Anaerobic oxidation of methane coupled with sulphate reduction: high concentration of methanotrophic archaea might be responsible for low stable isotope fractionation factors in methane

ABSTRACT

The changes in δ¹³CH₄ and δ¹²C¹H₃²H during sulphate-dependent anaerobic oxidation of methane (AOM) were described using dynamic modelling. The batch sulphate-dependent AOM at the nearly linear dynamics of methane oxidation with different enriched cultures originating from three marine sediments was simulated. The traditional Rayleigh equation for carbon and hydrogen stable isotopes in methane was derived from the basic dynamic isotope equation. The general and reduced models, taking into account the reaction stoichiometry and based on balances of chemical elements and their isotopes, describes a redistribution of stable isotope values in the sulphate-dependent AOM process. It was shown that AOM is the first and rate-limiting step in the whole AOM + SR (sulphate reduction) process. The different fractionation factors of carbon and hydrogen isotopes in methane were obtained for three marine sediments. It was concluded that during incubation the highest concentration of methanotrophic archaea might be responsible for the lowest fractionation factors of stable isotopes of carbon and hydrogen in methane. The interpretation of this phenomenon was suggested. Different concentrations of methanotrophic archaea can lead to variations of isotope fractionation factors.

KEYWORDS:

• basic dynamic isotope equation
• carbon-13
• hydrogen-2
• isotope fractionation
• methane
• ANME
• Rayleigh equation
• sulphate-dependent anaerobic oxidation of methane

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was carried out in 2019–2020 according to the plans of the Water Problems Institute of the Russian Academy of Sciences, Russia (N state registration under state assignment AAAA-A18-118022090104-8).