Biological nitrogen fixation in the oxygen-minimum region of the eastern tropical North Pacific ocean

Amal Jayakumar, Bonnie X. Chang, Brittany Widner, Peter Bernhardt, Margaret R. Mulholland, Bettie Ward

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Biological nitrogen fixation (BNF) was investigated above and within the oxygen-depleted waters of the oxygen-minimum zone of the Eastern Tropical North Pacific Ocean. BNF rates were estimated using an isotope tracer method that overcame the uncertainty of the conventional bubble method by directly measuring the tracer enrichment during the incubations. Highest rates of BNF (∼4 nM day-1) occurred in coastal surface waters and lowest detectable rates (∼0.2 nM day-1) were found in the anoxic region of offshore stations. BNF was not detectable in most samples from oxygen-depleted waters. The composition of the N 2-fixing assemblage was investigated by sequencing of nifH genes. The diazotrophic assemblage in surface waters contained mainly Proteobacterial sequences (Cluster I nifH), while both Proteobacterial sequences and sequences with high identities to those of anaerobic microbes characterized as Clusters III and IV type nifH sequences were found in the anoxic waters. Our results indicate modest input of N through BNF in oxygen-depleted zones mainly due to the activity of proteobacterial diazotrophs.

Original languageEnglish (US)
Pages (from-to)2356-2367
Number of pages12
JournalISME Journal
Issue number10
StatePublished - Oct 1 2017

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Microbiology


Dive into the research topics of 'Biological nitrogen fixation in the oxygen-minimum region of the eastern tropical North Pacific ocean'. Together they form a unique fingerprint.

Cite this