Melting glaciers destroy important climate data archives

As part of the Ice Memory initiative, researchers from the Paul Scherrer Institute (PSI), in collaboration with colleagues from the University of Friborg and the Ca’ Foscari University of Venice as well as the Institute of polar sciences of the Italian National Research Council (CNR), analyzed the ice. cores drilled in 2018 and 2020 on the Corbassière glacier in Grand Combin in the canton of Valais.

Now, a comparison of the two sets of ice cores, published in Natural geosciencesshows that global warming has made at least this glacier unusable as a climate archive.

The Corbassière glacier, in the Grand Combin massif, no longer provides reliable information on past climate and air pollution, because the melting of Alpine glaciers is progressing more quickly than previously thought. . This sobering conclusion was reached by researchers led by Margit Schwikowski, director of the Environmental Chemistry Laboratory at PSI, and Carla Huber, Ph.D. student and first author of the study, when They compared the signatures of particles locked in annual layers of ice.

Glaciers are invaluable for climate research. The climatic conditions and atmospheric compositions of past ages are preserved in their ices. Therefore, they can serve – in much the same way as tree rings and ocean sediments – as climate archives for research.

Normally, the amount of trace substances bound to particles in ice fluctuates with the seasons. Substances such as ammonium, nitrate and sulfate come from the air and are deposited on the glacier during snowfall; concentrations are high in summer and low in winter, because smaller amounts of polluted air can rise from the valley when the air is cold.

The 2018 ice core, drilled to depths of up to 14 meters in a preliminary study and containing deposits dating back to 2011, shows these fluctuations as expected. But the core drilled under the direction of PSI researcher Theo Jenk, taken in 2020 to a depth of 18 meters, only shows these fluctuations for the upper three or four annual layers. Deeper in the ice, i.e. further into the past, the curve indicating the concentration of trace substances becomes noticeably flatter and the total amount is lower. Schwikowski’s team talks about this in their study.

Carried away by meltwater

Their explanation for the observed discrepancy: between 2018 and 2020, the melting of the glacier must have been so strong that a particularly large quantity of water from the surface penetrated into the glacier and carried away the traces it contained in the depths.

“But apparently the water has not yet frozen, concentrating the trace substances,” concludes the environmental chemist, “instead, it has flowed and literally washed them away.” Of course, this distorts the signatures of the layered inclusions. Climate archives are destroyed. It’s like someone broke into a library and not only messed up all the shelves and books, but also stole a lot of books and mixed up the individual words into the remaining words, making it impossible to reconstruct the original texts.

The researchers looked at weather data from 2018 to 2020. As there is no weather station at the summit of Grand Combin, they combined data from surrounding stations and extrapolated it for the study area on the mountain. According to this calculation, it was warm on the glacier, consistent with the general climatic trend, but these years were not extreme values.

“We conclude that there was no single trigger for this strong melting, but that it was the result of many warm years in the recent past,” says Schwikowski. “It appears that a threshold has been crossed, which has now led to a relatively strong effect.”

An unexpected dynamic

Ultimately, the example of Grand Combin shows that the melting of glaciers is progressing more dynamically than experts thought.

“For a long time it has been clear that the glacial tongues are retreating. But we would not have thought that the areas feeding the high mountain glaciers would also be seriously affected, that is to say their highest part, where forms the ice replenishment,” says Schwikowski.

So far, researchers have looked at the distribution of oxygen isotopes in the ice, which can provide information about temperature changes, as well as trace ionic compounds such as ammonium, nitrate and carbon dioxide. sulfate. They then want to analyze to what extent the signatures of organic substances present in the ice are also affected.

Ice Memory: Antarctic ice core sanctuary

Another reason Schwikowski is interested in this issue is that she, along with other ice core experts from around the world, is participating in the initiative led by the Ice Memory Foundation. The goal of this research effort is to obtain ice cores from 20 threatened glaciers around the world in 20 years and collect them in a global climate archive. The cores, cut into sticks approximately one meter long and eight centimeters in diameter, recovered individually from the depths, must be stored permanently and securely in an ice cave at the Italian-French Concordia research station in Antarctica, managed by an international company. long-term governance.

Reliable temperatures near the South Pole, averaging minus 50 degrees Celsius, ensure that the cores will remain usable for studies in the future, even if global warming causes all Alpine glaciers to melt at some point. This is important because analysis methods are constantly improving and future generations of scientists could extract completely different information from the ice.

The Grand Combin ice core should be one of these 20 glacier samples.

“But we already realized, on the mountain, that this would not achieve anything,” says Schwikowski. “As I said, the 2018 test drilling still looked good. But on several occasions in 2020 we encountered thick, solid layers of ice that had formed in the meantime as the water melted and was freezing again. We encountered one of these particularly thick layers at a depth of 17 to 18 meters, which was beneath a very watery and soft layer. This transition caused us enormous problems. Especially when we drilled deeper and as we were removing it, the drill got stuck in the hard ice layer and we almost lost this expensive piece of equipment.

As other attempts on other parts of the glacier saddle encountered the same layer and the same difficulties, the researchers had to abandon the expedition. They actually wanted to drill 80 meters deep, down to the bedrock, to record the glacier’s entire record, which spans thousands of years. But that was not possible.

“And our analyzes now confirm this,” says Schwikowski. “At the Grand Combin, we are already too late.”

Race against time

It is feared that this will also be the case for other glaciers around the world that have not yet been sampled as part of Ice Memory. In the Alps, besides the Col du Dôme glacier on Mont Blanc at 4,250 meters above sea level, where the project team drilled for the first time in 2016, there is only the Colle Gnifetti on the border Italian-Swiss, which is even higher at 4,450 meters and therefore colder than the Grand Combin Glacier. The following year, the PSI team and partners from the Ice Memory Foundation were able to obtain an ice core whose signature was still intact.

Cores from Illimani in the Bolivian Andes, Belukha in the Russian Altai and Elbrus in the Caucasus have already been obtained. Last year there were also expeditions to Spitsbergen and Col del Lys in Italy; their analyzes are still pending. An expedition to Kilimanjaro, which has Africa’s only significant ice mass, failed last year due to political and administrative problems.

The project is a race against time. Success is by no means guaranteed. Setbacks like those of the Grand Combin become more likely every year.