TEOS-10

TEOS-10 was developed by the [https://scor-int.org/ SCOR(Scientific Committee on Oceanic Research)]/IAPSO(International Association for the Physical Sciences of the Oceans) Working Group 127 {{cite journal |last1=Pawlowicz |first1=R. |display-authors=etal |date= 2012 |title=An historical perspective on the development of the Thermodynamic Equation of Seawater--2010. |url=https://os.copernicus.org/articles/8/161/2012/ |journal=Ocean Science |volume=8 |issue=2 |doi=10.5194/os-8-161-2012 |pages=161–174 |bibcode=2012OcSci...8..161P |s2cid=13239620 |access-date=12 May 2021|doi-access=free }} which was chaired by Trevor McDougall. It has been approved as the official description of the thermodynamic properties of seawater, humid air and ice in 2009 by the Intergovernmental Oceanographic Commission (IOC){{cite conference |last=IOC. Reports of governing and major subsidiary bodies |location=Paris |date=16–25 June 2009 |title=Twenty-fifth Session of the Assembly |chapter-url= http://www.teos-10.org/pubs/IOC-XXV-3_e.pdf |page=4 |chapter=2.5 |publisher=UNESCO}} and in 2011 by the International Union of Geodesy and Geophysics (IUGG).{{cite conference |last= XXV General Assembly of the International Union of Geodesy and Geophysics |location=Melbourne |date=27 June – 8 July 2011 |title=Minutes of the Council Meeting |url= http://www.iugg.org/assemblies/2011melbourne/2011%20GA%20Melbourne%20CR_PART%20I.pdf |pages=54, Resolution:4}}

TEOS-10 is based on thermodynamic potentials. Fluids like humid air and liquid water in TEOS-10 are therefore described by the Helmholtz energy F(m,T,V)=F(m,T,m/ρ) or the specific Helmholtz-energy f(T,ρ)=F(m,T,m/ρ)/m. The Helmholtz energy has a unique value across phase boundaries.{{cite journal|last1=Feistel|first1=Rainer|display-authors=etal|title=Thermodynamic properties sea air|date=2010|url=https://os.copernicus.org/articles/6/91/2010/os-6-91-2010.pdf|journal=Ocean Science|volume=6|issue=1|pages=91–141|doi=10.5194/os-6-91-2010|bibcode=2010OcSci...6...91F|access-date=2 June 2021 |doi-access=free }} For the calculation of the thermodynamic properties of seawater and ice, TEOS-10 uses the specific Gibbs potential g(T,P)=G/m, G=F+pV, because the pressure is a more easily measurable property than density in a geophysical context. Gibbs energies are multivalued around phase boundaries and need to be defined for each phase separately.

The thermodynamic potential functions are determined by a set of adjustable parameters which are tuned to fit experimental data and theoretical laws of physics like the ideal gas equation. Since absolute energy and entropy cannot be directly measured, arbitrary reference states for liquid water, seawater and dry air in TEOS-10 are defined in a way that

• internal energy and entropy of liquid water at the solid-liquid-gas triple point are zero,
• entropy and enthalpy of seawater are zero at S_A (Absolute Salinity) = 35.16504 g/kg, T (Temperature) = 273.15 K, p (pressure) = 101325 Pa,
• entropy and enthalpy of dry air are zero at T (Temperature) = 273.15 K, p (pressure) = 101325 Pa.{{cite journal |last1=Feistel |first1=Rainer |title=Thermodynamic properties of seawater, ice and humid air: TEOS-10, before and beyond. |date= 2018 |url=https://os.copernicus.org/articles/14/471/2018/os-14-471-2018.pdf |journal=Ocean Science |volume=14 |issue=3 |pages=471–502 |doi=10.5194/os-14-471-2018 |bibcode=2018OcSci..14..471F |s2cid=56167674 |access-date=12 May 2021 |doi-access=free }}

File:DeltaSA final.jpg

TEOS-10 covers all thermodynamic properties of liquid water, seawater, ice, water vapour and humid air within their particular ranges of validity as well as their mutual equilibrium composites such as sea ice or cloudy (wet and icy) air.

Additionally, TEOS-10 covers derived properties, for example the potential temperature and Conservative Temperature, the buoyancy frequency, the planetary vorticity and the Montgomery and Cunningham geostrophic streamfunctions. A complete list of featured properties can be found in the [http://www.teos-10.org/pubs/TEOS-10_Manual.pdf TEOS-10 Manual].

The handling of salinity was one of the novelties in TEOS-10. It defines the relationship between Reference Salinity and Practical Salinity, Chlorinity or Absolute Salinity and accounts for the different chemical compositions by adding a regionally variable 𝛿SA (see Figure).{{cite journal|last1=Millero|first1=Frank J.|display-authors=etal|title=The composition of Standard Seawater and the definition of the Reference-Composition Salinity Scale |volume=55 | issue=1 |date=2008|url=https://os.copernicus.org/articles/6/91/2010/os-6-91-2010.pdf|journal=Deep Sea Research Part I: Oceanographic Research Papers|issn=0967-0637 |pages=50–72|doi=10.1016/j.dsr.2007.10.001|bibcode=2008DSRI...55...50M|access-date=2 June 2021}} TEOS-10 is valid for Vienna Standard Mean Ocean Water which accounts for different hydrogen- and oxygen-isotope compositions in water which affects the triple point and therefore phase transitions of water.

