PALEOCEANOGRAPHIC PERSPECTIVES ON COLUMBIA RIVER DISCHARGE DURING THE HOLOCENE

The Columbia River is among the largest river systems in North America (fourth in terms of discharge). Its flow influences North Pacific climate and ecosystems, while serving as an essential resource for agriculture, hydropower, shipping, and fisheries. Future warming is expected to influence snowpack, seasonal precipitation, and both atmospheric and sea-surface temperatures, but model projections disagree about both the sign and magnitude of the effects, so the resulting impacts on seasonal and annual river flows remain uncertain. This study assesses past variations in sea-surface salinity from δ¹⁸O in planktonic foraminifera at a seasonal scale over the Holocene along the Oregon margin, to better understand the impact of warming on river flows. Newly collected marine sediment cores off the Columbia River record the influence of the freshwater plume near the sea surface. Core descriptions document a thick, bioturbated Holocene sediment package with Holocene sedimentation rates of 60-80 cm/kyr and abundant foraminifera, sufficient for developing a high-resolution (century-scale) record of changes in the Columbia Plume. δ¹⁸O analysis of several planktonic foraminifera species in the seasonal succession are expected to document seasonal-scale variation in the sea-surface salinity record related to changing freshwater flows during the late Pleistocene and Holocene.