Keywords :
Chemistry (all); Biochemistry, Genetics and Molecular Biology (all); Physics and Astronomy (all); General Physics and Astronomy; General Biochemistry, Genetics and Molecular Biology; General Chemistry
Abstract :
[en] In the open ocean, calcium carbonates are mainly found in two mineral forms. Calcite, the least soluble, is widespread at the seafloor, while aragonite, the more soluble, is rarely preserved in marine sediments. Despite its greater solubility, research has shown that aragonite, whose contribution to global pelagic calcification could be at par with that of calcite, is able to reach the deep-ocean. If large quantities of aragonite settle and dissolve at the seafloor, this represents a large source of alkalinity that buffers the deep ocean and favours the preservation of less soluble calcite, acting as a deep-sea, carbonate version of galvanization. Here, we investigate the role of aragonite dissolution on the early diagenesis of calcite-rich sediments using a novel 3D, micrometric-scale reactive-transport model combined with 3D, X-ray tomography structures of natural aragonite and calcite shells. Results highlight the important role of diffusive transport in benthic calcium carbonate dissolution, in agreement with recent work. We show that, locally, aragonite fluxes to the seafloor could be sufficient to suppress calcite dissolution in the top layer of the seabed, possibly causing calcite recrystallization. As aragonite producers are particularly vulnerable to ocean acidification, the proposed galvanizing effect of aragonite could be weakened in the future, and calcite dissolution at the sediment-water interface will have to cover a greater share of CO2 neutralization.
Funding text :
We thank Dr. Rosie Oakes at the Met Office and Dr. Osamu Sasaki at the Tohoku University Museum for providing CT scans of pteropods and foraminifera. We thank Julien Sulpis for his assistance in processing three-dimensional geometry files. O.S. and J.J.M. were supported by the Dutch Ministry of Education via the Netherlands Earth System Science Centre (NESSC). The research work of P.A., and M. Wolthers is part of the Industrial Partnership Program i32 Computational Sciences for Energy Research that is carried out under an agreement between Shell and the Netherlands Organization for Scientific Research (NWO). M. Wolthers has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. [819588]). G.M. is a Research Associate with the Belgian Fund for Scientific Research F.R.S.-FNRS. Financial support for the work of G.M. was provided by the Belgian Fund for Scientific Research—F.R.S.-FNRS (project SERENATA, grant CDR J.0123.19).
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