Scientists Develop Antarctic Ice Dating Technique Using Krypton

Using a form of krypton, a chemical created when cosmic rays hit the planet, scientists have developed a new technique to more accurately date ancient Antarctic ice which could help them understand the forces that have triggered ice ages, according to a study published in Proceedings of the National Academy of Sciences.

“The ultimate thing we would like to know is what the climate was like in the past…because that helps us understand what the climate might be like in the future,” said Edward Brook, co-author of the report. Studying the contents of very old ice could help scientists understand how the relationship between greenhouse gases, which speed up global warming, and climate has evolved over time, he added.

Radiometric krypton dating uses krypton-81, a radioactive isotope of krypton—one of the rarest particles on Earth—that is produced by cosmic rays blasting into the Earth, which are stored in air bubbles within Antarctic ice. Unlike the better-known but more unstable dating technique that uses carbon-14, krypton does not interact chemically and has a half-life of approximately 230,000 years, nearly five times that of carbon-14. Other techniques to date old ice use the ice around a sample to approximate the age, and are not as accurate, said Brook.

Scientists have tried to develop the krypton dating technique for more than four decades. In 2011, a team of nuclear physicists at the Argonne National Laboratory in Lemont, Ill., near Chicago developed a new atom counter, the Atom Trap Trace Analysis, which finally made the technique possible.

In December 2011, researchers drilled into the Taylor Glacier in Antarctica, known for a five-story-high bright red waterfall that seeps through one of the ice caps’ cracks, and removed 660 pounds of ice through large cylinders. They put the samples in a giant vacuum chamber on-site, melted it and pumped the air into tanks.

The gas traveled from Antarctica to Switzerland, where experts separated the krypton from the rest of the air, and then to the Argonne lab, where scientists measured the krypton isotopes, according to Brook.

They determined that the ice they gathered was 120,000 years old.

Now, scientists can begin looking for more ancient ice than the oldest available ice core that has been found so far, which is approximately 800,000 years old, according to Christo Buizert, a postdoctoral researcher at Oregon State University and the lead author of the study. Scientists are hoping that the new technology will help them more accurately date ice back as far as 1.5 million years.

One of the main questions researchers are trying to answer is why the spacing of major climate cycles was smaller prior to the last million years. During the past 800,000 years, scientists believe, the Earth has shifted in and out of ice ages every 100,000 years, but these shifts occurred more frequently—every 40,000 years—before that. The answer might have implications for how scientists understand and predict the future of climate.

“Dating old ice accurately will help us build a better picture of how global warming might evolve,” said Brook.