Influences of sea ice on the Eastern Bering Sea: NCAR CESM simulations and comparison with observations

Abstract

We examine the influences of sea ice on the Eastern Bering Sea (EBS) regional oceanography on seasonal and inter-annual time scales using the National Center for Atmospheric Research-Community Earth System Model (NCAR CESM) simulations, comparing the modeling results with satellite and in situ observations when possible. While the modeled mean seasonal cycle of ice cover in the EBS middle shelf is generally within the uncertainty range of satellite observations, in the northern domain (north of 59°N), the simulation reaches its annual maximum in April instead of in March, as observed by satellite remote sensing; modeled ice reduction in late spring in the region is also slower than observations. Despite this bias, the simulation captures the observed seasonal transit of freshwater from the north to the south via ice advection; en route, the sea ice melts, cooling and freshening the local water column. On inter-annual time scales, modeling results suggest that extensive ice cover persisting into spring in the central EBS leads to cold anomalies in the bottom water, especially on the middle and inner shelves of the southern domain. The corresponding salinity anomalies are positive in the northern coastal domain, and weak but negative in the southern middle shelf. The associated 10-m ocean current anomalies are southward on the shelf and directed offshore in the slope region. Comparing years 1961-2005 versus years 2005-2050, the Probability Distribution Function of ice cover on the EBS middle shelf shifts northward by ~2° latitude.