The clumped isotope composition of carbonates is a valuable paleothermometer with diverse applications in geoscience including paleoaltimetry, paleoclimatology, biomineralization, diagenesis and human evolution. Results are usually expressed as Delta47 (referred as "cap 47"), which is the deviation of the ratio of isotopes of CO2 with molecular weight of 47 to those with a weight of 44 from the ratio expected if they were randomly distributed. Significant discrepancies in Delta47-temperature calibrations among laboratories add considerable uncertainty to these studies, and limit the applicability of Delta47 paleothermometry to temperature anomalies greater than about ± 5ºC. The proposed work will help identify the source(s) of interlaboratory Delta47 discrepancies by constraining the triple oxygen isotope compositions of all materials used in its measurement. These results will make progress toward a Dletal47 paleothermometer limited only by analytical precision that is able to resolve the much smaller temperature variations characteristic of many processes. It will also build the foundation for community inter-calibration efforts that will advance the work of the many disciplines currently applying Delta47 to societally relevant geological and environmental research questions. By building the foundation for community calibration efforts, it will strengthen existing domestic and international collaborations, as well as foster new ones, thereby helping to identify the most relevant and achievable future work.
The accuracy and precision of carbonate clumped isotope measurements improve significantly when interferences in mass spectrometer data associated with the abundance of 17O are corrected using parameters based on the global water pool. However, the new correction scheme incorrectly assumes that the abundance of 17O and 18O in the gases, waters and carbonates used to derive Delta47 follow a specific relationship in which 17O excess is zero. The proposed work will leverage existing CO2-water equilibration and abiogenic carbonate samples generated at multiple temperatures, as well as unique University of Washington analytical capabilities, to evaluate how 17O excess impacts Delta47. This diverse sample suite is representative of the isotopic compositions, precipitation methods and temperatures used by most clumped isotope laboratories, allowing the proposed work to provide important constraints on the magnitude of 17O excess variability in the many analytes used by the clumped isotope community. It will allow an evaluation of how 17O excess can be used to make the most accurate and precise Delta47 measurements when it is known in all analytes, as well as to develop - best practices - for the vast majority of institutions that cannot measure 17O excess directly. The latter will include suggestions both for re-evaluating previously published results, including Delta47-temperature calibrations, and for generating new data.
