Fig. 4 | Scientific Reports

Fig. 4

From: Emissions of mantle helium and abiotic methane at newly discovered black smokers along the Central Indian ridge (12°S–16°S)

Fig. 4

CH4 and He systematics. (a) δ13CCH4 versus 1/CH4 diagram and (b) CH4/3Heexcess versus δ13C diagram. The diamonds indicate samples from ROV. In (b), mixing lines represent hypothetical trends defined by the outermost samples from three PCA-based groups: the lowest δ13C (group 1), the lowest CH4/3He (group 2), and highest CH4/3He (group 3). The shaded region indicates the typical δ13C range of microbial methane (< -50‰31).

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