Award: OCE-0961038

Nitrogen is a major nutrient in the worldÆs oceans and is linked to the cycles of other elements such as carbon, phosphorus, and oxygen. Studies of the links between the atmosphere and ocean, in terms of nitrogen, suggest that human-made reactive nitrogen is the major contributor in the atmosphere. Deposition of this human-made reactive nitrogen via rain or particles falling from the atmosphere (aerosols) is estimated to rival the natural fixation of nitrogen from the atmosphere by biology in the ocean. This has a significant impact on the oceanic nitrogen and carbon budgets. As part of a major effort to measure chemical constituents in the ocean called GEOTRACES, atmospheric particles were collected on the surface of filters exposed to air during the ocean-going research cruises. These particles were then measured for their composition of reactive (inorganic) nitrogen. Different sources of reactive nitrogen contribute to different amounts of 14-N compared to 15-N contained in nitrate on the particles. The major goal of this project was to analyze and interpret these isotopes (i.e. 14-N, 15-N) of atmospheric nitrate in the context of the isotopic composition of nitrate in the North Atlantic Ocean. This has major implications for quantifying natural compared to human-made contributions to reactive nitrogen in the open ocean. Specifically, naturally fixed nitrogen by biology in the ocean produce a low amount of 15-N relative to 14-N, and budgets that calculate the amount of nitrogen fixation consider this biological process as the only input of low signal. Findings in this study show that nitrate in atmospheric particles also contains very low amount of 15-N compared to 14-N, in fact this signal is even lower than that for the natural biological signal. Therefore, new estimates of biological fixation will likely be lower if the atmospheric signal is included in geochemical nitrogen budgets. Furthermore, the isotopic signals in nitrate and ammonium found in atmospheric particles vary with location in the ocean, particularly close to continents compared to the open ocean. Ultimately, studies such as these can contribute to our understanding of the links between anthropogenic nitrogen deposition to the oceans and the oceanic nitrogen and carbon budgets. Beyond the basic research results, this project also contributed to the development of human resources. A young, female faculty member used resources from this project towards the establishment of her laboratory and training of a research technician. Additionally, two undergraduate students received training and mentoring in research and laboratory methods. Both undergraduates are female, and both have continued on to pursue science careers, one as a graduate student in climate related sciences and one as a research scientist in the private sector. Both have communicated that their experience doing hands-on research contributed to their continued interest in science and pursuit of scientific career. Results from this research have been disseminated within the scientific community via publications and conference presentations. Last Modified: 10/31/2013 Submitted by: Meredith G Hastings