Clumped isotopes in carbonates: state of the art and open questions 

Since its establishment almost 20 years ago, carbonate clumped isotope thermometry (Δ47, Δ48) has grown to the most widely applied branch of the rapidly evolving field of clumped isotope geochemistry. An increasing number of laboratories worldwide is implementing this technique and applying it to solve a broad range of Earth science questions. The introduction of carbonate-based standardisation (Bernasconi et al. 2021), together with recent efforts to improve temperature calibrations (e.g. Anderson et al. 2021), has solved inter-laboratory differences and greatly improved the confidence in temperature reconstructions based on Δ47. Discrepancies in absolute temperatures using different calibrations are now on the order of 1-2°C only. The next frontier in carbonate clumped isotopes is Δ48 which is even more analytically challenging than Δ47 but has the potential to solve long standing questions of equilibrium/disequilibrium precipitation of carbonates and better understand processes of biomineralization. An important remaining field that requires further research is related to the preservation of the original clumped isotope temperatures in deep time samples and the kinetics of C-O bond reordering. In this contribution, we will review the state-of-the-art analytical methods and calibrations and discuss open challenges in interpreting clumped isotope signatures of biogenic and inorganic carbonates with bond reordering models.Bernasconi et al. (2021) InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards. Geochemistry, Geophysics, Geosystems, 22(5),e2020GC009588..Anderson et al. (2021) A unified clumped isotope thermometer calibration (0.5–1100°C) using carbonate‐based standardization. Geophysical Research Letters, 48, e2020GL092069.