Water Mass Evolution and Circulation of the Northeastern Chukchi Sea in Summer: Implications for Nutrient Distributions

The region southeast of Hanna Shoal, in the Chukchi Sea, is characterized by areas of enhanced benthic biomass referred to as hotspots. At present it is unclear what factors dictate the locations of the hotspots. To shed light on this we use recent and historical shipboard data to investigate the seasonality of water masses and quantify the circulation patterns and their impact on nutrient distributions in the northeast Chukchi Sea. The depth-averaged circulation under light winds is characterized by a strong Alaskan Coastal Current (ACC) and northward flow through Central Channel. A portion of the Central Channel flow veers eastward, while the remainder progresses northward to Hanna Shoal where it bifurcates around both sides of the shoal. All of the branches converge southeast of the shoal and eventually join the ACC. The wind-forced response has two regimes: In the coastal region the circulation depends on wind direction, while on the interior shelf the circulation is sensitive to wind stress curl. In September and October the region southeast of Hanna Shoal is characterized by elevated amounts of winter water, a shallower pycnocline, and higher concentrations of nitrate. Sustained late-season phytoplankton growth spurred by this pooling of nutrients could result in enhanced vertical export of carbon to the seafloor, contributing to the maintenance of the benthic hotspots in this region.