As part of the European EPICA project (European Project for Ice Coring in Antarctica), European researchers*  have produced a new and very precise reconstruction of the temperature in the Antarctic during the last ice age. They have demonstrated that the climate seesaw between the Antarctic and Greenland, which had previously been revealed for a few climate events of large amplitude, is characteristic of the whole period studied because it also concerns shorter events. Synchronization of climate records in Greenland and the Antarctic was established using global changes in atmospheric methane content reliably recorded in air bubbles in ice at the two poles. More details about this climate relationship have been determined from new data from drilling at Dronning Maud Land (the part of the Antarctic facing the Atlantic Ocean), which have been added to data from drilling at Dome C. Higher snow accumulation at this site than on the central plateau of the Antarctic meant that researchers were able to establish a more detailed temperature graph from the ice core, and more precise synchronization with temperature variations in Greenland.

The circulation of the Atlantic Ocean has been implicated in this phenomenon. Between 55,000 and 20,000 years ago, many gradual small-amplitude warmings occurred in the Antarctic as Greenland was experiencing particularly cold conditions and as currents flowing from the ocean surrounding the Antarctic to the North Atlantic were weak. Conversely, cooling events in the Antarctic are associated with the revival of currents towards the North Atlantic and warming in Greenland. The amplitude of these Antarctic warmings seems to be linearly correlated with the duration of the corresponding warm events in Greenland. The study suggests that the quantity of heat accumulating in the ocean surrounding the Antarctic during phases in which oceanic circulation slows down determines the length of time during which circulation then returns to its full strength.

In France, the Laboratory of Glaciology and Environmental Geophysics (CNRS, Université Joseph Fourier Grenoble I), the Laboratory of Climate Sciences and the Environment (CEA, CNRS, Université de Versailles-St Quentin) and the Centre for Nuclear Spectrometry and Mass Spectrometry (CNRS, Université de Paris Sud) have worked specifically on the analysis of the methane contained in the air bubbles trapped in the ice.

Coordinated by the European Science Foundation (ESF), the EPICA project is financed by the 10 partner countries and by the European Union (current project "EPICA-MIS"). In France, it has benefited particularly from the logistical support of the Paul Emile Victor Polar Institute (IPEV) and the scientific support of the National Institute of Sciences of the Universe (INSU/CNRS).

Reference:
One-to-one coupling of glacial climate variability in Greenland and Antarctica, Nature, November 9, 2006.

*This project involves researchers from 10 European countries: Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Sweden, Switzerland and the United Kingdom.