Swiss science seeks answers to climate change in Antarctic ice

Researcher Florian Krauss stores Antarctic ice in a -50°C room at the University of Bern. Luigi Jorio / Swissinfo

Researchers at the University of Bern are studying some of the oldest ice samples on the planet using a revolutionary technique. Their goal is to shed light on one of the major mysteries of Earth’s climate.

Florian Krauss walks briskly. He has no time to waste. In a thermal bag he carries an ice rod the size of a bar of soap – too precious to be compromised. It’s a unique ice sample, dating back over 1.2 million years. “There’s no room for error, but it’s exciting to work with such special ice,” he says.

Krauss, a researcher at the University of Bern, retrieved the ice from a room kept at -50°C at the Institute for Climate and Environmental Physics. It’s the only ice core facility in Europe that can maintain this temperature and was designed to store ancient fragile ice cores.

The collection includes samples taken last January in Antarctica at a record depth of over 2,500 metres. They are being preserved as part of the European project Beyond EPICA – Oldest IceExternal link. The project’s goal is to analyse ice that was formed more than a million years ago to better understand how the climate has changed and, in the long run, to better assess the human impact on climate.

>> The ice analysed by the University of Bern belongs to the oldest continuous ice core extracted in Antarctica:

Krauss cleans the ice sample to remove possible contaminants and takes it to the lab. He wants to analyse the tiny air bubbles trapped in the ice to measure the concentration of carbon dioxide (CO₂) and other greenhouse gases.

This will give him an idea of the composition of the ancient atmosphere. He also hopes to solve one of the great enigmas of paleoclimatology: why the periods of formation and movement of glaciers (glaciations) became longer and more intense.

Scientists have reconstructed the climate of the past 800,000 years using a previous ice core, Krauss explains. “But we don’t know why, about a million years ago, the rhythm of Earth’s glaciations changed.” The new ice samples could provide crucial clues, contributing not only to our understanding of the past but also to improving predictions about the planet’s future climate.

The ice sample extracted at a depth of 2,492 metres in Antarctica is ready for analysis. Luigi Jorio / Swissinfo

Laser to extract air from ice

In the lab, Krauss places the ice inside a gold-coated cylinder at the centre of a metal device connected to dozens of tubes and wires. “That’s where the magic happens,” he says.

Inside the vacuum-sealed cylinder, an infrared beam irradiates the ice sample from top to bottom. The laser transforms the ice from solid to gas (water vapour), bypassing the liquid phase. This process, called sublimation, releases the air trapped in microscopic bubbles found in the oldest samples.

Compared to traditional mechanical methods, which involve grinding or slicing the ice into thin sections, sublimation offers the advantage of 100% extraction efficiency. “We collect all the air trapped in the ice without contaminating it with ambient air,” Krauss explains. What’s more, the absence of a liquid phase prevents any released CO₂ from dissolving in water, which could alter the results.

Once released, the air is immediately frozen at around -258°C. This allows it to be preserved and later analysed with a spectrometer to determine the concentration of CO₂, methane (CH₄), and nitrous oxide (N₂O), as well as the isotopic composition of carbon dioxide – useful for reconstructing past climate conditions.

Revolutionary technique for studying ancient ice

The University of Bern has been active in ice core research since the 1960s, and its novel method of studying ice is revolutionary and unique in the worldExternal link. It was developed in collaboration with the Swiss Federal Laboratories for Materials Science and Technology (EMPA) to precisely analyse the oldest ice samples.

Ice dating back more than 1.2 million years is so compressed that the air bubbles are no longer visible. More than 10,000 years of climate history are squeezed into one metre of ice. To be able to resolve the greenhouse gas changes in this compressed ice, scientists need a continuous, high-resolution and high-precision record that only the new sublimation technique can provide.

Another advantage of this method is the possibility of reusing the extracted air for further analysis. “It’s the perfect recycling,” says Hubertus Fischer, professor of experimental climate physics and head of the research group. “For a standard ice core, such a complex approach wouldn’t be justifiable. But it is when you have a very limited amount of ancient ice available,” he explains.

‘Devil is in the details’

Laboratories in the United States and Australia are trying to develop similar technologies, but so far, the Bern team is the pioneer in this technique. “I have no problem showing colleagues how it works,” says Fischer, who worked on the device for more than five years. “But it’s a very complex system – the devil is in the details.”

Sublimating ice is a technique that’s “very difficult to do”, Christo Buizert, head of ice analysis for COLDEX (Center for Oldest Ice Exploration), the US equivalent of the European Beyond EPICA project, said in 2023External link. “The fact that they’ve managed to get it working is very impressive,” he added.

The ancient ice analysis device developed at the University of Bern is unique in the world. Luigi Jorio / Swissinfo

The University of Bern has also developed a second techniqueExternal link to analyse the amount of noble gases trapped in the ice. These gases, including argon and krypton, help determine past ocean temperatures.

The climate story in 1.2-million-year-old ice

The University of Bern is one of 12 institutions from around ten countries participating in the Beyond EPICA project, launched in 2009. Each has its own specialisation.

The Swiss university is among those analysing greenhouse gases and chemical components dissolved in the ice. Research groups in other countries are studying for example the temperature evolution, the volcanic ashes contained in the ice or the crystallographic structure of the ice.

The goal is to reconstruct Earth’s climate history through the analysis of ice cores extracted in Antarctica. In this polar region, snow accumulates year after year, compacts and forms increasingly deep and ancient layers of ice.

After a previous ice core project about 20 years ago recovered ice dating back about 800,000 years, the Beyond EPICA project recently drilled an ice core at 2,500 metres’ depth with the goal of extending the climate record to 1.2-1.5 million years.

Aerial view of the Little Dome C drilling site in Antarctica, where ice was extracted as part of the European Beyond EPICA project. PNRA_IPEV

‘One of the most complex mysteries in climate science’

Thanks to these new samples, researchers hope to discover why the climate system changed so profoundly during the Mid-Pleistocene era. During that period, between 900,000 and 1.2 million years ago, the extent of ice sheets in the northern hemisphere underwent drastic variations, with a deep impact on the climate.

The interval between cold glacial and warm interglacial periods lengthened dramatically, from about 40,000 to 100,000 years, and the amount of ice on Earth during glacial times dramatically increased. According to the University of Bern, the reason for this change is “one of the most complex mysteries in climate science”.

The alternation between glacial and warm periods is linked to Earth’s orbital cycles around the Sun. But since the variation of these parameters has not changed over the past two million years, the Sun cannot be the cause of the change in ice age frequency, explains Fischer. “We suspect that variations in greenhouse gas concentrations in the atmosphere are behind it, and the only direct way to verify this is by analysing the air bubbles in the ice.”

Ice cores are also essential for improving climate models and predicting future climate evolution. Internationally, there is healthy scientific competition to extract the oldest ice samples, says Fischer. “But the European project is the only one that already drilled the complete continuous ice core, while Japanese and Australian institutes have just started their multi-year drilling efforts.”

Half the CO₂ compared to today

So far, Florian Krauss has analysed only a small portion of the ice samples from Antarctica and says it’s too early to draw firm conclusions.

But he is all but certain that carbon dioxide concentrations in the air bubbles are only about half the level of today’s atmosphere, where CO₂ is strongly elevated by fossil fuels burning and deforestation.

“By analysing ice cores, the human impact on the atmosphere and climate becomes evident,” he says.

The first results are expected to be published in spring 2026.

Edited by Gabe Bullard/vdv/ts