Reducing Uncertainties in Carbonate Clumped Isotope Analysis Through Consistent Carbonate‐Based Standardization

Abstract

About a decade after its introduction, the field of carbonate clumped isotope thermometry is rapidly expanding because of the large number of possible applications and its potential to solve long‐standing questions in Earth Sciences. Major factors limiting the application of this method are the very high analytical precision required for meaningful interpretations, the relatively complex sample preparation procedures, and the mass spectrometric corrections needed. In this paper we first briefly review the evolution of the analytical and standardization procedures and discuss the major remaining sources of uncertainty. We propose that the use of carbonate standards to project the results to the carbon dioxide equilibrium scale can improve interlaboratory data comparability and help to solve long‐standing discrepancies between laboratories and temperature calibrations. The use of carbonates reduces uncertainties related to gas preparation and cleaning procedures and ensures equal treatment of samples and standards. We present a set of carbonate standards of diverse composition, discuss how they can be used to correct for mass spectrometric biases, and demonstrate that their use significantly improves the comparability among four laboratories. We propose that the use of these standards or of a similar set of carbonate standards will improve the comparability of data across laboratories.

Analytical effects on clumped isotope thermometry: Comparison of a common sample set analyzed using multiple instruments, types of standards, and standardization windows

“…They are also much easier to transport and provide direct comparison across laboratories compared with equilibrated gases, which require a separate specialized vacuum line to prepare. As such, in step with other recent proposals, we recommend the frequent use of carbonate standards within each laboratory's standardization scheme, whether in conjunction with equilibrated gases or replacing them entirely.…”

“…A carbonate standard‐based method of standardization was also proposed that involves the use of in‐house carbonate standards of varying bulk isotopic composition and Δ 47 values to build the ARF. Carbonate standards can be used alone without the use of supplementary equilibrated gases or can be used as an additional correction (secondary transfer function, or STF) on top of the use of equilibrated gases. The carbonate standards approach has the benefit that it does not require the time‐consuming step of manufacturing equilibrated gases, and furthermore treats all standards identically to samples (which may or may not be the case with equilibrated gases, depending on lab group and procedure), but it still requires analyzing multiple standards during the run, reducing sample throughput.…”

Effects of different constants and standards on the reproducibility of carbonate clumped isotope (Δ47) measurements: Insights from a long‐term dataset

“…The Δ 47 thermometer has the potential to provide unique temperature constraints on geological samples, especially in settings where such information may be unobtainable with other geochemical tools. Since the initial proposal of this proxy, a number of different Δ 47 –T calibrations have been published, leading to reconstructed temperature discrepancies of up to 10–15°C based on the same Δ 47 value . Several hypotheses exist as to the origin of calibration differences, including different gas preparation procedures, different mass spectrometric corrections, and potentially different acid fractionation factors (e.g.…”

“…This problem is reflected in variations in the reported values of commonly used international standards, e.g. 0.340–0.404‰ for NBS‐19, 0.258–0.311‰ for ETH‐1, and 0.253–0.306‰ for ETH‐2 …”

Terrestrial microbialites provide constraints on the mesoproterozoic atmosphere

“…Samples of pristine carbonate laminae and secondary sparite were drilled at low speed using a Micromill to evaluate potential spatial variability in isotopic data. All data were collected prior to the establishment of current background and 17 O correction procedures (Bernasconi et al, 2018;Peterson et al, 2019), which can result in higher analytical uncertainties than present. This had the effect of limiting the sample size available for analysis.…”