The barrier layer in the western Tropical Atlantic Ocean

In the tropical oceans, where the temperature is roughly homogenous in the upper layer, vertical variations of salinity may be responsible for signifi cant density stratifications. In this study on the western Tropical Atlanti c Ocean, it is shown that fresh surface waters of the Amazon River discharg e may induce a strong halocline in the 3-30 m depth range. This halocline i nduces a pycnocline that acts as a barrier for mixing between the surface a nd the subsurface waters. The fresh surface waters are generally associated with positive anomalies of the sea surface temperature. These positive ano malies cover a large part of the basin in boreal summer-fall, following the maximum Amazon River discharge, which may have a significant importance fo r the ocean-atmosphere exchanges.