Effects of Improved 17O Correction on Interlaboratory Agreement in Clumped Isotope Calibrations, Estimates of Mineral‐Specific Offsets, and Temperature Dependence of Acid Digestion Fractionation. (22nd July 2019)

• Record Type: Journal Article
• Authors: Petersen, S. V.; Defliese, W. F.; Saenger, C.; Daëron, M.; Huntington, K. W.; John, C. M.; Kelson, J. R.; Bernasconi, S. M.; Colman, A. S.; Kluge, T.; Olack, G. A.; Schauer, A. J.; Bajnai, D.; Bonifacie, M.; Breitenbach, S. F. M.; Fiebig, J.; Fernandez, A. B.; Henkes, G. A.; Hodell, D.; Katz, A.; Kele, S.; Lohmann, K. C.; Passey, B. H.; Peral, M. Y.; Petrizzo, D. A.; Rosenheim, B. E.; Tripati, A.; Venturelli, R.; Young, E. D.; Winkelstern, I. Z.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 20:Number 7(2019)
• Page Start: 3495
• Page End: 3519
• Publication Date: 2019-07-22
• Subjects: clumped isotopes -- stable isotopes -- calibration -- standardization; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2018GC008127
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: 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: R 13 VPDB, 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, recorder of burial history or past diagenetic conditions). Here we reprocess 14 published clumped isotope calibration studies using updated 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 study makes 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. Key Points: Updates to 17 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