Winter currents and hydrographic conditions on the northern central Bering Sea shelf

Current observations obtained from the northern Bering shelf region in winter 1984–1985 indicate that midwinter circulation patterns differed from those during the rest of the year. Annual mean circulation in this region is dominated by vigorous northward currents (from 10 cm/s in Shpanberg Strait to more than 50 cm/s in Bering Strait). These northward currents are accompanied by a weak northwestward coastal flow south of St. Lawrence Island. In February–April 1985, however, flow was weakly (0–5 cm/s) southward through Shpanberg Strait and southeastward south of St. Lawrence Island while remaining northward through Anadyr and Bering straits. Comparison with current data obtained from previous years suggests that midwinter reversal of flow in Shpanberg Strait is a recurrent winter feature. It generally occurs at about the same time that the winter ice cover undergoes its major advance, and it is associated with strong northerly winds. Northward flow through Anadyr Strait persists, conversely, through the winter and is the northward extension of a western intensified northward flow over the Bering Shelf. Its source is Bering Sea water farther south, rather than water from the northern central shelf. The resultant “trapping” of shelf water on the northern central shelf, coupled with intensive regional ice formation during the same period as the flow reversal, led in 1985 to significant (about 1.5‰) brine enrichment. This salinity increase agrees qualitatively with historical data, which suggest that the northern central Bering shelf is the site both of sluggish winter circulation and of elevated salinities due to brine enrichment from ice formation.