THE SUMMER AND WINTER CIRCULATION AT THE RíO DE LA PLATA AND THE ADJACENT CONTINENTAL SHELF ­ A NUMERICAL CASE STUDY

SIMIONATO, C. G.; NUÑEZ, M. N.; ENGEL, M.

Mar del Plata, Argentina

Congreso; Joint Assembles of the International Association for Physical Sciences of the Oceans and International Association for Biological Oceanography - XII Coloquio Argentino de Oceanografía; 2001

International Association for the Physical Sciences of the Oceans

The 3-D baroclinic Hamburg Shelf Ocean Model has been applied to the Río de la Plata and the adjacent Continental Shelf in a set of case studies in order to analyze the differences between the summer and winter circulation in the area. Tides, river discharge and winds are considered as forcing. The resulting surface salinity distributions show a surprisingly good agreement with observations thus serving as a test for the reliability of the simulations. It turns out that the system variability is dominated by the winds. The circulation pattern displays important differences between both seasons. At the mouth of the estuary, residual transports and particle trajectories indicate that during the cold season the fresh water tends to move northwards along the Continental Shelf, whereas during summer this circulation is reversed at approximately 55.5º W, where it turns to the south. Along the shelf a tidal residual current , that seems to have its origin near the San Matías Gulf, follows the 50m isobath to the North. This current is intensified in winter by the prevailing winds but is weakened during the summer and almost null at the estuary south-westernmost part. As a result of these two features during the summer both, the estuary waters and those coming from the Brazilian Shelf, move southeastwards to higher depths, being able to produce important changes of the thermohaline properties of the oceanic waters. During the winter the motion of these waters tends to be northeastwards filling in the Shelf with fresh water.