Wind and buoyancy driven intermediate-layer overturning in the Sea of Okhotsk

Abstract

Dense shelf water (DSW) produced from sea-ice formation on the northern shelves of the Sea of Okhotsk flows out to intermediate depths (200–500 m) along the Sakhalin coast and is the densest water mass formed in the North Pacific. This intermediate-layer intrusion forms the lower limb of a meridional overturning circulation in the Sea of Okhotsk that is enhanced by strong tidal mixing near the Kuril Islands and closed by a surface wind-driven circulation that returns salinized water to the DSW formation regions. This meridional overturning circulation is referred to as the intermediate-layer overturning. This paper presents results from a series of numerical experiments that investigated the dynamics of this intermediate-layer overturning circulation. The effects of wind, air temperature, Amur River discharge and tidal mixing along the Kuril Island were examined and were all found to influence the overturning. In particular, it was found that stronger wind forcing enhances the DSW intrusion because (1) intensified circulation increases northward salinity flux from the Kuril Islands where saline water upwells from the intermediate layer, and consequently raises background salinity in the northern shelves where DSW forms and (2) the DSW volume flux from the northern polynyas increases under increased winds. The observed interannual time-scale variability ( < 10 years) of the intermediate-layer overturning is also discussed.