Tracing sources of atmospheric methane using clumped isotopes
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1.
California Institute of Technology
Abstract
We apply a recently developed measurement technique for methane (CH₄) isotopologues * (isotopic variants of CH₄— ¹³CH₄, ¹²CH₃D, ¹³CH₃D, and ¹²CH₂D₂) to identify contributions to the atmospheric burden from fossil fuel and microbial sources. The aim of this study is to constrain factors that ultimately control the concentration of this potent greenhouse gas on global, regional, and local levels. While predictions of atmospheric methane isotopologues have been modeled, we present direct measurements that point to a different atmospheric methane composition and to a microbial flux with less clumping (greater deficits relative to stochastic) in both ¹³CH₃D and ¹²CH₂D₂ than had been previously assigned. These differences make atmospheric isotopologue data sufficiently sensitive to variations in microbial to fossil fuel fluxes to distinguish between emissions scenarios such as those generated by different versions of EDGAR (the Emissions Database for Global Atmospheric Research), even when existing constraints on the atmospheric CH₄ concentration profile as well as traditional isotopes are kept constant.
Copyright and License
© 2023 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
Acknowledgement
Funding for the UMD Panorama mass spectrometer has come from U.S. NSF [NSF MRI EAR-1725766 MRI: Acquisition of a High Mass Resolution/High Sensitivity Isotope Ratio Mass Spectrometer for Earth Sciences 2017–2020 (J.F., A.J.K., R.R.D.)] as well as infrastructure support for the facility from the Geology Department, the College of Computer, Mathematics, and Natural Sciences, and the Provost's Office at UMD. Funding for the establishment of protocols for air sampling was provided by Water Resources Research Act Program Annual Base grant US Department of the Interior—US Geological Survey 2020, 2021 (J.F. and M.A.H.). Funding to support M.A.H. was provided by a UMD President's Postdoctoral Fellowship Program for providing funding that aided in supporting this work, and then by U.S. NSF grant (EAR-PF: 2052834) (M.A.H.). Finally, we thank Doug Rumble for providing samples of natural gas and for assistance during the commissioning of our mass spectrometer.
Contributions
M.A.H., A.B., and J.F. designed research; M.A.H., J.S., N.H., N.D.H., N.K., S.A.Y., A.J.K., A.B., and J.F. performed research; M.A.H., J.E., S.O., A.B., C.M., and J.F. contributed new reagents/analytic tools; M.A.H., R.R.D., and J.F. analyzed data; M.A.H. investigation, project administration, methodology, review and editing; J.S. methodology and investigation; N.H. methodology; J.S., N.D.H., S.A.Y., R.R.D., and C.M. review and editing; J.E. and S.O. investigation review and editing; J.F. investigation, project administration, methodology, review and editing; and M.A.H. and J.F. wrote the paper.
Data Availability
Model calculations data have been deposited in Digital Repository for the University of Maryland (DRUM) at http://hdl.handle.net/1903/31091 (42).
Conflict of Interest
The authors declare no competing interest.
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Additional details
- ISSN
- 1091-6490
- EAR-1725766
- National Science Foundation
- University System of Maryland
- United States Geological Survey
- EAR-2052834
- National Science Foundation
- Caltech groups
- Division of Geological and Planetary Sciences