COLLABORATIVE RESEARCH: IS NITROGEN FIXATION WIDESPREAD IN THE CHUKCHI AND BEAUFORT SEAS?

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The extent of summer Arctic sea ice loss is increasing and now occurs earlier in the year. As a result, it is predicted that the rate of growth of phytoplankton, the base of the marine food web that sustains subsistence marine harvests by native populations, will increase within the Arctic seas. The limited amount of available nitrogen, a required nutrient for phytoplankton, eventually will restrict the level of growth. Nitrogen gas dissolved in the ocean can be converted to a form readily utilizable by phytoplankton, but this has been considered primarily a warm-water process. The principal investigators of this project recently have observed this process in the Arctic Ocean, but there is so little data that its extent remains highly speculative. If it is widespread, it will change the way we think about future scenarios for the changing Arctic marine ecosystem, subsistence fishing, and, potentially, commercial fishing in the Arctic. The project will also contribute to workforce development. The principal investigator is an early-career, female scientist. She will use the project as a mechanism to entrain an undergraduate student into research. She will also use the project to sustain an existing educational collaboration between the Virginia Institute of Marine Sciences and Hampton University, a historically black university.It is hypothesized that microorganisms capable of fixing N2 (diazotrophs) are present in the Chukchi and Beaufort Seas, that they produce measurable rates of N2 fixation in near shore and offshore Arctic marine waters and that diazotroph community composition will differ between coastal sites, which are influenced by terrestrial inputs, versus open water sites. The Chukchi and Beaufort Seas will be sampled during a cruise in late summer 2016, when hydrographic and nutrient conditions are likely to favor diazotrophic populations. The impact that N2 fixation will have on Arctic ecosystems is dependent on its rate, spatial extent and the conditions that favor it. As a consequence, on each cruise the PIs propose to determine diazotroph community composition, examine their distributions based on the presence of the nitrogenase gene (nifH), measure rates of primary productivity and uptake of inorganic and organic N and C substrates using 15N and 13C tracer techniques, and to compare these to hydrographic, nutrient, and overall microbial community composition profiles made along cruise transects. The proposed work will determine the extent of active N2 fixation within the region in the context of other key biogeochemical and microbial community parameters.