The boundary currents east and north of Madagascar: 1. Geostrophic currents and transports

Abstract

Geostrophic currents and transports in the boundary currents near Madagascar are described for a section at 23°S off the east coast and at 12°S to the northeast of Cape Amber. These results are based on conductivity‐temperature‐depth and expendable bathythermograph sections made during cruises of the Marion Dufresne in 1984, 1985, and 1986, supplemented by those historical data that were sufficiently deep. The reference levels used are 1100 dbar at 12°S and 1170 dbar at 23°S, based on the results from 11 months of current meter records obtained in 1984–1985. Comparisons are made between the geostrophic current profiles and direct observations, both from moored current meters and from acoustic Doppler profiling in the Upper 200 m. The mean geostrophic transports above the chosen reference levels are 29.6 Sv northwestward off Cape Amber out to 115 km offshore and 20.6 Sv southward at 23°S out to 110 km offshore. The directly recorded currents show no detectable seasonal signal below 200 m: above that level other historical data suggest a seasonal amplitude in transport of approximately ±2 Sv at 12°S and ±0.3 Sv at 23°S.