The QUICCHE's Ocean Sciences Meeting 2024 poster is available for download by clicking here!

Overview:

The Cape Basin in the southeast Atlantic is a global hotspot of eddy kinetic energy, fed by a leakage of waters from the subtropical Indian Ocean via the Agulhas Current. A proportion of warm and salty Agulhas waters are vigorously stirred and mixed into the cooler and fresher Atlantic by co-interacting rings and eddies. The basin has been dubbed the Cape Cauldron. Until now the focus of physical studies in the Cape Cauldron has largely been on discrete, deep-reaching anticyclonic Agulhas rings, which can often be tracked for many months, sometimes years, using satellite altimetry. These rings and the warm and salty water masses they entrap have been studied extensively to estimate the magnitude of inter-ocean exchange, called Agulhas leakage, between the Indian and Atlantic Oceans. Yet, studies suggest that most Agulhas leakage is found outside these rings. We hypothesize that a large proportion of the Indian Ocean waters that leak into the Atlantic are to be found in submesoscale features generated by the mesoscale strain field. Observations of these features are lacking, as are estimates of the fluxes they affect. To fill this gap we propose to:

(1) Observe and characterize submesoscale features generated by the mesoscale eddy strain field within the Cape Cauldron for the first time.

(2) Make novel estimates of Agulhas leakage fluxes with these new observations, using theoretical eddy diffusivity and eddy flux frameworks.

(3) Relate diffusivity and fluxes to new and existing satellite altimeter observations to infer variability in Agulhas leakage.

We will collect new observations within the Cape Basin, targeting several dynamical regimes – e.g. filamentation, eddy interaction – to measure the related submesoscale features and estimate diffusivities. From these measurements we will quantify eddy heat and salt fluxes, similar to the way poleward heat flux has been estimated in the Southern Ocean. We will use both Eulerian and Lagrangian instrumentation, including moorings, an undulating CTD system, gliders, drifters, profiling floats, and microstructure turbulence profilers, capturing time and space scales from hours to seasons and from 1 to 100 km. Our new observations will be synthesized and analyzed with other datasets, including measurements from the SWOT crossover in the Cape Basin and output from a 1/60  simulation.