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Thermodynamic Properties of Seawater

Since the adoption of the 1978 Practical Salinity Scale (PSS-78) and the 1980 International Equation of State of Seawater (EOS-80) about three decades ago, only slow scientific progress was made on understanding the thermophysical properties of IAPSO Standard Seawater, handling regional seawater composition anomalies, or characterizing the thermodynamic properties of seawater in contact with ice or humid air. Meanwhile, the subsequent introduction of new international standards such as the temperature scale ITS-90 or the pure-water description IAPWS-95 had not been incorporated into official oceanographic standards.


First meeting of SCOR/IAPSO WG127 in May 2006 at the IOW

First meeting of SCOR/IAPSO WG127 in May 2006 at the IOW. From left to right: Chen-Tung Arthur Chen (Taiwan), Frank J. Millero (USA), Brian A. King (UK), Rainer Feistel (IOW), Daniel G. Wright (Canada, deceased July 2010), Trevor J. McDougall (AUS), Giles M. Marion (USA)


Recognising the need for a revised international standard on seawater properties, the Scientific Committee on Oceanic Research (SCOR) and the International Association for the Physical Sciences of the Oceans (IAPSO) established Working Group 127. This SCOR/IAPSO Working Group soon started a close cooperation with the International Association for the Properties of Water and Steam (IAPWS). On the occasion of the IAPWS 2008 International Conference in Berlin, the Special Issue “Thermophysical Properties of Seawater” of Ocean Science was established as a peer-reviewed and open-access resource for the wide range of scientific results produced by the work of WG 127, as well as by the IAPWS Subcommittee on Seawater.

The new international seawater standard TEOS-10, the International Thermodynamic Equation of Seawater 2010, was endorsed by Unesco/IOC in Paris 2009. It is based on a Gibbs function for seawater, that was first developed at the IOW 20 years ago, in combination with a redefinition of salinity in g/kg, and thermodynamic potentials for ice and humid air. All formulas are expressed in the 1990 temperature scale ITS-90. Properties can be computed from source code developed by WG127, the Seawater-Ice-Air library (SIA) and the Gibbs-Seawater library (GSW). SIA directly exploits the primary standards formulated as IAPWS documents, it is more comprehensive but slower. GSW is designed for oceanographic application, the faster routines are fits to SIA data points over the range of "Neptunian" conditions. Documents, code and background papers are available from the web sites and, as well as from the Special Issue "Thermophysical Properties of Seawater" of Ocean Science.

For the first time since the first international oceanographic standard of 1902, TEOS-10 provides tools for the analysis of seawater composition anomalies, such as those in the Baltic See or in the deep Pacific. Details are found in the publications listed below.

Selected material regarding TEOS-10

Gibbs function of seawater Article IAPWS-08
Gibbs function of liquid water Article IAPWS-09
Gibbs function of ice Article IAPWS-06
Melting and sublimation curves
Article IAPWS-11
Helmholtz function of fluid water Article IAPWS-95
Helmholtz function of humid air Article IAPWS-10
Composition of seawater Article  
Seawater salinity saturation Article  
Gibbs function of Baltic seawater Article  
Baltic composition anomaly
Ocean composition anomaly Article  
TEOS-10 formulation Manual  
TEOS-10 SIA library Article Code
TEOS-10 GSW library Article Code
Seawater Research Need Text  
Refractive Index Research Need Text