by Claire Eamer
Science can be a messy business. Just ask Tyler Kuhn. He’s spent a lot of time, over the past few years, searching through the slimy mud of melting permafrost or studying thousand-year-old caribou dung.
Kuhn is a wildlife harvest technician with the Yukon government and currently finishing a master’s degree in biological sciences at Simon Fraser University. For the past few years, he’s been involved in research that analyzes the genetic material of long-dead animals in order to learn more about the past.
In a recent Yukon Science Institute talk, Kuhn explained that the Yukon is a prime location for finding ancient DNA. That’s where the slime and the dung come in. It’s also a prime location for dating the DNA, and that’s because of the volcanoes.
So - volcanoes, slime, dung, and miniscule fragments of DNA. As science stories go, this one’s a winner!
First, the volcanoes. The Yukon, Kuhn explains, is downwind from the string of volcanoes that extends through southern Alaska and along the string of islands reaching across the Bering Sea. When a volcano erupts and spews ash into the air, the prevailing winds send the ash drifting eastward over the Yukon where it settles to the ground.
Millions of years of eruptions have deposited layers of volcanic ash, or tephra, over the southern Yukon, each chemically identifiable and many of them datable. An excellent place to see them is in the goldfields near Dawson, where miners shoot huge jets of water at frozen banks of muck to wash away the soil. Visible in the banks are lines of tephra. Each of those dated bands is a page in a calendar. Everything found above that band is younger, and everything below it is older.
“The oldest dated tephra I saw in Dawson this summer was 3 million years old,” Kuhn says.
And then we come to the slime. The frozen soil melts into slimy muck, sometimes releasing the remains of long-dead animals - teeth, bone fragments, even whole skulls or massive mammoth tusks. The tephra layers help date animal remains that may have been locked in a permafrost deep-freeze for tens of thousands of years or more. Some of the frozen bones and teeth are so well preserved that it’s still possible to retrieve DNA from them.
Kuhn says that’s unusual. Genetic material breaks down naturally after an animal dies, and does so pretty quickly, but frozen DNA lasts much better. The Yukon has bountiful supplies of frozen DNA. The bonefields of the Klondike are one source - and researchers at Pennsylvania State University are currently analyzing the finds from this summer’s field work in search of viable samples. Another source is the ice patches high on the mountains of the southern Yukon.
Here’s where dung comes into the story. The ice patches are melting as the climate warms, revealing dung left behind by thousands of generations of caribou in search of relief from the heat and insects of summer. Buried in the dung are teeth and bones, the remains of caribou that didn’t survive some long-ago summer. Kuhn has been able to retrieve genetic material from teeth and bones more than a thousand years old and compare it to the caribou that roam the same landscape today. They’re not the same.
“Caribou in the Southern Lakes region are actually different from caribou in the rest of the Yukon,” he says. They may look the same and, as he says, taste the same, but the genetic differences are clear.
And that takes us back to the volcanoes. Roughly 1200 years ago, a volcano near the Yukon-Alaska border blew its top in a huge explosion. The plume of ash spread across the southern Yukon, resulting in the White River ash, a layer of whitish soil, at least five centimetres thick, that is easy to see in cutbanks along roads and rivers in the Whitehorse area.
“This is a big volcano,” says Kuhn. “It was quite a bit bigger than Mount St. Helen’s.”
Kuhn’s analysis shows that Southern Lakes caribou from before the eruption are different from Southern Lakes caribou after the eruption. That might be because of the White River eruption and the massive cloud of ash that probably buried the lichens caribou depend on. The White River eruption could have forced the Southern Lakes caribou to move or even killed them off, allowing caribou from somewhere else to recolonize the region.
But something else was happening at the same time: the Medieval Warm Period, when temperatures rose for a few centuries, enough to affect plants and animals and weather patterns. Kuhn says it’s also possible that deep snow during the Medieval Warm Period whittled down caribou numbers to the point where only a few survived, with a limited range of genetic variation.
“I don’t think that’s the correct explanation, but it’s another possibility,” he says. It will take more sampling, both of DNA and of the layers of ash and soil, to determine which explanation is right.
For more information about ancient DNA and volcanoes, contact Tyler Kuhn at tskuhn@sfu.ca.
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. This week’s column was sponsored by the Yukon Science Institute.