Articles | Volume 8, issue 6
Ocean Sci., 8, 1123–1134, 2012

Special issue: Thermophysical properties of seawater

Ocean Sci., 8, 1123–1134, 2012
21 Dec 2012
21 Dec 2012

A global algorithm for estimating Absolute Salinity

T. J. McDougall1, D. R. Jackett2, F. J. Millero3, R. Pawlowicz4, and P. M. Barker1 T. J. McDougall et al.
  • 1School of Mathematics and Statistics, University of New South Wales, Sydney, Australia
  • 2Deceased, formerly of CSIRO, Hobart, Australia
  • 3Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL33149, USA
  • 4Dept. of Earth and Ocean Sciences, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada

Abstract. The International Thermodynamic Equation of Seawater – 2010 has defined the thermodynamic properties of seawater in terms of a new salinity variable, Absolute Salinity, which takes into account the spatial variation of the composition of seawater. Absolute Salinity more accurately reflects the effects of the dissolved material in seawater on the thermodynamic properties (particularly density) than does Practical Salinity.

When a seawater sample has standard composition (i.e. the ratios of the constituents of sea salt are the same as those of surface water of the North Atlantic), Practical Salinity can be used to accurately evaluate the thermodynamic properties of seawater. When seawater is not of standard composition, Practical Salinity alone is not sufficient and the Absolute Salinity Anomaly needs to be estimated; this anomaly is as large as 0.025 g kg−1 in the northernmost North Pacific. Here we provide an algorithm for estimating Absolute Salinity Anomaly for any location (x, y, p) in the world ocean.

To develop this algorithm, we used the Absolute Salinity Anomaly that is found by comparing the density calculated from Practical Salinity to the density measured in the laboratory. These estimates of Absolute Salinity Anomaly however are limited to the number of available observations (namely 811). In order to provide a practical method that can be used at any location in the world ocean, we take advantage of approximate relationships between Absolute Salinity Anomaly and silicate concentrations (which are available globally).