学術雑誌論文 Methane excess production in oxygen-rich polar water and a model of cellular conditions for this paradox

9 ( 3 )  , pp.327 - 334 , 2015-09
ISSN:1873-9652
内容記述
Summer sea ice cover in the Arctic Ocean has undergone a reduction in the last decade exposing the sea surface to unforeseen environmental changes. Melting sea ice increases water stratification and induces nutrient limitation, which is also known to play a crucial role in methane formation in oxygenated surface water. We report on an excess of methane in the marginal ice zone in the western Fram Strait. Our study is based on measurements of oxygen, methane, DMSP, nitrate and phosphate concentrations as well as on phytoplankton composition and light transmission, conducted along the 79°N oceanographic transect, in the western part of the Fram Strait and in Northeast Water Polynya region off Greenland. Between the eastern Fram Strait, where Atlantic water enters from the south and the western Fram Strait, where Polar water enters from the north, different nutrient limitations occurred and consequently different bloom conditions were established. Ongoing sea ice melting enhances the environmental differences between both water masses and initiates regenerated production in the western Fram Strait. We show that in this region methane is in situ produced while DMSP (dimethylsulfoniopropionate) released from sea ice may serve as a precursor for the methane formation. The methane production occured despite high oxygen concentrations in this water masses. As the metabolic activity (respiration) of unicellular organisms explains the presence of anaerobic conditions in the cellular environment we present a theoretical model which explains the maintenance of anaerobic conditions for methane formation inside bacterial cells, despite enhanced oxygen concentrations in the environment.
近年の温暖化に伴う北極域の海氷減少は、海洋の成層化を強め、栄養塩の制限をもたらし、ひいては酸化した表面水からのメタン生成に重要な役割を果たす。フラム海峡西部の氷縁域での過剰なメタンについて報告する。フラム海峡西部とノースイースト・ウォーター・ポリニヤを含む79°N線の断面で、酸素、メタン、DMSP、硝酸塩、リン酸塩の濃度と植物プランクトン組成、光透過について測定した。その結果、メタンはその場で生成されていること、海氷から放出されるDMSPはメタン生成の前駆物質になっていること、酸素濃度が高いのにもかかわらず、メタン生成が起こっていることなどを明らかにした。これらの観測結果を基に、酸素濃度が高いのにも関わらずバクテリアの細胞内でメタン生成が行われる嫌気性の条件が維持されることを説明するモデルを提唱した。

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