Award: OCE-2041539

Stable isotope patterns allow unique insights into natural processes because they can be used to relate mechanisms that take place at the atomic level to effects on much larger scales. All existing approaches to measure stable isotopes, however, have severely limited capabilities to measure isotopic variants of metabolites, drugs, oxyanions, and other compounds that are soluble in water. Our results demonstrate that a radically different approach, based on electrospray ionization Orbitrap mass spectrometry, is capable of measuring isotope signatures of intact water-soluble compounds directly, comprehensively and with high accuracy. Specifically, we used the nitrate oxyanion (NO3-) as a model for developing this new technology. Nitrate is the predominant form of bioavailable nitrogen in the ocean, and observations of its isotopes allows a means of understanding the nitrogen cycle in important details, including processes such as nitrogen fixation, nitrate assimilation, and denitrification. Human activities have profoundly altered global and local nitrogen biogeochemistry in ecosystems through fertilizer use and fossil fuel burning. A better understanding of the fate of anthropogenic nitrogen in modern environments through novel isotope fingerprinting approaches could be useful to better mitigate the dramatic long-term impact of anthropogenic nitrogen on the loss of biodiversity. For this reason we have developed methods to measure for the first time information encoded in the rare forms of nitrate molecules that contain more than one isotopic substitution ("clumped isotopes"). Together with theoretical predictions, newly developed software and laboratory protocols, this project has established a framework to test hypotheses and ask more nuanced mechanistic questions about nitrogen cycling in natural and human-impacted ecosystems. The resulting tools have been made available to several laboratories already and will open new areas of investigation into biogeochemistry. We expect that despite short-term technical delays, the progress made with support of the EAGER grant will in the longer term benefit every field that uses stable isotope analysis, including research on climate, the environment and health. Last Modified: 12/01/2022 Submitted by: Cajetan Neubauer