Hydrogen production and nitrogen fixation in the North Pacific Subtropical Gyre

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In this project, researchers at the University of Hawaii a Manoa will conduct a series of field and laboratory studies to develop a quantitative understanding of dissolved hydrogen (H2) cycling in the oligotrophic North Pacific Ocean. Dissolved H2 concentrations in the surface ocean typically range from 1-3 nM which represents 300-900% supersaturation relative to atmospheric concentrations. This persistent supersaturation of dissolved H2 in the surface waters of subtropical and tropical oceans makes the oceans a source of atmospheric H2 and compiled budgets of global H2 sources estimate marine emissions from 3 to 6 Tg H2 yr-1. The broad objectives of the research are: (1) to quantify the linkages and stoichiometry between H2 production and N2 fixation in surface seawater of the open ocean, and (2) to determine the factors that drive this relationship including the microbial community composition and the influence of light intensity. The field research will be conducted over a two-year period at Station ALOHA and will complement the ongoing Hawaii Ocean Time-series (HOT) program. Broader Impacts: Quantifying the H2 cycling in surface waters of the upper water column will constrain existing estimates of global marine H2 emissions. Furthermore, an improved understanding of H2 cycling will help predict potential effects of increasing anthropogenic emissions of H2 increase or a climate-driven change in the community structure of marine diazotrophs. These results will be valuable to microbial ecologists, biogeochemists, and climate change scientists. All resulting oceanographic and laboratory datasets will be archived in the online HOT and Center for Microbial Oceanography: Research and Education (C-MORE) data centers and made publicly available. At least one undergraduate student will be hosted through the C-MORE scholars program which particularly targets Native Hawaiians and Pacific Islanders majoring in an ocean or earth science-related field.