The absolute salinity of seawater, its real components and its measurands

Salinity is an essential quantity to calculate many of physical properties of oceans, but It is also a quantity hardly definable considering the complexity of the middle in its bio-geo-chemical composition and the imperfections of the existing measurement techniques. The TEOS-10 gives several definitions to the notion of absolute salinity, usable in function of the properties to study, but they are based on the concept of a constant elemental composition of seawater, so that, if its major inorganic components are well known, its real composition vary in time and space and its determination is still a challenge. Most of salinity calculations are based on conductivity measurements. This communication reviews other techniques which are used or could be used to assess the absolute salinity of seawater, and question about the mesurand of these techniques and the possibility to redefine the concept of salinity from physical properties.