TEOS-10
The Thermodynamic Equation of Seawater 2010
Historically, the different thermodynamic properties of seawater (including density, sound speed, and heat capacity) were independently specified with different correlation equations as a function of temperature, salinity, and pressure, based on different sets of laboratory measurements. However, thermodynamic theory can be used to show that these properties are all mathematically interrelated, and can all be defined by operations applied to a single state function.
For the highest precision in seawater properties, measurements of all thermodynamic properties have been combined into just such a state function (technically known as the Gibbs function), which, in turn, can be used to generate numerical estimates of the various properties in a thermodynamically consistent manner. By doing so, we can avoid “leaks” of energy in calculations that involve these properties.
Avoiding energy leaks in complex calculations is important, because it helps ensure that energy budgets can be properly determined for the earth/ocean/atmosphere system.
Once a particular property equation has been published in the scientific literature, others can use it. For most widespread use, this equation can be formulated into a standard. In seawater, densities were for many years calculated using the Equation of State 1980 (or EOS-80), as endorsed by various oceanographic organizations.
In 2010, the United Nations’ Intergovernmental Oceanographic Commission (IOC), along with SCOR and IAPSO, published and endorsed a standard for the Thermodynamic Equation of Seawater, known as TEOS-10. More information about TEOS-10 is available from www.teos-10.org.
In addition to providing a comprehensive basis for the thermodynamic properties of seawater, TEOS-10 also included a new definition for the salinity of seawater.
Known as Absolute Salinity, with units of grams of solute per kilogram of seawater, Absolute Salinity is now the official description of the salt content of seawater. This replaces the older “Practical Salinity’, based on a standard known as the Practical Salinity Scale (1978), in which salinities were represented by a unitless number.
The TEOS-10 Standard
Although the TEOS-10 standard is the best available description of the thermodynamic properties of seawater and of the composition of sea salt, as the frontiers of scientific and technical knowledge advance, eventually a new and better standard will appear. JCS promotes work in this area.