AUTHOR=Sade Ziv , Hegyi Shahar , Halevy Itay 

TITLE=Equilibration Times of Dissolved Inorganic Carbon During pH Transitions

JOURNAL=Frontiers in Earth Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.792858

DOI=10.3389/feart.2021.792858

ISSN=2296-6463

ABSTRACT=<p>Equilibration times of dissolved inorganic carbon (DIC) depend on conversion reactions between CO<sub>2</sub>(aq) and the dissociation products of carbonic acid [<italic>S</italic> = (H<sub>2</sub>CO<sub>3</sub>) + (HCO<sub>3</sub><sup>−</sup>) + (CO<sub>3</sub><sup>2−</sup>)]. Here, we develop analytical equations and a numerical model to calculate chemical equilibration times of DIC during pH transitions in buffered and unbuffered solutions. We approximate the equilibration degree of the DIC reservoir by the smaller of the CO<sub>2</sub>(aq) and <italic>S</italic> pools at the new pH, since the smaller pool is always farther from equilibrium during the chemical evolution. Both the amount of DIC converted and the rate of conversion differ between a pH increase and decrease, leading to distinct equilibration times for these general cases. Alkalinity perturbations in unbuffered solutions initially drive pH overshoots (increase or decrease) relative to the new equilibrium pH. The increased rates of DIC conversion associated with the pH overshoot yield shorter equilibration times compared to buffered solutions. Salinity has opposing effects on buffered and unbuffered solutions, decreasing and increasing equilibration times, respectively.</p>