800,000 YEARS AND THE REVOLUTION
OF THE RHYTHM OF GLACIATIONS
When, in 1994, the scientific document that would serve as a foundation for the EPICA project was written, the stated primary objective was to drill in a place that would provide ice older than that found at the Vostok site. The choice of a dome was important because, with the same accumulation, the age of the deepest layers of ice would be older there than at a site located on a flowline, as is the case for Vostok. There is greater thinning of the deep layers, and even if the accumulation at the site chosen at Dôme C was 30% higher than that at Vostok, the age calculated, far enough from the bedrock to limit the risks of perturbation of the ice layers, was estimated at 500,000 years. We thus started with the hope of covering five climatic cycles, twice as many as the drilling at Vostok, which at this time had just barely reached 250,000 years, and we still did not know that the fifth attempt, which was in progress, would prove successful. The EPICA project was then put into motion. A dozen years later we realized, with some satisfaction, that our prediction of 500,000 years was conservative. We have been able to access 800,000 years of archives at Dôme C—twice what Vostok would have provided—but above all, Dôme C has been the entrance into a different world from a climatic point of view.
Antarctica was formed thirty-five million years ago at a time when the opening of passages between Antarctica and Australia, on the one side, and South America, on the other, enabled the formation of a circum-Antarctic ocean current that isolated that continent from the rest of the world. That isolation, probably combined with a decrease in the concentration of carbon dioxide in the atmosphere, led to the formation of an ice sheet that has remained relatively stable since then. The ice sheets of the Northern Hemisphere