Collapsing tundra

Melting glaciers might not be the only problem Earth's arctic regions must contend with

From the air, they look like gouges in the otherwise pristine Alaskan landscape, puncture wounds across the tundra.

Michael Gooseff, an assistant professor of civil engineering, thinks these arctic scars—described as "thermokarsts"—could be another sign of the changing global environment.

The discovery of new thermokarst features in Alaska was by pure chance, Gooseff says.

In 2003, he and a colleague were flying along the Kuparak River in northern Alaska on another research project when the two noticed that one of the river's tributaries was particularly muddy. Gooseff admits he didn't pay the muddy water much mind, but at the urging of his colleague, Breck Bowden, the Patrick Chair in Watershed Science and Planning at the University of Vermont, the two decided to follow the mystery water back to its source.

They traced it back to a hill slope that had collapsed. Underneath the failed slope was a water track running through, which was picking up loose sediment.

At first, the two suspected heavy rains might have contributed to the slope collapse, but a closer look made them reconsider.

Gooseff and Bowden found that parts of the permafrost—the frozen soil common in arctic regions—were starting to melt.

A silent problem

Unlike the dramatic images of ice shelves tumbling into the sea, the formation of a thermokarst happens much more quietly, and goes much more unnoticed by the vast majority of people.

Gooseff explains, "Basically ice-rich sediment down in the subsurface had thawed enough so that the overlying soils had collapsed. And because water was running through it, the water was picking up that new loose sediment and carrying it downstream."

The researchers were astounded by what they found when their helicopter set down for a closer examination.

"When we landed, we saw that this was something like we'd never seen across the tundra landscape," he explains.

The two made their way into the thawed sinkholes, encountering newly-formed waterfalls ten feet high. "We were amazed by the size of the thermokarst feature," Gooseff says.

How widespread?

Thermokarst lake features are common in coastal areas underlain by permafrost. Gooseff and colleagues at the University of Vermont, the Marine Biological Laboratory, and the University of Alaska, Fairbanks, began wondering if more of these thermokarst features occurring on hill slopes existed in Alaska. They started surveying the region from the air to see. After a search of roughly 600 square kilometers around the original thermokarst feature, he says, "We were able to identify 35 or so of these, most of which did not show up on old aerial photos from the mid-'80s."

Another search around Feniak Lake in the central Brooks Mountain Range in northern Alaska yielded about 500 thermokarst features in an estimated 40- to 50-mile radius of the lake.

Gooseff and his colleagues have only been able to verify the existence of 120 of these features prior to 1985. He states, "There appears to be a big increase."

A cascade effect

Though some might argue a bit of loose sediment isn't as big a problem as melting glaciers, Gooseff says there might be more sediment hemorrhaging from the thermokarst features than one might believe.

Using just the one thermokarst as an example, the civil engineer says, "Our volumetric analyses suggested that we had enough sediment come out that could cover 20 kilometers of river if it was ten meters wide with one centimeter of sediment. That's the potential effect."

And he believes the loose sediment is causing more than just muddy water.

"The thing that really intrigues us is the effect—what is the effect of having all this sediment now going to the streams?" Gooseff asks. "These streams, these landscapes are fairly competent. They don't erode very quickly, and so you may get flood stages during snow melt each year that will erode this bank or that bank."

He says it could potentially cause a great deal of havoc as it makes its way downstream. "The biology—the fish, the algae that you have growing at the bottom of these streams, the macrophytes that grow—they are all tuned to a system that doesn't often carry a lot of sediment. They're not used to the potential smothering, so to speak."

And as sediment trapped in the ice melts, he believes carbon, phosphorus, nitrogen, and other materials—all previously sequestered in the ice—may be released.

Gooseff continues, "If we think about how the streams are connected to the ocean ecosystems, they move water, but they also move sediments and nutrients. That means a potentially increased load of both to these coastal ecosystems. There's a potential cascade all the way from these headwaters down to the oceans."

Tip of the proverbial iceberg

Not a lot is known about the formation of hill slope thermokarst, Gooseff says. He's already been asked by the National Park Service to do some monitoring work on its lands. "Nobody went around and documented zero for us back in the '80s and '90s, but now we have a baseline from which we can start and go from there."

Gooseff and a team of researchers are also submitting a proposal to the National Science Foundation to study the thermokarst more thoroughly. "How are these things changing over time? Is it fast or is it slow?" Gooseff asks.

He's also been speaking with colleagues in Canada and Russia to find out whether the thermokarst-like features are appearing in those countries as well.

"This does fit into the category of the canary in the coal mine, so to speak. The historic perspective on erosion in the arctic is fairly slow. We've had big ice shelves come off and that seemed irregular. This too seems irregular," Gooseff says. "I think that what is important here that this may very well be yet another line of evidence. We're seeing this on a broad enough scale that it shouldn't be taken lightly."

—Curtis Chan