Two ice cores pulled from the same Tibetan ice cap 23 years apart tell the same climate story, and that agreement is now at the center of a long-running scientific dispute. A new study in Science Advances argues that ice in the Guliya ice cap in northwestern Tibet preserves a record stretching back more than 100,000 years, and possibly beyond 128,000 years, far older than critics have accepted.

If the timescale holds, Guliya would be the only mountaintop ice record outside the polar regions reaching that far back, giving scientists a rare window into how Asia's climate behaved through the last ice age.

That matters beyond climate history — it bears on water. The glaciers of the Tibetan Plateau and surrounding mountains, often called the Third Pole, feed some of Asia's largest rivers. Understanding how this ice responded to past climate shifts helps scientists judge how it may respond as it melts today.

A Decades-Long Dating Dispute

The first Guliya core reached bedrock in 1992, and early work suggested its deepest ice might be hundreds of thousands of years old. Later studies challenged that. Researchers comparing Guliya with nearby cave records argued the upper part of the timeline needed to be compressed, and cores drilled about 30 kilometers away at Chongce were dated to only about 9,000 years at their base. A 2022 commentary in the journal Science Bulletin argued Guliya's basal ice was likely an order of magnitude younger than originally claimed, and some studies placed its record within the last 12,000 years or so.

The new paper, led by Lonnie Thompson of Ohio State University's Byrd Polar and Climate Research Center, answers that challenge with a second, independent set of cores drilled at Guliya in 2015. The oxygen isotope patterns in the 1992 and 2015 cores proved strikingly similar, which the team says shows the climate signal is real and reproducible rather than an artifact of a single drill site.

"Reproducibility of the records within a given ice cap is extremely important," Thompson said, according to Ohio State.

A Magnetic Timestamp Frozen in the Ice

Matching patterns alone do not fix an age. For that, the team looked for a known event recorded in the ice itself. More than 41,000 years ago, Earth's magnetic field weakened sharply during an episode known as the Laschamp geomagnetic excursion. With less magnetic shielding, more cosmic rays reached the atmosphere and produced extra radioactive beryllium and chlorine, which settled into snow and ice.

Measurements by colleagues at ETH Zurich and the Swiss Federal Institute of Aquatic Science and Technology detected that chemical signature in the Guliya ice. That anchor point, combined with comparisons to oxygen isotope records from Tibetan cave deposits, supports a timescale far longer than the Holocene-only interpretation.

Thompson argued the evidence fits a broader picture. "If we only had Holocene-era ice in Tibet, that would mean that the big ice sheets from the last ice age didn't persist through the early Holocene," he said. "But evidence shows that it did."

Ancient Ice and Asia's Water Tower

Guliya sits at roughly 20,000 feet (about 6,000 meters) on the Tibetan Plateau, a region that holds the largest store of ice outside the Arctic and Antarctica. High-altitude ice caps like Guliya are among many Tibetan ice reserves that supply fresh water to Central, South and Southeast Asia, and hundreds of millions of people depend on high-altitude glaciers for water, Ohio State has reported. Broader estimates put the number of people who benefit indirectly from Third Pole river basins at about 1.3 billion, according to Down To Earth.

Long ice records help scientists understand how moisture delivery to the plateau, including the monsoon and westerly winds, changed as the planet moved in and out of ice ages. That history is a test for the climate models used to project future rainfall, snowfall and glacier change in a region where small shifts can affect farming, hydropower and drinking water downstream.

The ice itself is a vanishing archive — and a fragile one. Thompson's group has documented warming across Tibet's Kunlun Mountains, and as high-altitude glaciers shrink worldwide, some of the oldest climate records on Earth are melting before scientists can recover them.

What Remains Unsettled

The study strengthens one side of the debate but does not end it. The age claims rest on combining several methods, and the paper's own title commits only to a timescale "exceeding 100,000 years." The 128,000-year figure is presented as a possibility, not a precise date for the oldest ice. Ice near the base of mountain glaciers can be folded or disturbed by flow, which is one reason other researchers have been cautious.

Critics who favored a much younger record have not yet published a response to the new paper. Independent dating methods, such as krypton-81 measurements of the ice, could provide a further check. Thompson's team plans further analysis of the 2015 cores to refine the timeline and examine other climate indicators preserved in the ice.

For readers, the takeaway is not that Tibet's glaciers are safe because they are old. It is that the plateau's ice holds information that cannot be recovered once it melts, and that information bears directly on water security for a large share of humanity.

The bottom line: matching cores drilled 23 years apart, plus a magnetic-field signature in the ice, support a Guliya record of more than 100,000 years. The dating fight is not over, but the case for a long Tibetan climate archive just got stronger.

What Readers Want to Know

What did the new Guliya study find? Ice cores drilled in 1992 and 2015 show matching climate patterns, and a magnetic-field signature supports a record older than 100,000 years, possibly beyond 128,000 years.

Why was Guliya's age disputed? Nearby cores and some dating studies suggested the record was much younger, within roughly the last 12,000 years at the top end of skeptics' estimates.

What is the magnetic timestamp? A weakening of Earth's magnetic field more than 41,000 years ago increased radioactive beryllium and chlorine in the atmosphere, leaving a detectable layer in the ice.

Why does Tibetan ice matter for water supply? Third Pole glaciers feed major Asian rivers that support hundreds of millions of people directly and an estimated 1.3 billion indirectly.

Is the debate settled? No. Critics have not yet responded, and the team plans more analyses to refine the timeline.

Why do old ice records matter as glaciers melt? They preserve climate history that is lost permanently when the ice melts, including clues to how monsoons and glaciers responded to past change.