Japan Geoscience Union Meeting 2015

Presentation information


Symbol A (Atmospheric and Hydrospheric Sciences) » A-AS Atmospheric Sciences, Meteorology & Atmospheric Environment

[A-AS21] Atmospheric Chemistry

Thu. May 28, 2015 11:00 AM - 12:45 PM 201B (2F)

Convener:*Yousuke Sawa(Oceanography and Geochemistry Research Department, Meteorological Research Institute), Nobuyuki Takegawa(Graduate School of Science and Engineering, Tokyo Metropolitan University), Yugo Kanaya(Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology), Kenshi Takahashi(Research Institute for Sustainable Humanosphere, Kyoto University), Hiroshi Tanimoto(National Institute for Environmental Studies), Chair:Motoki Sasakawa(National Institute for Environmental Studies)

11:30 AM - 11:45 AM

[AAS21-15] Variations of atmospheric methane concentration and its carbon and hydrogen isotopic ratios at Churchill, Canada

*Ryo FUJITA1, Shinji MORIMOTO1, Taku UMEZAWA2, Worthy Doug3, Shuji AOKI1, Takakiyo NAKAZAWA1 (1.Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, 2.National Institute for Environmental Studies, 3.Environment Canada)

Keywords:methane, carbon and hydrogen isotopic ratios, Hudson Bay Lowland, wetlands

Methane (CH4) is the second most important anthropogenic greenhouse gas after CO2. High-precision measurements of carbon and hydrogen stable isotopic ratios of CH413CH4 and δD-CH4) provide additional constrains to contributions of individual CH4 sources to atmospheric CH4 variations. Since 2007, we have conducted an air-sampling program at Churchill, Canada (58.44’N, 93.50’W) on the northern perimeter of the Hudson Bay Lowland, the second largest wetland area in the world i.e. one of the most important CH4 source regions at northern high latitudes. In this study, we present temporal variations of CH4, δ13CH4 and δD-CH4 at this site.
We observed long-term increase in the CH4 concentrations at Churchill since 2007, which is consistent with the trend reported by the global observation networks such as NOAA/ESRL/GMD. The CH4 concentration at Churchill is generally higher than that at Ny-Ålesund (78.55’N, 11.56’E), a northern high-latitude background station away from regional CH4 sources. On the other hand, δ13CH4 and δD-CH4 at Churchill are lower than those at Ny-Ålesund, plausibly reflecting regional CH4 emissions. Clear seasonal cycles of the CH4 concentration and δ13CH4 were observed; seasonal maximum and minimum of the CH4 concentration take place in January-February and June-July, respectively, while those of δ13CH4 were in May and October, respectively. Seasonal cycles of δD-CH4 were obscure but observable. The seasonal phases of these variables were up to one month earlier than those at Ny-Ålesund. The cause of the difference could be attributable to wetland emissions in the surrounding region. Short-term variations of the CH4 concentration were observed year around, but pronounced in summer. By inspecting relationships between the CH4 concentration and the isotopic ratios, we found that the predominant CH4 source of the short-term CH4 variations is wetlands in summer but fossil fuels in winter.