Ocean salinity measurements are important because surface salinity and temperature control the density and stability of the surface water. Thus, ocean mixing (of heat and gases) and water-mass formation processes are intimately related to variations of surface salinity. Ocean modelling and analysis of water mass mixing should be enabled by new knowledge of surface-density fields derived from surface salinity measurements. The importance of the ocean in the global hydrological cycle also cannot be overstated. Some ocean models show that sufficient surface freshening results in slowing down the meridional overturning circulation, thereby affecting the oceanic transport of heat.