Nature2014-06-17 2:07 PM

南极冰川消失的一个历史记录 Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation

论文摘要 

全球海平面自距今约2万年前的末次冰盛期以来已上升了超过100米,出现过几个幅度达到几米或更大的融水脉冲。在这些融水脉冲当中最剧烈的一个(“融水脉冲1A”)发生时,海平面在距今14,600 年前上升了约16米。这种海平面上升幅度强烈显示有来自南极的很大贡献,但迄今还没有明确的物理证据。现在,Michael Weber及同事发表了来自斯科舍海的随冰山漂流的碎屑的一个记录,发现早在距今19,000年前就有来自南极的脉冲化冰山释放的明确信号。最大的冰山释放事件发生在“融水脉冲1A”期间,从而为南极对海平面上升中的这样一次大跳跃所做贡献提供了人们长期所寻找的确认。

Abstract 

Our understanding of the deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (26,000–19,000 years ago)1 is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences2, 3, 4. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets5, but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A3, 6, 7, 8 and continuing into the late Holocene epoch. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced, providing a possible mechanism for rapid sea-level rise.

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