Collaborative research: Constraining the global ocean nitrogen cycle with multiple tracers in a biogeochemical inverse model

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Nitrogen (N) biogeochemical cycling in the marine environment is subject to complex biological and environmental feedbacks with unknown climate sensitivities. Past studies have attempted to characterize the marine N inventory using biogeochemical tracers, such as nutrient stoichiometry, nitrogen isotopes and N2 gas, but these studies have been a snapshot, focusing on a single process in a specific region of the ocean at a time. Such studies were forced to ignore other important and related controlling mechanisms. To resolve the magnitude and type of environmental controls on the processes that influence the N inventory, processes need to be considered simultaneously. Researchers from the University of California at Los Angeles propose to model the spatial distributions and rates of the primary N budget fluxes. In order to derive a global marine N budget, researchers propose to use an inverse model framework that is consistent with all available tracer data. The global ocean circulation model will contain biogeochemical cycles of tracers and will be constrained to optimize the fit to physical tracers (T, S, 14-C-age, CFCs). To examine how environmental variables affect the magnitude of each flux, they will be regressed against the modeling results, providing insight into the effects of anticipated climate change on the N budget. Furthermore, analysis of the inverse solution's error structure will allow researchers to examine the validity of tracer-related assumptions. This work could set up a statistically rigorous framework that will enable researchers to assimilate rapidly developing data streams and will highlight areas in the oceans where data is lacking, allowing resources to be used strategically. The project will provide education and training for undergraduate and graduate students, as well as a post-doc, and will provide important information and insights into the biogeochemical cycling of N necessary to understand the impact of changing climate on ocean processes.