Team hunts icefields for clues to climate

by Charles Ker
Staff writer

From the air, Trapridge Glacier resembles a pie crust scored and ready for global warming.

This is the view UBC's six-member glaciology team sees before landing via helicopter at its base camp steps from the glacier's edge. The lines visible on the surface are stress fractures in the ice caused by powerful forces under the glacier as it slides over an uneven bed.

Led by Prof. Garry Clarke, the UBC team is attempting to unlock secrets of these subglacial processes and their relationship to global climate change.

"Everyone is interested in coming up with computer models to predict future climates but the problem is that you have to wait for the future for any validation," says Clarke. "The only good way to develop computer models of world climate is by attempting to `predict' past climates."

For Clarke and company, glaciers hold the key.

A professor in UBC's Dept. of Earth and Ocean Sciences, Clarke has been studying Trapridge and many of the Yukon's 4,000 glaciers since 1969. For the last two decades he has been leading teams of graduate students up to Trapridge for month-long studies each summer.

The current team is observing glacial processes in action and plans to use what they learn to simulate the last ice age from 100,000 years ago to the present. Their efforts are part of a national study, called Climate System History and Dynamics, which is attempting to map the relationship between glaciers, oceans, peat bogs and the atmosphere.

"As the Earth heats up, the ice sheets melt and they do something to the ocean which responds and does something to the climate," says Clarke. "Everything is threaded together in a complex matrix."

So what does a tiny glacier on the southwest border of the Yukon and Alaska have to do with the effects of continental ice sheets bordering the oceans?

Clarke and others believe that the subglacial processes underlying Trapridge, which cause it to surge and retreat in regular cycles, mirror those of its continent-sized counterparts. A model of how water and sedimentation systems operate under Trapridge should shed light on how massive ice sheets gave water to the oceans during the last ice age and continue to do so today.

Clarke -- along with students, Jeff Kavanaugh, Gwenn Flowers and Dave Hildes, and surveyor Kuan-Neng Foo -- spend three days making camp before starting their daily treks onto the glacier. The researchers work on the glacier eight hours a day conducting experiments measuring how fast the glacier is sliding and what causes it to do so.

Half of the sliding motion, Clarke says, is caused by the ice sheet actually floating on its own drainage system. The other half is caused largely by the movement of materials forming the soft sedimentary bed and by the creeping of the ice itself.

Trapridge moves roughly 30 metres during a normal year and can advance up to a kilometre during a so-called surge which can last anywhere from two weeks to two years. Trapridge last surged in the 1940s, but a bulge at the bottom of the peninsula-shaped glacier hints that another surge may be imminent.

To collect their data, team members use hot water drills to bore about 40 holes 70 metres down to the glacier bed. They then drop a variety of sensors, designed at UBC, into the holes to measure things such as water pressure, sliding rate, electrical conductivity, ice quake frequency and the movement of underlying sediment.

How the glacier interacts with the bed -- known as ice bed coupling -- is measured with a ploughmeter, an instrument resembling a javelin with sensors bonded onto it. Once the glacier has frozen over the ploughmeter, the instrument's steel tip acts like a claw recording forces as it is dragged along the bed.

Clarke says that even though Trapridge is not considered a fast glacier, events happen with startling speed. The transition from a stately flow to a sudden onslaught of crackling ice quakes occurs within minutes, often ripping ploughmeters and other sensors from anchored positions in the bed.

Clarke's team has discovered that the whole system is based on water pressure which can vary from metre to metre along the bed. When pressure is high, the glacier floats freely and the process of ice bed coupling is greatly reduced. The team also has sensors which can measure the flow of water between the glacier and its bed as well as the chemistry of the lubricating layer of water.

Clarke hopes his team's modelling of water physics at Trapridge will be applied to the big ice sheets which play an integral role in determining world climate.

Says Clarke: "There seems to be evidence that the circulation of the oceans can flick on and off, a process which is triggered by the continental ice sheets. If these circulation patterns are altered in some way, then it's generally presumed that large-scale climate consequences will follow."