Diffusive summer methane flux from lakes to the atmosphere in the Alaskan arctic zone

Abstract

Please cite this article as: Sasaki, M., Kim, Y.-W., Uchida, M., Utsumi, M., Diffusive summer methane flux from lakes to the atmosphere in the Alaskan arctic zone, Polar Science (2016), AbstractDissolved methane concentrations (DM) in thirty lakes along Dalton Highway were measured in the open water season in 2008 and in 2012 to estimate diffusive flux from lake surfaces and to verify the enhancive effect of thawing permafrost on flux in the Alaskan arctic zone. An inverse relationship between lake size and DM was obtained in lakes in the regions as was found for European boreal lakes. There was no evidence indicating an effect of thawing permafrost on DM in these lakes. DM in lakes in the taiga region, however, were higher than those in the tundra region. All lake images on a map larger than 0.001 km 2 were analyzed, and the area and number distributions were obtained in order to calculate regional mass fluxes of diffusive methane. The total area of all lakes (339,733) in the Alaskan Arctic zone (northern region from 64.00°N) is 25.5×10 3 km 2 . Regional summer diffusive flux of methane from lakes in the Alaskan arctic zone was estimated to be 22 Gg CH 4 yr -1 . Average diffusive flux density (per lake area) was 0.86 g CH 4 m -2 yr -1 , which is similar to that in European boreal lakes.

Studying boundary layer methane isotopy and vertical mixing processes at a rewetted peatland site by unmanned aircraft system

“…The depth was in the range of few cm. 15 The water samples taken on 5 September 2018 within a radius of 100 m revealed highly different CH 4 concentrations (see Table 1). The highest CH 4 concentration of around 4770 ppm was measured from the water sample Z-4 in one of the small remaining water areas with a depth less than 5 cm within the former polder.…”

“…This resulted in low wind speed below 4 m s −1 of north-easterly direction at the observation site, similar to the conditions on 23 May 2018. In the morning, until 05:30 15 UTC, around 30 min before the first flight, fog was observed, which was denser towards the East. Starting around 09:00, before flight 3, shallow convective cumulus clouds were present.…”

“…The recent increase has been proposed to be related to enhanced emissions from tropical wetlands associated with the extremely wet season in 2009 in the Amazon region (Dlugokencky et al, 2009;Chen et al, 2010). 15 For separating natural and anthropogenic emission, the methane isotopic signature δ 13 C ‰ is of particular interest: Biologically produced methane has a typical δ 13 C ratio of -70 to -55 ‰ Nisbet et al, 2016), methane from fossil fuels has a typical value of -55 to -25 ‰ ( Kirschke et al, 2013), and methane from fires has values of -25 to -13 ‰ (Kirschke et al, 2013;Nisbet et al, 2016). Further, smaller differences in the isotopic signature are observed for different geographic regions.…”

“…Known sources in northern latitudes are permafrost areas (Sachs et al, 2010;France et al, 2016;Sasaki et al, 2016;Kohnert et al, 2018), the Arctic ocean (Yu et al, 2015;Mau et al, 2017) and wetlands (Bellisario et al, 1999). Each source region has a 25 unique isotopic signature, and mixing of different air masses results in a linear combination of the corresponding δ 13 C signature .…”

“…To contribute to constraining the source and vertical mixing processes of methane at different locations, a quadrocopter borne 15 sampling system has been developed. The aim is in-situ air sampling for obtaining the vertical distribution of the methane isotopic ratio in the lower troposphere (up to 1 km) for subsequent laboratory analyses.…”