FY 1981

Eastern Bering Sea ice dynamics and thermodynamics

Pease, C.H.

Chapter 13 in Eastern Bering Sea Shelf: Oceanography and Resources, D.W. Hood and J.A. Calder (eds.), Vol. 1, USDOC/NOAA/OMPA, 213–222 (1981)

During winter 1979, hydrographic, meteorological, and ice floe data were collected over the Bering Sea shelf. The ice pack extended to 59°N; however, there appeared to be little or no in-situ freezing in the study area. Hydrographic data from the marginal ice region (seaward limit of the ice) showed that less saline, cold (≅–1.4°C) waters existed in an upper layer; the lower layer was as much as 1°C warmer. Floes advected toward the south to southwest at rates as high as 0.5 m/sec during north-to-northeast wind events. Floes rotted along the margin in periods on the order of days. Little ridging of ice was observed over the open shelf. Rafting was prevalent among floes battered by wind and swell at the ice edge. We observed that in the fall, northerly winds cool the water of Norton Sound and the Bering Sea north of St. Lawrence Island until the water column is isothermal at freezing temperatures. Further cooling causes freezing. Under northerly wind conditions, ice is advected south into water where it is no longer in thermodynamic equilibrium. The resulting meltwater is mechanically mixed and is a source of cooling for the waters of the southern Bering shelf. These observations suggest that ice formation and movement in the Bering Sea can be likened to a conveyor belt: growth occurs primarily in the north, advection due to wind stress is generally southward, decay occurs at the thermodynamic limit, and the limit advances somewhat as meltwater cools the upper layer.