Triple Oxygen Isotope Composition of Stratospheric Carbon Dioxide as the Basis for a New Proxy of Marine and Terrestrial Biosphere Productivity

将研究二氧化碳（CO2）和分子氧（O2）氧同位素组成的异常，这是大气、生物圈和海洋之间总碳交换的新探测的基础。这些异常是涉及O2、臭氧（O3）、氧原子和CO2的平流层反应的结果。不同同位素的O+O2反应生成O3的速率不同。由此产生的O3异常随后被光化学转化为CO2，尽管其他有待研究的反应也可能起作用。CO2的异常伴随着相应的O2的异常（O3就是由O2形成的）。这种同位素特征只有在地球表面的呼吸/光合作用过程中才会被破坏。一旦平流层异常得到更好的量化，对流层中氧的同位素组成就可以用来推断全球平均海洋和陆地生物圈的生产力。冰芯中氧同位素组成的记录可以用来得出过去40万年中生物圈的生产力及其对环境变化的响应。这将使我们更好地了解地球的气候历史，从而更好地了解未来。在这个项目中，平流层空气样本将使用同位素比质谱法分析二氧化碳的同位素组成。与实验室实验和模拟相结合，这些测量将对导致观测到的成分的机制以及平流层二氧化碳和氧气到对流层的通量提供新的基于观测的约束。需要此信息来解释O2记录。

Anomalies in the oxygen isotope compositions of carbon dioxide (CO2) and molecular oxygen (O2), which are the basis for new probes of gross carbon exchanges between the atmosphere, biosphere, and oceans, will be investigated. These anomalies are the results of stratospheric reactions involving O2, ozone (O3), oxygen atoms, and CO2. The rates for O3 formation from the reaction O+O2 are different for different isotopic species. The resulting anomaly in O3 is then photochemically transferred to CO2, although other reactions to be studied might also contribute. Anomalies in CO2 are accompanied by corresponding anomalies in O2 (from which the O3 formed). This isotopic signature is destroyed only by respiration/photosynthesis processes at the Earth's surface. Once the stratospheric anomalies are better quantified, the isotopic composition of O2 in the troposphere can therefore be used to infer globally averaged marine and terrestrial biosphere productivity. Ice-core records of the O2 isotopic composition can then be used to derive the biospheric productivity and its response to environmental change for the past 400,000 years. This will lead to a better understanding of Earth's climate history, and therefore, future.In this project, stratospheric air samples will be analyzed for the isotopic composition of CO2 using isotope ratio mass spectrometry. Coupled with laboratory experiments and modeling, these measurements will provide new observation-based constraints on the mechanisms that lead to the observed compositions and on the fluxes of stratospheric CO2 and O2 to the troposphere. This information is needed to interpret the O2 record.