TABLE 3.

Summary of isotope delta and fractionation value ranges from the literature

Pathway	Substrate	δ13Csubstratea	δ2HCH4a	δ13CCH4a	Exptl εCH4-substratea	Refs
Bacterial	MPn	−100.7 to −95.86b		−39	−5.11 to 2.91	85, 104
Methyl based	QMA
	TMA	−36.9 to −29.5b		−97 to −83	−83 to −39	84, 86, 88, 93, 225
	DMA
	MMA
	MeOH	−46.2 to −37.7b		−129.6 to −46.4	−94 to −68	84–86, 88
	GB
	DMS	−24.4 to −18.6c			−54 to −44	86, 225
	MT
	MMPA
Hydrogenotrophic	CO2	−49.7c to 16.7b	−266 to −153	−108 to −60	−95 to −23	82, 84–87, 94, 226
Acetoclastic	Acetate	−36.4 to −22.1b	−396 to −266	−70 to −27	−35 to −6	84, 85, 87, 227

^aThe δ¹³C of the substrates (from the environment or experimental reagents), the δ²H of methane, the δ¹³C of methane, and the ¹³C fractionation factor (methane-substrate) ε, calculated from experiments as described elsewhere (84) and is commonly reported in the literature, are shown. All numbers reflect per mille (‰) values. δ²H is calculated using the Vienna Standard Mean Ocean Water standard, while δ¹³C is calculated using the Vienna Pee Dee Belemnite standard. Blank cells indicate no known reports in the literature as of October 2022.

^bReagent used in experiments.

^cFrom natural environments.