Causal Mechanisms of Sea-level and Freshwater Content Change in the Beaufort Sea

Sea level across the Beaufort Sea has risen at a rate exceeding 2 cm/yr during the past decade. The rapid sea level rise is dominantly halosteric, reflecting an increase in the region’s freshwater content by as much as 400 km3/yr. Here we study the nature and causal mechanism of this change and the attendant seasonal-to-decadal variation from 1992 to 2017 by quantifying their controlling processes using a coupled ocean circulation and sea ice model constrained by satellite and in situ observations. Surface stress and freshwaterflux associated with the melting and freezing of sea-ice are the primary driving forces of these variations, but their relative contribution varies with time-scale. Seasonal change is dictated by the sea-ice variation and interannual change is mostly wind-driven associated with Ekman transport. The two forcings, however, are equally important for decadalchanges that dominate the overall variation. Strengthening anticyclonic surface stresssurrounding the Beaufort Sea intensify the ocean’s lateral Ekman convergence into theregion near the surface where the water is relatively fresh, resulting in the domain’sincrease of both steric height and freshwater content. The strengthening stress alsoenhances sea-ice convergence into the Beaufort Sea where it draws heat from the oceanand melts, further increasing the region’s rise in sea level and freshwater content. Thedecadal variation amounts to a wind-driven coupled diabatic interaction between the ocean and sea-ice, whereby sea-ice serves as an extra-ocean conduit for freshwater transport.