Biochemical Barriers on the Path to Ocean Anoxia?

Stephen Giovannoni, Francis Chan, Edward Davis, Curtis Deutsch, Sarah Wolf

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


The kinetics of microbial respiration suggests that, if excess organic matter is present, oxygen should fall to nanomolar levels in the range of the Michaelis-Menten constants (Km). Yet even in many biologically productive coastal regions, lowest observed O2 concentrations often remain several orders of magnitude higher than respiratory Km values. We propose the hypoxic barrier hypothesis (HBH) to explain this apparent discrepancy. The HBH postulates that oxidative enzymes involved in organic matter catabolism are kinetically limited by O2 at concentrations far higher than the thresholds for respiration. We found support for the HBH in a meta-analysis of 1,137 O2 Km values reported in the literature: the median value for terminal respiratory oxidases was 350nM, but for other oxidase types, the median value was 67mM. The HBH directs our attention to the kinetic properties of an important class of oxygen-dependent reactions that could help explain the trajectories of ocean ecosystems experiencing O2 stress.

Original languageEnglish (US)
Article numbere0133221
Issue number4
StatePublished - Aug 1 2021
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Virology
  • Microbiology


  • Dissolved organic matter
  • Ocean respiration
  • Oxygen minimum zones
  • Oxygenase K


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