On the role of ocean circulation in seasonal and interannual ice-edge variations in the Bering Sea

Abstract

A 40 km-resolution ice—ocean model of the Bering Sea is used to investigate the effects of ocean circulation and vertical convection on the seasonal and interannual ice extent variations in the Bering Sea. The model is driven with daily time-varying atmospheric forcing from 1981–83. A series of sensitivity studies is carried out to examine the effects of the vertical diffusion and precipitation on the ice margin and the effect of stratification on the ocean circulation. For comparison, an ice-only simulation, with a motionless oceanic boundary layer of fixed depth, is also carried out. In the Aleutian Basin, the ice-ocean model exhibits a cyclonic ocean circulation which consists mainly of a baroclinic current component. On the eastern Bering Sea shelf the flow is mainly barotropic, with a northwestern shelf flow along the Alaskan coast and a return southeastern flow along the shelf break. The seasonal and interannual variability of the ice margin is significantly better simulated by the ice-ocean model than by the ice-only model, especially when an enhanced vertical diffusion is used. However, the seasonal cycle of ice extent exhibits too little ice in the southeastern Bering Sea and excessive ice in the northwest. The advance and retreat of the ice edge also tends to lag behind the observed results by a few weeks. The inclusion of precipitation improves the ice extent in the southeast. The results suggest that an enhanced vertical resolution, together with a more complete boundary layer formulation, will be required to achieve realistic seasonal simulations of the Bering Sea ice–ocean system.