West Antarctic ice-sheet history, Marie Byrd Land

I worked with John Stone, Greg Balco and Louis Sass III, (University of Seattle), collecting samples for 10Be and 26Al cosmogenic dating of erratics and bedrock on nunataks rising above the surface of the West Antarctic Ice Sheet.

<--Ice-moulded topography and eratics in Marie Byrd Land

A major implication of this work is that the Marie Byrd Land sector of the West Antarctic Ice Sheet has been thinning during the Holocene from ~10,400 years ago to the present. Probably, this is due to grounding line retreat, perhaps as a delayed response to the rise in global sea level following the deglaciation of the Northern Hemisphere ice sheets after the last Ice Age. This finding is similar to that discovered in the Ross Sea area where there is evidence of progressive retreat of the Ross Ice Shelf during the Holocene. If these results are put together with evidence of recent thinning of the ice sheet in the Bellingshausen Sea area of West Antarctica, as measured by satellite, then the Pacific sector of the West Antarctic Ice Sheet is on a trajectory of decline. The implications are profound in that they support the view that the West Antarctic Ice Sheet, which is largely grounded below sea level, is indeed susceptible to sea level change. Since the ice sheet accounts for a water volume equivalent to 5 m of global sea level, then clearly there is need for better understanding of the dynamics and future trajectory of the ice sheet.

Our main paper on thinning of the ice sheet is:

• Stone, J. O., Balco, G. A., Sugden, D. E., Caffee, M. C., Sass, L. C., Cowdery, S. G., Siddaway, C., 2003 Holocene deglaciation of Marie Byrd Land, West Antarctica. Science, 299, 99-102.

Mount Rea, Sarnoff Mountains, Marie Byrd Land, which exhibits ice moulding glacially deposited erratics-->

Another major finding is that the weathered summits of the nunataks are dotted with erratic boulders that have survived overriding by ice on more than one occasion. Remarkably, fragile tors and boulders have been covered by moving ice and yet unmodified. By looking at two isotopes we begin to model the type of history of exposure and weathering experienced by the summits over several glacial cycles. Presumably the summits features have survived because they were covered by cold-based ice. This is in contrast to the saddles between mountains which are often heavily ice moulded, presumably by warm-based ice. The remarkable selectivity of glacial erosion is demonstrated in the following paper:

• Sugden DE , Balco G, Cowdery SG, Stone JO, Sass LC, 2005, Selective glacial erosion and weathering zones in the coastal mountains of Marie Byrd Land, Antarctica. Geomorphology, 67, 317-334.[view abstract]