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

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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.