The once and future balmy Yukon

In the late 1960s, a helicopter pilot who had been transporting geologists along the Peel River came across a couple of small bones while strolling through the watershed between flights.

by Erling Friis-Baastad

In the late 1960s, a helicopter pilot who had been transporting geologists along the Peel River came across a couple of small bones while strolling through the watershed between flights. The bones once belonged to hadrosaurs, duck-billed dinosaurs that lived in the area during the Cretaceous Period.

In the summers of 2008 and 2009, Matthew Vavrek, then a McGill PhD student, was a member of an expedition that went back to the site on the Peel seeking more fossils. The scientists knew from previous experience that if someone could find fossils when not really searching for them, trained paleontologists should be able to find more when concentrating on the hunt.

“It’s just a matter of going back there and putting in time and really looking,” says Vavrek, now a contract assistant curator at the Royal Ontario Museum. “It was a sort of shotgun approach, looking for any kind of fossils we could find. Because so few fossils from before the ice age are known from the Yukon, anything we found would probably be of scientific interest.”

The scientists did unearth a couple of small dinosaur bones, but surprisingly, and more significantly, they found many plant fossils nearby. The fossil flora were at least 10 million years more recent than the dinosaur bones; they dated to the Paleogene Period rather than the Cretaceous, which ended a little over 65 million years ago. The unexpected trove of leaf fossils is helping researchers find answers to one of the most perplexing, urgent questions of our time: How might climate change affect living things in the North?

“I think the biggest thing about the site is that it really gives us a glimpse of how different the Arctic was in the past,” says Vavrek. Usually, when we talk about the planet being warmer long ago, what we’re talking about are not the tropical regions to the south, he says. It was the northernmost areas that saw the greatest temperature variations, just as it’s the Arctic that’s seeing the most climate change today.

The scientists discovered their plant fossils at the base of a steep, unstable cliff. Looking up, they could see the strata from which those rocks had fallen, but couldn’t manage the treacherous climb to that original matrix. Fortunately, the leaf imprints within the fallen rocks could be readily found by splitting the rocks with a hammer. Fossils, especially leaf fossils, create a weakened fault through the rocks that contain them. The rocks tend to fracture right where the treasures have been resting over the millennia.

The researchers had come across “the most diverse known Paleogene plant macrofossil assemblage in the Yukon Territory,” according to an abstract they later wrote for a report of their finds.

So what did that Paleogene Yukon look like? “A lot of the fossils we found in that area are members of plant families you would typically find in southeastern Asia and southeastern North America today,” says Vavrek. Angiosperms, flowering plants, such as plane trees and Katsura-like trees, were the most common. They also found fossils of dawn redwoods, or Metasequoia, a deciduous conifer related to the redwood of southern B.C.

From fossils discovered elsewhere in the Far North it appears the animal life that lived on and among these plants was also much different than what we associate with the Arctic today. Large hippopotamus-like mammals, small primates, turtles and even alligators could have been residents of the neighbourhood.

The Peel site then would have been similar to a lot of semi-tropical areas today, says Vavrek but adds: “In some ways, it is not a very good comparison for what we have today.” In those days, what is now the rich plant-fossil site in the Peel Watershed lay closer to the North Pole because of the rotation of the North American craton. The temperatures and humidity were somewhat semi-tropical, but the region received 24 hours of daylight through parts of the summer, and 24 hours of darkness during some of the not-so-cold winter.

That there’s no place quite like that in the world now doesn’t mean the future won’t include such a northern scenario again. What became of the warmth-loving flora and fauna? Why were similar species subsequently relegated to the semi-tropical regions?

There wasn’t a single cause for the disappearance, says Vavrek. “Small changes all added up to a very, very big change.” Such changes may have acted independently, but all helped bring on a cooling period.

For instance, far to the south, Australia broke away from Antarctica. This altered the patterns of oceanic currents, allowing cooler water to flow north.

As well, a sort of ‘vicious cycle’ could possibly have come into play. The loss of plant cover in the North might have meant that more heat and light were reflected upward rather than absorbed, hence further cooling. More expeditions back into Arctic deep time are needed before more concrete possibilities for future climates, and the associated challenges, are known.

Based in part on the Peel macrofossil floras, Vavrek concludes with a sort of good news/bad news scenario for climate change: “Earth will likely rebalance in 20,000 to 30,000 years from now.” Life on Earth will probably continue in some form, “but the biggest problem for us is, will we make it through, along with other animals we depend on?”

Or will alligator-like creatures pursue herds of turtle-like creatures beneath plane trees, without any interference from humans?

This column is co-ordinated by the Northern Research Institute at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.

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