In the western tropical Atlantic, upper ocean temperature tends to be homogeneous from the surface down to the so-called "isothermal layer depth" (ILD) and salinity is responsible for density stratification. Freshwater discharge from the world's largest river, the Amazon (with an averaged annual discharge of about 0.2 Sv), precipitation under the Intertropical Convergence Zone (ITCZ) and several oceanographic processes induce a strong halocline (and therefore pycnocline) in the top few meters, leading to a "mixed layer depth" (MLD) that is shallower than the ILD (