Low Δ12CH2D2 values in microbialgenic methane result from combinatorial isotope effects. (15th September 2020)

• Record Type: Journal Article
• Authors: Taenzer, Lina; Labidi, Jabrane; Masterson, Andrew L.; Feng, Xiahong; Rumble, Douglas; Young, Edward D.; Leavitt, William D.
• Is Part Of: Geochimica et cosmochimica acta. Volume 285(2020)
• Page Start: 225
• Page End: 236
• Publication Date: 2020-09-15
• Subjects: Methane -- Clumped isotopes -- Methanogenesis -- C-P lyase; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2020.06.026
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: Methane generated by microorganisms is most often depleted in the doubly substituted isotopologue 12 CH2 D2 relative to the stochastic reference distribution. To constrain the controls on depleted Δ 12 CH 2 D 2 values, we experimentally isolated the root cause with microorganisms that produce methane from methylphosphonate via the C-P lyase pathway. This mechanism of methane production preserves the three hydrogens from methylphosphonate and adds one hydrogen from water. When maintaining the same methylphosphonate source, but varying the D/H composition of growth medium water, we observed significant shifts in methane Δ 12 CH 2 D 2 values, but little to no change in Δ 13 CH 3 D values. We reproduced these observations with a model that considers only the combinatorial isotope effect. The variation in Δ 12 CH 2 D 2 values of product methane resulted from the differences in D/H between reactants water and methylphosphonate. This work validates the hypothesis that combinatorial effects can strongly influence methane Δ 12 CH 2 D 2 values, and must be considered for low temperature, abiotic or biotic systems where methane hydrogen is derived from multiple reservoirs.