title: Revising the nitrogen cycle in the Peruvian oxygen minimum zone.
abstract: The oxygen minimum zone (OMZ) of the Eastern Tropical South Pacific (ETSP) is 1 of the 3 major regions in the world where oceanic nitrogen is lost in the pelagic realm. The recent identification of anammox, instead of denitrification, as the likely prevalent pathway for nitrogen loss in this OMZ raises strong questions about our understanding of nitrogen cycling and organic matter remineralization in these waters. Without detectable denitrification, it is unclear how NH(4)(+) is remineralized from organic matter and sustains anammox or how secondary NO(2)(-) maxima arise within the OMZ. Here we show that in the ETSP-OMZ, anammox obtains 67% or more of NO(2)(-) from nitrate reduction, and 33% or less from aerobic ammonia oxidation, based on stable-isotope pairing experiments corroborated by functional gene expression analyses. Dissimilatory nitrate reduction to ammonium was detected in an open-ocean setting. It occurred throughout the OMZ and could satisfy a substantial part of the NH(4)(+) requirement for anammox. The remaining NH(4)(+) came from remineralization via nitrate reduction and probably from microaerobic respiration. Altogether, deep-sea NO(3)(-) accounted for only approximately 50% of the nitrogen loss in the ETSP, rather than 100% as commonly assumed. Because oceanic OMZs seem to be expanding because of global climate change, it is increasingly imperative to incorporate the correct nitrogen-loss pathways in global biogeochemical models to predict more accurately how the nitrogen cycle in our future ocean may respond.
authors.affiliation: Max Planck Institute for Marine Microbiology, D-28359 Bremen, Germany. plam@mpi-bremen.de
authors.forename: Phyllis
authors.initials: P
authors.lastname: Lam
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.forename: Marlene M
authors.initials: MM
authors.lastname: Jensen
authors.forename: Jack
authors.initials: J
authors.lastname: van de Vossenberg
authors.forename: Markus
authors.initials: M
authors.lastname: Schmid
authors.forename: Dagmar
authors.initials: D
authors.lastname: Woebken
authors.forename: Dimitri
authors.initials: D
authors.lastname: Gutiérrez
authors.forename: Rudolf
authors.initials: R
authors.lastname: Amann
authors.forename: Mike S M
authors.initials: MS
authors.lastname: Jetten
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
mesh_terms: D001419:Bacteria / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010568:Peru; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
chemical_list: D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D009569:Nitric Oxide; D009584:Nitrogen; D010100:Oxygen