Revisiting factors controlling methane emissions from high-Arctic tundra

• Published in: Biogeosciences
• Main Authors: Mastepanov, M., Sigsgaard, C., Tagesson, T., Strom, L., Tamstorf, M. P., Lund, M., Christensen, T. R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: TRACE GAS-EXCHANGE; VASCULAR PLANTS; ATMOSPHERIC METHANE; NORTHERN MINNESOTA; POLYGONAL TUNDRA; CARBON TURNOVER; WATER-TABLE; SOIL; PEATLANDS; WETLANDS; Arctic; Greenland; Tundra; Zackenberg
• Online Access: https://pure.au.dk/portal/en/publications/de3d8e72-fed3-47c5-85f7-0bdcd443f298; https://doi.org/10.5194/bg-10-5139-2013; https://pure.au.dk/ws/files/124267467/bg_10_5139_2013.pdf

The northern latitudes are experiencing disproportionate warming relative to the mid-latitudes, and there is growing concern about feedbacks between this warming and methane production and release from high-latitude soils. Studies of methane emissions carried out in the Arctic, particularly those with measurements made outside the growing season, are underrepresented in the literature. Here we present results of 5 yr (2006-2010) of automatic chamber measurements at a high-Arctic location in Zackenberg, NE Greenland, covering both the growing seasons and two months of the following freeze-in periods. The measurements show clear seasonal dynamics in methane emission. The start of the growing season and the increase in CH4 fluxes were strongly related to the date of snowmelt. Within each particular growing season, CH4 fluxes were highly correlated with the soil temperature (R-2 > 0.75), which is probably explained by high seasonality of both variables, and weakly correlated with the water table. The greatest variability in fluxes between the study years was observed during the first part of the growing season. Somewhat surprisingly, this variability could not be explained by commonly known factors controlling methane emission, i.e. temperature and water table position. Late in the growing season CH4 emissions were found to be very similar between the study years (except the extremely dry 2010) despite large differences in climatic factors (temperature and water table). Late-season bursts of CH4 coinciding with soil freezing in the autumn were observed during at least three years. The cumulative emission during the freeze-in CH4 bursts was comparable in size with the growing season emission for the year 2007, and about one third of the growing season emissions for the years 2009 and 2010. In all three cases the CH4 burst was accompanied by a corresponding episodic increase in CO2 emission, which can compose a significant contribution to the annual CO2 flux budget. The most probable mechanism of the late-season ...