflow and ventilation in Pleistocene glacial times.  

PubMed

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

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

2001-08-23

6

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

NASA Astrophysics Data System (ADS)

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

Zimov, N.; Zimov, S. A.

2011-12-01

7

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

NASA Astrophysics Data System (ADS)

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

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

8

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

PubMed Central

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).

2010-01-01

9

Molecular evidence for Pleistocene glacial cycles driving diversification of a North American desert spider, Agelenopsis aperta.  

PubMed

The influence of historical climatic vs. geological changes on species diversification patterns was investigated in a widely distributed North American desert spider, Agelenopsis aperta (Araneae: Agelenidae), with particular reference to Pleistocene glacial cycles and earlier patterns of mountain building. Levels of sequence divergence obtained from the mitochondrial gene, cytochrome oxidase I, dated to the Pleistocene, eliminating Rocky Mountain orogeny as a cause of diversification, as orogeny ended 4 million years ago. The results of phylogenetic and network analyses showed the presence of three geographically defined clades, which were consistent with the presence of at least three glacial refugia: (i) east of the Rocky Mountains; (ii) between the Rocky Mountains and Sierra Nevadas; and (iii) west of the Sierra Nevadas. In addition, populations within the Rocky Mountains exhibited significantly lower genetic diversity than populations east of the Rocky Mountains and the haplotypes found within the Rockies were a subset of eastern haplotypes. These patterns suggest that a post-Pleistocene range expansion occurred out of an eastern glacial refugium into the Rocky Mountains. Examination of phylogeographical studies of other North American desert taxa indicated that mountain building explained diversification patterns more effectively for some taxa but Pleistocene climate change was more important for others, including A. aperta. PMID:15488003

Ayoub, Nadia A; Riechert, Susan E

2004-11-01

10

Late Pleistocene glacial advances in the western Tibet interior  

NASA Astrophysics Data System (ADS)

It has long been observed that the timing of glacial advances is asynchronous across the Himalaya–Karakoram–Tibet Plateau (HKTP) but the climatic implications, if any, remain unclear. Resolving this question requires additional glacial chronologies from unique spatial and climatic regimes as well as an analysis of how glaciers within different regimes are likely to have responded to past climate changes. This study presents a 10Be–21Ne chronology from the Mawang Kangri range of western Tibet (˜34°N, 80°E); an arid high-elevation site. We identify advances at ˜123, 83, and 56 kyr, which agree reasonably well with sites in the immediate vicinity, but are asynchronous relative to sites across the entire HKTP, and relative to sites in the western HKTP. To evaluate HKTP-wide asynchroneity, we compile dated glacial chronologies and classify them by the approximate timing of their maximum recent advance. This result shows a strong spatial clustering of young (MIS 1–2) relative to older (MIS 3–5) maximum advances. Further comparison with modern precipitation, temperature, and topographic data show that the pattern of HKTP-wide asynchroneity is broadly independent of topography and can potentially be explained by local responses to changes in temperature at either very warm-wet or cold-dry sites. Sites that receive intermediate amounts of precipitation are more ambiguous, although spatial clustering of MIS 1–2 vs. MIS 3–5 advances is suggestive of past variations in precipitation at these sites. In western Tibet, no spatial or climatic correlation is observed with the timing of maximum glacial advances. We suggest this could arise from mis-interpretation of disparate boulder ages generated by a prolonged MIS-3/4 glacial advance in the western HKTP.

Amidon, William H.; Bookhagen, Bodo; Avouac, Jean-Philippe; Smith, Taylor; Rood, Dylan

2013-11-01

11

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

USGS Publications Warehouse

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

Waitt, Jr, R. B.

1985-01-01

12

Late Pleistocene Cosmogenic 36Cl Glacial Chronology of the Southwestern Ahklun Mountains, Alaska  

Microsoft Academic Search

Thirty-two cosmogenic 36Cl surface exposure ages constrain the timing of two late Pleistocene glacial advances in the western Ahklun Mountains, southwestern Alaska. Boulders were sampled from one early Wisconsin (sensu lato) and six late Wisconsin moraines deposited by ice-cap outlet glaciers and local alpine glaciers. Four moraine boulders deposited during an extensive early Wisconsin ice-cap outlet glacier advance have a

Jason P. Briner; Terry W. Swanson; Marc Caffee

2001-01-01

13

Late pleistocene chronology of glacial lake old crow and the north-west margin of the laurentide ice sheet  

Microsoft Academic Search

Late Pleistocene advances of the Laurentide Ice Sheet in the northern Cordillera diverted westward the regional preglacial arctic drainage of the Porcupine River, northern Yukon, Canada. Glacial advance caused flooding of glacial Lake Old Crow which occupied Old Crow Basin, originally inundated by the northward diversion of Peel River drainage by a lobe of the Laurentide Ice Sheet that occupied

Grant D. Zazula; Alejandra Duk-Rodkin; Charles E. Schweger; Richard E. Morlan

2004-01-01

14

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

NASA Astrophysics Data System (ADS)

Changes in Southern Ocean hydrography may have played an important role in the Middle Pleistocene Transition (MPT), particularly through their impact on ocean circulation and atmospheric CO2 concentrations. Here we present foraminiferal Mg/Ca and ?18O results for the subsurface dwelling planktonic foraminifer Neogloboquadrina pachyderma (sinistral) at the Ocean Drilling Program (ODP) Site 1090. Results are used to reconstruct upper ocean temperatures and derive seawater ?18O in the Subantarctic Atlantic Ocean during the MPT. The new records indicate that, starting at ˜1250 ka, glacial temperatures and local (ice volume corrected) seawater ?18O in the upper water column of the Subantarctic Atlantic Ocean decreased, pointing to cooler (˜2 °C) and fresher (˜0.4‰) conditions than in the preceding glacial stages. These upper ocean hydrographic changes broadly coincide with the increase in the power of the 100 ky glacial-interglacial cycle in both records and with a shift towards decreased deep ventilation in the glacial Southern Ocean. Our finding suggests that an increase in Southern Ocean stratification, driven by the observed freshening of the upper water column, may have reduced the exchange of carbon between the deep Southern Ocean and the atmosphere during glacial stages. This process may have contributed, in combination with other mechanisms, to lower glacial atmospheric CO2 concentrations during the MPT.

Rodríguez-Sanz, Laura; Graham Mortyn, P.; Martínez-Garcia, Alfredo; Rosell-Melé, Antoni; Hall, Ian R.

2012-09-01

15

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

SciTech Connect

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

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

1992-01-01

16

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

NASA Astrophysics Data System (ADS)

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.

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

1993-05-01

17

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

PubMed

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

Frerichs, W E

1968-03-29

18

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

SciTech Connect

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

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

2008-01-01

19

Late Pleistocene oscillations of Lake Owens, eastern California  

SciTech Connect

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.

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

1993-04-01

20

Oscillators and relaxation phenomena in Pleistocene climate theory.  

PubMed

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

Crucifix, Michel

2012-03-13

21

Late Pleistocene glacial chronology of the Pietrele Valley, Retezat Mountains, Southern Carpathians constrained by 10Be exposure ages and pedological investigations  

Microsoft Academic Search

The Southern Carpathians are located in the transition zone between Mediterranean and continental climates and constituted the major areas of ice accumulation in the Carpathians during Pleistocene glaciations. An absolute glacial chronology had not yet been established. In this study we constrain the glacial history of the Pietrele Valley in the Retezat Mountains located in the Southern Carpathians and find

Anne U. Reuther; Petru Urdea; Christian Geiger; Susan Ivy-Ochs; Hans-Peter Niller; Peter W. Kubik; Klaus Heine

2007-01-01

22

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

PubMed Central

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

2012-01-01

23

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)

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).

Dyck, K.; Ravelo, C.

2009-12-01

24

Glacial morphology of Serbia, with comments on the Pleistocene Glaciation of Monte Negro, Macedonia and Albania  

Microsoft Academic Search

Cvijic was the first to collect evidence on the glacial morphology of the Balkans, at the end of the 19th century. He reported the existence of glacial features on the three highest mountains of Serbia, Prokletije, Sara and Koritnik. The most recent investigations have been carried out using remote sensing techniques supplemented by field observations. This approach has led to

Ljubomir Menkovic; Miroslav Markovic; Tomas Cupkovic; Radmila Pavlovic; Branislav Trivic; Nenad Banjac

2004-01-01

25

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

27

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

USGS Publications Warehouse

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.

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

2004-01-01

28

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

29

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

SciTech Connect

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

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

1995-06-01

30

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

31

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

NASA Astrophysics Data System (ADS)

The movement of Late Wisconsin (<30,000 B.P.) ice-sheet lobes counter to the direction of regional drainage ponded large lakes (up to 5000 km2) in both the Upper Fraser River Valley in British Columbia and the Cooper River Valley in Alaska. Along the Fraser River, near Quesnel, glaciolacustrine sediment gravity-flow complexes contain thick (up to 10 m) and laterally extensive (up to 3 km) diamict units containing large rafts of poorly lithified Tertiary rocks. Diamicts offlap and thin away from Tertiary bedrock highs and were emplaced by subaqueous debris flows. These flows probably evolved from slumps and slides associated with the downslope failure of unstable Tertiary bedrock slopes triggered by rising lake levels, a process akin to “first-filling” slope failures around the margins of man-made lakes. In Alaska, along the Copper River Valley, massive and stratified diamicts were also deposited by debris flows and are interbedded with thin-bedded turbidites, poorly sorted gravels and normally graded diamicts. Debris flow deposits show basal grooves, internal compressional structures and rafted clasts that protrude from bed tops. Flows originated by slumping of rapidly deposited and underconsolidated glacial sediments around the basin margins; an important factor in flow generation has been the combination of steep substrate slopes and frequent earthquake shock. Observations in both British Columbia and Alaska stress the significance of sediment gravity-flow processes acting to deposit “glacial” sedimentary successions in large ice-contact lake basins.

Eyles, Nicholas

1987-06-01

32

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

33

Paleonutrient and productivity records from the subarctic North Pacific for Pleistocene glacial terminations I to V  

Microsoft Academic Search

Our study addresses fundamental questions of the mode and timing of orbital and millennial-scale changes in the meridional overturning circulation (MOC) of the subarctic North Pacific. Particular concerns are the vertical mixing, the present and past abundance of nutrients in surface waters despite strong stratification, and the North Pacific–North Atlantic seesaw of oscillations in sea surface temperature (SST). We do

Holger Gebhardt; Michael Sarnthein; Pieter M. Grootes; Thorsten Kiefer; Hartmut Kuehn; Frank Schmieder; Ursula Röhl

2008-01-01

34

Late-glacial climatic oscillations as recorded in Swiss lake sediments  

Microsoft Academic Search

Regional pollen assemblage zones for the late-glacial period of the Swiss Plateau\\u000aare introduced and defined. They include four major zones (Artemisia, Juniperus — Hippophae,\\u000aBetula, Pinus PAZ) with several subzones. Pollen and oxygen-isotope analyses on lacustrine\\u000asediments from several lakes in the area reveal four distinct phases of climatic oscillation in the\\u000atime period of 13000 — 9500 yr

A. F. Lotter; U. Eicher; H. J. B. Birks; U. Siegenthaler

1992-01-01

35

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

36

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

37

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

Microsoft Academic Search

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

Loukas Barton; P. Jeffrey Brantingham; Duxue Ji

2007-01-01

38

El Niño-Southern Oscillation extrema in the Holocene and Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

The El Niño-Southern Oscillation (ENSO) is the largest engine of interannual climate variability on the planet, yet its past behavior and potential for future change are poorly understood and vigorously contested. Reconstructions of past ENSO are indispensable for testing climate models tasked with predicting future ENSO activity in a warming world, but suitable geologic archives are scarce, especially for the last glacial period. Here we reconstruct mean climate and ENSO variability in the Holocene and Last Glacial Maximum (LGM) from oxygen isotopic ratios (?18O) of individual foraminifera retrieved from deep-sea sediments. Our results document coordinated adjustments of the tropical Pacific/ENSO system between two diametrically opposite states: an "amplified ENSO" state in the LGM associated with a reduced zonal temperature gradient, and a "damped ENSO" state in the Mid-Holocene with enhanced gradient. Orbital precession provided the switch between these states and acted as the dominant external driver of the tropical Pacific/ENSO system in the past 25,000 years. The linked response of the mean state and variability to orbital forcing provides an integrated framework for testing ENSO theory and models.

Koutavas, Athanasios; Joanides, Stephan

2012-12-01

39

Pleistocene climatic oscillations and the speciation history of an alpine endemic and a widespread arctic-alpine plant.  

PubMed

Even in cases in which geographic isolation appears to have driven the speciation of regional endemics, range shifts during the Pleistocene climatic oscillations may also have influenced their evolutionary history. Elucidating speciation history can provide novel insights into evolutionary dynamics following climatic oscillations. We demonstrated a sister relationship between the Japanese alpine endemic Cardamine nipponica and the currently allopatric, widespread arctic-alpine Cardamine?bellidifolia (Brassicaceae) based on internal transcribed spacer (ITS) sequences and 10 other nuclear genes. Speciation history was inferred using demographic parameters under the isolation with migration model. The estimated demographic parameters showed that the population size of C. nipponica was similar to that of C. bellidifolia and that gene flow occurred exclusively from C. nipponica to C. bellidifolia after speciation. The inferred speciation history, which included gene flow, suggests that geographic barriers between the peripheral C. nipponica and the widespread C. bellidifolia were reduced during the Pleistocene. The asymmetric introgression implies that genetic isolation may have been involved in the speciation of C. nipponica. Our results suggest that even currently allopatric species may not have diverged solely under geographic isolation, and that their evolutionary history may have been influenced by Pleistocene range dynamics. PMID:22329701

Ikeda, Hajime; Carlsen, Tor; Fujii, Noriyuki; Brochmann, Christian; Setoguchi, Hiroaki

2012-02-13

40

Glacier-dammed lakes and geological work of glacial superfloods in the Late Pleistocene, Southern Siberia, Altai Mountains  

Microsoft Academic Search

Quaternary glacier-dammed lakes of Southern Siberia produced cataclysmic superfloods-floodstreams at the initial and final glacial stages, when the ice dams were unstable. Consequently, the initial surface was greatly and geologically instantly transformed. Morphologic associations of mountainous scablands developed, similar to the diluvial complexes of the Channeled Scabland in North America: giant diluvial ramparts and terraces-bars, diluvial berms and giant current

Alexei N Rudoy

2002-01-01

41

Latest Pleistocene glacial chronology of the Uinta Mountains: support for moisture-driven asynchrony of the last deglaciation  

Microsoft Academic Search

Recent estimates of the timing of the last glaciation in the southern and western Uinta Mountains of northeastern Utah suggest that the start of ice retreat and the climate-driven regression of pluvial Lake Bonneville both occurred at approximately 16cal.ka. To further explore the possible climatic relationship of Uinta Mountain glaciers and the lake, and to add to the glacial chronology

Benjamin J. C. Laabs; Kurt A. Refsnider; Jeffrey S. Munroe; David M. Mickelson; Patrick J. Applegate; Brad S. Singer; Marc W. Caffee

2009-01-01

42

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

PubMed

Phylogeography has provided a new approach to the analysis of the postglacial history of a wide range of taxa but, to date, little is known about the effect of glacial periods on the marine biota of Europe. We have utilized a combination of nuclear, plastid and mitochondrial genetic markers to study the biogeographic history of the red seaweed Palmaria palmata in the North Atlantic. Analysis of the nuclear rDNA operon (ITS1-5.8S-ITS2), the plastid 16S-trnI-trnA-23S-5S, rbcL-rbcS and rpl12-rps31-rpl9 regions and the mitochondrial cox2-3 spacer has revealed the existence of a previously unidentified marine refugium in the English Channel, along with possible secondary refugia off the southwest coast of Ireland and in northeast North America and/or Iceland. Coalescent and mismatch analyses date the expansion of European populations from approximately 128,000 BP and suggest a continued period of exponential growth since then. Consequently, we postulate that the penultimate (Saale) glacial maximum was the main event in shaping the biogeographic history of European P. palmata populations which persisted throughout the last (Weichselian) glacial maximum (c. 20,000 BP) in the Hurd Deep, an enigmatic trench in the English Channel. PMID:15723670

Provan, Jim; Wattier, Remi A; Maggs, Christine A

2005-03-01

43

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

PubMed Central

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

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

2007-01-01

44

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

NASA Astrophysics Data System (ADS)

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

Verkulich, Sergey; Pushina, Zina; Tatur, Andrej

2010-05-01

45

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

46

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

47

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

NASA Astrophysics Data System (ADS)

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

Montgelard, Claudine; Matthee, Conrad A.

2012-07-01

48

Spatial and temporal variations of glacial erosion in the Rhône valley (Swiss Alps): insights from numerical modeling  

NASA Astrophysics Data System (ADS)

The present-day topography of the European Alps shows evidence of intense glacial reshaping. However, significant questions regarding Alpine landscape evolution during glaciations still persist. For example, large-scale topographic analyses suggest that glacial erosion is maximized at and above the glaciers' long-term Equilibrium Line Altitude. In contrast, measurements of long-term denudation rates from low temperature thermochronology suggest high erosion towards low altitudes, leading to an increase of local relief in response to glacial erosion. Based on sediment record, low-temperature thermochronology and burial cosmogenic nuclide dating, it has also been proposed that the mid-Pleistocene climatic transition from symmetric, 40kyr to asymmetric, 100kyr glacial/interglacial oscillations sets the onset of intense glacial erosion within the Alps. However, this climate threshold in glacial erosion has not been showed in other orogens, and positive feedbacks between climate periodicity and glacial erosion efficiency still remain to be proven. We focus on the Rhône valley (Swiss Alps), and use a numerical model to estimate patterns and magnitudes of glacial erosion. Comparing modeling results on an advanced reconstruction of the pre-glacial topography (Sternai et al., 2012) and the present-day landforms, we found that erosion propagates headward as the landscape evolves from a fluvial to a glacial state, leading to an initial increase of local relief in the major valley trunk followed by subsequent erosion at high elevations. We also test the mid-Pleistocene transition hypothesis by running a 2Myr numerical experiment including a shift from symmetric, 40kyr to asymmetric, 100kyr glacial/interglacial oscillations at 1Myr. Although the change of climate periodicity may have produced an intensification of glacial erosion, our results suggest that other factors such as an increase of rock uplift and/or progressive climate cooling are required to explain enhanced valley carving at approximately 1Myr.

Sternai, Pietro; Herman, Frédéric; Valla, Pierre; Champagnac, Jean-Daniel; Willett, Sean

2013-04-01

49

Antarctica and Glacial Ages  

Microsoft Academic Search

IN his interesting article on ``Antarctica and Glacial Ages''1, Prof. MacBride states: ``If we add the breadth of the ice-shelf to the length of the Beardmore Glacier, we arrive at a total extent of ice-floe of about five hundred miles, and this is considerably longer than any glacier the existence of which we have evidence in the Pleistocene Glacial Age.''

J. Reid Moir

1938-01-01

50

Record of Late Pleistocene Glaciation and Deglaciation in the Southern Cascade Range. II. Flux of Glacial Flour in a Sediment Core from Upper Klamath Lake, Oregon  

Microsoft Academic Search

During the late Wisconsin, glacial flour from alpine glaciers along the east side of the Cascade Range in southern Oregon was deposited in Upper Klamath Lake. Quantitative interpretation of magnetic properties and grain-size data of cored sediments from Caledonia Marsh on the west side of the lake provides a continuous record of the flux of glacial flour spanning the last

Joseph G. Rosenbaum; Richard L. Reynolds

2004-01-01

51

Variability in the El Nino— Southern Oscillation Through a Glacial-Interglacial Cycle  

Microsoft Academic Search

The El Nino—Southern Oscillation (ENSO) is the most potent source of inter- annual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for

Alexander W. Tudhope; Colin P. Chilcott; Malcolm T. McCulloch; Edward R. Cook; John Chappell; Robert M. Ellam; David W. Lea; Janice M. Lough; Graham B. Shimmield

2000-01-01

52

A latest Pleistocene and Holocene glacial history and paleoclimate reconstruction at Three Sisters and Broken Top Volcanoes, Oregon, U.S.A  

Microsoft Academic Search

At least three sets of moraines mark distinct glacial stands since the last glacial maximum (LGM) in the Three Sisters region of the Oregon Cascade Range. The oldest stand predates 8.1 ka (defined here as post-LGM), followed by a second between ?2 and 8 ka (Neoglacial) and a third from the Little Ice Age (LIA) advance of the last 300 years. The post-LGM

Shaun A. Marcott; Andrew G. Fountain; Jim E. O'Connor; Peter J. Sniffen; David P. Dethier

2009-01-01

53

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

Microsoft Academic Search

Marine, fluvial and cave sediments, and karst phenomena were studied and dated by 14C, U-series, and OSL methods to determine the evolution of the Namakdan diapir and the world's longest salt cave (3N Cave) during the Holocene and the Last Glacial. Sea-level oscillations, the uplift rate of the diapir and its surroundings, and erosion are the main factors influencing the

Jirí Bruthans; Michal Filippi; Mohammad Zare; Zdenka Churácková; Naser Asadi; Markus Fuchs; Ji?í Adamovi?

2010-01-01

54

Spatial and temporal variations of glacial erosion in the Rhône valley (Swiss Alps): Insights from numerical modeling  

NASA Astrophysics Data System (ADS)

The present-day topography of the European Alps shows evidence of intense glacial reshaping. However, significant questions regarding Alpine landscape evolution during glaciations still persist. In this study, we focus on the Rhône valley (Swiss Alps), and use a numerical model to estimate patterns and magnitudes of glacial erosion. Comparing modeling results on a reconstructed pre-glacial topography and the present-day landforms, we find that the landscape response to glaciation is more complex than a simple "buzzsaw" mechanism (by which glacial erosion sets the height of mountain ranges) or increase of relief due to localized valley incision. Instead, glacial erosion propagates headward as the landforms evolve from a fluvial to a glacial state, leading to an initial increase of local relief followed by subsequent erosion at high elevations. It has also been proposed that the mid-Pleistocene climatic transition of glacial/interglacial oscillations from periods of 40 kyr (with symmetric shapes) to periods of 100 kyr (with asymmetric shapes) promoted glacial erosion within the Alps. Although this change of climate periodicity may have contributed to enhance glacial erosion, our results suggest that other factors such as an increase in rock uplift and/or progressive climate cooling are required to explain enhanced glacial carving at ˜1Ma.

Sternai, Pietro; Herman, Frédéric; Valla, Pierre G.; Champagnac, Jean-Daniel

2013-04-01

55

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

Microsoft Academic Search

BACKGROUND: Circum-Antarctic waters harbour a rare example of a marine species flock – the Notothenioid fish, most species of which are restricted to the continental shelf. It remains an open question as to how they survived Pleistocene climatic fluctuations characterised by repeated advances of continental glaciers as far as the shelf break that probably resulted in a loss of habitat

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

2007-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

57

El Nino-like climate teleconnections in new england during the late pleistocene  

PubMed

A glacial varve chronology from New England spanning the 4000-year period from 17,500 to 13,500 calendar years before the present was analyzed for evidence of climate variability during the late Pleistocene. The chronology shows a distinct interannual (3 to 5 years) band of enhanced variability suggestive of El Nino-Southern Oscillation (ENSO) teleconnections into North America during the late Pleistocene, when the Laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today. This interannual variability largely disappears by the young end of the 4000-year chronology, with only the highest frequency components (roughly 3-year period) persisting. This record provides evidence of ENSO-like climate variability during near-peak glacial conditions. PMID:10807572

Rittenour; Brigham-Grette; Mann

2000-05-12

58

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

USGS Publications Warehouse

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

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

1997-01-01

59

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

PubMed Central

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.

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

2009-01-01

60

Glacial Isostatic Adjustment  

NSDL National Science Digital Library

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

Awad, Aida

61

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

62

Diversification within glacial refugia: tempo and mode of evolution of the polytypic fish Barbus sclateri.  

