Zusammenfassung
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.
