August 17, 2009 – Original Source: Chemical & Ingeneering News, Volume 87, Number 33, pp. 39 – 43
Features formed by melting permafrost provide clues to a changing Arctic landscape and climate.
There is a profound quietude north of Alaska’s Brooks Range, the string of mountains separating the boreal forest from the Arctic tundra. Traveling along the Dalton Highway, the one road to the Arctic Ocean, one sees little visible movement in the landscape aside from the trucks barreling up to the oil fields, an occasional camper, or subtle signs of wildlife. Every angle, every turn offers stillness and beauty; it is like driving straight into a postcard.
Yet the tranquility belies the dramatic change under way. The climate in the Arctic is warming more rapidly than nearly anywhere else. Sea ice is disappearing faster than models had predicted—everyone has seen the images of a polar bear stranded on a shrinking ice floe—and the frozen soil is warming as far as 65 feet below Earth’s surface, points out Syndonia Bret-Harte, a plant community and ecosystem ecologist at the University of Alaska’s Institute of Arctic Biology.
No one is more keenly aware of how quickly the environment is changing than the scientists at Toolik Field Station, the National Science Foundation’s Arctic long-term ecological research site, where Bret-Harte is the associate scientific director. Since the camp was established in the 1970s, researchers have returned summer after summer to conduct long-term studies of the plants, lakes, rivers, and wildlife. They see firsthand that in the carefully balanced environment of Alaska’s North Slope, small changes can have major consequences.
Now, a large group of scientists are collaborating to understand how the consequences of a warmer Arctic could impact its landscape and feed back into global warming. With a grant from NSF, they are studying the mechanics of thermokarsts, or features created when permafrost, or soil that has been frozen for years, melts, then collapses like a soufflé. Each scientist brings a different kind of expertise that can help create a complete picture of how a thermokarst changes the surrounding environment.
“The Arctic is a place where everything is about the minutest change in energy balance,” says William (Breck) Bowden, an aquatic ecologist at the University of Vermont, who has been coming to Toolik for more than 20 years.
Just how delicate is that balance? Consider a set of tire tracks visible in the tundra near a pump station off the Dalton Highway on Alaska’s North Slope. The tracks look freshly made, but are actually a relic from the 1940s, when a single vehicle passed over the surface of the tundra. All it takes is the weight and friction of the truck to expose the soil, making a small change to the albedo, or the amount of light being reflected away from the ground’s surface, and the area begins to melt. “And as it continues to melt, a new community of vegetation starts to grow there, and now we have a scar,” Bowden says.
Imagine, now, the impact of an all-out failure in the Arctic permafrost, which has been rock solid for hundreds, even thousands of years. If you were to cut deep into the ground, you’d find the permafrost looks a lot like brown concrete; fittingly, it serves as the structural foundation for the far north. But it only takes a small change—a little water winding its way down into the ground, warming the soil or melting ice buried deep within, for example—and that foundation gives way and a thermokarst forms.
The failure can happen in various ways: a slump on a hillside, a gulley, detachment of a top layer of tundra, or a ground collapse when glacial ice melts. After the initial breakdown, the feature continues to evolve for a period until it starts to stabilize and eventually heals over.
Scientists are suddenly more interested in thermokarsts because, well, there simply seem to be more of them. From photographs taken from a low-altitude flyover of the entire state in the early 1980s and data gathered in 2006, scientists believe the number of thermokarsts in the Alaskan landscape has doubled in that time. “This is a natural phenomena, but it appears to be accelerated by warming in the Arctic,” Bowden notes.
The thawing of soil that has been frozen for so many years and is chock-full of organic material has an immediate impact on the local environment. Nutrient-carrying sediment can be dumped into nearby lakes or streams, changing the water chemistry and stream dynamics; microbes and vegetation have access to more food, meaning different plants can thrive in the nutrient-rich soil; the albedo in that area changes, potentially allowing more permafrost to melt. And from a climate-change perspective, carbon that was locked away in the ice for hundreds or thousands of years could be rapidly released.
With $5 million in funding from NSF’s Arctic System Science Program, a group of roughly 25 scientists at Toolik, led by Bowden, have embarked on an expansive study of the short- and long-term impact thermokarsts could have on the Arctic landscape. By pooling their collective expertise, they want to understand how long it takes for ice to melt, how dramatic the changes to the local environment could be, and how long those changes might persist once the landscape begins to heal.
