College of Sciences


Ocean/Earth/Atmos Sciences



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Marine microbial dinitrogen (N2) fixation, the conversion of gaseous N2 to bioavailable species, is the primary source of new oceanic nitrogen (N). N is present in nucleic acids, amino acids, and proteins, and is essential to all life. Long considered to be a primarily oligotrophic ocean process, significant N2 fixation rates have recently been observed in coastal environments, including along the Cape Hatteras front. To see if elevated N2 fixation was a persistent feature in this region, N2 fixation rates and N2 fixer (diazotroph) abundance and gene expression were investigated through roughly monthly sampling at a field station (Jennette’s Pier) in the Outer Banks, NC, from June 2019 to August 2020, as well as a day-long cruise around the pier in August of 2019. In addition to rate and molecular samples, chlorophyll, and particulate N samples were collected and salinity/temperature profiles were measured. Using quantitative polymerase chain reaction techniques, we investigated the abundance and gene expression of diazotrophic (N2 fixing) cyanobacteria possibly responsible for these high coastal rates, and compared these results to N2 fixation rates measured using a variant of the 15N2 tracer assay. Diazotroph species investigated include Trichodesmium spp. and 5 endosymbiont cyanobacteria. Preliminary results suggest evidence of Gulf Stream intrusions within 300m from the shore, and a seasonal variability pattern of nitrogen fixation rates. This study provides useful measurements of coastal N inputs in the context of the global ocean N cycle and budget, and explores chemical and physical factors that affect these processes.


Biogeochemistry | Marine Biology | Oceanography



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Seasonal Variability in Diazotroph Abundance and Gene Expression at a Coastal N<sub>2</sub> Fixation Hotspot (Outer Banks, NC)