Environmental information from ice cores

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Abstract
Human activities have a serious impact on climate and on the natural composition of the atmosphere. Information recorded in polar ice cores over the last several hundred millennia is invaluable to studies aimed at understanding the preindustrial environmental system and anticipating the future evolution of the atmosphere. An excellent understanding of the mechanisms of the ice record formation as well as a good assessment of the present polar atmospheric composition (trace gases, aerosol) is a prerequisite to interpreting correctly the past variations of the measured parameters. This paper explains what and how atmospheric parameters are recorded. Ambient air samples are encapsulated and stored in the ice bubbled by relatively simple processes. The isotopic composition of the H2O (ice) lattice is a reliable paleothermometer. The interpretation of the chemical composition of deposited snow in terms of past atmospheric composition of deposited snow in terms of past atmospheric composition (trace gases, aerosol) is more intricate and necessitates detailed discussions. The data obtained from deep ice cores provide precise information on the ice age environmental conditions: when polar temperatures were some 10°C lower than now, atmospheric CO2 and CH4 contents were factors of 2 and 4 lower, respectively, than present conditions. At this time, sea salt and overall crustal dust depositions were significantly higher. The biogeochemical cycles of S and N were also disturbed according to modifications in source intensity and transport of gaseous precursors.