DIACHRONOUS ADVANCE AND RETREAT OF THE ANTARCTIC ICE SHEETS DURING THE LATE QUATERNARY

The last decade has been a time of significant advancement in our understanding of the magnitude and timing of Antarctic Ice Sheet expansion and retreat during the past 30 ka. One of the most significant observations has been that the ice sheet did not advance and retreat in concert with Northern Hemisphere ice sheets. Indeed, the various components of the Antarctic ice sheet did not advance and retreat from the continental shelf at the same time.

Marine geological data from around East Antarctica indicates that during the most recent glacial maximum the East Antarctic Ice Sheet (EAIS) advanced to the middle or mid-outer continental shelf in those areas that have been surveyed to date. While the timing of ice sheet expansion is unconstrained, retreat from the shelf was diachronous and occurred between approximately 30 ka and 25 ka in Prydz Bay (Domack et al., 1998) and Lutzow-Holm Bay ( ) and off the Queen Maud Land coast (Anderson et al., 2002). Off Northern Victoria Land, where the EAIS flowed over and through the Transantarctic Mountains and onto the continental shelf, retreat from the shelf took place between approximately 15 ka and 9 ka (Anderson et al., 2002).

Data from eastern Ross Sea and off Marie Byrd Land include spectacular subglacial geomorphic features that extend to the outer shelf. Radiocarbon ages of the oldest glacial marine sediments resting above subglacial deposits indicate that ice sheet retreat from the shelf was diachronous, as in East Antarctica. The earliest retreat from the shelf occurred in the eastern Ross Sea, prior to 20 ka years ago. This area was occupied by very extensive ice streams, hundreds of kilometers in length, flowing across a deforming bed. This implies gentle profiles, high rates of flow and discharge, and possibly contributed to the early, and apparently rapid, retreat of the ice sheet from the shelf. Offshore of Marie Byrd Land, the WAIS retreated from the shelf after approximately 15, 000 ka.

Geomorphic features on the seafloor either side of the Antarctic Peninsula indicate that the ice sheet was grounded on the outer shelf during the past, but the timing of ice sheet expansion and retreat is yet to be resolved.