0000-0002-5721-3061 (Selden), 0000-0001-8819-189X (Mulholland)

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Publication Title

Limnology and Oceanography








Examination of dinitrogen (N2) fixation in the Eastern Tropical South Pacific oxygen deficient zone has raised questions about the range of diazotrophs in the deep sea and their quantitative importance as a source of new nitrogen globally. However, technical considerations in the deployment of stable isotopes in quantifying N2 fixation rates have complicated interpretation of this research. Here, we report the findings of a comprehensive survey of N2 fixation within, above and below the Eastern Tropical South Pacific oxygen deficient zone. N2 fixation rates were measured using a robust 15N tracer method (bubble removal) that accounts for the slow dissolution of N2 gas and calculated using a conservative approach. N2 fixation was only detected in a subset of samples (8 of 125 replicated measurements) collected within suboxic waters (< 20 μmol O2 kg−1) or at the oxycline. Most of these detectable rates were measured at nearshore stations, or where surface productivity was high. These findings support the hypothesis that low oxygen/high organic carbon conditions favor non-cyanobacterial diazotrophs. Nevertheless, this study indicates that N2 fixation is neither widespread nor quantitatively important throughout this region.


© 2021 The Authors

This is an open access article under the terms of the Creative Commons Attribution Noncommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Data Availability

Article states: "Data presented here are available in the Supporting Material as well as on BCO-DMO (http://www.bco-dmo.org/project/742492)."

The Supporting Material can be found in the online version of this article at https://doi.org/10.1002/lno.11735.

Original Publication Citation

Selden, C.R., Mulholland, M.R., Widner, B., Bernhardt, P. & Jayakumar, A. (2021). Toward resolving disparate accounts of the extent and magnitude of nitrogen fixation in the Eastern Tropical South Pacific oxygen deficient zone. Limnology and Oceanography, 66(5), 1950-1960. https://doi.org/10.1002/lno.11735