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  • 1
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    Thresholds for Cenozoic bipolar glaciation (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-10-04
    Description: The long-standing view of Earth's Cenozoic glacial history calls for the first continental-scale glaciation of Antarctica in the earliest Oligocene epoch ( approximately 33.6 million years ago), followed by the onset of northern-hemispheric glacial cycles in the late Pliocene epoch, about 31 million years later. The pivotal early Oligocene event is characterized by a rapid shift of 1.5 parts per thousand in deep-sea benthic oxygen-isotope values (Oi-1) within a few hundred thousand years, reflecting a combination of terrestrial ice growth and deep-sea cooling. The apparent absence of contemporaneous cooling in deep-sea Mg/Ca records, however, has been argued to reflect the growth of more ice than can be accommodated on Antarctica; this, combined with new evidence of continental cooling and ice-rafted debris in the Northern Hemisphere during this period, raises the possibility that Oi-1 represents a precursory bipolar glaciation. Here we test this hypothesis using an isotope-capable global climate/ice-sheet model that accommodates both the long-term decline of Cenozoic atmospheric CO(2) levels and the effects of orbital forcing. We show that the CO(2) threshold below which glaciation occurs in the Northern Hemisphere ( approximately 280 p.p.m.v.) is much lower than that for Antarctica ( approximately 750 p.p.m.v.). Therefore, the growth of ice sheets in the Northern Hemisphere immediately following Antarctic glaciation would have required rapid CO(2) drawdown within the Oi-1 timeframe, to levels lower than those estimated by geochemical proxies and carbon-cycle models. Instead of bipolar glaciation, we find that Oi-1 is best explained by Antarctic glaciation alone, combined with deep-sea cooling of up to 4 degrees C and Antarctic ice that is less isotopically depleted (-30 to -35 per thousand) than previously suggested. Proxy CO(2) estimates remain above our model's northern-hemispheric glaciation threshold of approximately 280 p.p.m.v. until approximately 25 Myr ago, but have been near or below that level ever since. This implies that episodic northern-hemispheric ice sheets have been possible some 20 million years earlier than currently assumed (although still much later than Oi-1) and could explain some of the variability in Miocene sea-level records.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Deconto, Robert M -- Pollard, David -- Wilson, Paul A -- Palike, Heiko -- Lear, Caroline H -- Pagani, Mark -- England -- Nature. 2008 Oct 2;455(7213):652-6. doi: 10.1038/nature07337.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA. deconto@geo.umass.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18833277" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antarctic Regions ; Atmosphere/*chemistry ; Calcium ; Carbon Dioxide/*analysis ; *Cold Climate ; Greenhouse Effect ; History, 21st Century ; History, Ancient ; *Ice Cover ; Magnesium ; Oxygen Isotopes ; Seasons
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 2
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    Modelling West Antarctic ice sheet growth and collapse through the past five million years (2009)
    Nature Publishing Group (NPG)
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    Publication Date: 2009-03-20
    Description: The West Antarctic ice sheet (WAIS), with ice volume equivalent to approximately 5 m of sea level, has long been considered capable of past and future catastrophic collapse. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around approximately 15 kyr ago before retreating to near-modern locations by approximately 3 kyr ago. Prior collapses during the warmth of the early Pliocene epoch and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments. Until now, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31 ( approximately 1.07 Myr ago) and other super-interglacials.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pollard, David -- DeConto, Robert M -- England -- Nature. 2009 Mar 19;458(7236):329-32. doi: 10.1038/nature07809.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA. pollard@essc.psu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19295608" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Diatoms ; History, Ancient ; *Ice Cover ; *Models, Theoretical ; Oceans and Seas ; Oxygen Isotopes ; Seawater ; Snow ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    2.8 million years of Arctic climate change from Lake El'gygytgyn, NE Russia (2012)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2012-06-23
    Description: The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ~4 degrees to 5 degrees C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Melles, Martin -- Brigham-Grette, Julie -- Minyuk, Pavel S -- Nowaczyk, Norbert R -- Wennrich, Volker -- DeConto, Robert M -- Anderson, Patricia M -- Andreev, Andrei A -- Coletti, Anthony -- Cook, Timothy L -- Haltia-Hovi, Eeva -- Kukkonen, Maaret -- Lozhkin, Anatoli V -- Rosen, Peter -- Tarasov, Pavel -- Vogel, Hendrik -- Wagner, Bernd -- New York, N.Y. -- Science. 2012 Jul 20;337(6092):315-20. doi: 10.1126/science.1222135. Epub 2012 Jun 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Geology and Mineralogy, University of Cologne, Zuelpicher Strasse 49a, D-50674 Cologne, Germany. mmelles@uni-koeln.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22722254" target="_blank"〉PubMed〈/a〉
    Keywords: Arctic Regions ; *Climate Change ; *Cold Climate ; Geologic Sediments ; Ice Cover ; *Lakes ; Radiometric Dating ; Russia ; Time Factors
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Contribution of Antarctica to past and future sea-level rise (2016)
    Nature Publishing Group (NPG)
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    Publication Date: 2016-04-01
    Description: Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics-including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs-that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉DeConto, Robert M -- Pollard, David -- England -- Nature. 2016 Mar 31;531(7596):591-7. doi: 10.1038/nature17145.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA. ; Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27029274" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Atmosphere ; Calibration ; Climate Change/*statistics & numerical data ; Greenhouse Effect/statistics & numerical data ; *Ice Cover ; *Models, Theoretical ; Seawater/*analysis ; Temperature ; Time Factors ; Water Movements
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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