On the Cape Cauldron Dynamics: Some Physical Insights on the Turbulent Indo-Atlantic Exchange and Impact of Agulhas Waters In the Southern Africa Upwelling Region from a Hierarchy Of Regional Numerical Simulations

S. Speich, P. Penven and B. Blanke

Interocean exchange of heat and salt around Southern Africa is thought to be a key link in the maintenance of the global overturning circulation of the ocean. Most of Indian waters leakage to the Atlantic Ocean takes place through large current rings that pinch off from the Agulhas Retroflection. The Agulhas Retroflection and the shedding of large anticyclonic rings have been topic of theoretical and experimental research since more than twenty years. The Agulhas current is the most intense western boundary current of the world ocean and the retroflection region shows one of the highest signal of kinetic energy. Only recently it is appeared, from intensive Eulerian and Lagrangian observations and satellite data, that interocean exchange South of Africa is dynamically much richer and more complex than previously thought. Almost everywhere (inshore of the Agulhas Current, in and south of the return current and along the western South Africa coast) cyclonic structures develop and interact with the Agulhas Current, Retroflection and rings. More over, the Agulhas Current dynamics and variability and the rings shedding into the Atlantic are thought to have an impact on the dynamics and variability of the South Africa and South Benguela upwelling systems. This last topic is of particular importance as these ecosystems represent one of the major ...

In this work we examine the complex dynamics of the Agulhas Retroflection and interocean exchange by using a relatively high-resolution numerical model of the Southern Africa Indo-Atlantic region. Through a hierarchy of sensitivity experiments we investigate the role of the form and steepness of the bathymetry as well as open ocean and atmosphere forcings. The results are discussed in terms of physical processes inducing or influencing the Agulhas Retroflection, the rings shedding, the general cyclones genesis and dynamics in the region as well as the influence and interactions of Agulhas waters with the upwelling systems. Where possible, our results are confirmed by comparison with observations.