Presented at the 2014 Aquarius/SAC-D Science Team MeetingSea surface salinity (SSS) data from Aquarius and SMOS and the results of high-resolution numerical model are used to investigate the shelf-deep ocean exchanges in the southwestern Atlantic region, a region characterized by the freshwater discharge from the La Plata River. The satellite data shows strong seasonal variations of the location where the low salinity shelf waters are exported to the deep ocean: to the south of the La Plata River mouth during the summer and to the north during the winter. Analysis of a high-resolution model indicates Analysis of a high-resolution model shows three distinct modes of SSS variability. The first two represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the inter-annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.