Combinatorial and rate effects on the multiply-substituted isotope signatures in methane during biological production and consumption

Methane is an important energy source, a potent greenhouse gas and a potential proxy for extraterrestrial life.Constraining the sources and sinks of methane is crucial for understanding methane cycling on Earth and other planets.The relative abundances of multiply-substituted ("clumped") isotopologues 13 CH 3 D and 12 CH 2 D 2 (δ 13 CH 3 D and δ 12 CH 2 D 2 ) are potentially