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

碳酸盐岩的凝聚态同位素组成是一种非常有价值的古温度计，在古高度测量、古气候学、生物成矿作用、成岩作用和人类演化等地球科学领域有着广泛的应用。结果通常表示为Delta 47（称为“cap 47”），这是分子量为47的CO2同位素与分子量为44的同位素的比值与随机分布时预期比值的偏差。实验室之间Delta 47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Delta 47古温度测量法对大于± 5ºC的温度异常的适用性。拟议的工作将有助于通过限制其测量中使用的所有材料的三重氧同位素组成来确定实验室间Delta 47差异的来源。这些结果将使Dletal 47古温度计的进展，仅限于分析精度，能够解决许多过程中的温度变化小得多的特点。它还将为社区相互校准工作奠定基础，这将推动目前将Delta 47应用于社会相关地质和环境研究问题的许多学科的工作。通过为社区校准工作奠定基础，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17 O丰度相关的质谱仪数据中的干扰时，碳酸盐聚集同位素测量的准确度和精度显著提高。然而，新的校正方案错误地假设，用于推导Delta 47的气体、沃茨和碳酸盐中的17 O和18 O丰度遵循一种特定的关系，其中17 O过量为零。拟议的工作将利用现有的CO2-水平衡和非生物成因的碳酸盐样品在多个温度下产生，以及独特的华盛顿大学的分析能力，以评估如何17 O过量影响三角洲47。这种多样化的样品套件是代表的同位素组成，沉淀方法和温度所使用的大多数聚集的同位素实验室，允许拟议的工作提供重要的限制17 O过量的变化幅度在许多分析物中使用的聚集的同位素社区。它将允许评估如何使用17 O过量来进行最准确和精确的Delta 47测量，当它在所有分析物中已知时，以及为绝大多数无法直接测量17 O过量的机构开发-最佳实践。后者将包括重新评估先前发表的结果（包括Delta 47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.