We enter now in a new era of global Sea Surface Salinity (SSS) observing systems from Space with therecent successful launches of the ESA Soil Moisture and Ocean Salinity (SMOS) mission and the NASA Aquarius/SAC-D mission. These new satellite SSS observing systems are as well complemented by an increased number of devices deployed in situ. Finally, ocean color products can be used as well for tracking salinity via semi-conservative tracers such as dissolved organic matter absorption coefficient at 443 nm(acdm), light attenuation at 490 nm and chlorophyll concentration. With these new methods, we are now in an excellent position to revisit the SSS observed in the warm seas of the tropical Atlantic with multi-yeartime series of excellent remote sensing and concurrent in situ observations. The seasonal cycles in the spatial extent of low surface salinity waters of the major river plumes and freshwater pools of the tropical Atlantic oceans as the Amazon and Orinoco rivers can thus be analyzed in a new and original manner. In particular, the correlation between SSS and bio-optical properties measured from Space in the plume waters can now beestablished and analyzed over large spatial scales. In the frame of this PhD work, different major research topics were studied. First the correlations between sea surface salinity and absorption coefficient of colored detrital matter at 443 nm in the Amazon-Orinoco plume over 2010-2013 are studied. Then the conservative mixing relationship is robustely established based on two different approaches, a regional one over the whole Amazon plume and a local one. Once the SSS/acdm relationship established, it is used to retrieve a SSSproduct from 1998 to 2013 based on Ocean Color data. Finally, we attempt to explore the conservative mixing using a lagrangian approach.