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DNA frozen in permafrost muck reveals ancient ecosystem teeming with wildlife

University of Alberta scientist Duane Froese was on sabbatical last summer when he received a call from a Yukon miner who wanted to give him the heads-up about a site he planned to excavate. 

University of Alberta scientist Duane Froese examines an sheet of permafrost in the Yukon that has yieldd the bones of Ice Age animals [Credit: Brent Aloway/Edmonton Journal]
Like most Klondike miners, Tony Beets is a character. He’s tall, bushy-haired, drives fast and uses colourful language. 

But he’d also been incredibly helpful over the years, moving in heavy equipment for scientists such as Froese, exposing layers of ancient permafrost that yielded the frozen bones of woolly mammoths, scimitar cats, short-faced bears and other animals that lived in this part of the world before the last major Ice Age ended 11,500 years ago. 

Shortly before Froese arrived on the scene, his team already had unearthed some woolly mammoth bones that Beets had exposed. 

The fossil that stood out the most, however, was the skull of a horse that had lived in the Arctic during the last Ice Age. 

This was not the typical small Yukon horse that Froese and other paleontologists had found here and in other regions of the Arctic. This was a huge animal — a Clydesdale next to an Icelandic pony — that probably would have had an easier time outrunning scimitar cats, American lions and short-faced bears that prowled this ancient world around the same time. 

“The fossils of horses like these show up rarely in North America,” says Froese, who considers himself to be a geologist rather than a paleontologist. 

“To have some that are incredibly preserved in permafrost, and the chance to directly date them, is really significant. It was exciting to see more of these horses at a site where we could get a potentially rich record of the environment they were part of.” 

This isn’t the first time that scientists had found evidence of a “Lost World” in the western Arctic. 

Most people, however, barely noticed when Canadian Museum of Nature paleontologist Dick Harington found the bones of woolly mammoths, scimitar cats, eight-foot-tall beavers and other Ice Age animals in the Yukon while working on his PhD at the University of Alberta in the late 1960s and early 1970s. 

Harington’s findings, and those of others who followed, painted a remarkable picture of a vast steppe land that was free of ice because the climate was too dry to allow for the formation of glaciers that covered most of continent. 

In a world where a large percentage of the Earth’s water was locked up in those massive glaciers, ocean levels were so low that countless Siberian animals were able to cross over to Alaska and the Yukon by way of the Bering Land Bridge that connected the two continents. 

No one knows exactly why half of these Ice Age animals disappeared from the landscape so quickly. Most scientists attribute it to a rapidly warming climate that resulted in succulent grasses being replaced by woody shrubs and trees. 

Others believe that disease, or an extraterrestrial impact may have been responsible. A few even have suggested the humans who eventually followed these animals into Alaska and the Yukon hunted them to extinction. 

Working with geneticist Eske Willerslev, Yukon paleontologist Grant Zazula and other scientists from Australia, Scotland, England, and the United States, Froese found evidence at a site along the Yukon River in Alaska a few years ago that puts a new, radical spin on the debate. 

The evidence they found near Stevens Village showed that some Ice Age animals such as the woolly mammoth and the giant horse lived several thousand years longer than previously thought in so-called “ghost ranges” of the western Arctic. 

“Surprising as it might seem, it was not a shock when you consider the fact that large mammals like mammoths and horses survived through previous periods of rapid warming such as that which occurred at the end of the Pleistocene (Ice Age),” Froese says. “They must have found a refuge somewhere. So, there’s no reason why they couldn’t find one again.” 

What is surprising is how Froese and his colleagues came to this conclusion. The evidence they unearthed from that site along the Yukon River in Alaska didn’t come from fossils; it came from the DNA extracted from the hair, skin, feces, urine or possibly skin cells that the animals left behind. Frozen in permafrost, and uncontaminated by other genetic material that may have been deposited later on, this DNA was well enough preserved for scientists to be able to identify the animal from which it came. 

No one was more excited than Froese when the results came in. He was never convinced that all these Ice Age animals disappeared so quickly and completely from the landscape. Now, with this discovery, he believes the debate is over. 

“We know that these large mammals survived for many hundreds of thousands of years and through periods of warming,” he said. “The question has been why at this final warming interval were there so many extinctions? What our research result does is end the debate that there was a single cause.” 

