Small-scale ocean dynamics in the Cape Basin and its impact on the regional circulation

– Tonia CAPUANO – LEGOS, Toulouse, France –

Abstract: Oceanic mesoscale and submesoscale processes have a key role on the formation and transformation of subsurface water masses that participate in the Indo-Atlantic interocean exchange. The focus of this study is on the Cape Basin dynamics, characterized by a highly non-linear, turbulent regime. Eddies of both polarities, meanders and filaments spawned by the Agulhas Current contribute to such an intense turbulence and strongly affect the local water masses dynamics and thermohaline structure. We provide qualitative and quantitative evidence of the direct impact that these meso- and submesoscale structures, their dynamical interactions and their seasonal variability have on the regional thermocline and intermediate waters. We used a sequence of numerical simulations, of increasing horizontal and vertical resolutions, to show how Agulhas eddies are mainly generated through baroclinic instabilities and marked by a clear seasonality. This temporal variability is directly linked to the seasonal occurrence of several types of meso-submesoscale instabilities in the upper layers but also at intermediate depths. Finally, we point out that not only Agulhas rings but eddies of both polarity are involved in advecting Antarctic Intermediate Water varieties, whose mixing is majorly driven by the mesoscale strain field.