An observational description of currents over the Chukchi Sea continental slope

Understanding the structure and variability of currents and water properties over the Chukchi Sea continental slope is important because they determine the pathways and fate of heat, salt, nutrients, and biota exchanged between the shelf and deeper basin. A three-year time series of current and water property measurements made at a single mooring site in approximately 1000 m of water on the Chukchi Sea continental slope is presented. The water column is divided into three distinct layers: a near-surface layer to approximately 200 m depth with predominantly northwestward along-slope flow (the Chukchi Slope Current); a predominantly southeastward-flowing interior layer encompassing depths of approximately 200–850 m and comprised primarily of Atlantic Water (the Arctic Ocean Boundary Current); and a near-bottom layer with weak currents comprised of Arctic Deep Water. Temporal variability of observed currents, from daily to seasonal time scales, was common. Along-slope flows in the surface and interior layers were enhanced during the ice-free summer months. Under ice cover, current magnitudes were weaker, and in some months even reversed direction. The upper-layer currents were not significantly correlated with local winds nor with wind stress curl, even when using a variety of low-pass filter window lengths. We hypothesize that this surface, northwestward flowing Chukchi Slope Current is a manifestation of the Beaufort Gyre. The mooring data will be augmented with recent snapshots of upper ocean velocity collected across the continental slope by a fleet of saildrones outfitted with acoustic Doppler current profilers, allowing for an estimate of the cross-slope extent of the surface current.