The work, published in the Proceedings of the National Academy of Sciences, includes researchers from the National Science Foundation-funded Center for Oldest Ice Exploration (COLDEX), led by Oregon State University. Sarah Shackleton of Woods Hole Oceanographic Institution and John Higgins of Princeton University led the research and are among several US collaborators.
Shackleton explained that ice cores serve as time machines, allowing scientists to examine Earth's distant past. She noted that the Allan Hills ice samples effectively extend climate records far beyond previous limits. The oldest sample discovered dates back to a period marked by higher global temperatures and sea levels.
Ed Brook, director of COLDEX at Oregon State University, said the team originally hoped to find ice 3 million years old but exceeded this target significantly. COLDEX is among several international teams seeking to recover the oldest ice, with a European group recently reporting an ice core 1.2 million years old from East Antarctica.
COLDEX researchers are working in remote field camps in the Allan Hills, drilling to depths between 100 and 200 meters where ice flow and topography preserve very old layers close to the surface. Unlike other sites requiring drills over 2,000 meters deep, the unique conditions at Allan Hills allow for ancient ice to be sampled more readily.
Shackleton added that the region's severe winds and cold help preserve the ancient ice by sweeping away new snow and slowing glacial movement. The preserved air in these new cores is dated by measuring an isotope of argon, allowing direct age determination from the ice itself. Although records from this site are not continuous, the data reach roughly six times older than previous cores, forming what John Higgins called a "library of climate snapshots."
Temperature data show the region has cooled by around 12 degrees Celsius over 6 million years-the first direct measurement of such a trend in Antarctica. Further analysis aims to reconstruct past atmospheric greenhouse gas levels and ocean heat content.
Brook said COLDEX teams plan further fieldwork in the Allan Hills and aim to expand the climate record even further through extended studies from 2026 to 2031.
Co-authors include scientists from Oregon State, Princeton, University of Washington, Scripps Institution of Oceanography, University of Maine, Tongji University, and University of Minnesota. The project received support from the NSF Office of Polar Programs and the US Antarctic Program.
Research Report:Miocene and Pliocene ice and air from the Allan Hills blue ice area, East Antarctica
Related Links
COLDEX at Oregon State University
Beyond the Ice Age
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