High N<sub>2</sub> Fixation in and Near the Gulf Stream Consistent with a Circulation Control on Diazotrophy
Jaime B. Palter, Elana J. Ames, Mar Benavides, Afonso Gonçalves Neto, Julie Granger, Pia H. Moisander, Katie S. Watkins-Brandt, Angelicque White
Abstract
Abstract The stoichiometry of physical nutrient supply may provide a constraint on the spatial distribution and rate of marine nitrogen (N 2 ) fixation. Yet agreement between the N 2 fixation rates inferred from nutrient supply and those directly measured has been lacking. The relative transport of phosphate and nitrate across the Gulf Stream suggests that 3–6 Tg N year −1 must be fixed to maintain steady nutrient stoichiometry in the North Atlantic subtropical gyre. Here we show direct measurements of N 2 fixation consistent with these estimates, suggesting elevated N 2 fixation in and near the Gulf Stream. At some locations across the Gulf Stream, we measured diazotroph abundances and N 2 fixation rates that are 1–3 orders of magnitude greater than previously measured in the central North Atlantic subtropical gyre. In combination, rate measurements and gene abundances suggest that biogeochemical budgets can be a robust predictive tool for N 2 fixation hot spots in the global ocean.