Independent variations of CH₄ emissions and isotopic composition over the past 160,000 years

• Published in: Nature Geoscience
• Main Authors: Möller, Lars, Sowers, Todd, Bock, Michael, Spahni, Renato, Behrens, Melanie, Schmitt, Jochen, Miller, Heinrich, Fischer, Hubertus
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2013
• Subjects: 530 Physics; Antarctic; Dronning Maud Land; Antarc*
• Online Access: https://boris.unibe.ch/47732/1/ngeo1922.pdf; https://boris.unibe.ch/47732/

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.