The glaciers on the peaks of the Alps form a climate archive: Since they have existed for thousands of years, ice drilling allows a glimpse into the past. Near Ötzi’s location in the Eastern Alps, researchers have now used such an ice core analysis to determine that the ice there is only about 5,900 years old. Before that, the peaks were therefore free of ice. It was not until Ötzi’s time that the glaciers began to grow again. Today they are at risk from climate change. The new findings can help to better assess the reaction of glaciers to rising temperatures.
As a result of climate change, the millennia-old glaciers in the Alps are melting. On some peaks, the ice is likely to have disappeared in a few decades. In order to better assess how the glaciers will behave when the temperature rises, it helps to look into the past. Deep ice layers provide information about the climate at the time of their formation. Are ice-free Alps a novelty in our era of earth’s history, the 11,700-year Holocene? New research suggests that this is not the case.
Drilling site near Ötzi’s location
By means of drilling on the 3,518 meter high Weißseespitze, a team led by Pascal Bohleber from the Austrian Academy of Sciences has proven that the glaciers only formed at this height around 5,900 years ago. “That suggests that the summit was free of ice before that,” says Bohleber. “Our hypothesis is that at that time, even at high altitudes, there was no climate favorable for permanent glaciation, for example because it was too warm. After that, the conditions for glacier growth must have improved again. “
Ötzi was found just twelve kilometers away from the drilling site, at an altitude of 3,210 meters. According to dating, it lived around 5,300 years ago. “The ice cores indicate that the climate changed at that time. It was getting cooler and the glaciers were growing again. For people at the time, that meant that crossing the Alps was probably more dangerous, ”said Bohleber. According to the researchers, the Tisenjoch, the mountain pass that Ötzi crossed, was probably not permanently covered by ice at that time. Whether Ötzi died in the ice or was only surrounded by ice after his death cannot be determined today. When it was found, the pollen in the surrounding ice was analyzed, but no modern C14 dating was used to accurately determine the age of the ice layers. Today the corresponding ice is no longer preserved.
Glaciers as climate archives
Consistent with previous studies, the authors conclude that there was a warm phase 5,900 years ago. So far, this has mainly been demonstrated in lower regions. “The reconstructions of glacier minimum levels from other archives agree very well with our results. The warm phase 5,900 years ago is thus well secured, now also regionally up to the peaks, ”summarizes Bohleber. The icy climate archives that Bohleber and colleagues have now examined will, however, no longer exist in view of climate change. “We are lucky to be able to remove drill cores at all. Time is running out. There is only ten to twelve meters of ice left, and this climate archive could be gone in just a few years, ”says Bohleber.
However, especially with regard to climate change, their results provide valuable insights: while peaks over 4,000 meters were also covered by ice during the warm period around 6,000 years ago, according to earlier studies, the current drilling has shown that the glaciers at heights between 3,000 and 4,000 meters were not or were not at that time existed to a much smaller extent than today. They are obviously more prone to global warming than previously thought. “It is not that the melting of glaciers is unique throughout the Holocene,” the researchers write. On the other hand, the speed at which the ice is currently receding is worrying. “That should urgently be researched further,” says Bohleber. “The glacier past of the Holocene is an important background for this.”
Source: Pascal Bohleber (Austrian Academy of Sciences) et al., Scientific Reports, doi: 10.1038 / s41598-020-77518-9