How widespread and important is N2 fixation in the North Atlantic Ocean?

Reynolds, S.E., Mather, R.L., Wolff, G.A., Williams, R.G., Landolfi, A., Sanders, R. and Woodward, E.M.S. (2007) How widespread and important is N2 fixation in the North Atlantic Ocean? Global Biogeochemical Cycles, 21, GB4015. (doi:10.1029/2006GB002886).

Abstract

The spatial extent of N2 fixation in the Atlantic Ocean is examined by determining the isotopic composition of N in suspended particulate organic nitrogen (?15N PONsusp). The samples were collected from zonal and meridional transects of the Atlantic Ocean during a 3-year period. There is a consistent depleted ?15N PONsusp signal extending over the center of the northern subtropical gyre, which partly coincides with a region where the tracer N* increases westward following the gyre circulation. This nonconservative behavior of N* implies that N2 fixation is responsible for the depleted ?15N PONsusp. A mixing model suggests that N2 fixation over parts of the northern gyre provides up to 74% of the N utilized by phytoplankton. However, since the PONsusp represents only a small fraction of the total N pool, N2 fixation probably only plays a minor role in supplying new N to the euphotic zone in the surface waters of the northern subtropical gyre.

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