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Ocean Science An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/os-2017-71
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Sep 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Ocean Science (OS).
The density–salinity relation of standard seawater
Hannes Schmidt1, Steffen Seitz1, Egon Hassel2, and Henning Wolf1 1Physikalisch-Technische Bundesanstalt, Braunschweig, 38116, Germany
2Lehrstuhl für Technische Thermodynamik, Universität Rostock, Rostock, 18051, Germany
Abstract. The determination of salinity by means of electrical conductivity relies on a constant salt composition in the North Atlantic Ocean, as standard seawater, which is required for salinometer calibration, is produced therefrom. In order to verify the long-term constant composition of standard seawater, it was proposed to perform density measurements on standard seawater, as the seawater density is sensitive to all salt components. Thus, density measurements can detect any change in the composition of seawater. A conversion of the density values to salinity can be performed by means of a density–salinity relation. To use such a relation with a target uncertainty in salinity comparable to that in salinity obtained from conductivity measurements, a density measurement at an uncertainty level of 2 ppm is mandatory. In this article, a new density–salinity relation is presented based on such accurate density measurements. The underlying substitution measurement method is described, density corrections for uniform isotopic and chemical compositions are reported, and the density–salinity relation is presented. The comparison of densities calculated using the new relation with those calculated using the present reference equation of state TEOS-10 suggests that the density accuracy of TEOS-10 and that of some of its underlying density measurements are overestimated. The new density–salinity relation may be used to verify the constant composition of standard seawater by means of routine density measurements.

Citation: Schmidt, H., Seitz, S., Hassel, E., and Wolf, H.: The density–salinity relation of standard seawater, Ocean Sci. Discuss., https://doi.org/10.5194/os-2017-71, in review, 2017.
Hannes Schmidt et al.
Hannes Schmidt et al.
Hannes Schmidt et al.

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Short summary
A density–salinity relation for standard seawater was developed based on highly accurate density measurements. The relation makes it possible to determine salinity by density measurement at a level of accuracy that is comparable to that achieved by conductivity measurement. The relation may be used to verify the constant composition of standard seawater by means of routine density measurements.
A density–salinity relation for standard seawater was developed based on highly accurate density...
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