AIR CONTENT PALEO RECORD IN THE VOSTOK ICE CORE (ANTARCTICA) - A MIXED RECORD OF CLIMATIC AND GLACIOLOGICAL PARAMETERS

Under present-day climatic conditions the air content of ice shows a h igh sensitivity to the atmospheric pressure and hence to the elevation at the surface of the ice sheet. This observation has been used to in fer past ice sheet thickness variations of Antarctica and Greenland. A high-resolution air content profile (more than 1000 measurements) cov ering approximately the last 200,000 years was obtained along the 2546 -m long Vostok ice core. Three analytical techniques were used, leadin g to consistent results which show large amplitude and rapid air conte nt variations. The Vostok results support thicker/thinner ice in the c entral part of East Antarctica during warm/cold periods. However, cons traints imposed by ice sheet dynamics suggest that the Vostok air cont ent signal cannot be interpreted only in terms of ice sheet thickness variations. Apart from ice thickness changes, the two other potential sources of air content variations are atmospheric pressure and ice por ous volume at the air isolation level. Several atmospheric general cir culation models have been applied to the last glacial maximum. They sh ow atmospheric pressure changes which can only explain part of the air content variations in the Vostok ice core. On the other hand, the ice porous volume at the depth of air isolation undergoes fairly well-qua ntified thermal variations, but they are too small to play a dominant role in the Vostok signal. On the basis of new data concerning the pre sent day ice porous volume variations we suggest that a wind influence on ice porous volume at the air isolation level could be a source for the unexplained air content variations at Vostok. Equivalent contribu tions from elevation, air pressure, and nonthermal porous volume chang es could explain the air content drop during the penultimate deglaciat ion. Wind speed changes by about 7 m s-1 could be the source of the la rge and rapid air content variations observed during glacial stages.