Agulhas Ring Transport Efficiency From Combined Satellite Altimetry and Argo Profiles

Agulhas rings are one of the main processes contributing to the westward transport of Agulhas leakage water across the South Atlantic basin. Here we quantified the water transported and exchanged by three Agulhas rings by combining remote sensing altimetry and in situ Argo observations. Satellite velocities showed that two of the eddies formed within the Cape Basin west of South Africa at the beginning of 2013 and reached the Mid-Atlantic Ridge by the end of 2014. There, they merged forming the third eddy that dissipated a year later when it approached the Brazilian continental shelf. Eddy structure reconstructed from Argo profiles showed that the eddies were at least 1,500m deep and that their dynamics was strongly affected by the two open-ocean ridges encountered along their path. Between the ridges, eddy volumes were mostly conserved, but waters were continuously exchanged. During eddy dissipation, volume losses and water exchanges were more pronounced at depth. These findings highlight the importance of combining surface with in situ information to accurately represent Agulhas ring transport and exchanges. Overall, the eddies transported roughly 0.5 x 10(13)m(3) of water from the Cape Basin to west of 30 degrees W in a 3-year span. Lagrangian diagnostics indicated that, after an initial period of instability, the surface waters exchanged by the eddies along their tracks dispersed roughly in the same direction as the eddies, albeit at a much slower rate. These results further confirm that Agulhas eddies are the most efficient process for westward transport across the South Atlantic basin.