Circulation de bord ouest de l'Atlantique Sud: analyse d'observations lagrangiennes et hydrologiques

The "World Ocean Circulation experiment" (WOCE) program in the 1990s has produced the equivalent of 300 years of subsurface floats trajectories within the Antarctic Intermediate Water (AAIW) at 800dbar in the South Atlantic ocean, and several hydrological transects. In order to compute the western boundary circulation, the flow is vertically extrapolated by referencing geostrophic hydrological profiles to float speeds. Several transects normal to the continental slope and another one parallel to it off the coast give transports of the water masses with a good transversal and longitudinal resolutions. Floats at 800dbar sampled the Intermediate Western Boundary Current (IWBC) particularly well, and enable one to analyse it from 28°S at the bifurcation of the subtropical gyre return current in the South Atlantic to 2°S. Meridional and transversal structures of the IWBC are described along with the mesoscale activity in the vicinity of the western boundary. We observe two regions (28°S-21°S and 15°S-5°S) where the 50km width current at 800m follows a relatively regular continental slope. In-between, the bathymetry is perturbed and high values of eddy kinetic energy are found. Southward counter currents are detected and their origins and fates are determined thanks to the lagrangian measurements. Local perturbations of the flow in relation to the bathymetry are analysed using the floats, such as those related to capes and then entries/exits of the boundary current.