Lagrangian and satellite observations of the Brazilian Coastal Current

Abstract

The waters dominating the Brazilian Continental Shelf to the south of Santa Marta Cape (28°40′S) are marked by their strong interannual variability. Both the seasonal oscillation of the Brazil–Malvinas (Falkland) Confluence (BMC) region and the seasonal variations of the La Plata River and Patos Lagoon outflows are reflected in the seasonal changes of the vertical and horizontal water mass structure in the Southern Brazilian Shelf. In the region to the north of Santa Marta Cape, the shelf is mainly described in the literature as dominated by Tropical Waters (TW) transported southwards by the Brazil Current (BC). However, the first Lagrangian (buoy) measurements made on the inner Brazilian shelf have shown that a coastal current flowing in the opposite direction in relation to the BC occurred on the shelf as far north as 24°S during the 1993 austral autumn and winter. Recent papers have suggested that the arrival at low latitudes of cold waters originating in the BMC region is an anomalous phenomenon and that it can be either forced by local winds during wintertime or related to the ENSO. High-resolution sea surface temperature (SST) imagery and the Lagrangian measurements taken in 1993 and 1994 are used in this paper to describe the temperatures, velocity, energy and oscillations present in this coastal current. These two data sets show that the current is not only fed by waters of Subantarctic or coastal origin but also receives a contribution of TW at the surface by lateral mixing. By analysing a set of monthly averaged SST images from 1982 to 1995, this work suggests that the intrusion of cold waters transported by the coastal current can be a regular winter phenomenon occurring on the Brazilian shelf at latitudes up to the vicinity of 25°S. Given its consistency, this current is named here the Brazilian Coastal Current.