• sea surface salinity;
  • SMOS;
  • freshwater fluxes;
  • Tropical Atlantic;
  • seasonal variability;
  • river runoff

[1] Observations from the SMOS satellite are used to reveal new aspects of Tropical Atlantic sea surface salinity (SSS) variability. Over an annual cycle, the variability is dominated by eastern and western basin SSS “poles,” with seasonal ranges up to 6.5 pss (practical salinity scale), that vary out of phase by 6 months and largely compensate each other. A much smaller SSS range (0.08 pss) is observed for the region as a whole. The dominant processes controlling SSS variability are investigated using GPCPv2.2 precipitation (P), OAFlux evaporation (E), and Dai and Trenberth river flow (R) data sets. For the western pole, SSS varies in phase with P and lags R by 1–2 months; a more complex relationship holds for the eastern pole. The synthesis of novel satellite SSS data with E, P, and R enables a new approach to determining variability in Tropical freshwater fluxes and its potential impacts on the Atlantic ocean circulation.