A PALEOCEANOGRAPHIC PERSPECTIVE ON THE FINAL DAYS OF GLACIAL LAKE RUSSELL, PUGET SOUND, WASHINGTON

During the Late Pleistocene, Glacial Lake Russell formed at the southern margin of the Puget Lobe of the Cordilleran Ice Sheet as it retreated out of the Puget Sound region. Fresh water from the lake flowed through what is now the Chehalis River and discharged into the Pacific Ocean out of Grays Harbor, depositing sediment offshore in and around Grays Canyon. The discharge from Glacial Lake Russell via Grays Harbor eventually shut-off as ice retreated and opened a new drainage route for a lower elevation Lake Bretz via the Straits of Juan de Fuca. The timing of this final drainage of Glacial Lake Russell is not well constrained on land but may be readily identified and dated in the offshore sediment record. Here we present results from two jumbo piston cores (OC2006A-16JC and OC2006A-18JC) and their corresponding trigger cores, which were recovered from a fine-grained hemipelagic sediment package accumulating on a rise near the southern slope of Grays Canyon in ~700 m water depth on the upper continental slope.

Preliminary analysis of CT-scan imagery, Multi-sensor Core Logger data (gamma density, magnetic susceptibility), and scanning X-ray Fluorescence (XRF) geochemical data indicate that these cores capture the deglacial Pleistocene/Holocene transition and ultimate retreat of the Puget Lobe of the Cordilleran ice sheet, including inputs from the drainage of Glacial Lake Russell. Downcore δ¹⁸O on benthic foraminifera places the timeline of regional glacial retreat into global context, while radiocarbon dates constrain the absolute timing of these events. Salinity estimated from δ¹⁸O values on planktonic foraminifera as well as benthic and planktic foraminiferal faunal data identify major changes in ambient ocean conditions and fresh-water discharge to the ocean. This study will provide insight into the retreat of the southwestern Cordilleran Ice sheet and the impact of regional freshwater inputs associated with drainage of Glacial Lake Russell on the adjacent marine environment.