A modelling study of the response of Hatherton Glacier to Ross Ice Sheet grounding line retreat

摘要

The late Holocene retreat of the West Antarctic ice sheet is crucial information for assessing its current dynamics. However, data from this period for parts of the ice sheet where significant change has taken place, mainly the Ross Sea, are very sparse. Some significant dated deposits are from lakes dammed by valley glaciers, themselves dammed by the Ross Ice Sheet. The least age of these deposits is somewhat later than the retreat of the Ross Ice Sheet from the locality on account of the lagged response of the glacier. We present a model of the Hatherton Glacier, which examines its relationship to the Ross ice sheet, using dated margin data from ice-dammed lakes. Problems in modelling are the coupling with the Darwin Glacier, the unknown bed topography and the poorly known surface mass balance, which include blue ice areas. We infer the bed topography by tuning a valley glacier model, and use this model to (ⅰ) estimate the thickness of the Last Glacial Maximum (LGM) Ross Ice Sheet; and (ⅱ) estimate the response time of the Hatherton Glacier to changes in the Ross Sea ice sheet. The best fit of the glacier surface profile to the geological data occur if the LGM Ross Ice Sheet elevation is assumed to be 800 m higher than the present-day ice shelf surface. If the decay of the Ross Ice sheet is linear with time, the response time is of the order of several centuries. Step changes in the elevation of the Ross Ice Sheet lead to a response time around one thousand years. The dated deposits in the Hatherton Valley cannot be used directly as dates of Ross Ice Sheet grounding line retreat.