DEGLACIATION OF THE WEDDELL SEA SECTOR OF THE WEST ANTARCTIC ICE SHEET

Dating of glacial deposits in Marie Byrd Land, central West Antarctica, and the Ross Sea indicates that the West Antarctic Ice Sheet (WAIS) reached its maximum size thousands of years after the Northern Hemisphere ice sheets and that deglaciation continued into the Holocene. However, there is little evidence to constrain the timing of deglaciation in other important sectors of the WAIS. In particular, the timing of retreat of grounded ice from the Weddell Sea lacks numerical dating control. We are dating erratics from the Marble Hills in the southern Ellsworth Mountains to investigate the deglaciation history of this sector of the ice sheet.

Glacial erratics, spanning altitudes from 1390 to 980 meters, were collected from surfaces overrun during the last glacial maximum (LGM) and exposed as the ice sheet thinned. Cosmogenic Be-10 measurements yield apparent exposure ages ranging from 540,000 +/- 9500 years at the highest altitude to 2900 +/- 300 years at ~160 meters above the modern ice margin and less than 800 years for a sample at the ice margin. We interpret the majority of these dates, which greatly exceed the age of the LGM, as evidence of recycling from previously exposed deposits. However, five measurements of four samples yield a sequence of Holocene ages decreasing with altitude, suggestive of glacial thinning at ~5 cm/year. These latter results closely parallel the WAIS retreat chronology of the Ross Sea and Marie Byrd Land. Prolonged retreat in this sector of the ice sheet would indicate late opening of the Weddell Sea with significant implications for the establishment of present-day ocean circulation patterns.

Supported by National Science Foundation grant OPP-0230198.