A new study offers evidence that the Italian Alps are warming at an unprecedented rate, and part of that evidence comes from a single, dried-out leaf from a tree that grew thousands of years ago.
An international team of glaciologists led by The Ohio State University drilled a set of ice core samples from atop Mt. Ortles in northern Italy, at a site about 20 miles away from where scientists discovered the 5,000-year-old remains of Ötzi the Iceman.
Paolo Gabrielli, research scientist at Byrd Polar Research Center at Ohio State, said the team's ice core samples revealed something startling: The Alto dell'Ortles glacier, which for thousands of years did not show signs of melting in ice core samples, now appears to be shifting away from a constantly below-freezing state to one where its upper layers are at the melting point throughout the year.
"Our first results indicate that the current atmospheric warming at high elevation in the Alps is outside the normal cold range held for millennia," he said. "This is consistent with the rapid, ongoing shrinking of glaciers at high elevation in this area."
The team's research, which took place in 2011 but is only now being reported, revealed that the first 100 feet of Italian Alpine glacier is composed of thin, partly melted snow. Below 100 feet, the glacier is solid down to the frozen bedrock.
The layer of solid, topped by 100 feet of melty snow, suggests that snow accumulated atop the mountain and was packed down by more snow without ever melting for thousands of years. But starting at about 30 years ago, the ice core samples reveal the partial melting of each new year's snow.
The glaciologists are confident that the state of the glacier remained unchanged until about 30 years ago because of a preserved larch leaf they found during the course of their study. The leaf was found encased in ice, about 240 feet beneath the surface. Carbon dating of the larch leaf pinned it at 2,600 years old, meaning the tree it came from grew about 2,000 years after the death of Ötzi the Iceman.
"The leaf supports the idea that prehistoric ice is still present at the highest elevations of the region," Gabrielli said.
Chemical analysis of the ice core samples will reveal information about the climactic conditions of when the ice formed. Furthermore, the winter and summer layers of ice in the Italian Alps are easily identifiable, which will allow the researchers to obtain a clearer picture of the climate record.
"Ortles offers us the unique possibility to closely verify if and how regional environmental changes can interact with climatic changes of global significance," Gabrielli said.
Gabrielli and his colleagues presented their work in San Francisco this week at the 46th Annual Fall Meeting of the American Geophysical Union.