Comment on “The Effects of Secular Calcium and Magnesium Concentration Changes on the Thermodynamics of Seawater Acid/Base Chemistry: Implications for Eocene and Cretaceous Ocean Carbon Chemistry and Buffering” by Hain et al. (2015)

• Published in: Global biogeochemical cycles Vol. 32; no. 5; pp. 895 - 897
• Main Authors: Zeebe, Richard E., Tyrrell, Toby
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-05-2018
• Subjects: Buffers (chemistry); Calcium; Calcium carbonate; Calcium ions; Carbon dioxide; carbonic acid constants; Chemical equilibrium; CO2 system; Constants; Cretaceous; Eocene; Interaction models; Ionic interactions; Magnesium; Organic chemistry; reconstructions; Seawater; Seawater composition
• ISSN: 0886-6236; 1944-9224
• DOI: 10.1002/2017GB005786

Hain et al. (2015, https://doi.org/10.1002/2014GB004986, hereafter H15) calculated effects of changing [Ca2+] and [Mg2+] on the equilibrium constants of the CO2‐CaCO3 system in seawater based on a Pitzer ionic interaction model. We show here that critical results presented in H15 are fundamentally wrong. We therefore do not recommend using H15's stoichiometric equilibrium constants to correct for past changes in major‐ion seawater composition.
Key Points
We show here that critical results presented in H15 are fundamentally wrong
We do not recommend using H15's stoichiometric equilibrium constants to correct for past changes in major ion seawater composition