An ice core, a cylindrical sample of ice that preserves ancient air and serves as a "time capsule" for reconstructing Earth's past climate and environmental changes, is normally kept under strict low-temperature conditions at the National Institute of Polar Research (NIPR). The precious sample is now on public display at The Great Antarctic Exhibition at the National Museum of Emerging Science and Innovation (Miraikan) in Odaiba, Tokyo, through September 27, marking its first public exhibition in about 20 years. Other Antarctic ice displayed elsewhere in the exhibition contains numerous air bubbles and appears white. However, no air bubbles are visible in the ice core. The exposed section, where part of the core was cut away for analysis, is particularly transparent.
Provided by Miraikan
So, why is it transparent? According to ONODA-SHOUTEN, a long-established ice manufacturer in Tokyo's Kita Ward, ice turns white when it contains impurities or air. To produce transparent ice, the company stirs the water while freezing it, continuously removing impurity-rich portions and replacing them with pure water before cooling it indirectly for more than 60 hours. Wataru Sakai of the company's public relations section is puzzled by the contrast: "Ice cores are formed from accumulated snow and contain air, yet the ice in the photograph appears remarkably transparent."
If ice containing air normally turns white, why doesn't the ice core? According to the National Institute of Polar Research (NIPR), the ice appears transparent because, in the deeper portions of an ice core, the trapped air exists not as bubbles but as transparent crystals known as clathrate hydrates, in which water molecules form cage-like structures around air molecules.
The Dome Fuji Ice Core on display, part of NIPR's collection, was drilled at a depth of 2,499 meters and preserves information dating back about 340,000 years. Formed as snow accumulating on the Antarctic continent was gradually compressed over tens of thousands of years, the ice preserves a record of past environmental conditions. Even though it appears transparent, traces of the atmosphere, temperatures, precipitation, and other aspects of Earth's environment at the time the snow fell remain trapped within it.
The fact that one end of the ice core on display has been cut away is evidence that the sample was actually used for research. For analysis, sections of the core are cut out and then melted or shaved to extract ancient air, allowing researchers to reconstruct past climate change and other aspects of Earth's environmental history.
Original article was provided by the Science Portal and has been translated by Science Japan.