DISCHARGE HISTORY OF THE COLUMBIA RIVER THROUGH THE LAST DEGLACIATION AND THE HOLOCENE: PRELIMINARY RESULTS FROM CRUISE OC1706B

The Columbia River is one of the largest rivers to discharge into the northeast Pacific Ocean, with a drainage basin spanning >660,000 km² throughout most of the Pacific Northwest inland of the Cascade Range, and stretching into the Canadian and American Rockies. As such, this river system was the primary conduit for drainage of the southern margin of the Cordilleran Ice Sheet, including its ice-dammed glacial lakes Columbia and Missoula. In early June of 2017, the state-supported Oceangoing Research Vessel Program cruise OC1706B aboard the R/V Oceanus collected jumbo piston cores from the Washington/Oregon margin adjacent to the Columbia River. CHIRP sub-bottom profile data resolved two distinct units with varying thickness in the uppermost sediment column: a clear and presumably Holocene hemipelagic drape overlying a higher-density lithology punctuated by multiple high-amplitude reflectors in the basins. Coring sites were carefully selected on perched bathymetric rises and isolated step basins to avoid the complications of erosive turbidity currents. Preliminary benthic stable d¹⁸O isotope stratigraphies indicate that five sites recovered material deposited during or before the most recent glacial termination. Two 40’ jumbo piston cores on the continental slope south of the Astoria Canyon may have collected the entirety of the pre-Holocene high-density stratigraphic unit. Initial work done by three Research Experience for Undergraduate (REU) students at the College of Earth, Ocean, and Atmospheric Sciences, Oregon State University indicate that these cores contain records of the deglacial behavior of the Cordilleran Ice Sheet, as well as the discharge history of the Columbia River including major flood events of the Holocene and late Pleistocene. Here we present early results and discuss future research objectives with these materials.