CAREER: Robust Isotopic Constraints on Primary Productivity from First Principles

全球生物圈对气候变化的反应是不确定的。特别是，现在和过去的生物圈生产力很难估计，因为现有的工具在技术上具有挑战性，难以应用于生命能够茁壮成长的多种多样且往往知之甚少的自然环境。这项研究将通过一种将推动光合作用和呼吸作用的生化反应的理论和实验相结合的方法，改进对现在和过去生物圈生产力的估计。这些结果将用于确定过去几十年的表层海洋生产力模式，使用将向研究界提供的现有数据的新汇编。最后，该项目将支持一年一度的教师培训活动计划，目的是在目前缺乏课程和培训的初中和高中早期阶段开展全球变化科学。这位研究人员将与莱斯STEM项目办公室和哈里斯县教育部合作，接待教师进行夏季实验室体验，并举办为期一天的年度研讨会，以培训休斯顿学校的教师，开发有关全球变化科学的课程，并培养地球科学与核心科学/数学学科之间的早期联系。评估生物圈生产力过去变化的关键工具之一是稳定同位素分析。在这一系列方法中，分子氧(O2)的同位素组成已被广泛应用于约束生物地球化学碳循环，因为氧在代谢水平上与碳循环有关。18O/16O和17O/16O比值之间的协变，特别是O2的“三同位素”组成，对于确定现代和过去的生物圈生产力都是非常有用的。即使是10亿多年前从O2转移到岩石中的残余信号也被用于这一目的。然而，只有在充分理解生物分馏过程的情况下，这种同位素数据的解释才是合理的。O2上的信号相当微妙，三同位素测量的技术难度意味着很少有基础实验得到重复和验证。这个项目将使用新的实验和计算化学工具重新评估呼吸和光合作用的基本O2分馏因子。一个中心假设是，从第一原理到基准、改进和统一跨地球科学领域的氧三同位素示踪剂，生物氧同位素分馏可以被准确地预测。该项目还将测试生物氧同位素分馏对环境边界条件的敏感性，以评估环境强迫的同位素变异性对解释当地和全球氧气收支的影响。作为顶峰，过去20年收集的海洋三氧场数据将根据这些新信息进行汇编和重新解释。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 response of the global biosphere to climate change is uncertain. In particular, biosphere productivity in the present and in the past is difficult to estimate because the available tools are technically challenging to apply in the varied and often poorly understood natural environments in which life can thrive. This study will improve estimates of biosphere productivity in the present and the past through an approach that unifies theory and experiments on the biochemical reactions that drive photosynthesis and respiration. The results will be applied to determine patterns of surface-ocean productivity over the past several decades using a new compilation of existing data that will be made available to the research community. Finally, the project will support a program of annual teacher-training activities aimed at global-change science at the middle- and early-high school level, where curricula and training are currently lacking. Working with the Rice Office of STEM Engagement and the Harris County Department of Education, the investigator will host teachers for summer laboratory experiences and an annual 1-day workshop to train Houston school teachers, develop lessons on global-change science, and cultivate early connections between the geosciences and core science/math disciplines.One of the key tools for assessing past changes in biosphere productivity is stable-isotope analysis. Of this family of approaches, the isotopic composition of molecular oxygen (O2) has been applied widely to constrain the biogeochemical carbon cycle because oxygen is linked to carbon cycling at the metabolic level. Covariations between 18O/16O and 17O/16O ratios, in particular―the “triple-isotope” composition of O2―have been of great utility for determining both modern and past biosphere productivity. Even remnant signals, transferred more than a billion years ago from O2 into rocks, have been used for this purpose. However, the interpretations of such isotopic data are only justified if the biological fractionation processes are well understood. The signals on O2 are quite subtle, and the technical difficulty of triple-isotope measurements has meant that few of the foundational experiments have been repeated and validated. This project will re-evaluate the fundamental O2 fractionation factors for respiration and photosynthesis using new experiments and the tools of computational chemistry. A central hypothesis is that biological oxygen-isotope fractionation can be predicted accurately from first principles to benchmark, improve, and unify oxygen triple-isotope tracers across geoscience fields. The project will also test the sensitivity of biological O2 isotopic fractionation to environmental boundary conditions to evaluate the impacts of environmentally forced isotopic variability on the interpretation of local and global O2 budgets. As a capstone, the oceanographic triple-oxygen field data collected over the past 20 years will be compiled and re-interpreted in light of this new information.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.