Technical note: TEOS-10 Excel - implementation of the Thermodynamic Equation Of Seawater-2010 in Excel

This paper and associated software implement the Thermodynamic Equation Of Seawater - 2010 (TEOS-10) in Excel for an efficient estimation of Absolute Salinity (S-A), Conservative Temperature (Theta), and derived thermodynamic properties of seawater - potential density (sigma(Theta)), in situ density (rho S-A, Theta, p), and sound speed (c). Vertical profile template plots for these parameters are included as is an S-A-Theta diagram template, which includes plotting of the density field (computation of user-selected sigma(Theta) lines is included). Absolute Salinity can be directly measured with the aid of a densimeter (IOC, SCOR and IAPSO, 2010: p. 82), but in TEOS-10 its estimation relies on the interpolation of data from casts of seawater from the world ocean (IOC, SCOR and IAPSO, 2010), and the Excel workbook introduced here (TEOS-10 Excel, available at https://doi.org/10.5281/zenodo.4748829) includes a subset of the TEOS-10 look-up tables necessary for this estimation, namely the Absolute Salinity Anomaly [deltaSA_ref] and the Absolute Salinity Anomaly Ratio [SAAR_ref] look-up tables. As the user simply needs to paste new data into the spreadsheet to automatically compute the oceanographic parameters referred above, this tool may prove to be useful for all who are not comfortable using the full-featured TEOS-10 programming language environments (e.g. MATLAB, FORTRAN, C) but rather need a simpler way of computing fundamental properties of seawater (e.g. density, sound speed) while adhering to current standards. Returned values are the same (up to 15 decimal places; i.e. difference = 0.000000000000000) as the ones obtained with the MATLAB version of the GSW (Gibbs Sea Water) toolbox (McDougall and Barker, 2011) available at the PLOS-10 website (https://www.teos-10.org, last access: 13 April 2022). This paper describes the Excel workbook, its use, and the included VBA (Visual Basic for Applications) functions. Quality control against the GSW toolbox is also addressed, namely issues detected with the interpolated values returned by the toolbox when there are missing values in the reference look-up table. In these situations, the GSW toolbox replaces missing values with a level pressure horizontal interpolation of neighbour points, while it is clear from the testing results that vertical interpolation, which was then implemented in TEOS-10 Excel, returns a more robust solution.

Automated summary

This paper and associated software implement TEOS-10 in Excel, providing an efficient way to estimate Absolute Salinity, Conservative Temperature, and derived thermodynamic properties of seawater. The tool includes template plots for vertical profiles and an S-A-Theta diagram. It offers a simpler alternative to full-featured programming languages and adheres to current standards. The results obtained match those from the MATLAB version of the GSW toolbox.