HOLOCENE THINNING OF REEDY GLACIER, TRANSANTARCTIC MOUNTAINS, IN RESPONSE TO GROUNDING-LINE RETREAT OF THE WEST ANTARCTIC ICE SHEET

Determining the recent behaviour of the Siple Coast grounding line of the West Antarctic Ice Sheet (WAIS) is paramount to our understanding of the ice sheet – which contains the equivalent of ~6 m sea-level rise – and its likely reaction to predicted future climate change. The chronology of ice-sheet deglaciation since the last glacial maximum (LGM) compiled by Conway et al. (1999) suggests that recession of grounded ice in the Ross Sea Embayment occurred mainly during the Holocene in the absence of any significant sea-level or temperature rise. This reconstruction is limited, however, by a dearth of data from at or near the present-day grounding line, making it impossible to determine whether grounding-line recession has ceased or is ongoing. Furthermore, controversy still surrounds the former thickness of the West Antarctic Ice Sheet. Whether or not the LGM surface elevation was significantly different from today greatly affects our understanding of the ice sheet's behaviour and the contribution of West Antarctica to late-glacial and Holocene sea-level rise.

We report here evidence for Holocene thinning and steepening of Reedy Glacier (86˚S), an outlet glacier of the East Antarctic Ice Sheet flowing through the Transantarctic Mountains (TAM) and into the WAIS. Because Reedy Glacier emerges from the TAM ~100 km behind the Siple Coast grounding line, it is ideally positioned to record recent changes in West Antarctic ice thickness and grounding-line position. Through mapping and dating of depositional landforms adjacent to Reedy Glacier we have reconstructed the glacier-surface profile at the LGM and during subsequent deglaciation. These data will form a vital test of the ‘swinging-gate' model of West Antarctic deglaciation (Conway et al., 1999) and are helping ascertain whether retreat of the Siple Coast grounding line has ended or is ongoing. Moreover, the former surface profile of Reedy Glacier is providing geologic constraint of the LGM surface elevation of the WAIS.