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Progress in Earth and Planetary Science
Fig. 5 | Progress in Earth and Planetary Science

Fig. 5

From: Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

Fig. 5

Relations between \( {\updelta \mathrm{D}}_{{\mathrm{H}}_2} \) and \( {\updelta \mathrm{D}}_{{\mathrm{CH}}_4} \) in the two pure culture experiment sets (TP and MP). The results were divided into three subsets within each of the experimental sets according to the \( {\updelta \mathrm{D}}_{{\mathrm{H}}_2\mathrm{O}} \) label conditions: nonD2O-labeled (panels a and d); moderately D2O-labeled (panels b and e); and highly D2O-labeled conditions (panels c and f). The black arrow in each panel marks the trend in the temporal changes of the values. The horizontal dashed lines in each panel indicate the theoretical fractionation factors between CH4 and H2O. The vertical gray bar in each panel indicates the equilibrated \( {\updelta \mathrm{D}}_{{\mathrm{H}}_2} \) value calculated according to Horibe and Craig (1995)

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