LAST GLACIAL MAXIMUM (LGM) ICE SHEET EXTENT AND GLACIAL RETREAT HISTORY OF ANTARCTIC PENINSULA; PRELIMINARY RESULTS FROM NATHANIAL B. PALMER 2002 CRUISE

Recent models of maximum extent of ice during the Last Glacial Maximum (LGM) differ widely in terms of thickness and location of grounded ice in the Antarctic Peninsula region, largely due to a lack of adequate ground truth. In addition, the controls and timing of ice sheet retreat are poorly constrained. Such controls include both global (bipolar) forcing mechanisms such as eustasy and climate change, versus internal controls such as ice-bed interactions. It was the goal of the 2002 cruise of the Nathanial B. Palmer to obtain the necessary geological and geophysical data to study the maximum extent of the peninsula ice sheet during the LGM and the deglacial history of the region. During this cruise we obtained multibeam swath bathymetry, high-resolution 3.5 kHz seismic, deep tow side scan sonar, 62 sediment cores, and ~ 2200 km of seismic data to augment existing seismic and core datasets. Preliminary examination of these data reveal geomorphic evidence of grounded ice extending to the shelf break in many areas, such as mega-scale glacial lineations, grooves, drumlins, and line-sourced shelf break gullies. Preliminary analysis of multibeam data from Marguerite Bay Trough reveal interconnected channels interpreted as features created by subglacial meltwater. Sediment cores reveal till on the outer shelf in several locations, covered by ice sheet proximal gravely mud, and draped with glacial marine sediments. Long (> 12 m) sediment cores from Bransfield Basin provide important chrono-stratigraphic benchmarks for deglacial history in the region. Preliminary conclusions include more grounded ice in the region than previously believed, evidence of sub-ice sheet meltwater channels, and no ice shelf over the Bransfield Basin during this time period.