A two-dimensional model for the formation of Antarctic bottom water

Abstract

Previous theories of Antarctic Bottom Water (AABW) have been concerned with its composition and its quantity, a steady-state value of 20 × 10 6 m 3 sec −1 being an accepted value. It is desirable to understand how such a quantity of bottom water is being produced, and the way it achieves its properties of temperature and salinity. One important point not yet understood is the relative importance of buoyancy-driven and wind-driven motions in the production of AABW, since in most of the studies mentioned, dynamical effects have only been included in a crude fashion. Study of a model two-dimensional problem (essentially only a first step in the study of the physical problem) shows that only a weak flow of bottom water is produced by buoyancy-driven motions, but if the convection is forced by the addition of a surface wind stress parallel to the coast, the resulting flow of bottom water becomes much stronger, for winds of the observed strenth. The magnitude of the flow is almost independent of the buoyancy forcing, and is simply that due to the action of the wind stress on the surface (independent of the frictional mechanism used). On the other hand, the composition of the bottom water does depend on the buoyancy flux. If we now apply the results of this geophysical fluid dynamical problem to Antarctica, the most significant result is the large increase in the rate of formation of AABW in the presence of wind. However, the wind-forced convection can produce the observed quantity of AABW only if the entire coastline of Antarctica is considered as a source of AABW, and cannot produce enough if only the length of the coastline within the Weddell Sea is considered. It seems that three-dimensional effects, in the form of channelling by bottom topography and shelf curvature, must be important in increasing the amount of AABW formed.