By Emily Stone
Scientists Breck Bowden and Michael Gooseff were flying in a helicopter near Toolik Field Station in 2003, scouting for good field sites for river research when they spotted something peculiar.
Unlike the crystal clear Kuparuk River nearby, the Toolik River was a muddy brown, an unusual site in the Arctic where tundra streams don’t pick up much sediment because the ground is usually frozen. The men had the helicopter fly upstream to investigate. After 40 kilometers they saw the culprit: a small stream leading into the river had a huge, narrow crater on its shore that was dumping sediment into the river.
“It was a severe gash on what was otherwise a nondescript hillside,” said Gooseff, an assistant professor of civil and environmental engineering at Pennsylvania State University.
The feature is what’s known as a thermokarst failure. Thermokarst occurs when ice in the usually solid permafrost melts and the land gives way like a soufflé. When this happens on flat ground, the melted water pools into a thermokarst lake. When it happens on a slope, as was the case along the Toolik, the water rushes downhill and usually into a nearby body of water and the ground slumps after it, causing what’s called a thermokarst failure.
The helicopter landed by the gash. Bowden, a professor of watershed science and planning at the University of Vermont who is over six feet tall, was engulfed in it when he stood at the bottom. He guesses that it had formed within a few days of their arrival.
Standing there, he remembers looking around at all the other tiny streams that led into the region’s big rivers and thinking, “It wouldn’t take many of these on the landscape to have a fairly big impact.”
Bowden is now leading a project that includes Gooseff and 15 other principal investigators to discover what exactly these thermokarst features are doing to the landscape and river networks, and how they form in the first place. They’ve already established that there are many more of them than there were 25 years ago, the likely result of rising temperatures in the Arctic. As more thermokarst failures develop, researchers want to know how the additional nutrients dumped into rivers will affect aquatic ecosystems, how they’ll impact the plant communities that grow back after a thermokarst landslide, and how they’ll change the amount of carbon dioxide and methane being released into the atmosphere — all crucial questions in the study of climate change.
The group, which includes another couple dozen graduate students and technicians, is in the first year of a four-year, $5-million grant from the NSF’s Arctic System Science Program. They spent their first field season at Toolik this past summer picking their research sites and setting up equipment to monitor the changes happening in and near the thermokarst failures.
Previous research by Bowden, Gooseff and some of the other collaborators established that, at least in the area around the field station, there are many more thermokarst failures than there were in the early 1980s. The group did an aerial survey of 600 square kilometers around the station and compared their observations to an aerial survey that was done in the same area around 1980. They found 34 thermokarst, two-thirds of which were new. This data doesn’t necessarily correspond to the rest of the Arctic since different soil conditions, slope and climate affect thermokarst formation, but it does suggest that the features are growing in at least one large swath of Alaska.
The concern is that these features can have an outsized impact on the environment.
Bowden is interested in the nutrients that are usually held frozen in permafrost — what he describes as “brown concrete” — that are released into rivers when that permafrost melts. The addition of ammonium, nitrate and phosphate means that aquatic microbes and plants have much more to eat and can flourish in areas where their populations were previously limited by a lack of food. This can dramatically alter a river’s ecosystem.
He has set up water monitoring stations on rivers above and below thermokarst failures to compare the sediment and nutrients in the water before and after the thermokarst soil reaches it. Earlier research showed that the Toolik River thermokarst failure delivered more sediment to the river than was dumped into the Kuparuk River over the course of 18 years from a 132-square-kilometer section of watershed.
Other researchers in the group are looking at how plants react to thermokarst failures. “We have a suspicion that what they evolve into is a shrubby community,” Bowden said, instead of the low tundra grasses that dominate the region.
This is important because shrubs hold on to more sunlight than grasses, which warms the soil below. This can in turn release more stored carbon out of the warming soil. Additionally, warmer soil releases more nutrients for microbes to use as fuel. Microbes then release more methane into the atmosphere, which is a powerful greenhouse gas. Scientists in the thermokarst group are measuring this CO2 and methane release.
Other researchers are looking at remote sensing and computer modeling, as well as interviewing Native Alaskan communities nearby to learn about their memories of where thermokarst have occurred in the past.
Gooseff is taking a step back to try to figure out what causes the thermokarst failures in the first place. He has placed water and temperature sensors at various depths in and near several thermokarst features, as well as instruments above ground that measure rain, snow, sun and wind. His post doc, Dr. Sarah Godsey, set up cameras to take pictures of the thermokarsts every hour. Their goal is to be able to correlate the weather and soil data with physical changes in the permafrost and landscape.
Bowden notes that thermokarst are not a new occurrence. Scientists have been aware of them for years, and engineers have long studied them in the context of building roads, homes and pipelines.
“It is a natural phenomenon, but it appears to be one that is accelerating,” he said.