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Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues

Douglas, P. M. J. and Stolper, D. A. and Smith, D. A. and Anthony, K. M. Walter and Paull, C. K. and Dallimore, S. and Wik, M. and Crill, P. M. and Winterdahl, M. and Eiler, J. M. and Sessions, A. L. (2016) Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues. Geochimica et Cosmochimica Acta, 188 . pp. 163-188. ISSN 0016-7037. http://resolver.caltech.edu/CaltechAUTHORS:20160610-103423261

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Abstract

Methane is a potent greenhouse gas, and there are concerns that its natural emissions from the Arctic could act as a substantial positive feedback to anthropogenic global warming. Determining the sources of methane emissions and the biogeochemical processes controlling them is important for understanding present and future Arctic contributions to atmospheric methane budgets. Here we apply measurements of multiply-substituted isotopologues, or clumped isotopes, of methane as a new tool to identify the origins of ebullitive fluxes in Alaska, Sweden and the Arctic Ocean. When methane forms in isotopic equilibrium, clumped isotope measurements indicate the formation temperature. In some microbial methane, however, non-equilibrium isotope effects, probably related to the kinetics of methanogenesis, lead to low clumped isotope values. We identify four categories of emissions in the studied samples: thermogenic methane, deep subsurface or marine microbial methane formed in isotopic equilibrium, freshwater microbial methane with non-equilibrium clumped isotope values, and mixtures of deep and shallow methane (i.e., combinations of the first three end members). Mixing between deep and shallow methane sources produces a non-linear variation in clumped isotope values with mixing proportion that provides new constraints for the formation environment of the mixing end-members. Analyses of microbial methane emitted from lakes, as well as a methanol-consuming methanogen pure culture, support the hypothesis that non-equilibrium clumped isotope values are controlled, in part, by kinetic isotope effects induced during enzymatic reactions involved in methanogenesis. Our results indicate that these kinetic isotope effects vary widely in microbial methane produced in Arctic lake sediments, with non-equilibrium Δ_18 values spanning a range of more than 5‰.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.gca.2016.05.031DOIArticle
http://www.sciencedirect.com/science/article/pii/S0016703716302745PublisherArticle
ORCID:
AuthorORCID
Stolper, D. A.0000-0003-3299-3177
Sessions, A. L.0000-0001-6120-2763
Additional Information:© 2016 Elsevier Ltd. Received 9 November 2015, Accepted 18 May 2016, Available online 25 May 2016. Thanks to Nami Kitchen and Yanhua Shuai for help with clumped isotope measurements, Kat Dawson for help with culture preparation, Fenfang Wu for help with the water isotope measurement, Reto Wijker for help with the methanol δD measurement, Max Lloyd for performing the methanol δ^(13)C measurement, and Uri Ryb for help with developing the isotope mixing model. Dave Valentine provided helpful discussions on the results of the culture experiment. The development of the Ultra was funded by NSF-EAR, and PMJD was supported in part by Royal Dutch Shell.
Funders:
Funding AgencyGrant Number
NSFUNSPECIFIED
Royal Dutch ShellUNSPECIFIED
Subject Keywords:Methane; Clumped isotope geochemistry; Arctic; Carbon cycle; Greenhouse gases
Record Number:CaltechAUTHORS:20160610-103423261
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160610-103423261
Official Citation:P.M.J. Douglas, D.A. Stolper, D.A. Smith, K.M. Walter Anthony, C.K. Paull, S. Dallimore, M. Wik, P.M. Crill, M. Winterdahl, J.M. Eiler, A.L. Sessions, Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues, Geochimica et Cosmochimica Acta, Volume 188, 1 September 2016, Pages 163-188, ISSN 0016-7037, http://dx.doi.org/10.1016/j.gca.2016.05.031. (http://www.sciencedirect.com/science/article/pii/S0016703716302745)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67826
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:10 Jun 2016 18:20
Last Modified:19 Nov 2016 00:48

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