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

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. 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 to augment existing seismic and core datasets. Examination of these data reveals geomorphic evidence of grounded ice extending to the shelf break in many areas. Geomorphic evidence for a much expanded ice sheet includes mega-scale glacial lineations, grooves, drumlins, 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. This interpretation is supported by sediment cores, which sampled diamicton covered by ice sheet proximal gravely mud, draped with laminated glacial marine sediments. Further, radiocarbon dating of foraminifera tests reveals ice retreat from the outer shelf by 14,000-13,000 yr BP. This compares favorably with LGM retreat dates from the inner shelf at Palmer Deep by 13,000 yr BP, supporting the hypothesis of rapid retreat in the region.