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Press release
A novel method of dating ice cores helps us to understand deglaciation that occurred 250,000 years ago | |||
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Paris, March 14, 2003 |
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Working with
American, Russian, and Chinese scientists, researchers from the "Laboratoire
des sciences du climat et de ''environnement" (Laboratory for Climate
and Environment Sciences) in Saclay (a research unit run jointly by the
CEA [French Atomic Energy Authority] and by the CNRS - Institut Pierre
Simon Laplace)(1), and from the "Laboratoire de
glaciologie et géophysique de ''environnement" (Laboratory
for Glaciology and Environment Geophysics) in Grenoble (a research unit
run jointly by the CNRS and by the Université Joseph Fourier) (2)
have developed a new and more accurate method of dating ice core samples.
The measurements they have taken on the Vostok Antarctic ice core have
made it possible to reconstruct with great precision the sequence of events
of the deglaciation that occurred 250,000 years ago.
Over about the last twenty years, the research performed on the Vostok Antarctic ice core has shown a strong correlation between carbon dioxide content in the atmosphere and temperature over the last 420,000 years. The method used hitherto, which was based on isotopic analysis of the ice for evaluating temperature, and on analysis of air bubbles trapped in the ice for determining composition of the atmosphere, had its limitations. Uncertainty of about 1,000 years remained on the age difference between the ice and the air bubbles. The new method developed makes it possible to reduce that uncertainty by a factor of 5 using the air bubbles to determine not only temperature but also atmospheric composition. With the new method, temperature is estimated by very precise analysis of the isotopic composition of the argon in the air bubbles. The sequence of events can then be reconstructed precisely. The warming began in Antarctica, probably initiated by changes in insolation (3). The increase in carbon dioxide content started about 800 years later but took place a few thousand years before the thaw of the ice caps that marked the main stage of the deglaciation. This sequence is consistent with the idea that the increase in carbon dioxide contributed, through various retroactions, to amplifying the very low effect of the changes in insolation, and thus participated actively in deglaciation. Jean Jouzel, Director of the Institut Pierre Simon Laplace, Fédération de laboratoires de la région parisienne (Federation of Laboratories of the Paris Region), received the CNRS Gold Medal for 2002. http://www.cnrs.fr/cw/fr/pres/compress/medailleOr2002/index.html Notes: (1) LSCE: http://www.lsce.cnrs-gif.fr (2) LGGE: http://www-lgge.ujf-grenoble.fr/ (3) time during which the sun shines, i.e. amount of sunshine References: Nicolas Caillon, N., Jeff Severinghaus, Jean Jouzel, Jean Marc Barnola, Jiangcheng Kang and Volodya Lipenkov, Timing of Atmospheric C02 and Antarctic Temperature Changes Across Termination III, Science, March 14, 2003. Researcher
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