On the variability of the Bering Sea cold pool and implications for the biophysical environment

Abstract:

The Bering Sea experiences a seasonal sea ice cover, which is important to the biophysical environment found there. A pool of cold bottom water (<2^oC) is formed each winter as a result of the predominately local sea ice growth on the shelf and associated vertical mixing due to brine rejection. The extent and distribution of this Cold Pool (CP) is largely controlled by the extent of sea ice in the Bering Sea, which in recent winters has been much lower than average. The cold bottom water of the CP is important because it delineates the boundary between arctic and subarctic demersal fish species. A northward retreat of the CP will likely be associated with migration of arctic species toward the Chukchi Sea.

We use the Regional Arctic System Model (RASM) to examine variability of the extent and distribution of the CP in the Bering Sea during the period 1980-2018 and its relation to change in the sea ice cover. RASM is a high-resolution, fully-coupled, regional biophysical model. Its domain encompasses the entire marine cryosphere of the Northern Hemisphere, including the major inflow and outflow pathways, with extensions into North Pacific and Atlantic oceans. The components of RASM include: atmosphere, land hydrology, sea ice, ocean and marine biogeochemistry (BGC). The ocean BGC component in RASM is a medium-complexity Nutrients-Phytoplankton-Zoo-plankton-Detritus (NPZD) model. The sea ice model uses a BGC parameterization, in which biological activity is distributed throughout the ice column. RASM results confirm the direct correlation between the extent of sea ice and CP and show a smaller CP as a consequence of recent declines of the sea ice cover in the Bering Sea. In addition, we also examine changes in the phytoplankton functional groups over the recent decades and look at differences between the northern and southern Bering Sea.