Antarctic ice as old as 120 000 years

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iol scitech june 14 antarctic ice SUPPLIED As its formed and laid down over millennia, ice traps air bubbles, and the differing concentrations of various gases  particularly the greenhouse gas carbon dioxide  in this air allows scientists to reconstruct climate. Picture: BRISITH ANTARCTIC SURVEY

Cape Town - Lots of ice, please – and melted, not shaken or stirred.

That was the order from a team of US scientists who successfully used a new technique to confirm the age of a 120 000-year-old sample of Antarctic ice.

The new dating system that uses the noble gas krypton is expected to help climate scientists develop more accurate models of Earth’s previous climate changes, by identifying and analysing ice that is much older than the current available samples.

As it’s formed and laid down over millennia, ice traps air bubbles, and the differing concentrations of various gases – particularly the greenhouse gas carbon dioxide – in this air allows scientists to reconstruct climate.

Now they’ll be able to look much further back.

Christo Buizert, a postdoctoral researcher at Oregon State University and lead author of a paper in a recent issue of Proceedings of the National Academy of Sciences, explained that the oldest ice found in drilled cores is about 800 000 years old.

“With this new technique we think we can look in other regions and successfully date polar ice back as far as 1.5 million years. That’s very exciting because a lot of interesting things happened with the Earth’s climate prior to 800 000 years ago that we cannot study in the ice-core record,” he said.

Funded by the US National Science Foundation (NSF), Buizert and his colleagues used a krypton dating technique on ice drilled from Antarctica’s Taylor Glacier, opposite New Zealand.

Krypton dating is much like the more common carbon-14 dating technique, the NSF explained in a statement. But unlike carbon-14, krypton doesn’t interact chemically and is much more stable, with a half-life of around 230 000 years.

Krypton is produced by cosmic rays bombarding the Earth and then stored in air bubbles trapped within Antarctic ice. It has a radioactive isotope (Krypton-81) that decays very slowly, and a stable isotope (Krypton-83) that doesn’t decay. Comparing the proportion of stable-to-radioactive isotopes provides the age of the ice.

In their experiment at Taylor Glacier, the researchers used a new blue-ice drill to obtain several 300kg chunks of ice. They put this ice into a container and melted it to release the air from the bubbles, which was then stored in flasks.

The krypton was isolated and sent to the Argonne National Laboratory near Chicago, which first used krypton dating a decade ago, for analysis.

The lab uses an atom trap so sensitive it can capture and count individual atoms – the only instrument in the world with that capability. - Sunday Argus

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