The scientific relevance for measuring Sea Surface Salinity (SSS) is more and more recognized in the ocean and climate community. SSS plays an important role in the dynamics of the ocean circulation as salinity together with temperature controls the density of seawater and is a key tracer for the marine branch of the global hydrological cycle (more than 3/4 of the evaporation and precipitation occur above the ocean). Freshwater exchanges at the air-sea (precipitation and evaporation), land-sea (river runoff) and ice-sea (ice melt) interfaces lead to huge SSS variability and to large horizontal and vertical salinity gradients; locally this can result in thin, light and fresh surface layers isolated from deeper layers (e.g. barrier layers) and modify air-sea fluxes. In addition to these direct effects, SSS can also serve as a tracer of these various water masses characterized by contrasted chemical and biological properties so that a synoptic and permanent monitoring of SSS provides new insights into marine biology, bio-optics and biogeochemistry. It is also essential to understanding the ocean's interior water masses, knowing that they derive their underlying temperature and salinity properties during their most recent time at the surface. The project demonstrated the performance and scientific value of SMOS Sea Surface Salinity (SSS) products through a number of case studies on regions characterized by strong variability at various geographic and temporal scales.

• New SSS products allowed to gain insights into the advection pathways of the freshwater Amazon and Orinoco rivers plume along surface currents. For the first time, SMOS sampling capability thus enabled imaging the plume structure almost every 3 days with a spatial resolution of about 40 km.
• Over the western North Atlantic SMOS observations combined with in situ surface and profile measurements, satellite-derived surface currents, sea surface height (SSH), surface temperature (SST), and Chlorophyll (Chl) data, were used to reveal the evolution of the sea surface salinity (SSS) structure of the meandering Gulf Stream with an unprecedented space and time resolution.
• Analysis of the salinity structure of Tropical Instability Waves (TIWs) using SMOS data has shown that the phase speed of the westward propagation 17-day SSS signal at the equator varies from one year to another, being much faster during La Niña conditions.
• Spatial variability of SMOS salinity associated with rain rate has been analysed and preliminary results indicate that more than 70% of this variability is real, other effects (roughness, atmosphere) being relatively small.
• By computing anomalies with respect to 4-year monthly means, SMOS SSS systematic biases can be removed, the team demonstrated that SMOS has the potential of measuring SSS at monthly and 100x100km2 scale with a precision better than 0.2.
• This should be deepened in the future using in situ measurements made at less than 50cm from the sea surface.