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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)
    Details
    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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    The role of carbon dioxide during the onset of Antarctic glaciation (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-12-07
    Description: Earth's modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation ~33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth's climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO(2)) during major climatic change. Previously published records of alkenone-based CO(2) from high- and low-latitude ocean localities suggested that CO(2) increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO(2) levels, biasing long-term trends. Our results show that CO(2) declined before and during Antarctic glaciation and support a substantial CO(2) decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO(2) thresholds.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pagani, Mark -- Huber, Matthew -- Liu, Zhonghui -- Bohaty, Steven M -- Henderiks, Jorijntje -- Sijp, Willem -- Krishnan, Srinath -- DeConto, Robert M -- New York, N.Y. -- Science. 2011 Dec 2;334(6060):1261-4. doi: 10.1126/science.1203909.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA. mark.pagani@yale.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22144622" target="_blank"〉PubMed〈/a〉
    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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    Antarctic ice-sheet sensitivity to obliquity forcing enhanced through ocean connections (2019)
    Springer Nature
    Details
    Publication Date: 2019
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
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    Past extreme warming events linked to massive carbon release from thawing permafrost (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-04-07
    Description: Between about 55.5 and 52 million years ago, Earth experienced a series of sudden and extreme global warming events (hyperthermals) superimposed on a long-term warming trend. The first and largest of these events, the Palaeocene-Eocene Thermal Maximum (PETM), is characterized by a massive input of carbon, ocean acidification and an increase in global temperature of about 5 degrees C within a few thousand years. Although various explanations for the PETM have been proposed, a satisfactory model that accounts for the source, magnitude and timing of carbon release at the PETM and successive hyperthermals remains elusive. Here we use a new astronomically calibrated cyclostratigraphic record from central Italy to show that the Early Eocene hyperthermals occurred during orbits with a combination of high eccentricity and high obliquity. Corresponding climate-ecosystem-soil simulations accounting for rising concentrations of background greenhouse gases and orbital forcing show that the magnitude and timing of the PETM and subsequent hyperthermals can be explained by the orbitally triggered decomposition of soil organic carbon in circum-Arctic and Antarctic terrestrial permafrost. This massive carbon reservoir had the potential to repeatedly release thousands of petagrams (10(15) grams) of carbon to the atmosphere-ocean system, once a long-term warming threshold had been reached just before the PETM. Replenishment of permafrost soil carbon stocks following peak warming probably contributed to the rapid recovery from each event, while providing a sensitive carbon reservoir for the next hyperthermal. As background temperatures continued to rise following the PETM, the areal extent of permafrost steadily declined, resulting in an incrementally smaller available carbon pool and smaller hyperthermals at each successive orbital forcing maximum. A mechanism linking Earth's orbital properties with release of soil carbon from permafrost provides a unifying model accounting for the salient features of the hyperthermals.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉DeConto, Robert M -- Galeotti, Simone -- Pagani, Mark -- Tracy, David -- Schaefer, Kevin -- Zhang, Tingjun -- Pollard, David -- Beerling, David J -- England -- Nature. 2012 Apr 4;484(7392):87-91. doi: 10.1038/nature10929.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01002, USA. deconto@geo.umass.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22481362" target="_blank"〉PubMed〈/a〉
    Keywords: Antarctic Regions ; Arctic Regions ; Atmosphere/chemistry ; Calibration ; Carbon/*analysis ; Carbon Cycle ; Ecosystem ; Feedback ; *Freezing ; Global Warming/*history ; Greenhouse Effect/*history ; History, Ancient ; Italy ; Models, Theoretical ; Seawater/chemistry ; Soil/*chemistry ; *Temperature
    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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  • 6
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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)
    Details
    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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  • 7
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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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  • 8
    Electronic Resource
    Electronic Resource
    Climate: Is the past the key to the future? (1997)
    Springer
    Geologische Rundschau 86 (1997), S. 471-491 
    Details
    ISSN: 0016-7835
