Assessing kinetic fractionation in brachiopod calcite using clumped isotopes

David Bajnai (1) , Jens Fiebig (1) , Adam Tomašových (2) , Sara Milner Garcia (3) , Claire Rollion-Bard (3) , Jacek Raddatz (1) , Niklas Löffler (1) , Cristina Primo-Ramos (4) , Uwe Brand (5)

1 Institut für Geowissenschaften [Frankfurt am Main]
2 Institute of Earth Sciences
3 IPGP - Institut de Physique du Globe de Paris
4 IAU - Institut für Atmosphäre und Umwelt [Frankfurt/Main]
5 Brock University [Canada]

Brachiopod shells are the most widely used geological archive for the reconstruction of the temperature and the oxygen isotope composition of Phanerozoic seawater. However, it is not conclusive whether brachiopods precipitate their shells in thermodynamic equilibrium. In this study, we investigated the potential impact of kinetic controls on the isotope composition of modern brachiopods by measuring the oxygen and clumped isotope compositions of their shells. Our results show that clumped and oxygen isotope compositions depart from thermodynamic equilibrium due to growth rate-induced kinetic effects. These departures are in line with incomplete hydration and hydroxylation of dissolved CO 2. These findings imply that the determination of taxon-specific growth rates alongside clumped and bulk oxygen isotope analyses is essential to ensure accurate estimates of past ocean temperatures and seawater oxygen isotope compositions from brachiopods.

Domains: Geochemistry; Climatology

David Bajnai, Jens Fiebig, Adam Tomašových, Sara Milner Garcia, Claire Rollion-Bard, et al.. Assessing kinetic fractionation in brachiopod calcite using clumped isotopes. Scientific Reports, 2018, 8, pp.533. ⟨10.1038/s41598-017-17353-7⟩. ⟨insu-02160318⟩