Award: OCE-0850801

FINAL REPORT OUTCOMES: Documenting N2 Fixation in the Eastern Tropical South Pacific Oceanic life is ultimately controlled by the various inputs of nutrients, which provide sustenance for the base of the food chain, oceanic plants. Our study focused on a very unusual nutrient acquisition strategy used by marine phytoplankton, the conversion of inert nitrogen gas into utilizable, fixed nitrogen. We studied this process in a rather unique, but very poorly studied, portion of the global ocean, the Eastern Tropical South Pacific, a region in which other nutrients may be available, but fixed nitrogen is generally lacking. Here we asked the question: In these waters, do plants acquire fixed nitrogen when deeper water rich in fixed nitrogen is mixed up to the surface, or are there bacteria living in the surface ocean and fixing nitrogen? A theoretical analysis suggested that nitrogen fixation should be very important. Our answer, following two month long research cruises, is that it is primarily nutrients mixed up from the subsurface that fuels plant growth in this part of the ocean. We also learned what other N transformations take place in this unique region and how nitrogen fixation rates could be increased by the addition of certain trace elements. The nitrogen fixing organisms that we did detect were unlike those observed in other nutrient poor regions of the world oceans. We mapped this region in terms of plant growth rate and coupled this view of the surface ocean with the view from the deep benthos, to see how much food arrives to fuel life in the deep sea. We were an international collection of scientists, collaborating on aspects of this broad topic and are still in the process of disseminating our results in the scientific literature and at public meetings. Last Modified: 10/28/2013 Submitted by: Douglas G Capone