| Summary: | VII Encuentro de Oceanografía Física (EOF) - Expanding Ocean Frontiers Conference, VIII International Symposium on Marine Sciences, 6-8 July 2022, Las Palmas de Gran Canaria, España The opposite directions of the North and South Atlantic upper-thermocline western boundary currents, the Gulf Stream flowing north and the Brazil Current proceeding south, lead to very different behaviors of the Atlantic Meridional Overturning Circulation (AMOC) in the northern and southern basins. One consequence is that the only southern pathway for the returning AMOC is a zonal westward portal along the verge of the South Atlantic subtropical and tropical gyres, in what constitutes the South Atlantic GAteway (SAGA). A gravest empirical mode (GEM) analysis of historical GO-SHIP, NOAA and Argo data, when combined with altimetry data, shows substantial differences at central and intermediate levels (down to 1500-2000 m) between the subtropical and tropical gyres, with the intermediate waters that flow along the rim of both gyres diverting either south or north once they reach the western boundary. The GEM study is complemented with the analysis of water parcels arriving and departing from the SAGA array, calculated using the GLORYS12 reanalysis velocity fields and the OceanParcels tracking code. Specifically, we explore which waters arrive directly from the Southern Ocean through the SAGA and towards the equator along the western boundary and which waters recirculate, and how many times, within the tropical and subtropical gyres. The water-trajectory analysis confirms the validity of the GEMS-altimetry method to establish whether the zonal flow belongs to the subtropical- tropical gyres or it can be associated to the returning limb of the AMOC Peer reviewed
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