Effects of a shelf polynya on flow and water properties in the northern Bering Sea

We present long‐term (∼230‐day) measurements from three moorings in the vicinity of Saint Lawrence Island on the northern Bering Sea shelf. One mooring was deployed near the polynya which often exists south of the island. These data confirm the existence of strong (∼0.15 m s −1 ) flow toward Bering Strait northwest of the island (in Anadyr Strait) and suggest that regional circulation results in a moderate (∼ 0.03 5 m s −1 ) mean flow eastward along the southern coast of Saint Lawrence Island. Coherent variations in the regional circulation and variations in the geostrophic wind account for much of the low‐frequency current fluctuation south of Saint Lawrence Island. However, there were 11 events when offshore (northerly) winds coincided with the temperature following the freezing point, increasing salinity, and reversal of the current. This suggests that ice formation and the ensuing brine rejection affect flow in the vicinity of the polynya. Scaling of a simplified momentum equation indicates that the cross‐shelf density gradient was a possible mechanism for some of the reversals. Salinity data show a seasonal cycle as well as individual events of brine rejection. During an average event time of 65 hours, the salinity increased by 8×10 −3 g kg −1 h −1 ; the heat flux can be estimated as 535 Wm −2 . These fluxes correspond to an ice production of ∼5 m during winter 1981. Extrapolation of our results and comparison with the freshwater cycle suggest that brine rejection is an important component of the regional salt budget.