Ocean Modeling Discussion

Trevor J. McDougall on behalf of SCOR/IAPSO WG127, on Ocober 20, 2010 wrote:
Replacement of the EOS-80 definition of Seawater properties with TEOS-10

SCOR/IAPSO Working Group 127 on the Thermodynamics and Equation of State of Seawater has recommended the adoption of a new thermodynamic description of the properties of seawater, called the International Thermodynamic Equation Of Seawater – 2010 (TEOS-10 for short). This thermodynamic description of seawater properties, together with the Gibbs function of ice, has been endorsed by SCOR and IAPSO and has been adopted by the Intergovernmental Oceanographic Commission (IOC) at its 25th Assembly in June 2009 to replace EOS-80 as the official description of seawater and ice properties in marine science. The TEOS-10 computer software, the TEOS-10 Manual and many other documents may now be obtained from http://www.TEOS-10.org.

A notable difference of TEOS-10 compared with EOS-80 is the adoption of Absolute Salinity to be used in scientific journals to describe the salinity of seawater and to be used as the salinity argument in the TEOS-10 algorithms that give the various thermodynamic properties of seawater. Note, however, that we strongly recommend that the salinity that is reported to national databases remain Practical Salinity as determined on the Practical Salinity Scale of 1978 (suitably updated to ITS-90 temperatures as described in the TEOS-10 Manual). The practice of storing one type of salinity in national databases (Practical Salinity), but using a different type of salinity in publications (Absolute Salinity), is exactly analogous to our present practice with temperature; in situ temperature is stored in databases (since it is the measured quantity), but the temperature variable that is used in publications is a calculated quantity, being either potential temperature or Conservative Temperature.

The more prominent advantages of TEOS-10 compared with EOS-80 are:

• The Gibbs function approach allows the calculation of internal energy, entropy, enthalpy, potential enthalpy and the chemical potentials of seawater as well as the freezing temperature, and the latent heats of freezing and of evaporation. These quantities were not available from EOS-80 but are essential for the accurate accounting of heat in the ocean and for the consistent and accurate treatment of air-sea and ice-sea heat fluxes.
• For the first time the influence of the spatially varying composition of seawater can be systematically taken into account through the use of Absolute Salinity. In the open ocean, this has a non-trivial effect on the horizontal density gradient, and thereby on the ocean velocities and heat transports calculated via the thermal wind relationship.
• The new salinity variable, Absolute Salinity, is measured in SI units (e.g. g/kg).
• The thermodynamic quantities available from TEOS-10 are totally consistent with each other, while this was not the case with EOS-80.

From the web site, the document What every oceanographer needs to know about TEOS-10 (the TEOS-Primer for short) is a concise summary of the salient theoretical concepts which underpin TEOS-10, while the document Getting started with the GSW Oceanographic Toolbox of TEOS-10 guides the user through the steps required to process and publish physical oceanographic data using TEOS-10. The differences associated with using Absolute Salinity and Conservative Temperature compared with Practical Salinity and potential temperature are illustrated in this second document.

The GSW Oceanographic Toolbox of TEOS-10 is modelled on the SeaWater Matlab library of functions based on EOS-80. Oceanographers are now encouraged to visit the TEOS-10 web site http://www.TEOS-10.org and to download the computer software.