Density measurements of IAPSO Standard Seawater by hydrostatic weighing

摘要

In metrological terms, salinity of seawater remains one of the most problematic quantity used in the frame of ocean science. The main reason is because, despite a clear definition of salinity, the realization of the unit is still linked to the use of artifact of natural origin characterized by measurements of conductivity. The latter seems to be the only quantity capable to guarantee the necessary accuracy at the moment. However, the concept of salinity, but not the definition, is linked to the quantity of substance contained in seawater, that is not pure water, and conductivity measurement can only partially cover the physico-chemical aspects characterizing the thermodynamic behavior of seawater. In these cases, the measurement of the density is more appropriate and, thanks to its recent progresses, it seems to be a promising way to guarantee the traceability of salinity measurement in seawater. This work is a contribution to the measurement of the density of IAPSO standard seawater, using the method of hydrostatic weighing. Despite this method is limited to work at atmospheric pressure, it is the best approach in term of accuracy. The measurement method is, mainly, analyzed from the metrological point of view, focusing on the traceability chain supporting the reliability of the obtained results.