On the seasonal sea ice cover of the Sea of Okhotsk

Abstract

Free of ice 4 months of the year, the Sea of Okhotsk begins to freeze over in a few coastal locations in November, attains its maximum ice coverage usually in mid March, and by June retains ice in only a few coastal regions. This sequence is well recorded by satellite imagery from the Electrically Scanning Microwave Radiometer (ESMR) on board Nimbus 5. Four years of ESMR data reveal significant interannual variations in the maximum ice cover and in the smoothness of the growth and retreat periods. Of the years 1973–1976, the heaviest ice cover occurred in 1973, and the growth period most interrupted by temporary ice edge retreats was in 1974. Comparison of the general features of the cycle of sea ice distribution with basic oceanographic factors shows that ice forms first in cold, shallow, low‐salinity waters and then seems to drift in a direction approximating the Okhotsk‐Kuril current system. Two basic patterns of ice edge positioning which occur frequently in the ESMR data are identified as a rectangular structure and a wedge structure. Each of these is strongly correlated with the bathymetry of the region and with the known current system, suggesting that convective depth and ocean currents play an important role in determining ice patterns. Certain major interannual variations in the ice extents are accounted for by interannual contrasts in the atmospheric pressure fields.