PubMed

A diversity of evolutionary processes can be responsible for generating and maintaining biodiversity. Molecular markers were used to investigate the influence of Plio-Pleistocene climatic oscillations on the evolutionary history of taxa restricted to the freshwaters of a classical glacial refugium. Population genetic, phylogenetic and phylogeographical methods allowed the inference of temporal dynamics of cladogenesis and processes shaping present-day genetic constitution of Barbus sclateri, a polytypic taxon found in several independent river drainages in southern Iberian Peninsula. Results from different analyses consistently indicate several range expansions, high levels of allopatric fragmentation, and admixture following secondary contacts throughout its evolutionary history. Using a Bayesian demographical coalescent model on mitochondrial DNA sequences calibrated with fossil evidence, all cladogenetic events within B. sclateri are inferred to have occurred during the Pleistocene and were probably driven by environmental factors. Our results suggest that glaciation cycles did not inhibit cladogenesis and probably interacted with regional geomorphology to promote diversification. We conclude that this polytypic taxon is a species complex that recently diversified in allopatry, and that Pleistocene glaciation-deglaciation cycles probably contributed to the generation of biological diversity in a classical glacial refugium with high endemicity. PMID:19573028

Gante, Hugo F; Micael, Joana; Oliva-Paterna, Francisco J; Doadrio, Ignacio; Dowling, Thomas E; Alves, Maria Judite

2009-07-01

63

Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California  

Microsoft Academic Search

Pleistocene fluvial landforms and riparian ecosystems in central California responded to climate changes in the Sierra Nevada, yet the glacial history of the western Sierra remains largely unknown. Three glacial stages in the northwestern Sierra Nevada are documented by field mapping and cosmogenic radionuclide surface-exposure (CRSE) ages. Two CRSE ages of erratic boulders on an isolated till above Bear Valley

L. Allan James; Jon Harbor; Derek Fabel; Dennis Dahms; David Elmore

2002-01-01

64

Pacific Pleistocene Sediments: Planktonic Foraminifera Dissolution Cycles and Geochronology  

Microsoft Academic Search

Late Pleistocene equatorial Pacific sediments can be correlated by the ratios of certain solution-susceptible versus solution-resistant planktonic foraminifera. These ratios fluctuate in a cyclic manner whose timing is in phase with glacial-interglacial fluctuations established by oxygen isotope geo-chronology. Glacial stages are characterized by less solution of foraminifera than interglacial stages.

Peter R. Thompson; Tsunemasa Saito

1974-01-01

65

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

SciTech Connect

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.

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

1994-05-01

66

Pleistocene River Gravels and the Stonehenge Problem  

Microsoft Academic Search

ON the basis of evidence of glaciation in southern England the presence of glacial ice and associated outwash in areas formerly regarded as ice free throughout the Pleistocene period has been suggested1-3. In this account I examine the evidence in Wessex.

C. P. Green

1973-01-01

67

Guatemalan forest synthesis after Pleistocene aridity  

PubMed Central

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

Leyden, Barbara W.

1984-01-01

68

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

PubMed Central

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

2012-01-01

69

Transient nature of late Pleistocene climate variability.  

PubMed

Climate in the early Pleistocene varied with a period of 41 kyr and was related to variations in Earth's obliquity. About 900 kyr ago, variability increased and oscillated primarily at a period of approximately 100 kyr, suggesting that the link was then with the eccentricity of Earth's orbit. This transition has often been attributed to a nonlinear response to small changes in external boundary conditions. Here we propose that increasing variablility within the past million years may indicate that the climate system was approaching a second climate bifurcation point, after which it would transition again to a new stable state characterized by permanent mid-latitude Northern Hemisphere glaciation. From this perspective the past million years can be viewed as a transient interval in the evolution of Earth's climate. We support our hypothesis using a coupled energy-balance/ice-sheet model, which furthermore predicts that the future transition would involve a large expansion of the Eurasian ice sheet. The process responsible for the abrupt change seems to be the albedo discontinuity at the snow-ice edge. The best-fit model run, which explains almost 60% of the variance in global ice volume during the past 400 kyr, predicts a rapid transition in the geologically near future to the proposed glacial state. Should it be attained, this state would be more 'symmetric' than the present climate, with comparable areas of ice/sea-ice cover in each hemisphere, and would represent the culmination of 50 million years of evolution from bipolar nonglacial climates to bipolar glacial climates. PMID:19005552

Crowley, Thomas J; Hyde, William T

2008-11-13

70

The first glacial maximum in North America.  

PubMed

Despite marine evidence for at least 50 Pliocene-Pleistocene ice sheet advances, only the most recent one has been accurately reconstructed from terrestrial evidence, because there are few techniques for dating older glacial deposits. Here we show that the cosmic ray-produced nuclides beryllium-10 and aluminum-26 can be used to date tills that overlie paleosols. PMID:15653495

Balco, Greg; Rovey, Charles W; Stone, John O H

2005-01-14

71

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2010-09-01

73

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

Microsoft Academic Search

High-resolution continuous core material, geophysical measurements, and hundreds of archived core descriptions enabled to identify 13 Late Pleistocene Rhine-Meuse sedimentary units in the infill of the southern part of the North Sea basin (the Netherlands, northwestern Europe). This sediment record and a large set of Optical Stimulated Luminescence dates, 14C dates and biostratigraphical data, allowed to establish detailed relationships between

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

2007-01-01

74

Pleistocene Speciation in the Genus Populus (Salicaceae)  

PubMed Central

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

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

2012-01-01

75

Pleistocene speciation in the genus Populus (salicaceae).  

PubMed

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

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

2012-01-02

76

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

77

Hominin responses to environmental changes during the Middle Pleistocene in central and southern Italy  

NASA Astrophysics Data System (ADS)

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.

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

78

Outbursts From Glacial Lake Agassiz and Their Possible Impact on Thermohaline Circulation at the Start of the Younger Dryas, Preboreal Oscillation, and 8.2 ka Cold Event  

Microsoft Academic Search

During the last deglaciation of North America, the Laurentide Ice Sheet retreated downslope, impounding lakes along its margin. The area and volume of these proglacial lakes varied substantially through time as a result of the changing location of the ice margin, topography of the newly deglaciated surface, elevation of the overflow outlet from the lake, and differential isostatic rebound. Glacial

J. T. Teller; D. Leverington; J. Mann

2001-01-01

79

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

Microsoft Academic Search

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

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

2002-01-01

80

Pleistocene fluctuations of the Antarctic Ice Sheet in the Ross Embayment  

NASA Astrophysics Data System (ADS)

Past fluctuations of the marine-based Antarctic Ice Sheet in the Ross Embayment are reconstructed for the Pleistocene by developing a model for the glacimarine depositional sequences documented from the ANDRILL McMurdo Ice Shelf project drill core AND-1B. This model reveals glacial to interglacial fluctuations of the AIS in the Western Ross Embayment responding at orbital frequencies. Chronology is constrained by an age model based on 40Ar/39Ar dating of volcanic ashes and magnetostratigraphy. The glacimarine sequences in AND-1B appear to correlate one-to-one with cycles in the benthic ^18O record for the past ~0.8 Myr (Marine Isotope Stages 20-2). Five sequences between ~1.7 and 1.0 Myr can also be matched with specific intervals in the ^18O record, and indicate oscillations of the AIS grounding line operating at a 40-kyr frequency. This record provides new insight into the response of the AIS in the Ross Embayment across the Mid-Pleistocene Transition. Prior to 1.0 Myr, glacimarine sequences have 40-kyr duration, whereas subsequently 100-kyr glacimarine cycles can be clearly recognised in the core. During this "100-kyr world", subglacial to grounding-zone sedimentation dominates at the AND-1B site, with thin intervals of ice-shelf deposition during interglacials also preserved in the AND-1B sedimentary record. An unconformity in AND-1B that spans most (~200 kyr) of the Mid-Pleistocene Transition is inferred to represent large scale expansion of AIS in the Ross Embayment at ~0.8 Myr. Prior to the Mid-Pleistocene Transition, interglacial periods are characterised by open-water conditions with high abundances of volcanoclastic deposits and occasional diatomaceous sediments, indicating that the marine based ice sheet was more dynamic during this interval.

McKay, R. M.; Naish, T. R.; Powell, R. D.

2009-04-01

81

Late Pleistocene glaciation of the Diancang and Gongwang Mountains, southeast margin of the Tibetan plateau  

Microsoft Academic Search

Late Pleistocene glaciations on Mt. Diancang and Mt. Gongwang were investigated and the chronostratigraphy of the glacial advances were developed based on the geomorphic features and numerical ages of thermoluminescence (TL) and AMS radiocarbon dating. Glaciers disappeared ?1300 years ago on Mt. Diancang and several earlier glacial advances, occurred at 3–5, 10, 15–22ka and one during MIS 3. The glacial

Jianqiang Yang; Wei Zhang; Zhijiu Cui; Chaolu Yi; Kexin Liu; Yuanjiang Ju; Xiaoyong Zhang

2006-01-01

82

Late Pleistocene Glaciation of the Southwestern Ahklun Mountains, Alaska  

Microsoft Academic Search

Glacial deposits in the southwestern Ahklun Mountains, southwestern Alaska, record two major glacier advances during the late Pleistocene. The Arolik Lake and Klak Creek glaciations took place during the early and late Wisconsin, respectively. During the Arolik Lake glaciation, outlet glaciers emanated from an ice cap centered over the central portion of the Ahklun Mountains and expanded beyond the present

Jason P. Briner; Darrell S. Kaufman

2000-01-01

83

Probability of moraine survival in a succession of glacial advances.  

USGS Publications Warehouse

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

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

1984-01-01

84

COMBINATION OF NUMERICAL DATING TECHNIQUES USING 10 BE IN ROCK BOULDERS AND 14 C IN RESILIENT SOIL ORGANIC MATTER FOR RECONSTRUCTING GLACIAL AND PERIGLACIAL PROCESSES IN A HIGH ALPINE CATCHMENT DURING THE LATE PLEISTOCENE AND EARLY HOLOCENE  

Microsoft Academic Search

Glacier fluctuations and palaeoclimatic oscillations during the Late Quaternary in Val di Rabbi (Trentino, Northern Italy) were reconstructed using a combination of absolute dating techniques ( 14 C and 10 Be) and soil chemical characterisation. Extraction and dating of the stable fraction of soil organic matter (SOM) could give valuable information about the minimum age of soil formation and contributed

Filippo Favilli; Markus Egli; Dagmar Brandova; Susan Ivy-Ochs; Peter W. Kubik; Paolo Cherubini; Wilfried Haeberli

2009-01-01

85

Plio-pleistocene African climate  

SciTech Connect

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.

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

1995-10-06

86

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

NASA Astrophysics Data System (ADS)

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.

Kowler, A. L.

2010-12-01

87

Upper Middle Pleistocene climate and landscape development of Northern Germany  

NASA Astrophysics Data System (ADS)

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.

Urban, B.

2009-04-01

88

Pleistocene variability of Antarctic Ice Sheet extent in the Ross Embayment  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

89

Astronomical forcing and mathematical theory of glacial-interglacial cycles  

NASA Astrophysics Data System (ADS)

There are three important features of a proxy time series recorded during the Late Pleistocene. They are: 1) 100 000-year cycle as a dominant control of global glacial-interglacials through the late Quaternary, 2) fluctuations with periods of about 40 and 20 thousand years (their contribution to dispersion is no more than 20%), 3) ''Red-noise'' behavior of the time series. Direct influence of the insolation change created by fluctuations of the eccentricity is too weak to cause the observed 100 000-year climate fluctuations. Therefore, other mechanisms of such a rhythm are proposed. On the basis of the equation of the heat budget, the equation describing dynamics of zonally averaged temperature is developed. Various combinations of terms of this equation are discussed. They present a linear response to the Milankovitch periodicity, the Langeven stochastic equation, the equation of delay oscillator, the stochastic equation of spontaneous transitions, and the equation of stochastic resonance. Orbitally-induced changes in the solar energy flux received by the Earth play an important role as a mechanism starting process of climate changes which is supported and intensified by different feedbacks within the climate system. Positive anomalies of solar radiation serve as a mechanism causing reorganization of the climate only in rare cases when inclination of Earth axis of rotation increases and, simultaneously, perihelion takes place during the summer time (for the Northern Hemisphere).

Kislov, A. V.

2009-02-01

90

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

Microsoft Academic Search

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

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

2009-01-01

91

Late Pleistocene dune activity in the central Great Plains, USA  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

92

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

NASA Astrophysics Data System (ADS)

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.

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

2012-01-01

93

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

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

McDonald, D E; Daniels, S R

2012-03-12

94

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

PubMed Central

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.

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

2012-01-01

95

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

Microsoft Academic Search

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

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

2011-01-01

96

The thermal evolution of the western equatorial Pacific warm pool during the Pleistocene and late Pliocene epochs  

NASA Astrophysics Data System (ADS)

The late Pliocene and Pleistocene epochs have been characterized by a series of climate cycles generally referred to as ice ages. The ice ages not only involved high latitude climate oscillations as this designation implies, but also variability in low latitude tropical climate. A number of studies, including the series presented in this document, support a relatively novel perspective of the ice ages. This "low-latitude" perspective is based on recent observations that suggest that not only did the tropics experienced clear climatic cycles during the glaciations, but also that tropical climate changes preceded those in continental ice volume by several thousand years. This thesis dissertation focused on reconstructing the temperature and hydrological evolution of the western equatorial Pacific (WEP) warm pool over the late Pliocene (2.3 to 3.1 Ma) and Pleistocene (1.3 to 0.45 Ma) Epochs using the foraminiferal Mg/Ca Paleothermometry technique and foraminiferal oxygen isotopes. Climate reconstructions are based on sediments from Ocean Drilling Program (ODP) Hole 806B on the Ontong Java Plateau, a site regarded to have remarkably constant sedimentation rates and very good foraminiferal preservation. These records indicate that: (1) during the Pleistocene, WEP warm pool sea surface temperature (SST) cycles switched from a dominant period of 41 ky before ˜950,000 (ky) to a period of ˜100 ky after this time; (2) Pleistocene and Late Pliocene SST cycles in the WEP warm pool are synchronous and have a similar magnitude to SST cycles in the eastern equatorial Pacific cold tongue; (3) equatorial Pacific SST cycles precede continental ice volume changes by several thousand years during the late Pliocene and Pleistocene Epochs and; (4) a marked east-west equatorial Pacific zonal temperature gradient existed during the Late Pliocene, in contrast with previous inferences. The character of tropical Pacific climate evolution, suggests that variability in radiative forcing by atmospheric greenhouse gases and the associated feedbacks (i.e. water vapor, ice albedo, etc.) played a major role in driving tropical climate evolution on glacial to interglacial time scales during the late Pliocene and Pleistocene epochs.

Medina Elizalde, Martin Andres

97

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

PubMed Central

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

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

2011-01-01

98

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

PubMed

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

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

2011-11-21

99

Late Pleistocene Variations in Oxygen Minimum Zone: Southern California Margin  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

100

Constraints on the Pleistocene chronology of sediments from the Lomonosov Ridge  

Microsoft Academic Search

Despite its importance in the global climate system, age-calibrated marine geologic records reflecting the evolution 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

Matthew O'Regan; John King; Jan Backman; Martin Jakobsson; Heiko Pälike; Kathryn Moran; Clifford Heil; Tatsuhiko Sakamoto; Thomas M. Cronin; Richard W. Jordan

2008-01-01

101

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

Microsoft Academic Search

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

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

2007-01-01

102

A Latest Pleistocene and Holocene Chronology of Alpine Glaciation for western North America  

Microsoft Academic Search

We are developing a cosmogenic 10Be chronology of late-Pleistocene and Holocene alpine glaciation from sites across the western United States and southwestern Canada in order to address spatial and temporal glacier variability in response to postulated climate forcings. A number of studies have interpreted several Holocene glacial advances in western North America, but age control is based largely on relative

S. A. Marcott; P. U. Clark; J. D. Shakun; E. Brook; A. Novak; P. T. Davis; M. W. Caffee

2009-01-01

103

The Pleistocene of Denmark: A review of stratigraphy and glaciation history  

Microsoft Academic Search

Climatically dependent environmental changes and the advance and retreat of glaciers have controlled the development of sedimentary successions in Denmark during the Middle and Late Pleistocene. Over the last four glacial-interglacial cycles radical alternations of marine and terrestrial environments, combined with eustatic and isostatic response to glaciation, has lead to the following geological history. The first Quaternary glaciation reached the

Michael Houmark-Nielsen

2004-01-01

104

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

Microsoft Academic Search

Repeated glacial events during the Pleistocene fragmented and displaced populations throughout the northern continents. Different models of the effects of these climate-driven events predict distinct phylogeographic and population genetic outcomes for high-latitude faunas. The role of glaciations in (i) promoting intraspecific genetic differentiation and (ii) influencing genetic diversity was tested within a phylogeographic framework using the rodent Microtus oeconomus .

KURT E. G ALBREATH; JOSEPH A. C OOK

2004-01-01

105

Pleistocene Glaciation and the Stability of North Atlantic Thermohaline Circulation  

NASA Astrophysics Data System (ADS)

Geochemical profiles from the North Atlantic Ocean suggest that the vertical ?13C structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the Pleistocene, despite large changes in ice volume and iceberg delivery from nearby landmasses. After the Mid-Pleistocene Transition (MPT), warmer interglaciations may have resulted in periodically (and present-day) open sea ice conditions in the Norwegian-Greenland Sea. The high ?13C deep water that forms in the NGS region today may be geologically unusual and restricted to the few extreme interglaciations of the late Pleistocene. Over most of the Pleistocene, Norwegian Sea Overflow Water appears to have had low ?13C values, similar to Southern Ocean Water, and is seen as a mid-depth low-?13C layer between 1 and 2 km depth south of the Greenland-Scotland Ridge. If northern source deep waters can have variable ?13C , then this likelihood must be considered when inferring past circulation changes from benthic ?13C records. The larger ice volumes attained after the MPT may also have resulted in the periodically large and rapid discharges of freshwater associated with Heinrich events. Only such extreme freshwater perturbations appear to be able to significantly disrupt the THC from its normal mode that characterizes most of the Pleistocene. With the modern configuration of land and ice, it seems unlikely that future alterations to high latitude run-off would constitute a density perturbation as large as a Heinrich event. The question remains whether proposed hydrographic changes at high latitudes would fall outside the range of the glacial-interglacial boundary conditions under which North Atlantic THC appears to have been relatively stable.

Raymo, M. E.; Oppo, D. W.; McManus, J. F.

2004-12-01

106

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

Microsoft Academic Search

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

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

2006-01-01

107

Late Pleistocene deposits at Wing, Rutland.  

PubMed

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

Hall, A R

1980-05-01

108

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

PubMed

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

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

2013-02-11

109

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

SciTech Connect

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.

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

1996-03-01

110

Earth's glacial record and its tectonic setting  

NASA Astrophysics Data System (ADS)

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

Eyles, N.

1993-09-01

111

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

NASA Astrophysics Data System (ADS)

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).

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

2013-04-01

112

Cenozoic Glacial History Revisited  

Microsoft Academic Search

Recent geological discoveries have shaken the long-standing view of Earth's Cenozoic glacial history, which traditionally calls for the first continental-scale glaciation of East Antarctica in the earliest Oligocene (~33.6 Ma), followed by the onset of major Northern Hemispheric glacial cycles in the late Pliocene about 30 million years later. For example, new evidence from Arctic and North Atlantic oceans suggests

R. Deconto; D. Pollard; P. Wilson; M. Pagani

2009-01-01

113

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

USGS Publications Warehouse

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

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

2006-01-01

114

Extended Late Pleistocene Sea Level Record  

NASA Astrophysics Data System (ADS)

Several hundred new closed system 230Th/234U and radiocarbon dates and the addition of more cores and coral samples from the islands of Barbados, Kiritimati and Araki contribute to an enhanced sea level record for the late Pleistocene ranging from the present to 240,000 yrs BP. Application of more rigorous sample screening criteria, including redundant 231Pa/235U dates have resulted in more closed system ages and better sea level resolution. In addition, a multibeam survey has mapped an extensive glacial lowstand reef on a ridge south of Barbados that is capped by a set of pinnacle reefs that grew during the early deglaciation. Among our new observations, the more detailed Barbados sea level record now resolves a Younger Dryas still- stand and a sea level drop between 16,140 and 14,690, overlapping the timing of H1 by some age estimates. The coral ages bracketing melt water pulse 1A have been further refined to 14,082 +/- 28 yrs BP and 13,632 +/- 32 yrs BP (2-sigma). The Isotope Stage 3 interstadial ended with sea level near 87.5 meters below present at 29,500 years ago before dropping to full glacial levels. The last glacial sea level lowstand began as early as 26,000 yrs BP. Extensive dating of Marine Isotope Stage 3 interstadial reefs on the islands of Araki and Barbados have added considerable resolution to this time interval and reliably bracket lowstand intervals separating the interstadials. A new diagenesis model has improved our prospecting success for closed system ages from older reefs and added some critical dates to the sparse closed-system data set for MIS-5 and MIS-7 high stand reefs..

Fairbanks, R. G.; Cao, L.; Mortlock, R. A.

2006-12-01

115

A Phase-Space Model for Pleistocene Ice Volume  

NASA Astrophysics Data System (ADS)

We present a phase-space model that simulates Pleistocene ice volume changes based on Earth's orbital parameters. In constructing the model, we attempt to separate terms representing direct orbital forcing of ice volume change from terms representing internal forces of change. The evolution equation is first-order, except during terminations, when it is second-order. The transition between the two states is governed by a threshold in phase space, i.e., a combination of ice volume and its rate of change. Timing of terminations agrees well with age estimates for Late Pleistocene terminations. The average phase at which model terminations begin is approximately 90±90° before the maxima in all three orbital cycles. The large variability in phase is likely caused by interactions between the three cycles and ice volume. Unlike previous ice volume models, this model reproduces an increase in 100-kyr power during the mid-Pleistocene transition without any change in model parameters. This supports the hypothesis that Pleistocene variations in the 100-kyr power of glacial cycles could be caused by changes in Earth's orbital parameters, such as amplitude modulation of the 100-kyr eccentricity cycle, rather than changes within the climate system. Phase-space trace of the filtered ice-volume record (color denotes orbital forcing). Black line indicates the termination threshold.

Imbrie, J. Z.; Imbrie-Moore, A.; Lisiecki, L. E.

2010-12-01

116

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

PubMed Central

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

Spellman, Garth M; Klicka, John

2006-01-01

117

A northern glacial refugium for bank voles (Clethrionomys glareolus)  

PubMed Central

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.

Kotlik, Petr; Deffontaine, Valerie; Mascheretti, Silvia; Zima, Jan; Michaux, Johan R.; Searle, Jeremy B.

2006-01-01

118

Deep-sea pleistocene biostratigraphy.  

PubMed

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

Lidz, L

1966-12-16

119

Glacial integrative modelling.  

PubMed

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

Ganopolski, Andrey

2003-09-15

120

Late Pleistocene deglaciation chronology in the NW of the Iberian Peninsula using cosmic-ray produced 21Ne in quartz  

Microsoft Academic Search

Late Pleistocene glaciations in the NW Iberian Peninsula over Serra de Queixa and Serra de Xurés, all with granite substrata, were studied by mass spectrometry using cosmogenic 21Ne. Rock cores were drilled in glacial polished surfaces and push-moraine boulders, and were analyzed to determine their integral exposure time to cosmic rays. First results, which are consistent with the relative geomorphologic

D. Fernandez Mosquera; K. Marti; J. R. Vidal Romani; A. Weigel

2000-01-01

121

Evidence for obliquity forcing of glacial Termination II.  

PubMed

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. PMID:19679773

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

2009-08-13

122

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

Microsoft Academic Search

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

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

2008-01-01

123

Downslope processes and products on the Wilkes Land compared to other Antarctic margins: Relevance to glacial history  

Microsoft Academic Search

Sediment cores collected from the Wilkes Land margin show slope and base-of-slope sedimentation dominated by gravity flow processes during Pleistocene glacial times. Slumps and initial debris flow products dominate the upper slope. Sediments of the lower slope and upper continental rise contain crudely stratified to laminated intervals, which represent the transition between an end member of a debris flow and

C. Escutia; C. H. Nelson; D. Warnke; G. D. Acton; A. Barcena; L. Burckle; C. S. Franzee

2003-01-01

124

Volume of Antarctic Ice at the Last Glacial Maximum, and its impact on global sea level change  

Microsoft Academic Search

The volume of Antarctic ice at the Last Glacial Maximum is a key factor for calculating the past contribution of melting ice sheets to Late Pleistocene global sea level change. At present, there are large uncertainties in our knowledge of the extent and thickness of the formerly expanded Antarctic ice sheets, and in the timing of their release as meltwater

Michael J. Bentley

1999-01-01

125

Possible mechanisms for glacial earthquakes  

Microsoft Academic Search

The large glacial earthquakes reported on by Ekström et al. (2003, 2006) and Tsai and Ekström (2007) have previously been evaluated in terms of their seismic characteristics. In this paper we attempt to take constraints such as known glacial ice properties, outlet glacier size, calving style, and meltwater variability to construct a self-consistent physical model of the glacial earthquake process.

Victor C. Tsai; James R. Rice; Mark Fahnestock

2008-01-01

126

Glacial Geology of Wisconsin.  

ERIC Educational Resources Information Center

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

Madison Public Schools, WI.

