Internal Tide Generation at the Vitória-Trindade Ridge - South Atlantic

The generation, propagation and surface manifestation of internal tides at the Vitória-Trindade Ridge, a 950 km long east-west submarine seamount chain located around 20°S in the southwestern South Atlantic, were investigated using ~20 years of sea surface height anomaly data from different satellite altimeters, and numerical results from a high resolution regional HYCOM simulation. We found a dominant phase-locked semidiurnal internal tide generated at the ridge, with surface amplitude of 2.5 cm and wavelength of 120 km for the M2 component. Smaller amplitudes, between 1.0 and 2.0 cm were associated to the S2 component. The M2 internal tide radiate both poleward and equatorward for more than 1000 km, before decaying below noise level. Numerical results indicate maximum isopicnal displacements on the order of 100 m at thermocline levels, and a coherent mode-1 M2 internal tide energy flux around 100 W/m. Although smaller than fluxes reported in highly energetic regions such as the Hawaiian Islands, this value is significant when compared to fluxes generated nearby at the Brazilian slope. The results also indicate that the ridge geometry acts as a lens for the poleward propagating internal tide, with a focal region located about 300 km to the south. Chlorophyll-a maps of the South Atlantic show that the Vitoria-Trindade Ridge seamounts are hot-spots of high phytoplankton biomass, surrounded by oligotrophic oceanic waters. It is hypothesized that the locally generated internal tides may play an important role in sustaining the observed complex marine food webs, by bringing nutrient-rich subsurface waters to the euphotic zone.