Methane efflux from bubbles suspended in ice‐covered lakes in Syowa Oasis, East Antarctica

Abstract

[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.

Modeling the impediment of methane ebullition bubbles by seasonal lake ice

“…In agreement with the findings of Sasaki et al (2009), we observed the opening of ebullition seeps throughout the thaw period, indicated by (1) open holes in ice at the locations of former ice-trapped bubbles, (2) rapid but short-lived (usually < 1 min, but occasionally > 10 min) streams of bubbles escaping from ice through puddles of water on the ice surface, and (3) the lack of gas escape from gas pockets in ice when punctured with an ice spear. We observed that seep sites with higher ebullition flux opened earlier, presumably due to thinner ice between encapsulated bubbles.…”

“…The fraction of CH 4 that escapes to the atmosphere from seasonally ice-covered lakes depends on these biogeochemical processes. Previously, Sasaki et al (2009) measured the CH 4 concentration of bubbles trapped within lake ice in Antarctica and used aerial imaging to estimate the total volume of gas trapped before the ice melts. Elsewhere, others have measured dissolved CH 4 concentrations beneath winter lake ice or the CH 4 diffusion rate following ice-off to estimate net springtime emissions (e.g., Michmerhuizen et al, 1996;Phelps et al, 1998;Smith and Lewis, 1992).…”

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

“…Sasaki et al, (2009Sasaki et al, ( , 2010 reported that approximately two-times larger flux from frozen bubbles (ebullition) in lake ice than diffusive methane flux during the open water season is released in Syowa Oasis, east Antarctica. Bastiviken et al, (2004) also reported that estimated total methane flux (ebullition + diffusion + storage) from all Swedish lakes (95,762) was 105 Gg CH 4 yr -1 and that the flux corresponded to 5~10% of total flux from wetlands.…”

Air‐lake exchange of methane during the open water season in Syowa Oasis, East Antarctica

“…One process is the exchange between air and the lake water surface caused by the chemical potential difference, and the other is direct efflux from bubbles suspended in lake ice early in the melting season. Sasaki et al [2009] estimated the flux of methane from ice bubbles in Syowa Oasis. Though another possible process was ebullition from unfrozen lakes, no bubbling was found, perhaps because of insufficient observations with a bubble trap.…”