127

Repeated Pleistocene glaciation of the East Siberian continental margin  

NASA Astrophysics Data System (ADS)

During the Pleistocene glaciations, Arctic ice sheets on western Eurasia, Greenland and North America terminated at their continental margins. In contrast, the exposed continental shelves in the Beringian region of Siberia are thought to have been covered by a tundra landscape. Evidence of grounded ice on seafloor ridges and plateaux off the coast of the Beringian margin, at depths of up to 1,000m, have generally been attributed to ice shelves or giant icebergs that spread oceanwards during glacial maxima. Here we identify marine glaciogenic landforms visible in seismic profiles and detailed bathymetric maps along the East Siberian continental margin. We interpret these features, which occur in present water depths of up to 1,200m, as traces from grounding events of ice sheets and ice shelves. We conclude that the Siberian Shelf edge and parts of the Arctic Ocean were covered by ice sheets of about 1km in thickness during several Pleistocene glaciations before the most recent glacial period, which must have had a significant influence on albedo and oceanic and atmospheric circulation.

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

2013-10-01

128

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

Microsoft Academic Search

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,

Bruce L. Hardy

2010-01-01

129

Alaska PaleoGlacier Atlas: A Geospatial Compilation of Pleistocene Glacier Extents  

NSDL National Science Digital Library

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

Manley, William

130

A remarkable collection of Late Pleistocene reindeer ( Rangifer tarandus) remains from Woerden (The Netherlands)  

Microsoft Academic Search

Woerden, in the central part of The Netherlands, is a locality where the amateur-archaeologist Pieter Stoel collected several thousands of fossil mammalian remains of Pleistocene age. The stratigraphically-mixed assemblage includes a broad variety of taxa including species that are indicative of interglacial conditions such as Hippopotamus sp. as well as species that inhabited the area during glacial episodes e.g. Mammuthus

Thijs van Kolfschoten; Inge van der Jagt; Zoë Beeren; Vasiliki Argiti; Judith van der Leije; Hans van Essen; Freek S. Busschers; Pieter Stoel; Hans van der Plicht

2011-01-01

131

A MIDDLE PLEISTOCENE PALEOSOL SEQUENCE FROM DAWSON RANGE, CENTRAL YUKON TERRITORY  

Microsoft Academic Search

Four paleosols were inter- sected in a core drilled into the colluvial fill of a largely buried meltwater channel that was last active during the youngest of the pre-Reid glaciation (0.99-0.78 Ma) in the Dawson Range, Yukon Territory. The paleosols are classified as Podzols. The sedimentary sequence and paleosols indicate that at least two middle Pleistocene glacial and interglacial periods

Lionel E. JACKSON; Charles TARNOCAI; Robert J. MOTT

132

The Late Pleistocene Ross Ice Sheet and Eustatic Sea Level Rise  

Microsoft Academic Search

Radiocarbon dates obtained from central Ross Sea foraminifera indicate that glacial ice reached its maximum position in the Ross Embayment after 13.8 14C ka, suggesting that deglaciation of this major sector of the Antarctic ice sheet lagged the onset of Late Pleistocene eustatic sea level rise by 4-5 ky. The 13.8 14C date is the youngest of 18 14C dates

K. J. Licht; J. T. Andrews

2002-01-01

133

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

Microsoft Academic Search

The Pleistocene is very poorly represented in Antarctic continental shelf settings. Most piston cores do not penetrate last-glacial age diamictons. Moreover, nearly all sedimentary records have been subjected to the erosional effects of multiple expansions of the WAIS. No existing sediment core recovered from the continental shelf preserves a complete record of the last 1.2 Ma. The ANDRILL-MIS drillcore (AND-1B)

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

2010-01-01

134

Late Pleistocene glaciation of the Hulifang Massif of Gongwang mountains in Yunnan Province  

Microsoft Academic Search

Late Pleistocene glaciation was restricted to only a few high mountains in eastern China. The Gongwang mountains constitute\\u000a one of the typical places once glaciated. Geomorphic mapping of the area and the TL dating provides evidence for at least\\u000a four distinct glaciations. YJT-I glacial advance occurred about 100 ka BP and two TL absolute ages (101,100 ± 7780 a BP;

Zhang Wei; Cui Zhijiu; Feng Jinliang; Yi Chaolu; Yang Jianqiang

2005-01-01

135

Recurring middle Pleistocene outburst floods in east-central Alaska  

USGS Publications Warehouse

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.

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

136

Antarctica and Glacial Ages  

Microsoft Academic Search

PROF. A. P. COLEMAN1 contends that the late Palæozoic glacials of the southern hemisphere could never have been formed upon a large, single continent-Gondwana-as visualized by supporters of the hypothesis of continental drift. He has protested that, for such an ice-cap to have developed, there must have been sources of evaporation at hand in the shape of warm seas, and

Alex. L. Du Toit

1939-01-01

137

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

Microsoft Academic Search

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

Salt Lake; Coyote Lake

2001-01-01

138

New Findings concerning the Pleistocene glaciation of the Leh Basin  

NASA Astrophysics Data System (ADS)

As a part of the Upper Indus Valley the Basin of Leh is located between the northern lying Ladakh Range and the Stok Range in the south. Here, the bottom of the Upper Indus Valley is situated between 3200 and 3300 m a.s.l. Like for most parts of High Asia, researches concerning the Pleistocene landscape evolution of this Intramontane Basin have also left contradictions. To push the problem of extent and timing of the former glaciation three up to now unexplored valleys of the Ladakh Range, which are tributaries of the Leh Basin, have been investigated. U-shaped profiles, transfluence passes, glacial rounded ridges and peaks mantled with moraine material, roches moutonneés, glacial flank polishings and ground moraines document the former glaciation of the research area. The ice fillings of the tributaries reached a minimum thickness up to 540 m. Even at the valley outlets and on the orographic right side of the Leh Basin the glaciation was more than 350 m thick. Based on these empirically extracted results, theoretical snow line considerations lead to the conclusion that the whole Leh Basin was filled up by a former Indus Valley glacier. An ice injection limited to the nourishment areas of the Ladakh Range valleys couldn't have caused to the reconstructed ice cover (down to 3236 m a. s. l.), which is proved by extended ground moraine complexes. Only an Indus ice stream network, nourished by inflowing glaciers of the Ladakh- and Stok Range explain the widespread existence of the glacial sediments. The good preservation of moraine material, even at the valley flanks steeper than 30° seems to be inconsistent with the assumption of other authors that the ice streams accumulating these sediments occurred during the penultimate glacial cycle or earlier. Also in recent times the extreme climatic conditions of the investigation area are very favourable for frost weathering, solifluction and abluation. During the Pleistocene this frost and snow cover induced activity must have been much more intensive. This lead to the conclusion that the reconstructed ice filling of the Leh basin occured during the last glacial cycle (MIS 2-4).

Achenbach, H.

2009-04-01

139

Geomagnetic Reversals and Pleistocene Chronology  

Microsoft Academic Search

The palaeontology and palaeomagnetic stratigraphy of several Atlantic and Pacific cores has been determined to establish the age relationship of various palaeontological boundaries which have been used to define a Pliocene-Pleistocene boundary in deep sea sediments.

B. Glass; D. B. Ericson; B. C. Heezen; N. D. Opdyke; J. A. Glass

1967-01-01

140

Late Pleistocene carbonate dissolution in the Venezuela Basin, Caribbean Sea  

SciTech Connect

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

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

1985-01-01

141

Constraining Late Pleistocene Pluvial Lake Chronologies in Northeastern Nevada  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

142

Millennial climate oscillation spied  

SciTech Connect

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

Kerr, R.A.

1996-01-12

143

Onset of “Hudson Strait” Heinrich events in the eastern North Atlantic at the end of the middle Pleistocene transition (?640 ka)?  

Microsoft Academic Search

Heinrich events are well documented for the last glaciation, but little is known about their occurrence in older glacial periods of the Pleistocene. Here we report scanning XRF and bulk carbonate ?18O results from Integrated Ocean Drilling Program Site U1308 (reoccupation of Deep Sea Drilling Project Site 609) that are used to develop proxy records of ice-rafted detritus (IRD) for

David A. Hodell; James E. T. Channell; Jason H. Curtis; Oscar E. Romero; Ursula Röhl

2008-01-01

144

Late Pleistocene divergence between eastern and western populations of wood ducks (Aix sponsa) inferred by the 'isolation with migration' coalescent method  

Microsoft Academic Search

During the Late Pleistocene, glaciers sundered many species into multiple glacial refugia where populations diverged in allopatry. Although deeply divergent mitochondrial DNA (mtDNA) lineages often reflect the number of refugia occupied, it is unlikely that popula- tions that split during the recent Wisconsin glaciations will have reached reciprocal monophyly. We examined mtDNA control region sequences from eastern and western populations

JEFFREY L. PETERS; WILLIAM GRETES; KEVIN E. OMLAND

2005-01-01

145

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

PubMed Central

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

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

2012-01-01

146

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

PubMed

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

Steele, Craig A; Storfer, Andrew

2006-08-01

147

Late Pleistocene marine birds from southern Peru: distinguishing human capture from El Niño-induced windfall  

Microsoft Academic Search

The Central Andean hyperarid littoral has abundant marine fauna that would have been attractive to the earliest inhabitants. Whether people hunted or scavenged marine animals during the terminal Late Pleistocene have social and technological implications for understanding ancient Andean foraging. The periodic phenomenon of El Niño\\/Southern Oscillation (ENSO) disrupts marine food chains and results in the death of significant numbers

Susan D. deFrance

2005-01-01

148

Late Pleistocene to recent climate change in Córdoba Province, Argentina: Geomorphological evidence  

Microsoft Academic Search

Repeated episodes of climate change affected the Córdoba Plains during the Late Pleistocene and Holocene. Many of the geomorphologic features of Córdoba Province were developed in response to climatic oscillations, and their development can be correlated to changes in precipitation and hydrologic regimes. Alternating periods marked by dry climate and high evapotranspiration rates were interspersed with more humid intervals, and

Claudio A. Carignano

1999-01-01

149

Late Pleistocene Environments of the Central Ukraine  

Microsoft Academic Search

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

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

2001-01-01

150

What drives glacial cycles  

SciTech Connect

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

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

1990-01-01

151

The consequences of pleistocene climate change on lowland neotropical vegetation  

SciTech Connect

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

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

1994-06-01

152

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

NASA Astrophysics Data System (ADS)

This study establishes for the first time the chronology and limnological history of Lake Amora (Dead Sea basin, Israel), whose deposits (the Amora Formation) comprise one of the longest exposed lacustrine records of the Pleistocene time. The Amora Formation consists of sequences of laminated primary aragonite and silty-detritus, Ca-sulfate minerals, halite and clastic units. This sedimentary sequence was uplifted and tilted by the rising Sedom salt diapir, exposing ˜320 m of sediments on the eastern flanks of Mt. Sedom (the Arubotaim Cave (AC) section). The chronology of the AC section is based on U-disequilibrium dating ( 230Th- 234U and 234U- 238U ages) combined with floating ?18O stratigraphy and paleomagnetic constraints. The determination of the 230Th- 234U ages required significant corrections to account for detrital Th and U. These corrections were performed on individual samples and on suites of samples from several stratigraphic horizons. The most reliable corrected ages were used to construct an age-elevation model that was further tuned to the oxygen isotope record of east Mediterranean foraminifers (based on the long-term similarity between the sea and lake oxygen isotope archives). The combined U-series- ?18O age-elevation model indicates that the (exposed) Amora sequence was deposited between ˜740 and 70 ka, covering seven glacial-interglacial cycles (Marine Isotope Stages (MIS) 18 to 5). Taking the last glacial Lake Lisan and the Holocene Dead Sea lacustrine systems as analogs of the depositional-limnological environment of Lake Amora, the latter oscillated between wet (glacial) and more arid (interglacial) conditions, represented by sequences of primary evaporites (aragonite and gypsum that require enhanced supply of freshwater to the lakes) and clastic sediments, respectively. The lake evolved from a stage of rapid shifts between high and low-stand conditions during ˜740 to 550 ka to a sabkha-like environment that existed (at the AC site) between 550 and 420 ka. This stage was terminated by a dry spell represented by massive halite deposition at 420 ka (MIS12-11). During MIS10-6 the lake fluctuated between lower and higher stands reaching its highest stand conditions at the late glacial MIS6, after which a significant lake level decline corresponds to the transition to the last interglacial (MIS5) low-stand lake, represented by the uppermost part of the Formation. ?18O values in the primary aragonite range between 6.0 and -1.3 ‰, shifting cyclically between glacial and interglacial intervals. The lowest ?18O values are observed during interglacial stages and may reflect short and intense humid episodes that intermittently interrupted the overall arid conditions. These humid episodes, expressed also by enhanced deposition of travertines and speleothems, seem to characterize the Negev Desert, and in contrast to the overall dominance of the Atlantic-Mediterranean system of rain patterns in the Dead Sea basin, some humid episodes during interglacials may be traced to southern sources.

Torfstein, Adi; Haase-Schramm, Alexandra; Waldmann, Nicolas; Kolodny, Yehoshua; Stein, Mordechai

2009-05-01

153

Glacial Legacies of New York State  

NSDL National Science Digital Library

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

Mcguire, Tom

154

Optimal hunting and Pleistocene extinction  

Microsoft Academic Search

A basic assumption of the Pleistocene extinction, or overkill hypothesis, is that rates of human predation on numerous genera of megafauna exceeded prey replacement rates. Previous assessments of this hypothesis have often stressed the technological or organizational capabilities of Paleolithic hunters to harvest prey in sufficient numbers to threaten extinction. Optimal foraging models and ethnographic observations of modern hunters-gatherers provide

David Webster; Gary Webster

1984-01-01

155

Dynamics of Pleistocene population extinctions in Beringian brown bears.  

PubMed

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

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

2002-03-22

156

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

NASA Astrophysics Data System (ADS)

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

Gaigalas, Algirdas; Fedorowicz, Stanis?aw

2009-10-01

157

Shorelines of Glacial Lake Hitchcock  

NSDL National Science Digital Library

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

Newton, Bob

158

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

NASA Astrophysics Data System (ADS)

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.

Liu, Tanzhuo; Broecker, Wallace S.

2013-04-01

159

Science Sampler: Glacial ice action  

NSDL National Science Digital Library

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

Bourdeau, Virginia

2008-10-01

160

The Last Glacial Maximum.  

PubMed

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

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

2009-08-01

161

The last glacial maximum  

USGS Publications Warehouse

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

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

2009-01-01

162

Glacial-interglacial organic carbon record fromthe Makassar Strait, Indonesia: implications for regional changes in continental vegetation  

Microsoft Academic Search

Recent studies convincingly show that climate in the Western Pacific Warm Pool and other equatorial\\/tropical regions was significantly colder (by B3-4? 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

Katherine Visser; Robert Thunell; Miguel A. Goni

163

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

PubMed

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

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

2013-05-15

164

New mitochondrial DNA data affirm the importance of Pleistocene speciation in North American birds.  

PubMed

The timing of origin of modern North American bird species in relation to Pleistocene glaciations has long been the topic of significant discussion and disagreement. Recently, Klicka and Zink (1997) and Avise and Walker (1998) enlivened this debate by using calibrated molecular distance values to estimate timing of speciations. Here we use new molecular studies to test their conclusions. Molecular distance values for 39 pairs of proven sister species, 27 of which are based on new data, alter the currently perceived pattern that avian species splits occurred mainly in the Pliocene and early-mid-Pleistocene. Mitochondrial DNA divergence values for this set of taxa showed a skewed distribution pointing toward relatively young speciation times, in contrast to the pattern presented by Klicka and Zink (1997) for 35 sister plus non-sister species pairs. Our pattern was not significantly different from that of Avise and Walker (1998) for "intraspecific phylogroups," some of which are species. We conclude that the entire Pleistocene, including the last two glacial cycles (<250,000 years ago), was important in speciations of modern North American birds. A substantial number of speciations were both initiated and completed in the last 250,000 years. Simultaneously, many taxa began to diverge in the Pleistocene but their speciations are not yet complete (per Avise and Walker 1998). The suggestion that durations of speciations average two million years is probably a substantial overestimate. PMID:15212392

Johnson, Ned K; Cicero, Carla

2004-05-01

165

Geochemistry of glacial sediments in the area of the Bend massive sulfide deposit, north-central Wisconsin  

USGS Publications Warehouse

Geochemical exploration in northern Wisconsin has been problematic because of thick glacial overburden and complex stratigraphic record of glacial history. To assess till geochemical exploration in an area of thick glacial cover and complex stratigraphy samples of glacial materials were collected from cores from five rotasonic boreholes near a known massive sulfide deposit, the Bend deposit in north-central Wisconsin. Diamond drilling in the Bend area has defined a long, thin zone of mineralization at least partly intersected at the bedrock surface beneath 30-40 m of unconsolidated glacial sediments. The bedrock surface has remnant regolith and saprolite resulting from pre-Pleistocene weathering. Massive sulfide and mineralized rock collected from diamond drill core from the deposit contain high (10s to 10,000s ppm) concentrations of Ag, As, Au, Bi, Cu, Hg, Se, Te, and Tl. Geochemical properties of the glacial stratigraphic units helped clarify the sequence and source areas of several glacial ice advances preserved in the section. At least two till sheets are recognized. Over the zone of mineralization, saprolite and preglacial alluvial and lacustrine samples are preserved on the bedrock surface in a paleoriver valley. The overlying till sheet is a gray, silty carbonate till with a source hundreds of kilometers to the northwest of the study area. This gray till is overlain by red, sandy till with a source to the north in Proterozoic rocks of the Lake Superior area. The complex glacial stratigraphy confounds down-ice geochemical till exploration. The presence of remnant saprolite, preglacial sediment, and far-traveled carbonate till minimized glacial erosion of mineralized material. As a result, little evidence of down-ice glacial dispersion of lithologic or mineralogic indicators of Bend massive sulfide mineralization was found in the samples from the rotasonic cores. This study points out the importance of determining glacial stratigraphy and history, and identifying favorable lithologies required for geochemical exploration. Drift prospecting in Wisconsin and other areas near the outer limits of the Pleistocene ice sheets may not be unsuccessful, in part, because of complex stratigraphic sequences of multiple glaciations where deposition dominates over erosion. ?? 2004 Elsevier B.V. All rights reserved.

Woodruff, L. G.; Attig, J. W.; Cannon, W. F.

2004-01-01

166

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

NASA Astrophysics Data System (ADS)

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

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

167

The legacy of Pleistocene glaciation and the organization of lowland alluvial process domains in the Puget Sound region  

NASA Astrophysics Data System (ADS)

Alluvial rivers of the eastern Puget lowland, a landscape shaped by scour and fill from the Cordilleran ice sheet, continue to respond to patterns of deposition and scour by the last-glacial-age ice sheet 18,000 years after deglaciation. Topography revealed by valley cross sections created from high resolution LIDAR digital elevation models shows that rivers are aggrading in valleys eroded by subglacial runoff and degrading in valleys incised by rivers post-glaciation. Slope-area analysis of river profiles shows that profile concavity varies systematically between river segments in the two valley contexts. Concavity indices ( ?) in mountain headwaters (0.3 < ? < 0.9) compare to those of many world rivers (0.2 < ? < 1.0), but in the lowlands these indices differ between valleys created by subglacial fluvial erosion (5 < ? < 45) and post-glacially incised river valleys that grade to base levels set by these relict glacial valleys or by post-glacial sea levels (1 < ? < 7). Dramatic differences in river pattern, landforms, and dynamics occur in valleys having contrasting (aggrading vs. degrading) and incomplete responses to Pleistocene glaciation, creating discrete valley-scale heterogeneities in fluvial process domains along and between rivers. These results point to the importance of valley-scale organization of alluvial process domains along and between rivers having profiles remaining in disequilibrium from Pleistocene glaciation. They also point to the potential usefulness of slope-area analysis of longitudinal profiles in distinguishing among different river valley process domains in lowland alluvial landscapes.

Collins, Brian D.; Montgomery, David R.

2011-03-01

168

Surface Water Variations During Late Pleistocene Sapropel Formation in the Mediteranean Sea: Results of Isotope and Geochemical Analyses  

NASA Astrophysics Data System (ADS)

The formation of Mediterranean sapropels has been attributed to orbitally-induced climate change and associated watermass circulatory modulation. The development of deep-water anoxia and enhanced surface productivity, two potential consequences of flow modification, are important conditionings for sapropel formation. These processes would have been affected by changes in surface water circulation that are driven by variations in temperature and salinity. These constraints may be used to understand the mechanism of sapropel formation across the entire basin. To assess surface water salinity and temperature variations, samples were selected along a basin-wide transect (ODP Sites 977, 975, 963, 964, 969, and 967). Single-species planktonic foraminifera were isolated, split and analyzed for O-18 and Mg/Ca ratios. Throughout the Late Pleistocene high amplitude oscillations (as much as 4ppt) in the O-18values are associated with glacial/interglacial transitions suggesting major changes in surface salinities. Throughout the transect, relative salinity minima are associated with sapropel formation. Oxygen isotope averages generally co-vary along the W-E salinity gradient with notable anomalies that may be attributed to local circulation (Site 974) and significant Nile discharge (Site 967). Sea-surface temperatures derived from Mg/Ca ratios generally follow O-18 signatures. There is a slight decoupling associated with deglaciation where O-18 minima lead maximum Mg/Ca ratios. Overall, sapropel events are coeval with sea surface warming which, when combined with lower salinities, contribute to reduced deep ventilation. Such conditions are evident at Sites 967 and 969, where critical components of deep and intermediate waters are formed. Differential salinity and temperature gradients between eastern and western basins suggests modes of differential sedimentary organic preservation across the transect.

Howell, M. W.; Miller, J.; Schrag, D.; Billups, K.

2001-12-01

169

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

PubMed

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

Berkland, J O; Raymond, L A

1973-08-17

170

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

SciTech Connect

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

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

1990-02-20

171

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

PubMed

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

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

2013-02-05

172

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

173

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

NASA Astrophysics Data System (ADS)

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.

Tormey, Daniel

2010-11-01

174

Molecular biogeography of Europe: Pleistocene cycles and postglacial trends  

PubMed Central

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

Schmitt, Thomas

2007-01-01

175

Paleotopography of glacial-age ice sheets  

Microsoft Academic Search

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

R. L. Edwards

1995-01-01

176

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

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

177

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

USGS Publications Warehouse

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

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

2010-01-01

178

Chronology for fluctuations in late pleistocene Sierra Nevada glaciers and lakes  

SciTech Connect

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

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

1996-11-01

179

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

PubMed

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

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

2001-03-22

180

Molecular evidence for Pleistocene refugia at the eastern edge of the Tibetan Plateau.  

PubMed

The role of the Quaternary ice ages in forming the contemporary genetic structure of populations has been well studied in a number of global regions. However, due to the different nature of glaciations and complex topography, their role in shaping eastern Eurasian genetic diversity, particular in areas surrounding the Tibetan Plateau have remained largely unstudied. We aimed to address this question by examining the genetic structure of an alpine forest-associated taxon, the blood pheasant (Ithaginis cruentus) to infer its phylogeographic history. We detected three phylogenetic lineages and four current population groups. By comparing molecular and palaeovegetation data, we found that major glaciations during the Pleistocene have had a major impact upon the current genetic diversity of this species. Coalescent simulations indicate that the populations retreated to different refugia during some glacial periods in the Pleistocene, but persisted through the last glacial maximum (LGM). The most significant recent population expansion was found to have occurred before the LGM, during which palaeoclimatic data indicate that the climate was both warmer and wetter than today. In contrast, during the LGM populations may have adopted an altitudinal shift strategy in order to track changes in alpine glaciers, exemplifying a general response for montane species in the region where alpine glaciations were not large enough to cause qualitative changes in vegetation. Although analysis based on a plumage related gene showed that divergent selection may have contributed to current patterns of intra-specific diversity, demographic isolation is inferred to have played a more dominant role. PMID:21689184

Zhan, Xiangjiang; Zheng, Yifang; Wei, Fuwen; Bruford, Michael W; Jia, Chenxi

2011-06-20

181

African climate change and faunal evolution during the Pliocene–Pleistocene  

Microsoft Academic Search

Environmental theories of African faunal evolution state that important evolutionary changes during the Pliocene–Pleistocene interval (the last ca. 5.3 million years) were mediated by changes in African climate or shifts in climate variability. Marine sediment sequences demonstrate that subtropical African climate periodically oscillated between markedly wetter and drier conditions, paced by earth orbital variations, with evidence for step-like (±0.2 Ma)

Peter B. deMenocal

2004-01-01

182

African climate change and faunal evolution during the Pliocene-Pleistocene  

Microsoft Academic Search

Environmental theories of African faunal evolution state that important evolutionary changes during the Pliocene-Pleistocene interval (the last ca. 5.3 million years) were mediated by changes in African climate or shifts in climate variability. Marine sediment sequences demonstrate that subtropical African climate periodically oscillated between markedly wetter and drier conditions, paced by earth orbital variations, with evidence for step-like (+\\/-0.2 Ma)

Peter B. Demenocal

2004-01-01

183

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

PubMed

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

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

1992-07-15

184

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

NASA Astrophysics Data System (ADS)

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

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

2005-08-01

185

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

NASA Astrophysics Data System (ADS)

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

Mange, Maria A.; Otvos, Ervin G.

