Seasonal Circulation over the Southwestern Atlantic Shelf: Models and Observations

ELBIO D. PALMA; RICARDO P. MATANO; ALBERTO R. PIOLA

Bahia Blanca, Argentina

Conferencia; Science and Management of Estauries and Coasts (ECSA 44); 2008

Estuarine and Coastal Sciences Asociation

The Southwestern Atlantic Shelf is the largest continental shelf of the southernhemisphere, and one of the most biologically productive areas of the world ocean. Inthis study we aim to improve our knowledge of the circulation patterns over this vastregion through the analysis of long-term numerical simulations that, for the first time,includes all the major forcings of the region: winds, tides, freshwater discharges, andwestern boundary currents. The numerical experiments indicate that south of 40°S theshelf circulation is dominated by a general northeastward flow controlled by lowsalinity discharges, tidal mixing and wind forcing, and the offshore influence of theMalvinas Current farther north. The comparison of surface model currents with theavailable measurements indicates good agreement, less than 10% error both inmagnitude and direction. The region from 40°S to 33°S presents the highest seasonalvariability, with intrusions of cold subantarctic waters and the northward expansion ofmixtures of the Río de la Plata waters in late fall and a slower retraction of the plumeduring spring-summer. One of the main conclusions of this study is that the neighboringwestern boundary currents have an important effect on the shelf circulation, the mostevident of which is the increase of alongshelf transport as compared to tidal and windforcing. More subtle dynamical effects include the upstream influence of the MalvinasCurrent in the form of a northward flowing middle-shelf current and the steady shelfbreakupwelling generated by interactions of the Brazil Current with the shelftopography.