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Ocean Science An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Mar 2020

Submitted as: research article | 25 Mar 2020

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This preprint is currently under review for the journal OS.

Current estimates of K1* and K2* appear inconsistent with measured CO2 system parameters in cold oceanic regions

Olivier Sulpis1,2, Siv K. Lauvset3, and Mathilde Hagens4 Olivier Sulpis et al.
  • 1Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands
  • 2Department of Earth and Planetary Sciences, McGill University, Montreal, Canada
  • 3NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Bergen, Norway
  • 4Soil Chemistry and Chemical Soil Quality, Wageningen University and Research, Wageningen, the Netherlands

Abstract. Seawater absorption of anthropogenic atmospheric carbon dioxide (CO2) has led to a range of changes in carbonate chemistry, collectively referred to as ocean acidification. Stoichiometric dissociation constants used to convert measured carbonate system variables (pH, pCO2, dissolved inorganic carbon, total alkalinity) into globally comparable parameters are crucial for accurately quantifying these changes. The temperature and salinity coefficients of these constants have generally been experimentally derived under controlled laboratory conditions. Here, we use field measurements of carbonate system variables taken from the Global Ocean Data Analysis Project version 2 and the Surface Ocean CO2 Atlas databases to evaluate the temperature dependence of the carbonic acid stoichiometric dissociation constants. By applying a novel iterative procedure to a large dataset of 948 surface-water, quality-controlled samples where four carbonate system variables were independently measured, we show that the set of equations published by Lueker et al. (2000), currently preferred by the ocean acidification community, overestimates the stoichiometric dissociation constants at low temperatures, below ~ 8 °C. We apply these newly derived temperature coefficients to high-latitude Argo float and cruise data to quantify the effects on surface-water pCO2 and calcite saturation states. These findings highlight the critical implications of uncertainty in stoichiometric dissociation constants for future projections of ocean acidification in polar regions, and the need to improve knowledge of what causes the CO2 system inconsistencies in cold waters.

Olivier Sulpis et al.

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Olivier Sulpis et al.

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