Deep within an ice cap in northwestern Tibet, researchers have uncovered evidence of a frozen record extending more than 128,000 years into the past. The findings, published in the journal Science Advances, suggest that high-altitude ice in the region has survived since the last ice age, providing an extraordinary glimpse into Earth's ancient climate history. This discovery extends the known glacial record for the area by over 100,000 years, making these the oldest ice cores ever recovered from this part of Tibet.
The study relied on ice cores collected from the Guliya Plateau in 1992 and again in 2015. Despite being drilled 23 years apart, the samples displayed strikingly similar patterns of oxygen isotopes, which scientists use to reconstruct past environmental conditions. Lonnie Thompson, lead author of the study and a professor at The Ohio State University's Byrd Polar Research Center, emphasized that this reproducibility is critical for validating the reliability of the climate record over time.
Determining the precise age of ice frozen for tens of thousands of years required advanced dating methods involving radioactive isotopes of beryllium and chlorine. These naturally occurring elements decay at predictable rates, allowing researchers to identify specific historical events preserved in the ice. The team detected chemical signatures linked to the Leschamp Geomagnetic Excursion, a disturbance in Earth's magnetic field that occurred more than 41,000 years ago. By comparing these findings with oxygen isotope records from nearby Tibetan cave deposits, the researchers concluded that the Guliya ice record likely extends well beyond 128,000 years.
This timeline revision corrects earlier interpretations which suggested the Guliya ice cap only reached back to the middle of the Holocene, the geological epoch beginning nearly 12,000 years ago. Thompson noted that if the ice were limited to the Holocene, it would imply that large ice sheets from the last ice age did not persist through the early Holocene. However, the new evidence confirms their survival. Outside of polar regions, this is currently the only mountaintop ice core record extending so far back, distinguishing it significantly from records in places like Huascarán, which only reach 30,000 years.
The Guliya ice cap's high elevation and surrounding terrain likely created conditions that allowed ancient ice to remain intact through major environmental shifts. With a more precise timeline established, researchers can now better investigate fundamental questions about the history of Earth's glaciers, including when glaciation began and how natural processes of ice loss occurred. Future analyses of additional samples aim to integrate other climate indicators into this expanded historical framework, potentially revealing details previously overlooked due to uncertainties regarding the ice's age.
Sources: ScienceDaily.