Along Silver Creek, a 10-kilometre creek bed in the southwest corner of the Yukon, Derek Turner searches for evidence of previous glaciations.
While most studies agree there have been at least three different edges or extents of glacial coverage of the Yukon, there are theories that the glacial coverage was not all that neat and tidy. Some boundaries mask multiple glaciations, some of which are smaller and covered parts of the Yukon at different times.
Part of Turner’s work, as a PhD student at Simon Fraser University, is to confirm when glaciations happened.
Turner does his research within reach of the Kluane Lake Research Station, run by the Arctic Institute of North America.
He uses the station as a base camp from which to hike out to different spots on the creek. Riley Gibson, his assistant, and a local geologist from Whitehorse, hikes out with him. They are gone all day, sometimes days at a time, climbing mountains and cliffs.
Turner and Gibson look for preserved sediments in the strata of old sediment on the edge of Silver Creek.
Beringia – that large area of unglaciated northern Yukon, and parts of Siberia – helped preserve its own regional plant, animal and even insect history in permafrost, freezing and preserving peat beds from thousands of years ago.
“Those peat beds can tell us a lot,” says Turner. “They preserve plant life, ants, beetles, everything you’d find on a forest floor – a forest floor from 130,000 years ago.”
Knowing what was around during that time period – before and after a glaciation – helps researchers understand the warming cycles in between.
“If we’re going to understand climate change – especially for this region – we can study those peat beds to understand how fast or how slow it warmed up; we can determine a lot from the beds,” says Turner. “For instance, we can determine that 130,000 years ago this area had a boreal forest. And we can see how these warm periods changed coming into and out of glaciations across different regions. Peat beds are full of information.”
It’s important to figure out which parts of the Yukon glaciers covered, and when. It’s also important to know how a region was affected by rapid temperature change.
“You want to know what happens in different regions, what weather patterns happened, if it warmed up slowly or quickly, and how the environment reacted to these changes,” says Turner. “How warm were the warm periods?”
Dating the glaciers takes more than radiocarbon dating, which is only accurate from today back to 30,000 to 50,000 years ago. Turner studies the different layers of tephra in the rock strata. Tephra is volcanic ash – this particular tephra is from Alaskan volcanoes – and you can date the sediment using the tephra.
“You extract little shards of glass and you analyze their chemistry and then compare those with a database of dated samples. So, since you know that certain dated tephras are 130,000 years old – if the chemistry of your sample matches this sample really well, then you can say that your sample is 130,000 years old and therefore the sediments and the peat that is with that tephra is 130,000 years old.”
Turner will later analyze and date the tephra found in the peat beds at the University of Alberta-Edmonton this fall.
It’s important to time-stamp the tephra, and by relation, the peat beds. In this way, Turner is trying to time-map Silver Creek and White River.
“I think it’ll be a pretty good contribution to be able to say – pick any point in the last 200,000 years and I will be able to tell you what climate was like and what was going on at Silver Creek and White River.”
But Turner realizes he’s far from that goal. And that while he might eventually be able to tell someone what happened at Silver Creek, he’d be guessing if he tried to tell you what happened several kilometres away from the creek.
“You need a higher resolution of samples around to get a really good feel to what the climate was like and that’s what these tephra beds allow you to do – to correlate with different areas where other people have done research.”
There’s a handful of researchers doing what Turner is doing. “We’re still sort of in the dark ages in doing this,” he says. “There’s still a lot of work to be done. And there’s so much unexplored area that we’re getting only pinpricks in a dark sky.”
Eventually he’ll be able to look at other research done around Yukon and Alaska, and correlate, getting a more regional feel of – not only what Silver Creek looked like – but what Beringia looked like, what the Yukon looked like at this time.
In that way, they can make much more broad implications on what the climate was like 130,000 years ago. And, eventually, be able to give us a better picture of what the future might hold for the Yukon as it is affected by climate change.
“This is a lifetime’s work. Many people’s lifetimes of work,” he says. Research already done earlier in the 60s and 70s on the White River contributes to Turner’s own on Silver Creek.
“It’s one of the joys of being a Quaternary geologist – your work is studying the last 2.6 million years. You don’t study the whole thing by yourself. ”
As well, the sections along Silver Creek were first discovered by George Denton, a PhD student at Harvard University, and his hiking partner, Sir Edmund Hillary.
“They were able to date some of the beds using radiocarbon dating—but since that has a certain maximum limit – they were able to only discuss the geology older than that in broad terms. Now we can actually go in – and we have the technology to say, ‘Yes, this is what it is, and this is when it was.’ So we have much more data at our fingertips now than they would have had forty years ago.”
Turner uses tools Denton and Hillary didn’t have. “I use Google Earth sometimes to look at the stratigraphy in the cliffs around the creek. The resolution is so good you can actually make out the different beds.”
He uses Google Earth to get an idea of where to hike next, so he can more closely examine those layers. On such a long creek, inaccessible by boat and often by vehicle, it’s a handy way of finding out where to look deeper to uncover more evidence of glacial events in the area. But Google Earth doesn’t make everything easy. “We still have to pull ourselves up the side of the cliff using willow branches,” says Turner.
For more information about research at Kluane Lake Research Station, contact Derek Turner at dgturner@sfu.ca, or Ruth Klinkhammer, Arctic Institute Director of Communications, at r.klinkhammer@ucalgary.ca
This column is co-ordinated by the Northern Research Institute at Yukon College with financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.