Feng, Xiaolei, Steiner, Zvi and T. Redfern, Simon A. (2021) Fluorine incorporation into calcite, aragonite and vaterite CaCO3: Computational chemistry insights and geochemistry implications. Geochimica et Cosmochimica Acta, 308 . pp. 384-392. DOI 10.1016/j.gca.2021.05.029.

Preview	Text Feng etal.pdf - Accepted Version Available under License Creative Commons: Attribution-Noncommercial-No Derivative Works 4.0. Download (1MB) | Preview
Preview	Text Feng Supplementary.pdf - Supplemental Material Available under License Creative Commons: Attribution-Noncommercial-No Derivative Works 4.0. Download (183kB) | Preview
	Text Feng_GCA.pdf - Published Version Restricted to Registered users only Download (629kB) | Contact

Abstract

The abundant occurrence of calcium carbonate minerals in marine sediments and their high fluorine content suggests that fluorine is a good candidate for reconstructing paleoceanographic parameters. However, the potential of fluorine as a paleoproxy had hardly been explored, and fundamental insights into the behaviour of fluorine in biogenic carbonates and marine sediments is required. A first-principles modelling approach is used here to analyse the incorporation mechanisms of fluorine into crystalline calcium carbonates. We compute F incorporation into the CaCO3 lattice via a number of mechanisms, but concentrate on comparison of the energetics of the two easiest substitution mechanisms: replacing one oxygen atom within the carbonate group to form a (CO2F)- group as against a substitution involving replacement of the CO3 group by two fluorine ions to form a CaF2 defect. These incorporation mechanisms are fundamentally different from that of iodine into calcium carbonates, where a carbon atom is replaced. Our simulations suggest that the substitution of by is the most favoured and that fluorine is preferentially incorporated into the three naturally-occurring polymorphs of calcium carbonate in the order vaterite aragonite calcite. These results explain the previously-reported preponderance of fluorine in aragonite corals, and lend support to the use of F/Ca as a proxy for ocean pCO2.

Actions (login required)

View Item