Copper River discharges in the Northern Gulf of Alaska: freshwater distribution and evolution during the July 2019 freshet

The Gulf of Alaska basin is a high nitrate, low chlorophyll (HNLC) region that is influenced by coastal runoff and iron through their respective roles in mediating stratification and in fueling productivity that is otherwise limited by dissolved iron concentrations. This study utilizes data collected from two research cruises, conducted as part of the Northern Gulf of Alaska (NGA) Long-Term Ecological Research (LTER) program during July 2019, to examine the movement of the Copper River’s discharge. High-resolution salinity data from a towed undulating conductivity-temperature-salinity sensor during each of the cruises reveal the near-surface salinity distributions over the NE Gulf of Alaska shelf in the vicinity of the outflow plume. The two cruises were separated by three weeks, during which time the Copper River discharged approximately 13 km^3 of freshwater, a sufficient freshwater volume to account for the observed decrease in shelf salinity covering a 4700 km^2 region. Satellite tracked-drifters show the influence of wind in controlling the distribution of near-surface waters in the study region. Our investigation raises additional questions about the mechanistic control of freshwater distributions in the NE Gulf of Alaska related to the influence of Prince William Sound drainage contributions to the northern shelf in summer, and the role of Copper River freshwater in supplying iron to the HNLC waters of the central Gulf of Alaska.