Open AccessChanges in the global atmospheric methane budget over the last decades inferred from 13 C and D isotopic analysis of Antarctic firn air
Author(s) -
Bräunlich Maya,
Aballain Olivier,
Marik Thomas,
Jöckel Patrick,
Brenninkmeijer Carl A. M.,
Chappellaz Jerome,
Barnola JeanMarc,
Mulvaney Robert,
Sturges William T.
Publication year - 2001
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jd900190
Subject(s) - firn , methane , atmospheric methane , sink (geography) , atmospheric sciences , biomass burning , environmental science , mixing ratio , geology , chemistry , glacier , aerosol , meteorology , geomorphology , physics , geography , cartography , organic chemistry
The atmospheric trend of methane isotopic ratios since the mid‐20th century has been reconstructed from Antarctic firn air. High volume air samples were extracted at several depth levels at two sites in East Antarctica. Methane concentration and its 13 C/ 12 C and D/H ratios were determined by gas chromatography, mass spectrometry, and infrared spectroscopy. A firn air transport model was applied to reconstruct past atmospheric trends in methane and its isotopic composition. By subsequent application of an atmospheric model, changes in methane sources and OH sink compatible with the past atmospheric trends are explored. In step with increasing methane mixing ratios, δ 13 C increased by ∼1.7‰ over the last 50 years. These changes mainly reflect a shift in relative source strength toward the heavier anthropogenic methane source, such as biomass burning and methane of nonbiological origin. The δD (CH 4 ) showed a period of decline between the 1950s and 1975, followed by a gradual increase of 0.55‰/yr, also toward the heavier anthropogenic source. Dependent on possible changes in the OH sink, to which δD of methane is very sensitive, the inferred isotopic trends of δ 13 C and δD over the last 50 years constrain the relationship between natural and anthropogenic sources over the last century. The observed δD minimum around 1975 suggests that the slowing down in the methane source growth took place during this period.