Skip to main content
U.S. flag

An official website of the United States government

Most Earth-surface calcites precipitate out of isotopic equilibrium

February 14, 2019

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). Here, we constrain the equilibrium relations linking temperature, 18αcc/w, and clumped isotopes (Δ47) based on the composition of extremely slow-growing calcites from Devils Hole and Laghetto Basso (Corchia Cave). Equilibrium 18αcc/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 Δ47 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.

Publication Year 2019
Title Most Earth-surface calcites precipitate out of isotopic equilibrium
DOI 10.1038/s41467-019-08336-5
Authors Mathieu Daëron, Russell N Drysdale, Marion Peral, Damien Huyghe, Dominique Blamart, Tyler B. Coplen, Franck Lartaud, Giovanni Zanchetta
Publication Type Article
Publication Subtype Journal Article
Series Title Nature Communications
Index ID 70202191
Record Source USGS Publications Warehouse
USGS Organization WMA - Earth System Processes Division