Anaerobic methanotrophy and the rise of atmospheric oxygen

D. C. Catling, M. W. Claire, K. J. Zahnle

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)

Abstract

In modern marine sediments, the anoxic decomposition of organic matter generates a significant flux of methane that is oxidized microbially with sulphate under the seafloor and never reaches the atmosphere. In contrast, prior to ca 2.4 Gyr ago, the ocean had little sulphate to support anaerobic oxidation of methane (AOM) and the ocean should have been an important methane source. As atmospheric 02 and seawater sulphate levels rose on the early Earth, AOM would have increasingly throttled the release of methane. We use a biogeochemical model to simulate the response of early atmospheric 02 and CH4 to changes in marine AOM as sulphate levels increased. Semi-empirical relationships are used to parameterize global AOM rates and the evolution of sulphate levels. Despite broad uncertainties in these relationships, atmospheric 02 concentrations generally rise more rapidly and to higher levels (of order approx. 10(-3) bar versus approx. 10(-4) bar) as a result of including AOM in the model. Methane levels collapse prior to any significant rise in 02, but counter-intuitively, methane re-rises after 02 rises to higher levels when AOM is included. As 02 concentrations increase, shielding of the troposphere by stratospheric ozone slows the effective reaction rate between oxygen and methane. This effect dominates over the decrease in the methane source associated with AOM. Thus, even with the inclusion of AOM, the simulated Late Palaeoproterozoic atmosphere has a climatologically significant level of methane of approximately 50 ppmv.
Original languageEnglish
Pages (from-to)1867-1888
Number of pages22
JournalPhilosophical Transactions of the Royal Society. A, Mathematical, Physical and Engineering Sciences
Volume365
Issue number1856
DOIs
Publication statusPublished - 15 Jul 2007

Keywords

  • Oxygen
  • Methane
  • Methanotrophy
  • Archaean
  • Proterozoic
  • atmospheric evolution
  • Methane oxidation rates
  • Archean sulfur cycle
  • Gas hydrate
  • Early history
  • Sea sediments
  • Sulfate reduction
  • Marine-sediments
  • Early Earth
  • Great oxidation
  • Hamersley basin

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