0000-0001-8819-189X (Mulholland), 0000-0003-3848-7013 (Bernhardt), 0000-0002-1527-2717 (Widner), 0000-0002-5721-3061 (Selden), 0000-0001-5212-6228 (Chappell), 0000-0001-7473-4873 (Clayton)

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Global Biogeochemical Cycles






Dinitrogen (N2) fixation can alleviate N limitation of primary productivity by introducing fixed nitrogen (N) to the world's oceans. Although measurements of pelagic marine N2 fixation are predominantly from oligotrophic oceanic regions, where N limitation is thought to favor growth of diazotrophic microbes, here we report high rates of N2 fixation from seven cruises spanning four seasons in temperate, western North Atlantic coastal waters along the North American continental shelf between Cape Hatteras and Nova Scotia, an area representing 6.4% of the North Atlantic continental shelf area. Integrating average areal rates of N2 fixation during each season and for each domain in the study area, the estimated N input from N2 fixation to this temperate shelf system is 0.02 Tmol N y-1, an amount equivalent to that previously estimated for the entire North Atlantic continental shelf. Unicellular group A cyanobacteria (UCYN-A) were most often the dominant diazotrophic group expressing nifH, a gene encoding the nitrogenase enzyme, throughout the study area during all seasons. This expands the domain of these diazotrophs to include coastal waters where dissolved N concentrations are not always depleted. Further, the high rates of N2 fixation and diazotroph diversity along the western North Atlantic continental shelf underscore the need to reexamine the biogeography and activity of diazotrophs along continental margins. Accounting for this substantial, but previously overlooked source of new N to marine systems, necessitates revisions to global marine N budgets.


© 2019 The Authors.

This is an open access article under the terms of the Creative Commons Attribution-Noncommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial, and no modifications or adaptations are made.

Data Availability

Article states: "Data presented in the body and supporting information of this manuscript have been deposited in the National Aeronautics and Space Administration (NASA) repository, SeaBASS and is publicly available at the following DOI address: 10.5067/SeaBASS/CLIVEC/DATA001."

Link to data matching referenced DOI is as follows: https://doi.org/10.5067/SeaBASS/CLIVEC/DATA001.

Original Publication Citation

Mulholland, M. R., Bernhardt, P. W., Widner, B. N., Selden, C. R., Chappell, P. D., Clayton, S., . . . Hyde, K. (2019). High rates of N2 fixation in temperate, western North Atlantic coastal waters expands the realm of marine diazotrophy. Global Biogeochemical Cycles, 33, 1-15. doi:10.1029/2018GB006130

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