Abstract
Abstract. Airborne and ground-based measurements of methane (CH4), carbon dioxide (CO2) and boundary layer thermodynamics were recorded over the Fennoscandian landscape (67–69.5° N, 20–28° E) in July 2012 as part of the MAMM (Methane and other greenhouse gases in the Arctic: Measurements, process studies and Modelling) field campaign. Employing these airborne measurements and a simple boundary layer box model, net regional-scale (~ 100 km) fluxes were calculated to be 1.2 ± 0.5 mg CH4 h−1 m−2 and −350 ± 143 mg CO2 h−1 m−2. These airborne fluxes were found to be relatively consistent with seasonally averaged surface chamber (1.3 ± 1.0 mg CH4 h−1 m−2) and eddy covariance (1.3 ± 0.3 mg CH4 h−1 m−2 and −309 ± 306 mg CO2 h−1 m−2) flux measurements in the local area. The internal consistency of the aircraft-derived fluxes across a wide swath of Fennoscandia coupled with an excellent statistical comparison with local seasonally averaged ground-based measurements demonstrates the potential scalability of such localised measurements to regional-scale representativeness. Comparisons were also made to longer-term regional CH4 climatologies from the JULES (Joint UK Land Environment Simulator) and HYBRID8 land surface models within the area of the MAMM campaign. The average hourly emission flux output for the summer period (July–August) for the year 2012 was 0.084 mg CH4 h−1 m−2 (minimum 0.0 and maximum 0.21 mg CH4 h−1 m−2) for the JULES model and 0.088 mg CH4 h−1 m−2 (minimum 0.0008 and maximum 1.53 mg CH4 h−1 m−2) for HYBRID8. Based on these observations both models were found to significantly underestimate the CH4 emission flux in this region, which was linked to the under-prediction of the wetland extents generated by the models.
Highlights
Temperatures at high northern latitudes have been observed to be increasing at a rate of twice the global average over the past two decades (Forster and Ramaswamy, 2007)
With a mean planetary boundary layer (PBL) mole fraction of 89 ppb for carbon monoxide (CO) and 26 ppt for hydrogen cyanide (HCN), both species remained at mole fractions throughout the flight that are representative of a typical background for the summer at these latitudes (Vay et al, 2011; O’Shea et al, 2013a)
As part of the MAMM field project, airborne measurements of CH4 and CO2 were collected in the European Arctic in summer 2012
Summary
Temperatures at high northern latitudes have been observed to be increasing at a rate of twice the global average over the past two decades (Forster and Ramaswamy, 2007). It has been suggested that this rise will continue (Parmentier et al, 2013). This is likely to have significant consequences for natural greenhouse gas emissions in the region, which contain potentially large sources that are known to be highly sensitive to changes in temperature, such as the boreal wetlands and the reservoirs of carbon that are sequestered in permafrost and as methane hydrates (Smith et al, 2004; Zimov et al, 2006a, b; Ping et al, 2008). Palaeo-records indicate that strong positive feedbacks exist between climate and greenhouse gas emissions in the region, whereby warming causes enhanced emissions that in turn lead to further warming (Walter et al, 2007; Nisbet and Chappellaz, 2009). Recent studies have already reported newly identified or growing CH4 emissions from some of these carbon reservoirs (Westbrook et al, 2009; Shakhova et al, 2010; Kort et al, 2012; Anthony et al, 2012)
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