Scientists have successfully dated 120,000-year-old Antarctic ice using a new method called radiometric krypton dating. The technique will allow them to study ice that is more than 1 million years old, which will reveal important details about the planet’s ancient climate cycles, according to a report released Monday.
Accurately dating ancient ice is critical because it contains little air bubbles that scientists can analyze to construct a record of the composition of the atmosphere throughout history. Ice cores can be used to determine the composition of the air as well as temperature at the time.
By studying the past climate, scientists can better understand the effects that greenhouse gas concentrations in the atmosphere have on temperatures — and can then make more accurate predictions about how the climate will change in the future.
“The oldest ice found in drilled cores is around 800,000 years old, and with this new technique, we think we can look into 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 a lead author of the report.
“That is very exciting because a lot of interesting things happened with the Earth’s climate prior to 800,000 years ago that we currently cannot study in the ice core record.”
Results of the radiometric krypton dating will be published this week in the Proceedings of the National Academy of Sciences. The National Science Foundation and the U.S. Department of Energy funded the study.
Krypton dating is much like the carbon-14 dating technique that measures the decay of a radioactive isotope. Unlike carbon, krypton is a noble gas — it doesn’t interact chemically and is more stable — with a half-life of about 230,000 years. Carbon-14 is reliable for dating objects only up to about 50,000 years old, so it isn’t useful for ancient ice.
About a decade ago, scientists drilled a two-mile-long ice core in Antarctica that revealed 800,000 years of the planet’s climate history. During the early period, concentrations of heat-trapping gases in the atmosphere, like carbon dioxide, typically rose with the temperature, website Live Science reported.
But scientists want to go even farther back in time, to what is known as the mid-Pleistocene transition, which took place 900,000 to 1.2 million years ago. Because of shifts in Earth’s orbit, warmer and cooler periods naturally occur, according to Live Science. Prior to the transition, those shifts happened about every 41,000 years — but afterward, the shifts switched to 100,000-year cycles.
Some scientists believe a change in greenhouse gas levels in the atmosphere spurred the mid-Pleistocene transition, but to be sure, they must find ice that is almost twice as old as the oldest scientists have found so far.
“Why was there a transition from a 40,000-year cycle to a 100,000-year cycle?” study author Buizert said Monday. “Some people believe a change in the level of atmospheric carbon dioxide may have played a role. That is one reason we are so anxious to find ice that will take us back further in time.”
Though most people would think the oldest ice could simply be found at the bottom of the Antarctic ice pack, researchers said it’s not that simple.
“Very old ice probably exists in small isolated patches at the base of the ice sheet that have not yet been identified, but in many places it has probably melted and flowed out into the ocean,” Edward Brook, an Oregon State University geologist and a co-author of the krypton dating study, said in a press release Monday.
Last year researchers said they had identified regions in Antarctica they believe could have the oldest ice, including some that could be 1.5 million years old.
“The mid-Pleistocene transition is a most important and enigmatic time interval in the more recent climate history of our planet,” Hubertus Fischer, an experimental climate physics professor at the University of Bern in Switzerland and a lead author of the study, said in a press release in November 2013.
Information on greenhouse gas concentrations from that time can be gained only from an Antarctic ice core covering the last 1.5 million years, and finding a core that old will be scientists’ next challenge.