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Title: Dual stable isotopes of CH 4 from Yellowstone hot-springs suggest hydrothermal processes involving magmatic CO 2

Volcanism and post-magmatism contribute significant annual methane (CH 4) fluxes to the atmosphere (on par with other natural sources such as forest fire and wild animal emissions) and have been implicated in past climate-change events. The Yellowstone hot spot is one of the largest volcanic systems on Earth and is known to emit CH 4 (as well as carbon dioxide (CO 2) and other gases), but the ultimate sources of this CH 4 flux have not been elucidated. In this paper, we use dual stable isotope analysis (δ 2H and δ 13C) of CH 4 sampled from ten high-temperature geothermal pools in Yellowstone National Park along with other isotopic and gas analyses to evaluate potential sources of methane. The average δ 13C and δ 2H values of CH 4 emitted from hot springs ( 26.7 (± 2.4) and - 236.9 (± 12.0) ‰, respectively) are inconsistent with microbial methanogenesis but do not allow distinction between thermogenic and abiotic sources. Correlation between δ 13C CH4 and δ 13C of dissolved inorganic C (DIC) is consistent with DIC as the parent C source for the observed CH 4, or with equilibration of CH 4 and DIC. Methane formation temperatures estimated by isotopicmore » geothermometry based on δ 13C CH4 and δ 13C CO2 ranged from ~ 250–350 °C, which is just below previous temperature estimates for the hydrothermal reservoir. Further, the δ 2H H2O of the thermal springs and the measured δ 2H CH4 values are consistent with equilibration between the source water and the CH 4 at the formation temperatures. Though the ultimate origin of the CH 4 could be attributed to either abiotic of themorgenic processes with subsequent isotopic equilibration, the C 1/C 2+ composition of the gases is more consistent with abiotic origins for most of the samples. Finally, our data support the hypothesis that subsurface rock-water interactions are responsible for at least a significant fraction of the CH 4 flux from the Yellowstone National Park volcanic system.« less
Authors:
ORCiD logo [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [1] ;  [2]
  1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Montana State Univ., Bozeman, MT (United States). Dept. of Land Resources and Environmental Sciences. Thermal Biology Inst.
Publication Date:
Report Number(s):
PNNL-SA-121866
Journal ID: ISSN 0377-0273; PII: S0377027316304164
Grant/Contract Number:
AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Journal of Volcanology and Geothermal Research
Additional Journal Information:
Journal Volume: 341; Journal ID: ISSN 0377-0273
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Montana State Univ., Bozeman, MT (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Methane; Stable isotopes; Hydrothermal; Yellowstone National Park; Deep carbon; Greenhouse gas
OSTI Identifier:
1364362