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Drilling deep on Alaska's Mount Hunter for ice cores that reveal historic climate changes

As warm a summer as Alaska's has experienced, there's still plenty of ice and this year a team of researchers drilled some 700 feet – more than two football fields – deep into a glacier on Mount Hunter, seeking a glimpse at 1,000 years of climate history. And to collect some icy souvenirs.

Mount Hunter, elevation 14,573 feet, is the neighbor of Mount McKinley, North America's highest peak. And that where researcher Erich Osterberg led a team from Dartmouth College, the University of Maine the University of New Hampshire this spring and early summer.

"We drilled two 700-foot, 4-inch-wide holes to bedrock through the glacier on Mount Hunter, the third-highest peak in the Alaska Range," says Osterberg, an assistant professor in Dartmouth's Department of Earth Sciences. An unusual lack of storms allowed the team to complete the ice-core drilling and an array of supporting field research quickly and efficiently. "Alaska's exceptionally warm summer this year also drew attention to the shifting climate picture," he adds.

With a $1.1 million grant from the National Science Foundation (NSF), Osterberg collaborated with professor Cameron Wake of the University of New Hampshire and professor Karl Kreutz and professor Sean Birkel of the University of Maine. Also participating were the National Park Service, the U.S. Ice Drilling Program Office, and students from several colleges.

The field season started at the beginning of May with Kreutz, Wake and their crew flying to into the Alaska Range by ski plane. Osterberg and his student arrived in short order. The team first climbed to Denali's 14,000-foot level, acclimating to the altitude. Equipment and supplies were brought to the site by helicopter and drilling began. In response to a request from the National Park Service, all of the power for the drilling was supplied by renewable power — in this case, a combination of solar and wind.

"This project is part of a new push in our field to narrow the focus down on our understanding of climate change," Osterberg says. He says large-scale projections such as those released by the Intergovernmental Panel on Climate Change (IPCC) are not finely focused enough to account for changes in specific regions such as central Alaska.

"To understand how fast the glaciers in the Alaska Range are going to melt in the future, we need to understand how much the glaciers responded to past changes in temperature and snowfall, specifically in central Alaska. These ice cores will provide our first annual snowfall record in this region."

Like tree rings, the cores can provide data from their annual layers. Studies of the ice cores will concentrate on the chemistry of the ice — how much dust is in it, how much sea salt is in it — and determine the relative amounts of chemical elements.

"If we can assess temperature, snowfall, and storminess, we can get a really good understanding of how the climate of central Alaska has varied in the past," Osterberg says.

In mid-June, all the ice cores, drilling personnel, and equipment were flown off of Mount Hunter by helicopter and ski plane. The cores were then packed in freezer trucks and driven to the National Ice Core Laboratory in Denver, Colo., where they are put in frozen storage. "We will go there in October to cut the cores into slabs that will then get shipped to Dartmouth for sampling, using our ice core melting system," says Osterberg.

This summer field work was the culmination of six years of exploration to find the best spot to collect the longest record of climate possible from this area, going from glacier to glacier in Denali National Park with ice-penetrating radar. The team also maintained weather stations in the area for the last five years, with the goal of relating the weather in the mountains to the snow chemistry.

Studies that focus on the movement of the glacier over time will be conducted in collaboration with University of New Hampshire professor Joseph Licciardi.

"What is neat about this project is that we are using ice core data and combining it with this very different sort of data to get a complete picture of not just how the climate in central Alaska changed in the past, but how the glaciers responded," Osterberg says.

Over the past few years, graduate students Seth Campbell and Dom Winski have been lead authors on four publications on the research, with two more under review.

The National Science Foundation-funded effort has a long timeline, with at least two years of laboratory work remaining. "We have to melt 682 feet of core twice and sample it, with thousands of samples going to the mass spectrometers, ion chromatographs and all these other instruments that we use. And that's just to get the data," says Osterberg. "Then we have to interpret the data using statistical analyses, compare it to other records, and incorporate all this into our glacier and climate models."

Joseph Blumberg is a science and technology writer for Dartmouth College with more than 30 years experience.

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