### Abstract

The NOAA Eq. Pac. CO_{2} system data set (≃ 2500 water samples) has been evaluated to assess the internal consistency of measurements and calculations involving CO_{2} fugacity and pH(T). This assessment represents the first large scale field comparison of pH(T) and f(CO_{2}) data. Comparisons of direct discrete CO_{2} fugacity (f(CO_{2})) measurements with CO_{2} 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(CO_{2}), C(T), A(T) and pH(T) in seawater. CO_{2} 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(CO_{2}) (measured), and CO_{2} fugacity calculated from C(T) and pH(T), f(CO_{2}) (C(T), pH(T)), indicate that the precision of f(CO_{2}) calculations is good relative to direct measurements. In contrast, due to the extreme sensitivity of f(CO_{2}) and [H^{+}](T) calculations to relatively small errors in both C(T) and A(T), CO_{2} 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(CO_{2}) require the use of direct pH(T) measurements.

Original language | English (US) |
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Pages (from-to) | 63-73 |

Number of pages | 11 |

Journal | Marine Chemistry |

Volume | 60 |

Issue number | 1-2 |

DOIs | |

State | Published - Feb 1998 |

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### Keywords

- Carbon dioxide
- Fugacity
- Measurements
- Seawater
- Spectrophotometric pH
- Thermodynamic calculations

### ASJC Scopus subject areas

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

### Cite this

_{2}fugacity and pH(T) in seawater: A comparison of direct measurements and thermodynamic calculations.

*Marine Chemistry*,

*60*(1-2), 63-73. https://doi.org/10.1016/S0304-4203(97)00080-7