Large tundra methane burst during onset of freezing

• Published in: Nature Vol. 456; no. 7222; pp. 628 - 630
• Main Authors: Mastepanov, Mikhail, Sigsgaard, Charlotte, Dlugokencky, Edward J., Houweling, Sander, Ström, Lena, Tamstorf, Mikkel P., Christensen, Torben R.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.12.2008; Nature Publishing Group
• Subjects: air temperature; analysis; Animal, plant and microbial ecology; Applied ecology; Arctic Regions; Atmosphere; Atmosphere - chemistry; Atmospheric chemistry; Autumn; Biological and medical sciences; chemistry; Cold Climate; Distribution; Earth and Related Environmental Sciences; Ecotoxicology, biological effects of pollution; Emissions; Environmental aspects; Freezing; Fundamental and applied biological sciences. Psychology; gas emissions; Geovetenskap och miljövetenskap; Geovetenskap och relaterad miljövetenskap; Greenhouse gases; Greenland; Growing season; Humanities and Social Sciences; Latitude; letter; metabolism; Methane; Methane - analysis; Methane - metabolism; methane production; methanogens; Methods; multidisciplinary; Natural Sciences; Naturgeografi; Naturvetenskap; Permafrost; Physical Geography; Science; Seasonal distribution; Seasons; Soil; Soil - analysis; soil bacteria; soil temperature; Summer; Terrestrial ecosystems; Terrestrial environment, soil, air; Tundra; tundra soils; Tundras; Wetlands; Winter; Arctic Region; United States; Arctic; Europe; PN, Arctic; Greenland; Arctic regions; High latitude; Methane; Natural origin pollution; Warming; Refreezing; Gas emission; Permafrost; Aquatic environment; Ecosystem; Greenhouse gas; Air pollution; Polar region; Simulation model; Tundra; Wetland; Freeze
• ISSN: 0028-0836; 1476-4687; 1476-4687; 1476-4679
• DOI: 10.1038/nature07464

Permafrost methane: Arctic emissions revisited A late-autumn 'shoulder' is a regular feature of the seasonal cycles of atmospheric methane at high latitudes, but the sources of this burst of methane remain obscure. Mastepanov et al. now report methane flux measurements from a high Arctic setting during the onset of soil freezing. The total emissions during this freeze-in period are roughly equal to the amount of methane emitted during the entire summer season. Including the observed methane burst in an atmospheric chemistry and transport model improves agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 600N. These results suggest that permafrost-associated freeze-in bursts of methane from tundra regions may be an important, previously unrecognized component of the seasonal distribution of methane emissions at high latitudes. A late-autumn shoulder is consistently observed in the seasonal cycles of atmospheric methane at high latitude sites, but the sources responsible remain uncertain. This study reports methane flux measurements from a high Arctic setting during the onset of soil freezing. The integral of the emissions during this freeze-in period amount to approximately the same amount of methane emitted during the entire summer season. It is found that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60°N. The results suggest that permafrost associated freeze-in bursts of methane emissions from tundra regions could be an important component of the seasonal distribution of methane emissions from high latitudes. Terrestrial wetland emissions are the largest single source of the greenhouse gas methane 1 . Northern high-latitude wetlands contribute significantly to the overall methane emissions from wetlands, but the relative source distribution between tropical and high-latitude wetlands remains uncertain 2 , 3 . As a result, not all the observed spatial and seasonal patterns of atmospheric methane concentrations can be satisfactorily explained, particularly for high northern latitudes. For example, a late-autumn shoulder is consistently observed in the seasonal cycles of atmospheric methane at high-latitude sites 4 , but the sources responsible for these increased methane concentrations remain uncertain. Here we report a data set that extends hourly methane flux measurements from a high Arctic setting into the late autumn and early winter, during the onset of soil freezing. We find that emissions fall to a low steady level after the growing season but then increase significantly during the freeze-in period. The integral of emissions during the freeze-in period is approximately equal to the amount of methane emitted during the entire summer season. Three-dimensional atmospheric chemistry and transport model simulations of global atmospheric methane concentrations indicate that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60° N. Our findings suggest that permafrost-associated freeze-in bursts of methane emissions from tundra regions could be an important and so far unrecognized component of the seasonal distribution of methane emissions from high latitudes.