The region along the Brazilian coast situated between 22 S and 28 S is usually referred in the literature as the Southeast Brazilian Bight (SBB). In its central part, (22-24 S), the continental shelf reaches width over 200 km and the water mass structure is strongly influenced by intrusions of Tropical Water (TW) and South Atlantic Central Water (SACW), induced by the meandering of the southward flowing Brazil Current (BC). During the austral Summer, mostly due to the prevailing northeasterly winds, there is a very well defined stratification of the water column, with frequent occurrence of intense coastal upwelling, especially in the region around Cabo Frio (22 S). The combination of this wind driven upwelling with the shelf break upwelling induced by BC cyclonic meanders constitute a mechanism responsible for pumping up oxygen- and nutrient-rich SACW to the euphotic zones in the inner parts of the continental shelf. Incidentally, these shallower regions between 23 and 27 S are the most important spawning regions for the Brazilian Sardine (Sardinella Aurita).
While the coastal upwelling practically disappears during the austral Winter, the meander-induced shelf break upwelling is a mechanism that can occur in any season. This process was observed during three quasi-synoptic oceanographic cruises carried out in the SBB in Jan/93, Jul/93 and Jan/94. The frequent occurrence of this mechanism certainly acts positively in the maintainance of the primary production over the continental shelf during all year. In spite of the year-round occurrence of shelf break upwelling, there are times when anomalously cold (T<16C at 28 S) and low salinity water (S<32 at 28) water is observed in the entire water column in the inner shelf (depth < 100m). During these events, the SACC is constrained to the outer regions of the continental shelf. AVHRR observations of the sea surface temperature suggest the origin of this cold water might be located far to the south, at latitudes higher than 30 S. This northward penetration of this southern shelf water is a seasonal phenomenon, observed during the winter time. However, this penetration usually does not reach latitudes lower than 28 S. The outbreak of this water mass into the SBB, in latitudes as low as 23 S, is apparently an interannual feature which has been, among other things, associated with recruitment failure of the Sardinella Aurita.