The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination

QUATERNARY SCIENCE REVIEWS

卷:114

Article

Schaefer, Joerg M.^1,2  Putnam, Aaron E.¹  Denton, George H.^3,4  Kaplan, Michael R.¹  Birkel, Sean^3,4  Doughty, Alice M.⁵  Kelley, Sam⁶  Barrell, David J. A.⁷  Finkel, Robert C.⁸  Winckler, Gisela^1,2  Anderson, Robert F.^1,2  Ninneman, Ulysses S.⁹  Barker, Stephen¹⁰  Schwartz, Roseanne¹  Andersen, Bjorn G.¹¹  Schluechter, Christian^12,13 

[1] Lamont Doherty Earth Observ, Geochem, Palisades, NY 10964 USA

[2] Columbia Univ, Dept Earth & Environm Sci, New York, NY 10027 USA

[3] Univ Maine, Dept Earth Sci, Orono, ME 04469 USA

[4] Climate Change Inst, Orono, ME 04469 USA

[5] Victoria Univ Wellington, Wellington 6140, New Zealand

[6] SUNY Buffalo, Dept Geol, Buffalo, NY 14260 USA

[7] GNS Sci, Dunedin, New Zealand

[8] Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 95064 USA

[9] Univ Bergen, Dept Earth Sci, N-500 Bergen, Norway

[10] Cardiff Univ, Sch Earth & Ocean Sci, Cardiff CF10 3AT, S Glam, Wales

[11] Univ Oslo, Dept Geol, N-0316 Oslo, Norway

[12] Univ Bern, Inst Geol Sci, CH-3012 Bern, Switzerland

[13] Univ Bern, Oeschger Ctr Climate Change Res, CH-3012 Bern, Switzerland

关键词: Ice ages;    Terminations;    Marine Isotope Stage 4;    Paleoclimate;    Last Glacial Maximum;    Moraines;    Surface exposure dating;    Cosmogenic nuclides;   

DOI  :  10.1016/j.quascirev.2015.02.009

来源: Elsevier

【 摘 要 】

Glacial maxima and their terminations provide key insights into inter-hemispheric climate dynamics and the coupling of atmosphere, surface and deep ocean, hydrology, and cryosphere, which is fundamental for evaluating the robustness of earth's climate in view of ongoing climate change. The Last Glacial Maximum (LGM, similar to 26-19 ka ago) is widely seen as the global cold peak during the last glacial cycle, and its transition to the Holocene interglacial, dubbed 'Termination 1 (T1)', as the most dramatic climate reorganization during this interval. Climate records show that over the last 800 ka, ice ages peaked and terminated on average every 100 ka (100 ka world'). However, the mechanisms pacing glacial interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood. Here we show evidence for a full glacial maximum in the Southern Hemisphere 65.1 +/- 2.7 ka ago and its 'Unfinished Termination'. Our Be-10 chronology combined with a model simulation demonstrates that New Zealand's glaciers reached their maximum position of the last glacial cycle during Marine Isotope Stage-4 (MIS-4). Southern ocean and greenhouse gas records indicate coeval peak glacial conditions, making the case for the Southern Glacial Maximum about halfway through the last glacial cycle and only 15 ka after the last warm period (MIS-5a). We present the hypothesis that subsequently, driven by boreal summer insolation forcing, a termination began but remained unfinished, possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the North Atlantic through Heinrich Stadial 6 to drive a full termination. Yet the Unfinished Termination left behind substantial ice on the northern continents (about 50% of the full LGM ice volume) and after another 45 ka of cooling and ice sheet growth the earth was at inter-hemispheric Last Glacial Maximum configuration, when similar orbital forcing hit maximum-size northern ice sheets and ushered in T1 and thus the ongoing interglacial. This argument highlights the critical role of full glacial conditions in both hemispheres for terminations and implies that the Southern Hemisphere climate could transition from interglacial to full glacial conditions in about 15,000 years, while the Northern Hemisphere and its continental ice-sheets required half a glacial cycle. (C) 2015 Elsevier Ltd. All rights reserved.

【 授权许可】

Free