A team of US researchers has extracted in East Antarcticain the Allan Hills regionthe oldest ice core ever found on Earth. Has well 6 million years and the tiny air bubbles that he trapped during the transformation from snow to ice reveal the composition that had the atmosphere during the called era Miocene. By analyzing the ice core it was possible to obtain unprecedented information, which is fundamental for reconstructing the climate of the past. In particular, it turned out that 6 million years ago Antarctica was about 12 °C warmer compared to today and that its next cooling was gradual.
The discovery was made by a group of researchers coordinated by Sarah Shackleton (Woods Hole Oceanographic Institution) And John Higgins (Princeton University), members of the Center for Oldest Ice Exploration (COLDEX): the research was then published in the journal Proceedings of the National Academy of Sciences. Its usefulness does not only concern the knowledge of past climatic variations, but is also fundamental for make predictions about the future evolution of the climate globally.
How the oldest ice ever found on Earth was discovered
The extraction of cores of such ancient ice was possible in a region of eastern Antarctica on the edge of the ice sheet, the Allan Hills, where the slow flow of the ice and the topography of the mountains allow its found relatively close to the surface (at 100-200 m depth). In this area, the strong wind also helps to remove the recent snow, exposing the ice, while the extreme cold preserves it by slowing its movement. Ancient ice, in fact, is usually very deep and difficult to reach: so far the oldest ice found on the planet, extracted in Antarctica, dated back to 800,000 years ago ea 1.2 million years ago. This finding therefore represents a absolute record. To reveal that the ice dates back to 6 million years ago was the analysis of a Argon isotope present inside tiny air bubbles.
The reconstruction of the climate of the past: Antarctica 12 °C warmer than today
The air bubbles contained in the extracted core were trapped during the process by which the snow, which contains a lot of air, is compacted by the weight of other snow and turns into ice over time. Theirs composition corresponds to what the atmosphere had at the time of the snow falling: this allows us to discover what the atmosphere was like in the past and how it was different from that of today. In particular, very significant is the greenhouse gas contentlike carbon dioxide, since it is strictly related to the temperature of the planet in the period of time examined (in fact we know that at a higher concentration of CO2 correspond to higher temperatures).
The Miocene temperature was reconstructed by analyzing the oxygen isotopes contained in the ice, which are found in different proportions depending on the value this parameter had at the time. It was thus discovered that Antarctica was 6 million years ago about 12 °C warmer compared to today and that its next cooling was gradual and not sudden. At that time also the sea level was higher compared to the current one. Knowing how the climate has varied throughout the Earth’s history is useful for understand climate change ongoing and for make predictions on its evolution. They will be carried out in the coming months further drillingwith the aim of identifying even older ice.
