WEST ANTARCTIC ICE SHEET GROUNDING EVENTS ON THE MIDDLE SHELF OF THE WHALES DEEP PALEO-ICE-STREAM TROUGH IN EASTERN ROSS SEA, ANTARCTICA

A large-area multibeam survey collected during February-March 2015 from the Nathaniel B Palmer RVIB imaged the Whales Deep paleo-ice-stream trough in an area of eastern Ross Sea that strictly drained ice from the central part of the West Antarctic Ice Sheet (WAIS) during the last glacial advance. The new geomorphological data provide evidence showing a cluster of grounding zone wedges (GZWs) on the middle shelf. The backstepping stacking pattern from seismic stratigraphic data requires that the WAIS experienced at least four pauses (i.e., grounding events) during its overall retreat. These geophysical data permit two possible interpretations of how the grounding line migrated during retreat. In the first scenario, each grounding event involved a small (10-20 km) retreat of the grounding line to a more landward position on the middle shelf followed by a pause in retreat before the next landward translation of the grounding line. In the second scenario, each grounding event ended with a larger-scale retreat of grounded and floating ice to the inner shelf followed by a major re-advance to the middle shelf. To determine which of these two end-member scenarios best describes the WAIS retreat from this sector of Ross Sea, we evaluated a new 16-station grid of Kasten and Jumbo-Piston cores that were also acquired in 2015. The cores were acquired using the multibeam survey and cover the length of the paleo-ice-stream trough. Our ongoing analyses of the core data include an integration of visual core descriptions aided by x-ray images, granulometry, water contents, total organic carbon, shear strengths, diatom and foraminiferal assemblage data. To date, the core analyses reveal a single transgressive succession from proximal diamict overlain by sub-ice-shelf and/or open-marine sediments. These data support the first scenario, suggesting that an ice shelf remained continuously intact through the time that the grounding line moved successively landward by small-scale translations until the end of the fourth grounding event. The data show that only the fourth grounding event ended with an abrupt and long-distance retreat of both grounded and floating ice.