The Siberian Coastal Current: A wind- and buoyancy-forced Arctic coastal current

Authors

  • Thomas J. Weingartner,

  • Seth Danielson,

  • Yasunori Sasaki,

  • Vladimir Pavlov,

  • Mikhail Kulakov


Abstract

We describe circulation and mixing in the Siberian Coastal Current (SCC) using fall shipboard measurements collected between 1992 and 1995 in the western Chukchi Sea. The SCC, forced by winds, Siberian river outflows, and ice melt, flows eastward from the East Siberian Sea. It is bounded offshore by a broad (∼60 km) front separating cold, dilute Siberian Coastal Water from warmer, saltier Bering Sea Water. The alongshore flow is incoherent, because the current contains energetic eddies and squirts probably generated by frontal (baroclinic) instabilities. These enhance horizontal mixing and weaken the cross-shore density gradient along the SCC path. Eventually, the SCC converges with the northward flow from Bering Strait, whereupon it deflects offshore and mixes with that inflow. Deflection occurs where the alongshore pressure gradient vanishes. That location varies on synoptic and seasonal timescales, because this gradient depends on the winds, buoyancy fluxes, and the sea level difference between the Pacific and Arctic Oceans. Deflection usually occurs on the Chukchi shelf, but the SCC occasionally flows southward through Bering Strait. Such events are short lived (1–10 days) and occur mainly in fall and winter under northerly winds. SCC transport is likely small (∼0.1 Sv), but its dilute waters could substantially freshen the Bering Strait inflow and affect the disposition of Pacific waters in the Arctic Ocean. Arctic river outflows should preferentially form surface-advected fronts rather than bottom-advected fronts because vertical-mixing energy is low on arctic shelves. Surface-advected fronts are more susceptible to upwelling winds (and for the SCC, the pressure gradient between the Pacific and Arctic Oceans) than bottom-advected fronts. The SCC never developed in fall 1995 because of anomalously steady upwelling winds. The western Chukchi shelf could have formed upper halocline source water in the winter of 1995–1996.

Ancillary