The project, which currently has four years of funding, was officially launched this summer. This year, the group is focusing its research on three thermokarsts that are readily accessible to the field station. A rather sizable number of the principal investigators (PIs)—there are 17—and graduate and postdoctoral students involved in the project had their first group meeting at Toolik this summer to pound out the details of what should be studied.
From a coordination perspective, it’s a bear of an undertaking. Although PIs usually spend a few weeks at Toolik at the start of the summer, their students are responsible for keeping up the daily grind of sample collection. And data are generally analyzed long after everyone has returned to civilization.
But there is one major factor working in the scientists’ favor: the Toolik culture. The station sits on a pristine lake about 350 miles north of Fairbanks—in other words, smack in the middle of nowhere. When camp is full, there are about 120 researchers and support staff on site, and with the nearest bar or shopping mall an eight-hour drive away, it’s hard not to get to know most everyone. During the hour when dinner is served, anyone not out in the field can be found in the camp’s one dining hall; inevitably, over an Alaskan beer and a hot meal, the conversation turns to the day’s work.
It’s no surprise, then, that an accidental discovery of a thermokarst several years ago by two Toolik scientists would eventually spark the interest of a number of researchers at the camp.
As with many scientific discoveries, the thermokarst project was a product of serendipity. In July 2003, Bowden and Michael N. Gooseff, an environmental engineer at Pennsylvania State University, were in a helicopter, scanning the landscape for potential research sites for a project to study thawed zones along the edges of rivers. Flying down the Kuparuk, a river just west of the field station that snakes its way from the North Slope up to the Arctic Ocean, the researchers noted that the water was as beautiful and blue as ever. They decided to head over the next ridge to check out the Toolik River. But instead of a clear blue stream, they were greeted by muddy, brown, all-around nasty-looking water.
The idea of a chocolate-brown river might not seem odd to someone living in the lower 48, where water is constantly moving and rain can easily wash sediment into it. But as Gooseff points out, when the ground is frozen solid, even heavy rain doesn’t disturb much.
After flying up about 25 miles, they came to a water track that was pouring tons of sediment into the Toolik River. As they followed the stream, they saw a large rip in the tundra: a freshly formed thermokarst. “We flew over it a couple of times and were just amazed by this gash,” Gooseff recalls.
The helicopter set down, and the pair saw that a huge gulley had formed. The hole in the ground was so deep that Bowden, who is at least 6’2”, was fully immersed as he stood on a small carpet of tundra that had surfed to the bottom. As the earth wrung itself out, so much water was released that a small waterfall had even formed.
The scientists believe the ground had collapsed somewhere from hours up to a few days before they stumbled upon it. Their discovery provided an amazing opportunity to study the feature in depth from its genesis.
The vast collaboration around thermokarsts that subsequently came together has several broad objectives. The researchers want to know how and why thermokarsts occur and to generate a predictive model that could help identify environments where a failure is more likely.
“It’s easy to say there was a failure of the ice, but it doesn’t mean we know the mechanics,” Gooseff says. For Alaskans, ground stability is critical when assessing both new and old infrastructure. “The Dalton Highway certainly has met some of those challenges in various ways—there wasn’t a specific landscape model of permafrost stability when they built that road back in the ’70s,” he adds.
Gooseff is part of that “how and why” team. Along with Antoni Lewkowicz, a permafrost expert and geography professor at the University of Ottawa, he will be responsible for coming up with the model of how thermokarsts form and how long one might persist in a given environment.
Gooseff is trying to figure out the dynamics of heating and cooling at different locations inside and out of the three thermokarsts near Toolik. On a basic level, this means keeping careful track of the temperature at various points along and down into the permafrost. By drilling a hole into the ground and inserting a simple polyvinyl chloride pipe with temperature sensors situated at various depths, then planting those pipes across the feature, he can develop a profile of how the ground temperature is changing.
Meteorological stations are set up to track the wind direction and speed, air temperature, relative humidity, and barometric pressure—all the variables the scientists will need to plug into their model.
“The Arctic is a place where everything is about the minutest change in energy balance.”
