Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation

• Published in: Nature (London) 2014-06, Vol.510 (7503), p.134-138
• Main Authors: Weber, M. E., Clark, P. U., Kuhn, G., Timmermann, A., Sprenk, D., Gladstone, R., Zhang, X., Lohmann, G., Menviel, L., Chikamoto, M. O., Friedrich, T., Ohlwein, C.
• Format: Article
• Language: English
• Subjects: 704/106/2738; 704/106/413; Climate models; Deep water; Deglaciation; General circulation models; Global warming; Holocene; Humanities and Social Sciences; Ice; Ice sheets; Icebergs; letter; Meltwater; Methods; multidisciplinary; Natural history; Science; Sea level
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13397

Two well-dated, high-resolution records of iceberg-rafted debris are presented that document variability in Antarctic Ice Sheet discharge during the last deglaciation. A history of Antarctic ice loss Global sea levels have risen by more than 100 metres since the last glacial maximum around 20,000 years ago, with several meltwater pulses of several metres or more. In the most dramatic of these — meltwater pulse 1A — sea level rose by about 16 metres at 14,600 years ago. This magnitude of sea level rise strongly suggests major Antarctica contributions, but to date there has been no firm physical evidence. Now Michael Weber and colleagues present a record of iceberg rafted debris from the Scotia Sea and show clear signals of pulsed iceberg release from Antarctica as early as 19,000 years ago. The largest iceberg release occurred during meltwater pulse 1A, providing the long-sought confirmation of Antarctic contributions to this major jump in sea-level rise. 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 sequences 2 , 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 sheets 5 , 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 1A 3 , 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 De