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

碳酸盐岩的块状同位素组成是一种有价值的古温标，在古高程、古气候学、生物矿化、成岩作用和人类进化等地球科学领域有着广泛的应用。结果通常表示为Delta47（称为“cap 47”），即分子量为47的CO2同位素与分子量为44的CO2同位素的比值与随机分布的期望比值的偏差。各实验室之间Delta47温度校准的显著差异为这些研究增加了相当大的不确定性，并限制了Delta47古测温对大于±5ºC的温度异常的适用性。拟议的工作将通过限制其测量中使用的所有材料的三氧同位素组成来帮助确定实验室间Delta47差异的来源。这些结果将使Dletal47古温度计取得进展，该古温度计仅受分析精度的限制，能够解决许多过程中特征的小得多的温度变化。它还将为社区相互校准工作奠定基础，这将推动目前将Delta47应用于与社会相关的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可实现的未来工作。利用基于全球水体的参数校正了与17O丰度相关的质谱仪数据的干扰，显著提高了碳酸盐团块同位素测量的准确性和精密度。然而，新的修正方案错误地假设，用于推导Delta47的气体、水和碳酸盐中17O和18O的丰度遵循一种特定的关系，即17O过剩为零。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生成的非生物成因碳酸盐样品，以及华盛顿大学的独特分析能力，来评估17O过量对Delta47的影响。这种多样化的样品组代表了大多数团块同位素实验室使用的同位素组成、沉淀方法和温度，从而允许提出的工作为团块同位素群落使用的许多分析物中17O过量变异的大小提供重要约束。它将允许评估如何使用17O过量来进行最准确和精确的Delta47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17O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.