❄️ This ice contains 6-million-year-old air: a record!

In the Allan Hills region of Antarctica, glaciologists have uncovered a 6-million-year-old ice core, preserving samples of Earth's atmosphere from a very ancient era. This major discovery opens a direct window onto the climate mechanisms of an Earth that was warmer than it is today.

This breakthrough is the result of work by the Center for Old Ice Exploration (COLDEX), an American scientific collaboration. Researchers targeted areas where mountainous topography and slow glacial flows naturally bring the oldest layers close to the surface. Unlike deep drilling that requires going down several kilometers, this approach allowed them to reach ancient ice by drilling only about a hundred meters.

A dive into the climatic past

Direct dating of the ice was made possible by analyzing the argon isotopes trapped in the micro air bubbles. This method, described in Proceedings of the National Academy of Sciences, provides an intrinsic measure of age without relying on external geological deductions. It confirms that these samples constitute the oldest ice archives ever found.

These cores form a library of exceptional climate snapshots. This data dates back to a period when global temperatures were significantly higher and sea levels were much higher than what we know today. They capture atmospheres from the late Miocene and Pliocene.

Analysis of the oxygen isotopes contained in the ice itself revealed a gradual cooling of about 12 degrees Celsius over 6 million years in this region of Antarctica. This is the first direct measurement of this long-term trend, which confirms the climate reconstructions of this geological era established from other natural indicators.

The secrets of exceptional preservation

The preservation of this ancient ice so close to the surface results from a combination of unique environmental factors. The katabatic winds, particularly violent in the Allan Hills, constantly sweep away the fresh snow layer that could cover and alter the ancient strata. This natural wind erosion gradually exposes the most archaic ice.

The extreme cold that permanently reigns in this area also plays an important role. It significantly slows the movement of the ice, keeping it almost stationary. This near-immobility preserves the integrity of the layers over geological timescales, preventing their mixing or deformation, unlike regions where the flow is faster.

These conditions make the area both conducive to discovery and extremely difficult for scientific work. Teams must operate during missions lasting several months in a particularly hostile environment. Their perseverance is nevertheless rewarded by easier access to ice that would otherwise be inaccessible without deep drilling.