Abstract

Geostrophic transport calculations from historical data of the equatorial South Atlantic are presented for the investigation of the flow field in the South Equatorial Current region. On the basis of water mass distribution, the potential density surface of σ1 = 32.15 kg m–3 is used as a reference for geostrophic shears. This reference surface is located at a depth of 1000 to 1200 m and represents the boundary between the upper branch of the Circumpolar Deep Water and the Upper North Atlantic Deep Water. The southern band of the South Equatorial Current (SSEC) is fed by the Benguela Current, which crosses the Greenwich Meridian south of 20S. West of the Greenwich Meridian the subtropical gyre has its northernmost current band as the westward flowing SSEC. The SSEC was found to be a broad sluggish flow between 10S and 25S. The transport of the SSEC in the upper 500 m is in the order of 20 Sv, with surface velocities of around 10 cm s–1. At 30W the SSEC turns northward. A small part of the water turns poleward south of 10S to form the Brazil Current, whereas the bulk of the flow contributes to the North Brazil Current and the South Equatorial Countercurrent (SECC). The SECC seems to cross the entire South Atlantic eastward to at least the Greenwich Meridian, but part of the flow might contribute to the middle branch of the South Equatorial Current flowing westward. The northernmost current band sampled is the eastward flowing South Equatorial Undercurrent. From this data no seasonality in the geostrophic field can be proven.

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