Evolution of the Deep Western Boundary Current of Antarctic Bottom Water in the Brazil Basin

Abstract

A synthesis of WOCE (and other) hydrographic data shows that the deep western boundary current of Antarctic Bottom Water has a double-core structure, and that it is differentially modified during its northward transit through the Brazil Basin. At 25°S, it descends about 200 m while continuing equatorward as a paired, double-core current over the relatively broad, sloping topography of the western region. The downslope core is faster, 4?6 cm s?1 versus 3 cm s?1, and is coincident with the high-density core. Equatorward of 19°S the cores begin to diverge and by 15°S, the velocity cores have separated and the high-speed pattern has inverted. Between 13° and 11°S the colder, slower-flowing branch (around 3 cm s?1) deepens by 350 m, with a noticeable decrease in the vertical stratification of overlying water characteristics. Subsequently, it continues to the equator toward the Romanche?Chain Fracture Zones. The warmer, faster-flowing branch (around 8 cm s?1) proceeds to the equator along the continental slope, eventually becoming the flow entering the equatorial channel.