The primary goal for most teams on Mount Logan is getting to the top of Canada's highest peak. But next summer a crew will be on the mountain with a much different objective; they aim to bring back ice cores containing as much as 100,000 years of climatic history.

Ice cores are used to understand changes in the atmosphere over long periods of history. The individual layers of ice can be read like tree rings, providing clues on the atmospheric chemistry, temperature and precipitation at different periods of time.

"Mount Logan is ideal because it is high and cold, and has a big summit plateau covered with a nice slab of ice," says David Fisher, one of the project leaders.

As the ice accumulates, its immense weight compresses the layers, squeezing as much as 90 percent of the ice's history into the bottom 10 percent of the ice cap. Since the ice on the summit plateau is horizontal, the layers build up undisturbed over time.

With the ice on the plateau estimated to be about 200 metres deep, the bottom 10 to 15 metres of ice might represent 100,000 years of time, while the upper 190 metres might represent only 10,000 years.

Logan's summit plateau stands at 5,340 metres, placing it in the high troposphere layer of the atmosphere. The moisture that reaches this level comes from out in the Pacific Ocean, where there are no major sources for atmospheric pollution.

At high elevation this moisture is deposited as snow and later turns to ice. Fisher says that ice cores taken from the summit plateau should "show you what to expect from clean Pacific air, as clean as you are going to get these days."

The team also plans to drill at a site located 30 kilometres away from the summit plateau at an elevation of 3,017 metres. This site is in the low troposphere, the atmospheric layer that goes up to seven kilometers in elevation.

Researchers with Fisheries and Oceans Canada hope that information on pollutants found in ice cores drilled at this lower site will help to explain changes in productivity in the upper layers of the ocean.

Ice cores from the two sites on Logan will also be compared with cores from the Devon Island Ice Cap, located in the eastern Arctic. Moisture here comes from yet another source, Eurasia.

Glaciologists hope that comparing the different sites will help explain why temperatures are now "out-of-phase" between the Pacific Northwest and the eastern Arctic. While the climate has been warming noticeably in the Yukon and Alaska over the last few decades, the eastern Arctic has shown no significant change during this same period.

The situation is different over the long-term however. At the end of the last Ice Age, 10,000 years ago, temperatures were warmer on both sides of the Arctic, gradually cooling until a time about 300 years ago known as the Little Ice Age.

Temperatures gradually began to increase again, but in the eastern Arctic this warming leveled off very close to the time that pollution started to enter the Arctic at very high levels in the 1950s.

An ice core has been drilled on Logan before. In the 1980s another team drilled down 100 metres, retrieving a core containing 350 years worth of ice layers. This time the crew hopes to drill down 217 metres, all the way to bedrock.

Gerry Holdsworth, the team leader for that drilling project, will be on Logan next summer as well. Equipment was helicoptered into the site this summer. Next summer a small crew will climb to the summit plateau, and then stay there for as much as five weeks drilling through the ice cap.

The cores will be flown off the mountain, and on to the Geological Surveys lab in Ottawa. From there samples will be sent to various labs around the world.

Even the chips produced in the drilling will be put to use. They will be melted down and analyzed for pollen records.

"This should definitely produce new information on the climatic record," says Fisher. "We expect that because it is so cold there the ice could be from the last Ice Age," says Fisher.

David Fisher can be contacted at fisher@nrcan.gc.ca. For more information on ice cores, check the website for the National Glaciology Program at http://members.tripod.com/~thrust_2/glaciology/one.html.