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Aug. 12 () –
Researchers have unearthed an ice core up to five million years old in the Ong Valley in the Transantarctic Mountains, possibly the oldest ever recovered.
The method used to measure the age of the core, published in The Cryospherecould pave the way for the investigation of other older ice cores, reports Nature.com.
Several international teams are racing to extract the oldest continuous ice cores, hoping to produce seamless timelines of atmospheric conditions that they extend to about 1.5 million years ago.
The new method, however, could make it possible to date even older ice cores deposited by glaciers. which are easier to access because they are closer to the surface.
That’s the view of lead author Marie Bergelin, a glacial geologist who was part of the Ong Valley Ice Project while at the University of North Dakota at Grand Forks. Instead of searching deep underground, Bergelin asked: “Where else can we potentially find old ice? Where else can we go and find unique deposits?”
Drilling deep for continuous ice cores costs millions of dollars and can take more than a decade of planning and fieldwork. In search of old ice that would not require such a large investment, Bergelin and his colleagues settled in the Ong Valley because previous estimates suggested that ice buried under one of its glacial drifts (rock material transported by a glacier) it is over a million years old.
After the glaciers slid into this valley, its ice surface began to sublimate, turning into water vapor. That left a protective layer of rocky material with preserved ice underneath.
The sediment-filled ice of the Ong Valley probably cannot provide the detailed climate record that continuous cores do. But it could still yield new information.
The researchers collected their ice core during the 2017-18 field season, choosing a mining site far from any rockfall areas that might have contaminated the sample. Based on what they know about how ice was deposited in this region, they developed a model of how rare isotopes of beryllium, aluminum, and neon accumulated in the ice debris over time. High-energy cosmic rays from outer space collide with rocky material at or near the surface to create these isotopes. After comparing the model predictions with the isotope profile measured in the 10-meter-long ice core, they were able to estimate that some of the ice, down to a certain depth, was about 3 million years old.
Below that depth, isotope concentrations were much higher than expected, leading the team to conclude that two separate ice masses are stacked on top of each other in this part of the Ong Valley. They estimate that the oldest and deepest is between 4.3 and 5.1 million years old.
