Contribution of triple oxygen isotopes measurement by Cavity Ring Down spectroscopy and Clumped isotopes to the understanding of kinetics effect in cold water corals.
Authors: Pesnin Marie , Chaillot Justin , Clauzel Thibault , Rollion-Bard Claire , Nomade Sebastien , Kassi Samir , Lartaud Franck , Daëron Mathieu 
Published: March 2024

Kinetic isotopes effect (KIEs) describes a very common phenomenon related to change in chemical reaction rate due isotopic substitution. If in biological sciences, KIEs has received a lot of interest with the aim at understanding reaction mechanisms, their control on the isotopic composition of biogenic carbonate has long been overlooked. However, the initial assumption that isotopic fractionation primarily reflects a thermodynamic equilibrium process in the H2O-DIC-CaCO3 system is challenged by a growing number of observations. Not accounting for these disequilibrium effects leads to inaccurate estimates of carbonate growing temperature. In this scientific context, Triple oxygen isotopes systematic can help constraining kinetics isotopes fractionation associated with metabolic reactions implicated in biocarbonates formation. We thus took advantage from recent development in spectroscopic technique (VCOF-CRDS) to measured O17isotopic anomalies in CO2produced by carbonate acid reaction [1]. These samples were also analyzed for their &#948;13C, &#948;18O and &#916;47 composition using a more classical mass spectroscopy technic. In this contribution we investigated cold-water corals (CWC) known to display strong isotopic disequilibria. For this 1st application, we selected four modern CWC species for which calcification conditions (T, S, pH, &#948;18Owater, &#916;17Owater and &#948;13CDIC) are independently constrained. The measured isotopic signatures were compared to their respective expected values based on environmental constrains, assuming &#8220;pseudo-equilibrium&#8221; carbonate precipitation. In particular, corals &#916;17O signatures were compared to the newly established equilibrium for O17 fractionation between calcite-water based on slow growing carbonates from Laghetto Basso and Devils Hole, measured using the same VCOF-CRDS technic [2]. We finally compared our experimental data with theoretical predictions for KIEs on DIC isotopic composition [3]. Interestingly, the correlation slope among &#916;47 - &#916;17O disequilibrium differ from the previous one derived from dual clumped (&#916;47 - &#916;48) isotopic measurements of the same species [4]. This founding suggesting that other biological parameter(s) should be taken into account to resolve CWC isotopic disequilibria. [1] Chaillot. J., Dae&#776;ron. M., Casado, M., Landais. A., Pesnin. M., Clauzel. T., Kassi. S. (in prep) Triple oxygen analyses of carbon dioxide, water and carbonates using VCOF-CRDS.[2] Clauzel, T., Chaillot, J., Pesnin, M., Jautzy, J., Kessy, S., Dae&#776;ron, M. (in prep) Advancing triple oxygen isotope analysis of carbonate and water using V-shaped Cavity Optical Feedback Cavity Ring-Down Spectroscopy (VCOF-CRDS): Calibration and implications for paleoclimate reconstruction.[3] Guo. W. (2020). Kinetic clumped isotope fractionation in the DIC-H2O-CO2 system: Patterns, controls, and implications. Geochimica et Cosmochimica Acta, 268, 230-257. [4] Davies. A. J., Guo. W., Bernecker. M., Tagliavento. M., Raddatz. J., Gischler. E., Floter. S., Fiebig. J. (2022). Dual clumped isotope thermometry of coral carbonate. Geochimica et Cosmochimica Acta, 338, 66-78.