ICE SHEET RECONSTRUCTION AND GLACIAL RETREAT HISTORY OF ANTARCTIC PENINSULA DURING THE LAST GLACIAL MAXIMUM (LGM)

Recent models of ice sheet extent 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. Further, the controls and timing of ice sheet retreat are poorly constrained. During the 2002 cruise of the Nathaniel B. Palmer we obtained multibeam swath bathymetry, high-resolution chirp sonar, deep-tow side scan sonar, 62 sediment cores, and ~ 2200 km of seismic data augmenting an extensive seismic and core database. Analysis of these data greatly expands previous estimates of maximum extent of grounded ice during the LGM. Geomorphic evidence for grounded ice includes mega-scale glacial lineations (300-650m crest-to-crest spacing, in excess of 20 km long), grooves, drumlins, ice stream boundary ridges, and line-sourced shelf break gullies. Mega-scale glacial lineations are draped with a thin veneer of glacial marine sediments imaged by chirp sonar, suggesting that these features were formed during the most recent glacial maximum. Sediment core analysis support these interpretations, sampling gray diamicton in several locations in the outer-shelf overlain by olive green glacial marine sediments. Preliminary radiocarbon (AMS) dating of foraminifera tests sampled from outer shelf cores suggest a pullback beginning just prior to ~ 16,700-15,800 yr BP, slightly earlier than the more inland Palmer Deep area at ~ 13,000 yr BP.