Temperature dependence of calcite dissolution kinetics in seawater

Abstract

Knowledge of calcite dissolution kinetics in seawater is a critical component of our understanding of the changing global carbon budget. Towards this goal, we provide the first measurements of the temperature dependence of calcite dissolution kinetics in seawater. We measured the dissolution rates of 13 C-labeled calcite in seawater at 5, 12, 21, and 37°C across the full range of saturation states (0 < Ω = < 1). We show that the dissolution rate is non-linearly dependent on Ω and that the degree of non-linearity both increases with temperature, and changes abruptly at "critical" saturation states (Ωcrit). The traditional exponential rate law most often utilized in the oceanographic community, R=k(1-Ω) n , requires different fits to k and n depending upon the degree of undersaturation. Though we

An experimental study of gypsum dissolution coupled to CaCO3 precipitation and its application to carbon storage

“…where the precipitation rate constant kwas taken to be equal to 1.0 × 10 -7.06 as reported by Naviaux et al (2019) and values of kN and Γ were respectively set to either 1 or 2 mol/s and 2.0 × 10 10 in agreement with the values recommended by Pham et al (2011) for calcite nucleation. Note that Eqn.…”

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

“…Area‐specific dissolution rates of coccoliths and foraminifera (i.e., in units of mass per unit surface area per time) have generally been measured in well‐mixed conditions, where particles are stirred or shaken in a large volume of seawater. In these experiments, measured rates reflect the inherent reaction rate between carbonate and seawater, with no influence of diffusion and boundary layer dynamics (Sjoberg & Rickard, ; Subhas et al, ; Naviaux et al, ). In these experiments, coccoliths appear to dissolve more slowly than foraminifera whether normalized by mass, or by surface area (Honjo & Erez, ; Keir, ; Subhas et al, ).…”

Reduced CaCO3Flux to the Seafloor and Weaker Bottom Current Speeds Curtail Benthic CaCO3Dissolution Over the 21st Century

“…For each model, the CSD was computed for each year from 2006 to 2100 using seawater density, [ Ca 2 + ] SW , [ CO 3 2 ‐ ] SW , K sp * , and the equations of Boudreau, Middelburg, and Meysman (). Below the CSD , seawater is undersaturated with respect to calcite, and dissolution should, according to classical chemical kinetics theory, occur at a rate determined by the slowest step of the overall reaction (equation ; Morse & Arvidson, ; Naviaux et al, ). The slowest step or “kinetic barrier” controlling the rate of calcite dissolution at the seafloor is either the transport of molecular reactants and products across the diffusive boundary layer (DBL; Schlichting, ) at the sediment‐water interface (typically a few hundred micrometers to a few millimeters thick for deep‐sea conditions; Sulpis et al, ), or processes within the sediment such as molecular diffusion through the porewaters and reactions at mineral grain surfaces (Boudreau, ; Boudreau & Guinasso, ; Sulpis et al, ).…”

“…As the salinity of the deep ocean is nearly invariant and the seawater calcium concentration ([Ca 2+ ] SW ) is practically conservative (i.e., [Ca 2+ ] SW = f (S P )), the saturation state of the deep ocean with respect to calcite, Ω C , see equation (2) Riley and Tongudai (1967) and the calcite stoichiometric solubility constant (K sp the slowest step of the overall reaction (equation (1); Morse & Arvidson, 2002;Naviaux et al, 2019). The slowest step or "kinetic barrier" controlling the rate of calcite dissolution at the seafloor is either the transport of molecular reactants and products across the diffusive boundary layer (DBL; Schlichting, 1979) at the sediment-water interface (typically a few hundred micrometers to a few millimeters thick for deep-sea conditions; Sulpis et al, 2018), or processes within the sediment such as molecular diffusion through the porewaters and reactions at mineral grain surfaces (Boudreau, 2013;Boudreau & Guinasso, 1982;Sulpis et al, 2017).…”