Microscale Distribution of Environmental Proxies in Snow

Abstract

During a snowfall, chemical compounds from the atmosphere are deposited on the ground. If the snow does not melt completely, as is the case on polar and alpine glaciers, these impurities remain inside the snow cover. Compacted by subsequent snowfalls, the snow gradually turns into firn and later into ice. Deposits thus trapped in the glacier ice form invaluable archives of past climates and original atmospheric composition. These archives can be brought back to the surface through ice cores for later analysis. However, in order to make the information contained therein comprehensible, the processes that led to the embedding must be understood. In particular, the recrystallization of the snow cover by snow metamorphism can lead to a redistribution or a loss of the embedded compounds. Because snow on the Earth's surface is physically relatively close to its melting point, there is a high vapor pressure. Similar to red-hot structural steel, which is highly ductile and continuously transforms its shape, the snow structure also changes. Inside the snow cover, the high vapor pressure causes water molecules of the snow crystals to be released constantly (sublimation) and to be deposited on adjacent ice surfaces (re-sublimation). This structural transformation can also have an influence on the contaminants present and can cause the movement of chemical compounds to different positions in the snow cover. Thus, a closer examination of the processes taking place during this rearrangement is needed, because the chemical composition found in the ice might no longer correspond to that originally deposited by the snow crystals, leading to errors when estimating past atmospheric conditions from ice cores. In this thesis we investigated the influence of snow metamorphism on the (re)distribution of ions, trace elements and stable water isotopes in the snow cover. They all represent important environmental indicators of past atmospheric conditions and play an important role in the interpretation of ice cores.