Hydrographic conditions in the surface layers over the slope-open ocean transition area near the Brazil-Malvinas confluence during austral summer 1990

Abstract

The Confluence 3 cruise during February 1990 provides the first hydrographic survey of the Brazil-Malvinas Confluence region with such a refined spatial resolution over the continental slope. It is also the first survey in the region ever obtained in an austral summer. The austral summer 1990 atmospheric conditions were anomalously warm over the region. The surface waters were separated from the underlying waters by a thin and sharp seasonal thermocline which hid the real location of the Brazil-Malvinas thermocline front on infrared satellite imagery. The surface salinity was influenced by the large Rio de La Plata runoff which was anomalously high by a factor of 3. Salinity values less than 32 psu were encountered. These low salinity waters were entrained by the surface east-west front away from the coast. Four types of fronts were observed in the surface layer: (i) an east-west front associated with the structure of the seasonal thermocline separating cold, low salinity, oxygen supersaturated and productive waters to the south from warm, salty, weakly undersaturated and poor chlorophyll a waters to the north, (ii) a north-south front in salinity due to the outflow of the Rio de La Plata, (iii) a shelf break front between the shelf water and the Malvinas Water characterized by higher Chl a values, and (iv) a front between the Malvinas Water and the Brazil-Malvinas return flow.