The sea surface salinity in the Tropical Atlantic between 10 degree S and 30 degree N -- seasonal and interannual variations (1977-1989)

The seasonal and interannual variations of the Sea Surface Salinity (SSS) are analysed in the Tropical Atlantic (15 degree S-30 degree N, 80 degree W-15 degree E) from observations collected by merchant ships between 1977 and 1989 and earlier by ORSTOM research vessels. The harmonic analysis of SSS shows a well defined seasonal cycle both within a 5 degree N-15 degree N zonal belt and west of 50 degree W at higher latitudes. In the eastern Atlantic between 10 and 20 degree N (along the shipping lanes West Africa-South Africa and West Africa-Brazil), SSS increased from 1977 to 1985, particularly near 10 degree N. SSS variability is mostly related to the river outflow (Amazon, Orinoco and Congo) west of 40 degree W and in southern Gulf of Guinea. In the eastern Atlantic, precipitation associated with the ITCZ largely control the SSS seasonal variations.