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: R13VPDB, R17VSMOW, R18VSMOW, 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.

The exclusive use of carbonate reference materials is a robust method for the standardization of clumped isotope measurements • Measurements using different acid temperatures, designs of preparation lines, and mass spectrometers are statistically indistinguishable • We propose new consensus values for a set of 7 carbonate reference materials and updated guidelines to report clumped isotope measurements

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Geology of the Sample Site Andros Island, the largest island on the Great Bahama Bank, sits atop more than six kilometers of nearly 100% carbonate rock. The 4442-meter-long Andros Number 1 well was drilled into north-central Andros Island by the Stafford and Bahamas Oil companies in 1947. The core is now housed by the Florida State Geological Survey in Tallahassee, FL. The core spans the Pleistocene through the Early Cretaceous according to approximate microfossil dating and correlation with the stratigraphy of Florida (Spencer, 1967). The core material was discussed by Illing (1954) and Spencer (1967) and petrographically and geochemically described by Goodell and Garman (1969; Fig. DR1). The foraminifera and bivalve fossils, occasional reefal debris, and common pelletal muds found in the core support the interpretation of marine deposition for the entire sedimentary sequence. Some faulting and uplift occurred within the Great Bahama Bank during the Early Cretaceous, however, it is likely that the burial history of all samples from the Andros core follows an essentially linear increasing depth and temperature trend (Elberli and Ginsburg 1987). While it is true that periods of erosion are observed in core sediments, their magnitude is likely minor and no tectonic uplifts are known to have occurred (Goodell and Garman, 1969; Elberli and Ginsburg, 1987). Today, deposits on the interior of the Great Bahama Bank are generally oolitic and coralgal sands in higher-energy areas that grade into pelletal muds (Illing 1954). Most of this modern material is aragonitic, but early diagenesis has resulted in no aragonite present below ~35 m depth (Goodell and Garman, 1969; Beach, 1993). All material studied from this core is 100% carbonate, but the mineralogy varies from calcite to dolomite. Offshore cores analyzed by Melim et al. (2002) indicate a shift from aragonite-dominated mud to mature microsparitic limestone and complete alteration by marine pore fluids within 100-150 m of sea level. Recrystallization of material at ~250 m depth indicates complete dolomitization and a degree of diagenetic stabilization relatively soon after deposition, consistent with diagenetic models (Beach 1993; Whitaker et al. 1994; Melim et al. 2001; Melim et al. 2002). Marine waters have been shown to flow consistently through the upper ~400 m of the Great Bahama Bank (from the center of the platform outward) and are likely agents of lithification as well as dolomitization (e.g. Whitaker et al. 1994). Sample Characterization Samples taken from the core's uppermost layers are entirely micritic dolomite mud with no visible grains. By 250m depth, dolomite is entirely recrystallized with microspar, which is the likely result of near-surface diagenesis and lithification as described above. Foraminifera, bivalve, and coral fragments are still visible within the entirely recrystallized micritic matrix. From ~450 m to 3500 m depth, limestone beds are interbedded with dolomites, with both commonly preserving pellet traces and fossil outlines. Specifically...