Methane emission bursts from permafrost environments during autumn freeze‐in: New insights from ground‐penetrating radar

Abstract

Large amounts of methane (CH4) are known to be emitted from permafrost environments during the autumn freeze‐in, but the specific soil conditions leading up to these bursts are unclear. Therefore, we used an ultrawide band ground‐penetrating radar in Northeast Greenland in autumn 2009 to estimate the volumetric composition inside the soil through dielectric characterization from 200 to 3200 MHz. Our results suggest a compression of the gas reservoir during the phase transition of soil water, which is accompanied by a peak in surface CH4 emissions. About 1 week thereafter, there seems to be a decompression event, consistent with ground cracking which allows the gas reservoir to expand again. This coincides with the largest CH4 emission, exceeding the summer maximum by a factor of 4. We argue that these complementary measurement techniques are needed to come to an understanding of tundra CH4 bursts connected to soil freezing.

Toward a statistical description of methane emissions from arctic wetlands

“…4d), which bears a resemblance to component B because of its large width. This site features no permafrost, so despite the seasonal ground freezing, the physical mechanisms proposed to lie behind the autumn CH 4 burst cannot be at work (Mastepanov et al 2008, 2013; Pirk et al 2015). However, we cannot fully exclude the presence of this flux component at Kobbefjord, because our measurements never continued long enough into the freeze-in period (November–December).…”

“…The Zackenberg site featured two clearly distinct flux components during the growing season, which responded differently to the timing of snowmelt, as expected from the bi-component hypothesis. Zackenberg and Adventdalen showed a third component during the autumnal freeze-in period, which is presumably caused by physical mechanisms in permafrost regions (Pirk et al 2015). The absence of such large CH 4 autumn bursts at Kobbefjord, where seasonal ground freezing without permafrost occurs, remains to be investigated in future studies with measurements covering this period.…”

“…Mastepanov et al (2013) additionally reported a third component at the Zackenberg site during the autumnal freeze-in period. This final component is, however, most likely related to physical releases of stored gases in the soil rather than instantaneous methane production (Mastepanov et al 2008; Pirk et al 2015). …”

Snowpack fluxes of methane and carbon dioxide from high Arctic tundra

“…Accordingly, we refer to the time from the end of the autumnal active layer freeze‐in to the beginning of ground thawing after snowmelt as the cold season (typically November–May for high Arctic sites). The autumnal freeze‐in can feature sudden emission bursts, which have been suggested to be related to the physical release of stored gases through frost‐induced ground fissures [ Mastepanov et al , , ; Pirk et al , ]. Once the active layer is completely frozen, the photosynthetic carbon assimilation typically ceases, and microbial activity decreases to very small rates compared to the growing season [ Björkman et al , ].…”

A synthesis of the arctic terrestrial and marine carbon cycles under pressure from a dwindling cryosphere

“…At this site, a large peak in emissions was observed during the freeze-in period, likely related to the formation of ice in the ground that lowers the pore space and raises pressure, which causes gases to be squeezed out of the ground (Pirk et al 2015). Similar large peaks of methane have since been observed in Adventdalen, Svalbard (Pirk et al 2017) and in Alaska (Zona et al 2016), showing that the winter season is a dynamic period that has to be included in observations to accurately assess annual methane budgets.…”