Major late-winter features of ice in northern Bering and Chukchi Seas as determined from satellite imagery

Abstract

Imagery from the ERTS-1, DAPP and NOAA 2/3 VHRR satellite systems were used for identification of recurring features of the movement and distribution of sea ice in the Bering and Chukchi seas during late winter. Data acquired during March and April of 1973 and 1974 show several such features including: 1) a shear zone of variable width along the west coast of Alaska which separates landfast ice from drifting sea ice; 2) an area of generally broken pack ice between Bering Strait and Point Hope; 3) persistent polynya off south-facing coasts, such as that east of Point Hope, south of the Seward and Chukchi Peninsula and south of the larger islands; 4) convergence zones on the north sides of St. Lawrence and Nunivak Islands, and 5) narrow shear zones extending generally southward from the boundaries of the Bering Strait and from the east and west ends of St. Lawrence Island. The pattern observed is consistent with a general southward drift of sea ice under the influence of the prevailing northerly winds present in the area during this time of year. Closure of ice against south-facing coasts, reflecting northward ice drift, occurred about 10% of the time. These episodes probably correlate either with short periods of dominantly south winds or drift under the influence of north setting currents when prevailing north winds were light.