Climate change causes ice to disappear from caves in Austria

For the first time, a group of geologists from the University of Innsbruck have extensively recorded the gain and loss of ice in alpine ice caves over the past 2,000 years. They closely examined eight ice caves in four Austrian federal states.

Charlotte Honiat and Tanguy Racine from the Department of Geology pack ice samples into the Tyrolean Guffert Eisschacht for further laboratory analysis. Image credit: University of Innsbruck.

Tanguy Racine, a geologist, warns that ice found in small caves is particularly at risk of soon disappearing and with it an important climate archive. Details of the research can be found in the journal Scientific reports.

There are several thousand ice caves identified worldwide, and Austria is one of the countries with the highest density of ice caves – but only some have been explored in detail. In recent years, a group of scientists from the universities of Innsbruck and Belfast have thoroughly examined eight ice caves with descending morphology in Styria, Tyrol, Carinthia and Upper Austria, adopting a research method comparative.

There are already good studies of unique ice caves. However, this was the first time that a comparative analysis was carried out and we focused on the development of ice in several caves which are also in comparable contexts: similar altitude and steep to vertical sloping geometry.

Tanguy Racine, Geologist, Quaternary Research Group, Department of Geology, University of Innsbruck

Christoph Spötl leads the research group on the Quaternary.

His thesis dealt with the subject in detail. The bodies of ice in these caves are shaped by solid precipitation: in winter, snow falls, slips into the cave and turns into ice at low temperatures.

Similar development of ice caves and glaciers

By applying the radiocarbon technique, the researchers established the age of the ice layers in the caves, which are often several meters thick.

To date the ice, we focused on the tiniest wood inclusions in the ice layers. The age of these wooden fragments, fallen into the caves outside, can be determined with precision,Tanguy Racine elucidates the process.

The large database of a total of 107 dates of wood ice inclusions paints a reliable picture of the gain and loss of ice in the cave – the so-called mass balance – covering a period of almost 2,000 years old. This method allowed the researchers to confirm the hypothesis that historically recorded glacial advances, such as during the “little ice age”, are also illustrated by the increase in ice mass in ice caves and coincide in the time.

We can document comparable ups and downs in the development of ice in ice caves and glaciers for the period of the past two millennia. For both, the amount of snow that falls in the winter and the heat of the summers are essential. The results also show us that much of the underground ice in Austria originates from the “Little Ice Age” between around the 15th and 19th centuries.

Tanguy Racine, Geologist, Quaternary Research Group, Department of Geology, University of Innsbruck

Massive declines in recent decades

In recent years, the balance sheet of ice caves has obviously been negative.

Glaciers are not the only ones to show an above-average negative mass balance, especially in recent decades. The ice caves have also been hit hard by the consequences of rising temperatures and falling rainfall,says Tanguy Racine.

We are witnessing a rate of ice retreat that has not been observed at any time during our measurement period over the past 2000 years. To give a few examples: monitoring in the Guffert Eisschacht in Steinberg am Rofan showed a decrease of almost three meters in snow surface between 2019 and 2021, while Eisgruben Eishöhle in Sarstein in Upper Austria lost 10 meters of thickness of ice in 40 years. The ice loss at Kraterschacht in the Sengsen Mountains in Upper Austria is 20 meters in 20 years.

Tanguy Racine, Geologist, Quaternary Research Group, Department of Geology, University of Innsbruck

The reason for this development, comparable to glaciers, is human-triggered climate change.

Root continues, “Especially for medium-sized and smaller ice caves, we have to assume that they will massively lose ice mass or even become completely ice-free in the next few years or decades. The clock is ticking loudly.”

The Innsbruck team plans to selectively source ice cores from alpine ice caves in the coming years and keep them cool to safeguard valuable climate information for future science.

Journal reference:

Root, TMF, et al. (2022) Multicentennial mass balance of perennial ice deposits in alpine caves reflects glacier evolution during the Late Holocene. Scientific reports.