Large uncertainties in the budget of atmospheric methane, an important greenhouse gas, limit the accuracy of climate change projections1,2. Thaw lakes in North Siberia are known to emit methane3, but the magnitude of these emissions remains uncertain because most methane is released through ebullition (bubbling), which is spatially and temporally variable. Here we report a new method of measuring ebullition and use it to quantify methane emissions from two thaw lakes in North Siberia. We show that ebullition accounts for 95 per cent of methane emissions from these lakes, and that methane flux from thaw lakes in our study region may be five times higher than previously estimated3. Extrapolation of these fluxes indicates that thaw lakes in North Siberia emit 3.8 teragrams of methane per year, which increases present estimates of methane emissions from northern wetlands (< 6–40 teragrams per year; refs 1, 2, 4–6) by between 10 and 63 per cent. We find that thawing permafrost along lake margins accounts for most of the methane released from the lakes, and estimate that an expansion of thaw lakes between 1974 and 2000, which was concurrent with regional warming, increased methane emissions in our study region by 58 per cent. Furthermore, the Pleistocene age (35,260–42,900 years) of methane emitted from hotspots along thawing lake margins indicates that this positive feedback to climate warming has led to the release of old carbon stocks previously stored in permafrost.
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We thank S. P. Davidov and D. A. Draluk for contributions to the research; D. Nidzgorski and E. Carr for field assistance; the Northeast Science Station for logistic support; K. Dutta, T. Schuur and the University of Florida for helping to prepare the radiocarbon targets; S. Marchenko and V. Romanovskii for assistance in analysing Cherskii climate records; and E. Dlugokencky, J. Hobbie, T. Schuur, D. Valentine, and M. S. Bret-Harte for constructive reviews. Research funding was provided by the National Science Foundation through the Russian-American Initiative on Shelf-Land Environments of the Arctic (RAISE) of the Arctic System Science programme (ARCSS) and Polar Programs, the Environmental Protection Agency STAR Fellowship programme, and the NASA Earth System Science Fellowship programme.Author Contributions K.M.W. was the primary investigator in this study, responsible for study design, field work, laboratory measurements, GIS and isotope analyses, data analysis, interpretation and writing. S.A.Z. and F.S.C. contributed to project planning, experimental work, and interpretation of results. J.P.C. assisted with isotope analyses and interpretation. D.V. contributed to the study design and interpretation of the GIS analysis of lake area change. All co-authors provided constructive comments on the manuscript.
This file contains supplementary figures 1–4 and legends, Supplementary Methods, Supplementary equations, Supplementary Tables 1 and 2, and 1 supplementary reference.