Scientists have uncovered ice and air that is 6 million years old from a shallow ice core in the Arran Hills of East Antarctica. They believe this ancient ice showcases a preserved surface snowpack or permafrost due to the development of the East Antarctic Ice Sheet during the mid-Miocene to late Miocene epochs.
Ancient ice extracted from the ALHIC1902 ice core. Image credit: Shackleton et al., doi: 10.1073/pnas.2502681122.
“Ice cores function as time machines, allowing researchers to glimpse Earth’s past,” stated Dr. Sarah Shackleton, a scientist at the Woods Hole Oceanographic Institution.
“With the Allan Hills Core, our timeline extends much further than we previously thought was possible.”
“This is a groundbreaking discovery for the NSF-funded Center for Oldest Ice Exploration (COLDEX),” remarked Dr. Ed Brook, COLDEX director and paleoclimatologist at Oregon State University.
“We were aware that the ice in this area was ancient. Our initial estimates placed its age at around 3 million years, or perhaps slightly older, but this discovery has far surpassed our expectations.”
COLDEX is engaged in a friendly race with various international teams to push the ice core record beyond its historical 800,000-year threshold.
A European research team recently reported finding a continuous ice core dating back 1.2 million years deep within East Antarctica.
For months, the team operated in a remote field camp within East Antarctica’s Arran Hills, drilling 100 to 200 meters into the outskirts of several ice sheets, where ice movement and rugged mountain landscapes work together to safeguard ancient ice and bring it closer to the surface for easier retrieval.
In contrast, obtaining the oldest continuous ice cores from archaeological sites in East Antarctica necessitates drilling deeper than 2,000 meters.
“We are still exploring the specific conditions that enable such ancient ice to remain near the surface,” Dr. Shackleton explained.
“Besides the terrain, factors like intense winds and extreme cold may play a role.”
“The winds can disperse newly fallen snow, while the cold can slow down accumulation until the ice is nearly stationary.”
This makes the Arran Hills one of the premier locations globally for discovering shallow, ancient ice, while also being one of the most challenging environments for fieldwork.
The air trapped within these new ice cores enables scientists to directly ascertain the age of the ice by precisely measuring isotopes of the rare gas argon.
This direct dating method means that scientists can derive age indicators directly from the ice, instead of making assumptions based on accompanying features or deposits.
While this ancient ice record doesn’t form a continuous stretch, its age is unparalleled, the researchers noted.
“By dating multiple samples, our team has compiled a library of ‘climate snapshots’ approximately six times older than previously recorded ice core data, supplemented by more detailed younger data from other Antarctic ice cores,” Dr. Higgins stated.
Temperature records derived from oxygen isotope measurements in the ice indicate that the region underwent a gradual cooling of about 12 degrees Celsius (22 degrees Fahrenheit) over an extended timespan.
This marks the first direct assessment of the cooling extent in Antarctica over the past six million years.
Ongoing analyses of these ice cores aim to reconstruct atmospheric greenhouse gas levels and ocean heat content, which hold significant implications for understanding the drivers of natural climate change.
“The COLDEX team plans to return to the Arran Hills for additional drilling in the coming months, potentially yielding more detailed snapshots and even older ice,” Dr. Brook shared.
“In light of the unexpectedly ancient ice recovered in the Arran Hills, we are preparing a comprehensive, long-term study of the region with the goal of extending the record even further, which we hope to commence between 2026 and 2031.”
The team’s paper has been published today in Proceedings of the National Academy of Sciences.
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S. Shackleton et al. 2025. Miocene and Pliocene ice and air from the Allan Hills blue ice belt in East Antarctica. PNAS 122 (44): e2502681122; doi: 10.1073/pnas.2502681122
Source: www.sci.news
