EAR-PF: Investigating the utility of cherts for constraining the long-term evolution of oxygen isotopes in the oceans

贾斯汀·海尔斯博士被授予博士后研究金，与莱斯大学和宾夕法尼亚州立大学合作，研究整个地球历史上海水的海洋氧同位素组成。海洋是地球表面最重要的氧气储存库。它的同位素组成随冰的体积而变化，并受到百万年时间尺度上与固体地球相互作用的影响。海洋矿物记录了这些变化：它们继承了海洋的氧同位素组成。然而，海洋矿物系统显示出长期的长期变化，无法简单地用温度或海洋同位素组成的变化来解释。海洋被认为是由海水和海底岩石之间的高温和低温相互作用所缓冲的。如果这些相互作用在十亿年的时间尺度上没有变化，海洋沉积岩的氧同位素组成主要与海水温度和全球冰量的变化有关。然而，如果这些相互作用确实发生变化，海水的氧同位素组成可能会发生长期变化，向更重的组成。通过测量古燧石样品的三重氧同位素组成，将有可能限制海洋氧同位素组成，并最终推进我们对整个地球历史的地表环境的理解。PI将与本科生合作进行研究项目，并通过职业日活动向当地学校提供外展服务。最近的实验结果表明，二氧化硅，沉淀在最常见的地球表面条件下，形式与可预测的温度依赖抵消氧同位素组成的水，其氧是最终获得的。在实践中，基于氧分馏的地质温度计系统取决于水的氧的假设。通过约束这种关系，可以完全约束形成二氧化硅的氧同位素和温度。然而，由于海相硅质岩几乎普遍存在成岩蚀变，因此有必要确定这种方法对海水氧测定的影响。通过对南加州中新世至上新世Monterey和Sisquoc地层中硅质相的表征和三重氧同位素分析，研究了海相硅质岩的成岩蚀变作用，（蛋白石-A，Opal-CT和微石英）该奖项反映了NSF的法定使命，并通过使用基金会的智力价值进行评估，被认为值得支持和更广泛的影响审查标准。

Dr. Justin Hayles has been awarded a postdoctoral fellowship to work with at Rice University and Pennsylvania State University to study oceanic oxygen isotope compositions of seawater throughout Earth history. The ocean is the most important reservoir of oxygen on Earth's surface. Its isotopic composition varies with ice volume and is influenced by interactions with the solid Earth on million-year timescales. Marine minerals record these variations: they inherit the oceans' oxygen-isotope composition. Marine mineral systems, however, show long-term secular variations that are not easily explained by changes in temperature or ocean isotopic composition exclusively. The ocean is thought to be buffered by high- and low-temperature interactions between seawater and seafloor rocks. If these interactions do not vary on billion-year timescales, the oxygen-isotope compositions of marine sedimentary rocks mostly relate to changes in seawater temperature and global ice volume. However, if these interactions do vary there could be a secular change in the oxygen isotope composition of seawater toward heavier compositions. By measuring the triple-oxygen isotope composition of ancient chert samples, it will be possible to constrain oceanic oxygen isotope compositions and ultimately advance our understanding of the surface environment throughout Earth history. The PI will work with undergraduates on research projects and provide outreach to local schools through career day events.Recent experimental results have demonstrated that silica, precipitated under most common Earth surface conditions, forms with a predictable temperature dependent offset in oxygen isotope composition from the water which its oxygen was ultimately derived. In practice, the oxygen fractionation based geothermometer system depends on the assumption of the oxygen of the water. By constraining this relationship, it is possible to fully constrain the oxygen isotopes and temperature which the silica formed from. However, because marine cherts are nearly ubiquitously diagenetically altered it is necessary to determine what effects, if any, there will be on the determination of seawater oxygen using this method. The effects of diagenetic alteration of marine cherts will be done through the characterization and triple oxygen isotope analysis of silica phases from the Miocene to Pliocene Monterey and Sisquoc formations of Southern California where three phases of silica (Opal-A, Opal-CT and microquartz) are known to exist.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.