[A-CG50] 海洋表層－大気間の生物地球化学

[ACG50-P02] Methane concentration of late summer brash sea ice in the Pacific Sector of the Arctic Ocean

武田 龍栄¹、*野村 大樹¹、亀山 宗彦¹、戸澤 愛美¹、秋野 僚太¹、塩崎 拓平²、角皆 潤³、八田 真理子⁴、村田 昌彦⁴、藤原 周⁴ (1.北海道大学、2.東京大学、3.名古屋大学、4.JAMSTEC)

キーワード：メタン、海氷、北極海

To understand the factors controlling the methane concentration of late summer Arctic brash ice in the Chukchi Sea, we collected sea-ice samples during 2021 by a wire mesh pallet cage from the side of the R/V Mirai. Each sea-ice sample was then melted in a gas-tight plastic bag under dark, cool conditions (+4°C). We measured physical and biogeochemical parameters such as salinity, oxygen stable isotopic ratios, turbidity, microbial community structure by 16S rRNA gene analysis, and concentrations of chlorophyll-a and nutrients in addition to methane concentration and its stable carbon isotopic ratios. The samples of brash ice were multiyear ice based on satellite back-trajectory analysis. Methane concentrations for sea ice ranged from 0.9 to 94.4 nmol L^–1 (mean ± standard deviation: 19.1 ± 19.9 nmol L^–1), which was generally higher concentration than those of surface water during the observation period (14.2 ± 4.3 nmol L^–1). The ice sampled collected during our study was multiyear ice. Therefore, organic matter decomposition was progressed and created internal anaerobic environment in sea ice. The increase in methane concentration in this sea ice would be due to anaerobic decomposition of organic matter by microorganisms. We plan to identify the cause by comparing and analyzing the results of 16S rRNA gene analysis of bacteria in sea ice and methane stable carbon isotopic ratios. We will also evaluate the impact of sea ice melting on methane concentrations in the surface ocean.