By examining thin wafers of ice between crossed polarizers, scientists determine the orientation, shape, and size of the ice crystals. A crystal's orientation is indicated by its color under
polarized light, and is used to determine whether a given ice segment has undergone deformation significant enough to distort the ice record (for example, researchers originally located a period of rapid and intense climate change in the last
interglacial; ice crystal research, however, revealed that sections of the ice segments upon which these findings were based may have been disturbed or removed due to shearing). In the upper part of the GISP2 core, crystal size increases with depth;
this segment from 333 m is made up of mid-sized crystals. Minute air bubbles appear in the photo as small round inclusions, the most visible being in the large orange crystal near the center of the photo. These samples of fossil air provide scientists
and policy-makers with direct evidence of past atmospheric composition for the last 200,000 years, documenting the effects that modern man has had on Earth's atmosphere and providing information that is crucial to informed scientific and political
debates about greenhouse warming.
Photo Credits:
Anthony Gow
United States Army Corps of Engineers, Cold Regions Research and Engineering Laboratory.
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