[1] This is the first estimation of methane efflux from bubbles in lake ice in Antarctica. Bubbles suspended in shallow ice in 20 lakes were observed as part of the operations of the 45th Japanese Antarctic Research Expedition in ice-free rocky areas along the eastern coast of Lützow-Holm Bay (Syowa Oasis) in East Antarctica in 2004. Anomalous methane concentrations in bubbles suspended in lake ice and anomalous dissolved methane concentrations in lake water were frequently found. Methane concentrations in bubbles varied of 5 orders of magnitude, from 1.9 ppmv to 18% vol/vol. A procedure that makes estimations of methane flux from ice bubbles possible has been developed, on the basis of a relationship between bubble-density distribution, brightness observed by digital photographs, and methane concentration in bubbles. Such a procedure applied to Lake Oyako Ike in the Skarvsnes area, where the maximum methane concentration was observed, suggests that total bubble volume is about 0.6% of ice volume and the mass of methane in bubbles in the lake is about 74 kg. Almost all gases in bubbles are released to the atmosphere in the early ice melt season (a period of a few weeks in December and January). By applying area fraction frequency distributions to methane concentration ranges for 20 lakes surveyed, extrapolation to the whole Syowa Oasis, including 110 lakes, would give a provisional estimate of total emission of about 2 tons-CH 4 /yr.
Three low NOx combustors, i.e. a lean premixing combustor, a rich-lean two stage combustor and a lean diffusion flame combustor, were tested in order to find out a suitable combustion concept for an automotive ceramic gas turbine combustor. The prevaporization-premixing lean combustion was proposed as the most promising candidate to meet Japanese 10 mode regulation for gasoline passenger car.
The required conditions for the uniform premixture formation in the prevaporization-premixing tube were achieved by a fine droplet size atomizer and by means of swirl and turbulent generator. Air ratio range, air loading and other dimension criteria in the lean primary combustion zone were also proposed in the present paper.
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.
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