CIRCULATION AND WATER PROPERTIES OF THE SOUTHWEST INDIAN-OCEAN, SPRING 1987

The results obtained during a cruise in the south-western Indian Ocean, from South Africa to Mauritius in September 1987, are presented. Temperature, salinity, oxygen and nutrients were measured at 70 CTD stations, 20 nautical miles apart. The data perspective is enhanced by NOAA satellite infrared imagery and Geosat altimetry. The major features encountered on the cruise were two intense cyclonic eddies in the vicinity of the Mozambique Ridge and the Mozambique Basin and which seemed to form part of the broader western boundary region of the southern Indian Ocean. Evidence was found of a significant equatorward flux at the Madagascar Ridge, which provided input of water from higher latitudes. The passage of North Atlantic Deep Water was constrained by the bottom topography south of the Madagascar Ridge, and this led to a reduction of its salinity and oxygen concentration. The positive correlation between the CTD results and the altimetry enabled the identification, tracking and description of a number of eddies in the region. The transition zone of these eddies from east of Madagascar to the African continent was identified, and so was the apparent closure of the southern entrance of the Mozambique Channel to migrating eddies.