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Temporal Variations of the Mole Fraction, Carbon, and Hydrogen Isotope Ratios of Atmospheric Methane in the Hudson Bay Lowlands, Canada
Author(s) -
Fujita Ryo,
Morimoto Shinji,
Umezawa Taku,
Ishijima Kentaro,
Patra Prabir K.,
Worthy Douglas E. J.,
Goto Daisuke,
Aoki Shuji,
Nakazawa Takakiyo
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2017jd027972
Subject(s) - bay , arctic , atmospheric sciences , mole fraction , environmental science , methane , wetland , atmospheric methane , isotopes of carbon , carbon cycle , climatology , oceanography , environmental chemistry , greenhouse gas , total organic carbon , chemistry , geology , ecosystem , ecology , organic chemistry , biology
We have conducted simultaneous measurements of the mole fraction and carbon and hydrogen isotope ratios (δ 13 C and δD) of atmospheric methane (CH 4 ) at Churchill (58°44′N, 93°49′W) in the northern part of the Hudson Bay Lowlands (HBL), Canada, since 2007. Compared with the measurements at an Arctic baseline monitoring station, Ny‐Ålesund, Svalbard (78°55′N, 11°56′E), CH 4 mole fraction is generally higher and δ 13 C and δD are lower at Churchill due to regional biogenic CH 4 emissions. Clear seasonal cycles in the CH 4 mole fraction, δ 13 C, and δD are observable at Churchill, and their seasonal phases in summer are earlier by approximately 2 weeks than those at Ny‐Ålesund. Using the one‐box model analysis, the phase difference is ascribed to the different seasonal influence of CH 4 emissions from boreal wetlands on the two sites. Short‐term CH 4 variations are also observed at Churchill throughout the year. The analysis of the observed isotopic signatures of atmospheric CH 4 confirmed that the short‐term CH 4 variations are mainly produced by biogenic CH 4 released from the HBL wetlands in summer and by fossil fuel CH 4 transported over the Arctic in winter. Forward simulations of an atmospheric chemistry‐transport model, with wetland CH 4 fluxes prescribed by a process‐based model, show unrealistically high CH 4 mole fractions at Churchill in summer, suggesting that CH 4 emissions assigned to the HBL wetlands are overestimated. Our best estimate of the HBL CH 4 emissions is 2.7 ± 0.3 Tg CH 4 yr −1 as an average of 2007–2013, consistent with recent estimations by inverse modeling studies.