The salinity signature of the cross-shelf exchanges in the Southwestern Atlantic Ocean: Satellite observations

Highlights

• Satellite salinity sensors capture low-salinity detrainment events fromshelves
• SW Atlantic low-salinity detrainmentscause highest basin-scale variability
• In summer low-salinity detrainmentscause extended low-salinityanomalies

Abstract

Satellite-derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study theshelf-open ocean exchanges in the western South Atlantic near 35ºS. Away from the tropics, theseexchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well-definedseasonal pattern of SSS during the analyzed period and of the location of the export of low-salinity shelfwaters. In spring and summer, low-salinity waters over the shelf expand offshore and are transferred to theopen ocean primarily southeast of the river mouth (from 36ºSto37º300S). In contrast, in fall and winter,low-salinity waters extend along a coastal plume and the export path to the open ocean distributes alongthe offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of thealong-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export ofshelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluenceand mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mix-tures of low-salinity shelf waters are swiftly driven toward the ocean interior along the axis of the Brazil/Mal-vinas Confluence. In winter, episodic wind reversals force the low-salinity coastal plume offshore wherethey mix with tropical waters within the Brazil Current and create a warmer variety of low-salinity waters inthe open ocean.