A Unified Clumped Isotope Thermometer Calibration (0.5–1,100°C) Using Carbonate‐Based Standardization

Abstract

The potential for carbonate clumped isotope thermometry to independently constrain both the formation temperature of carbonate minerals and fluid oxygen isotope composition allows insight into long‐standing questions in the Earth sciences, but remaining discrepancies between calibration schemes hamper interpretation of temperature measurements. To address discrepancies between calibrations, we designed and analyzed a sample suite (41 total samples) with broad applicability across the geosciences, with an exceptionally wide range of formation temperatures, precipitation methods, and mineralogies. We see no statistically significant offset between sample types, although the comparison of calcite and dolomite remains inconclusive. When data are reduced identically, the regression defined by this study is nearly identical to that defined by four previous calibration studies that used carbonate‐based standardization; we combine these data to present a composite carbonate‐standardized regression equation. Agreement across a wide range of temperature and sample types demonstrates a unified, broadly applicable clumped isotope thermometer calibration.

InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards

“…In addition, a reanalysis of samples from five previous calibrations by Anderson et al. (2021) using carbonate standardization revealed no significant differences in temperature dependence of Δ 47 between the different sample sets. This, solved a long standing debate about variations in slope among calibrations…”

“…These studies yielded statistically indistinguishable slopes and intercepts despite the use of independent sample sets and in the case of Peral et al (2018), a different analytical system. In addition, a reanalysis of samples from five previous calibrations by Anderson et al (2021) using carbonate standardization revealed no significant differences in temperature dependence of Δ 47 between the different sample sets. This, solved a long standing debate about variations in slope among calibrations A possible limitation of carbonate standardization is that available carbonates have a smaller range in δ 47 and, perhaps more importantly, a smaller range in Δ 47 values than what is achievable with heated and equilibrated gases.…”

“…Achieving the best possible reproducibility and accuracy is especially important when reconstructing small temperature changes for the reconstruction of climate change and/or the study of high temperature processes where the sensitivity of the clumped isotope thermometer is low. We emphasize that the improvements in interlaboratory comparability that can be achieved with carbonate standardization, coupled with the reductions in the uncertainties of the temperature calibrations (e.g., Anderson et al, 2021), is decreasing the uncertainties in temperature reconstructions to levels comparable or better than other temperature proxies.…”

Marine temperatures underestimated for past greenhouse climate

“…Clumped isotope compositions for the analysed calcites and aragonites range from 0.580 to 0.609 (I-CDES 53 ; excluding separated diagenetic calcites from the apical area and spar cements), which correspond to temperatures ranging from 20.0 to 29.5 °C based on the Anderson et al 54 equation. Anderson et al 54 found that inorganic, and most biogenic, carbonates (including aragonite) show the same temperature dependence; thus, their equation can confidently be applied to reconstruct palaeotemperatures for aragonites and calcites. Reconstructed aragonite and calcite Δ 47 palaeotemperatures from the same belemnite are consistently within error of each other, and are in agreement with other biotic aragonites from the sample (Fig.…”

Full Propagation of Analytical Uncertainties in Δ47 Measurements

“…This, of course, is not a problem in itself, but the InterCarb results unambiguously demonstrate that these standardization uncertainties are both necessary and sufficient to explain the inter‐laboratory scatter observed in this large data set ( N = 5,329). Going one step further, it could be argued that the ongoing persistence of inter‐laboratory discrepancies in Δ 47 calibrations (Petersen et al., 2019) is due, at least in part, to largely ignored standardization errors (Anderson et al., 2021). Whatever the case, it seems likely that future comparisons between results obtained in different laboratories would greatly benefit from more accurate error estimates.…”