Methane production and bubble emissions from arctic lakes: Isotopic implications for source pathways and ages
Article first published online: 2 AUG 2008
Copyright 2008 by the American Geophysical Union.
Journal of Geophysical Research: Biogeosciences (2005–2012)
Volume 113, Issue G3, September 2008
How to Cite
2008), Methane production and bubble emissions from arctic lakes: Isotopic implications for source pathways and ages, J. Geophys. Res., 113, G00A08, doi:10.1029/2007JG000569., , , , and (
- Issue published online: 2 AUG 2008
- Article first published online: 2 AUG 2008
- Manuscript Accepted: 11 APR 2008
- Manuscript Revised: 19 MAR 2008
- Manuscript Received: 9 AUG 2007
- arctic lakes;
 This study reports an atmospheric methane (CH4) source term previously uncharacterized regarding strength and isotopic composition. Methane emissions from 14 Siberian lakes and 9 Alaskan lakes were characterized using stable isotopes (13C and D) and radiocarbon (14C) analyses. We classified ebullition (bubbling) into three categories (background, point sources, and hot spots) on the basis of fluxes, major gas concentrations, and isotopic composition. Point sources and hot spots had a strong association with thermokarst (thaw) erosion because permafrost degradation along lake margins releases ancient organic matter into anaerobic lake bottoms, fueling methanogenesis. With increasing ebullition rate, we observed increasing CH4 concentration of greater radiocarbon age, depletion of 13CCH4, and decreasing bubble N2 content. Microbial oxidation of methane was observed in bubbles that became trapped below and later within winter lake ice; however, oxidation appeared insignificant in bubbles sampled immediately after release from sediments. Methanogenic pathways differed among the bubble sources: CO2 reduction supported point source and hot spot ebullition to a large degree, while acetate fermentation appeared to contribute to background bubbling. To provide annual whole-lake and regional CH4 isofluxes for the Siberian lakes, we combined maps of bubble source distributions with long-term, continuous flux measurements and isotopic composition. In contrast to typical values used in inverse models of atmospheric CH4 for northern wetland sources (δ13CCH4 = −58‰, 14C age modern), which have not included northern lake ebullition as a source, we show that this large, new source of high-latitude CH4 from lakes is isotopically distinct (δ13CCH4 = −70‰, 14C age 16,500 years, for North Siberian lakes).