    Keywords: Key words Climate change ; Paleoclimatology ; Cretaceous ; Holocene ; Quaternary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The climate of the Holocene is not well suited to be the baseline for the climate of the planet. It is an interglacial, a state typical of only 10% of the past few million years. It is a time of relative sea-level stability after a rapid 130-m rise from the lowstand during the last glacial maximum. Physical geologic processes are operating at unusual rates and much of the geochemical system is not in a steady state. During most of the Phanerozoic there have been no continental ice sheets on the earth, and the planet’s meridional temperature gradient has been much less than it is presently. Major factors influencing climate are insolation, greenhouse gases, paleogeography, and vegetation; the first two are discussed in this paper. Changes in the earth’s orbital parameters affect the amount of radiation received from the sun at different latitudes over the course of the year. During the last climate cycle, the waxing and waning of the northern hemisphere continental ice sheets closely followed the changes in summer insolation at the latitude of the northern hemisphere polar circle. The overall intensity of insolation in the northern hemisphere is governed by the precession of the earth’s axis of rotation, and the precession and ellipticity of the earth’s orbit. At the polar circle a meridional minimum of summer insolation becomes alternately more and less pronounced as the obliquity of the earth’s axis of rotation changes. Feedback processes amplify the insolation signal. Greenhouse gases (H2O, CO2, CH4, CFCs) modulate the insolation-driven climate. The atmospheric content of CO2 during the last glacial maximum was approximately 30% less than during the present interglacial. A variety of possible causes for this change have been postulated. The present burning of fossil fuels, deforestation, and cement manufacture since the beginning of the industrial revolution have added CO2 to the atmosphere when its content due to glacial-interglacial variation was already at a maximum. Anthropogenic activity has increased the CO2 content of the atmosphere to 130% of its previous Holocene level, probably higher than at any time during the past few million years. During the Late Cretaceous the atmospheric CO2 content was probably about four times that of the present, the level to which it may rise at the end of the next century. The results of a Campanian (80 Ma) climate simulation suggest that the positive feedback between CO2 and another important greenhouse gas, H2O, raised the earth’s temperature to a level where latent heat transport became much more significant than it is presently, and operated efficiently at all latitudes. Atmospheric high- and low-pressure systems were as much the result of variations in the vapor content of the air as of temperature differences. In our present state of knowledge, future climate change is unpredictable because by adding CO2 to the atmosphere we are forcing the climate toward a “greenhouse” mode when it is accustomed to moving between the glacial–interglacial “icehouse” states that reflect the waxing and waning of ice sheets. At the same time we are replacing freely transpiring C3 plants with water-conserving C4 plants, producing a global vegetation complex that has no past analog. The past climates of the earth cannot be used as a direct guide to what may occur in the future. To understand what may happen in the future we must learn about the first principles of physics and chemistry related to the earth’s system. The fundamental mechanisms of the climate system are best explored in simulations of the earth’s ancient extreme climates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050155
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  • 9
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    Tidally Driven Interannual Variation in Extreme Sea Level Frequencies in the Gulf of Maine (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-29
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    Greenland-Wide Seasonal Temperatures During the Last Deglaciation (2018)
    American Geophysical Union
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    Publication Date: 2018-02-19
    Description: The sensitivity of the Greenland ice sheet to climate forcing is of key importance in assessing its contribution to past and future sea level rise. Surface mass loss occurs during summer, and accounting for temperature seasonality is critical in simulating ice sheet evolution and in interpreting glacial landforms and chronologies. Ice core records constrain the timing and magnitude of climate change but are largely limited to annual mean estimates from the ice sheet interior. Here we merge ice core reconstructions with transient climate model simulations to generate Greenland-wide and seasonally resolved surface air temperature fields during the last deglaciation. Greenland summer temperatures peak in the early Holocene, consistent with records of ice core melt layers. We perform deglacial Greenland ice sheet model simulations to demonstrate that accounting for realistic temperature seasonality decreases simulated glacial ice volume, expedites the deglacial margin retreat, mutes the impact of abrupt climate warming, and gives rise to a clear Holocene ice volume minimum. ©2018. American Geophysical Union. All Rights Reserved.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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