biostudies-literatureUnknown8(1)Bajnai DBrachiopod 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 CO₂. These findings imply that the determination of taxon-specific growth rates alongside clumpScientific reports533https://www.ebi.ac.uk/biostudies/studies/S-EPMC5765054biostudies-literatureAssessing kinetic fractionation in brachiopod calcite using clumped isotopes.PMC5765054Milner Garcia STomasovych ABrand UBajnai DFiebig JLoffler NPrimo-Ramos CRaddatz JRollion-Bard CfalseAssessing kinetic fractionation in brachiopod calcite using clumped isotopes.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 CO₂. These findings imply that the determination of taxon-specific growth rates alongside clump2018-01-01T00:00:00Z2018 Jan2026-05-05T21:54:16.094Z2019-03-27T00:14:52ZS-EPMC57650542932325310.1038/s41598-017-17353-7