Anammox bacteria drive fixed nitrogen loss in hadal trench sediments

Bo Thamdrup*, Clemens Schauberger, Morten Larsen, Blandine Trouche, Lois Maignien, Sophie Arnaud-Haond, Frank Wenzhöfer, Ronnie N. Glud

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Benthic N2 production by microbial denitrification and anammox is the largest sink for fixed nitrogen in the oceans. Most N2 production occurs on the continental shelves, where a high flux of reactive organic matter fuels the depletion of nitrate close to the sediment surface. By contrast, N2 production rates in abyssal sediments are low due to low inputs of reactive organics, and nitrogen transformations are dominated by aerobic nitrification and the release of nitrate to the bottom water. Here, we demonstrate that this trend is reversed in the deepest parts of the oceans, the hadal trenches, where focusing of reactive organic matter enhances benthic microbial activity. Thus, at ∼8-km depth in the Atacama Trench, underlying productive surface waters, nitrate is depleted within a few centimeters of the sediment surface, N2 production rates reach those reported from some continental margin sites, and fixed nitrogen loss is mainly conveyed by anammox bacteria. These bacteria are closely related to those known from shallow oxygen minimum zone waters, and comparison of activities measured in the laboratory and in situ suggest they are piezotolerant. Even the Kermadec Trench, underlying oligotrophic surface waters, exhibits substantial fixed N removal. Our results underline the role of hadal sediments as hot spots of deep-sea biological activity, revealing a fully functional benthic nitrogen cycle at high hydrostatic pressure and pointing to hadal sediments as a previously unexplored niche for anaerobic microbial ecology and diagenesis.

Original languageEnglish
Article numbere2104529118
JournalProceedings of the National Academy of Sciences of the United States of America
Volume118
Issue number46
Number of pages7
ISSN0027-8424
DOIs
Publication statusPublished - 16. Nov 2021

Bibliographical note

Publisher Copyright:
© 2021 National Academy of Sciences. All rights reserved.

Keywords

  • Denitrification
  • Hadal trenches
  • Marine biogeochemistry
  • Microbial ecology

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