Assessments on the fate of the Agulhas Rings and their transport in the South Atlantic estimated by combining satellite altimetry and in situ observations

• Main Author: Laxenaire, Rémi
• Other Authors: Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université Paris Saclay (COmUE), Sabrina Speich, Alexandre Stegner
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2019
• Subjects: Ocean mesoscale dynamics; Eddy characteristics; Heat Transport; Dynamique océanique à mésoéchelle; Caractéristiques tourbillonnaires; Transport de chaleur; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; South Atlantic Ocean
• Online Access: https://theses.hal.science/tel-02293794; https://theses.hal.science/tel-02293794v2/document; https://theses.hal.science/tel-02293794v2/file/76741_LAXENAIRE_2019_archivage.pdf

The Indo-Atlantic interocean heat exchanges are tightly linked to global ocean circulation and climate. They are principally achieved by the Agulhas Rings (AR) which are investigated in this thesis by means of 24 years of daily satellite-altimetry maps and Argo floats profiles.By applying the TOEddies eddy identification and tracking algorithm, developped in this study, 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 eddy 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 which allows to estimate their in-route evolution. In particular, we show modification of an AR, transitioning from a surface to a subsurface intensified eddy while it subduct when entering the South Atlantic subtropical gyre. This transformation results in the creation of two Mode Water cores which concentrate most of the heat content of this AR.Finally, an estimate of AR geographical distribution was obtained from the numerous eddies detected in the Cape Basin and South Atlantic Ocean. It shows that AR generally subduct when they leave the Cape Basin. Moreover, for each eddy sufficiently sampled by Argo floats, we were able to estimate its heat content anomaly with respect of the environment. AR heat content anomalies result to be important all along their trajectories even if they release heat along their path. Combining both eulerian and lagrangian methods, we estimate the sub-surface heat transport achieved by their AR while they propagate in the South Atlantic. Les échanges de chaleur entre ...