Temperature dependence of CO2 fugacity in seawater

Catherine Goyet, Frank J. Millero, Alain Poisson, Deborah K. Shafer

Research output: Contribution to journalArticlepeer-review

41 Scopus citations

Abstract

Ideally, the correction of the measured CO2 fugacity (fCO2) at temperature Tm to fCO2 at the in-situ temperature Tin should be made by using at least 2 known parameters (pH-AT, CT-AT,...) and the reliable constants for carbonic acid. In practice however, a measured CO2 property pair is not always available. When fCO2 is measured alone, one must make an estimate of the effect of temperature on seawater fCO2 from the accurate knowledge of seawater salinity and temperature and the approximate knowledge of the carbonate parameters. In this paper we present an empirical relationship that can be used to estimate the effect of temperature on fCO2. The equation is of the form: f{hook}CO2[t] - f{hook}CO2[20]=A + Bt + Ct2 + Dt3 + Et4 where fCO2[t] and fCO2[20] represent fCO2 at temperatures t°C and 20°C, respectively; the parameters A, B, etc. are functions of the ratio X = CT/AT: A = (a0 + a2X +a4X2) (1 + a1X+ a3X2) B = (b0 + b2X +b4X2) (1 + b1X+ b3X2) C = (c0 + c2X +c4X2) (1 + c1X+ c3X2) D = (d0 + d2X +d4X2) (1 + d1X+ d3X2) E = e0 + e1X + e2X2ln(X) + e3exp(X) + e4/ln(X) where the parameters ai, bi, etc. are functions of salinity. The 25-parameter equation is fitted by the values of fCO2 calculated using the constants of Goyet and Poisson (1989), when X varies from 0.8 to 1.0, t varies from -1dgC to 40°C, and S varies from 30 to 40. For Tm - Tin within ± 10°C, direct measurements of fCO2 as a function of the temperature (from -I to 30°C verify this equation within less than ±5 μatm.

Original languageEnglish (US)
Pages (from-to)205-219
Number of pages15
JournalMarine Chemistry
Volume44
Issue number2-4
DOIs
StatePublished - Dec 1993

ASJC Scopus subject areas

  • Oceanography
  • Chemistry(all)
  • Environmental Chemistry
  • Water Science and Technology

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