期刊
MARINE CHEMISTRY
卷 205, 期 -, 页码 100-112出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.marchem.2018.08.001
关键词
Chemical oceanography; Dissolution kinetics; Ocean acidification
资金
- NSF GRFP
- Resnick Sustainability Institute
- NSF [OCE1220600, OCE1220302]
- CALMED project [CTM 2016?79,547-R]
- Generalitat de Catalunya (MERS) [2017 SGR 1588]
- ICTA-UAB excellence program [MDM-2015-0552]
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 (Omega = 0.99-0.2) by dissolving C-13-labeled calcites in natural seawater undersaturated with respect to calcite. C-13-label was incorporated into biogenic calcite by culturing marine calcifiers in C-13-labeled natural seawater. Net dissolution rates were calculated as the slope of seawater delta C-13 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.
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