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Potential glacial‐interglacial changes in stable carbon isotope ratios of methane sources and sink fractionation
Author(s) -
Schaefer Hinrich,
Whiticar Michael J.
Publication year - 2008
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2006gb002889
Subject(s) - last glacial maximum , sink (geography) , atmospheric methane , fractionation , ice core , isotopes of carbon , environmental science , isotope fractionation , holocene , methane , interglacial , stable isotope ratio , environmental chemistry , glacial period , carbon cycle , wetland , radiocarbon dating , atmospheric sciences , greenhouse gas , chemistry , geology , climatology , oceanography , ecology , total organic carbon , paleontology , ecosystem , biology , quantum mechanics , physics , cartography , organic chemistry , geography
Past atmospheric methane emissions can be constrained by δ 13 CH 4 records from ice cores only if changes to source δ 13 CH 4 signatures and sink isotope effects with varying environmental and climatic conditions are accurately known. We present reconstructions of such changes based on paleodata and recent systems observations. The results are specific for budget scenarios and are reported here for two alternative types of budgets, one including aerobic methane emissions (AMP) from plants and the other type without AMP. Shifting atmospheric δ 13 CO 2 potentially led to 13 CH 4 enrichment by 0.8‰ in the preindustrial Holocene (PIH) (∼150–11,000 years (a) B.P.) and ∼0.3–0.6‰ at the Last Glacial Maximum (LGM) (∼18,000 a B.P.) relative to today. Differing distribution of C 3 and C 4 plant precursor material may account for 13 CH 4 enrichment of ∼0.4‰ (PIH) and ∼0.6–1.1‰ (LGM). Temperature‐dependent fractionation and varying methanogenic pathways in wetlands may lead to atmospheric 13 CH 4 depletion by ∼0.1–1.2‰. Sink fractionation today (7.4‰) is higher than during the PIH (∼7.0‰) and the LGM (∼5.7‰). The cumulative effect of all processes is ∼0.8‰ 13 CH 4 enrichment in the PIH and ∼1–1.2‰ 13 CH 4 depletion at the LGM. Budget reconstructions will be inaccurate if these changes are not included.