[Eoas-seminar] Seminar 11:00 Thursday at COAPS

[eoas-seminar at lists.fsu.edu]

Title :Reconstruction of Agulhas Rings paths and thermohaline structures by satellite altimetry and Argo profiling float data.
Speaker: Remi Laxenaire
Location: COAPS conference room (2nd floor, Research A, Innovation Park)
Time: Thursday Sept. 12th at 11:00 AM
Abstract :
The Indo-Atlantic interocean heat exchanges are tightly linked to global ocean circulation and climate. They are principally achieved by the Agulhas Rings (AR), the largest mesoscale eddies of the world ocean, which are investigated in this study by means of 24 years (1993-2016) of daily satellite-altimetry maps and Argo floats profiles.

By applying the TOEddies eddy identification and tracking algorithm to daily maps of Absolute Dynamical Topography (ADT), we estimate Agulhas Rings origins, paths and lifetime. The main novelty lies in the detection of numerous eddies splitting and merging events that leads to the definition of a network of trajectories instead of a biunivocal identification between an eddy with a single trajectory. The results obtained by the network differ considerably with previous estimates connecting eddies formed in the Indian Ocean upstream of the Agulhas Current to eddies in the Brazil Current.

The collocation of the reconstructed segments of AR trajectories with Argo profiling floats gives access to their thermohaline structure. These data allow to estimate the evolution of AR along their trajectories. In particular, we show en route modification of an AR, transitioning from a surface to a subsurface intensified eddy subducting when entering the South Atlantic subtropical gyre. Moreover, in the Cape Basin, before its subduction, this AR undergoes to very intense air-sea interactions that lead to a very deep mixing layer. Here the eddy upper-core of Indian Ocean thermocline waters are significantly cooled. These waters transform into mode waters once the eddy subducts into the ocean interior.

Finally, an estimate of AR geographical distribution from the numerous eddies detected in the Cape Basin and South Atlantic Ocean show that the reconstructed AR is not an exception as AR generally subduct when they leave the Cape Basin.
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