Disproportional contribution of geological sources to Mackenzie Delta methane emissions revealed from airborne eddy-covariance measurements

Jorg.Hartmann [ at ] awi.de


Arctic wetlands associated with permafrost as well as thawing permafrost emit the greenhouse gas methane (CH4). Two important contributors are recent microbial activity in the active layer or taliks (biogenic CH4), and deeper fossil sources where pathways through the permafrost exist (geologic CH4). Current emission estimates vary strongly between different models. Moreover, there is still disagreement between bottom-up estimates from local field studies, and topdown estimates from atmospheric measurements. Here, we quantify permafrost CH4 emissions directly on the regional scale, based on the Airborne Measurements of Methane Fluxes Campaigns (AIRMETH) in the Mackenzie River Delta region, Canada, in July 2012 and 2013 [Kohnert et al., 2014]. The Mackenzie Delta is the second largest Arctic delta (13,000 km2). Our measurements covered an area extending 320 km from west to east (140°58’W to 133°22’W) and of 240 km from north to south (69°33’N to 67°26’N). The study area comprises the delta itself, the adjacent Yukon coastal plain, and Richards Island north east of the delta. The area surrounding the delta is described as continuous permafrost zone where the permafrost reaches a thickness of 300 m along the coastal plain and 500 m on Richards Island. In the delta itself the discontinuous permafrost reaches a maximum thickness of 100 m. The northern part of the study area is crossed by geological faults and underlain by oil and natural gas deposits. We analyse the regional pattern of CH4 fluxes and estimate the contribution of geologic emissions to the total CH4 budget of the delta. CH4 fluxes were calculated with a time-frequency resolved version of the eddy-covariance technique [Metzger et al., 2013], followed by the calculation of flux topographies [Mauder et al., 2008]. The result is a 100 m resolved gridded flux map within the footprints of the flight tracks. The results provide the first regional estimate of CH4 release from the Mackenzie Delta and the adjacent coastal plain. We distinguish geological gas seeps from biogenic sources by their strength, and show that geologic sources contribute strongly to the annual CH4 budget of the study area: One percent of the covered area contains the strongest geological seeps which contribute disproportionately to an annual emission estimate. The contribution of geological sources to CH4 emission warrants further attention, in particular in areas where permafrost is vulnerable to increased geologic gas migration due to thawing and opening of new pathways. The presented map can be used as a baseline for future CH4 flux studies in the Mackenzie Delta. References Kohnert, K.; Serafimovich, A.; Hartmann, J. and Sachs, T. [2014]: Airborne measurements of methane fluxes in alaskan and canadian tundra with the research aircraft “polar 5”. In Reports on Polar and Marine Research, volume 673. Alfred Wegener Institue Bremerhaven, pp. 81. Mauder, M.; Desjardins, R.L. and MacPherson, I. [2008]: Creating surface flux maps from airborne measurements: Application to the Mackenzie area GEWEX study MAGS 1999. Boundary-Layer Meteorology, 129:431–450, 2008. Metzger, S.; Junkermann, W.; Mauder, M.; Butterbach-Bahl, K.; Trancón y Widemann, B.; Neidl, F.; Schäfer, K.; Wieneke, S.; Zheng, X. H.; Schmid, H. P. and Foken, T. [2013]: Spatially explicit regionalization of airborne flux measurements using environmental response functions. Biogeosciences, 10(4):2193–2217, 2013. doi:10.5194/bg-10-2193-2013.

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International Converence on Permafrost, 20 Jun 2016 - 24 Jun 2016, Potsdam.
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Kohnert, K. , Serafimovic, A. , Metzger, S. , Hartmann, J. and Sachs, T. (2016): Disproportional contribution of geological sources to Mackenzie Delta methane emissions revealed from airborne eddy-covariance measurements , International Converence on Permafrost, Potsdam, 20 June 2016 - 24 June 2016 .

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