2005-12-01

186

Onset of “Hudson Strait” Heinrich events in the eastern North Atlantic at the end of the middle Pleistocene transition (?640 ka)?  

Microsoft Academic Search

Heinrich events are well documented for the last glaciation but little is known about their occurrence in older glacial periods of the Pleistocene. Here we report scanning XRF and bulk carbonate ?18O results from Integrated Ocean Drilling Program (IODP) Site U1308 (re-occupation of Deep Sea Drilling Project (DSDP) Site 609) that are used to develop proxy records of ice-rafted detritus

David A. Hodell; James E. T. Channell; Jason H. Curtis; Oscar E. Romero; Ursula Röhl

2008-01-01

187

The Mid-Pleistocene Transition: Deep Sea Temperature And Global Ice Volume From Mg/Ca and ?18O In Benthic Foraminifera  

NASA Astrophysics Data System (ADS)

The mid-Pleistocene transition (MPT), which occurred between ~1 to 0.7 Ma, is recorded in benthic foraminiferal oxygen isotope (?18Ob) records as a shift in the periodicity of northern hemisphere glaciations from low amplitude 41-kyr to large amplitude 100-kyr glacial-interglacial cycles. The MPT has variably been attributed to either global cooling associated with a long-term decreasing trend in greenhouse gases, or changes in internal ice sheets dynamics, independent of changes in atmospheric pCO2. Evidence in support of global cooling during the MPT is inconclusive. Whereas, sea surface temperature (SST) records from upwelling regions show a cooling trend throughout the Pleistocene, no discernible SST trend is observed in the Western Pacific Warm Pool (WPWP). The ostracode Mg/Ca record of Dwyer et al., (1995) suggests a cooling from the late Pliocene to Pleistocene, but the record is of low resolution and does not document the transition. Here we present a new high-resolution record of benthic foraminifera Mg/Ca from North Atlantic DSDP site 607. The Mg/Ca-based bottom water temperature (BWT) allows us to quantify the extent of global cooling and, paired with ?18Ob, to estimate the concomitant increase in ice volume. The new BWT record shows a shift in both the periodicity (from ~41 to 100 kyr) and amplitude (from ~2 to 4° C) of glacial-interglacial cycles from the late Pliocene-early Pleistocene to the late Pleistocene, and is generally coherent with the ?18Ob record. Across the MPT, glacial periods become progressively cooler and suggest a long term cooling of ~2° C associated with the increase in ice volume. The long term cooling of the high latitude, as recorded in BWT, in contrast with the stability of WPWP SST suggests that changes in meridional transport of heat and moisture might have played a key role in the MPT.

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

2006-12-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

189

North Atlantic climate evolution through the Plio-Pleistocene climate transitions  

NASA Astrophysics Data System (ADS)

During the Plio-Pleistocene, the Earth witnessed the growth of large northern hemisphere ice sheets and profound changes in both North Atlantic and global climate. Here, we present a ~ 3.2 Myr long, orbitally-resolved alkenone sea surface temperature (SST) record from Deep Sea Drilling Project (DSDP) Site 607 (41°N, 33°W, water depth 3427 m) in the North Atlantic Ocean. We employ a multi-proxy approach comparing these new observations with existing bottom water temperature (BWT) and stable isotope time series from the same site and SST time series from other sites, shedding new light on Plio-Pleistocene climate change. North Atlantic temperature records show a long-term cooling with two major steps occurring during the late Pliocene (3.1 to 2.4 Ma) and the mid-Pleistocene (1.5 to 0.8 Ma), closely timed with intervals of major change in northern hemisphere ice sheets. Existing evidence suggests that the late Pliocene cooling may have been caused by a thresholded response to secular changes in atmospheric carbon dioxide (CO 2). While an explanation for the mid-Pleistocene cooling may involve glacial-interglacial changes in atmospheric CO 2, it seems to also require a change in the behavior of the ice sheets themselves. North Atlantic climate responses were closely phased with benthic oxygen isotope (? 18O) changes during the "41 kyr world," indicating a strong common northern hemisphere high latitude imprint on North Atlantic climate signals. After the mid-Pleistocene transition (MPT), North Atlantic SST records and the Site 607 benthic carbon isotope (? 13C) record are more closely phased with ? 18O, whereas BWT significantly leads ? 18O in the 100 kyr band, suggesting a shift from a northern to a southern hemisphere influence on North Atlantic BWT. We propose that the expansion of the West Antarctic ice sheet (WAIS) across the MPT increased the production and export of Antarctic Bottom Water from the Southern Ocean and subsequently controlled its incursion into the North Atlantic, especially during glacial intervals. It follows that the early 100 kyr response of BWT implies an early response of the WAIS relative to the northern hemisphere deglaciation. Thus, in the "100 kyr world," both northern hemisphere and southern hemisphere processes affect climate conditions in the North Atlantic Ocean.

Lawrence, K. T.; Sosdian, S.; White, H. E.; Rosenthal, Y.

2010-12-01

190

Effects of climatic and geological processes during the pleistocene on the evolutionary history of the northern cavefish, Amblyopsis spelaea (teleostei: amblyopsidae).  

PubMed

Climatic and geological processes associated with glaciation cycles during the Pleistocene have been implicated in influencing patterns of genetic variation and promoting speciation of temperate flora and fauna. However, determining the factors promoting divergence and speciation is often difficult in many groups because of our limited understanding of potential vicariant barriers and connectivity between populations. Pleistocene glacial cycles are thought to have significantly influenced the distribution and diversity of subterranean invertebrates; however, impacts on subterranean aquatic vertebrates are less clear. We employed several hypothesis-driven approaches to assess the impacts of Pleistocene climatic and geological changes on the Northern Cavefish, Amblyopsis spelaea, whose current distribution occurs near the southern extent of glacial advances in North America. Our results show that the modern Ohio River has been a significant barrier to dispersal and is correlated with patterns of genetic divergence. We infer that populations were isolated in two refugia located north and south of the Ohio River during the most recent two glacial cycles with evidence of demographic expansion in the northern isolate. Finally, we conclude that climatic and geological processes have resulted in the formation of cryptic forms and advocate recognition of two distinct phylogenetic lineages currently recognized as A. spelaea. PMID:23550752

Niemiller, Matthew L; McCandless, James R; Reynolds, R Graham; Caddle, James; Near, Thomas J; Tillquist, Christopher R; Pearson, William D; Fitzpatrick, Benjamin M

2012-12-20

191

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

PubMed Central

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

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

2012-01-01

192

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

PubMed

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

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

2012-12-21

193

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

194

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

PubMed

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

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

2006-12-19

195

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

Microsoft Academic Search

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

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

2011-01-01

196

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

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

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

2011-03-25

197

Glacial climate in the tropics  

SciTech Connect

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

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

1996-06-28

198

Pleistocene lake level changes in Western Mongolia  

Microsoft Academic Search

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

P. S. Borodavko

2009-01-01

199

Evolution of the nocturnal Nearctic Sphaeropthalminae velvet ants (Hymenoptera: Mutillidae) driven by Neogene orogeny and Pleistocene glaciation.  

PubMed

The influence of historical climatic and geological changes on patterns of species diversification was investigated in a widely distributed group of North American nocturnal mutillids (Hymenoptera: Mutillidae: Sphaeropthalminae), with particular focus on Pleistocene glacial cycles and earlier patterns of Neogene mountain building. We collected molecular data from two nuclear intergenic regions (internal transcribed spacer regions 1 and 2; approximately 2600 bp in total) to produce the first phylogeny of nocturnal Nearctic mutillids. Bayesian inference of the combined data returned a well-resolved tree with posterior probabilities of over 95% for most nodes. This tree suggested the monophyly of the nocturnal, primarily Nearctic, Sphaeropthalminae genera, but the paraphyly of the three largest genera (Odontophotopsis, Photomorphus and Sphaeropthalma). Dates of species divergences were obtained using r8s (PL and NPRS) and BEAST with the date of Dominican amber set at three different dates (15 Ma, 20 Ma, and 45 Ma) to account for uncertainty in the fossil age. The derived dates ranged from the Pleistocene to the Middle Miocene, suggesting that both recent Pleistocene glaciation cycles and older orogenic events, albeit to a somewhat greater extent, were both causes of major diversification in western North America. Examination of other phylogeographical studies using North American desert taxa indicated that diversification patterns are explained by either mountain building or Pleistocene climate change, depending on the taxa in question. PMID:20363339

Pitts, James P; Wilson, Joseph S; von Dohlen, Carol D

2010-04-02

200

Glacially driven sequence development in an active pull apart basin, eastern Austria  

NASA Astrophysics Data System (ADS)

Austria's largest Pleistocene Basin, the Mitterndorf Basin, formed as a releasing bend along the sinistral strike-slip Vienna Basin Transfer fault. It extends over an area of about 270 km² along the eastern most limits of the Alps. Two mountain front alluvial fans toe out into the southern basin while the northern part is covered by extensive floodplain deposits. Subsidence can be constrained to start somewhere around the late Middle Pleistocene. Accommodation space was provided by vertical slip rates of approx. 0.5 - 1 mm/a. Since that time sediments were preserved, providing a sedimentological archive reflecting climate change and the associated change in lithofacies. During glacial periods, periglacial conditions and low vegetation density in the Alpine hinterland caused high sediment supply which is manifested in up to 35 m thick coarse grained, massive fluvial facies. Transport of material was mainly provided by nival streams under bed load conditions. With the end of glacial periods, the switch to high discharge to sediment supply ratios generally leads to fluvial incision. Intersection points of the main interfan channels are shifting from the apex downstream. The formation of overbank fines at the distal fan position and along the entire floodplain of the basin mark a switch from braided to meandering conditions. The effect of subsidence becomes now more important as sediment supply is decreased, resulting in alluvial fan headcut erosion, and, if sufficient time is available, may lead to total through trenching. In the stratigraphic record sequences which are associated with warm periods are generally not exceeding some dm to m. Fan surfaces which got abandoned are exposed to widespread soil formation which mark sequence boundaries to the following coarse grained, massive facies of glacial periods. Generally the fluvial facies in the Mitterndorf Basin is shown to be deposited in stratigraphic cycles controlled by the impacts of Glacials and Interglacials and, as a long term effect, by subsidence. Effects of different vertical displacement velocities on the basin's sequence development could be described by using high resolution fault information. Precise age and climate relevant information derive from rich terrestrial mollusc assemblages, 14C and OSL data covering times from late Middle Pleistocene up to the Holocene.

Salcher, B.; Wagreich, M.

2009-04-01

201

Paleotopography of glacial-age ice sheets  

SciTech Connect

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.

Edwards, R.L. [Univ. of Minnesota, Minneapolis, MN (United States)

1995-01-27

202

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

NASA Astrophysics Data System (ADS)

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

Barrows, Timothy T.; Hope, Geoffrey S.; Prentice, Michael L.; Fifield, L. Keith; Tims, Stephen G.

2011-09-01

203

Constraints on the Pleistocene chronology of sediments from the Lomonosov Ridge  

NASA Astrophysics Data System (ADS)

Despite its importance in the global climate system, age-calibrated marine geologic records reflecting the evolution 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.

O'Regan, Matthew; King, John; Backman, Jan; Jakobsson, Martin; PäLike, Heiko; Moran, Kathryn; Heil, Clifford; Sakamoto, Tatsuhiko; Cronin, Thomas M.; Jordan, Richard W.

2008-03-01

204

Glaciers and Late Quaternary glacial deposits of Turkey  

NASA Astrophysics Data System (ADS)

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.

Çiner, A.

2003-04-01

205

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

Microsoft Academic Search

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

STEPHEN C. PORTER; TERRY W. SWANSON

2008-01-01

206

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

Microsoft Academic Search

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

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

207

Synchronous glacial response to changing patterns of precipitation across the central Andes during the last glacial termination  

NASA Astrophysics Data System (ADS)

Quantifying paleoclimatic conditions and past climate change is fundamental to advancing understanding of the Earth's climate and improving our ability to predict future climate change. Glacial records provide a means to constrain the timing and magnitude of past climate change within the terrestrial realm and can be integrated with other paleoclimate proxies to help elucidate the dynamic interactions, feedbacks, and teleconnections within the climate system. Here we present glacial chronologies from a suite of high-altitude peaks that span the tropical-subtropical central Andes of South America and compare these results to paleoclimatic records derived from marine, lake, landslide, and ice-core archives. The central Andes lie at the transition between humid tropical climates in the north and arid subtropical climates to the south, making the region particularly sensitive to changing precipitation patterns. Previous studies have spurred debate as to whether glacier advance throughout the central Andes was regionally synchronous due to broad-scale climatic forcing or asynchronous due to localized climatic perturbations and whether or not tropical-subtropical glacial chronologies are in phase with Northern Hemisphere ice sheets. Here we show that glacial advance and retreat in the high central Andes was synchronous throughout the last glacial-interglacial transition and was predominantly driven by large-scale shifts in atmospheric circulation and changing patterns of precipitation. The timing of glacial advance coincides with periods of high lake levels on the Puna-Altiplano plateau, increased snow accumulation revealed by tropical ice-cores, and enhanced landslide activity. These data reveal an Early Glacial ice advance and regionally wet conditions prior to ~22-25 ka followed by a relatively dry period during the Northern Hemisphere glacial maximum (~21 ka). Subsequently, the central Andes experienced a pronounced increase in moisture and a substantial readvance of alpine glaciers from ~15-17 ka, coincident with Heinrich Event 1. Following this major readvance, glaciers retreated rapidly with a minor advance/standstill during the Younger Dryas/Antarctic cold reversal at ~11-14 ka. In the arid southern central Andes, glaciers vanished from the high peaks by ~8-9 ka, whereas in the northern regions, more humid conditions allow glaciers to persist to the present day. We further show that humid conditions and glacial advances in the central Andes are in phase with periods of reduced Atlantic thremohaline circulation and proposed southerly shifts in the mean position of the Inter Tropical Convergence Zone (ITCZ). Although large-scale shifts in the ITCZ may be the dominant source of hydroclimatic variability, we suggest that additional changes in the intensity of the El Nino Southern Oscillation and/or shifts in the annual timing of monsoonal moisture delivery may further amplify (or dampen) the regional impact of global climate change.

Clarke, B. A.; Strecker, M. R.; Bookhagen, B.; Wittmann, H.; Rood, D. H.

2011-12-01

208

Ice-free conditions in north central British Columbia during the Last Glacial Maximum?  

NASA Astrophysics Data System (ADS)

Biological remains and magnetic susceptibility analyses of radiometrically dated sediments from Babine Lake (54 49’N, 126 07’W) in north-central British Columbia, Canada indicate that lacustrine conditions existed at the last glacial maximum (LGM) in the Canadian Cordillera. AMS radiocarbon dating on pollen concentrates from lake sediments between 6 and 7.5 metres below the surface sediment - water interface resulted in ages ranging from 11 to 23 KBP. Although there are two inversions in the radiocarbon ages, all are Pleistocene in age and are much older than the expected Holocene age of the lake. Pollen abundance and diversity are relatively low with spruce and pine dominating the pollen assemblages and reflect what the primary conifer genera would be on non-glaciated landscapes during the LGM. The pollen recovered in the samples is in excellent condition and does not appear to be reworked. The presence of Cladocera (water fleas) in the sediment strongly support our hypothesis that standing water or lacustrine conditions occurred at the site at a time when it is generally assumed most of the land was covered with the Cordilleran ice sheet. Magnetic susceptibility measurements suggest that after a period of instability, sediment deposition appears to have been relatively constant until the end of the Pleistocene. The data presented here indicates Babine Lake maintained some level of non-glaciated surface during the LGM and, along with other data from central British Columbia, suggests the possibility of a non-coalesced Cordilleran Ice sheet during the latest Pleistocene glaciation.

Pellatt, M. G.; Lacourse, T.

2009-12-01

209

Overdeepenings in glacial systems: Processes and uncertainties  

NASA Astrophysics Data System (ADS)

Workshop on Glacial Overdeepening; Zurich, Switzerland, 20-21 April 2012 Glacially overdeepened valleys and basins are common features in high mountain belts and their forelands. These overdeepenings are of practical and scientific interest, representing sites of potential lake formation; influencing the dynamics and hydrology of ice masses; presenting opportunities for glacial and climate reconstruction; and raising management issues related to aggregate, groundwater, and hydrocarbon resources and radioactive waste disposal in deep geological repositories. Although the basic principles of glacial erosion are generally known, the formation of overdeepened valleys beneath glaciers and ice sheets remains incompletely understood.

Fischer, Urs H.; Haeberli, Wilfried

2012-08-01

210

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

PubMed Central

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

2012-01-01

211

Invertebrate drift in a glacial river and its non-glacial tributary  

Microsoft Academic Search

SUMMARY 1. Invertebrate drift was studied in a glacially fed river and a non-glacial tributary in western Norway. Samples were taken during two consecutive 24-h periods in May, July and October 1997. The 3 months are characterized by snowmelt, ice melt and rainfall runoff, respectively. The main glacial river has colder, more turbid water, especially during the period of maximum

S. J. Saltveit; I. Haug; J. E. Brittain

2001-01-01

212

Braided oscillators  

NASA Astrophysics Data System (ADS)

A generalized oscillator algebra is proposed and the braided Hopf algebra structure for this generalized oscillator is investigated. Using the solutions for the braided Hopf algebra structure, two types of braided Fibonacci oscillators are introduced. This leads to two types of braided Biedenharn-Macfarlane oscillators as special cases of the Fibonacci oscillators. We also find the braided Hopf algebra solutions for the three dimensional braided space. One of these, as a special case, gives the Hopf algebra given in the literature.

Yildiz, A.

2002-03-01

213

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

214

Connecting Soils and Glacial Geology  

NSDL National Science Digital Library

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

Dolliver, Holly

215

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

Microsoft Academic Search

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

Cajus G. Diedrich

216

Glacial effects limiting mountain height.  

PubMed

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

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

2009-08-13

217

Electrokinetic remediation of metal contaminated glacial tills  

Microsoft Academic Search

This paper presents the results of an experimental investigation which studied the feasibility of using the electrokinetic process to remediate contaminated clays of glacial origin, otherwise known as glacial tills. An overview of the electrokinetic phenomena, as well as previously performed laboratory and field investigations, is first presented. The methodology of the electrokinetic experiments which were conducted to investigate the

K. R. Reddy; A. B. Shirani

1997-01-01

218

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

NASA Astrophysics Data System (ADS)

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

Vaughan-Hirsch, David

2013-04-01

219

Glacial-driven vicariance in the amphipod Gammarus duebeni.  

PubMed

We have examined the genetic diversity using mitochondrial COI and ND2 sequence data from 306 specimens of the amphi-Atlantic-distributed amphipod Gammarus duebeni. Marine populations from the Atlantic Ocean, the Baltic and North Sea, as well as freshwater populations from Ireland, Cornwall and Brittany were analysed. G. duebeni is a complex of five allopatric lineages. Freshwater populations result from multiple invasions of marine ancestors, represented by distinct lineages. We interpret the recent distribution of lineages as the outcome of a series of spatio-temporal vicariant events caused by Pleistocene glaciations and sea level changes. The freshwater lineages are therefore regarded as 'glacial relicts'. Furthermore, inter-specific competition with, for example, Gammarus pulex (which is absent in Ireland and western Brittany) may be another important determinant in the distribution of freshwater G. duebeni. In Ireland and Brittany, three freshwater refugia are suggested. The significantly limited gene flow detected among marine populations is more likely due to inter-specific competition than to salinity. The G. duebeni-complex represents a model system for the study of allopatric speciation accompanied by major habitat shifts. The pattern of spatio-temporal origins of the freshwater entities we describe here provides an excellent system for investigating evolutionary adaptations to the freshwater environment. Our data did not confirm the presently used subspecies classification but are only preliminary in the absence of nuclear genetic analyses. PMID:19654046

Krebes, L; Blank, M; Jürss, K; Zettler, M L; Bastrop, R

2009-08-03

220

Radiolarian Indices of Paleoproductivity Variation in the late Pleistocene Benguela Upwelling System, ODP Site 1084  

NASA Astrophysics Data System (ADS)

Changes in export productivity play a significant role in ocean carbon budgets and global climate change. Proxies for export productivity can be difficult to interpret: benthic foraminifera accumulation rates (BFAR) can be affected by carbonate dissolution in organic-carbon rich sediments; bulk opal can be affected by silica limitation of source waters. Recent work (Lazarus et al. 2006; Mar. Micropal.) has shown that a new index based on radiolarian faunal changes (WADE ratio) correlates well to total organic carbon (TOC) values from the same samples over the long term (latest Miocene-Recent) history of productivity in the Benguela Upwelling System (BUS). We present new data on variation in export productivity proxies (WADE, TOC, carbonate, radiolarian opal, BFAR) for the last glacial-interglacial cycle from ODP Site 1084, located just offshore from the main coastal upwelling cells of the BUS. Our age model, from mean Quaternary sedimentation rates (Leg 175 Scientific Results), is in accordance with cyclic variation in other climate sensitive parameters (carbonate and color reflectance). Although opal content and radiolarian preservation is only moderate in our samples, WADE values vary significantly and suggest higher productivity during the last glacial, in accordance with current interpretations of BUS history. Radiolarian opal accumulation is also higher during the last glacial, suggesting that silica limitation (opal paradox) conditions did not dominate over this time period. Similar results for bulk opal have been reported from late Quaternary piston cores from the more northerly Congo upwelling region (Schneider et al, 1997; Paleoc.). We conclude that WADE ratios are a useful proxy for late Pleistocene productivity in the BUS at glacial- interglacial time scales.

Bittniok, B. B.; Lazarus, D. B.; Diester-Haass, L.; Billups, K.; Meyers, P.

2006-12-01

221

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

NASA Astrophysics Data System (ADS)

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.

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

2008-04-01

222

Younger Dryas paleotopographic modeling of the Northwestern Outlet of glacial Lake Agassiz  

Microsoft Academic Search

Overflow from glacial Lake Agassiz has been implicated in altering thermohaline circulation in the North Atlantic Ocean, and in bringing about widespread cooling at several times, namely during the Younger Dryas, the PreBoreal Oscillation, and the 8.2 ka event. The eastward routing of overflow from Lake Agassiz into the Great Lakes-St. Lawrence during the Younger Dryas has been questioned recently,

J. T. Teller; Z. Yang

2009-01-01

223

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)

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.

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

224

Towards understanding the role of the Bering Strait in the Plio-Pleistocene climate change  

NASA Astrophysics Data System (ADS)

The Bering Strait is the gateway between Pacific and Arctic, plays an important role in global freshwater cycle and eventually influences on climate change. The glacial Pacific Ocean had well-ventilated and nutrient-depleted glacial North Pacific Intermediate Water (GNPIW) above ~2000 m. GNPIW is a thicker and more deeply penetrating water mass than today's North Pacific Intermediate Water (NPIW). The source of GNPIW was likely in the Bering Sea based on neodymium isotope evidence. During Heinrich Event 1 in the early deglacial period, deep water extending to a depth of ~2500 m formed in the North Pacific. Modeling simulations suggest that a closed Bering Strait is essentially required for salinity built-up in the North Pacific to form the deep water. First opening of the Bering Strait was suggested to be in the latest Miocene and have repeated opening and closure by eustatic sea-level change associated with climate changes. However, our knowledge on the history about the opening/closure is limited due to lack of appropriate samples. During the IODP Expedition 323, Pliocene to Pleistocene marine sediment was continuously recovered from the Bering Sea. At the northern Bering continental slope sites (U1343 and U1344), the period with high abundance of diatom species Neodenticula seminae is terminated around 0.8-0.9 Ma, which appears to coincide with the Mid-Pleistocene Transition (MPT). While Neodenticula seminae is an endemic and predominant diatom in the modern subarctic Pacific and the Aleutian basin of the Bering Sea, the occurrence of this species is reported from the sediments between 0.84 and 1.25 Ma in the northern North Atlantic. This suggests a significantly intensified Arctic Throughflow and adaptive environment for N. seminae production from the Bering Strait to the Greenland Sea during the MPT. The observations of hydrography and the modern re-appearance of this taxon since 1999 in the Labrador Sea due to the melting of the Arctic Sea ice also suggests the specific requirements by this species: low salinity and high dissolved silicon concentrations. During the glacial cycles of the last 800 kyr, a limited input of Pacific water into the Arctic Ocean or disconnection was suggested by decreased abundances of N. seminae. Furthermore, repeated abundance peaks of radiolarian species Cycladophora davisiana, indicating cold and well ventilated intermediate water, suggest enhancement of intermediate to deep water formation in the Bering Sea during glacial periods, when the Bering Strait was closed. This research used samples and data provided by the IODP. We acknowledge the IODP Expedition 323 Shipboard Scientists.

Okazaki, Y.; Onodera, J.; Teraishi, A.; Suto, I.

2011-12-01

225

Synchronous extinction of North America's Pleistocene mammals  

PubMed Central

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

Faith, J. Tyler; Surovell, Todd A.

2009-01-01

226

Synchronous extinction of North America's Pleistocene mammals.  

