A model for the structure of the Antarctic Slope Front

Abstract

The Antarctic Slope Front is an oceanic front that appears to be a semi-permanent feature situated above or near long sections of the shelf break of the Antarctic continental shelf. These sections include the shelf break of the Ross and Weddell Seas. It is distinguished by a V-shaped structure, unique to coastal Antarctica, in which isopycnals slope downward from near the surface on both the shallow (continental shelf) and the deep (continental slope) sides, toward the bottom near the upper part of the slope. In the regions where it is observed, the overflow of dense water from the shelf down the slope is observed or presumed to occur. Such overflows entrain fluid from the overlying stratified environment into the downflow, and this entrainment acts as a distributed sink of the overlying fluid. A model of this frontal structure is constructed here, consisting of the downslope flow modelled as a plume, and the overlying fluid governed by quasi-geostrophic dynamics, with the effect of the plume on the latter being represented by a suitable distribution of sinks. The alongslope currents follow from geostrophy and potential vorticity conservation. Two distinct flow regimes are found. In the first regime, a realistic depiction of the two-sided V-shaped structure is obtained, where most of the fluid flowing off the shelf enters the downflow at the top of the slope constituting the shallow side of the V, and fluid from offshore enters the deep side of the V. Alongslope flow in this region is mostly eastward. In the second regime, where most of the fluid flowing off the shelf passes over the downflow, only the shallow side of the V is present, and alongslope flow is westward near the shelf break and eastward further offshore.