TY - JOUR

T1 - Discrete water column measurements of CO2 fugacity and pH(T) in seawater

T2 - A comparison of direct measurements and thermodynamic calculations

AU - McElligott, S.

AU - Byrne, R. H.

AU - Lee, K.

AU - Wanninkhof, R.

AU - Millero, F. J.

AU - Feely, R. A.

N1 - Funding Information:
This work was supported by the Ocean-Atmosphere Carbon Exchange Study (OACES) and the Climate and Global Change Program of the National Oceanic and Atmospheric Administration (NA46GP00071), as well as, by the National Science Foundation (OCE-9019629). The authors would like to thank Dr. David W. Chipman and an anonymous reviewer for their critical reviews of this manuscript.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

PY - 1998/2

Y1 - 1998/2

N2 - The NOAA Eq. Pac. CO2 system data set (≃ 2500 water samples) has been evaluated to assess the internal consistency of measurements and calculations involving CO2 fugacity and pH(T). This assessment represents the first large scale field comparison of pH(T) and f(CO2) data. Comparisons of direct discrete CO2 fugacity (f(CO2)) measurements with CO2 fugacity calculated from total inorganic carbon (C(T)), total alkalinity (A(T)) and spectrophotometric pH (pH(T) = -log[H+](T)) indicate that a variety of improvements are needed in the parameter measurements and thermodynamic relationships used to relate f(CO2), C(T), A(T) and pH(T) in seawater. CO2 fugacity calculated from C(T) and pH(T) or A(T) and pH(T) agree with direct measurements to no better than 1%. Comparisons of measured fugacity, f(CO2) (measured), and CO2 fugacity calculated from C(T) and pH(T), f(CO2) (C(T), pH(T)), indicate that the precision of f(CO2) calculations is good relative to direct measurements. In contrast, due to the extreme sensitivity of f(CO2) and [H+](T) calculations to relatively small errors in both C(T) and A(T), CO2 fugacity, as well as [H+](T), calculated from C(T) and A(T) are very imprecise and render comparisons with direct measurements of little use. Consequently, precise calculations of f(CO2) require the use of direct pH(T) measurements.

AB - The NOAA Eq. Pac. CO2 system data set (≃ 2500 water samples) has been evaluated to assess the internal consistency of measurements and calculations involving CO2 fugacity and pH(T). This assessment represents the first large scale field comparison of pH(T) and f(CO2) data. Comparisons of direct discrete CO2 fugacity (f(CO2)) measurements with CO2 fugacity calculated from total inorganic carbon (C(T)), total alkalinity (A(T)) and spectrophotometric pH (pH(T) = -log[H+](T)) indicate that a variety of improvements are needed in the parameter measurements and thermodynamic relationships used to relate f(CO2), C(T), A(T) and pH(T) in seawater. CO2 fugacity calculated from C(T) and pH(T) or A(T) and pH(T) agree with direct measurements to no better than 1%. Comparisons of measured fugacity, f(CO2) (measured), and CO2 fugacity calculated from C(T) and pH(T), f(CO2) (C(T), pH(T)), indicate that the precision of f(CO2) calculations is good relative to direct measurements. In contrast, due to the extreme sensitivity of f(CO2) and [H+](T) calculations to relatively small errors in both C(T) and A(T), CO2 fugacity, as well as [H+](T), calculated from C(T) and A(T) are very imprecise and render comparisons with direct measurements of little use. Consequently, precise calculations of f(CO2) require the use of direct pH(T) measurements.

KW - Carbon dioxide

KW - Fugacity

KW - Measurements

KW - Seawater

KW - Spectrophotometric pH

KW - Thermodynamic calculations

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U2 - 10.1016/S0304-4203(97)00080-7

DO - 10.1016/S0304-4203(97)00080-7

M3 - Article

AN - SCOPUS:0031924080

VL - 60

SP - 63

EP - 73

JO - Marine Chemistry

JF - Marine Chemistry

SN - 0304-4203

IS - 1-2

ER -