A baroclinic model of motions on Antarctic continental shelves

Abstract

Formation of Antarctic Bottom Water takes place by the mixing of dense shelf water with warmer fresher open-ocean water along the edge of the continental shelves in such areas as the Weddell and Ross seas. The amount formed depends critically on the structure of the outflow from the shelf; this outflow is produced geostrophically by the strong east-west salinity and density gradient on the shelf. Since the effective freezing of sea ice produces a surface salinity influx which varies only in the north-south direction, it is necessary to seek a mechanism for the east-west density gradient. Such a mechanism is found in the geostrophically-induced upwelling which occurs on the western boundary of the shelf: the mixing of denser subsurface water with lighter surface water induces a net east-west density gradient. This corresponds to a geostrophic outflux of dense subsurface water in a boundary layer which grows in thickness as time increases. Downwelling occurs on the southern and eastern shelf boundaries. The predicted density distribution agress well with observations; only the northward fluxes are to small. Hence it is probable that several years of forcing are necessary before a limit cycle is achieved.