Ice drilled from the Guliya ice cap in northwestern Tibet may be more than 128,000 years old, according to Lonnie Thompson of Ohio State University’s Byrd Polar Research Center and a team of international colleagues. If the estimate stands, the cores hold fragments of the last ice age in a place where earlier work suggested no such record survived. The oldest ice they reach would be the oldest recovered from that part of the Tibetan Plateau, extending its glacial history by more than 100,000 years.
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Thompson, a professor of earth sciences, is the lead author of the study in Science Advances, titled “Additional evidence supports a timescale exceeding 100,000 years for the Guliya ice cap, Tibetan Plateau.” His Ohio State co-authors are Mary Davis and Ellen Mosley-Thompson. The team also includes Juerg Beer of the Swiss Federal Institute of Aquatic Science and Technology, Christof Vockenhuber and Marcus Christl of ETH Zurich, Tandong Yao of the Chinese Academy of Sciences, and Ninglian Wang and Ling Fang of Northwest University in China. The U.S. National Science Foundation funded the work.
A record the older timescale had written off
The question of how old Guliya’s ice is has a history. Thompson’s group published an earlier ice-core record from the same cap in a 1997 paper in Science on the last glacial cycle in a Qinghai-Tibetan ice core, and later work argued the preserved record stopped in the Holocene, the epoch that began roughly 12,000 years ago. A cutoff that young carries an implication. Large ice sheets from the last ice age would then have vanished from the plateau before the Holocene began, leaving nothing for a core to sample.
Thompson says the evidence shows otherwise. In the Ohio State account he said evidence shows the ice sheets did persist, and he describes Guliya as the only mountaintop ice core going back that far. For comparison, the other high-mountain record cited in the study, from Huascaran in the Andes, reaches back only about 30,000 years.
How beryllium, chlorine and cave records set the clock
Dating ancient ice without annual layers is the hard part, and the team leaned on three lines of evidence, as the ScienceDaily report on the study describes. First, cores were drilled on the Guliya Plateau in 1992 and again in 2015, and their oxygen isotope patterns closely matched despite the 23-year gap. Thompson stressed that reproducibility within a single ice cap is extremely important, because a repeat core can show how the ice behaved over time.
Second, the researchers measured radioactive beryllium and chlorine isotopes to pick out the Laschamp geomagnetic excursion, a disturbance of Earth’s magnetic field more than 41,000 years ago that left chemical signatures in the ice. The same event has been traced in the nitrate record of an Antarctic ice core, which is why it works as a shared time marker. Third, the team compared Guliya’s oxygen isotope curves with records from nearby Tibetan cave deposits. From those comparisons the study concludes that the record may stretch back well over 128,000 years.
What remains an estimate
The wording matters. Ohio State’s release on the findings says the ice appears to preserve fragments from the last ice age, and the 128,000-year figure is an age the record may reach, inferred by matching the ice against cave records rather than read directly from a layer count. The release also says Guliya’s topography likely helps preserve the old ice, which is a suggestion and not a measured result.
The stakes extend past a single mountain. Ice cores are among the few archives that hold ancient air, dust and isotopes in layers, and tropical and subtropical high-altitude cores are scarce because glaciers there are shrinking quickly. A record reaching beyond the last interglacial, if the dating survives scrutiny, would let researchers compare conditions on the roof of Asia with the Greenland and Antarctic cores that dominate the literature. The Guliya result is built on repeated drilling that gave the team a second core to test the first against. The cave records used for matching are themselves dated independently, which gives the cross-check some weight. Reproducing the signal from two cores drilled 23 years apart is what lets the team argue that the record reflects the climate and not noise from one borehole. The authors still describe their work as additional evidence in a long-running debate, not a closed case, and independent laboratories dating the same ice would be the natural next test.
The paper itself is the document to watch, and the team plans to analyze additional samples to test how other climate indicators fit the longer timeline. Thompson framed the larger stakes as a question about when ice began forming on the planet and what natural processes of loss looked like, a question the Guliya cores are now positioned to address.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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