A team of U.S. scientists has uncovered the oldest directly dated ice and air known to exist on Earth in the Allan Hills region of East Antarctica. This remarkable 6-million-year-old ice, along with the minuscule air bubbles trapped within it, offers an exceptional glimpse into the planet”s climatic history, as reported in a recent study published in the Proceedings of the National Academy of Sciences.
The ice sample, dated by researchers at 6 million years, originates from an epoch characterized by significantly warmer temperatures and elevated sea levels compared to current conditions. The research initiative was spearheaded by Sarah Shackleton from the Woods Hole Oceanographic Institution and John Higgins from Princeton University. Both scientists are affiliated with the National Science Foundation-funded Center for Oldest Ice Exploration, known as COLDEX, a collaborative effort involving 15 research institutions led by Oregon State University.
“Ice cores function as time machines, allowing scientists to explore what our planet was like in the past,” said Shackleton, who has extensive experience in ice core drilling at the Allan Hills site. “The cores from Allan Hills enable us to delve back in time much further than we previously thought possible.”
This discovery marks a significant milestone for COLDEX, which was established in 2021 to investigate the Antarctic ice sheet, the largest ice body on Earth, as noted by COLDEX Director Ed Brook, a paleoclimatologist within OSU”s College of Earth, Ocean, and Atmospheric Sciences. “We were aware that the ice in this area was ancient. Initially, we hoped to uncover ice around 3 million years old, but this finding surpasses our expectations,” Brook explained.
COLDEX is engaged in a global effort to extend the ice core record beyond its existing limit of 800,000 years. Recently, a European team announced the discovery of a continuous ice core that extends back 1.2 million years within East Antarctica.
The COLDEX teams are investigating a unique environment for ancient ice. They have set up a remote field camp in the Allan Hills, where they drill to depths of one to two hundred meters at various sites. These locations feature a combination of ice flow and rugged mountain terrain that helps preserve the ancient ice and makes it more accessible. In contrast, retrieving the oldest continuous ice cores from other areas in East Antarctica necessitates drilling to depths exceeding 2,000 meters.
“We are still researching the specific conditions that enable such ancient ice to remain close to the surface,” Shackleton noted. “The combination of topography, strong winds, and extreme cold likely plays a role. The wind erodes fresh snow, while the cold halts the ice”s movement. This makes the Allan Hills one of the premier locations worldwide for discovering shallow ancient ice, albeit a challenging fieldwork environment.”
The air trapped in the newly discovered cores allows scientists to directly date the ice by measuring an isotope of the noble gas argon. This method of direct dating indicates the age of the ice based on measurements taken from the ice itself, rather than inferring age from associated features or deposits. Although the ice records are not continuous, their age is unparalleled, according to the researchers. By dating numerous samples, Higgins stated, “the team has compiled a library of what we refer to as “climate snapshots” that are approximately six times older than any previously recorded ice core data, complementing the more detailed younger data obtained from cores in Antarctica”s interior.”
Temperature records derived from oxygen isotope measurements in the ice indicate a gradual, long-term cooling trend of about 12 degrees Celsius, or roughly 22 degrees Fahrenheit. This represents the first direct assessment of cooling in Antarctica over the past 6 million years.
Current research efforts focused on these ice cores aim to reconstruct atmospheric greenhouse gas levels and ocean heat content, which are vital for understanding the drivers of natural climate change. A COLDEX team is scheduled to return to the Allan Hills for further drilling in the upcoming months, with hopes of gathering more detailed climate snapshots and potentially even older ice, Brook added.
“Given the remarkably ancient ice we have found at Allan Hills, we have also planned a comprehensive long-term study of this area to extend the records even further back in time, with the aim of conducting this research between 2026 and 2031,” he stated.
Additional contributors to the study include Julia Marks Peterson, Christo Buizert, and Jenna Epifanio from Oregon State; Valens Hishamunda, Austin Carter, and Michael Bender from Princeton; Lindsey Davidge, Eric Steig, and Andrew Schauer from the University of Washington; Sarah Aarons, Jacob Morgan, and Jeff Severinghaus from the Scripps Institution of Oceanography at the University of California, San Diego; Andrei V. Kurbatov and Douglas Introne from the University of Maine; Yuzhen Yan from Tongji University; and Peter Neff from the University of Minnesota.
COLDEX receives support from the National Science Foundation”s Office of Polar Programs, the Science and Technology Center Program at the NSF Office of Integrative Activities, and Oregon State University. Fieldwork in Antarctica is facilitated by the U.S. Antarctic Program and funded through the NSF. Ice drilling support is provided by the NSF U.S. Ice Drilling Program, with ice sample curation conducted by the NSF Ice Core Facility in Denver, Colorado.
