Nutrient-Rich Gravity Current Formed by Upwelling in Barrow Canyon: High-Resolution Observations

Abstract

The distribution of nutrients influences the Chukchi Sea's rich ecosystems and affectsthe biogeochemistry of the central Arctic. Nutrients that become limiting in the late summer can be replenished episodically by physical processes that are likely to change in concert with Arctic climate trends. Here we report on unique, simultaneous, physical, and biogeochemical measurements of one such process: upwelling in Barrow Canyon. High-resolution transects of a towed vehicle, which was equipped with physical, turbulence, and biogeochemical sensors, captured the upwelling of dense, salty, and nitrate-rich waters into the shallow regions of Barrow Canyon. Upwelling drastically modifies the nitrate distribution of Barrow Canyon through the vertical advection of Atlantic Water from the Canada Basin and through turbulent flux across the nutricline. Upwelled waters form a highly sheared gravity current that is susceptible to both baroclinic and symmetric instabilities. The current exhibits transverse circulation common to frictional gravity currents. Our observations suggest that rapid and dramatic nutrient changes in Barrow Canyon can be accomplished by upwelling; the subsequent formation of unstable jets and fronts enhances the irreversible flux of upwelled nutrients to less dense waters in the Chukchi sea.