Seasonal variations of sea ice and ocean circulation in the Bering Sea: A model‐data fusion study

Abstract

A 9‐km coupled ice‐ocean model (CIOM) was implemented in the entire Bering Sea to investigate seasonal cycles of sea ice and ocean circulation under atmospheric forcing. Sea ice cover with a maximum of 0.6 × 106 km2 in February to late March was reasonably reproduced by the Bering‐CIOM and validated by Special Sensor Microwave/Imager (SSM/I) measurements. The model also captures some important spatial variability and downscaling processes such as polynyas and ridging, which the SSM/I measurements cannot reproduce because of their coarse (25 km) resolution. There are two distinct surface ocean circulation patterns in winter and summer on the Bering shelves because of the dominant winds, which are northeasterly in winter and southwesterly in summer. Summer low‐temperature, high‐salinity water mass (<3°C) on the Bering shelf is formed locally during winter because of strong vertical convection caused by salt injection when ice forms, wind, and wind‐wave mixing on the shelf. The northward volume transport across the 62.5°N line, with an annual mean of 0.8 ± 0.33 Sv (1 Sv = 106 m3 s−1) that is consistent with the measurements in the Bering Strait, has barotropic structure, which transports heat flux (with an annual mean of 7.74 TW; 1 TW = 1012 W) northward. The Anadyr Current advects warmer, saltier water northward during summer; nevertheless, it reverses its direction to southward during winter because of predominant northeasterly and northerly wind forcing. Therefore, the Anadyr Current advects cold, salty water southward. The volume transport on the broad midshelf is northward year round, advecting heat (3.3 ± 2.4 TW) and freshwater (−8 ± 10 × 104 practical salinity unit (psu) m3 s−1) northward. One important finding is that the Anadyr Current and the midshelf current are out of phase in volume and heat transports. The Alaskan Coastal Current also transports heat and freshwater northward on an annual basis. The Bering‐CIOM also captures the winter dense water formation along the Siberian coast, which is promoted by the downwelling favorable northeasterly wind, and the summer upwelling due to the basin‐scale upwelling favorable southwesterly wind, which brings up the cold, salty, and nutrient‐rich water from the subsurface to the surface within a narrow strip along the west coast. This upwelling found in the model was also confirmed by satellite measurements in this study.