Millennial-scale Variability in Antarctic Ice-Sheet Discharge Throughout the Last Deglaciation From Scotia Sea Records of Iceberg-Rafted Debris
Tuesday, 16 December 2014: 5:45 PM
The deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (LGM; 26,000 – 19,000 years ago) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences. 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, but comparable records from the Southern Ocean of the AIS are lacking due to 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 19,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after Meltwater Pulse 1A (MWP-1A) and continuing into the late Holocene. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to MWP-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 and providing a possible mechanism for rapid sea-level rise.