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Science 24 April 2009:
Vol. 324. no. 5926, pp. 506 - 508
DOI: 10.1126/science.1168909
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Reports

14CH4 Measurements in Greenland Ice: Investigating Last Glacial Termination CH4 Sources

Vasilii V. Petrenko,1,*,{dagger} Andrew M. Smith,2 Edward J. Brook,3 Dave Lowe,4 Katja Riedel,4 Gordon Brailsford,4 Quan Hua,2 Hinrich Schaefer,4 Niels Reeh,5 Ray F. Weiss,1 David Etheridge,6 Jeffrey P. Severinghaus1

The cause of a large increase of atmospheric methane concentration during the Younger Dryas–Preboreal abrupt climatic transition (~11,600 years ago) has been the subject of much debate. The carbon-14 (14C) content of methane (14CH4) should distinguish between wetland and clathrate contributions to this increase. We present measurements of 14CH4 in glacial ice, targeting this transition, performed by using ice samples obtained from an ablation site in west Greenland. Measured 14CH4 values were higher than predicted under any scenario. Sample 14CH4 appears to be elevated by direct cosmogenic 14C production in ice. 14C of CO was measured to better understand this process and correct the sample 14CH4. Corrected results suggest that wetland sources were likely responsible for the majority of the Younger Dryas–Preboreal CH4 rise.

1 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
2 Australian Nuclear Science and Technology Organisation (ANSTO), Private Mail Box 1, Menai, NSW 2234, Australia.
3 Department of Geosciences, Oregon State University, Corvallis, OR 97331, USA.
4 National Institute of Water and Atmospheric Research Ltd., Post Office Box 14901, Kilbirnie, 301 Evans Bay Parade, Wellington, New Zealand.
5 DTU Space, National Space Institute, Technical University of Denmark, Ørsteds Plads, Building 348, DK-2800 Kongens Lyngby, Denmark.
6 Commonwealth Scientific and Industrial Research Organisation, Marine and Atmospheric Research, Private Mail Box 1, Aspendale, VIC 3195, Australia.

* Present address: Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA.

{dagger} To whom correspondence should be addressed. E-mail: vasilii.petrenko{at}colorado.edu

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