The data will help scientists understand the relationship between fluxes of water and energy, as well as permafrost and landscape stability in the Arctic. For example, they want to know how water from a rainstorm moves into the subsurface at different locations inside and outside the thermokarst. “Is there something that has changed because you don’t have that organic mat anymore inside the thermokarst?” Gooseff asks.
Eventually, they will use those measurements to develop numerical models of heat and water transport in the subsurface and try to “virtually” force the landscape to fail.
Another goal of the project is to understand how the ecology will change as a result of this sudden rift in the tundra. For example, Bowden and Gooseff published a paper in the Journal of Geophysical Research last summer showing that the thermokarst dumped more sediment into the Toolik River than would have been delivered over the course of 18 years from the vast Kuparuk River basin (2008, 113, 2026). Now, they want to know how a river and the community living in it will be affected by a sudden influx of sediment.
Bowden is focused on streams, specifically studying how an influx of sediment and nutrients from a thermokarst can change the water-stream chemistry and, as a consequence, alter life in the stream.
On a basic level, it is clear that dumping a bunch of dirt into an Arctic stream smothers the benthic community, the things living at the bottom of the stream. It also makes it harder for fish to see and irritates their gills.
But carbon, nitrogen, and phosphorus—the food of life, so to speak—also adhere to the surfaces of the sediment. The thermokarst, by proxy, becomes “a mechanism for transporting nutrients through the system,” Bowden adds.
His group is trying to determine exactly how much of each element is being released into the water, and how far downstream its effect is seen. Bowden has placed automated samplers above and below where the sediment flows into the Toolik River. The machine collects water samples four times a day, then combines them into a 1-L bottle that gives a daily snapshot of the stream’s activity.
There are also nearby sensors for precipitation, light level, and the flow rate of the river, all necessary for figuring out how nutrients will behave in the river. Another instrument sits in the river and records temperature and electrical conductivity, and it uses an optical sensor to measure dissolved oxygen, which can be used to calculate the carbon balance of the stream.
Though it all sounds rather automated, retrieving data is no joke. By all accounts, life at the field station has gotten much cushier in recent years than it was in the early days of the camp. The food at the station is so good that people talk about gaining “the Toolik 10” during a summer stay. There are showers, albeit with strict rules about how often and for how long they can be used (two minutes, twice a week), and a large sauna that can be followed by a dip in the chilly lake to fill the cleanliness gaps.
Those comforts are a much-needed reward for long days in the field. Getting out to the Toolik thermokarst, for example, involves a short drive followed by a one-and-a-half-mile hike. Part of that walk is along a gravel path, but part is through the tundra: The verdant moss is like walking uphill on soft mattresses; the tough tussocks that dot the area are about the size of a baseball—and are about as easy to balance on. As Bowden likes to say: “Step on a tussock, break an ankle, step in-between, break an ankle.” Now, imagine making that hike while in waders, rain boots, and a mosquito net, and carrying more than 50 lb of samples and equipment.
Bowden’s students go out several times a week, rain or shine, to pick up samples. They are collecting so much water that it is easier for them to do some of the lab work right there in the field rather than carry it all back to camp. At the field station, they do some good old-fashioned chemistry to determine the concentration of each nutrient in the water.
Even before they determined the concentration of the elements being released into the stream over time, the team members already have a sense of what the environment could look like in the coming years. Scientists at Toolik had been conducting long-term studies of the effects of adding nutrients to the Kuparuk. By dripping ammonium, nitrate, and phosphate into the river, they showed algal biomass increased 10-fold, while fish grew faster and the insect population shifted.
The thermokarst team is also trying to understand how that influx of nutrients and warmer soil could affect plant life in the surrounding area. From looking at the scars of healing thermokarsts, it is clear that 20 or 30 years after a feature is formed, the landscape “is very much dominated by shrubs” rather than the usual tussocks, says Michelle Mack, a plant ecologist at the University of Florida.
A shrubbier environment may not sound like a big deal to those of us walking the tree-lined streets of the lower 48, but small changes matter in the Arctic. “Shrub tundra has different energy-exchange characteristics” compared with the tussock tundra that dominates the North Slope, Mack says. Shrubs reflect more radiation in the summer, trapping more heat in the atmosphere, but they also act as insulation for the tundra in the winter, keeping the soil warmer.
