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A Kinetic Pressure Effect on Calcite Dissolution in Seawater

Dong, Sijia and Subhas, Adam V. and Rollins, Nick E. and Naviaux, John D. and Adkins, Jess F. and Berelson, William M. (2018) A Kinetic Pressure Effect on Calcite Dissolution in Seawater. Geochimica et Cosmochimica Acta, 238 . pp. 411-423. ISSN 0016-7037. http://resolver.caltech.edu/CaltechAUTHORS:20180720-100933524

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Abstract

This study provides laboratory data of calcite dissolution rate as a function of seawater undersaturation state (1-Ω) under variable pressure. ^(13)C-labeled calcite was dissolved in unlabeled seawater and the evolving δ^(13)C composition of the fluid was monitored over time to evaluate the dissolution rate. Results show that dissolution rates are enhanced by a factor of 2-4 at 700 dbar compared to dissolution at the same Ω under ambient pressure (10 dbar). This dissolution rate enhancement under pressure applies over an Ω range of 0.65 to 1 between 10 dbar and 700 dbar. Above 700 dbar (up to 2500 dbar), dissolution rates become independent of pressure. The observed enhancement is well beyond the uncertainty associated with the thermodynamic properties of calcite under pressure (partial molar volume ΔV), and thus should be interpreted as a kinetic pressure effect on calcite dissolution. Dissolution at ambient pressure and higher pressures yield non-linear dissolution kinetics, the pressure effect does not significantly change the reaction order n in Rate = k(1-Ω^)n, which is shown to vary from 3.1±0.3 to 3.8±0.5 from 10 dbar to 700 dbar over Ω = 0.65 to 0.9. Furthermore, two different dissolution mechanisms are indicated by a discontinuity in the rate-undersaturation relationship, and seen at both ambient and higher pressures. The discontinuity, Ω_(critical) = 0.87±0.05 and 0.90±0.03 at 10 dbar and 1050 dbar respectively, are similar within error. The reaction order, n, at Ω > 0.9 is 0.47±0.27 and 0.46±0.15 at 10 dbar and 700 dbar respectively. This Ω_(critical) is considered to be the threshold between step retreat dissolution and defect-assisted dissolution. The kinetic enhancement of dissolution rate at higher pressures is related to a decrease in the interfacial energy barrier at dissolution sites. The impact of pressure on the calcite dissolution kinetics implies that sinking particles would dissolve at shallower depth than previously thought.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.gca.2018.07.015DOIArticle
ORCID:
AuthorORCID
Subhas, Adam V.0000-0002-7688-6624
Additional Information:© 2018 Elsevier. Received 16 January 2018, Accepted 9 July 2018, Available online 20 July 2018. This work was supported by NSF Ocean Acidification grants (numbers OCE1220600 and OCE1220302), USC Dornsife Doctoral Fellowship and Elizabeth and Jerol Sonosky Fellowship for Earth and Ocean Sciences. The authors would like to thank Jun Shao for helping with Fig. 1 in this paper using Ocean Data View, and Aaron Celestian for his help with XRD. We acknowledge the work by USC machine shop machinists (Don Wiggins and colleagues) who built our pressure vessel and undergraduate student Laura Morine for her help running alkalinities. We also thank Dr. Alfonso Mucci, Dr. Bernard Boudreau, and two anonymous reviewers for their valuable and constructive comments on the original manuscript draft.
Funders:
Funding AgencyGrant Number
NSFOCE-1220600
NSFOCE-1220302
University of Southern CaliforniaUNSPECIFIED
Record Number:CaltechAUTHORS:20180720-100933524
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180720-100933524
Official Citation:Sijia Dong, Adam V. Subhas, Nick E. Rollins, John D. Naviaux, Jess F. Adkins, William M. Berelson, A kinetic pressure effect on calcite dissolution in seawater, Geochimica et Cosmochimica Acta, Volume 238, 2018, Pages 411-423, ISSN 0016-7037, https://doi.org/10.1016/j.gca.2018.07.015. (http://www.sciencedirect.com/science/article/pii/S0016703718303910)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88053
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:23 Jul 2018 14:49
Last Modified:13 Aug 2018 17:26

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