Under present-day climatic conditions the air content of ice shows a high sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet. This observation has been used to infer past ice sheet thickness variations of Antarctica and Greenland. A high-resolution air content profile (more than 1000 measurements) covering approximately the last 200 000 years was obtained along the 2546-m long Vostok ice core. Three analytical techniques were used, leading to consistent results which show large amplitude and rapid air content variations. The Vostok results support thicker/thinner ice in the central part of East Antarctica during warm/cold periods. Apart from ice thickness changes, the two other potential sources of air content variations are atmospheric pressure and ice porous volume at the air isolation level, but these do not explain all the variation. Wind speed changes by about 7 m s-1 could be the source of the large and rapid air content variations observed during glacial stages. -from Authors