Ice Core Chemistry: Implications for our Past Atmosphere

Abstract

Listen

Translate article

By virtue of their geographical position and meteorological conditions, polar regions are of interest for many environmental studies. First, located far from continents (where local sources such as wind blown dust, biogenic emissions or anthropogenic sources dominate), arctic and antarctic regions are recognized as having the cleanest atmospheric environment of the northern and southern hemisphere respectively. The atmosphere in the marginal regions of Greenland and Antarctic ice sheets is strongly influenced by trace gases and aerosols emitted by the surrounding high latitude oceans while further inland, this marine input is strongly decreased. The relative remoteness of continental polar regions suggests that their atmospheres represent the best modern example of the “background atmosphere” for their respective hemispheres and are therefore very sensitive to any natural and/or anthropogenic change. A second interesting feature of polar regions lies in their meteorological conditions (their well marked seasonal cycle with a long polar night, and their extremely cold temperatures and dryness). Some oxidation reactions of key tropospheric species, for instance, dimethylsulphur emitted by the ocean, are probably considerably reduced (due to the quasiabsence of photochemistry during winter and the decreased speed of some chemical reactions at lower temperatures) compared to the situation at more temperate latitudes. From this point of view, polar regions can be considered as a kind of “giant natural laboratory” in which it is probably much simpler than elsewhere to check the complex chemistry governing biogenic cycles (S, N and C). A third and unique specificity of polar regions comes from the solid precipitation which accumulates on polar ice sheets. Assuming a good knowledge of the relation linking the composition of the atmosphere and that of the snow, studies of polar ice make it possible to reconstruct the paleoenvironment of the Earth as far as several hundred thousands of years back.