Arctic regional methane fluxes by ecotope as derived using eddy covariance from a low-flying aircraft

摘要

The Arctic terrestrial and sub-sea permafrost region containsapproximately 30 % of the global carbon stock, and therefore understandingArctic methane emissions and how they might change with a changing climate isimportant for quantifying the global methane budget and understanding itsgrowth in the atmosphere. Here we present measurements from a new in situflux observation system designed for use on a small, low-flying aircraft thatwas deployed over the North Slope of Alaska during August 2013. The systemcombines a small methane instrument based on integrated cavity outputspectroscopy (ICOS) with an air turbulence probe to calculate methane fluxesbased on eddy covariance. We group surface fluxes by land class using a mapbased on LandSat Thematic Mapper (TM) data with 30 m resolution. We findthat wet sedge areas dominate the methane fluxes with a mean flux of2.1 µg m s during the first part of August. Methane emissions from the Sagavanirktok River have the second highest atalmost 1 µg m s. During the second half of August,after soil temperatures had cooled by 7 °C, methane emissionsfell to between 0 and 0.5 µg m s for all areasmeasured. We compare the aircraft measurements with an eddy covariance fluxtower located in a wet sedge area and show that the two measurements agreequantitatively when the footprints of both overlap. However, fluxes fromsedge vary at times by a factor of 2 or more even within a few kilometersof the tower demonstrating the importance of making regional measurements tomap out methane emissions spatial heterogeneity. Aircraft measurements ofsurface flux can play an important role in bridging the gap betweenground-based measurements and regional measurements from remote sensinginstruments and models.