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Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone

Nature Geoscience volume 6, pages 228234 (2013) | Download Citation

Abstract

Oxygen minimum zones are expanding globally, and at present account for around 20–40% of oceanic nitrogen loss. Heterotrophic denitrification and anammox—anaerobic ammonium oxidation with nitrite—are responsible for most nitrogen loss in these low-oxygen waters. Anammox is particularly significant in the eastern tropical South Pacific, one of the largest oxygen minimum zones globally. However, the factors that regulate anammox-driven nitrogen loss have remained unclear. Here, we present a comprehensive nitrogen budget for the eastern tropical South Pacific oxygen minimum zone, using measurements of nutrient concentrations, experimentally determined rates of nitrogen transformation and a numerical model of export production. Anammox was the dominant mode of nitrogen loss at the time of sampling. Rates of anammox, and related nitrogen transformations, were greatest in the productive shelf waters, and tailed off with distance from the coast. Within the shelf region, anammox activity peaked in both upper and bottom waters. Overall, rates of nitrogen transformation, including anammox, were strongly correlated with the export of organic matter. We suggest that the sinking of organic matter, and thus the release of ammonium into the water column, together with benthic ammonium release, fuel nitrogen loss from oxygen minimum zones.

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Acknowledgements

We wish to thank the Peruvian government for access to their territorial waters. We sincerely thank the cruise leader M. Frank as well as the crews of the cruises M77-3 and 4 onboard R/V Meteor for their support at sea. We are grateful for the technical and analytical assistance of G. Klockgether, I. Boosmann, V. Leon, I. Grefe and A. Ellrott. We thank N. P. Revsbech, who generously provided the STOX sensors, and T. Ferdelmann for offering valuable comments to improve the article. This study was supported by the Deutsche Forschungsgemeinschaft through the Sonderforschungsbereich 754 ‘Climate-Biogeochemistry Interactions in the Tropical Ocean’ and the Max Planck Society.

Author information

Author notes

    • Sergio Contreras

    Present address: Large Lakes Observatory, University of Minnesota Duluth, Minnesota 55812, USA

    • Aurélien Paulmier

    Present address: Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, UMR 5566, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France and Instituto del Mar del Perú (IMARPE), Esquina Gamarra y General Valle, S/N Chucuito, Lima, Peru

Affiliations

  1. Max Planck Institute for Marine Microbiology, 28195 Bremen, Germany

    • Tim Kalvelage
    • , Gaute Lavik
    • , Phyllis Lam
    • , Sergio Contreras
    • , Aurélien Paulmier
    •  & Marcel M. M. Kuypers
  2. GEOMAR Helmholtz Centre for Ocean Research Kiel, 24105 Kiel, Germany

    • Lionel Arteaga
    • , Andreas Oschlies
    •  & Lothar Stramma
  3. Institute for General Microbiology, 24118 Kiel, Germany

    • Carolin R. Löscher

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Contributions

T.K., G.L. and M.M.M.K. designed the study. T.K., G.L., S.C. and A.P. performed 15N-labelling experiments. T.K., G.L. and P.L. analysed the data. C.R.L. carried out functional gene analyses. L.A. and A.O. modelled export production rates. L.S. provided CTD and ADCP data. T.K., G.L., P.L. and M.M.M.K. wrote the manuscript with input from all co-authors..

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Sergio Contreras or Aurélien Paulmier or Marcel M. M. Kuypers.

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DOI

https://doi.org/10.1038/ngeo1739

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