16:45 〜 17:00
[ACG46-06] Dynamics of dissolved methane and its biogeochemical controlling factors in the Arctic Ocean
キーワード：メタン、北極海、地球温暖化
Methane is the second most important greenhouse gas in the atmosphere after carbon dioxide. Atmospheric methane levels have risen dramatically, and global warming has become one of the major environmental issues facing the world today. As the most sensitive region to global warming, the Arctic atmospheric temperature has increased by more than 3°C since the industrial era, twice the global average warming rate (Milner et al., 2007). Especially, continental shelves contain huge amounts of methane, which significantly contributed to the Arctic climate change processes (Shakhova et al., 2010).
Samples and data for the research were from R/V Mirai cruises (MR20-05C and MR21-05C) and IBRV Araon 2016 cruise. The samples were mainly analyzed by the GC-FID, using the headspace method (Magenl et al., 2014) to measure the methane concentration. Additionally, some samples were analyzed by the GC-IRMS (Hirota et al., 2010), which allowed to quantify the methane concentration as well as to determine the stable carbon isotope ratios.
The results show that methane concentrations in the Arctic Ocean water range from 0.18–58.9 nmol L−1, with an average of 14.98 nmol L−1. Most surface water were oversaturated with methane compared to the atmosphere, which indicates that this region is an active source of methane. In the continental shelf region, methane concentration increases gradually from the surface to the bottom, while the maximum nutrient concentrations were also detected in the bottom layer. Significant correlations between methane and phosphate, silicate, or nitrate suggest that methane production may be related to the degradation of organic matter in the sediment, suggesting a biological source. This was also supported by the lower carbon stable isotope ratios and higher concentrations of methane in the region. In the slope and basin regions, high methane concentrations were observed near the pycnocline. This spatial heterogeneity in methane distribution was likely originated from the shelf sediments. Methane was trapped within the pycnocline of the Bering Sea Water and transported into these regions.
An on-board methane culture experiment was conducted to study the production and consumption of methane in seawater. The results suggested that methane was not always oxidized in surface seawater but might also be produced. Perhaps the lids made of butyl rubber may have a negative effect on the activity of biological methane oxidation.
Samples and data for the research were from R/V Mirai cruises (MR20-05C and MR21-05C) and IBRV Araon 2016 cruise. The samples were mainly analyzed by the GC-FID, using the headspace method (Magenl et al., 2014) to measure the methane concentration. Additionally, some samples were analyzed by the GC-IRMS (Hirota et al., 2010), which allowed to quantify the methane concentration as well as to determine the stable carbon isotope ratios.
The results show that methane concentrations in the Arctic Ocean water range from 0.18–58.9 nmol L−1, with an average of 14.98 nmol L−1. Most surface water were oversaturated with methane compared to the atmosphere, which indicates that this region is an active source of methane. In the continental shelf region, methane concentration increases gradually from the surface to the bottom, while the maximum nutrient concentrations were also detected in the bottom layer. Significant correlations between methane and phosphate, silicate, or nitrate suggest that methane production may be related to the degradation of organic matter in the sediment, suggesting a biological source. This was also supported by the lower carbon stable isotope ratios and higher concentrations of methane in the region. In the slope and basin regions, high methane concentrations were observed near the pycnocline. This spatial heterogeneity in methane distribution was likely originated from the shelf sediments. Methane was trapped within the pycnocline of the Bering Sea Water and transported into these regions.
An on-board methane culture experiment was conducted to study the production and consumption of methane in seawater. The results suggested that methane was not always oxidized in surface seawater but might also be produced. Perhaps the lids made of butyl rubber may have a negative effect on the activity of biological methane oxidation.