Abstract
Recent thinning and loss of Antarctic ice shelves has been followed by near synchronous acceleration of ice flow that may eventually lead to sustained deflation and significant contraction in the extent of grounded and floating ice. Here, we present radiocarbon dates from foraminifera that constrain the time elapsed between a previously described paleo-ice-shelf collapse and the subsequent major grounding-line retreat in the Whales Deep Basin (WDB) of eastern Ross Sea. The dates indicate that West Antarctic Ice Sheet (WAIS) grounding-line retreat from the continental shelf edge was underway prior to 14.7 ± 0.4 cal kyr BP. A paleo-ice-shelf collapse occurred at 12.3 ± 0.2 cal kyr BP. The grounding position was maintained on the outer-continental shelf until at least 11.5 ± 0.3 cal kyr BP before experiencing a 200-km retreat. Given the age uncertainties, the major grounding-line retreat lagged ice-shelf collapse by at least two centuries and by as much as fourteen centuries. In the WDB, the centuries-long delay in the retreat of grounded ice was partly due to rapid aggradational stacking of an unusually large volume of grounding-zone-wedge sediment as ice-stream discharge accelerated following ice-shelf collapse. This new deglacial reconstruction shows that ongoing changes to ice shelves may trigger complex dynamics whose consequences are realized only after a significant lag.
Highlights
During the Last Glacial Maximum (LGM), i.e., from 24,000 to 19,000 years ago, mass balance had shifted to positive and the extent of ice flow from East and West Antarctica expanded towards the Antarctic continental shelf edge (Fig. 1a)[21,22,23,24,25,26]
Eleven dates were obtained from sub-ice-shelf sediments that accumulated on the outer continental shelf prior to the ice-shelf collapse
Its stratigraphic location atop diamict deposited on the GZW2 foreset indicates that a third grounding-line shift away from the continental shelf edge had occurred by 14.7 ± 0.4 cal kyr BP, (Fig. 2a,b; Table 1)
Summary
Reconstructing ice-sheet retreat from the geology of continental shelf trough basins.During the Last Glacial Maximum (LGM), i.e., from 24,000 to 19,000 years ago, mass balance had shifted to positive and the extent of ice flow from East and West Antarctica expanded towards the Antarctic continental shelf edge (Fig. 1a)[21,22,23,24,25,26]. The subsequent retreat of grounded and floating ice is well recorded in the sedimentology and geomorphology of paleo-ice-stream trough basins that were partly backfilled with grounding zone wedges (GZWs) and post-glacial sediment successions[21,25,26,27,28] The former locations of the ice-sheet grounding line are best reconstructed from the morphological boundary between a gently, landward-dipping GZW topset (the surface to which the ice stream was grounded) and a steeply seaward-dipping GZW foreset (the basinward-dipping marine depositional surface). The physical reconstructions have continually been improved as more marine data have been acquired These improved stratigraphic frameworks are important because they highlight the locations from which a chronology of ice-sheet and ice-shelf retreat from the outer continental shelves can best be obtained
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call