EAGER: Reducing uncertainty in clumped isotope thermometry by evaluating the effect of 17O excess

碳酸盐的块状同位素组成是一种有价值的古温度计，在地球科学中具有广泛的应用，包括古测高、古气候学、生物矿化、成岩作用和人类演化。结果通常表示为Delta47(称为“CAP 47”)，它是分子量为47的二氧化碳的同位素与重量为44的二氧化碳的同位素的比率与随机分布时预期的比率的偏差。各实验室间Delta47温度校准的显著差异给这些研究增加了相当大的不确定性，并限制了Delta47古测温仪对大于±5℃的温度异常的适用性。拟议的工作将通过限制在其测量中使用的所有材料的三重氧同位素组成，帮助确定实验室间Delta47差异的来源(S)。这些结果将使Dletal47古温度计取得进展，只受分析精度的限制，能够解决许多过程中温度变化小得多的特点。它还将为社区间校准工作奠定基础，这将推动目前将Delta47应用于具有社会意义的地质和环境研究问题的许多学科的工作。通过建立社区校准工作的基础，它将加强现有的国内和国际合作，并促进新的合作，从而帮助确定最相关和最可实现的未来工作。当使用基于全球水池的参数校正与17O丰度相关的质谱仪数据中的干扰时，碳酸盐块状同位素测量的准确度和精确度显著提高。然而，新的修正方案错误地假设了用于获得Delta47的气体、水和碳酸盐中17O和18O的丰度遵循17O过剩为零的特定关系。拟议的工作将利用现有的二氧化碳-水平衡和在多种温度下产生的非生物成因碳酸盐样本，以及华盛顿大学独特的分析能力，以评估170氧过量如何影响Delta47。这套多样化的样品代表了大多数成团同位素实验室使用的同位素组成、沉淀方法和温度，使拟议的工作能够对成团同位素社区使用的许多分析物中的17O过量变异性的大小提供重要的限制。它将允许评估如何使用17O过量进行最准确和最精确的Delta47测量(在所有分析物中都已知)，并为无法直接测量17O过量的绝大多数机构开发最佳实践。后者将包括重新评估之前发布的结果(包括Delta47温度校准)和生成新数据的建议。

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.