Editing Paleoclimatology (section)

== Ice Cores: Trapped Atmospheric Archives ==

Ice cores extracted from the deep interiors of the Greenland and Antarctic ice sheets, as well as high-altitude mountain glaciers, are among the most valuable paleoclimate archives. As snow falls year after year, it compresses into solid ice, forming distinct annual layers that can preserve hundreds of thousands of years of climate data.

=== Paleothermometry (Water Isotopes) ===
The ice itself acts as a historical thermometer. Water molecules (H2O) naturally contain different isotopes of oxygen—specifically, lighter Oxygen-16 and heavier Oxygen-18. Because water molecules containing Oxygen-16 are lighter, they evaporate more easily from the oceans. Conversely, the heavier Oxygen-18 molecules precipitate out more readily as rain or snow as the air mass travels toward the poles.

The ratio of these two isotopes in an ice core layer is highly dependent on the temperature at the time the snow fell. During cold glacial periods, the ice contains even less of the heavy Oxygen-18. By measuring this isotopic ratio, scientists can reconstruct highly accurate localized temperature records spanning up to 800,000 years in Antarctica.

=== Ancient Air Bubbles ===
Crucially, as snow compresses into glacial ice, it traps tiny bubbles of ambient air. These bubbles are not proxies; they are actual, preserved physical samples of the ancient atmosphere. By crushing the ice in a vacuum and analyzing the released gases, scientists can directly measure historical concentrations of key trace greenhouse gases, including CO2, CH4, and N2O. This direct record definitively proves the tight coupling between atmospheric CO2 concentrations and global temperatures throughout the Pleistocene epoch.