Water mass characteristics and geostrophic circulation in the South Brazil Bight: Summer of 1991

Abstract

A hydrographic survey on board the German ship FS Victor Hensen was carried out in Brazilian coastal waters between Santos (23°56'S) and Rio de Janeiro (22°54'S) from January 15 to January 22, 1991. Analyses of conductivity‐temperature‐depth (CTD) data collected during this cruise show that the geostrophic flow and water mass structure of the Brazil Current in that region have characteristics similar overall to those in the better observed Cabo Frio region. The uppermost 200 m of the water column is dominated by the warm, highly saline Tropical Water flowing predominantly to the southwest. This flow direction appears to persist to approximately 900 m, the maximum depth reached by the CTD casts. The water lying between 250 and 750 m has the characteristics of South Atlantic Central Water (SACW). Below 750 m, down to 900 m, the water characteristics are those of Antarctic Intermediate Water. The thermohaline structure and geostrophic calculations indicate the presence of a meandering pattern, with a trough that appears to be the early stage of formation of a cold‐core eddy over the upper slope region. This feature extends from the surface down to approximately 500 m depth and is apparently associated with the intrusion of SACW onto the continental shelf. The geostrophic computations (with respect to two reference levels, 750 and 900 dbar) yield maximum current values in the range 0.6–0.7 m s−1. The southwestward volume transport, averaged over the entire domain, was approximately 7.3 Sv with respect to 750 dbar and 8.8 Sv with respect to 900 dbar.