EAR-PF: Seeing through carbonate diagenesis using the triple oxygen isotope system

NSF EAR博士后奖学金授予乔丹·沃斯特布罗克博士，在诺亚·J·普拉夫斯基博士的指导下，他将在耶鲁大学开展研究和教育活动。这个项目调查碳酸盐岩如何很好地保存岩石形成的初始环境条件。在海洋环境中形成的碳酸盐通常被用来重建过去的海洋温度，以观察海洋在冰期和间冰期循环(温室/冰库气候)之间如何变化。碳酸盐岩中氧同位素比值被用来计算这些岩石的形成温度。然而，使用传统的氧同位素比值测量(即只使用氧-18/氧-16比值)很难确定岩石中测得的氧同位素比值是来自初始沉积还是沉积后氧同位素比值发生了变化。将使用一种新的氧同位素测量技术，该技术着眼于额外的氧同位素比率(氧-17/氧-16比率)，以更好地约束海相碳酸盐岩的沉积环境。这一额外的变量将使海洋科学家能够利用岩石记录更好地确定古代海洋环境的条件。例如，生物学家和古生物学家也许能够使用这一工具来观察影响珊瑚生存能力或可能影响进化的微环境变化。作为STEM领域的一名女性，Jordan Wostbrock博士将通过招聘一名本科生女性作为实验室助理，指导本科生研究经验，并担任耶鲁女性科学项目的导师，积极寻求女性参与STEM。该项目将使用碳酸盐的三重氧同位素组成(结合17O/16O和18O/16O测量)来研究蚀变过程中氧同位素的变化。这将是碳酸盐岩三重氧同位素体系在海洋环境中的首次深入应用，并将集中于两个主要任务：1)测量巴哈马地台已知成岩环境的三重氧同位素组成，以建立配备三重氧同位素的反应输运模型；2)测量太古代至白垩纪碳酸盐岩的三重氧同位素组成，以探索所观察到的氧同位素值的增加是否与海洋同位素组成、温度或保存质量的变化有关。沃斯特布罗克博士将结合其他地球化学系统，如锶和钙以及水文条件，来预测浅海环境中碳酸盐氧同位素组成的变化。更好地了解浅海环境中的成岩作用将改变我们对岩石记录如何保存海洋地球化学的理解。更好地了解海洋动力学将有助于预测海洋在气候变化期间如何对外部力量作出反应。这项研究将试图解决一个有50年历史的问题，即碳酸盐记录中看到的长期变化是保存问题，海洋氧同位素组成的变化，还是海洋温度的变化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

An NSF EAR Postdoctoral Fellowship has been granted to Dr. Jordan Wostbrock to carry out research and educational activities at Yale University under the mentorship of Dr. Noah J. Planavsky. This project investigates how well carbonate rocks preserve the initial environmental conditions under which the rock formed. Carbonates that form in marine settings are commonly used to reconstruct past ocean temperatures to see how oceans change between glacial and interglacial cycles (greenhouse/icehouse climates). The ratios of oxygen isotopes in carbonate rocks are used to calculate the temperature in which these rocks formed. However, using traditional measurements of the oxygen isotope ratios (i.e. using only the Oxygen-18/Oxygen-16 ratio) makes it difficult to figure out if the oxygen isotope ratios measured in the rock are from the initial deposition or if the oxygen isotope ratios have changed after deposition. A novel oxygen isotope measurement technique that looks at an additional oxygen isotope ratio (the Oxygen-17/Oxygen-16 ratio) will be used to better constrain the depositional environments of marine carbonate rocks. This additional variable will enable marine scientists to better determine the conditions of ancient marine environments using the rock record. For example, biologists and paleontologists might be able to use this tool to look at micro-environmental changes that affect coral survivability or that might have impacted evolution. As a female in a STEM field, Dr. Jordan Wostbrock will actively seek female engagement in STEM by recruiting an undergraduate woman as an assistant in the laboratory, mentor undergraduate research experiences, and serve as a mentor for the Women in Science at Yale program. This project will use the triple oxygen isotope composition (combined 17O/16O and 18O/16O measurements) of carbonates to examine how oxygen isotope values change during alteration. It will be the first in-depth application of the triple oxygen isotope system of carbonates in a marine setting and will focus on two main tasks: 1) Measure the triple oxygen isotope compositions of a known diagenetic environment of the Bahama Platform to create a triple oxygen isotope equipped reaction transport model and 2) Measure the triple oxygen isotope compositions of Archean through Cretaceous carbonate rocks to explore whether the observed increase in oxygen isotope values is related to changing ocean isotopic composition, temperature, or preservation quality. Dr. Wostbrock will combine other geochemical systems such as Sr and Ca as well as hydrologic conditions to predict how carbonate oxygen isotope composition changes in the shallow marine environment. A better understanding of diagenesis in shallow marine settings will change our understanding of how the rock record preserves ocean geochemistry. Better understanding of ocean dynamics will assist in the prediction of how oceans respond to external forces during a changing climate. This study will try to address the 50-year-old question as to whether the secular change seen in the carbonate record is a preservation issue, a change in oxygen isotope composition of the ocean, or a change in ocean temperature.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.