A high-resolution coupled ice–ocean model of winter circulation on the Bering Sea Shelf. Part II: Polynyas and the shelf salinity distribution

Abstract

The sea ice component of a regional high-resolution ocean model is improved, with particular attention to accurate representation of the salinity budget for the coupled system. The impact of this improvement is shown first using a one-dimensional test and then the realistic model simulation of the Eastern Bering Sea for the relatively high sea ice extent winter of 2009–10. Improvements to the model ice–ocean salt flux parameterization are demonstrated by comparison of model shelf salinity fields with observations from moorings and CTDs. As polynya regions can strongly influence winter salinity distributions on the Bering Sea shelf, model ice concentrations are compared to satellite estimates for several regions. Areas with a tendency to exhibit higher than average winter open water area include St. Lawrence Island and the southern coast of the Chukotka Peninsula. A new methodology is proposed analyzing the evolution of the salinity distribution with the aid of salt flux tracers that track occurrence of brine and meltwater separately. These demonstrate how cold winters on the Bering Sea shelf are characterized by a freshening and stratifying of the mid- to outer-shelf and an increase of salinity on the inner shelf. Use of an ice-age tracer in the model reveals an anticyclonic circulation of sea ice in mid-winter, as the Bering slope current and Anadyr current recirculate ice that has been transported south–southwestward by the predominant winds. The characteristics of coastal polynya regions are quantitatively compared and a model transect extending from the St. Lawrence polynya to the shelf break is analyzed to help illustrate the temporal and spatial variability of stratification and circulation occurring as the sea ice advances and retreats over the winter season.