In austral winter, biological productivity at the Angolan shelf reaches its maximum. The alongshore winds, however, reach their seasonal minimum suggesting that processes other than local wind-driven upwelling contribute to near-coastal cooling and nutrient supply, one possibility being mixing induced by internal tides (ITs). Here, we apply a three-dimensional ocean model to simulate the generation, propagation and dissipation of ITs at the Angolan slope and shelf. Model results are validated against moored acoustic Doppler current profiler and other observations. Simulated ITs are mainly generated in regions with a critical/supercritical slope typically between the 200- and 500-m isobaths. Mixing induced by ITs is found to be strongest close to the shore and gradually decreases offshore thereby contributing to the establishment of a cross-shore sea surface temperature gradient. The available seasonal coverage of hydrographic data is used to design sensitivity simulations. Seasonal variations in stratification results in substantial temporal differences in IT characteristics, such as their wavelengths, sea surface convergence patterns and baroclinic structure, additionally showing strong spatial variations. However, seasonal variations in the domain-integrated generation, onshore flux and dissipation of IT energy are weak. By defining a parameter - the relative change of the vertical density gradient - to evaluate the relative mixing strength, it is shown, nevertheless, that mixing due to ITs is more effective at weakening the stratification during austral winter. We argue this is because less energy is required to mix the water column in austral winter than in austral summer.

Multiyear turbulence measurements from oceanographic moorings in the equatorial Atlantic and Pacific cold tongues reveal similarities in deep cycle turbulence (DCT) beneath the ML and above the core of the Equatorial Undercurrent (EUC). Diurnal composites of turbulence kinetic energy dissipation rate, $\epsilon$, clearly show the diurnal cycles of turbulence beneath the ML in both cold tongues. Despite differences in surface forcing, EUC strength and core depth, DCT persists at all three sites, and is consistent between the sites. Time-mean values of $\epsilon$ at 30 m depth are nearly identical at all three sites. Variations of averaged values of $\epsilon$ in the deep cycle layer below 30 m range to a factor of 10 between sites. A proposed scaling in depth that isolates the deep cycle layers and of $\epsilon$ by the product of wind stress and current shear collapses vertical profiles at all sites to within a factor of 2.