icecore

An ice core is a cylindrical sample drilled from an ice sheet or glacier that preserves layers formed by snowfall over long timescales. As successive layers accumulate, they become compressed into ice, recording a chronological archive of past climate.

Each layer represents snowfall from a specific time, and in many regions annual layers can be distinguished. Air bubbles trapped within the ice preserve snapshots of ancient atmospheric composition when the layer formed, while the chemical and physical properties of the ice contain climate information. The isotopic composition of water molecules, including ratios such as oxygen-18 to oxygen-16 and deuterium to hydrogen, serves as a proxy for past temperatures. The concentration of greenhouse gases such as carbon dioxide, methane, and nitrous oxide is determined from the trapped air. Layers of volcanic ash, dust, and other impurities provide time markers and records of volcanic activity and aridity.

Dating ice cores combines layer counting with markers such as volcanic tephra and synchronization to other climate proxies. A known offset exists between the age of the gas within the bubbles and the surrounding ice, requiring careful interpretation. Ice cores thus yield records that can extend hundreds of thousands of years, though the length varies by site and conditions.

Notable cores include Antarctic records such as Vostok and EPICA Dome C, and Greenland records such as GISP2 and GRIP. EPICA Dome C reaches back nearly 800,000 years in some interpretations, while Vostok extends to several hundred thousand years. Greenland cores generally cover shorter intervals but illuminate more recent climatic variations.

Applications of ice-core data include reconstructing past temperatures, precipitation patterns, atmospheric composition, and the timing of rapid climate events. They are foundational for understanding natural climate variability and for validating climate models.