THE RIO DE LA PLATA ESTUARY RESPONSE TO WIND VARIABILITY IN SYNOPTIC TO INTRA-SEASONAL SCALES: II CURRENTS VERTICAL STRUCTURE AND ITS IMPLICATIONS ON THE SALT WEDGE STRUCTURE.

SIMIONATO, C. G.; MECCIA, V. L.; GUERRERO, R. A.; DRAGANI, W. C.; NUÑEZ, M. N.

JOURNAL OF GEOPHYSICAL RESEARCH

American Geophysical Union

Lugar: Washington D.C., EE.UU.; Año: 2007 vol. 112 p. 1 - 15

0148-0227

The first ADCP current data collected at two locations of the Río de la Plata salt wedge during a period of around 6 month and salinity profiles gathered at and around those locations are used to study the vertical structure of currents response to wind variability in synoptic to intra-seasonal time scales and its implications on stratification.  Results indicate that the estuary rapidly responds to prevailing southwesterlies/northeasterlies with currents that decay towards the bottom with only little rotation in depth. For the less frequent southeasterlies/northwesterlies the estuary develops a strong vertical structure with a defined inversion in current direction between surface and bottom layers. These patterns derive from estuary?s geometry and bathymetry. Results have important implications on the salinity vertical structure that are verified on the analyzed profiles. Firstly, the combination of the bathymetry and coastline with the prevailing wind variability is highly favorable to the maintenance of a salt wedge structure in this estuary. Secondly, weakening and eventually breakdown of stratification can only occur for intense and/or persistent southeasterly winds, which even can be very strong, are not frequent. This can explain why the Río de la Plata displays the unusual feature of being an area of spawning and nursery for a number of coastal species that use the wedge as an essential element for their reproduction. Results show that stratification is highly affected by short term wind variability -which is its major characteristic in the area- changing the classical concept of summer-winter seasonality as the main feature of estuarine variability.