Methane production and bubble emissions from arctic lakes: isotopic implications for source pathways and ages

K.M. Walter; J.P. Chanton; F.S. Chapin III; E.A.G. Schuur; S.A. Zimov

doi:10.1029/207JG000569

Treesearch

Methane production and bubble emissions from arctic lakes: isotopic implications for source pathways and ages

Informally Refereed

Authors:

K.M. Walter, J.P. Chanton, F.S. Chapin III, E.A.G. Schuur, S.A. Zimov

Year:

2008

Type:

Scientific Journal

Station:

Pacific Northwest Research Station

DOI:

https://doi.org/10.1029/207JG000569

Source:

Journal of Geophysical Research. 113: G00A08

Download (PDF 3.04 MB)

Download (PDF 3.04 MB): https://research.fs.usda.gov/download/treesearch/35103.pdf

Abstract

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 ¹³C_CH4, 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 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.

Keywords

methane production, bubble emissions, arctic lakes, isotopic, pathways, ages, greenhouse gas

Citation

Walter, K.M.; Chanton, J.P.; Chapin III, F.S.; Schuur, E.A.G.; Zimov, S.A. 2008. Methane production and bubble emissions from arctic lakes: isotopic implications for source pathways and ages. Journal of Geophysical Research.113: G00A08.