“Dirty” ice

During its formation, glacier ice traps air bubbles and numerous solid impurities, that can be opportunely studied and provide important and precious data on the history of our planet. The coarser debris usually come from the mountain slopes closer to the glacier or to its base: the examination of glacial deposits is very important to reconstruct glaciers that are now extinct however they do not usually supply interesting information regarding present-day glaciers (which we already have information about with regard to expanse and position).
Smaller fragments, fine dusts that may come from far away carried by the wind, are more interesting. Observing their distribution one can, for example, reconstruct the direction of winds, while an analysis of the dust composition can occasionally lead to some surprises: grains of sand from the Sahara Desert are wide-spread on Alpine glaciers, and it is not improbable to find traces of particularly violent volcanic eruptions in the form of great amounts of volcanic ash. The study of the composition of these ashes often allows us to identify the volcano from which they derive, and this provides us with information on the winds that carried them and on the strength of the explosion. If the ashes comes from historic volcanic events it is also possible to date the level of ice in which these were found. On the other hand, the possibility of dating the different levels of ice makes it possible to assess the time of very ancient volcanic events.
The study of dust in Antarctica and in Greenland, for example, shows that the concentration during the last glacial episode is much higher than today: this fact makes us infer that during glaciation, atmospheric circulation along the meridians was more ‘energetic’ due to greater differences in temperature between the tropical and polar zones and that the arid and desert zones were more wide-spread. The discovery of pollutants of industrial origin in cores of glaciers very far from anthropic settlements, such as those of the Himalayas or of the Karakorum, enable us to study how these substances are propagated in the atmosphere and, in some cases, to establish who is the “culprit”.

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