PubMed

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

Faith, J Tyler; Surovell, Todd A

2009-11-23

227

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

NASA Astrophysics Data System (ADS)

Stratigraphy and age control of late Pleistocene loess, associated glacial outburst flood deposits and flood-cut unconformities in the Channeled Scabland, Washington State, United States, indicate a significant Cordilleran ice sheet advance during marine Oxygen Isotope Stage 4. Glacial outburst flood deposits from stage 2 (classic Bretz flood deposits, ca 21 to 13 ka) and related features in the Channeled Scabland overlie a widespread layer of loess that contains buried soils and the Mount St. Helens set C tephra (ca 46 ka). This loess in turn overlies deposits of the penultimate episode of giant outburst floods and an unconformity cut by those floods. Regional trends in the thickness, texture, and overall composition of the older loess are strikingly similar to those from the youngest loess, known to be derived from stage 2 flood deposits. We conclude that the older loess also is derived from fine-grained flood deposits. Luminescence ages, tephrochronology, and soil development rates indicate that the bulk of deposition of the older loess occurred during stage 3, following glacial outburst flooding marked by a regional flood-cut unconformity. The apparent cyclical pattern of cold-climate buried soils, flood deposits, and thick loess accumulations demonstrate that sediment supply renewed by flood episodes is a major control on accumulation of loess on glacial timescales.

McDonald, Eric V.; Sweeney, Mark R.; Busacca, Alan J.

2012-06-01

228

Glacial geomorphology and geographic information systems  

NASA Astrophysics Data System (ADS)

Recent developments in the field of glacial geomorphology have dramatically increased the need to acquire, maintain, manipulate, and analyze large amounts of landform, landscape and sediment data. The use of Geographic Information Systems (GIS) has provided new platforms and tools for analysis and visualization of geomorphic data. Glacial geomorphologists have used GIS to integrate multi-source data, manage multi-scale studies, identify previously unrecognized spatial and temporal relationships and patterns in geomorphic data, and to link landform data with numerical models as part of model calibration and verification. GIS-based analyses associated with numerical modeling are improving our understanding of glacial landscape evolution and are allowing new quantitative and systematic examinations of spatial and temporal patterns of glacial landforms and processes. This has allowed for the development of insights and concepts that would be unlikely to arise using traditional methods alone. Key recommendations for future research and applications in glacial geomorphology include enhanced GIS education and dissemination, the development of standards and conventions for glacial geomorphic data, community projects to collect data into readily accessible databases, and enhanced use of linked GIS — model frameworks to address major issues in glacial geomorphology.

Napieralski, Jacob; Harbor, Jon; Li, Yingkui

2007-11-01

229

Expanding Ice Sheets on the Antarctic Peninsula during the Plio/Pleistocene Recorded in Continental Rise Sediment Drifts  

NASA Astrophysics Data System (ADS)

Sediment drifts on the continental rise west of the Antarctic Peninsula are located within 125 km from the continental shelf edge, the main contributor of terrigenous sediment during both glacial and interglacial periods. The composition of drift deposits continuously recorded changes in ice sheet volume and thermal regime as well as sea surface temperatures (SSTs) and sea ice extent. The coarse-grained terrigenous sediment (pebbles and coarse sand), a proxy for iceberg-rafted debris (IRD), was analyzed in sediments spanning the last 3.1 m.y. at Ocean Drilling Program (ODP) Sites 1101 and 1096. IRD is deposited in both glacial intervals, dominated by fine-grained laminated mud and interglacial units consisting of bioturbated muds enriched in biogenic components. Contents of biogenic opal, which reflect diatom abundance, are relatively high from 3.1-2.2 Ma. Calcareous nannofossils are present within interglacial sediments from 2.2-0.76 Ma. Both findings suggest warm SSTs and limited sea ice over the drifts during interglacial periods before the Late Pleistocene. Quartz grains picked from the IRD fraction and imaged with a scanning electron microscope (SEM) show an abrupt change in surface microtextures at 1.35 Ma. During the Late Pliocene to Early Pleistocene, many quartz grains are completely weathered and only a few show signs of crushing and abrasion, indicating that glaciers were too small to inundate the Antarctic Peninsula topography. Debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass unmodified through the glaciers. Glaciers expanded in size during glacial periods from 1.35-0.76 Ma. The IRD accumulation during those periods was very high and diverse dropstone lithologies document supply from sources throughout the Antarctica Peninsula. Conditions that spawned the large polar ice sheet identified at the Last Glacial Maximum have been present on the Antarctic Peninsula during glacial periods since approximately 0.76 Ma. Since then, IRD supply has been relatively low and maxima in IRD content occurred during interglacials when sedimentation rates were low. Pebble shapes indicate the dominance of basal glacial transport paths. Quartz sand grains show high relief, fracture and abrasion common under thick ice and dropstone lithologies are more restricted.

Cowan, E. A.; Hillenbrand, C.

2007-12-01

230

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

NASA Astrophysics Data System (ADS)

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

Zieli?ski, Tomasz

2007-01-01

231

Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition.  

PubMed

Earth's climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum. PMID:22879512

Elderfield, H; Ferretti, P; Greaves, M; Crowhurst, S; McCave, I N; Hodell, D; Piotrowski, A M

2012-08-10

232

OSL dating without sand lenses: Late Pleistocene alluvial fan aggradation in the Lost River Range, Idaho  

NASA Astrophysics Data System (ADS)

Along the western front of the Lost River Range (LRR) in Idaho, USA, numerous sheetflood-dominated alluvial fans extend 2-6 km from the mountain front. Despite their geomorphic significance within the basin, these fans are largely inactive under modern conditions and are hypothesized to be remnants of glacial climate (e.g. Pierce and Scott, 1982). To investigate climate and glaciation as potential drivers of fan aggradation, the first goal of this study was determining how best to apply optically stimulated luminescence (OSL) dating as deposits lacked sand lenses and were predominately clast-supported sheetflood gravels with a sandy matrix. The second goal of the study was to investigate the Quaternary climate conditions that promote alluvial fan aggradation, including the importance of glacial activity vs. general glacial climate conditions as drivers of sedimentation. Five fans that represent the variation in late Pleistocene glaciation within contributing basins (0-80% of basin area) were selected for dating and geomorphic mapping. Samples for OSL dating were largely collected by excavating material from under light-safe tarps or at night, with samples for equivalent dose estimates sieved to retain the <2mm portion. Sediment chemistry for dose rate (DR) estimation was analyzed for numerous grain sizes. Sand grain size fractions (<2 mm and 0.15-2.0 mm) produced the highest DR estimates, pebbles (>5 mm) the lowest, with results from bulk samples generally in between. Bulk sample DR estimates were preferred, likely providing the best estimate of the average dose from the sediment. Partial bleaching is not suggested by equivalent dose distributions, but overdispersion values of >20% for some samples may result from the heterogeneity in the sediment DR. Despite potential DR problems, resulting ages are consistent with fan morphology and multiple ages from single surfaces show good agreement. Ages from 31 OSL samples ranged from ~4-60 ka and with mapped fan surfaces suggest aggradation during four distinct intervals: 0-10 ka, 10-20 ka, 20-35 ka and 35-60 ka. Surprisingly, the timing of deposition is similar for all fans, regardless of past glacial extent within contributing basins. The majority of fan aggradation occurred during the late Pleistocene, with deposition during the Holocene limited to ~10% of total fan surface area. The greater extent of late Pleistocene surfaces, steeper slopes and dominance of coarser sheetflood facies suggests greater transport capacity of streams and sediment delivery to fans between 10-60 ka. Regional climate records indicate generally cold climate in the LRR throughout 10-60 ka, but more variable moisture delivery. Cold conditions may have increased transport capacity with greater effective moisture and higher spring discharges in response to increased winter snowpacks . Concurrently, sediment delivery may have increased by mobilization of stored hillslope sediment, decreased vegetation cover or increased sediment production by glaciation, enhanced weathering rates and more effective frost weathering. Overall, this research shows that glacial climate conditions, not necessarily glaciation, enhance hillslope sediment supply and fan aggradation in the LRR of Idaho.

Kenworthy, M.; Rittenour, T. M.; Pierce, J. L.

2011-12-01

233

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

SciTech Connect

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

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

1996-01-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

235

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

236

Canyon Creek: A late Pleistocene vertebrate locality in interior Alaska  

USGS Publications Warehouse

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

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

1981-01-01

237

Late Pleistocene marine transgression of North Slope coastal plain  

SciTech Connect

Two late Pleistocene marine transgressions of contrasting character are recorded by deposits of the Arctic coastal plain. Deposits of the oldest trangression extend from Harrison Bay west to near Barrow and contain a fauna that documents interglacial conditions. Five thermoluminescence (TL) dates on the marine deposits average 127 Ka and indicate a correlation with oxygen isotope stage 5e. Sedimentary structures characteristic of the swash zone occur at altitudes within the commonly accepted range (6 not equal 4m) for eustatic high sea level at that time, showing that this part of the coastal plain has been tectonically stable for the past 125,000 years. Deposits of the youngest transgression are glaciomarine sediments that contain ice-rafted erratics of Canadian provenance. They compose the flaxman member of the Gubik Formation and occur locally along the Beaufort Sea coast and inland to altitudes of about 7 m. TL dates on these sediments suggest that the Flaxman transgression occurred between 70 and 80 ka and is correlative with deposits dated to this interval that are exposed near sea level on the North Carolina coastal plain. However, the deep-sea oxygen-isotope record is commonly interpreted to indicate that sea level was below its modern position at that time. The present altitude of the Flaxman deposits cannot be attributed to tectonism because their distribution includes the part of the coastal plain determined to be tectonically stable for the past 125 ka. Isostatic depression and subsequent elevation are unlikely considering the correlative deposits of North Carolina. This paradox could be explained if enormous volumes of floating glacial ice were produced by the rapid breakup of a large part of the Laurentide ice sheet, and recent work indeed suggests that the Hudson Bay lowlands were ice free at this time.

Carter, L.D.

1985-04-01

238

Possible Mechanisms for Glacial Earthquakes  

NASA Astrophysics Data System (ADS)

Tsai and Ekstrom (JGR-ES, subm. 2006) presented a seismic source analysis of the recently discovered glacial earthquakes (MS ~ 4.6 - 5.1) in Greenland and identified a number of features that must be explained by any theory that fully describes them. Among the important features are mechanisms consistent with stick- slip motion of large masses of ice, pronounced seasonality in the timing of events, and occurrence only in regions of very high ice flow speeds. An open question is whether such earthquakes are an end member to a spectrum of episodic glacier motions, including surges, but following the same basic mechanisms, or whether they involve some fundamentally distinct process. Here, we present seven possible mechanisms for the initiation of glacial earthquakes and discuss them relative to observations. They are as follows: (1) shear failure with tensile crevassing of near-surface marginal ice, thus decreasing lateral support; (2) penetration of meltwater at high hydraulic head to the glacier bed, possibly aided by crevassing in the rapid ice flow and causing local pressure lift-off; (3) elevation of fluid pressure at the bed by changing subglacial drainage systems or merger of adjacent cavities; (4) generation of melt through shear heating, thus softening till or other bed material by increased porosity; (5) exhaustion of thermal strengthening in till deformation by frictional heating of pore fluid as temperature passes 4°C and weakening ensues; (6) other means of till instability at the glacier bed, such as transition to rate-weakening, possibly due to change of strain rate regime, or to dilatant strengthening with subsequent shear localization, or to breaking of force chains along locked arrays of boulder-like particles; and (7) calving induced stress changes. With suitable choice of parameters, models of all are able to qualitatively capture some observational features. For example, all models can produce inherently unstable sliding which lead to earthquake-like events; all models are modulated by annual temperature variations; and under the right conditions the models may have a limited size range over which they can generate earthquakes. However, many of the model parameters (e.g. basal water pressures and small-scale bed geometry) are poorly constrained by current observations. Some models depend sensitively on certain parameters (e.g. model (3) and changing basal water pressures) whereas others are insensitive to the same parameters (e.g. model (7)). While some major predictions can be made similar for the various models, or perhaps combinations of them, they will have predictions for secondary features which should help distinguish the correct model(s). For example, model (3) predicts smaller cavities prior to glacial earthquake events, model (4) predicts increased basal water pressures during events, and model (7) predicts large calving events occurring prior to events.

Tsai, V. C.; Rice, J. R.

2006-12-01

239

Glacial erosion and expected permafrost thickness of Fennoscandia and adjacent regions  

NASA Astrophysics Data System (ADS)

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

Amantov, Aleksey

2013-04-01

240

Martian Glacial Melt and Atmospheric Methane  

Microsoft Academic Search

We compare possible sources of basal melt in martian glaciers and find that methane hydrate clathrate is an interesting possibility. If present in modern remnants of glacial ice, methane hydrate may also be a reservoir for atmospheric methane.

D. S. McMenamin; G. E. McGill

2006-01-01

241

The Idea of Marine Exogenic Processes in Glacial and Contemporary Periods  

NASA Astrophysics Data System (ADS)

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

Matishov, G. G.

2009-04-01

242

The Evolution of an Ecosystem: Pleistocene Extinctions  

Microsoft Academic Search

It is generally assumed that evolution is an issue of looking at how a species fits into its environment. This over-constrains our thinking; we should look at how the species and the ecosystem evolve together. The current theories of the Pleistocene extinction (Climate change and Overkill by H. sapiens) are inadequate. Neither explains why: (1) browsers, mixed feeders and non-ruminant

Elin Whitney-Smith

243

Late Pleistocene Faunal Extinctions in Southern Patagonia  

Microsoft Academic Search

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

Vera Markgraf

1985-01-01

244

Pleistocene chronology of continental margin sedimentation  

Microsoft Academic Search

Commonly accepted models for the evolution of continental margins link sediment erosion, transport and deposition to eustasy. To test these models, we constructed an oxygen isotope record from 520 m of Pleistocene sediment recovered by the Ocean Drilling Program Leg 174A from the New Jersey continental slope. The ?18O record was calibrated to SPECMAP oxygen isotope time scale [Imbrie et

Cecilia M. G McHugh; Hilary Clement Olson

2002-01-01

245

New Pleistocene vertebrate fauna from El Salvador  

Microsoft Academic Search

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

Juan Carlos Cisneros

2005-01-01

246

Pleistocene age determinations from california and Oregon.  

PubMed

Mollusks have been collected from Pleistocene marine deposits at Tomales Bay, California, and Cape Blanco, Oregon. Dating by the carbon-14 and thorium-230-uranium-234 methods suggests that the shells are at least 33,000 years old. The more probable age of the Tomales Bay locality is >/= 50,000 years. PMID:17754819

Richards, H G; Thurber, D L

1966-05-20

247

The Pleistocene mammals of Costa Rica  

Microsoft Academic Search

Fossil mammals are known from 41 localities of Pleistocene age in Costa Rica. Most of these mammals are proboscideans referable to the gomphothere Cuvieronius hyodon. One occurrence of Haplomastodon waringi is known, and Mammuthus columbi from Costa Rica is the southernmost record of Mammuthus in Central America. Less well documented are occurrences of megatheriid and mylodontid ground sloths and glyptodonts.

Spencer G. Lucas; Guillermo E. Alvarado; Eduardo Vega

1997-01-01

248

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

NASA Astrophysics Data System (ADS)

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

Jin, Haiyan; Jian, Zhimin

2013-06-01

249

Molluscan response to early Pleistocene rapid warming in the Sea of Japan  

NASA Astrophysics Data System (ADS)

Major changes occurred in the benthic molluscan fauna of the Sea of Japan continental shelf during the transition from Pleistocene glacial to interglacial stages, owing to rapid warming associated with the inflow of the warm Tsushima Current. Molluscan associations representing this transition occur in the lower Pleistocene Omma Formation in central Japan and suggest that there were two patterns of faunal change. The first was when warm-water species migrated into the Sea of Japan and lived along with cold-water species, accompanied by a northward shift in species ranges. The second pattern involved the migration of warm-water mollusks shortly after the local extinction of cold-water species. In the latter, it is possible that benthic molluscan communities with very low diversity and density existed temporarily and locally at inner shelf depths (<100 m) during the warming phase. Such a community has no modern analogue, but may have resulted from a marine climate with a higher seasonality than occurs today. These findings show that episodes of rapid warming have severe impacts on offshore benthic communities and molluscan species that include patterns not represented by modern faunal distributions.

Kitamura, Akihisa; Omote, Hiroko; Oda, Motoyoshi

2000-08-01

250

The influence of Pleistocene refugia on the evolutionary history of the Japanese hare, Lepus brachyurus.  

PubMed

We performed a phylogeographic analysis of the Japanese hare, Lepus brachyurus, using the mitochondrial cytochrome b gene (1140 bp). In total, 119 haplotypes were recovered from 197 samples isolated from 82 localities on three main islands of the Japanese archipelago: Honshu, Sikoku, Kyushu, Sado Island and the Oki Islands. Results showed two distinct clades at a genetic distance of 3.5%, equivalent to an estimated 1.2 million years. The two clades, encompassing seven subclades, showed an apparent geographic affinity to Kyushu, Shikoku and the nearby area of Honshu (southern group) by one clade, whereas the other clade covered the remaining area of Honshu (northern group). The landscape shape interpolation analysis exhibited a higher genetic diversity in the southern parts of central Honshu (northern group) and Shikoku and Kyushu regions (southern group), suggesting the existence of multiple geographical origins of population expansion in each clade. The Bayesian skyline plot analysis showed that lineage diversifications occurred about 0.35, 0.20 and 0.05 million years ago (Mya), which coincide closely with the glacial-interglacial cycles during the Pleistocene. Therefore, we suggest that the Japanese hare population once inhabited northern and southern refugia, and subsequently developed several populations through local demographic fluctuations. The present day demarcation in the northern and southern geographic groups is considered to be a temporal remnant of Pleistocene population dynamics and the geographic boundary between them could move or fade away in time. PMID:20822403

Nunome, Mitsuo; Torii, Harumi; Matsuki, Rikyu; Kinoshita, Gohta; Suzuki, Hitoshi

2010-09-01

251

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

PubMed

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

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

2010-12-02

252

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

PubMed

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

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

2007-12-12

253

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

PubMed Central

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

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

2007-01-01

254

Bridging the "beech-gap": New Zealand invertebrate phylogeography implicates Pleistocene glaciation and Pliocene isolation.  

PubMed

The existence of areas of lower endemism and disjunction of New Zealand biota is typified by Nothofagus beech trees (hence "beech-gap") and have been attributed to a variety of causes ranging from ancient fault-mediated displacement (20-25 million years ago) to Pleistocene glacial extirpation (< 1.8 million years ago). We used cytochrome oxidase I and 12S mtDNA sequence data from a suite of endemic invertebrates to explore phylogeographic depth and patterns in South Island, New Zealand, where the "beech-gap" occurs. Phylogeographic structure and genetic distance data are not consistent with ancient vicariant processes as a source of observed pattern. However, we also find that phylogeographic patterns are not entirely congruent and appear to reflect disparate responses to fragmentation, which we term "gap," "colonization," and "regional." Radiations among congenerics, and in at least one instance within a species, probably took place in the Pliocene (2-7 million years ago), possibly under the influence of the onset of mountain building. This orogenic phase may have had a considerable impact on the development of the biota generally. Some of the taxa that we studied do not appear to have suffered range reduction during Pleistocene glaciation, consistent with their survival throughout that epoch in alpine habitats to which they are adapted. Other taxa have colonized the beech-gap recently (i.e., after glaciation), whereas few among our sample retain evidence of extirpation in the most heavily glaciated zone. PMID:11794778

Trewick, S A; Wallis, G P

2001-11-11

255

Simple stochastic models for glacial dynamics  

Microsoft Academic Search

Glacial-interglacial events have several nonlinear and stochastic characteristics. Recent studies suggested additional stochastic nonlinear features (not necessarily related to the large-scale dynamics of the glacial cycle) in the timescale of 1–100 kyr including (1) strong long-range correlations in the magnitude of climate variable increments as well as (2) a wide multifractal spectrum. Realistic climate models should reproduce these properties of

Yosef Ashkenazy; Don R. Baker; Hezi Gildor

2005-01-01

256

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

NASA Astrophysics Data System (ADS)

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

Ugan, Andrew; Byers, David

2007-12-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

258

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

SciTech Connect

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.

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

1994-08-01

259

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

260

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

261

Inter-specific gene flow dynamics during the Pleistocene-dated speciation of forest-dependent mosquitoes in Southeast Asia.  

PubMed

Tropical forests have undergone repeated fragmentation and expansion during Pleistocene glacial and interglacial periods, respectively. The effects of this repeated forest fragmentation in driving vicariance in tropical taxa have been well studied. However, relatively little is known about how often this process results in allopatric speciation, since it may be inhibited by recurrent gene flow during repeated secondary contact, or to what extent Pleistocene-dated speciation results from ecological specialization in the face of gene flow. Here, divergence times and gene flow between three closely-related mosquito species of the Anopheles dirus species complex endemic to the forests of Southeast Asia, are inferred using coalescent based Bayesian analysis. An Isolation with Migration model is applied to sequences of two mitochondrial and three nuclear genes, and 11 microsatellites. The divergence of An. scanloni has occurred despite unidirectional nuclear gene flow from this species into An. dirus. The inferred asymmetric gene flow may result from the unique evolutionary adaptation of An. scanloni to limestone karst habitat, and therefore the fitness advantage of this species over An. dirus in regions of sympatry. Mitochondrial introgression has led to the complete replacement of An. dirus haplotypes with those of An. baimaii through a recent (approximately 62 kya) selective sweep. Speciation of An. baimaii and An. dirus is inferred to have involved allopatric divergence throughout much of the Pleistocene. Secondary contact and bidirectional gene flow has occurred only within the last 100 000 years, by which time the process of allopatric speciation seems to have been largely completed. PMID:20444081

Morgan, Katy; Linton, Yvonne-Marie; Somboon, Pradya; Saikia, Prasanta; Dev, Vas; Socheat, Duong; Walton, Catherine

2010-04-23

262

Late Pliocene to Pleistocene sensitivity of the Greenland Ice Sheet in response to external forcing and internal feedbacks  

NASA Astrophysics Data System (ADS)

The timing and nature of ice sheet variations on Greenland over the last ˜5 million years remain largely uncertain. Here, we use a coupled climate-vegetation-ice sheet model to determine the climatic sensitivity of Greenland to combined sets of external forcings and internal feedbacks operating on glacial-interglacial timescales. In particular, we assess the role of atmospheric pCO2, orbital forcing, and vegetation dynamics in modifying thresholds for the onset of glaciation in late Pliocene and Pleistocene. The response of circum-Arctic vegetation to declining levels of pCO2 (from 400 to 200 ppmv) and decreasing summer insolation includes a shift from boreal forest to tundra biomes, with implications for the surface energy balance. The expansion of tundra amplifies summer surface cooling and heat loss from the ground, leading to an expanded summer snow cover over Greenland. Atmospheric and land surface fields respond to forcing most prominently in late spring-summer and are more sensitive at lower Pleistocene-like levels of pCO2. We find cold boreal summer orbits produce favorable conditions for ice sheet growth, however simulated ice sheet extents are highly dependent on both background pCO2 levels and land-surface characteristics. As a result, late Pliocene ice sheet configurations on Greenland differ considerably from late Pleistocene, with smaller ice caps on high elevations of southern and eastern Greenland, even when orbital forcing is favorable for ice sheet growth.

Koenig, Sebastian J.; Deconto, Robert M.; Pollard, David

2011-09-01

263

Discriminant Function Analysis of Spectral Gamma Data as a Tool for Regional Stratigraphic Correlation of Pleistocene Deposits  

NASA Astrophysics Data System (ADS)

The protection of groundwater resources is a growing environmental concern in North America. A key requirement in glacial terrains is an understanding of the subsurface distribution and lithologic characteristics of thick, regionally extensive Pleistocene till deposits, as they are a dominant control on regional groundwater flow and contaminant migration. Regional correlation is often problematic when based on lithologic or textural characteristics alone. This paper presents the results of one of the first studies that has utilized borehole and outcrop spectral gamma measurements as tool for regional correlation of tills. A hand-held Exploranium GPX-21 gamma spectrometer and 2SNA-1000 spectral sonde were used to obtain more than 400 measurements on Pleistocene tills and deltaic deposits in the Greater Toronto Area. To quantify separation of each unit, a discriminant function was applied to classify the data. Successful classification of greater than 75% of the stratigraphic units was achieved using this method. Crossplots and three-component plots show that the most sedimentary units have a unique spectral gamma signature. Clay-rich glaciolacustrine strata (e.g. Sunnybrook diamict, Thorncliffe and Scarborough clays) are characterized by more abundant Th, K and U when compared to sandy deltaic units and subglacial tills (e.g. Newmarket and Halton Tills). The element ratios for each unit show a regional consistency, except for the Halton Till, which has a variable spectral signature that reflects the composition of underlying deposits. This association reflects the sub-glacial reworking and incorporation of pre-existing deposits into the till during ice readvance. The results show that many Pleistocene units have unique spectral gamma signatures and that gamma is a useful attribute for regional stratigraphic studies in southern Ontario.

