The shelf and coastal waters off southern Brazil

Abstract

The data collected on three oceanographic cruises undertaken in 1956 indicate that the main branch of the Brazil Current flows southwards along the continental slope, where it reaches maximum velocity, and further, that a well defined limit is found between the warm and saline tropical water from the north and that situated over the central part of the shelf. This is especially the case during the summer months (October-March). Below the Brazil Current a water layer of lower salinity and temperature is found. This water mass is formed near the western extremity of the Subtropical Convergence where it sinks and flows northwards to reappear near or at the surface in an area situated between the lighter, south-flowing, tropical water, and the coastal water. Such a distribution of density across the Current is to be expected in view of the dynamics of ocean currents. There are, however, evidences which indicate the occurrence of upwelling from moderate depths, in particular near Cabo Frio where the prevailing winds from NE drive the surface waters offshore. It is further suggested that the upwelling is maintained by a thermohaline mechanism as the density of the cold and low salinity water is decreased by heating from solar radiation. In order to maintain dynamic stability, the heated water must consequently flow out of the area and be replaced by water from below which in turn suffers the same decrease of density, and so on. Such mechanism might, together with prevailing winds, be responsible for permanent or periodic upwelling near other regions in the tropical and subtropical zone of the oceans where salinity decreases with depth.