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The dissolution behavior of biogenic calcites in seawater and a possible role for magnesium and organic carbon

Subhas, Adam V. and Rollins, Nick E. and Berelson, William M. and Erez, Jonathan and Ziveri, Patrizia and Langer, Gerald and Adkins, Jess F. (2018) The dissolution behavior of biogenic calcites in seawater and a possible role for magnesium and organic carbon. Marine Chemistry, 205 . pp. 100-112. ISSN 0304-4203.

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We present the dissolution kinetics of mixed planktic foraminifera, the benthic foraminifera Amphistegina, the coccolithophore Emiliania huxleyi, and the soft coral Rhythismia fulvum in seawater. Dissolution rates were measured across a large range of saturation states (Ω = 0.99–0.2) by dissolving ^(13)C-labeled calcites in natural seawater undersaturated with respect to calcite. ^(13)C-label was incorporated into biogenic calcite by culturing marine calcifiers in 13C-labeled natural seawater. Net dissolution rates were calculated as the slope of seawater δ^(13)C versus time in a closed seawater-calcite system. All calcites show distinct, nonlinear, dependencies on seawater saturation state when normalized by mass or by specific surface area. For example, coccolith calcite dissolves at a similar rate to inorganic calcite near equilibrium when normalized by surface area, but dissolves much more slowly far from equilibrium. Mass loss from foraminiferal tests is correlated with a decrease in Mg/Ca of the solid, indicating that Mg-rich phases are preferentially leached out at even mild undersaturations. Dissolution also appears to strongly affect test B/Ca. Finally, we provide an interpretation of surface area-normalized biogenic calcite dissolution rates as a function of their Mg and organic carbon content. Near-equilibrium dissolution rates of all calcites measured here show a strong, nonlinear dependence on Mg content. Far-from-equilibrium dissolution rates decrease strongly as a function of organic carbon content. These results help to build a framework for understanding the underlying mechanisms of rate differences between biogenic calcites, and bear important implications for the dissolution of high-Mg calcites in view of ocean acidification.

Item Type:Article
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URLURL TypeDescription
Subhas, Adam V.0000-0002-7688-6624
Adkins, Jess F.0000-0002-3174-5190
Additional Information:© 2018 Elsevier B.V. Received 13 February 2018, Revised 25 July 2018, Accepted 2 August 2018, Available online 12 August 2018.
Subject Keywords:Chemical oceanography; Dissolution kinetics; Ocean acidification
Record Number:CaltechAUTHORS:20180813-154925391
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Official Citation:Adam V. Subhas, Nick E. Rollins, William M. Berelson, Jonathan Erez, Patrizia Ziveri, Gerald Langer, Jess F. Adkins, The dissolution behavior of biogenic calcites in seawater and a possible role for magnesium and organic carbon, Marine Chemistry, Volume 205, 2018, Pages 100-112, ISSN 0304-4203, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88790
Deposited By: Tony Diaz
Deposited On:13 Aug 2018 23:28
Last Modified:24 Oct 2019 17:01

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