Water and Environmental Research Center
Seminars
2 October 2009
Determining C and H sources to CH4 production using stable isotopes and radiocarbon ages.
Laura Brosius
Shelby Bakkan and Laura Brosius auger through 1.5m thick ice in order to install a methane bubble trap
Abstract
Methane production in Siberian thaw lakes is estimated to be 3.8 Tg CH4 per year. When entered into global models, this estimate increases northern wetland CH4 emissions <6-40 Tg CH4 per year) by 10-63% (Walter et al 2006). Methane release of this magnitude from Siberian and other northern lakes, such as those in Alaska, may be linked to the rich carbon resources available to sediment-dwelling methanogens. Researchers posit that methanogens in upper-latitude thermokarst lakes utilize high-quality carbon (C) stocks made available by thaw of permafrost beneath and around the margins of lakes (Walter et al 2006, 2008). The potential for enhanced availability of this C as a result of projected climate warming and associated permafrost thaw makes C source contributions to methane production important to understand. Based on the 14C radiocarbon ages and stable isotope composition of emitted CH4, we suggest that thawed permafrost, made recently bioavailable through the deepening of taliks and/or by thermokarst erosion and deposition of shoreline, C to anaerobic sediments and drives CH4 production in some interior Alaska thermokarst lakes. We further propose that methanogens utilizing permafrost C also utilize pore water derived from melted permafrost ice as a hydrogen (H) source.