Presented at the Global Ocean Salinity and the Water Cycle WorkshopSubtropical salinity maximum regions are particularly important because the salty subtropical underwater (STW) is formed by subduction of surface waters in these areas. In all oceans, the STW is transported equatorward from the formation region and are tightly related to the Subtropical-Tropical Cell. In the South Indian Ocean (SIO), the salinity maximum is further poleward (25S-38S) and eastward (60E-120E) compared to those in other oceans, and significantly impacts the circulation of the eastern basin. The STW forms a strong haline front with the fresh Indonesian Throughflow waters. This haline front overwhelms the temperature contribution to density gradients and establishes the eastward Eastern Gyral Current, an important upstream source for the Leeuwin Current. In the present work, we analyze the variability of the Sea Surface Salinity (SSS) maximum using multi-source datasets. These datasets include Aquarius, SMAP and SMOS satellite data, an Argo-based gridded product and the ECCO Ocean State Estimate v.4. The SIO salinity maximum pool is characterized by a strong oscillatory seasonal cycle of contraction and expansion. The pool reaches minimum area in October and maximum in April. Most of this seasonal oscillatory pattern occurs in the poleward side of the pool, with oceanic processes (advection and entrainment) controlling the contraction phase. From 2004 to 2014 a clear reduction in the pool area is identified in Argo data, mostly due to a freshening in the equatorward side of the pool. To get a better understanding of interannual to decadal variations in the pool area, ECCO outputs are presently being analyzed.