Scientists have successfully identified the age of 120,000-year-old Antarctic ice using radiometric krypton dating — a new technique that may allow them to locate and date ice that is more than a million years old. This will allow them to reconstruct the climate much farther back into Earth's history and potentially understand the mechanisms that have triggered the planet to shift into and out of ice ages.
A team of scientists has successfully identified the age of 120,000-year-old Antarctic ice using radiometric krypton dating — a new technique that may allow them to locate and date ice that is more than a million years old.
The ability to discover ancient ice is critical, the researchers say, because it will allow them to reconstruct the climate much farther back into Earth's history and potentially understand the mechanisms that have triggered the planet to shift into and out of ice ages.
Results of the discovery are being published this week in the Proceedings of the National Academy of Sciences. The work was funded by the National Science Foundation and the U.S. Department of Energy.
"The oldest ice found in drilled cores is around 800,000 years old and 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," said Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the PNAS article. "That is very exciting because a lot of interesting things happened with Earth's climate prior to 800,000 years ago that we currently cannot study in the ice core record."
Krypton dating is much like the more-heralded carbon-14 dating technique that measures the decay of a radioactive isotope — which has constant and well-known decay rates — and compares it to a stable isotope. Unlike carbon-14, however, krypton is a noble gas that does not interact chemically and is much more stable with a half-life of around 230,000 years. Carbon dating doesn't work well on ice because carbon-14 is produced in the ice itself by cosmic rays and only goes back some 50,000 years.
Krypton is produced by cosmic rays bombarding 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 does not decay. Comparing the proportion of stable-to-radioactive isotopes provides the age of the ice.
Though scientists have been interested in radiokrypton dating for more than four decades, krypton-81 atoms are so limited and difficult to count that it wasn't until a 2011 breakthrough in detector technology that krypton-81 dating became feasible for this kind of research. The new atom counter, named Atom Trap Trace Analysis, or ATTA, was developed by a team of nuclear physicists led by Zheng-Tian Lu at Argonne National Laboratory near Chicago.
In their experiment at Taylor Glacier in Antarctica, the researchers put several 300-kilogram (about 660 pounds) chunks of ice into a container and melted it to release the air from the bubbles, which was then stored in flasks. The krypton was isolated from the air at the University of Bern, Switzerland, and sent to Argonne for krypton-81 counting.
"The atom trap is so sensitive that it can capture and count individual atoms," said Buizert, who is in OSU's College of Earth, Ocean, and Atmospheric Sciences. "The only problem is that there isn't a lot of krypton in the air, and thus there isn't much in the ice, either. That's why we need such large samples to melt down."
The group at Argonne is continually improving the ATTA detector, researchers there say, and they aim to perform analysis on an ice sample as small as 20 kilograms in the near future.
Written By: Science Daily
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