Coastal upwelling along the Uruguayan coast: Structure, variability and drivers

Abstract

Summertime upwelling along the Uruguayan coast is studied for the first time using observational data and a high resolution regional ocean model. Simulations are performed with the CROCO model, with a horizontal resolution of 1/36° forced with NCEP-DOE daily mean winds and daily Río de la Plata discharges, together with climatological surface heat fluxes. A comparison between model results and actual observations indicates that the model reproduces seasonal, interannual and daily variability of the region. This allowed evaluating the role of the wind and freshwater discharge in the development of intense upwellings by running the model under different experimental setups. A Maximum Covariance Analysis between daily mean NCEP-DOE winds and satellite sea surface temperature data (MUR-GHRSST) was performed to identify intense observed summer coastal upwelling. The simulations were used to characterize the horizontal and vertical structure of observed intense upwellings along the Uruguayan coast in terms of temperature, salinity, vertical velocity and currents as well as their evolution for the first time. Finally, interannual simulations performed under different boundary conditions demonstrated the primary role of wind and secondary role of freshwater discharge anomalies in the generation of coastal upwelling. We also found that La Niña induces regional wind anomalies and river discharges that strongly favor upwelling in the Uruguayan estuarine coast, while El Niño does the opposite. • The 3-D structure of summertime upwelling along the Uruguayan coast was for the first time described using the CROCO model. • Climatological upwelling, centered at the oceanic coast was identified. • Subseasonal intense upwellings, centered at the estuarine coast, were identified and fully described. • Winds are the primary upwelling driver with secondary contribution of river discharge. • Wind and freshwater discharge conditions favor the development of upwelling during La Niña years.