TY - JOUR

T1 - Temperature dependence of CO2 fugacity in seawater

AU - Goyet, Catherine

AU - Millero, Frank J.

AU - Poisson, Alain

AU - Shafer, Deborah K.

N1 - Funding Information:
We wish to thank Dr. E.T. Peltzer for providing the seawaterf rom the equatorial Pacific Ocean, M.E.Tracy and R.J. Adams for technical assistancew ith the measurements, Drs. C.S. Wong and R. Wanninkhoffo r review- ing and helpingu s to improvet he manuscript. We also wish to acknowledget he support of the Oceanographic section of the National Science Foundation grant OCE-91815137t, he Office of Naval Research,t he National Oceanographica nd Atmospheric Administration,t he Departmento f Energy grant DE-FGO2-ER60980,a nd the National Aeronautic and Space Administrationg rant NAGW-2431. This is contribution No. 8234 of the Woods Hole Oceanographic Institution.

PY - 1993/12

Y1 - 1993/12

N2 - 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.

AB - 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.

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U2 - 10.1016/0304-4203(93)90203-Z

DO - 10.1016/0304-4203(93)90203-Z

M3 - Article

AN - SCOPUS:0027801804

VL - 44

SP - 205

EP - 219

JO - Marine Chemistry

JF - Marine Chemistry

SN - 0304-4203

IS - 2-4

ER -