Calcite dissolution kinetics at the sediment-water interface in natural seawater.

The absorption, or uptake, of anthropogenic CO2 by the oceans results in a decrease in pH and carbonate ionconcentration, [CO32−]; as a consequence, the saturation state of seawater with respect to CaCO3 minerals(calcite, aragonite) falls, leading to a shallowing of their saturation depths and triggering an increase in theirdissolution at the seafloor. Nearly one-third of the seabed is composed of CaCO3-rich sediments, and theirdissolution is the ultimate marine sink of anthropogenic CO2. Despite numerous past studies, much confusionand uncertainty still surround our understanding of the rates and kinetics of CaCO3 dissolution at the deepseafloor. Results from in situ studies disagree with laboratory studies, most of which have been carried out underconditions, e.g., mineral suspensions, that are not representative of processes at the seafloor. Herein, we reportmeasurements of the dissolution rate of calcite, formed into synthetic sediment disks by mixing various amountsof this mineral with montmorillonite. These disks were placed in a stirred-flow reactor and exposed to a range ofsaturation states and shear stress conditions to simulate conditions at the sediment-water interface