Journal
NATURE GEOSCIENCE
Volume 6, Issue 10, Pages 885-890Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NGEO1922
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Funding
- European Research Council
- Schweizerischer Nationalfonds
- Deutsche Forschungsgemeinschaft
- European Union's Seventh Framework programme [243908]
- Office of Polar Programs (OPP)
- Directorate For Geosciences [0944584] Funding Source: National Science Foundation
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During the last glacial cycle, greenhouse gas concentrations fluctuated on decadal and longer timescales. Concentrations of methane, as measured in polar ice cores, show a close connection with Northern Hemisphere temperature variability, but the contribution of the various methane sources and sinks to changes in concentration is still a matter of debate. Here we assess changes in methane cycling over the past 160,000 years by measurements of the carbon isotopic composition delta C-13 of methane in Antarctic ice cores from Dronning Maud Land and Vostok. We find that variations in the delta C-13 of methane are not generally correlated with changes in atmospheric methane concentration, but instead more closely correlated to atmospheric CO2 concentrations. We interpret this to reflect a climatic and CO2-related control on the isotopic signature of methane source material, such as ecosystem shifts in the seasonally inundated tropical wetlands that produce methane. In contrast, relatively stable delta C-13 values occurred during intervals of large changes in the atmospheric loading of methane. We suggest that most methane sources-most notably tropical wetlands-must have responded simultaneously to climate changes across these periods.
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