A Numerical Study of the Circulation of the Bering Sea Basin and Exchange with the North Pacific Ocean

Abstract

A limited-area, primitive equation, three-layer hydrodynamic model, with realistic coastlines and bathymetry and ?° resolution, is used to investigate the circulation of the Bering Sea basin and the adjacent North pacific ocean. The westward flowing Alaskan Stream to the south of the Aleutian Island chain is specified as a boundary condition at inflow and outflow ports with a constant throughput of 15 Sv (Sv = 1 ?106 m3 s?1). Atmospheric forcing is based an the Hellerman and Rosenstein monthly climatological wind field. The model is spun up over 50 years and the statistics of the final decade are described. The general features of the model circulation as discussed below are consistent with available hydrographic and buoy drift observations. The model Alaskan Stream separates from the Aleutian Island chain near 175°; beyond this point there is strong interannual variability associated with meandering and occasional eddy shedding along the northern arm of the western subarctic gyre. There is a generally cyclonic, but spatially complex and nonstationary, circulation within the Bering See basin, fed by inflow through the Aleutian passes; outflow is confined to Kamchatka Strait and varies seasonally, between 8.5 Sv in summer and 13 Sv in winter. A region of intense eddy activity lies west-northeast of Bowers Ridge. The model predicts seasonal reversals in the Bering slope current that are not clearly evident in the temporally sparse observational database. The numerical study demonstrates that flow instabilities contribute to substantial interannual variability in the circulation of the Bering Sea and adjacent northwest Pacific Ocean.