Sudden changes in a glacial world.

The most characteristic records of the millennial variability of climate during the last glacial period may be separated into two classes of signals: Greenland and Antarctic. The Greenland type is found over the whole North American and Euro-Asian continental blocks. Continental cooling associated with the maximum ice sheet extension, and resulting surges on the marine margins have affected the whole latitude range, with a probable strong albedo feedback due to winter snow cover. At the opposite, the surface temperature of tropical oceans did not change as much, which created large seasonal meandering of the Intertropical Convergence Zone (ITCZ), and facilitated meridional atmospheric vapour transport towards cold continents, and heat transfer in particular to the southern hemisphere. The rapid growth of ice sheets facilitated periodic surges and decreases in meridional overturning circulation. We propose that the major difference in the characteristics of the 'Greenland' and 'Antarctic' classes of climate variability result mostly from the difference in continent/ocean distribution in both hemispheres. (C) 2004 Academie des sciences. Publie par Elsevier SAS. Tous droits reserves.