Mutually consistent thermodynamic potentials for fluid water, ice and seawater: a new standard for oceanography

Abstract

Abstract.A new seawater standard for oceanographic and engineering applications has been developed that consists of three independent thermodynamic potential functions, derived from extensive distinct sets of very accurate experimental data. The results have been formulated as Releases of the International Association for the Properties of Water and Steam, IAPWS (1996, 2006 and are expected to be adopted internationally by other organizations in subsequent years. In order to successfully perform computations such as phase equilibria from combinations of these potential functions, mutual compatibility and consistency of these independent mathematical functions must be ensured. In this article, a brief review of their separate development and ranges of validity is given. We analyse background details on the conditions specified at their reference states, the triple point and the standard ocean state, to ensure the mutual consistency of the different formulations, and the necessity and possibility of numerically evaluating metastable states of liquid water. Computed from this formulation in quadruple precision (128-bit floating point numbers), tables of numerical reference values are provided as anchor points for the consistent incorporation of additional potential functions in the future, and as unambiguous benchmarks to be used in the determination of numerical uncertainty estimates of doubleprecision implementations on different platforms that may be customized for special purposes.

A global algorithm for estimating Absolute Salinity

“…The Practical Salinity S P and the density ρ lab of each seawater sample are measured in the laboratory at 25 • C and at atmospheric pressure (assumed to be p = 0 dbar, or an absolute pressure P of exactly 101 325 Pa) using a vibrating tube densimeter (Kremling, 1971). The Absolute Salinity of the seawater sample is estimated from the laboratory density measurement and the TEOS-10 equation of state (Feistel, 2008), IAPWS (2008), Feistel et al (2008), IOC et al (2010)), essentially by solving the equation ρ lab = ρ(S A , 25 • C, 0 dbar) for S A . In detail, the laboratory data were used to determine the density difference δρ = ρ lab − ρ (S R , 25 • C, 0 dbar) and this density difference was used with the partial derivative of density with respect to Absolute Salinity at 25 • C and 0 dbar, namely…”

Thermodynamic properties of sea air

“…liquid and gaseous) water, and a Gibbs function g Ih (T , P ) for ice (IAPWS, 2009a(IAPWS, , 2009bFeistel et al, 2008b). Mathematical details of those correlation functions are given in the appendix.…”

“…On this 92 R. Feistel et al: Thermodynamic properties of sea air basis, together with IAPWS, the SCOR 2 /IAPSO 3 Working Group 127 (WG127) on Thermodynamics and Equation of State of Seawater in cooperation with UNESCO-IOC 4 developed a proposal for a new international standard for oceanography, TEOS-10 5 (IOC, 2010), which has replaced the currently valid 1980 International Equation of State of Seawater (EOS-80, Fofonoff and Millard, 1983) after almost three decades without formal updates to account for progress in this field (Feistel, 2008a, b;Feistel et al, 2008b;IAPWS, 2008a;IOC, 2009).…”

“…Quantitative information is scarce about fundamental quantities such as entropy or enthalpy of humid air, or the latent heat of seawater. In this paper we propose to replace this inhomogeneous collection by consistent, thermodynamically rigorous formulas derived from a minimum set of comprehensive and most accurate thermodynamic potentials of fluid water, ice, seawater (Feistel, 2008a, b;Feistel et al, 2008b) and humid air which provide all thermodynamic equilibrium properties of those substances as well as their combinations and mutual phase equilibria over a wide range of conditions. When an official standard formulation for humid air becomes available which covers wider ranges of conditions than the present CIPM-2007 formula (Picard et al, 2008), the building-block concept proposed here will permit its easy incorporation into the suggested system of equations derived by thermodynamic rules.…”

Thermophysical property anomalies of Baltic seawater

“…Any change of this constant is compensated by the conditions, Eq. (4.12), imposed on the freely adjustable coefficients of seawater at the specified reference state (Feistel et al, 2008a). Using the FREZCHEM model, the absolute salinity,…”