Dual clumped isotopes in foraminiferal calcite reveal kinetic bias in some species

Abstract Clumped isotope (∆ 47 ) analyses of foraminifera provide a powerful means to reconstruct upper and bottom water temperatures, independent of seawater δ 18 O and elemental composition. We show statistically significant disequilibrium in the dual (∆ 47 -∆ 48 ) clumped isotope composition of some large benthic foraminifera, while other large benthic foraminifera plot within analytical uncertainty of ∆ 47 –∆ 48 equilibrium. This deviation suggests the influence of reaction kinetics, such as kinetic effects during CO 2 absorption or a combination of ion attachment/detachment effects at the solution-crystal interface and slight DIC disequilibrium. Measured core-top, planktic and deep-sea benthic foraminifera plot within the 95% confidence level of empirical ∆ 47 -∆ 48 equilibrium, although additional measurements are required to confidently exclude kinetic ∆ 47 -∆ 48 bias. Dual clumped isotope measurements of large benthic foraminifera from the Eocene of the Paris and Hampshire basins that conform with ∆ 47 -∆ 48 equilibrium (95% confidence level) further support existing evidence for surface ocean temperatures ~12–17 °C warmer than today.