Abstract:
Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation
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 icebergrafted
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,
providing a possible mechanism for rapid sea-level rise.
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