Seasonal and interannual variability of the Bering Slope Current

Time series of sea-surface height anomalies derived from satellite altimeters and absolute dynamic topography are used to examine variability in the geostrophic surface currents in the Eastern Bering Sea. The data suggest that the primary source of water to the eastern boundary currents of the Bering Sea is flow from the North Pacific through Amukta Pass, an Aleutian pass located at ~172°W. The Aleutian North Slope Current (ANSC) is strongest and most variable in the winter months. Upon turning the corner to feed the Bering Slope Current (BSC), the ANSC bifurcates, resulting in a westward flow at ~54°N in addition to the northwestward flowing BSC. This westward countercurrent has not been previously observed. In the winter, the BSC flows strongly to the northwest and is located near the shelf-break. During the rest of the year, the mean flow is broadly northwestward, but weaker and farther from the shelf break. A continuous northwestward-flowing current is rarely observed in the altimetry data except during winter months, as it is overwhelmed by mesoscale variability. The strength of the BSC in winter is correlated with the Multivariate ENSO Index and the North Pacific Index on interannual timescales.