Denali Ice
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Every spring, mountain climbing parties from
across the globe gather at a base camp on the Kahiltna Glacier in
preparation for scaling North America's highest peak. More than 1,000
climbers registered with the National Park Service this year to climb
the 20,320-foot Mt. McKinley. Among them were seven scientists from the
University of Maine and University of New Hampshire.
While the other alpine adventurers had their sights set on the summit,
the university researchers searched for the best location to drill and
extract an ice core from Kahiltna and nearby Upper Yetna Glacier. Their
goal: to learn about climate past to better predict its future.
"These glaciers have certainly been here for thousands of years, if not
longer," says Karl Kreutz, associate professor of Earth sciences
affiliated with the University of Maine Climate Change Institute and a
co-principal investigator on the expedition in May with Cameron Wake, a
research associate professor at the University of New Hampshire Climate
Change Research Center.
"Here in the upper part of the glacier, the snow that falls from year to
year doesn't melt; it just keeps on piling up," Kreutz says. "When you
(drill an ice core) straight down, you get something that essentially
looks like tree rings. You have layer upon layer of snow that's fallen,
allowing you to reconstruct how the climate has been changing over time.
You're going back in time the deeper you go into the glacier."
Like the pages of a history book, the layers of snow and ice that
accumulate each year on the glacier tell a story. Chemicals contained in
the layers have the potential to yield information on such climate
controls as pollution transport, temperature and atmospheric
circulation.
"Ice cores are really the best way to look at long records of
atmospheric pollution," says Erich Osterberg, a postdoctoral researcher
at Dartmouth who did his Ph.D. work at UMaine's Climate Change
Institute. "Every year, new snowfalls and it takes the pollution down
with it. It's an ideal record for us."
For instance, previous work in Alaska by the Climate Change Institute
has proven to be an accurate gauge of the economic growth of the
Pacific-Asian region. The manmade pollutants Osterberg found in his
Alaskan ice core work in 2001–02 correlate with the growth of Asian
industry.
"Starting in the '70s or even the late '60s when economic growth really
started picking up, particularly in China, you could see this really
good correlation," he says. "It doesn't really matter what you look at.
You can look at their GDP, you can look at their energy output, you can
look at their CO2 output and they all match pretty well. It's been going
up quite quickly the last 30 years."
While the science of analyzing the chemistry of ice cores can be quite
complex, the actual process of removing a 3-inch column of snow and ice
from a glacier is fairly simple. The ice core drill looks much like the
auger used by ice fishermen. A fiberglass pipe running through the
middle of the drill holds the core as it is pulled to the surface. Deep
cores are hoisted using a winch and cable.
The Denali cores the UMaine-UNH team retrieved this past May were 20
meters long. The deepest cores ever extracted measured more than 3,200
meters (nearly 2 miles) long, drilled in East Antarctica by a European
team of researchers.
Perhaps the trickiest part of a coring expedition comes once the ice is
pulled to the surface. Any melting of the core results in loss of
climate information contained in its distinct layers. Cores are packed
in insulated boxes and buried in the snow until time for transport.
Within five days of retrieval, the Denali ice cores were flown to
Anchorage for freezer storage. From there, they were sent in insulated
containers via Federal Express to Boston. There, a freezer truck
transported the cores to UNH and UMaine.
UMaine maintains two ice core freezers containing more than 1,500 meters
of ice drilled from around the world.
"From a place like Alaska, cargo services are in place to make it
happen," says Kreutz. "But working Asia, for example, it becomes much
more of a challenge to get a piece of ice back to the laboratory. You
might be dealing with carrying pieces of ice on the backs of Yaks or
other animals or trekking through the mountains."
Despite all the planning that goes into an expedition like the Denali
trip, the hauling of 3,000 pounds of gear to do the drilling and the
shipping of a 60-foot-longcolumn of ice across the continent, it is
still the fieldwork that draws Kreutz and many of his colleagues to this
research.
"The winter landscape has always fascinated me," he says. "In addition
to the exciting science that goes on, to be able to come to a place like
this and live in this environment for a time is really great. Working in
the lab and doing the science back home at the university can be quite
exciting, but for many of us, being out here in the field, collecting
samples, living in this environment is really a big part of why we do
it."
by Ron Lisnet
September-October, 2008
