Jamie Kaaren Lucarelli , Hannah Carroll, Ben Elliott, Tyler B Coplen, Robert Eagle , Aradhna Tripati

Rationale: Carbonate clumped isotope geochemistry has primarily focused on mass spectrometric determination of m/z 47 CO2 for geothermometry, but theoretical calculations and recent experiments indicate paired analysis of the m/z 47 (13C18O16O) and m/z 48 (12C18O18O) isotopologues (referred to as Δ47 and Δ48) can be used to study non-equilibrium isotope fractionations and refine temperature estimates. We utilize a multi-year and multi-instrument dataset to constrain Δ47 and Δ48 values for 27 samples, including standards and Devils Hole cave calcite, and study equilibrium Δ47-Δ48, Δ47-temperature, and Δ48-temperature relationships.
Methods: A total of 5,465 Δ47 and 3,400 Δ48 measurements of carbonates, and 183 Δ47 and 195 Δ48 measurements of gas standards from 2015-2021 from multiple mass spectrometers were used. We compare results to previously published findings.
Results: We report Δ47 and Δ48 values for 27 carbonates. We provide further experimental constraints on the equilibrium relationship between Δ47 and Δ48. We report Δ47 and Δ48 relationships with temperature using a combination of theory and experimental regression-form acid digestion fractionation factors, Δ*63-47 and Δ*64-48.
Conclusions: This large dataset provides Δ48 values of carbonate standards for use in carbonate standard-based standardization. A robust Δ47-Δ48 equilibrium regression was determined with data presented here and from previously published datasets. Regressions for Δ47 and Δ48 relationships with temperature are also presented.