Similar to glaciers, ice also forms in some caves. Now researchers have for the first time systematically examined mass gains and losses in Austrian ice caves over the past 2000 years. The effects of cold and warm phases in the past are clearly evident - and also the extreme effects of the current climate change: the enormous ice retreat of recent times could soon lead to a total loss of the valuable climate archives in some caves, the scientists report.
Abysmal, difficult to access and therefore little explored: several thousand ice-bearing caves are known worldwide - Austria is one of the countries with the greatest density of these frosty natural wonders. Researchers from the Universities of Innsbruck and Belfast have been working on their investigation for a number of years. They focused on the common category of shaft-shaped ice caves. Their ice bodies form from solid precipitation in a similar way to glaciers: snow falls and slides into the cave in winter and then subsequently turns into ice. If more is formed through this process than melts in the summer, a frosty body will eventually grow in the cave.
For the current study, the team led by Tanguy Racine from the University of Innsbruck carried out investigations in eight shaft-shaped ice caves in Tyrol, Styria, Upper Austria and Carinthia. “There are already studies on individual ice caves. However, we wanted to do a comparative analysis for the first time and therefore focused on the development of several caves that are in comparable settings: similar altitudes and a steeply to vertically sloping geometry,” explains Racine.
Dateable inclusions in the ice
The team was able to use the radiocarbon method to determine the age of the layers of ice in the caves, which are often many meters thick. "We concentrated on the smallest inclusions of wood in the ice layers. Because the age of these pieces of wood, which fell into the caves from the outside, can be precisely determined,” explains Racine. In total, the scientists carried out 107 datings of wood inclusions and then combined the data with other investigation results. As they explain, the evaluations revealed a precise picture of the increase and decrease in ice in the ice caves - the so-called mass balance. The period stretched back up to 2000 years in the past.
As the researchers report, their results make it clear that the ice in the caves represents a valuable climate archive. For example, they were able to use the datable inclusions in the ice to show that widespread ice retreat occurred during a known warm climate anomaly between 850 and 1200 AD. For the so-called Little Ice Age between 1400 and 1850 AD, the team was also able to demonstrate a positive ice mass balance at all the locations examined. “We can document a comparable ups and downs in ice development in ice caves and glaciers over the last two millennia. For both of them it is important how much snow falls in winter and how warm the summers are. The results also show us that much of the underground ice in Austria dates from the Little Ice Age, between about the 15th and 19th centuries,” reports Racine.
Extreme losses in the last decades
The results make it clear that there have already been periods with negative mass balances in the past - but the current extent is unprecedented, the researchers emphasize: "We are seeing a speed of ice retreat that has not been observed in any period in our measurement period of the last 2000 years observed,” says Racine. “It is not only glaciers that show an above-average negative mass balance, especially in the last few decades. The ice in the ice caves is also severely affected by the consequences of the rise in temperature and the reduction in precipitation,” says the scientist.
Specifically, the researchers report, for example, in the case of the crater shaft in the Sengsen Mountains in Upper Austria, a loss of ice thickness of 20 meters in 20 years. "Especially for the medium-sized and smaller ice caves, we have to assume that they will lose a massive amount of ice mass or even become completely ice-free in the next few years or decades," says Racine. In the coming years, the research team is therefore planning to take targeted ice cores from alpine ice caves and store them in a cool place. In this way they want to preserve the valuable climate information stored in them for science in the long term before the ice in the caves has dissolved in water. "The clock is ticking," Racine concludes.
Source: University of Innsbruck, specialist article: Scientific Reports, doi: 10.1038/s41598-022-15516-9