title: Cold season emissions dominate the Arctic tundra methane budget.
abstract: Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for ≥ 50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 °C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 ± 5 (95% confidence interval) Tg CH4 y(-1), ∼ 25% of global emissions from extratropical wetlands, or ∼ 6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182; Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom; dzona@mail.sdsu.edu.
authors.forename: Donatella
authors.initials: D
authors.lastname: Zona
authors.affiliation: Institute of Biometeorology, National Research Council, Firenze, 50145, Italy;
authors.forename: Beniamino
authors.initials: B
authors.lastname: Gioli
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138;
authors.forename: Róisín
authors.identifier: http://orcid.org/0000-0003-1373-1550
authors.initials: R
authors.lastname: Commane
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138;
authors.forename: Jakob
authors.initials: J
authors.lastname: Lindaas
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138;
authors.forename: Steven C
authors.initials: SC
authors.lastname: Wofsy
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099;
authors.forename: Charles E
authors.initials: CE
authors.lastname: Miller
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099;
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Dinardo
authors.affiliation: Department of Physics, University of Helsinki, FI-00014 Helsinki, Finland;
authors.forename: Sigrid
authors.initials: S
authors.lastname: Dengel
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80304; Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305;
authors.forename: Colm
authors.initials: C
authors.lastname: Sweeney
authors.affiliation: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80304;
authors.forename: Anna
authors.initials: A
authors.lastname: Karion
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4R2;
authors.forename: Rachel Y-W
authors.initials: RY
authors.lastname: Chang
authors.affiliation: Atmospheric and Environmental Research, Inc., Lexington, MA 02421;
authors.forename: John M
authors.initials: JM
authors.lastname: Henderson
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182;
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Murphy
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182;
authors.forename: Jordan P
authors.initials: JP
authors.lastname: Goodrich
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182;
authors.forename: Virginie
authors.initials: V
authors.lastname: Moreaux
authors.affiliation: Water and Environmental Research Center, University of Alaska Fairbanks, Fairbanks, AK 99775-7340; International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK 99775-7340;
authors.forename: Anna
authors.initials: A
authors.lastname: Liljedahl
authors.affiliation: Numerical Terradynamic Simulation Group, College of Forestry & Conservation, The University of Montana, Missoula, MT 59812;
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Watts
authors.affiliation: Numerical Terradynamic Simulation Group, College of Forestry & Conservation, The University of Montana, Missoula, MT 59812;
authors.forename: John S
authors.initials: JS
authors.lastname: Kimball
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182;
authors.forename: David A
authors.initials: DA
authors.lastname: Lipson
authors.affiliation: Department of Biology, San Diego State University, San Diego, CA 92182; Department of Earth, Environment and Ecosystems, Open University, Milton Keynes, MK7 6AA, United Kingdom.
authors.forename: Walter C
authors.initials: WC
authors.lastname: Oechel
mesh_terms: D001110:Arctic Regions; D003080:Cold Temperature; D004784:Environmental Monitoring; D008697:Methane / Q000032:analysis*; D008962:Models, Theoretical; D012621:Seasons; D012987:Soil; D065929:Tundra; D053833:Wetlands
chemical_list: D012987:Soil; D008697:Methane
keywords: aircraft; fall; permafrost; warming; winter