Clumped Oxygen Isotope Signature of Marine Dissolved Oxygen

海洋环境中光合作用产生的氧气与生物消耗的氧气之间的平衡对调节地球大气的组成和地球气候的长期稳定起着至关重要的作用。准确测量海洋环境中氧气的生产和消耗的能力是建立对氧气和地球气候的过去、现在和未来的知情理解的核心。测量海水中不同氧同位素(即氧-16、氧-17和氧-18)的丰度是一种强大的分析工具，可以用来确定光合作用和生物耗氧量。这是可能的，因为产生或消耗氧气的生物反应倾向于优先利用不同的氧同位素。这一分析工具已用于研究海洋初级生产力已有二十年之久，然而，呼吸作用等生物地球化学过程如何优先选择和利用不同的氧同位素仍存在重大不确定性。为了消除这种不确定性，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现场部署，这些分析针对的是在一个分子(又名)中包含两个稀有氧同位素的氧分子。“簇”，即17O18O和18O18O)。这项工作将量化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被用来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全国中学生科学竞赛的内容创作，该竞赛每年有数千名学生参加。将聚集的O2同位素测量应用于海水中的溶解氧，有望给出比以前更好的关于总初级生产力和海洋氧气循环的机械观点。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还原酶和代谢超氧化物和过氧化氢等活性氧物种的酶的同位素特征。生物研究将以常见的和数量丰富的光养生物和异养生物为目标，以探索海洋水柱中同位素特征和分馏因子的预期广度。将在多个候选航次中的一个航次中采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块状氧同位素方法进行分析。最后，他们将利用实验室对丛生O2的研究结果来建立一个环境数据解释模型，目的是提高现场测量总初级生产量的准确性和精确度。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.