Description: The glacial history of the Antarctic Ice Sheet in the Weddell Sea embayment during the Last Glacial Maximum (LGM; 23-19 ka) is a matter of debate. Existing onshore and offshore data suggest two alternative reconstructions for the LGM ice sheet extent. One scenario shows an ice sheet grounding line that had advanced to (or at least close to) the shelf edge throughout the Weddell Sea, embayment. The other reconstruction concludes that the grounding line in the two main cross shelf troughs was located only slightly farther offshore than today. Here we present new data from multibeam swath bathymetry surveys, acoustic sub-bottom profiles and sediment cores collected during recent and past British and German marine expeditions. These data provide new constraints on the glacial history of the eastern part of the Weddell Sea embayment. A previously unknown, stacked grounding zone wedge discovered in the outer shelf part of Filchner Trough possibly marks the northernmost position of the LGM grounding line within this palaeo-ice stream trough. Crescentic moraines and a predominantly smooth seabed morphology mapped north of the Brunt Ice Shelf reveal a complex glacial history with repeated advances of grounded ice or episodic retreats, controlled by a hard seafloor substrate. We will compare new radiocarbon dates obtained from the sediment cores to existing chronologies and use them to reconstruct the timing of the last maximum ice sheet advance and post-LGM retreat. Finally, we will set our new findings into context with results from ice sheet models and discuss their implications for Antarctica's contribution to global meltwater pulses during the last deglaciation.

Description: The geochemical and geochronological fingerprint of rock debris eroded and carried by ice streams may be used to identify the provenance of iceberg-rafted debris (IRD) in the marine sediment record. During ice retreat following glacial maxima, it has been shown that there is an increase in IRD accumulation in marine sediments underlying the western limb of the Weddell Gyre. Here we present IRD provenance records from sediment core PS1575-1 in the NW Weddell Sea, and interpret these records in terms of the geographic sequence of ice sheet retreat in the Weddell Sea embayment during the most recent deglaciation. We first characterize the source areas of eroded debris around the Weddell Sea Embayment, using published mapping of the embayment and new material from: 1. Till in modern moraines at the edges of ice streams, including the Foundation Ice Stream, the Academy Glacier, and the Recovery Glacier; and 2. Subglacial till and proximal glaciomarine sediment from existing cores located along the front of the Filchner and Ronne Ice Shelves, collected on past expeditions of the RV Polarstern. The analyses on these samples include 40Ar/39Ar hornblende and biotite thermochronology and U-Pb zircon geochronology on individual mineral grains, and K-Ar thermochronology, Nd isotopes, and clay mineralogy on the clay grain size fraction. Results so far indicate that samples along the front of the Filchner and Ronne Ice Shelves record the geochemical and geochronological fingerprint that would be expected from tracing ice flow lines back to the bedrock terranes. The Ronne (west), Hughes (central), and Filchner (east) sectors have distinguishable provenance source signatures, and further subdivision is possible. In core PS1575-1, downcore IRD provenance changes reflect iceberg output and ice sheet retreat from the different sectors of the embayment through the last deglaciation. The detrital provenance method of interpreting the geographic sequence of ice retreat can equally be applied to previous deglaciations of the Weddell Sea Embayment.