Virna L. Meccia

The Río de la Plata Estuary Response to Wind Variability in Synoptic Timescale: Salinity Fields and Salt Wedge Structure

ABSTRACT Meccia, V.L.; Simionato, C.G., and Guerrero, R.A., 2013. The Río de la Plata estuary response to wind variability in synoptic timescale: salinity fields and salt wedge structure. The Río de la Plata estuary response to wind variability in a synoptic timescale is studied with the Estuarine, Coastal and Ocean Model forced by tides, runoff, and idealized winds. Ancillary conductivity, temperature, and depth data from synoptic oceanographic cruises are used to validate the conclusions derived from the simulations. Results show that the estuarys response to wind variability can be explained in terms of four characteristic patterns associated with winds that blow with a dominant component either along or across the estuary axis. Cross-estuary winds from the SW produce a northward displacement of the surface salinity front toward the Uruguayan coast and cause downwelling between Montevideo and Punta del Este. Reciprocally, under NE winds, the surface salinity front migrates to the SW and upwelling between Montevideo and Punta del Este occurs. Along-estuary winds with a downstream component produce a net outflow of continental surface waters and inflow of bottom shelf waters, resulting in an intensification of the stratification. In opposition, winds with an upstream component produce a weakening of the vertical structure. Stratification can be destroyed by strong or persistent SE winds, which are not frequent in the region, and it recovers in a relatively short period (10–15 days) after wind relaxation. Consequently, the salt wedge structure is observed in the Río de la Plata during most of the year. This implies that significant vertical mixing events producing exchanges of water and properties between the surface and the bottom waters occur only a few times a year. As a consequence, the Río de la Plata shows strong retentive features, favoring biota by retaining eggs and larvae—and favoring pollutant accumulation.