The 1999 expedition team collecting the ice core from Dome du Goûter on the shoulder of Mont Blanc. Credit: LGGE/OSUG, Bruno Jourdain.

The first ice core from the European Alps dating back to the last Ice Age, and holds clues to 12,000 years of human and environmental history, has been found.

Glaciers hold layers of history preserved in ice, offering unique insights into Earth’s past that can also help us interpret the future.

Trapped amidst the frozen water are microscopic deposits of dust, pollen, and even pollutants that scientists can use to examine environmental changes through time.

The Desert Research Institute’s Ice Core Lab has used this technique to highlight atmospheric lead pollution and economic turbulence in Ancient Rome.

Now, their latest study found that a glacier in the French Alps dates back to the last Ice Age – the oldest known glacier ice in the region.

Study co-author Nathan Chellman carefully preparing longitudinal ice core samples for high-resolution measurements in DRI’s Ice Core Lab. Credit: DRI/ Jessi LeMay.

Intact record

Serving as a record that spans through the development of agriculture in Western Europe and the advent of industrialisation, the glacier holds insights into an era of rapid change.  

The new study examines a 40-metre-long ice core from Mont Blanc’s Dôme du Goûter. Using radiocarbon dating techniques, the research team found that the glacier provides an intact record of aerosols and climate dating back at least 12,000 years.

Glacier ice offers the most detailed record of past atmospheric aerosols, small droplets and particles in the air such as desert dust, sea salts, sulphur from volcanic eruptions, soot from forest fires, as well as pollutants and other emissions from human activities, and this is the first ice core record from the European region that extends back to the last climatic transition.

Aerosols play an important role in regional climate through their interactions with clouds and solar radiation, and the insights offered by the ice record can help inform accurate climate modelling for both the past and future.  

Joe McConnell, Director of DRI’s Ice Core lab who co-authored the study, said: “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.

“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.

“On top of that, you have humans going from hunter-gatherers with a very low population through the development of agriculture, domestication of animals, mining, etc, and then a vast population increase and the clearing 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 centre of Europe – where much of Western civilisation evolved.” 

An ice sample on the melter during continuous ice core chemical analyses in the lab. Credit: Sylvain Masclin.

Driving Earth’s climate

The glacier’s location in the Alps is important because it serves as a more intact record of Europe’s local climate than those found in distant Arctic ice.

Many aerosols play important roles in driving Earth’s climate, so scientists would like to know how sources and concentrations in the air have varied in the past.  

Lead author Michel Legrand said: “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.”

The ice core analysed in this study was first collected in 1999 by some of the study’s French authors.

It was stored in a freezer in France for more than 20 years before McConnell and his team brought it to DRI’s Ice Core Lab in Reno, Nevada, where specialised equipment and methods known as continuous flow analysis allowed it to be melted down and the chemistry measured, layer by icy layer.  

Co-author Werner Aeschbach said: “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.” 

Co-author Nathan Chellman said: “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.

Strong wind patterns

The historic age of the ice at the base of the core, around 40 metres deep into the glacier, surprised the researchers.

Another core collected from a glacier located less than 100 metres away at Col du Dome was found to contain ice only about a century old, despite being much deeper.

The scientists attribute this to the strong wind patterns found on Mont Blanc.  

Co-author Susanne Preunkert, who was a member of the field team that collected the ice core in 1999, said: “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.”

Uncovering more stories entombed in the ice 

This study is only the beginning of the Mont Blanc ice record’s story, as the researchers plan to continue analysing it for indicators of human history.

The first step in uncovering every ice core’s record is to use isotopes and radiocarbon dating to establish how old each layer of ice is.

Now, with that information, the scientists can take an even deeper look at what it can tell us about past human civilisations and their impact on the environment.  

McConnell said: “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.”

The information can also be used to help interpret how changes in aerosols impact the climate and improve modelling to help us understand current and future climatic shifts. 

McConnell added: “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.” 

The study is published in PNAS Nexus.