Bangalore: Researchers in Antarctica have uncovered a 9.44-metre-long ice core, which contains ice that is 5 million years old. It is believed to be the oldest ice specimen ever found.
The testing and study of ice samples presents great potential for understanding the ancient climate and the changing climate of today. Methods used by researchers to measure ice age may help study other older ice samples.
The extraction was carried out by a team of researchers from several US institutions and organizations: University of North Dakota, Berkeley Geochronology Center, Vanderbilt University, and the University of Vermont,
The findings were published last month in the journal cryosphere,
Unlike conventional ice core extraction, which requires drilling deep beneath layers of sedimentary ice, this specimen was found buried under a rock in the Ong Valley in the Transantarctic Mountains.
Millions of years ago, this ice flowed into the valley as part of a glacier and came into contact with the surface in the process, after which it is believed to have been covered with debris and rock.
Ice ages in this region were previously estimated to be over a million years, as measured by the effects of cosmic rays from space on the quartz crystals present in the ice. Previously, the oldest excavated ice was 8,00,000 years old.
The extracted sample is composed of two different ice masses stacked together. The upper, new ice mass is thought to be about 220,000 years old, and is said to have come from within the glacier. But the mass beneath it is older, having been exposed to surface and covered with rock after initial burial, estimated to be 4.3 million–5.1 million years old.
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snowflakes and drifting snow
Ice cores are obtained by drilling into meter-thick ice and obtaining long tubes of icy material, or “cores”. The core consists of layers of ice formed by seasonal snowfall and deposition, which pile up by year, with the topmost part of the ice being the most recent.
These cores can be harvested at different time periods and content, providing information about the climate of the time when the ice was freshly fallen snow. Fresh ice can trap air bubbles and may also contain atmospheric particles, indicating the nature of ancient climates.
Scientists are continually attempting to create a microclimate record of the past by obtaining samples of ice cores that are expected to extend as far back as 1.5 million years ago. However, digging deeper is more expensive and can take a long time, even decades.
A 2016 study showed that the ice buried in the Ong Valley was at least 1.1 million years old, possibly more than 2.6 million years old. The estimates were made through a method called cosmogenic nuclide dating.
The researchers behind the new findings used these findings to map the ice excavations identified in the 2016 study.
cosmogenic nuclide dating
Cosmogenic nuclides are rare isotopes of elements that form when cosmic rays—high-energy protons and nuclei whistling through space—interact with the nucleus of an atom on Earth, releasing protons and neutrons from the atom. These isotopes or nuclides also form in rocks, meteorites and planetary atmospheres.
The terrestrial cosmic nuclides measured in the previous study were of beryllium (Be), aluminum (Al), and neon (Ni) within the debris mixed with ice.
In the latest study the team of researchers collected its ice core in 2017-2018. They also developed a model that predicted how rare isotopes of Be, Ne, and Al formed in the ice, and used the predictions to measure the isotope profile of a core about 10 meters long.
After tracing ice dating back hundreds of thousands of years, they discovered ice dating back three million years. But as they progressed further beneath the depths of the ice, the isotopic concentrations were even higher, leading them to conclude that the ice bottom may be 5.1 million years old.
However, the researchers did not measure carbon isotope levels.
The findings will provide clues into past climate over the past millions of years, and will also provide ice core samples more than a million years old.
(Edited by Nida Fatima Siddiqui)
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