The Klondike region is known worldwide as a famous place for finding gold. But some scientists head there looking for others sorts of buried treasure -- evidence of really, really old permafrost.

The proof lies in ice wedge casts that have been dated at three million years old. Located in the White Channel gravels, ancient streambeds located well above the valley floors in the Klondike, these casts contain evidence of the earliest known permafrost in North America.

One of the neat things about permafrost is that it is a geologic representation of climate and you can see ice wedges within the geologic record, explains Duane Froese, a Ph.D. candidate in geography at the University of Calgary who is the lead researcher studying the ice wedges.

When we find them, they are very unambiguous, very clear indictors and they can be used to say what the environment and temperatures were like in the past.

Ice wedges -- common features in both arctic and alpine tundra areas -- form when temperatures drop and cracks form in the frozen soil, extending down into the permafrost. In the spring meltwater runs through these cracks, forming v-shaped masses of ground ice that can continue to grow for long periods of time.

When the ice melts out, sediments slump into the now-empty space, forming a cast of the ice wedge, and proving that permafrost once was found in that area.

People have reported seeing ice wedge casts in the Klondike since the 1970s, but back then no one knew how old they were. Now researchers have sophisticated techniques such as fission-tracking that can be used to date the volcanic ash that once trickled down into the cracks with the spring meltwater.

The dates for the ash also provide a date for the ice wedges, and confirm that it was cold enough at the time to form permafrost.

Other evidence has suggested that the climate was warm during this time, as much as 4-5 degrees warmer than it is today, but Froese thinks that the discrepancy just stems from the fact that they are dealing with such huge intervals of time.

A variety of methods are used to date ash, pollen and other materials from that time, and the margin of error for all of them is usually no better than 50,000 years. That allows enough time for the climate to warm up and cool down again, and some of these changes might have been quite rapid.

The ice wedges provide the first clear evidence of when the warmer times came to an end, and an arctic system started to develop. We know that three million years ago vegetation was growing in the High Arctic and coniferous trees were growing up to 80 degrees north, so what we are seeing is the changing of that ecosystem.

The permafrost is starting to come and go, so with those changes we are moving into the ice ages and developing a new ecosystem adapted to colder temperatures.

In most of Canada, the ice age record only goes back 12,000 to 14,000 years, and Froese says that the Dawson area is the best place in North America and very possibly the world to study ancient permafrost and ice age geology.

Also, Dawson's two buried treasures gold and ancient ice wedges usually go together, and often it is placer miners working the gravels who spot the permafrost formations.

The miners do us a great service; several of them know what they are looking for, says Froese.

For more information Duane Froese can be contacted at dgfroese@ucalgary.ca.