World’s oldest ice core? | Polarjournal
In Ong Valley in the Transantarctic Mountains, researchers have recovered what may be the oldest ice core ever discovered. Photo: Jaakko Putkonen

While several teams in East Antarctica are drilling continuous ice cores in search of 1.5 million-year-old ice, another research group in the Transantarctic Mountains has discovered what may be the oldest ice at a relatively shallow depth under a blanket of rock. In a study published in the journal The Cryosphere, the researchers estimate the ice recovered from Ong Valley in the Miller Range to be between three and five million years old.

Drilling projects in search of the oldest ice, with the goal of expanding the planet’s climate record, are being conducted mainly in East Antarctica, where the ice has been deposited layer by layer by precipitation and therefore more cleanly than, for example, in Ong Valley in the Transantarctic Mountains. In East Antarctica, however, the researchers have to drill extremely deep, almost to bedrock, to reach ice that is 1.5 million years old. The oldest ice core from there so far dates back 800,000 years.

In contrast, in the Transantarctic Mountains, which separate East and West Antarctica, the research team recovered an ice core that was only almost ten meters long and filled with sediment. They estimate that this ice, up to five million years old, may be the oldest ever found. The new method for determining the age of the core could pave the way for research on other older ice samples deposited by glaciers. These are much more accessible because they are closer to the surface, making projects much cheaper and faster to implement than deep drilling for continuous ice cores.

The Ong Valley is located in the Miller Range of the Transantarctic Mountains. Map: GoogleEarth

Marie Bergelin, a glacial geologist at the University of North Dakota and lead author of the study, and her colleagues chose Ong Valley as the sampling site because previous estimates suggest the ice buried under glacial debris is more than a million years old. After the glaciers slid into Ong Valley, the surface ice turned to water vapor and a protective blanket of rock material with preserved ice underneath remained.

Climate records from the sediment-filled ice core are probably not as detailed as those from continuous cores, but they could still provide new information.

Aerial view of Ong Valley showing glacial debris of different ages. The cores were taken in the middle part. Photo: Bergelin et al. 2022

The research team collected the cores for the current study during the 2017/2018 field season at a location far from rockfall areas to rule out sample contamination. For age determination, they developed a model for how rare isotopes of beryllium, aluminum and neon accumulate in ice deposits over time. The isotopes are formed when high-energy cosmic rays strike rock material at or near the surface. After comparing the model predictions with the measured isotope profile in the ten-meter ice core, they were able to estimate that part of the ice to a certain depth is about three million years old, making it the world’s oldest ice recovered to date.

Below ten meters, isotope concentrations were much higher than expected, leading the team to conclude that two separate ice masses are layered on top of each other in this part of Ong Valley. The team estimated the older, deeper ice mass to be between 4.3 and 5.1 million years old.

Jaakko Putkonen, a geologist at the University of North Dakota in Grand Forks, works on the sediment-rich ice core. Photo: Marie Bergelin

Other researchers are critical of the results and miss the analysis of carbon isotopes, which could reveal a different age of the ice. In addition, it is questionable whether the model can be applied to ice outside Ong Valley.

Bergelin counters that measuring three isotopes should be sufficient; most studies use only one or two. Moreover, the carbon isotope 14C decays too quickly for dating ice millions of years old. She believes the model can be applied to other Antarctic regions with similar isolated and buried ice masses.

Still, the study sparked excitement about the age of the ice and its importance for future research. Paleoclimatologist Yuzhen Yan says the study provides “very strong evidence that ice cores or ice samples can be preserved for 3 or 4 million years.” This opens up new opportunities for future drilling, Yan said.

But for now, Bergelin and her team are busy analyzing ice from 2.5 to 5 million years ago, when temperatures and carbon dioxide levels were higher than today. Knowledge of this time could also shed light on how the planet is responding to man-made climate change today.

“We have found and dated this ice to be some of the oldest,” Bergelin says. “Now, the future is to look at what we can get out of it.”

Julia Hager, PolarJournal

Link to the study: M. Bergelin, J. Putkonen, G. Balco et al. Cosmogenic nuclide dating of two stacked ice masses: Ong Valley, Antarctica. The Cryosphere, 16, 2793-2817, 2022.

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