Figure 1 (inset).
Dome C CH4 and δD, 600 - 800 KYrBP, with stacked benthic δ18O values.
Click image for full figure.
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Orbital and millennial-scale features of atmospheric CH4 over the past
800,000 years.
Nature
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.)
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ABSTRACT:
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.
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