Vertical structure and temporal variability of currents over the Chukchi Sea continental slope

Abstract

Observations from a single mooring site on the northern Chukchi Sea continental slope near the 1000-m isobath are presented. This site was occupied consecutively for three years (spanning September 2014–August 2017). Vertically the flow divides into three depth ranges: the upper ~200 m, ~200–~850 m and near-bottom flow. In the upper ~200 m, the mean flow was northwestward and strongest in the summer months. During winter months, currents decreased in magnitude, and in some years even reversed in direction. Satellite-tracked drifter trajectories (drogue depth ~30 m) show this along-slope flow persists at least from 156 to 165 °W, with an average velocity of ~17 cm s−1. This northwestward flowing current is the Chukchi Slope Current. From ~250 m to ~850 m, the flow reversed; this weak flow is the Arctic-wide cyclonic boundary current advecting Atlantic Water. The mean flow at ~900 m is weak and on an annual time scale not significantly different from 0 cm s−1. It consists of Arctic deep water. In the upper two layers, currents vary on the scale of days to seasons, with short-term reversals common. Currents below 40 m were not significantly correlated with local winds nor wind stress curl. We hypothesize that the northwestward flowing Chukchi Slope Current is a consequence of dynamics associated with the Beaufort Gyre.