Collins, S. V.; Boyce, J. I.

2004-05-01

264

Glacial-lake deposits in the Mount Harper area, Yukon-Tanana Upland  

NASA Astrophysics Data System (ADS)

During the past year, two new C14 ages and pollen data threw light on some events in the Pleistocene history of the Yukon-Tanana Upland. Woody debris within a volcanic ash layer previously described (Weber, 1982) was dated, as well as some organic material from farther down in the same section. The locality with the new ages is an actively thawing 15-m-high cutbank in unconsolidated sediment on the Middle Fork of the Fortymile River about 16 km southeast of Mount Harper. Mount Harper, with an elevation of 1,994 m, is the highest point in the Yukon-Tanana Upland and has repeatedly supported active glacial systems. A detailed description of the sediments is given.

Weber, F. R.; Ager, T. A.

265

Identifying glacial refugia in a geographic parthenogen using palaeoclimate modelling and phylogeography: the New Zealand stick insect Argosarchus horridus (White).  

PubMed

We have used phylogeographic analysis of mitochondrial DNA (COI and COII genes) and ecological niche modelling (ENM) to reconstruct the population history of Argosarchus horridus (White), a widespread species of New Zealand stick insect. These data were used to address outstanding questions on the role of glacial refugia in determining the distribution and genetic structure of New Zealand species. Phylogeographic analysis shows a general pattern of high diversity in upper North Island and reduced diversity in lower North Island and South Island. The ENM indicates that during the last glacial maximum, A. horridus was largely restricted to refugia around coastal areas of North Island. The ENM also suggests refugia on the northeast coast of South Island and southeast coast of North Island and this prediction is verified by phylogeographic analysis, which shows a clade restricted to this region. Argosarchus horridus is also most likely a geographic parthenogen where males are much rarer at higher latitudes. The higher levels of genetic variation in northern, bisexual populations suggest southern and largely unisexual populations originated from southwardly expanding parthenogenetic lineages. Bayesian skyline analysis also provides support for a recent population size increase consistent with a large increase in geographic distribution in the late Pleistocene. These results exemplify the utility of integrating ENM and phylogeographic analysis in testing hypotheses on the origin of geographic parthenogenesis and effects of Pleistocene environmental change on biodiversity. PMID:19840262

Buckley, Thomas R; Marske, Katharine A; Attanayake, Dilini

2009-10-13

266

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

PubMed Central

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.

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

2012-01-01

267

Last Glacial Maximum lacustrine and fluviatile Formations in the Tibesti and other Saharan mountains, and large-scale climatic teleconnections linked to the activity of the Subtropical Jet Stream  

Microsoft Academic Search

In the mountains of the central Sahara (lat ca. 20° to 22°N, long 16° to 19°E) and particularly in the Tibesti mountains, important lacustrine formations developed during the late Pleistocene, primarily during the Last Glacial Maximum (LGM). Two main phases, separated by a brief regression, intervened between ca. 20,000 and 15,500 BP, and between 15,000 and 12,500 BP. Pollen analyses

Jean Maley

2000-01-01

268

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

PubMed

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

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

2006-11-06

269

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

SciTech Connect

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.

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

1985-01-01

270

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

SciTech Connect

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

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

1994-12-23

271

Orbital- to Centennial-Scale Asian Monsoon Changes From Chinese Speleothem Records During the Late Pleistocene  

NASA Astrophysics Data System (ADS)

We have pieced together 230Th dated and annual-layer counted stalagmite oxygen isotope records from several caves in Southeast China, which are separated by long distances. We show that the isotope records are very similar on orbital to decadal time scales, and therefore represent climate change over a large geographic area. Modern cave investigations indicate that dripwater isotopic values are close to that of summer rainfall and summer layers make up 2/3rds to 3/4ths of annual layer thickness. Three past 100-year isotope records from caves on a south-north transect generally follow the East Asian summer monsoon (EASM) index reconstructed from the meteorological data. These results confirm that Chinese speleothem isotope records can be regarded as a proxy of the EASM strength. The Late Pleistocene EASM is dominated by a ~23 ky cyclicity, synchronous within dating errors with summer (July 21) insolation at 65°N. Millennial-scale strong monsoon events in the last and penultimate glacial period show similar changes in duration and frequency over the ice age cycle, suggesting that ice volume changes affect the rhythm and pacing of monsoon events. However, the EASM events of the last glacial period are not identical to their Greenland counterparts, perhaps because of ties to South Hemisphere climate. Decadal-centennial fluctuations of the Holocene EASM have significant correlations with solar-induced 14C variations and temperature changes over Greenland.

Wang, Y. J.; Cheng, H.; Edwards, R.; Kong, X. G.; Chen, S. T.; Wu, J. Y.

2008-12-01

272

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

NASA Astrophysics Data System (ADS)

This work describes the history of late Pleistocene glaciations in the central Sayan-Tuva Upland (southern Siberia). Geological and geomorphological analysis as well as 10Be surface-exposure dating revealed the glacier fluctuations in this continental area. The available published data show that the glaciers were formed in the MIS 6 and probably survived in the MIS 5. Data are also available concerning glacial advances in different periods of MIS 4, MIS 3 and MIS 2. ELAs were 2030-2230 m. Two distinct 10Be exposure ages groups are highlighted reflecting the time of formation of glacial deposits in the MIS 2 associated to the Big Sayan Ridge outlet glaciers. The Sentsa - Sailag group (terminal moraine) has a mean exposure age of 16.44 ± 0.38 ka. The Jombolok (terminal moraine) - Jombolok (outwash plain) group has a mean exposure age of 22.80 ± 0.56 ka. The last glaciation that occurred at MIS 2 is characterized by the absence of ice cap on the Azas volcanic Plateau and of ice field in the Todza Basin. The thickness of the valley glacier was 300-400 m. At MIS 2, the terminal moraines were ˜1300-1400 m a.s.l. in the Tissa, Sentsa, Jombolok and Sailag river valleys.

Arzhannikov, Sergei G.; Braucher, Regis; Jolivet, Marc; Arzhannikova, Anastasia V.; Vassallo, Riccardo; Chauvet, Alain; Bourlès, Didier; Chauvet, Frédéric

2012-08-01

273

Calcium Oscillations  

PubMed Central

Calcium signaling results from a complex interplay between activation and inactivation of intracellular and extracellular calcium permeable channels. This complexity is obvious from the pattern of calcium signals observed with modest, physiological concentrations of calcium-mobilizing agonists, which typically present as sequential regenerative discharges of stored calcium, a process referred to as calcium oscillations. In this review, we discuss recent advances in understanding the underlying mechanism of calcium oscillations through the power of mathematical modeling. We also summarize recent findings on the role of calcium entry through store-operated channels in sustaining calcium oscillations and in the mechanism by which calcium oscillations couple to downstream effectors.

Dupont, Genevieve; Combettes, Laurent; Bird, Gary S.; Putney, James W.

2011-01-01

274

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

USGS Publications Warehouse

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.

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

1997-01-01

275

Climatic inferences from glacial and palaeoecological evidence at the last glacial termination, southern South America  

Microsoft Academic Search

There is uncertainty about the interhemispheric timing of climatic changes during the last glacial-interglacial transition. Different hypotheses, relying on different lines of evidence, point variously to the Northern Hemisphere leading the Southern Hemisphere and vice versa, or to synchrony between the hemispheres. Southern South America is well placed to test the various alternatives using both glacial and palaeoecological evidence. We

R. D. McCulloch; M. J. Bentley; R. S. Purves; N. R. J. Hulton; D. E. Sugden; C. M. Clapperton

2000-01-01

276

Late Pleistocene stalagmite growth in Wolkberg Cave, South Africa  

NASA Astrophysics Data System (ADS)

Little is known about the sequence of climate and environmental change in southern Africa during the last glacial period, in spite of the intimations from records, such as Antarctic ice cores and archaeological sites, that very marked changes took place which would have had profound effects on vegetation and animal distributions across the sub-continent. High-resolution, (semi-) continuous climate and environmental records can be extracted from suitable cave speleothems. Speleothems are reasonably abundant in southern Africa, but their occurrence is patchy in time and space and the records can be difficult to interpret. Here we report our assessment of the stalagmite W5 from Wolkberg Cave in the northeastern part of South Africa, as an archive for glacial-period climatic and environmental shifts. The cave is located at 1450 m asl, in the dolomitic limestones of the Transvaal System in an area currently dominated by C4 grass vegetation. Nine U/Th dates show growth from 58 to 46 ka, and a second brief phase ca. 40 ka, indicating that the available moisture was sufficient to allow speleothems to form. The ?18O and ?13C values along the growth axis show variability in the order of 2‰ for the former, while variability in the latter is characterized by a shift from values near - 2‰ in the older section to + 2‰ or more in the younger part. These high ?13C values are probably the combined result of CO2 degassing of the percolating soil water prior to the carbonate precipitation in the cave chamber, the increasing dominance of C4 over C3 vegetation, and the high percentage of aragonite towards the stalagmite's top. The retrieved data point towards increasingly drier and colder conditions during the growth period of the stalagmite. Furthermore, the high-frequency variations of ?18O values indicate the presence of short term climate oscillations that are probably linked to shifts of the Intertropical Convergence Zone.

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

2009-05-01

277

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

PubMed

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

Galbreath, Kurt E; Cook, Joseph A

2004-01-01

278

Multiple unrelated founding events for the long-distance Pleistocene dispersal of the Salangid, Neosalanx taihuensis: a general demographic model for inshore-orientated freshwater fish.  

PubMed

The Salangid icefish Neosalanx taihuensis (Salangidae) originated from inshore of the East China seas and underwent adaptive freshwater radiation from the mid-Miocene to the early Pleistocene. The distribution of its genetic diversity presents a random pattern inconsistent with contemporary hydrological structure. In the present study, coalescent simulations were used to analyze its Pleistocene dispersal history. Population history simulation supported the hypothesis of long-distance dispersal during the Pleistocene based on multiple unrelated founding events. This analogous genetic pattern has been described for other inshore-orientated freshwater fish, and may represent a general history dispersal model for the phylogeography of these species. From network analysis, three subclades (Clades 1-3) grouped consistently with three probable ancestral haplotypes (H36, H27, and H33). Demographic analysis also revealed that the ancestral haplotype group (Clade 1) dispersed into freshwater during an interglacial age about 0.35Ma, while Clades 2 and 3 dispersed about 0.12 and 0.145Ma, respectively. The N. taihuensis population remained relatively small for a considerable amount of time during the Pleistocene ages, with population expansion events mainly occurring after the last glacial maximum (LGM). PMID:21081172

Zhao, Liang; Zhang, Jie; Liu, Zhijin; Li, Ming

2010-11-21

279

Glacial Productivity Regimes in the Southern Ocean  

NASA Astrophysics Data System (ADS)

The contemporary Antarctic Circumpolar Current (ACC) is a weak CO2 sink despite high nutrient levels because productivity is limited by iron availability. During glacial periods much greater iron availability should have significantly enhanced productivity and CO2 drawdown. However, there is ongoing debate on the physical and biological mechanisms in the Southern Ocean causing the lowering of the glacial CO2 concentrations. Most paleochemical proxies indicate a latitudinal shift in the zone of enhanced glacial primary productivity and intensified CO2 drawdown but no overall increase in biogenic export. Other lines of explanation involve physical mechanisms restricting the Southern Ocean/atmosphere gas exchange via surface water stratification or sea ice coverage. However, the validity of such hypotheses to represent the major or sole mechanism steering the CO2 draw-down, has been questioned, based on theoretical grounds and numerical modeling, respectively. Here we present evidence for last glacial Southern Ocean conditions from biological proxies. We could detect resting spores of the diatom genus Chaetoceros as a proxy to indicate iron induced extensive diatom blooms across the entire Atlantic sector of the ACC, particularly in the seasonal sea-ice covered zone (SIZ) during the last glacial. In addition, we used the ecological information of the radiolarian Cycladophora davisiana gathered from plankton and surface sediment investigations of the Sea of Okhotsk to notify high glacial phytodetritus export in this area. The areal and downcore distribution patterns of these primary producer and phytodetritus feeding, deep living protozoans point to the occurrence of a high productive biological regime, dominated by fast growing thin-walled diatoms and non siliceous primary producer (e.g. Phaeocystis), which lead to high export of organic matter to the deep ocean. The dominance of the deep living radiolarian Cyladophora davisiana in glacial SIZ sediments indicates that organic carbon export to mesopelagic depths was at least ten-fold higher than today.

Abelmann, A.; Rainer, G.; Victor, S.

2006-12-01

280

High latitude regulation of low latitude thermocline ventilation and planktic foraminifer populations across glacial-interglacial cycles  

NASA Astrophysics Data System (ADS)

One of the earliest discoveries in palaeoceanography was the observation in 1935 that the (sub)tropical planktic foraminifer Globorotalia menardii became absent or extremely rare in the Atlantic Ocean during glacials of the late Pleistocene. Yet a mechanistic explanation for G. menardii's extraordinary biogeographic behaviour has eluded palaeoceanographers for 75 years. Here we show that modern G. menardii, along with two other species that also suffer Atlantic population collapses during glacials, track poorly ventilated waters globally in their thermocline habitats. The ventilation states of low latitude thermoclines are 'set', to a first order, by intermediate water masses originating at high latitudes. In the modern Atlantic this control on low latitude thermocline ventilation is exerted by relatively poorly ventilated, southern-sourced Antarctic Intermediate Water (AAIW) and sub-Antarctic Mode Water (SAMW). We suggest that the glacial Atlantic foraminifer population collapses were a consequence of a low latitude thermocline that was better ventilated during glacials than it is today, in line with geochemical evidence, and driven primarily by a well-ventilated, northern-sourced intermediate water mass. A ventilation mechanism driving the glacial population collapses is further supported by our new constraints on the precise timing of these species' Atlantic proliferation during the last deglaciation — occurring in parallel with a wholesale, bipolar reorganisation of the Atlantic's thermocline-to-abyssal overturning circulation. Our findings demonstrate that a bipolar seesaw in the formation of high latitude intermediate waters has played an important role in regulating the population dynamics of thermocline-dwelling plankton at lower latitudes.

Sexton, Philip F.; Norris, Richard D.

2011-11-01

281

QUANTIFICATION OF GLACIAL EROSION IN THE ALPS USING VERY LOW-TEMPERATURE THERMOCHRONOLOGY (OSL & AHe)  

NASA Astrophysics Data System (ADS)

The impact of glaciations on the topography of the Alps is still unclear: Long-term denudation rate determined by low-T thermochronology are in the range of 0.2 to 1 mm/yr, and increased during the Plio-Quaternary by 3 fold (Vernon et al., 2008). Such an increase is also documented by peri-alpine sediment budget (Kuhleman, 2000), with a similar increase in sediment yields since 5-3 Ma. This increase was considered as evidence of a climatically-driven surface process change, attributed to increased precipitation (Cederbom et al., 2004) and erosion by glacial processes (Champagnac et al., 2007). The timing of the onset of intense glacial erosion as well as its rates are still ambiguous. The glacial erosion seems to have accelerated around 0.9 Ma as suggested by the ten fold increase of incision rates of a valley in the Central Alps (Häuselmann et al., 2007), and by information about vegetation and sedimentologic changes (Muttoni et al., 2003). There is however no direct quantification of topographic change during the Plio-Quaternary. We present here how we use OSL-thermochronology, a new thermochronometer of exceptionally low closure temperature (about 30°-40°C) (Herman et al subm.), new {U-Th}/He on apatites data, and a glacial erosion model (Herman and Braun 2008) to estimate topographic changes in the Alps in response to glaciations. Because of their low closure temperature, OSL and AHe thermochronology enables quantification of events of less than 1 Ma at very small wavelength of the topography. We collected two vertical profiles, one in the Zermatt Valley (Valais) and one in Maurienne Valley (Savoy). We infer from these results changes in topography, date and quantify relief creation under glacial-interglacial cycles. Cederbom, C.E, et al., Climate induced rebound and exhumation of the European Alps. Geology 32, 709-712 (2000). Champagnac, J.-D., et al., Quaternary erosion-induced isostatic rebound in the western Alps. Geology 35, 195-198 (2007). Haüselmann P., et al.,et al. Abrupt glacial valley incision at 0.8 Ma dated from cave deposits in Switzerland. Geology 35, 33-42 (2007). Herman F. and Braun J. Evolution of the glacial landscape of the Southern Alps of New Zealand: Insights from a glacial erosion model, J. Geophys. Res., 113, F02009, doi:10.1029/2007JF000807 (2008). Herman F., Rhodes E.J. and Braun J. A new thermochronometer reveals steady state relief and exhumation in a small active orogen during the last glacial cycle, submitted. Kuhlemann J., et al., Quantifying tectonic versus erosive denudation by the sediment budget: the Miocene core complexes of the Alps, Tectonophysics 330, 1-23 (2000). Muttoni G., et al., Onset of major Pleistocene glaciations in the Alps. Geology 31, 989-992 (2003). Vernon, A.J., et al., Increase in late Neogene denudation of the European Alps confirmed by analysis of a fission-track thermochronology database. Earth and Planetary Science Letters, 270 (3-4), pp. 316-329 (2008).

Champagnac, J.; Herman, F.; Rhodes, E. J.; Fellin, M.; Jaiswal, M.; Schwenninger, J.; Reverman, R. L.

2009-12-01

282

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

NASA Astrophysics Data System (ADS)

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

Colin de Verdière, Alain; Te Raa, L.

2009-10-01

283

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

284

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

PubMed

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

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

2008-10-01

285

Geodesy: Modeling Earth's Post-Glacial Rebound  

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

286

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)

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.

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

2011-12-01

287

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

Microsoft Academic Search

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

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

2006-01-01

288

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

PubMed

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

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

2013-03-18

289

Pleistocene vertebrates of the Yukon Territory  

NASA Astrophysics Data System (ADS)

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

Harington, C. R.

2011-08-01

290

Bahamian Pleistocene model for some Mississippian oolites  

SciTech Connect

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

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

1989-08-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

292

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

PubMed

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

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

2013-09-23

293

Glacial-interglacial variability of the Greenland Ice Sheet in the Pliocene  

NASA Astrophysics Data System (ADS)

Significant built-up of ice caps on Greenland is believed to have begun in the Pliocene (5.33 - 2.58 Ma). The ice sheet has likely been highly dynamic, and paced by Milankovitch orbital cycles, variations in atmospheric carbon dioxide concentrations (pCO2 [ppmv]) and internal forcings, and feedbacks related to both local energy balance and far-field influences. The likely locations, extents and volumes of continental ice on Greenland during the Pliocene remain largely unconstrained. Feedback mechanisms involving coupling between ice sheets and sea ice have been proposed to have a significant impact on the Pleistocene climate-cryospheric system and the pacing of glacial-interglacial cycles. Here, we show the results of a sensitivity study exploring (i) the sensitivity of Northern Hemisphere sea ice to forcing and (ii) the impact of sea ice on northern-hemispheric climatic and cryospheric evolution through the Plio-Pleistocene. We investigate the threshold for the growth and decay of the Greenland Ice Sheet and the ice sheet's impact on sea ice extent and thickness with a coupled GCM-ice sheet model using combining sets of orbital parameters, and pCO2 levels. Additionally, we test the dynamic response of vegetation and assess the vegetation feedback under the prescribed orbits and pCO2. The paleoclimate simulations use both modern and ice-free isostatically equilibrated Greenland topography with modern (control) and cold and warm boreal summer orbits, and a range of pCO2 levels chosen to broadly represent both warm Pliocene and cold Pleistocene conditions. Model simulations are compared with available sea surface temperature and other proxy data on and around Greenland. We find that Pliocene Greenland (at elevated CO2 levels) is highly sensitive to orbital forcing. Sea ice-albedo feedback has important effects on the hydrological cycle and largely governs insulation receipts at the surface. Sea ice cover modifies moisture availability by controlling the air-sea fluxes and alters the atmospheric circulation and has far reaching effects by controlling heat and moisture transport. Vegetation changes over ice-free Greenland significantly impact summer temperature with consequences for glacial onset during colder orbital periods. Given our model results, we conclude that internal processes and feedbacks are capable of significantly modifying thresholds for inception and decay of ice on Greenland, especially in the Pliocene, when CO2 concentrations were comparable to today.

Koenig, S. J.; Deconto, R.; Pollard, D.

2010-12-01

294

Fire regimes during the last glacial  

NASA Astrophysics Data System (ADS)

Fire regimes during the last glacial A.-L. Daniau (1), S.P. Harrison (1) and P.J. Bartlein (2) (1) School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK (2) Department of Geography, University of Oregon, Eugene, OR 97403, USA Sedimentary charcoal records document changes in fire regime. We have identified 67 sites which have records for some part of the last glacial and have used the 30 of these sites with better-than millennial-resolution to analyse changes in global fire regimes. Fire was consistently lower during the glacial than during the Eemian and Holocene. Within the glacial, Marine Isotope Stage (MIS) 3 is characterised globally by more fire than MIS 2. The signal for MIS 4 is less clear: there is more fire in the northern hemisphere and less fire in the southern hemisphere than during MIS 2 and 3. The records, most particularly records from the northern extratropics, show millennial-scale variability in fire regimes corresponding to the rapid climate changes associated with Dansgaard-Oeschger (D-O) cycles. Most of the D-O cycles during the last glacial and all of the Heinrich Stadials are apparent in the composite global record of the high-resolution sites: fire increases during D-O warming events and decreases during intervals of cooling. Our analyses show that fire regimes show a lagged response to rapid climate changes of ca 100-200 years in the case of D-O warming events, ca 0-100 years in the case of D-O cooling events and ca 200 years in the case of Heinrich Stadials. The strong climatic variability experienced during the glacial resulted in important changes in fire regimes even though the base level of biomass burning was less than today.

Daniau, A.; Harrison, S. P.; Bartlein, P. J.

2009-12-01

295

Multiple steady states of Northern Hemisphere ice sheets and the timing of glacial cycles  

NASA Astrophysics Data System (ADS)

Wax and Wane of large Northern Hemisphere ice sheet occurred in the past few million years, characterized by a transition from a period of 40 thousand years cycle with small amplitude of ice sheet change to 100 thousand year cycle with a large amplitude, known as the Middle Pleistocene transition. Although the characteristics of the glacial cycle is well observed, the mechanism what determines the 100ka cycle and what controls the terminations are still under debate. Here we show that the pattern of the growth of the ice sheets during a glacial cycle follows the hysteresis (multiple steady states) structure of North American ice sheet versus insolation by modelling the three dimensional ice sheet. The 100 ka termination is punctuated by Northern American ice sheet responding basically to the precession cycle and summer insolation through its delayed bedrock depression and the large scale calving. Terminations occur when the summer insolation increases after a minimum eccentricity even under constant CO2 level. Obliquity modifies the role of precession and becomes important for a glacial cycle especially when the eccentricity is small. The North American ice sheet is slightly more favorable for faster growth than Eurasian ice sheet when the ice sheet expands over Labrador and Hudson Bay, and suppresses the growth of Eurasian ice sheet through the atmospheric planetary wave feedback. As a result, the North American ice sheet can have affected the hemispheric climate and punctuated the ice sheet change in Eurasia and in Antarctica through CO2 and sea level change. Furthur we show that a cooling due to, for example, the draw down of long term CO2 level of 20ppm or so at most from 240ppm to 220ppm is enough for a switch from 40 ka cycle response to 100 ka cycle response of Northern Hemisphere ice sheet.

Abe-Ouchi, A.; Saito, F.; Kawamura, K.; Raymo, M. E.

