Circulation of the Chukchi Sea shelfbreak and slope from moored timeseries

Abstract

Abstract Data from a year-long mooring array across the shelfbreak/upper-slope of the Chukchi Sea are used to describe and quantify the circulation and water masses of the region. The timeseries revealed the year-round existence of the eastward-flowing shelfbreak jet and, seaward of this, the westward-flowing Chukchi Slope Current. In the mean the slope current is estimated to transport 0.57\u202f±\u202f0.04\u202fSv of Pacific water, while the bottom-intensified shelfbreak jet transports 0.009\u202f±\u202f0.003\u202fSv towards Barrow Canyon. The slope current is surface-intensified in summer and fall, and in winter and spring it becomes middepth-intensified, moves shoreward, and weakens. Two extreme states of the circulation were identified: (1) an enhanced slope current and reversed (westward-flowing) shelfbreak jet; and (2) a strong eastward-flowing shelfbreak jet and weak slope current. The former state occurs when the wind stress curl on the Chukchi shelf is positive, and the latter state occurs when the curl is negative. A simple theoretical model is used to determine the changes in sea surface height due to such wind stress curl forcing, which is consistent with the observed changes in flow seaward of the shelf – both in amplitude and phase – via geostrophic set up. Shelfbreak upwelling occurred throughout the year, but there was no correlation between the regional wind conditions and the upwelling. Furthermore, there was no apparent relationship between upwelling and the extreme slope current/shelfbreak jet events. A comparison of water mass signals between the Chukchi slope array and a mooring at the head of Barrow Canyon supports the notion that the slope current is fed by the outflow of Pacific water from the canyon.