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Science. 2015 Apr 24;348(6233):428-31. doi: 10.1126/science.aaa4326. Epub 2015 Mar 5.

Methane cycling. Nonequilibrium clumped isotope signals in microbial methane.

Author information

1
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
2
Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada.
3
MARUM Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen D-28359, Germany.
4
Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA.
5
Department of Animal Science, Pennsylvania State University, University Park, PA 16802, USA.
6
U.S. Geological Survey (USGS), Woods Hole Coastal and Marine Science Center, Woods Hole, MA 02543, USA.
7
Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland and Labrador A1B 3X5, Canada.
8
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
9
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
10
Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721, USA.
11
Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
12
NASA Ames Research Center, Moffett Field, CA 94035, USA.
13
Department of Geosciences, University of Rhode Island, Kingston, RI 02881, USA.
14
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. sono@mit.edu.

Abstract

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.

PMID:
25745067
DOI:
10.1126/science.aaa4326
[Indexed for MEDLINE]
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