Mount Logan ice cores tell a tale of the past
For two years in a row, Geological Survey of Canada researcher Christian Zdanowicz trudged up Canada's highest mountain with a group of other scientists in order to dig holes in the ice.
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With one hand on the drill cable and one hand on the dial, Mike Wacszkiewicz controls an ice drill 5340 metres up Mount Logan.
(photo: Hakan Samuelsson)
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The Mount Logan Ice Core Project is a multi-year, multi-national scientific effort to improve our understanding of past and possible future climates in the Pacific region. Over the course of two years, long columns of ice, hundreds of metres of them, have been extracted from three different elevations on Mount Logan and shipped to southern labs for analysis.
Ice cores are one of the important tools available to us to reconstruct the climates of the past. They belong to a group of climate indicators called proxies -- what Zdanowicz calls "natural archives."
Proxies record indirect evidence of climatic conditions like temperature, precipitation, length of season, and the movement of air currents. Other climate proxies include tree rings, sediment layers at the bottoms of lakes and oceans and in peat bogs, and growth layers in coral reefs.
Ice cores from the world's permanent ice sheets are among the best climate proxies, partly because they extend so far back in time and partly because they contain components of the atmosphere itself.
"They're frozen atmospheric moisture, so they're very direct records of what was in the air," Zdanowicz explains. "You can get both a climatic picture and atmospheric composition from the same record."
Permanent ice sheets form where the temperature remains below freezing all year round. Instead of melting, the snow accumulates. As more and more snow falls, the snow beneath it is compressed and turned into ice. Seasonal and annual layers of snow can still be identified in the ice centuries after they fell.
The best ice cores, says Zdanowicz, come from remote locations where the snow is unlikely to be disturbed. The high icefields of Mount Logan, almost six kilometres above sea level, certainly qualify as remote.
Over the course of the 2001 and 2002 field seasons, three teams retrieved ice cores from three elevations on Mount Logan. An American-led team took several samples from a site 3015 metres above sea level. The longest core, drilled straight down into the ice sheet, was 345 metres long. The team stopped drilling at that point, not because the drill hit bedrock but because it ran out of cable.
A Japanese team working at 4200 metres also stopped before reaching bedrock for the same reason. At 220 metres of depth, a good 20 metres beyond where they expected to reach bedrock, they ran out of cable and had to give up.
The Canadian-led team, working at 5340 metres above sea level, encountered the opposite situation. Radar soundings had led them to expect to reach bedrock after more than 200 metres of drilling, but they encountered it at 190 metres.
Nevertheless, the Canadian core will probably show the longest time record, says Zdanowicz. That's because it was taken from near the centre of the ice sheet where the ice is subject to the least amount of movement.
Ice sheets, he explains, are dynamic things, flowing down the sides of mountains, pooling in valleys, compressing and fracturing as they move. As they flow, the layers of ice become thinner and thinner, spreading across the surface of the rock just like water spreading across a table.
The centre of the ice sheet is more like a deep pool, with very little outward movement. The layers of ice extracted by the ice drill at the 5340-metre level might contain a record of atmospheric events and composition going back up to 15,000 years, to the last ice age.
The Mount Logan cores will join a select group of deep cores that are helping researchers reconstruct the last few thousand years of the world's climatic history, but they will fill a special niche, Zdanowicz says.
Other northern hemisphere ice cores come from areas like Greenland and Canada's eastern Arctic, where the North Atlantic Ocean plays a huge role in climate. Mount Logan's snows are made up of moisture picked up in the Pacific region, as far south as the equator.
"We are filling in a hole in the data," says Zdanowicz.
The work required to establish the length of time represented by the ice core, and the chronological markers it contains, is going on right now in a number of laboratories around the world. Other researchers are, and will be, analyzing the ice in exhaustive detail to pull a wealth of information from it.
How do they do it? Check next week's yourYukon column for some of the answers.
- For more information about the Mount Logan Ice Core Project, go to sts.gsc.nrcan.gc.ca/ice2001.
