Measurements of carbon-14 of methane in Greenland ice: investigating methane sources during the Last Glacial Termination

We present the first measurements of 14C of methane (14CH4) in ancient glacial ice. 14CH4 should distinguish unambiguously between wetland and fossil (clathrate or other geologic CH4) contributions to abrupt atmospheric CH4 increases observed at times of rapid warming in Greenland ice cores. 1000-kg-sized ice samples, dating to the Younger Dryas - Preboreal (around 11,600 yr BP) and Oldest Dryas - Bølling (around 14,700 yr BP) abrupt climatic transitions, were obtained from an ablation site in West Greenland. Measured 14CH4 values (28 - 35 pMC) were higher than predicted under any scenario based on sample age. Sample 14CH4 appears to be elevated by in- situ CH4 production in the ice for some samples as well as by a second process that is likely direct cosmogenic production of 14CH4 molecules in the ice. 14C of CO and CO2 was measured to better understand these processes and corrections were applied to sample 14CH4. Although the corrected results have substantial uncertainties, they suggest that wetland sources were responsible for the majority of the Younger Dryas - Preboreal CH4 rise. The uncertainties in the corrected results for the Oldest Dryas - Bølling transition are too large to draw conclusions about 14CH4 changes during that transition. © 2008 American Geophysical Union

Keywords

Carbon 14, Methane, Greenhouse gases, Isotopes, Ice, Drill cores, Glaciers, Greenland, Arctic regions

Citation

Petrenko, V. V., Smith, A. M., Severinghaus, J. P., Brook, E. J., Lowe, D., Riedel, K., Brailsford, G., Hua, Q., Reeh, N., Schaefer, H., Weiss, R. F. & Etheridge, D. M. (2008). Measurements of carbon-14 of methane in Greenland ice: investigating methane sources during the Last Glacial Termination. Paper presented at the AGU Fall Meeting 2008, San Francisco, California, 15 to 19 December 2008. In Eos Transactions, AGU, 89(53), Fall Meeting Supplement, U34A-05. Retrieved from: https://abstractsearch.agu.org/meetings/2008/FM/U34A-05.html