The Arctic tundra is sinking. Landslides and sinkholes the size of football fields dot the landscape.

“If there were houses and roads and buildings up there, people would be freaking out,” says Rose Cory, an environmental scientist at UNC. We’d be clamoring for reasons why the earth is swallowing our infrastructure. Cory could provide answers. And she could also tell us why we should be very concerned no matter where we live.

For years, climate scientists haven’t included the melting permafrost in their climate change models. Now, the big thaw is on. Permafrost is adding CO2 to the atmosphere. But Cory discovered that there’s more to the equation—those landslides and sinkholes are exposing once-frozen carbon to sunlight and adding more CO2 to the atmosphere than scientists had ever suspected.

Arctic permafrost is essentially underground soil that’s been frozen for thousands of years. For a long time, scientists have known that as global temperatures rise and permafrost melts during summers, bacteria are consuming organic carbon in the soil. The bacteria convert the carbon into carbon dioxide and expel it back into the atmosphere. The added CO2—a greenhouse gas—contributes to the global warming trend.

“But we thought the bacteria respire CO2 in the dark, below the surface,” Cory says. “And we didn’t know the timing or other controlling factors. All we knew was there was a lot of potential to turn organic carbon into CO2.”

Those unknowns were why climatologists didn’t include melting permafrost in their climate change models.

A few years ago, though, geologists spotted huge sinkholes and landslides in the Arctic. Cory suspected that the carbon—once destined to convert into CO2 in the dark underground—would now convert to CO2 while being exposed to the Arctic summer sunlight—24 hours a day. She wanted to find out whether that mattered.

On the colder side of Alaska’s north slope, 460 miles north of Fairbanks, Cory sets up shop each summer at the U.S. Arctic Long Term Ecological Research site. She arrives before May 1 so she doesn’t miss the annual freshet—when snow and ice melt within a few days and lay bare the brown tundra.

Beneath the surface of the tundra is permafrost. In some areas, ice below the surface holds the soil in place. When that ice melts, the ground slumps, creating landslides and sinkholes that scientists call thermokarsts. [Thermo refers to heat; karst, derived from German, refers to sinking land.]

Click to read photo caption. Photo by Rose Cory

Sometimes the thermokarsts are small—like the footprint of a house. Often, though, they’re larger than a football field. They can range in depth from a few feet to several meters. Many thermokarsts are near lakes, streams, and rivers—bodies of water rife with bacteria. Those are the thermokarsts Cory studies.

Click to read photo caption. Photo by Rose Cory

To get to them, she sometimes walks two miles while carrying backpacks full of experimentation devices and gallon jugs for water collection. Other times she helicopters for many miles.

Once on site, she can see how the release of ancient carbon affects the water. Streams turn golden-brown. Viewed from above, some lakes turn light blue from the influx of carbon. “It’s like when you put a tea bag in hot water,” she says. The chemical components of the tea plant dissolve and gives the water color.

Click to read photo caption.

In the case of a thermokarst, the once-frozen organic carbon changes the color and composition of the warmer surface waters.

Cory’s team then samples the water near the thermokarst, as well as water downstream, upstream, and from nearby waterways that have collected carbon deposits from surface soil runoff. Cory feeds the carbon-rich water to bacteria. Some samples she exposes to ultraviolet light. Other samples she doesn’t. Then she measures the rate at which the bacteria convert the carbon into CO2.

Click to read photo caption.

She did that at seven thermokarsts and twenty other sites during the summers of 2010 and 2011.

Turns out that bacteria can convert 40 percent more of the ancient carbon into CO2 when the carbon is exposed to ultraviolet light—a component of sunlight. Cory also found that 40 percent more of the ancient carbon was converted into CO2 than was the carbon from typical surface soil runoff.

Click to read photo caption. Photo by Rose Cory

According to Cory, ultraviolet light slightly alters the ancient carbon, making it more palatable to bacteria.

“We’re not sure why bacteria prefer that carbon,” Cory says. “But we think the sunlight breaks down the carbon into molecules that are more readily passed through the bacterial cell membranes.”

Whatever the reason, the ancient carbon is more reactive. This might be good news for the bacteria, but not for the rest of us.

Cory says that the Arctic permafrost contains more than twice the amount of carbon currently in the atmosphere.

“But that carbon has been frozen for thousands of years, so it hasn’t participated in the carbon cycle,” she says. “With the earth getting warmer, that’s all changing.”

Thermokarsts, Cory says, could play a major role in what some scientists fear has become an unstoppable positive feedback loop:

The earth warms. Permafrost thaws. Organic carbon seeps into the sunlight. Bacteria respire the carbon into the atmosphere as CO2. The added greenhouse gas contributes to global warming. Warmer Arctic summers melt more permafrost. More thermokarsts form. More CO2 is released. The earth warms.

This cycle, Cory says, could double the amount of CO2 in the atmosphere. When and how that might play out is still unclear, but Cory’s research suggests that thermokarsts hurry the process.

She isn’t a geologist but knows from other research that more thermokarsts are popping up each summer.

“We think the landscape could eventually become riddled with them,” she says. “In some places it already is.”

See video
Sarah Godsey, Penn State University

Rose Cory is an assistant professor of environmental sciences and engineering in the UNC Gillings School of Global Public Health. She received funding from the National Science Foundation. Her research was published in the Proceedings of the National Academy of Sciences in February 2013.