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Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years.

Dome C Antarctic dD and CH4 plot, 600 - 800 KYrBP.

Figure 1 (inset).
Dome C CH4 and δD, 600 - 800 KYrBP, with stacked benthic δ18O values.
Click image for full figure.

Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years.

Vol. 453, No. 7193, pp. 383-386, 15 May 2008.
doi: 10.1038/nature06950

Laetitia Loulergue1, Adrian Schilt2, Renato Spahni2,4, Valérie Masson-Delmotte3, Thomas Blunier2,4, Bénédicte Lemieux1, Jean-Marc Barnola1, Dominique Raynaud1, Thomas F. Stocker2, Jérôme Chappellaz1
1 Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS-Université Joseph Fourier Grenoble, 54 Rue Moliére, 38402 St Martin d'Hères, France
2 Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland, and Oeschger Centre for Climate Change Research, University of Bern, Erlachstrasse 9a, CH-3012 Bern, Switzerland
3 Institut Pierre Simon Laplace/Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-University Versailles-Saint Quentin, CE Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
4 Present addresses: Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol BS8 1RJ, United Kingdom (R.S.); Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen OE, Denmark (T.B.)
Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between ~350 and ~800 parts per 109 by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of ~1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is ~380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by ~100,000 yr glacial-interglacial cycles up to ~400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending periglacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles.
Download data from the WDC Paleo archive:
EPICA Dome C Ice Core 800KYr CH4 Data, Text or Excel format.

To read or view the full study, please visit the Nature website.
It was published in Nature, Vol. 453, No. 7193, pp. pp. 383-386, 15 May 2008. doi: 10.1038/nature06950
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