2012-04-01

296

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

PubMed

The Pleistocene was an epoch of extreme climatic and environmental changes. How individual species responded to the repeated cycles of warm and cold stages is a major topic of debate. For the European fauna and flora, an expansion-contraction model has been suggested, whereby temperate species were restricted to southern refugia during glacial times and expanded northwards during interglacials, including the present interglacial (Holocene). Here, we test this model on the red deer (Cervus elaphus) a large and highly mobile herbivore, using both modern and ancient mitochondrial DNA from the entire European range of the species over the last c. 40 000 years. Our results indicate that this species was sensitive to the effects of climate change. Prior to the Last Glacial Maximum (LGM) haplogroups restricted today to South-East Europe and Western Asia reached as far west as the UK. During the LGM, red deer was mainly restricted to southern refugia, in Iberia, the Balkans and possibly in Italy and South-Western Asia. At the end of the LGM, red deer expanded from the Iberian refugium, to Central and Northern Europe, including the UK, Belgium, Scandinavia, Germany, Poland and Belarus. Ancient DNA data cannot rule out refugial survival of red deer in North-West Europe through the LGM. Had such deer survived, though, they were replaced by deer migrating from Iberia at the end of the glacial. The Balkans served as a separate LGM refugium and were probably connected to Western Asia with genetic exchange between the two areas. PMID:23927498

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

2013-08-09

297

Paleoclimate in north-east Anatolia during the Quaternary deduced from glacial archives  

NASA Astrophysics Data System (ADS)

Today's climate of the northern part of the eastern Black Sea Mountains is humid with a mean annual precipitation over 2000 mm. The moisture is directly transported from the Black Sea. Field evidence indicate that this area was glaciated during past. Ice build-up can be therefore explained by a moisture transport system similar to today. Analogous to the north, the southern part of these mountains is relatively dry, although the field evidence in Çoruh Valley in Yusufeli, for instance, point to even more extensive glaciations. To accumulate more ice volume in the southern part, a different moisture transport than today is needed, for instance the moisture transport path may have changed in the past. But the time when this ice-build up (recorded by glacial deposits and erosional features) took place is still unclear. To construct the chronology of these glaciations with cosmogenic 10Be and 36Cl, we collected 14 samples from erratic boulders and glacially abraded bedrock in the Çoruh Valley in Yusufeli in the southern part and 41 samples in the Ba?yayla valley in the northern part. According to the existing data, glaciers advanced around 21 ka in the Kavron and Verçenik valleys in the northern part during the Last Glacial Maximum (LGM) (Akçar et al. 2007; 2008). While a Lateglacial advance archived around 15 ka in the Verçenik valley, Younger Dryas is recorded around 12 ka in the Kavron valley. Our first results from Çoruh valley indicate presence of two pre-LGM glaciations (>35 ka and >70 ka), a LGM advance (not dated yet) and a Lateglacial extent around 14 ka. Both field and dating evidence from the southern part of the eastern Black Sea Mountains enriches our knowledge about the glacier build-up and moisture transport during the Late Pleistocene, which can be interesting for our understanding of changes atmospheric circulation patterns during colder periods.

Reber, R.; Akçar, N.; Yavuz, V.; Tikhomirov, D.; Vockenhuber, C.; Kubik, P. W.; Schlüchter, C.

2012-04-01

298

Decoding Aerial Photographs of Glacial Landscapes - Indicators of Ground Waters.  

National Technical Information Service (NTIS)

Characteristics of landscape indicators of ground waters are described for the following: four glacial types of landscape, including hilly-moraine, drumlin, morainic plain and terminal-moraine; three water-glacial types of landscape, including kame (and o...

G. Y. Meer V. K. Markovskii

1969-01-01

299

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

PubMed Central

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

2013-01-01

300

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

PubMed

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

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

2012-03-01

301

Neutrino oscillations  

SciTech Connect

The interest in neutrino oscillations is such that there are several experiments approved or planned for the near future. There are experiments already complete which have searched for oscillations particularly between nu/sub ..mu../ ..-->.. nu/sub e/. We shall concentrate here on accelerator experiments and try to show the principal limitations on the experimental sensitivity to changes in neutrino flavor. We shall give a critical review of the methodology that has been used or proposed for accelerator experiments.

White, D.H.

1982-01-01

302

Northernmost (?) Glacial Lake Algonquin Series Shorelines, Sudbury Basin, Ontario  

Microsoft Academic Search

Shorelines of Lake Algonquin, the largest of the glacial lakes of the Great Lakes area, are well known in southern Ontario, but are sporadic and difficult to trace northward onto the Precambrian shield. Improved knowledge of the extent and uplift pattern for Algonquin shorelines is needed to support geophysical models of isostatic response, interpretation of glacial and glacial lake history,

Andrew J. Heath; Paul F. Karrow

2007-01-01

303

Mechanisms and toy models of the glacial cycles  

Microsoft Academic Search

Given the above climate feedbacks as our ingredients for making glacial theories, we now describe some of the physical mechanisms and models proposed for explaining the main features of the glacial cycles. As done throughout these lectures, we concentrate on conceptual (toy) models that attempt to explore the role of a limited number of feedbacks at a time. 9.1 Glacial

Eli Tziperman

304

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

ERIC Educational Resources Information Center

|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…

Pape, Bruce; Francek, Mark A.

1992-01-01

305

Glacial fragmentation induced by eruptive activity: Popocatépetl Volcano (México)  

Microsoft Academic Search

Ice-volcano interactions at volcanoes depend on eruptive behavior, glacier characteristics and time scales. High- intensity eruptions occurred in a short span of time can provoke dramatic glacial changes whilst intermittent eruptive behavior of variable intensity over years can generate gradual glacial changes. Popocatépetl volcano hosted a small glacial area when it started to erupt in December 1994. Over 12 years

P. Julio-Miranda; H. Delgado-Granados

2007-01-01

306

Glacial cycles: Toward a new paradigm  

Microsoft Academic Search

The largest environmental changes in the recent geological history of the Earth are undoubtedly the successions of glacial and interglacial times. It has been clearly demonstrated that changes in the orbital parameters of our planet have a crucial role in these cycles. Nevertheless, several problems in classical astronomical theory of paleoclimate have indeed been identified: (1) The main cyclicity in

Didier Paillard

2001-01-01

307

Potential flood volume of Himalayan glacial lakes  

NASA Astrophysics Data System (ADS)

Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the risk of such flooding, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes flooded. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e. the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability because it requires no particular expertise to carry out. We calculated PFVs for more than 2000 Himalayan glacial lakes using the ASTER data. The distribution follows a power-law function, and we identified 49 lakes with PFVs of over 10 million m3 that require further detailed field investigations.

Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

2013-01-01

308

Climate Change Affects Glacial Water Source  

NSDL National Science Digital Library

This video discusses how the populous areas west of the Andes are largely desert and rely on glacial meltwater as an important source of fresh water. Because the Peruvian glaciers high in the Andes are in rapid retreat, scientists are monitoring the steadily shrinking glaciers and the impact of their reduction on local populations.

Thinktv; Domain, Teachers'

309

In-Stream Metabolism Differences Between Glacial and Non-Glacial Streams in Southeast Alaska  

NASA Astrophysics Data System (ADS)

As glacier ice gives way to successional vegetation, streams located in glacier-containing watersheds receive decreased contributions from glacial meltwater and increased contributions from terrestrial landscapes. These changes result in increased water temperature, increased shading from vegetation, and changes in the composition and concentration of organic matter delivered to the stream from the landscape. Organic matter and source water contributions from the surrounding landscape can influence in-stream metabolism through both biotic and abiotic factors. The impact of these landscape controls on the in-stream cycling of carbon and nutrients is not well understood in glacial systems. Here, we are focusing on understanding the differences in processing of organic carbon by heterotrophic microbial communities between glacial and non-glacial streams. In this study, the metabolism in streams receiving glacial meltwater was compared to the metabolism of streams located in nearby non-glaciated watersheds to determine the effect of changing inputs of glacial meltwater on stream metabolism. In particular, we tested the hypothesis that decreased inputs of glacier meltwater will result in increased net ecosystem metabolism (NEM) in coastal streams in southeast Alaska. Dissolved oxygen and carbon dioxide measurements as well as temperature and PAR values were collected at 10-minute increments at each study site for 4 days. This data was used to generate diel curves to establish community respiration (CR24) and gross primary production (GPP) estimates. Lab-scale mesocosms containing sediment and stream water from each end-member stream were used to quantify the relative importance of glacial contributions to respiration rates in the surface sediments. Ultimately, this will provide a better understanding of the changing in-stream processing capabilities in watersheds affected by land cover changes resulting from glacial recession.

Nassry, M. Q.; Scott, D.; Vermilyea, A.; Hood, E. W.

2011-12-01

310

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

Microsoft Academic Search

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

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

2004-01-01

311

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

SciTech Connect

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

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

1993-03-01

312

Glaciers, glacial lakes and glacial lake outburst floods in the Mount Everest region, Nepal  

Microsoft Academic Search

Recent climate changes have had a significant impact on the high-mountain glacial environment. Rapid melting of glaciers has resulted in the formation and expansion of moraine-dammed lakes, creating a potential danger from glacial lake outburst floods (GLOFs). Most lakes have formed during the second half of the 20th century. Glaciers in the Mount Everest (Sagamartha) region, Nepal, are retreating at

Samjwal Ratna BAJRACHARYA; Pradeep MOOL

2009-01-01

313

Chronostratigraphical investigations on Pleistocene fluvioglacial terraces of NW-Austria  

NASA Astrophysics Data System (ADS)

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

Terhorst, B.

2009-04-01

314

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

Microsoft Academic Search

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

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

2005-01-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

316

Potential flood volume of Himalayan glacial lakes  

NASA Astrophysics Data System (ADS)

Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

Fujita, K.; Sakai, A.; Takenaka, S.; Nuimura, T.; Surazakov, A. B.; Sawagaki, T.; Yamanokuchi, T.

2013-07-01

317

Predators and scavengers in Early Pleistocene southern Asia  

Microsoft Academic Search

Although several large carnivores are recognised in the Early Pleistocene of southern Asia, little is known about their predatory vs. scavenging behaviour, or their chief prey. Here, we present new, late Pliocene to late Early Pleistocene data from the Pabbi Hills, Pakistan. Although carnivore remains were rare, several were found associated with large fossil accumulations that probably represent feeding areas.

R. W. Dennell; R. Coard; A. Turner

2008-01-01

318

Early Pleistocene chronology of the Vrica section (Calabria, Italy)  

Microsoft Academic Search

Two alternative age models are presented for the Pleistocene part of the Pliocene-Pleistocene boundary stratotype section at Vrica (Calabria, southern Italy). Both age models, or chronologies, are based on the correlation of the characteristic sapropel pattern to the summer insolation time series of astronomical solution La90. The first age model is based on the assumption that the succession is continuous,

L. J. Lourens; F. J. Hilgen; I. Raffi; C. Vergnaud-Grazzini

1996-01-01

319

Early Pleistocene chronology of the Vrica Section (Calabria, Italy)  

Microsoft Academic Search

Two alternative age models are presented for the Pleistocene part of the Pliocene-Pleistocene boundary stratotype section at Vrica (Calabria, southern Italy). Both age models, or chronologies, are based on the correlation of the characteristic sapropel pattern to the summer insolation time series of astronomical solution La90. The first age model is based on the assumption that the succession is continuous,

L. J. Lourens; F. J. Hilgen; I. Raffi; C. Vergnaud-Grazzini

1996-01-01

320

Late Pleistocene marine chronology of the Gippsland Lakes region, Australia  

Microsoft Academic Search

Thermoluminescence dating is used to define the chronology of the coastal barriers of the Gippsland Lakes region, Australia. The area evidences ? long history of marine deposition extending back ?? the Middle Pleistocene. However, the majority of Pleistocene barriers have formed since the Last Interglacial during two phases at 59 to 72 ka and 40 to 48 ka corresponding to

E. A. Bryant; D. M. Price

1997-01-01

321

The Pleistocene rivers of the English Channel region  

Microsoft Academic Search

The Pleistocene history of river systems that enter the English Channel from northern France and southern England is reviewed. During periods of low sea-level (cold stages) these streams were tributaries of the Channel River. In southern England the largest, the River Solent, is an axial stream that has drained the Hampshire Basin from the Early Pleistocene or late Pliocene. Other

Pierre Antoine; Jean-Pierre Coutard; Philip Gibbard; Bernard Hallegouet; Jean-Pierre Lautridou; Jean-Claude Ozouf

2003-01-01

322

The isotopic ecology of late Pleistocene mammals in North America  

Microsoft Academic Search

Mammoths and mastodons are common in Pleistocene deposits, yet these proboscideans and many other animals disappeared suddenly ?10,000 years ago. In this study, we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late Pleistocene extinction. We analyzed specimens from six sites in Florida, ranging

Paul L. Koch; Kathryn A. Hoppe; S. David Webb

1998-01-01

323

The isotopic ecology of Late Pleistocene mammals in North America  

Microsoft Academic Search

Abstract Mammoths and mastodons are common in Pleistocene deposits, yet these proboscideans and many other animals disappeared suddenly f 10,000 years ago. In this study, we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel,apatite in order to test nutritional hypotheses for late Pleistocene . extinction. We analyzed specimens from six sites in

P. L. Koch; K. A. Hoppe; S. D. Webb

1998-01-01

324

Late pleistocene faunal extinctions in southern patagonia.  

PubMed

Major environmental changes recorded in pollen records from various sites in southern Patagonia and Tierra del Fuego are also reflected in pollen and cuticle data from dung of the late Pleistocene groundsloth. The most prominent change was the large-scale reduction of steppe environment about 10,000 years ago, which coincides with the latest dates for extinctions of many large grazers such as the giant groundsloth. Stress on food resources for all the large grazers may well have hastened their extinction. Hunting pressure by paleoindians may have been the final blow. PMID:17737905

Markgraf, V

1985-05-31

325

Indications of pleistocene man on Sardinia  

NASA Astrophysics Data System (ADS)

Human fossils found in a Pre-Neolithic cave deposit (Corbeddu cave, Sardinia) represent the first human remains associated with an endemic impoverished island fauna. Radiocarbon dating by AMS in Utrecht provided the chronological framework of the cave sediments for better understanding of the time-related human activities. The aberrant morphology of the human fossils and the unique character of worked deer bones discovered, suggest the development of an endemic Pleistocene human culture, adapted to the restricted island conditions and the hunting of ochotonids and deer.

Hofmeijer, G. Klein; Sondaar, P. Y.; Alderliesten, C.; van der Borg, K.; de Jong, A. F. M.

1987-11-01

326

Ethological inferences on Pleistocene rhinoceroses of Europe  

Microsoft Academic Search

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

Paul Mazza; A. Azzaroli

1993-01-01

327

Low latitude hydro-climatic changes during the Plio-Pleistocene: evidence from high resolution alkane records in the southern South China Sea  

NASA Astrophysics Data System (ADS)

High resolution records of long chain n-alkane biomarkers from the southern South China Sea reveal tightly response of n-alkane distribution to hydro-climate changes over the past 5 Ma, with increasing longer chain n-C31 alkanes indicating a correlation with drier conditions and increasing shorter chain n-C27 alkanes with wetter conditions. The variations of the C31/C27 ratio, or the alkane chain length index, imply humid conditions before 2.9 Ma, progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1.2 Ma. This long term hydro-climate trend is superimposed by glacial dry and interglacial wet patterns over the Plio-Pleistocene glacial cycles. Combined with other proxy records, our results indicate that precipitation over the tropical Asia-Pacific strengthened before the onset of the northern hemisphere glaciation and the mid-Pleistocene climate transition at about 1.2 Ma. These dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late Cenozoic.

Li, Li; Li, Qianyu; Tian, Jun; Wang, Hui; Wang, Pinxian

2013-10-01

328

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

PubMed

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

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

2013-04-10

329

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

PubMed Central

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

2012-01-01

330

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

PubMed Central

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

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

2007-01-01

331

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

PubMed

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

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

2007-05-30

332

Pleistocene Submarine Groundwater Discharge Along the Atlantic Continental Shelf, New England: The Role of Ice Sheets  

NASA Astrophysics Data System (ADS)

Well bores have long shown that relatively fresh groundwater exists far offshore beneath the Atlantic continental shelves of North and South America. This freshwater was emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and parts were over-run by the Laurentide Ice Sheet. Details of the emplacement mechanism of the fresh water remain poorly understood. At issue is whether the recharge occurred locally through meteoric seepage or was a more regional process driven by ice sheets. These two mechanisms predict very different distributions of water beneath the shelf, and identifying which dominated would help predict whether freshwater is widespread beneath the shelf or isolated in discrete pockets. Here we present results from high-resolution paleohydrologic models of groundwater flow and solute transport beneath the continental shelf from New Jersey to Maine over the last 2 million years. Our analyses show that freshwater emplacement beneath New England's continental shelf was dominated by the presence of the Laurentide Ice Sheet, which the models show increased recharge rates by four times relative to modern levels. Our analyses further suggest that the presence of fresh to brackish water more than 100 km offshore New Jersey was facilitated by discharge from submarine springs along the Baltimore and Hudson Canyons, with outflow rates close to 1 cm/yr during the last glacial maximum (LGM). We estimate that the volume of emplaced Pleistocene continental shelf freshwater (< 1 ppt) to be 1200 km3 in New England, 4300 km3 along the North and South American shelf, and 106,000 km3 along passive margins globally. This water represents a potentially valuable, albeit non-renewable resource for coastal megacities.

Cohen, D.; Person, M.; Peng, W.; Gable, C.; Hutchinson, D.; Marksammer, A.; Brandon, D.; Kooi, H.; Koos, G.; Evans, R.; Lizarralde, D.

2008-12-01

333

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

334

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

PubMed

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

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

2009-12-03

335

Mackenzie Glacial Outburst Floods into the Arctic Ocean 13,000-10,000 Years ago  

NASA Astrophysics Data System (ADS)

An unconformity with an area of at least 9400 km2 and a relief of about 100 m in the eastern Beaufort continental shelf and adjacent coastlands near the Mackenzie Delta is attributed to fluvial erosion during deglaciation of the northwest Laurentide Ice Sheet. On northeast Richards Island, the unconformity is overlain by a fluvial gravel or gravelly lag of pebble to boulder-size material. Optical dating of eolian sand above and below the unconformity constrains erosion and deposition to between about 13.0 and 10.1 ka. Additional optical dates from fluvial sand above gravel indicate an age of about 11.8 ka. If the active margin of the Laurentide Ice Sheet had retreated nearly 600 km southeast of Richards Island by 13 ka, as shown in the Dyke et al. (2003) reconstruction of deglaciation, then a local source of glacial meltwater is discounted. Instead, the fluvial activity was likely associated with outburst flooding from distant glacial lakes into the Arctic Ocean. An earlier episode of flooding shortly after about 13 ka possibly coincided with the onset of the Younger Dryas, and a later episode between about 11.8 ka and 10.1 ka possibly coincided with the onset of the Pre-Boreal Oscillation at about 11.3 ka. The new geological evidence from the Mackenzie Delta region supports recent proposals that massive discharges of glacial meltwater issued northward along the Mackenzie River during deglaciation of the Laurentide Ice Sheet.

Murton, J.; Bateman, M.

2008-12-01

336

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

USGS Publications Warehouse

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

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

1999-01-01

337

Anharmonic Oscillator.  

National Technical Information Service (NTIS)

The paper considers the anharmonic oscillator defined by the differential equation (-the second derivative with respect to x + 1/4 squared + 1/4 lambda(x to the 4th power))Phi(x) = E(lambda)Phi(x) and the boundary condition lim Phi(x) = o as x approaches ...

C. M. Bender T. T. Wu

1969-01-01

338

Impact Oscillators  

Microsoft Academic Search

An impact oscillator is the term used here to represent a system which is periodically driven in some way and which also undergoes intermittent or a continuous sequence of contacts with motion limiting constraints. This important class of non-smooth dynamical systems not only exhibits typical characteristics of smooth nonlinear systems, such as generic bifurcations, multiple solutions and chaos, but also

S. R. Bishop

1994-01-01

339

Ventilation of the glacial deep Pacific Ocean.  

PubMed

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

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

2004-11-12

340

Identification of Late Pleistocene Ice-Rafted Debris (IRD) on the New Jersey Shelf  

NASA Astrophysics Data System (ADS)

The purpose of this study is to evaluate the potential for ice-rafted debris (IRD) on the New Jersey shelf and develop procedures for IRD identification on a shelf environment using a variety of techniques to assess texture and age of the sediments. Pleistocene New Jersey shelf sedimentology is strongly defined by glacially driven sea level changes. IRD and its provenance may be identified on a shelf environment through analysis of grain size distribution, heavy mineral content (higher % suggests non-fluvial processes), mineralogical point counts (anomalous mineralogy indicates distal source), isotopic dating methods (age value determination to narrow down potential source rocks), and surface texture analysis (specific glacial transport features). IRD must be differentiated from sediment derived from the NJ bedrock. Likely sources for IRD include the bedrock of Maine and of the southeastern Canadian Shield. Duncan and Goff (2001) reported iceberg grounding along the NJ shelf. IRD is typically identified in the deep sea through anomalously large grain size within pelagic mud, but different methods are needed for the shelf, where regressive shoreline processes, subaerial exposure, fluvial downcutting, and deposition and reworking during transgression have influenced the sediment composition found today. We analyzed grab samples in or near the features believed to be iceberg scour marks and downcore samples from recent Geoclutter drilling in the same area. The coarse grain size fractions of shelf samples were separated by phi classes before heavy mineral separation methods were employed. Initial analyses show high percentages of heavy minerals in the 2 phi and 3 phi size fractions, consistent with past NJ shelf studies. Hornblende grains were hand-picked from select samples for K-Ar dating, providing age values of about 0.96 ± 0.03 Ga for three sites within iceberg scours. Mineral content of each size fraction is determined by point count. Qualitative assessment of surface textures of select grains as seen with a Hitachi S-2500 SEM is useful in interpretation of source and transport.

Turner, R. J.; Christensen, B. A.; Wampler, J.; Uptegrove, J.; Goff, J.

2004-12-01

341

Pleistocene climatic cycling drives intra-specific diversification in the intermediate horseshoe bat (Rhinolophus affinis) in Southern China.  

PubMed

The repeated formation and loss of land-bridges during the Pleistocene have had lasting impacts on population genetic structure. In the tropics, where island populations persisted through multiple glacial cycles, alternating periods of isolation and contact are expected to have driven population and taxonomic divergence. Here, we combine mitochondrial and nuclear sequence data with microsatellites to dissect the impact of Pleistocene climate change on intra-specific diversification in the horseshoe bat Rhinolophus affinis. This taxon shows considerable morphological and acoustic variation: two parapatric subspecies (himalayanus and macrurus) occur on mainland China and a third (hainanus) on Hainan Island. Our phylogeographic reconstruction and coalescent analyses suggest the island subspecies formed from an ancestral population of himalayanus via two colonization events c. 800,000 years before present. R. a. hainanus then recolonized the mainland, forming macrurus and thus a secondary contact zone with himalayanus. Finally, macrurus recolonized Hainan following the LGM. We found that all three biological events corresponded to known periods of land-bridge formation. Evidence of introgression was detected between macrurus and both its sister taxa, with geographical proximity rather than length of separation appearing to be the biggest determinant of subsequent genetic exchange. Our study highlights the important role of climate-mediated sea level changes have had in shaping current processes and patterns of population structure and taxonomic diversification. PMID:20561192

Mao, Xiu Guang; Zhu, Guang Jian; Zhang, Shuyi; Rossiter, Stephen J

2010-06-17

342

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

USGS Publications Warehouse

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

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

2008-01-01

343

Glacial bed forms at Findelengletscher, Zermatt, Switzerland  

NASA Astrophysics Data System (ADS)

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.

Madella, Andrea; Nyffenegger, Franziska; Schlüchter, Christian

2013-04-01

344

The Role of Topography in Glacial Inception  

NASA Astrophysics Data System (ADS)

We test the influence of model topography on glacial inception using a coupled atmosphere-slab ocean version of NCAR’s Community Climate System Model (CCSM3). Simulations employ a modern orbital configuration and greenhouse gas concentrations representing both recent (year 1990) and hypothetically lower present-day values in accordance with Ruddiman’s Early Anthropogenic Hypothesis (240 ppm CO2 and 450 ppb CH4). The model is run at two different resolutions: a relatively coarse horizontal configuration (T42, approximately 2.8 degrees) and comparatively fine resolution (T85, approximately 1.4 degrees). Although under contemporary greenhouse forcing the extent of permanent boreal snow cover in the two model configurations is similar, imposing lower concentrations of CO2 and CH4 generates much more extensive glacial inception in the T85 experiment (150% increase) than in the T42 version (80% increase). Furthermore, the spatial patterns of glacial inception differ considerably. Only the T85 resolution produces widespread permanent snow cover over the Rocky Mountains and on Baffin Island, consistent with geologic evidence for ice sheet nucleation in northeastern Canada. Although much of the enhanced sensitivity in the higher-resolution simulations is directly attributable to the colder and wetter conditions around elevated topography, some of the response also appears to be driven dynamically and remotely as a function of the simulated elevation of Greenland. The colder conditions over and downstream of the Greenland Ice Sheet in the modern T85 simulation promote a smaller cooling locally under lowered greenhouse forcing that seems to activate a wave-1 dynamical response in the atmospheric pressure field. The resulting circulation anomalies favor stronger upslope wind flow from the Pacific Ocean over the northern Rocky Mountains, enhancing the regional development of a permanent snow pack. Although these experiments are driven by greenhouse forcing rather than historical orbital variations, we believe that our findings apply to the general mechanisms of glacial inception.

Vavrus, S. J.; Philippon-Berthier, G.; Kutzbach, J. E.; Ruddiman, W. F.

