Thawing Permafrost in the Arctic Will Speed Up Global Warming
Vegetation grows on the “active layer,” the top section of the tundra that thaws during the summer and may be only a foot and a half deep; the underlying permafrost remains frozen year-round and can be hundreds of feet deep. “After a big rainstorm, you shouldn’t see a whole bunch of sediment running down a stream because there just isn’t much to give up,” says Gooseff. The scientists followed the muddy water upstream about 20 miles until they found what has since been named the Toolik River thermokarst. An underground ice wedge had melted, creating a tunnel as the water ran off. Then, perhaps a few days before Gooseff and Bowden came across it, the tunnel collapsed, forming a deep gully about 150 feet long with a waterfall at its head. “We have a great picture of Breck standing in the thermokarst on a rafted piece of tundra. Breck is, what, six-two, and he’s dwarfed by this waterfall.”
When thermokarsts occur near lakes and rivers, they inject sediment and nutrients into waterways, potentially altering the aquatic ecology. Even if they crop up on hills far from streams, the movement of tons of soil, and the resulting release of carbon, nitrogen, and phosphorous, creates gulches, thus changing water flow and plant species.
Thermokarsts are a natural part of the tundra landscape, but the discovery in 2003 prompted scientists to wonder if there really were more of them taking shape, or if they were just noticing them more. So they compared aerial photos of the area from 1985 and 2006. “There are actually more of them, and they’re forming at a greater rate,” says Bowden, who is interested in how sediment and runoff change water chemistry. “We think there are significantly more thermokarsts now than in the past.” Bowden is overseeing a first-of-its-kind, five-year, $5 million project to study thermokarsts on the North Slope, funded by the National Science Foundation’s Office of Polar Programs.
To get to the three core thermokarst sites near Toolik, there are two options: fly or walk. On a day when Gooseff’s colleagues have called dibs on the helicopter, we don mosquito nets, rain jackets, and rubber boots and hike three miles to a lake called NE-14. After nearly an hour and a half, we crest a final hill and see the lake and the two thermokarsts on its shore, one old and one new. Both are horseshoe-shaped with the ends pointing toward the lake, middle collapsed. The 30-year-old one to the west is “healed.” It’s no longer expanding, and its bottom and walls are covered in thick willow bushes (the formations stop spreading as steep sides gradually give way to gentle slopes). The thermokarst to the east is “active”—an apt description, since as we walk its perimeter, a suitcase-size chunk of tundra gives way, landing with a loud plop in the mud below.
We slide down the eroding slope, and Gooseff, who focuses on modeling how these structures form and how long they grow, steps expertly from one overturned tussock to another to avoid sinking into the thigh-deep mud. Permafrost looks like brown concrete and is frozen solid. When it melts, the result is a goopy mess. Moving away from the walls toward the drier center, Gooseff points to fresh moose, grizzly, and wolf tracks. Suddenly a wolf appears, perhaps startled out of its den by our presence. As I fumble for my camera, Gooseff starts howling—not, as I first thought, to lure the wolf back but rather in an attempt to draw the other scientists’ attention to it. But the four, squished into a two-person tent to avoid the swarming mosquitos, are oblivious as they pore over data.
Down in the thermokarst, Gooseff installs sensors to measure soil moisture. By scattering these and ground-temperature sensors at various depths, he’ll develop a profile of how subsurface temperature changes and how water moves through the soil. He’s also tracking other variables—wind speed and direction, barometric pressure, humidity, and air temperature—with meteorological stations at each site. Eventually he’ll plug these measurements into models to see what conditions cause the landscape to fail. “On the one hand,” says Bowden, thermokarsts are “an interesting indicator that things are changing in the Arctic. On the other hand, it raises some questions about, well, if we accelerate this process, what does it mean for the landscape processes in the Arctic?”
The cranberries growing on the tundra can be easily overlooked. Gazing out, the vast, rolling expanse appears to be a homogeneous sea of cotton grass. But crouch down and a rich vegetative mix emerges. The cotton grass is obvious because it grows on the tussocks that cover the tundra like raised paving stones. About eight inches tall and wide, the wobbly growths make any trek across the tundra a challenging feat. “Step on the top and break an ankle, or step in between and break an ankle,” Bowden says wryly. Growing around the tussocks, among lichens and mosses, is an array of familiar plants in stunted sizes, perhaps a few inches tall: birch, willow, bog rosemary, rhododendron, blueberry, cranberry. At a glance, the baby-pea-sized cranberries hardly seem worth the effort a 700-pound grizzly bear must have to exert to get its fill. But just one taste of the tart yet sweet burst of flavor makes plopping down to hunt for more seem like a splendid way to spend a sun-drenched afternoon.