Observations of Internal Tides at the Vitoria-Trindade Ridge, South Atlantic Ocean

The Vitoria-Trindade Ridge (VTR) has been shown, based on satellite altimetry, to be an important region for the generation of internal tides (ITs) that radiate southward and northward into the South Atlantic Ocean. Here, nearly 1 year of unprecedented high-density in situ velocity and temperature data collected at this undersampled region, were used to investigate and quantify the IT properties and variability. About 90% of the total tidal energy can be accounted for by the IT in the semidiurnal band. The data depict a dominant surface-intensified mode-1 vertical structure associated with progressive baroclinic waves, with a less prominent mode-2 growing in importance from January to June. Values of energy conversion from the barotropic to the baroclinic semidiurnal tides are comparable to other important sites of IT generation in the world ocean. Energy conversion and the highly coherent energy fluxes are strongly related with the springneap cycle, indicative that the observed IT are predominantly generated at the observational site. Fluxes and conversion are modulated by significant changes in the vertical stratification of the upper ocean, which are observed to occur during the different months of observations. Plain Language Summary Internal tides (ITs) are waves that propagate in the ocean interior with the same frequencies of the surface tides, and which can transfer energy for long distances affecting remote regions. Such waves are generated in the vertically stratified ocean, when the surface tides encounter steep topography. One such region is the Vitoria-Trindade Ridge (VTR), located at similar to 20.5 degrees S in the western South Atlantic. Here, unprecedented data collected by instrumented mooring at the VTR were used to investigate and quantify the properties and variability of these waves. It was shown that IT at semidiurnal frequencies account for most of the energy at the mooring site. The data allowed also for the vertical structure of the circulation associated with the IT to be determined, the amount of energy converted from the surface to the IT to be computed, and the direction and intensity of the IT energy fluxes to be evaluated. A strong relationship was observed to occur between the IT at the VTR and changes in the vertical stratification of the water column along the year.