Tracking AAIW Properties, Transformations and Paths in the South Atlantic from Argo Floats Data and a Global Ocean Model

The Atlantic Meridional Overturning Circulation is closed by cold fresh Antarctic Intermediate Water (AAIW) that is modified to warm, salty varieties by air-sea fluxes and interior mixing in the Atlantic and southwestern Indian Ocean. AAIW is a prominent water mass that lies above the deep water and spreads below the subtropical thermocline in the Southern Hemisphere. It is characterized by a salinity minimum at depth and it is the most extensive of all the intermediate water masses. In the Atlantic, the AAIW core can be traced across the equator and into the North Atlantic as far as 20°N

Here we propose an updated and more detailed description of the AAIW distribution, circulation and transformation in the entire South Atlantic Ocean, via an extensive analysis of Argo profiling float data. In particular, we use the offline mass-preserving Ariane Lagrangian diagnostic tool (http://www.univ-brest.fr/lpo/ariane) to calculate AAIW pathways in a 3D velocity field that blends absolute velocity information at 1000 m derived from the ANDRO dataset (http://wwz.ifremer.fr/lpo/Produits/ANDRO), geostrophic velocity profiles obtained over the vertical by the thermal wind equation, and a wind-induced Ekman surface circulation.

Particular emphasis will be given to interocean and meridional exchanges, and identification of areas where major water mass transformations occur. The sensitivity of the results to various constraints applied on the vertical velocity field at the AAIW level will also be presented.