Clumped Oxygen Isotope Signature of Marine Dissolved Oxygen

海洋环境中光合作用产生的氧气和生物消耗的氧气之间的平衡，在调节地球大气层的组成和地球气候的长期稳定方面发挥着关键作用。准确测量海洋环境中氧气的生产和消耗的能力对于了解氧气和地球气候的过去、现在和未来至关重要。测量海水中溶解氧中不同氧同位素（即氧-16、氧-17和氧-18）的丰度是一种强大的分析工具，可用于确定光合作用和生物耗氧量的大小。这是可能的，因为产生或消耗氧的生物反应倾向于优先利用不同的氧同位素。这一分析工具已被用于研究海洋初级生产力20年，然而，仍然有很大的不确定性，在生物地球化学过程，如呼吸如何优先选择和利用不同的氧同位素。为了解决这种不确定性，哈佛大学的研究人员将对新兴的氧同位素分析进行基于实验室的校准和海上实地部署，这些分析针对的是一个分子中含有两种稀有氧同位素的氧分子（也称为“稀有氧同位素”）。“团块”，即17 O 18 O和18 O 18 O）。这项工作将量化在海洋生态系统中发生的几个最重要的涉及氧的反应的聚集氧同位素特征。这些氧同位素特征将用于改进目前测量全球海洋总氧产量的方法和假设。这项研究还将通过一名研究生和两名本科生的指导，帮助培养下一代地球科学家。该项目还将促进研究人员参与为每年有数千名学生参加的全国中学生科学竞赛创作内容。聚集的O2同位素测量海水中溶解氧的应用，准备给一个更大的机械总初级生产力和海洋氧循环比以前达到的观点。为了实现聚集氧同位素方法的分析潜力，这些研究人员将表征与酶水平反应，整个生物体和海洋水柱相关的聚集氧同位素效应。酶水平的研究将包括末端-O2还原酶和代谢活性氧物质（如超氧化物和过氧化氢）的酶的同位素表征。生物研究将针对常见的和数量丰富的光养生物和异养生物，以探索海洋水柱中同位素特征和分馏因子的预期范围。将在多个候选航行中的一个航行中收集海洋水柱溶解氧样本，并使用传统的三重氧同位素技术和新开发的聚团氧同位素方法进行分析。最后，他们将利用基于实验室的聚集O2研究结果，建立一个解释环境数据的模型，目的是提高初级生产总值实地测量的准确性和精度。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The balance between photosynthetic production of oxygen and biological consumption of oxygen in the marine environment plays a critical role in regulating the composition of Earth’s atmosphere and the long-term stability of Earth’s climate. The ability to accurately measure the production and consumption of oxygen in the marine environment is central to building an informed understanding of the past, present, and future of oxygen and Earth’s climate. Measurement of the abundance of different oxygen isotopes (i.e. oxygen-16, oxygen-17, and oxygen-18) in dissolved oxygen in seawater is a powerful analytical tool that can be used to determine the magnitude of photosynthesis and biological oxygen consumption. This is possible because biological reactions that produce or consume oxygen tend to preferentially utilize different isotopes of oxygen. This analytical tool has been used for two decades to investigate ocean primary productivity, however, there is still significant uncertainty in how biogeochemical processes such as respiration preferentially select and utilize different oxygen isotopes. To remedy this uncertainty, researchers at Harvard University will perform a lab-based calibration and sea-going field deployment of emerging oxygen isotope analyses that target molecules of oxygen that contain two rare oxygen isotopes inside of one molecule (a.k.a. “clumps”, i.e. 17O18O and 18O18O). This work will quantify the clumped oxygen isotope signatures of several of the most consequential oxygen-involving reactions that occur in the marine ecosystem. These oxygen isotope signatures will be used to refine current methods and assumptions for the measurement of gross oxygen production in the global ocean. This research will also help train the next generation of Earth scientists through the mentorship of one graduate student and two undergraduate students. This project will also facilitate the participation of researchers in content creation for a national science competition for middle and high school students that reaches thousands of students annually. The application of clumped O2 isotope measurements to dissolved oxygen in seawater is poised to give a greater mechanistic view of gross primary productivity and marine oxygen cycling than previously attainable. To realize the analytical potential of clumped oxygen isotope methods, these researchers will characterize the clumped oxygen isotope effects associated with enzyme-level reactions, whole organisms, and the marine water column. Enzyme-level studies will include isotope characterization of a terminal-O2 reductase and enzymes that metabolize reactive oxygen species such as superoxide and hydrogen peroxide. Organism studies will target common and numerically abundant phototrophs and heterotrophs to explore the expected breadth of isotope signatures and fractionation factors in the marine water column. Marine water column dissolved oxygen samples will be collected during one of multiple candidate cruises and analyzed using both traditional triple oxygen isotope techniques and newly developed clumped oxygen isotope methods. Lastly, they will employ the results of lab-based study of clumped O2 to build a model for the interpretation of environmental data with the aim of improving the accuracy and precision of field measurements of gross primary production.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.