2009-12-01

345

Concerning Evidence for Fingerprints of Glacial Melting  

Microsoft Academic Search

DOUGLAS, B.C., 2008. Concerning evidence for fingerprints of glacial melting. Journal of Coastal Research, 24(2B), 218-227. West Palm Beach (Florida), ISSN 0749-0208. Recent investigations of tide gauge and hydrographic data point to the conclusion that twentieth-century global sea- level rise was about 1.8 mm\\/y, with significant decadal and longer variability. Ocean thermal expansion can account for about 0.5 mm\\/y of

Bruce C. Douglas

2008-01-01

346

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

PubMed Central

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

Fedorov, Vadim B; Stenseth, Nils Chr

2002-01-01

347

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

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.

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

2009-01-01

348

Early Pleistocene climate cycles in continental deposits of the Lesser Caucasus of Armenia inferred from palynology, magnetostratigraphy, and 40Ar/ 39Ar dating  

NASA Astrophysics Data System (ADS)

Plio-Pleistocene diatomitic sequences in the Shamb paleo-lake (South Armenia, Lesser Caucasus) offer a rare opportunity to give new insights on the paleo-climate of Western Asia. We present an integrated palynological, 40Ar/ 39Ar geochronologic and magnetostratigraphic study for the most complete section in the sedimentary deposits of the Shamb paleo-lake. 40Ar/ 39Ar dating of two volcaniclastic layers provided ages of 1.24 ± 0.03 and 1.16 ± 0.02 Ma (2? ?). Magnetostratigraphic data show that the entire Shamb section is of reversed polarity which, combined with 40Ar/ 39Ar dating, suggests that the entire section correlates with part of the Matuyama period (1.785-1.070 Ma). Pollen assemblages and macroremains diversity clearly show an alternation of glacial and interglacial phases. Age calibrations and accumulation rate extrapolation allow a direct correlation of climate changes with the global isotopic curve, and show that the Shamb section probably ranges from approximately 1.300 to 1.080 Ma (marine isotopic stages 40 to 31). The vegetation of the Lesser Caucasus developed in a mosaic pattern in a Pleistocene continental, mostly arid climate, comparable to the present-day climate. The observed vegetation changes record a dominant climate response to the obliquity orbital parameter, but the influence of precession could not be established from the Shamb data. Pollen and macroflora both indicate that glacial periods were cold and dry and that interglacials were warm with local humidity. The Early Pleistocene climatic model for Western Asia is thus similar to the climatic model for the Mediterranean area.

Joannin, Sébastien; Cornée, Jean-Jacques; Münch, Philippe; Fornari, Michel; Vasiliev, Iuliana; Krijgsman, Wout; Nahapetyan, Samuel; Gabrielyan, Ivan; Ollivier, Vincent; Roiron, Paul; Chataigner, Christine

2010-03-01

349

Post-glacial expansion into the Paleozoic Plateau: evidence of an Ozarkian refugium for the Ozark minnow Notropis nubilus (Teleostei: Cypriniformes).  

PubMed

Genetic variation was examined within the Ozark minnow Notropis nubilus using complete mtDNA cytochrome b gene sequences from 160 individuals representing 30 localities to test hypotheses on the origin of the distribution. Phylogenetic analyses revealed three strongly supported clades of haplotypes consistent with geographic distributions: a clade from the Western Ozarks, a clade from the Southern Ozarks and a clade from the Northern Ozarks and upper Mississippi River basin. The estimated mean ages of these clades indicated that they diverged during pre-Illinoian glacial cycles extending from the late Pliocene into the early Pleistocene. Results of demographic analyses based on coalescent approaches supported the hypothesis that the Paleozoic Plateau was not a refugium for N. nubilus during periodic glacial advances. There is evidence of a genetic signature of northern expansion into the Paleozoic Plateau from a Southern Ozarkian refugium. Populations expanded out of drainages in the Northern Ozarks into the Paleozoic Plateau during the late Pleistocene. Subsequently, the two regions were isolated due to the recent extirpation of intervening populations caused by the loss of suitable habitat. PMID:21039494

Berendzen, P B; Dugan, J F; Gamble, T

2010-10-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

351

The Atlantic-Mediterranean watershed, river basins and glacial history shape the genetic structure of Iberian poplars.  

PubMed

Recent phylogeographic studies have elucidated the effects of Pleistocene glaciations and of Pre-Pleistocene events on populations from glacial refuge areas. This study investigates those effects in riparian trees (Populus spp.), whose particular features may convey enhanced resistance to climate fluctuations. We analysed the phylogeographic structure of 44 white (Populus alba), 13 black (Populus nigra) and two grey (Populus x canescens) poplar populations in the Iberian Peninsula using plastid DNA microsatellites and sequences. We also assessed fine-scale spatial genetic structure and the extent of clonality in four white and one grey poplar populations using nuclear microsatellites and we determined quantitative genetic differentiation (Q(ST) ) for growth traits in white poplar. Black poplar displayed higher regional diversity and lower differentiation than white poplar, reflecting its higher cold-tolerance. The dependence of white poplar on phreatic water was evidenced by strong differentiation between the Atlantic and Mediterranean drainage basins and among river basins, and by weaker isolation by distance within than among river basins. Our results suggest confinement to the lower river courses during glacial periods and moderate interglacial gene exchange along coastlines. In northern Iberian river basins, white poplar had lower diversity, fewer private haplotypes and larger clonal assemblies than in southern basins, indicating a stronger effect of glaciations in the north. Despite strong genetic structure and frequent asexual propagation in white poplar, some growth traits displayed adaptive divergence between drainage and river basins (Q(ST) >F(ST)), highlighting the remarkable capacity of riparian tree populations to adapt to regional environmental conditions. PMID:22624974

Macaya-Sanz, D; Heuertz, M; López-de-Heredia, U; De-Lucas, A I; Hidalgo, E; Maestro, C; Prada, A; Alía, R; González-Martínez, S C

2012-05-24

352

Treponemal infection in a Pleistocene bear.  

PubMed

The age and origins of the organisms that cause syphilis (treponemes) have long been matters for controversy. The widely-held belief that Columbus's ship brought the disease from the New World to Europe rests on identification of the classic lesions in Inca, Aztec and Mississippian bones that date from 1,000 to 3,000 years before present. But these were not confirmed by immunological techniques. We have observed lesions characteristic of treponemal infection in a Pleistocene bear from Indiana (dated 11,500 years BP) which give a positive result when tested with the antisera used by the US Center for Disease Control for verification of syphilis infection. This is the earliest detection of treponemal disease using contemporary techniques. PMID:3627242

Rothschild, B M; Turnbull, W

353

Nuclear DNA sequences from late Pleistocene megafauna.  

PubMed

We report the retrieval and characterization of multi- and single-copy nuclear DNA sequences from Alaskan and Siberian mammoths (Mammuthus primigenius). In addition, a nuclear copy of a mitochondrial gene was recovered. Furthermore, a 13,000-year-old ground sloth and a 33,000-year-old cave bear yielded multicopy nuclear DNA sequences. Thus, multicopy and single-copy genes can be analyzed from Pleistocene faunal remains. The results also show that under some circumstances, nucleotide sequence differences between alleles found within one individual can be distinguished from DNA sequence variation caused by postmortem DNA damage. The nuclear sequences retrieved from the mammoths suggest that mammoths were more similar to Asian elephants than to African elephants. PMID:10555277

Greenwood, A D; Capelli, C; Possnert, G; Pääbo, S

1999-11-01

354

Evidence for range stasis during the latter Pleistocene for the Atlantic Coastal Plain endemic genus, Pyxidanthera Michaux.  

PubMed

The general phylogeographical paradigm for eastern North America (ENA) is that many plant and animal species retreated into southern refugia during the last glacial period, then expanded northward after the last glacial maximum (LGM). However, some taxa of the Gulf and Atlantic Coastal Plain (GACP) demonstrate complex yet recurrent distributional patterns that cannot be explained by this model. For example, eight co-occurring endemic plant taxa with ranges from New York to South Carolina exhibit a large disjunction separating northern and southern populations by >300?km. Pyxidanthera (Diapensiaceae), a plant genus that exhibits this pattern, consists of two taxa recognized as either species or varieties. We investigated the taxonomy and phylogeography of Pyxidanthera using morphological data, cpDNA sequences, and amplified fragment length polymorphism markers. Morphological characters thought to be important in distinguishing Pyxidanthera barbulata and P. brevifolia demonstrate substantial overlap with no clear discontinuities. Genetic differentiation is minimal and diversity estimates for northern and southern populations of Pxyidanthera are similar, with no decrease in rare alleles in northern populations. In addition, the northern populations harbour several unique cpDNA haplotypes. Pyxidanthera appears to consist of one morphologically variable species that persisted in or near its present range at least through the latter Pleistocene, while the vicariance of the northern and southern populations may be comparatively recent. This work demonstrates that the refugial paradigm is not always appropriate and GACP endemic plants, in particular, may exhibit phylogeographical patterns qualitatively different from those of other ENA plant species. PMID:20819166

Wall, Wade A; Douglas, Norman A; Xiang, Qiu-Yun Jenny; Hoffmann, William A; Wentworth, Thomas R; Hohmann, Matthew G

2010-09-01

355

Paleoceanography of the Okhotsk Sea During the Last Glacial Cycle Deduced From Radiolarian Record  

NASA Astrophysics Data System (ADS)

Paleoceanographic record contained in the Okhotsk Sea sediments provide pertinent information on global climate change during the late Pleistocene. This stems from its unique oceanographic nature with seasonal sea-ice cover in this relatively low latitude setting resulting in formation of the North Pacific Intermediate Water (NPIW). In order to unravel siliceous microfossil record in the Okhotsk Sea, we have acquired four piston-cores and more than a dozen multiple cores, together with flux materials from four time-series sediment traps at two locations, were obtained in the area during the 1998-1999 periods on board R/V Professor Khromov, Far East Hydrometeological Institute, Russia, as part of "Joint Japanese-Russian-U. S. Study of the Sea of Okhotsk". Seasonal fluxes of radiolarians (No. shells m-2 day-1) showed significant maxima during summer through autumn at both trap stations. The radiolarian fluxes during August to November accounted for 60-87 percent of total annual flux, suggesting that the radiolarian production is significantly controlled by the sea-ice coverage. The radiolarian accumulation rates (RAR: No. shells cm-2 kyr-1) from piston cores, varied substantially, roughly corresponding to the glacial-interglacial cycles. Especially the RAR of Cycladophora davisiana, the dominant radiolarian taxon in the Holocene Okhotsk Sea sediments, contributed much to this trend. The last occurrence (LO) of Lychnocanomma nipponica sakaii in the Okhotsk Sea is at about 50ky BP, which is synchronous with that in the North Pacific. Such a synchronous nature of the LO of this species is important for biostratigraphy of the North Pacific and the northern marginal seas for the late Pleistocene.

Takahashi, K.; Okazaki, Y.; Yoshitani, H.

2001-05-01

356

Male strategies and Plio-Pleistocene archaeology.  

PubMed

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

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

2002-12-01

357

Paleomagnetic chronology of pliocene-early pleistocene climates and the plio-pleistocene boundary in new zealand.  

PubMed

The paleomagnetic chronology established for a Pliocene-Early Pleistocene sequence of marine sediments in New Zealand reveals that marked climatic coolings based on Foraminifera and oxygen isotope ratios in the late Cenozoic preceded the Pliocene-Pleistocene boundary, which is taken to be at the base of the Gilsá geomagnetic polarity event (1.79 million years ago). Major temperature fluctuations occur from the upper Gauss (Middle Pliocene) to middle Matuyama (Early Pleistocene). The first major Pliocene cooling spans the Gauss-Matuyama boundary (2.43 million years ago). A uniform and rapid (40 centimeters per 1000 years) rate of deposition is shown for the moderately shallow marine environment. PMID:17736221

Kennett, J P; Watkins, N D; Vella, P

1971-01-22

358

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

359

Late Ordovician (Ashgillian) glacial deposits in southern Jordan  

Microsoft Academic Search

The Late Ordovician (Ashgillian) glacial deposits in southern Jordan, comprise a lower and upper glacially incised palaeovalley system, occupying reactivated basement and Pan-African fault-controlled depressions. The lower palaeovalley, incised into shoreface sandstones of the pre-glacial Tubeiliyat Formation, is filled with thin glaciofluvial sandstones at the base, overlain by up to 50 m of shoreface sandstone. A prominent glaciated surface near

Brian R. Turner; Issa M. Makhlouf; Howard A. Armstrong

2005-01-01

360

Reorganization of Ice Sheet Flow Patterns in Arctic Canada Prior to the Mid-Pleistocene Transition  

NASA Astrophysics Data System (ADS)

The Foxe sector of the Laurentide Ice Sheet (LIS) experienced a complex and dynamic interplay between cold-based, non-erosive ice on uplands, fast-moving outlet glaciers that carved deep fiords through the Arctic Cordillera, and even more erosive ice streams that occupied larger straits and sounds, transporting ice from the Foxe Dome to calving margins in Baffin Bay and the Labrador Sea. The high topography of Baffin Island forms a broad barrier to the flow of ice to these calving margins and gradually has been dissected since the onset of Northern Hemisphere glaciation. However, evidence for the evolution of LIS erosion and basal thermal regime patterns during successive glaciations is poorly preserved in the geologic record. We use a new approach utilizing published till geochemistry and cosmogenic radionuclide (CRN) data to constrain the development of the fiorded coastline and the distribution of cold-based ice across central Baffin Island in both spatial and temporal domains over many glacial-interglacial cycles. The combination of till geochemistry data, which is used to characterize till weathering, and modeled CRN burial-exposure histories provides strong evidence for a shift in basal thermal regimes across the interior plateaux of Baffin Island between 1.9 and 1.2 Ma. While it may be coincidence that this time interval abuts the onset of the mid-Pleistocene transition (MPT), it has been hypothesized that changes in subglacial conditions were potentially an important mechanism in altering LIS dynamics across the MPT. Prior to this time, ice was likely wet-based and erosive across the majority of the Baffin Island interior, but by 1.9-1.2 Ma, some parts of the landscape became perpetually covered by cold-based ice during glaciations, a pattern that persisted through the last glacial cycle. The modern fiord system also must have developed by this time, and preferential channeling of ice flow into major fiords may have been sufficient to effectively shut off ice flow across the landscape between outlet glaciers. These results imply that there was a major shift in the basal thermal regime across the northeastern LIS, and the subsequent expansion of cold-based ice and the concentration of ice flow in fewer outlet systems across this region may help explain the cause of the MPT from 41- to 100-kyr glacial cycles.

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

2010-12-01

361

The circumboreal tundra-taiga interface: late Pleistocene and Holocene changes.  

PubMed

Creating a global perspective on past treeline changes is problematic due to the varying methods and definitions used. A general lack of a detailed description of the modern treeline position and vegetation complicates any comparative analysis of the magnitude of the most important changes. However, one seemingly common factor in most regions was an extremely rapid dispersal of trees when climate warmed drastically from full glacial conditions. Most Arctic treelines reached their northernmost positions in the early Holocene and receded to present positions starting at about 5.8 ka. The early occupation of the northernmost sites in ice-free and early deglaciated areas was possible because of the close proximity of invading trees in nearby glacial refugia, particularly in Fennoscandia and northern Russia. In Canada, the Northwest Territories and Quebec-Labrador were out of phase with this general trend due to their late deglaciation. However, even here colonization was rapid, indicating that the tree species were present adjacent to the glaciers. Following this trend and based on the present evidence, we propose a scenario of a continuous but modest occupation of eastern Beringia by spruce during the late-Pleistocene instead of an exceptionally rapid spread of conifers from the glacial refugium south of the Laurentide ice sheet (2000 to 3000 km in about 200 years), which typically has been assumed. Macrofossil evidence of scattered occurrences of "exotic species" (for instance Siberian larch in central Sweden) far from their natural range limits in the early Holocene highlight the disparity between pollen and macrofossil analyses. It questions the validity of assigned pollen percentages to indicate the presence of a species within a region as these species were not observed in the pollen record. Thus, it is likely that trees were present at any given site well before the rise in pollen abundance. There is still a large potential to improve our knowledge about the environmental history of the circumboreal treeline areas. In particular, future research should concentrate not only on patterns of species displacement, but on finding the factors, apart from climate, which cause treeline shifts. PMID:12374054

Payette, S; Eronen, M; Jasinski, J J P

2002-08-01

362

Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model.  

PubMed

Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle. PMID:16281042

Braun, Holger; Christl, Marcus; Rahmstorf, Stefan; Ganopolski, Andrey; Mangini, Augusto; Kubatzki, Claudia; Roth, Kurt; Kromer, Bernd

2005-11-10

363

Transient simulations of the last Glacial Cycle with an AOGCM  

NASA Astrophysics Data System (ADS)

Using FAMOUS, a fast atmosphere-ocean general circulation model (AOGCM), a number of transient climate runs simulating the last 120kyr have been carried out. This is the first time such experiments have been done with an AOGCM, providing a three-dimensional simulation of both atmosphere and ocean over this period, including internally generated temporal variability over periods from days to millennia and physically detailed representations of important processes such as clouds and precipitation. Although the model is fast, computational restrictions mean that the rate of change of the forcings has been increased by a factor of 10, making each experiment 12kyr long. Atmospheric greenhouse gases (GHGs), northern hemisphere ice sheets and variations in solar radiation arising from changes in the Earth's orbit are treated as forcing factors, and are applied both separately and combined in different experiments. The long-term temperature changes on Antarctica match well with reconstructions derived from ice-core data, as does variability on timescales longer than 10kyr. Last Glacial Maximum (LGM) cooling on Greenland is reasonably well simulated, although our simulations do not reproduce the abrupt, millennial scale climate shifts seen in northern hemisphere climate proxies or their slower southern hemisphere counterparts. The spatial pattern of sea surface cooling at the LGM matches reasonably proxy reconstructions reasonably well. There is significant anti-correlated variability in the strengths of the Atlantic Meridional Overturning Circulation (AMOC) and the Antarctic Circumpolar Current (ACC) on timescales greater than 10kyr in our experiments. GHG forcing weakens the AMOC and strengths the ACC, whilst the presence of northern hemisphere icesheets strengthens the AMOC and weakens the ACC. The structure of the AMOC at the LGM is found to be sensitive to the details of the ice-sheet reconstruction used. The precessional component of the orbital forcing induces ~20kyr oscillations in the AMOC and ACC, whose amplitude is mediated by changes in the eccentricity of the Earth's orbit. These forcing influences combine, to first order, in a linear fashion to produce the ocean variability seen in the run with all forcings and set the deep-water properties of the global ocean, which is key to determining the carbon inventory of the glacial ocean.

Smith, R. S.; Gregory, J. M.

2010-12-01

364

Mössbauer effect study of a pleistocenic Brazilian fossil  

NASA Astrophysics Data System (ADS)

Some preliminary Mössbauer effect results for a pleistocenic bone fossilized by mineralization process are presented. The presence of some iron-sulphur compounds permits to infer a correlation between the oxidation state of iron and the environmental conditions of fossilization.

de Araújo, J. H.; Kunrath, J. I.; da Costa, M. I.; Vasquez, A.; Alves, C.; Dantas de Oliveira, L. D.

1991-11-01

365

PLEISTOCENE MULTI-GLACIER HYPOTHESIS SUPPORTED BY NEWLY EXPOSED GLACIAL SEDIMENTS, SOUTH TWIN ISLAND, THE BRONX, NEW YORK  

Microsoft Academic Search

Based on our previous studies of ice-eroded features on the bedrock here and elsewhere in southeastern New York, we found evidence of three glaciations, with ice flow from the NNE (Glacier I of Table 1), from the NNW (Glaciers II and\\/or III, which created the spectacular set of parallel striae oriented N32°W-S32°E at South Twin Island), and from the NNE

John E. Sanders; Charles Merguerian; Jessica Levine; Paul M. Carter

366

40Ar/39Ar chronology of Late Pliocene and Early Pleistocene geomagnetic and glacial events in southern Argentina  

NASA Astrophysics Data System (ADS)

K-Ar dating and paleomagnetic directions from the lava sequence atop Cerro del Fraile, Argentina, contributed to the nascent Geomagnetic Polarity Time Scale (GPTS), recording the Réunion event, and the Olduvai and Jaramillo subchrons [Fleck et al., 1972]. New stratigraphy, paleomagnetic analyses, 40Ar/39Ar incremental heating ages, and unspiked K-Ar dating of 10 lava flows on Cerro del Fraile place these eruptions between 2.181±0.097 and 1.073±0.036 Ma and enhance this unique record, which includes seven tills interbedded with the lavas. The Réunion event is recorded by three lavas with transitional, normal, and reversed polarity that yielded identical 40Ar/39Ar isochron ages and a weighted mean age of 2.136±0.019 Ma. When combined with 40Ar/39Ar ages from lavas on Réunion Island and a normal tuff in the Massif Central, the age of the Réunion event is 2.137±0.016 Ma and is older by ˜50 kyr than the 2.086±0.016 Ma Huckleberry Ridge event. The onset and termination of the Olduvai are similarly constrained to 1.922±0.066 Ma and 1.775±0.015 Ma, whereas the onset of the Jaramillo occurred 1.069±0.011 Ma. A discordant age spectrum from another transitional lava gave a total fusion age of 1.61 Ma and an unspiked K-Ar age of 1.43 Ma. It is uncertain whether this corresponds to the Gilsa, Gardar, Stage 54, or Sangiran events, or represents an unrecognized period of geomagnetic instability. Deposition of till on the piedmont surface prior to 2.186 Ma and six subsequent tills between 2.186 Ma and ˜1.073 Ma mark frequent glaciations of southern South America during marine oxygen isotope stages 82 to 48.

Singer, Brad S.; Brown, Laurie L.; Rabassa, Jorge O.; Guillou, Hervé

367

Three Holocene and late Pleistocene glacial stages inferred from moraines in the Lingshi and Thanza village areas, Bhutan  

Microsoft Academic Search

Moraines formed by valley glaciers in Lingshi area, northwestern Bhutan constitute three distinct stages with contrasts in the spatial distribution and size of moraines, and surface features such as clasts, soils and vegetation. Moraines in the Thanza Village area, northern Bhutan, show three stages with similar characteristics to those in the Lingshi area. Using morphostratigraphic criteria, these three stages correlate

Shuji Iwata; Chiyuki Narama; Karma

2002-01-01

368

Hypsometric analysis to identify spatially variable glacial erosion  

NASA Astrophysics Data System (ADS)

Relatively little research has been undertaken on the use of digital elevation models to recognize the spatially variable glacial imprint of a landscape. Using theoretical topographies and a landscape evolution model, we investigate to what extent the hypsometric analysis of digital elevation models may be used to recognize the glacial signature of mountain ranges. A new morphometric parameter, which we term the hypsokyrtome (from the Greek: ipsos = elevation, kyrtoma = curvature), is derived from the gradient of the hypsometric curve. The efficacy of the hypsometric integral and hypsokyrtome is tested through the study of the Ben Ohau Range, New Zealand, whose glacial imprint has been described previously. With a numerical model we further test the geomorphic parameters in describing the morphologies of regions subject to diverse climatic and tectonic conditions. The hypsokyrtome is highly sensitive to glacial erosion, and the maps produced provide insights into the spatial distribution of glacial erosion. We use SRTM data and focus on two alternative geomorphic settings: the European Alps and the Apennines. The former has been affected by both fluvial and glacial erosion while the latter mainly exhibits a fluvially dominated morphology. The correlation between elevations with increased glacial erosion and Last Glacial Maximum (LGM) equilibrium line altitudes (ELAs) suggests the prevalence of a "glacial buzz saw" in the Alps, indicating that climate may put a limit on alpine topography.

Sternai, P.; Herman, F.; Fox, M. R.; Castelltort, S.

2011-09-01

369

Abrupt Climate Oscillations During the Last Deglaciation in Central North America  

Microsoft Academic Search

Evidence from stable isotopes and a variety of proxies from two Ontario lakes demonstrate that many of the late glacial—to—early Holocene events that are well known from the North Atlantic seaboard, such as the Gerzensee-Killarney Oscillation (also known as the Intra-Aller¿d Cold Period), Younger Dryas, and Preboreal Oscillation, also occurred in central North America. These results thus imply that climatic

Zicheng Yu; Ulrich Eicher

1998-01-01

370

The Preboreal oscillation around the Nordic Seas: terrestrial and lacustrine responses  

Microsoft Academic Search

The occurrence of an early Preboreal climatic cooling\\/oscillation (PBO) in lacustrine and glacial records from northwest Europe, Iceland and Greenland is reviewed and documented. The often subtle response of the proxy records to this oscillation, in combination with its short duration, make it difficult to detect. Owing to its chronostratigraphic position between the 10 000-9900 and 9600-9500 14C plateaux (c.

S. Björck; M. Rundgren; Ó. Ingólfsson; S. Funder

1997-01-01

371

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

SciTech Connect

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.

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

1985-01-01

372

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

SciTech Connect

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.

Cocker, M.D. (Georgia Geologic Survey, Atlanta, GA (United States))

1993-03-01

373

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

SciTech Connect

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.

Dethier, D.P. [Williams College, Williamstown, MA (United States); Reneau, S.L. [Los Alamos National Lab., NM (United States)

1996-06-01