Abstract
Biologically available nitrogen (N) limits phytoplankton growth over much of the ocean. The rate at which N is removed from the contemporary ocean by denitrifying bacteria is highly uncertain1,2,3. Some studies suggest that N losses exceed inputs2,4,5,6; others argue for a balanced budget3,7,8. Here, we use a global ocean circulation model to simulate the distribution of N2 gas produced by denitrifying bacteria in the three main suboxic zones in the open ocean. By fitting the model to measured N2 gas concentrations, we infer a globally integrated rate of water-column denitrification of 66±6 Tg N yr−1. Taking into account isotopic constraints on the fraction of denitrification occurring in the water column versus marine sediments, we estimate that the global rate of N loss from marine sediments and the oceanic water column combined amounts to around 230±60 Tg N yr−1. Given present estimates of N input rates, our findings imply a net loss of around 20 ± 70 Tg of N from the global ocean each year, indistinguishable from a balanced budget. A balanced N budget, in turn, implies that the marine N cycle is governed by strong regulatory feedbacks.
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Acknowledgements
This study was supported by NSF grants OCE-1131548 and OCE-1131768 and by the Gordon and Betty Moore Foundation.
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C.D. and T.D. designed the study. T.D. carried out the simulations. T.D. and C.D. wrote the paper, with input from B.C., A.D. and F.P. T.D. and F.P. designed the ocean circulation model. B.C. and A.D. provided the Nxs data.
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DeVries, T., Deutsch, C., Primeau, F. et al. Global rates of water-column denitrification derived from nitrogen gas measurements. Nature Geosci 5, 547–550 (2012). https://doi.org/10.1038/ngeo1515
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DOI: https://doi.org/10.1038/ngeo1515