Analysing gasses in ice cores

Glacier ice formed by compression of snow contains small amounts of atmospheric air in the bubbles of the ice. In the upper approx. 80 m of an ice sheet, snow is gradually transformed to ice. This zone, called firn, is open porous and air can move freely within this zone. At the bottom of the firn, small amounts of air are closed off in ice cavities, forming gas bubbles.

The gas bubbles are still locked up in the ice when an ice core is retrieved. By melting or crushing the ice, the samples of past atmospheric air can be released from the ice and analysed. In this way, the composition of the atmosphere can be determined hundreds of thousand years back in time. Some of the results obtained in this way are described in the section Reconstructing past atmospheres.

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