ICE RECORDS OF THE PAST ENVIRONMENT

Information recorded in polar ice cores over the last several hundred millennia is invaluable to studies aimed at understanding the pre-industrial environmental system and anticipating the future evolution of the climate and the atmosphere. The isotopic composition of the ice (H2O) matrix is a reliable paleothermometer. Ambient air samples are encapsulated and stored in the ice bubbles by relatively simple processes. The interpretation of the chemical composition of deposited snow in terms of past atmospheric trace gases and aerosol composition is more intricate and necessitates detailed discussions. It has been found from deep Antarctic and Greenland ice core studies that, in comparison with present climate, ice age environmental conditions correspond to about 6-degrees-C cooler temperatures and atmospheric CO2 and CH4 Contents lower by factors of nearly 2 and 4, respectively. The biogeochemical cycles of S and N were also affected by climatic changes producing modifications in source intensity and transport of gaseous precursors. Sulfate is the major atmospheric sulfur compound. It has mainly a marine biogenic origin, but cataclysmic volcanic eruptions contribute sporadically to the atmospheric sulfur budget by huge SO2 emissions, ultimately detected in polar ice by H2SO4 spikes. Nitrate' the next most important ion determined in polar precipitation, exhibits concentration changes which are presently poorly understood, but which could be linked with the polar ozone hole problem. Finally, continental dust and sea-spray aerosol components are also present in the ice at much higher concentrations during ice ages than during interglacial periods due to an intensification of their production and long range transport under glacial climatic conditions.