On the total geostrophic circulation of the South Atlantic Ocean: Flow patterns, tracers, and transports

Abstract

The South Atlantic Ocean receives waters from the North Atlantic, the Weddell Sea, and from the Circumpolar Current through the Drake Passage. The circumpolar and North Atlantic waters are of widely different characteristics (temperature, salinity, oxygen and nutrients) but of overlapping density ranges, and as they enter the South Atlantic are caught up in the circulation imposed by the winds and thermohaline processes. Interleaving of these different characteristics takes place in various ranges of depth and density, and more than a dozen vertical extrema are created in the tracer fields. These are spread by lateral flow in recognizable layers. These patterns as seen on vertical sections and on isopycnals can be taken to indicate the sense of flow in various areas and depths, and I have used them, with the density field, to add the barotropic component to the baroclinic flow defined by the density field. This gives the total geostrophic flow at all depths in a manner that appears to be consonant with the tracer patterns, and that satisfies continuity of mass. The resulting flow field has the traditional western boundary current from the Weddell Sea to the equator, beneath a poleward flow north of 50°S. In the upper waters the flow pattern shows a cyclonic gyre in the Weddell Sea, a northward flow from the Antarctic along the western boundary from 55°S to 40°S, an anticyclonic gyre between 15°S and 40°S, and an eastward flow near 10°S. Below the upper layer the axis of the anticyclonic gyre shifts southward, to 35°S at 1500 m, and at greater depths the gyre is confined to the Brazil Basin, west of the Mid-Atlantic Ridge and north of the Rio Grande Rise. Below the crest of the Mid-Atlantic Ridge in the Brazil Basin waters from the south flow northward along the Ridge, and part of them crosses the Ridge at or near the equator and returns southward in the eastern basin, joined by waters from the North Atlantic. The northward abyssal flow in the Brazil Basin is not confined to the western boundary but extends some distance across the basin, diverted only slightly at 3500 m by the small deep remnant of the overlying anticyclonic gyre. From 3000 to 4000 decibars the flow within the Weddell Sea and the Argentine Basin form a single cyclonic gyre and the flow within the Cape Basin is cyclonic below 3000 m. © 1990.