This isn’t the first time that environmental DNA has been used to detect the presence of an animal or other life form. 

Scientists have been using scat and hair to identify the presence of grizzly bears and other animals in the wild for several years now. They’ve even used water samples to establish the presence of Asian carp in the Great Lakes even though no live specimens were found. 

Detecting the presence of animals in DNA frozen and preserved in ice, however, is a whole new ball game that got started in Siberia several years ago, and it is not one that all scientists are comfortable playing. 

“It is controversial among the paleontology community who want the dated bones,” says Froese. 

“But we did have some success with that site we worked in Alaska where we found the mammoth DNA, and we plan to try this approach again this coming summer.” 

Having grown up in Cranbrook, B.C., where people tended to be teachers, engineers and foresters, Froese never dreamt that he would one day be sifting through permafrost in the Arctic searching for fossils and the DNA of ancient animals. 

Nor did he think it would be exciting to do so in conditions that have produced everything from hordes of mosquitoes to snowstorms at their field sites. 

But he got hooked on the challenge of unravelling the history of the ancient past after spending a few summers in the field working with the Geological Survey in the Yukon and the Northwest Territories. 

“Some of the sites we’d work on seemed to be in the strangest places,” he recalls. “One month we’d be in an old gravel pit outside of Inuvik in the Northwest Territories or along an exposure by an abandoned trail. Then . . . we’d be in the spectacular valley in the Canyon Ranges of the Mackenzie Mountains. 

“But I gradually began to understand how there was this big puzzle about the evolution of the Arctic climate that we were trying to piece together. The ages of things that we were dating at one site — whether it was a record of glaciation or fossils — had to be consistent with changes that occurred at other sites. And if they weren’t, why weren’t they? 

“It was an intuitive way of thinking about the ancient world that appealed to me.” 

Froese got to know Beets when he was a graduate student working on a site in the Klondike in those early days. 

“He’s a bit of a character, which you have to be careful about saying in the Klondike because once you start, you end up saying it about everyone. But Tony is an original.” 

A few summers ago, Froese dropped by to see if Beets had any new exposures he was working on. That’s when the miner told him about the ‘muck’ section he eventually would excavate. 

Muck, says Froese, is organic, rich silt that is full of the permafrost that miners have to remove to get at the gold in the stream gravels. 

Most of it accumulated during the cold stages of the Pleistocene — the times when much of North America and almost all of Canada, except for part of the Yukon, was covered by ice sheets. 

“It’s also the place where much of the carbon we worry about with future climate change is stored,” says Froese. “In fact, the volume of carbon in muck deposits across Alaska, Yukon and Siberia is comparable to the amount of carbon presently in the Earth’s atmosphere.” 

In addition to the mine site, Froese hopes to expand his research in the Old Crow Flats of the Yukon where he, Harington and other paleontologists have found so many Ice Age animals. 

Here, the sedimentary and fossil record from the early to middle part of the last Ice Age is almost as well preserved as some colder sites in Siberia, which have revealed the remains of mammoths that still had their eyes, trunks and fur in place. 

Froese concedes that the prospect of finding a perfectly preserved mammoth in the Old Crow Flats or elsewhere has occurred to him even though the permafrost there is not as rock-hard cold as it is in many parts of Siberia. 

“Frankly, the idea of finding a full mammoth in ice scares me,” he says. 

“We’ve found partial mummies (the term given to the frozen carcasses in the permafrost, even though they’re not typically ‘mummified’ but have a lot of soft tissue preservation) over the years. 

“And the way you know that they’re close is because there is a wretched smell that you pick up about a hundred metres away, long before you see anything. Typically the muck has a bit of a sweet smell — kind of like peat or maybe a horse barn — but not so when a soft animal tissue is thawing.” 

“If a mammoth came out of the Klondike” says Froese, “it would be incredibly interesting, and I’m sure a career highlight, but no doubt a very messy thing to deal with.” 

That said, he is more focused these days on what environmental DNA research might reveal in the future and whether it might reveal that horses, mammoths and other Ice Age animals lived even longer than we now think. 

“I find it exciting to think that only a few grams of sediment in permafrost can potentially link a specific part of the geological record to the large mammal community such a mammoth,” he says. 

“It’s going to he fun testing what we discovered along the Yukon River at other sites.” 

Author: Ed Struzik | Source: The Edmonton Journal [November 19, 2011]

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