TEOS-10 includes the Gibbs Seawater (GSW) Oceanographic Toolbox which is available as open source software in MATLAB, Fortran, Python, C, C++, R, Julia and PHP. While TEOS-10 is generally expressed in basic SI-units, the GSW package uses input and output data in commonly used oceanographic units (such as g/kg for Absolute Salinity S_A and dbar for pressure p).{{cite book |last1=McDougall |first1=T.J. |last2= Barker |first2=P.M. |date=2011 |title=Getting started with TEOS-10 and the Gibbs Seawater (GSW) Oceanographic Toolbox|pages=28 |publisher=Trevor J. McDougall |department=SCOR/IAPSO WG127 |isbn=978-0-646-55621-5 |access-date=16 May 2021 |url=http://www.teos-10.org/pubs/gsw/v3_04/pdf/Getting_Started.pdf}}

In addition to the GSW Oceanographic Toolbox, the Seawater-Ice-Air (SIA) Library is available for Fortran and VBA (for the use in Excel), and covers the thermodynamic properties of seawater, ice and (moist) air. In contrast to the GSW Toolbox, the SIA-Library exclusively uses basic SI-units.{{cite book |last1=IOC, SCOR and IAPSO |date=2010 |title=The international thermodynamic equation of seawater – 2010: Calculation and use of thermodynamic properties|pages=171 |department= Intergovernmental Oceanographic Commission, Manuals and Guides No. 56 |publisher=UNESCO (English) |access-date=16 May 2021 |url=http://www.teos-10.org/pubs/TEOS-10_Manual.pdf}}

EOS-80 (Equation of State of Seawater -1980) uses Practical Salinity measured on the PSS-78 (Practical Salinity Scale of 1978) scale that itself is based on measurements of temperature, pressure and electrical conductivity. Thus, EOS-80 did not account for different chemical compositions of seawater.

EOS-80 consisted of separate equations for density, sound speed, freezing temperature and heat capacity but did not provide expressions for entropy or chemical potentials. {{cite web|last=McDougall|first=Trevor|title=The International Thermodynamic Equation of Seawater – 2010: Introductory lecture slides|url=http://www.teos-10.org/pubs/TEOS-10_slides_for_Oceanography.pdf|access-date=4 June 2021|publisher=SCOR/IAPSO Working group 127}} Therefore, it was not a complete and consistent description of the thermodynamic properties of seawater. Inconsistencies in EOS-80 appear for example in the heat content at high pressure, depending on which equation is used for the calculation. Furthermore, EOS-80 was not consistent with meteorological equations while TEOS-10 is valid for humid air as well as for seawater.

EOS-80 provided expressions for potential temperature, which removes the effect of pressure on temperature but not for Conservative Temperature,{{cite journal|last1=McDougall|first1=T. J.|title=Potential enthalpy: A conservative oceanic variable for evaluating heat content and heat fluxes|volume=33 | issue=5 |pages=945–963 |date=2003|url=https://os.copernicus.org/articles/6/91/2010/os-6-91-2010.pdf|journal=Journal of Physical Oceanography|doi=10.1175/1520-0485(2003)033<0945:PEACOV>2.0.CO;2|bibcode=2003JPO....33..945M|access-date=4 June 2021|doi-access=free}} which is a direct measure for potential enthalpy and therefore heat content.

In TEOS-10 the current standard for temperature scales, ITS-90 (International Temperature Scale of 1990) is used, while EOS-80 used the IPTS-68 (International Practical Temperature of 1968).{{cite journal |last1=Rusby |first1=R.L. |pages=1153–1161 |date=1991 |title= The conversion of thermal reference values to the ITS-90|journal=The Journal of Chemical Thermodynamics |volume=23 |number=12 |access-date=4 June 2021 |url=https://www.sciencedirect.com/science/article/pii/S002196140580148X| doi=10.1016/S0021-9614(05)80148-X|bibcode=1991JChTh..23.1153R |url-access=subscription }} In the SIA-Library of TEOS-10 implementations to convert outdated into current scales are included.

TEOS-10 was derived using absolute pressure P while EOS-80 used the pressure relative to the sea surface 𝑝_sea. They can be converted by: P/Pa = 101325 + 10000 ∙ 𝑝_sea/dbar (see Atmospheric Pressure).

• [http://www.teos-10.org/ TEOS-10 Website]
• [http://www.teos-10.org/pubs/gsw/html/gsw_contents.html The Gibbs-Seawater (GSW) Oceanographic Toolbox functions]
• [http://www.teos-10.org/pubs/TEOS-10_Primer.pdf TEOS-10 Primer]
• [http://www.teos-10.org/pubs/TEOS-10_Manual.pdf TEOS-10 Manual]

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Category:International standards

Category:Thermodynamics