CaltechAUTHORS
  A Caltech Library Service

Temperature Dependence of Calcite Dissolution Kinetics in Seawater

Naviaux, John D. and Subhas, Adam V. and Rollins, Nick E. and Dong, Sijia and Berelson, William M. and Adkins, Jess F. (2019) Temperature Dependence of Calcite Dissolution Kinetics in Seawater. Geochimica et Cosmochimica Acta, 246 . pp. 363-384. ISSN 0016-7037. http://resolver.caltech.edu/CaltechAUTHORS:20181205-100011581

[img] PDF - Accepted Version
See Usage Policy.

1984Kb
[img] MS Word (Supplementary data 1) - Supplemental Material
See Usage Policy.

348Kb

Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20181205-100011581

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 = Ca^(2+)[CO_3^(2-)/Ksp'< 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 (Ω_(crit_). 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 calculate a similar activation energy to other studies far from equilibrium (25±2 kJ/mol), the exponential rate law could not be used to mechanistically explain our near equilibrium results. We turn to an alternative framework, derived from crystal nucleation theory, and find that our results are consistent with calcite dissolution kinetics in seawater being set by the retreat of pre-existing edges/steps from Ω=1-0.9, defect-assisted etch pit formation from Ω=0.9-0.75, and finally homogenous etch pit formation from Ω=0.75-0. The Ω_(crit) s for each mechanism are shifted significantly closer to equilibrium than they occur in dilute solutions, such that ocean acidification may cause marine carbonates to enter faster dissolution regimes more readily than would be expected from previous studies. We use the observed temperature dependence for each dissolution mechanism to calculate step kinetic coefficients (β, cm/s), densities of active nucleation sites (n_s, sites/m^2), and step edge free energies (α, mJ/m^2). Homogenous dissolution is well explained within the surface nucleation framework, but defect-assisted dissolution is not. Dissolution is initiated via step-propagation at all temperatures, but the defect-assisted mechanism is skipped over at 5°C, potentially due to a lack of nucleation sites. The surface nucleation framework enhances our understanding of calcite dissolution in seawater, but our results suggest that a complete theory will also need to incorporate the role of solution/surface speciation and complexation.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.gca.2018.11.037DOIArticle
ORCID:
AuthorORCID
Subhas, Adam V.0000-0002-7688-6624
Additional Information:© 2018 Published by Elsevier Ltd. Received 1 August 2018, Revised 26 November 2018, Accepted 27 November 2018, Available online 5 December 2018. We would like to thank the anonymous journal reviewers as well as Oleg Pokrovsky and Henry Teng for the insightful comments and suggestions they gave that helped to improve this manuscript. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 1745301, as well as NSF grant Numbers OCE1220302, OCE1559004 and 1559215. John Naviaux and Adam Subhas would also like to thank the Resnick Sustainability Institute at Caltech for fellowship support.
Group:Resnick Sustainability Institute
Funders:
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1745301
NSFOCE-1220302
NSFOCE-1559004
NSFOCE-1559215
Resnick Sustainability InstituteUNSPECIFIED
Record Number:CaltechAUTHORS:20181205-100011581
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20181205-100011581
Official Citation:John D. Naviaux, Adam V. Subhas, Nick E. Rollins, Sijia Dong, William M. Berelson, Jess F. Adkins, Temperature dependence of calcite dissolution kinetics in seawater, Geochimica et Cosmochimica Acta, Volume 246, 2019, Pages 363-384, ISSN 0016-7037, https://doi.org/10.1016/j.gca.2018.11.037. (http://www.sciencedirect.com/science/article/pii/S0016703718306677)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91499
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:05 Dec 2018 18:12
Last Modified:20 Dec 2018 16:09

Repository Staff Only: item control page