RAPID RETREAT OF THE WESTERN MARGIN OF THE NORTHERN AND SOUTHERN CORDILLERAN ICE SHEET IN RESPONSE TO ABRUPT DEGLACIAL SEA-SURFACE TEMPERATURE WARMING

Sea surface temperatures (SST) likely played a role in the response of the Cordilleran ice sheet to climate change during the last deglaciation, yet this relationship has yet to be directly assessed. A detailed study of ice-proximal marine sediments near southeast Alaska and southern British Columbia are used to determine the relationship between the western Cordilleran ice sheet and local SST change. Marine sediment core EW0408-85JC (59.56°N, -144.15°W; 682 m water depth) contains glaciomarine sediments discharged by the southeast Alaskan glacial margin from the northwestern Cordilleran ice sheet. Ten degrees of latitude to the south, marine sediment core MD02-2496 (48.98°N, -127.04°W; 1243 m water depth) records a southwestern Cordilleran ice sheet signal, which contains glaciomarine sediments discharged from the Puget Lobe and southeast British Columbia glacial margin. Previously published alkenone and Mg/Ca SST records from these two well-dated cores suggest abrupt warming at the onset of the Bølling warm period and cooling during the Younger Dryas cold event, signifying synchronous climate forcing along the western margin of the Cordilleran ice sheet. Geochemical analyses of glaciomarine sediment provenance data (Ca/K, Ca/Sr, K/Sr, Ti/Al) record western Cordilleran ice sheet response to synchronized SST changes in the same cores. Principle component analysis (PCA) of the sediment geochemistry using empirical orthogonal functions (EOF) further distinguish process-related signals in the sediment provenance data, which help to parse out regional glacial histories. Based on preliminary results, the Cordilleran ice sheet may have retreated synchronously across its western marine-terminating margin to abrupt SST warming of 3-4 °C in <400 years.