The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination
The Southern Glacial Maximum 65,000 years ago and its Unfinished Termination
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DOI：
10.1016/j.quascirev.2015.02.009
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发表时间：
2015-04
影响因子：
4
通讯作者：
J. Schaefer;A. Putnam;G. Denton;M. Kaplan;S. Birkel;A. Doughty;Sam Kelley;D. Barrell;Robert C. Finkel;G. Winckler;Robert F. Anderson;U. Ninneman;S. Barker;R. Schwartz;B. G. Andersen;C. Schluechter
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作者：
J. Schaefer;A. Putnam;G. Denton;M. Kaplan;S. Birkel;A. Doughty;Sam Kelley;D. Barrell;Robert C. Finkel;G. Winckler;Robert F. Anderson;U. Ninneman;S. Barker;R. Schwartz;B. G. Andersen;C. Schluechter
最大冰川及其终止为半球间气候动力学以及大气、表层和深海、水文学和冰冻圈的耦合提供了关键的见解，这对于评估持续气候变化下地球气候的稳健性至关重要。末次盛冰期（LGM）是末次冰期旋回中的全球冷峰，其向全新世间冰期的过渡被称为“终止1”（T1），是这一时期最剧烈的气候重组。气候记录显示，在过去的800 ka，冰河时代达到顶峰，平均每100 ka（“100 ka世界”）结束。然而，冰川-间冰期转换的机制仍然存在争议，特别是半球表现和潜在的轨道到区域驱动力的冰川极大期和随后的终止仍然知之甚少。我们的10 Be年代学结合模型模拟表明，新西兰的冰川达到了最后一个冰川周期的最大位置在海洋同位素阶段-4（MIS-4）。南部海洋和温室气体记录表明，同时代的高峰冰川条件，使情况下，南部冰川最大约中途通过最后一次冰期循环，只有15 ka后，最后一次温暖期（MIS-5a）。我们提出的假设，随后，北半球夏季日照强迫的驱动下，终止开始，但仍未完成，可能是因为北方冰盖只有适度的大，不能提供足够的融水通过海因里希体育场6驱动一个完整的终止北大西洋。然而，未完成的终结在北方大陆上留下了大量的冰（约占整个LGM冰量的50%），在又一个45 ka的冷却和冰盖生长之后，地球处于半球间的末次冰期最大配置，当类似的轨道强迫击中最大尺寸的北方冰盖并迎来T1时，因此正在进行的间冰期。这一论点突出了两个半球的完整冰川条件对终止的关键作用，并暗示南半球气候可能在大约15，000年内从间冰期过渡到完整冰川条件，而北方半球及其大陆冰盖需要半个冰川周期。
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, ∼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’. Our10Be 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.