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International Geological Congress Oslo 2008

August 6-14th

Alex DeMoor

Our work over the last five years has concentrated on the collection of undisturbed box (kasten) cores from areas of the NW Weddell Sea formally covered by the Larsen A and B Ice Shelves (LIS-A, LIS-B). We have obtained detailed sediment chronologies using both radiogeochemical (210Pb and 14C) and physical properties methods on over 15 cores. Sediment accumulation rates range from 0.40 to 0.02 mm/yr across the broad expanse of the LIS-B during the Holocene. Accumulation rates beneath the ice shelf are spatially related to: (1) distinct flow sectors of ice drainage, inherited from the tributary glaciers feeding into the shelf system, (2) broad scale circulation patterns for ocean waters that flow into the interior of the Larsen B embayment, and (3) the distance of the core site from the grounding line within each flow sector. For example the lowest rates of accumulation are consistently from cores within the SCAR inlet sector, which receives ice primarily from the Leppard and Flask glaciers. The SCAR inlet core sites are some 50 km from the grounding line. The SCAR inlet sector is also the sub-ice shelf basin that receives direct inflow of water, along the western boundary current of the Weddell Gyre. A transect of four cores from one flow sector (the Crane system) spans a distance of ~60 km, with sediment accumulation decreasing by an order of magnitude at a rate of -0.33 to -0.11 mm/yr (within the first 10 km), for the early and middle Holocene respectively, and by -0.034 mm/yr, (in the last 12 km) for the middle Holocene. Conversion of our accumulation rate data (via dry bulk density calculation) to total sediment flux results in values for sub ice shelf sedimentation of 30-600 g/m2yr. These results provide for a first order estimate of the erosive rates within the glacial catchment/tributary zone. Following break up of the ice shelf accumulation rates may have been higher than 2000 mm/yr, such as found within restricted fjords. These higher rates (at least three orders of magnitude greater) can not be entirely explained by post break up surge of tributary glaciers rather they suggest purging of sediment reservoirs both within and along the glacial margins and along the subglacial interface following ice shelf break up.

DeMoor, Alex, Hamilton College, Geosciences, Clinton--New York, United States, ademoor@hamilton.edu (Presenting);

Domack, Eugene, Hamilton College, Geosciences, Clinton--New York, United States, edomack@hamilton.edu; Roe, Kimberly, Hamilton College, Geosciences, Clinton--New York, United States, kroe@hamilton.edu; Gilbert, Robert, Queen's University,

Geography, Kingston--ONTARIO, Canada, robert.gilbert@queensu.ca; Leventer, Amy, Colgate University, Geology, Hamilton--New York, United States, aleventer@mail.colgate.edu; Folk, Leandra, Hamilton College, Geosciences, Clinton--New York, United States, lfolk@hamilton.edu

Kimberly Roe