Ice Cores
Cores from ice sheets and mountain glaciers provide especially good records of past climate. The thickness of tree-ring-like annual layers preserved in some cores reveals the history of snowfall.
Air bubbles are trapped as snow turns to ice. These bubbles provide the only direct samples of atmospheric composition in the past, before measurements were made and recorded. The ratio of oxygen isotope concentrations is commonly used to infer past temperatures. Concentrations of wind-blown dust, sea salt, pollen, forest fire smoke, and volcanic ash reveal conditions upwind. Information about variations in the Sun’s intensity and the composition of space dust can even be obtained from micrometeorites and isotopes in the ice.
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Ice Cores
The thickness of the layers can reveal the history of snowfall. Air bubbles trapped in the ice bubbles provide the only direct samples of atmospheric composition in the past before measurements were made. (Photo courtesy of National Science Foundation and United States Geological Survey) |
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