Correction on Interlaboratory Agreement in Clumped Isotope Calibrations, Estimates of Mineral‐Specific Offsets, and Temperature Dependence of Acid Digestion Fractionation

The clumped isotopic composition of carbonate‐derived CO2 (denoted Δ47) is a function of carbonate formation temperature and in natural samples can act as a recorder of paleoclimate, burial, or diagenetic conditions. The absolute abundance of heavy isotopes in the universal standards VPDB and VSMOW (defined by four parameters: RVPDB, R 17 VSMOW, R 18 VSMOW, and λ) impact calculated Δ47 values. Here, we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured T‐Δ47 relationship. Using the updated parameters, we reprocess 14 published calibration data sets measured in 11 different laboratories, representing many mineralogies, bulk compositions, sample types, reaction temperatures, and sample preparation and analysis methods. Exploiting this large composite data set (n = 1,253 sample replicates), we investigate the possibility for a “universal” clumped isotope calibration. We find that applying updated parameters improves the T‐Δ47 relationship (reduces residuals) within most labs and improves overall agreement but does not eliminate all interlaboratory differences. We reaffirm earlier findings that different mineralogies do not require different calibration equations and that cleaning procedures, method of pressure baseline correction, and mass spectrometer type do not affect interlaboratory agreement. We also present new estimates of the temperature dependence of the acid digestion fractionation for Δ47 (Δ*25‐X), based on combining reprocessed data from four studies, and new theoretical equilibrium values to be used in calculation of the empirical transfer function. Overall, we have ruled out a number of possible causes of interlaboratory disagreement in the T‐Δ47 relationship, but many more remain to be investigated. Plain Language Summary Measured stable and clumped isotope values are fundamentally tied to established compositions of international standard materials. When these standard compositions are updated, it impacts previously published isotope measurements such as those used to define the clumped isotope calibration relationship (the foundation for use of this isotopic proxy as a paleothermometer, ©2019. American Geophysical Union. All Rights Reserved. RESEARCH ARTICLE 10.1029/2018GC008127 Special Section: Clumped Isotope Geochemistry: From Theory to Applications Key Points: • Updates to O correction parameters and international standard compositions affect clumped isotopic compositions • Reprocessing published calibration data using new parameters and consistent methodology slightly improves interlaboratory agreement • There is no evidence (within error) for mineral‐specific offsets in calibration equation or temperature dependence of acid digestion fractionation Supporting Information: • Supporting Information S1 • Table S2 • Text S4 • Data Set S1 • Data Set S2 Correspondence to: S. V. Petersen, sierravp@umich.edu Citation: Petersen, S. V., Defliese, W. F., Saenger, C., Daëron, M., Huntington, K. W., John, C. M., et al (2019). Effects of improved O correction on interlaboratory agreement in clumped isotope calibrations, estimates of mineral‐specific offsets, and temperature dependence of acid digestion fractionation. Geochemistry, Geophysics, Geosystems, 20, 3495–3519. https://doi.org/10.1029/2018GC008127 Received 13 DEC 2018 Accepted 24 APR 2019 Accepted article online 31 MAY 2019 Published online 22 JUL 2019 PETERSEN ET AL. 3495 recorder of burial history or past diagenetic conditions). Here we reprocess 14 published clumped isotope calibration studies usingupdated international standard compositions and identical data processing procedures to see if these changes would eliminate previously observed interlaboratory discrepancies in clumped isotope calibration relationships. We find that this update tightens the clumped isotope calibration relationship within most laboratories and improves overall agreement between laboratories but does not eliminate all interlaboratory differences. We also propose “best practices” for data processing and dissemination going forward. This studymakes progress toward resolving discrepancies in clumped isotope calibration relationships between laboratories by eliminating a number of possible causes and moves the clumped isotope community closer toward our ultimate goal of applying this powerful new proxy routinely to exciting science questions.