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Most Earth-surface calcites precipitate out of isotopic equilibrium.

ABSTRACT: Oxygen-isotope thermometry played a critical role in the rise of modern geochemistry and remains extensively used in (bio-)geoscience. Its theoretical foundations rest on the assumption that 18O/16O partitioning among water and carbonate minerals primarily reflects thermodynamic equilibrium. However, after decades of research, there is no consensus on the true equilibrium 18O/16O fractionation between calcite and water (18?cc/w). Here, we constrain the equilibrium relations linking temperature, 18?cc/w, and clumped isotopes (?47) based on the composition of extremely slow-growing calcites from Devils Hole and Laghetto Basso (Corchia Cave). Equilibrium 18?cc/w values are systematically ~1.5‰ greater than those in biogenic and synthetic calcite traditionally considered to approach oxygen-isotope equilibrium. We further demonstrate that subtle disequilibria also affect ?47 in biogenic calcite. These observations provide evidence that most Earth-surface calcites fail to achieve isotopic equilibrium, highlighting the need to improve our quantitative understanding of non-equilibrium isotope fractionation effects instead of relying on phenomenological calibrations.

SUBMITTER: Daeron M

PROVIDER: S-EPMC6347637 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Most Earth-surface calcites precipitate out of isotopic equilibrium.

Daëron M M Drysdale R N RN Peral M M Huyghe D D Blamart D D Coplen T B TB Lartaud F F Zanchetta G G

Nature communications 20190125 1

Oxygen-isotope thermometry played a critical role in the rise of modern geochemistry and remains extensively used in (bio-)geoscience. Its theoretical foundations rest on the assumption that 18O/16O partitioning among water and carbonate minerals primarily reflects thermodynamic equilibrium. However, after decades of research, there is no consensus on the true equilibrium 18O/16O fractionation between calcite and water (18αcc/w). ...[more]

PMID: 30683869

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Most Earth-surface calcites precipitate out of isotopic equilibrium.

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Most Earth-surface calcites precipitate out of isotopic equilibrium.

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