Presented at the 2014 Ocean Sciences MeetingThis study investigates causes for the formation and the variability of the Sea Surface Salinity maximum (SSS>36) centered near 18°S-124°W in the South Pacific Ocean over the 1990-2011 period at the seasonal timescale and above. We use two monthly gridded products of SSS based on in-situ measurements, high-resolution along-track Voluntary Observing Ships thermosalinograph data, new SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation. All products reveal a seasonal cycle of the location of the 36-isohaline barycentre of about ±400 km in longitude in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity. They also show a low frequency westward shift of the barycentre of 1400 km from the mid 1990's to early 2010's that could not be linked to the El Niño Southern Oscillation phenomena. In the model, the processes maintaining the 22-year equilibrium of the high salinity in the mixed layer are the surface forcing (~+0.73 pss yr-1), the horizontal salinity advection (~-0.36 pss yr-1) and processes occurring at the mixed layer base (~-0.35 pss yr-1).