The absolute salinity of seawater and its measurands

Salinity is an essential quantity to calculate many of the physical properties of oceans, but it is also a quantity hard to define considering the complexity of this material 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 the 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 varies in time and space and its determination is still a challenge. Most salinity calculations are based on conductivity measurements. This publication reviews other techniques which are used or could be used to assess the absolute salinity of seawater and questions the measurand of these techniques and the possibility to redefine the concept of salinity from physical properties.