Methane sources in arctic thermokarst lake sediments on the North Slope of Alaska

• Published in: Geobiology
• Main Authors: Matheus Carnevali, P. B., Rohrssen, M., Williams, M. R., Michaud, A. B., Adams, H., Berisford, D., Love, G. D., Priscu, J. C., Rassuchine, O., Hand, K. P., Murray, A. E.
• Other Authors: NSF IGERT Program in Geobiological Systems, NASA Astrobiology Institute, Astrobiology of Icy Worlds, NASA Astrobiology Science and Technology for Exploring Planets (ASTEP)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: north slope; permafrost; Thermokarst; Alaska
• Online Access: http://dx.doi.org/10.1111/gbi.12124; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fgbi.12124; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gbi.12124

Abstract The permafrost on the N orth S lope of A laska is densely populated by shallow lakes that result from thermokarst erosion. These lakes release methane ( CH 4 ) derived from a combination of ancient thermogenic pools and contemporary biogenic production. Despite the potential importance of CH 4 as a greenhouse gas, the contribution of biogenic CH 4 production in arctic thermokarst lakes in A laska is not currently well understood. To further advance our knowledge of CH 4 dynamics in these lakes, we focused our study on (i) the potential for microbial CH 4 production in lake sediments, (ii) the role of sediment geochemistry in controlling biogenic CH 4 production, and (iii) the temperature dependence of this process. Sediment cores were collected from one site in S iqlukaq L ake and two sites in S ukok L ake in late O ctober to early N ovember. Analyses of pore water geochemistry, sedimentary organic matter and lipid biomarkers, stable carbon isotopes, results from CH 4 production experiments, and copy number of a methanogenic pathway‐specific gene ( mcrA ) indicated the existence of different sources of CH 4 in each of the lakes chosen for the study. Analysis of this integrated data set revealed that there is biological CH 4 production in S iqlukaq at moderate levels, while the very low levels of CH 4 detected in S ukok had a mixed origin, with little to no biological CH 4 production. Furthermore, methanogenic archaea exhibited temperature‐dependent use of in situ substrates for methanogenesis, and the amount of CH 4 produced was directly related to the amount of labile organic matter in the sediments. This study constitutes an important first step in better understanding the actual contribution of biogenic CH 4 from thermokarst lakes on the coastal plain of A laska to the current CH 4 budgets.