Methane cycling. Nonequilibrium clumped isotope signals in microbial methane.

TitleMethane cycling. Nonequilibrium clumped isotope signals in microbial methane.
Publication TypeJournal Article
Year of Publication2015
AuthorsWang DT, Gruen DS, Lollar BSherwood, Hinrichs K-U, Stewart LC, Holden JF, Hristov AN, Pohlman JW, Morrill PL, K├Ânneke M, Delwiche KB, Reeves EP, Sutcliffe CN, Ritter DJ, Seewald JS, McIntosh JC, Hemond HF, Kubo MD, Cardace D, Hoehler TM, Ono S
Date Published2015 Apr 24
KeywordsAnimals, Carbon Cycle, Carbon Isotopes, Cattle, Groundwater, Hydrogen, Methane, Methanomicrobiales, Temperature

Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane's clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on (13)CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

Alternate JournalScience
PubMed ID25745067