Tibetan Ice May Be More Than 128,000 Years Old, Stretching Back Through the Last Ice Age

Keypoints:

• Ohio State University researchers re-examined ice cores from the Guliya Plateau in northwestern Tibet
• The cores were drilled in 1992 and 2015 at about 19,370 to 20,340 feet above sea level
• Both show similar oxygen isotope patterns
• The record may reach back more than 128,000 years
• Earlier studies suggested Guliya's record stopped about 12,000 years ago

Scientists say ice buried on Tibet's Guliya Plateau survived the last ice age. The team, led by Lonnie Thompson of The Ohio State University's Byrd Polar Research Center, re-examined cores drilled in 1992 and 2015. The sites sit at roughly 19,370 to 20,340 feet above sea level. The deepest layers appear far older than earlier estimates suggested.

Both cores show similar oxygen isotope patterns. Oxygen isotopes in ice work as a thermometer for past climate. Cores drilled 23 years apart that match closely suggest the signals are real and not sampling errors.

Dating ice is hard because researchers need reliable markers inside it. The team used isotopes of beryllium and chlorine, along with clues from Earth's magnetic history. They compared the results with oxygen records from nearby Tibetan cave deposits. Together, the evidence suggests the oldest ice may be older than 128,000 years.

Earlier work had pointed to a much shorter record. Some studies said it ended about 12,000 years ago, during the Holocene. The Holocene began about 11,700 years ago. Thompson said that if Tibet held only Holocene ice, the big ice sheets of the last ice age would not have lasted into the early Holocene. The new evidence suggests they did.

The finding matters because mountain ice cores are rare. Outside the polar regions, Thompson said, this is the only core from a mountaintop that goes back so far. Rugged terrain and freezing temperatures likely helped preserve it.

Guliya's dating has been debated for years. Some earlier estimates put the 1992 core's base at hundreds of thousands of years, while other methods gave much younger limits. This study narrows the argument without ending it.

Better dating also lets scientists revisit chemical and biological signals already stored in the ice. A clearer clock means a clearer view of how Asia's climate once responded to change.