Limnological applications of the Thermodynamic Equation of Seawater 2010 (TEOS-10)

The new Thermodynamic Equation of Seawater 2010 (TEOS-10) provides a highly accurate, thermodynamically consistent, and complete representation of all thermodynamic properties of seawater over a wide range in temperature and salinity. These properties include density, sound speed, heat capacity, enthalpy, chemical potential, and many others. Here we provide simple procedures by which limnological studies can take advantage of TEOS-10. These require replacing the TEOS-10 salinity argument, seawater Absolute Salinity S-A, with a limnological salinity S-a. In typical natural waters where anion concentrations are dominated by HCO3- or Cl-, S-a can be approximated by the solution salinity S-a(soln), obtained by summing the concentrations of different dissolved constituents in a complete chemical analysis after multiplying by their molar masses. Slightly better results can be obtained, especially at very low salinities where silicic acid Si(OH)(4) is an important constituent, by using a density salinity S-a(dens) carefully defined by dividing the solution salinity into an ionic and a nonionic part and changing the weighting factors for each in the summation. In cases where the dominant anion is HCO3-, which covers the majority of inland waters, measurements of electrical conductivity can be used to estimate the ionic salinity, which will be approximate to 60% greater than the Absolute Salinity of seawater of the same conductivity. The resulting estimates of that part of density in excess of pure water density at the same temperature will be accurate within +/-10%.