A glacier on Mont Blanc holds something remarkable: a frozen archive stretching back more than 12,000 years. This discovery offers an unusually detailed record of Earth’s changing climate and atmosphere that is preserved in layers of ice.
The glacier, located on the Dôme du Goûter in the French Alps, contains the oldest known glacier ice in the region.
Scientists from the Desert Research Institute (DRI) in Nevada, in collaboration with researchers from France and Germany, studied a 40-meter-long ice core originally collected in 1999.
The results of the analysis show that the glacier has remained intact since the end of the last Ice Age.
Extensive record of aerosols
The team applied radiocarbon dating to determine the age of the ice layers within the core. The analysis revealed a continuous archive of aerosols preserved through time.
The aerosols included microscopic particles and droplets such as dust, soot, sea salt, volcanic sulfur, and human-made pollutants. These samples are essential for reconstructing both regional and global climate patterns.
“For the first time, we have a fairly complete Alpine record of atmospheric and precipitation chemistry going all the way back to the Mesolithic Period,” said Joe McConnell, Director of DRI’s Ice Core Lab.
“And that’s a big deal, because you have two major climate states – glacial and interglacial – and to get a record of atmospheric precipitation chemistry across that huge climate change tells you the most extreme natural aerosol concentrations that you’d expect.”
Europe’s climate history in an ice core
According to McConnell, the ice core also captures evidence from a time when humans transitioned from small, low-density hunter-gatherer groups to developing agriculture, domesticating animals, engaging in mining, and eventually clearing large areas of land.
“All of that is happening around this ice core site. It spans the full range of natural and anthropogenic change, and it’s right in the center of Europe – where much of Western civilization evolved,” said McConnell.
The location in the Alps is crucial. It gives researchers a close-up look at Europe’s climate history without relying on Arctic records, which are farther from pollution sources.
“Ice cores collected from glaciers and ice sheets can provide such information, but since these droplets and particles stay in the air only for a few days to maybe a week, records developed from glaciers close to the sources often are the most informative,” explained study lead author Michel Legrand.
A long-awaited analysis
Although the ice core was collected more than two decades ago, it remained frozen in France until recently.
The ice was then transported to DRI’s lab in Reno, where advanced techniques like continuous flow analysis were used to melt and measure the chemistry of each layer.
“Determining what year or period of time a layer in the ice represents can be challenging, so here we used a unique combination of radiometric methods to establish the chronology in the ice,” said study co-author Werner Aeschbach.
“We were relieved to find that even under the unusually warm climate of the 20th century, the cold temperatures at over 14,000 feet near Mont Blanc’s peak had preserved the glacier so that the ice record hadn’t yet been impacted by melting,” said co-author Nathan Chellman.
The depth of the ice core told its own story. While the Dôme du Goûter ice contained ancient layers more than 12,000 years old, a nearby glacier less than 100 meters away held ice only about a century old. The difference likely comes from stronger wind patterns at the Dôme site.
“It’s exciting to find the first ice core from the European Alps containing an intact record of climate that extends back through the current ten-thousand-year warm period and into the very different climate of the last ice age,” noted study co-author Susanne Preunkert.
Ice core reveals climate changes
By studying the chemistry preserved in the ice, researchers identified a shift of about 3 degrees Celsius between the last Ice Age and the present Holocene Epoch.
Pollen data showed that summer temperatures during the Ice Age were about 2 degrees cooler in western Europe and 3.5 degrees cooler in the Alps.
Phosphorous levels in the ice also gave insights into vegetation changes. Levels were low during the Ice Age, rose sharply during the early Holocene as forests spread, and then declined again with modern agriculture and industrial land-clearing.
Sea salt concentrations helped the team track wind patterns. Higher sea salt levels during the Ice Age suggest stronger westerly winds across western Europe. Since sea salt affects cloud formation and solar radiation, it plays a direct role in climate dynamics.
Dust aerosols told a more intense story. During the Ice Age, dust concentrations were eight times higher than in the Holocene. That’s a much bigger difference than current climate models predict, which usually suggest just a doubling.
The discrepancy might be due to Saharan dust reaching Europe more frequently during colder, drier periods.
More to come from the ice
This study marks just the beginning. With a firm timeline now established, researchers plan to analyze the ice for signs of human activity across the centuries.
“Now we can start to interpret all these other records that we have of lead and arsenic and other things like that, in terms of human history,” said McConnell.
Beyond the historical context, the ice core also helps scientists improve climate models. McConnell said that if you’re really going to go back and examine all possible climate states – past and future – you need a model that captures true climate variability.
“It’s a laudable goal, but to evaluate how good the models are, you’ve got to be able to compare them to observations, right? And that’s where the ice cores come in.”
As the team continues their work, this ancient glacier may reveal even more about how natural forces and human activity have shaped Europe’s past – and how they might shape its future.
The full study was published in the journal PNAS Nexus.
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