Shrub tundra also tends to store less carbon belowground than tussock, or nonacidic, tundra. “When you think of a shrubbier landscape, it’s one where more of the carbon is aboveground, where you don’t have these long-term accumulations of soil organic matter,” she adds. In other words, it suddenly becomes much harder to rebuild the permafrost that was lost when the feature formed.
As a result, more carbon dioxide is exhaled into the atmosphere. Gaius R. Shaver, a senior scientist at the Marine Biological Laboratory’s Ecosystems Center, has conducted a long-term experiment at Toolik, where plots of tundra are given extra nutrients and compared with undisturbed tundra. The hip-level shrubs in the plots with extra food are a stark contrast to the stubby tussock tundra in the area. Yet even though there is more plant material to breathe in carbon dioxide, he found the carbon uptake was more than offset by the loss of carbon and nitrogen from deep within the soil in that area. Shaver and several colleagues reported that the nutrient-rich system exhaled nearly 2 kg more carbon per sq meter over the course of 20 years than in the control plots (Nature 2004, 431, 440).
Mack is now studying the three core thermokarst sites near Toolik, as well as three other thermokarsts, to figure out how vegetation comes back after that disruption and whether the newly arrived shrubs will persist even after the ground has completely healed.
Within the sites, there are areas that have slumped just this year and others where the collapse happened 20 or 30 years ago. The variety allows her group to carefully survey which plants are growing in each area and compare variables like leaf concentration and area, soil pH and texture, and soil availability.
While understanding the changes a thermokarst can bring about on a local level is important, the project is also interested in the features’ impact beyond the Arctic environment. If climate change is leading to more thermokarsts, the scientists want to know whether those features could then feed back into further warming.
There is twice as much organic carbon stored in the soil and permafrost as there is in the atmosphere, says Ted Schuur, an ecosystem ecologist at the University of Florida whose broad studies of permafrost thaw thermokarsts in the steppe tundra of Siberia and Alaska led to an estimate of the carbon packed away across the Arctic (Science 2006, 312, 1612).
Understanding whether thermokarsts will lead to the release of that carbon is critical, particularly because it’s a feedback mechanism that has been ignored. The public tends to think about fossil fuel usage and tropical deforestation as the two main contributors to a changing carbon cycle. And in theory, people can control the amount of oil and gas they burn or how many acres of trees they cut down.
Yet permafrost contains layers upon layers of carbon that has been locked away for tens of thousands of years. “If you think about carbon coming out of the permafrost, it’s far from where people are, it’s created by a warming world, but once it is kind of going, it’s going with its own positive feedback, far from our influence,” Schuur says. “I think it really does represent this emissions source kind of out of our control. That’s different than what’s going on right now.”
As Bret-Harte, Toolik’s associate scientific director, puts it, “We can’t make a treaty to say, ‘Let’s stop thermokarsts and fires,’ like you can with fossil fuels.”
Schuur is trying to understand how quickly that carbon might be released by looking at the age of the organic material coming out of thermokarsts.
To capture the carbon being emitted by the tundra, Schuur encloses an area of the ground with a covered chamber, simulating total darkness to shut off photosynthesis in order to measure ecosystem respiration. “Everything that is metabolizing is adding carbon dioxide to your chamber,” he notes.
Carbon dioxide is collected on a trap—a molecular sieve—that is sent back to Schuur’s lab at the University of Florida. There, the sieve is heated to desorb the CO2, which is purified and frozen. That purified CO2 is then reduced to graphite, which is pounded into a “target” that is sent to the University of California, Irvine, where Schuur’s collaborators analyze the carbon-14 content with an accelerator mass spectrometer.
It is too early to say how old the material is that is coming out of the thermokarsts near Toolik, but preliminary results should be in by this winter. The scientists hope there will be an opportunity to meet in person to discuss their early findings at a conference in December.
Those first results should provide the fuzzy outlines of a picture of how thermokarsts impact the Arctic landscape. But even then, the researchers point out, there’s no easy solution to slowing down that release. “We’re not going to be here rolling out insulation mats over the tundra,” Schuur says. “There won’t be a direct mitigation. Our best mitigation is slowing down overall warming.”