When the Deep Freeze Thaws

The melting of Arctic permafrost has vast implications for our global climate. CALS professor James Bockheim is studying cores of the frozen soil to gain a glimpse into their future.

AFTER FOUR DECADES STUDYING some of the planet’s coldest soils, James Bockheim has gained a formidable vocabulary to describe the interplay between ice and soil. Analyzing a core of permafrost—the permanently frozen soils found near the Earth’s poles and on some mountaintops—he points out vein ice threading the length of the core. He speaks of cryoturbation, the mixing of soil layers caused by freezing and thawing ice, and notes the formation of lens ice, puck-like discs that form above the permafrost layers.

These features make permafrost samples beautiful, often resembling the mixed batters of a marbled cake. But they also have important implications for the planet’s climate, says Bockheim, a CALS professor of soil science. Although permafrost and other cold soils make up only 16 percent of all soil, they hold 50 percent of all soil carbon, making Arctic soils a deep freezer for vast stores of the greenhouse gas. But many researchers fear that as global warming thaws permafrost layers, that carbon will be released into the atmosphere, exacerbating changes in climate.

Bockheim and Kao-Kniffin are trying to glimpse into the future of polar soils by learning from their past.

Last spring, that question took Bockheim and postdoctoral researcher Jenny Kao-Kniffin to Barrow, Alaska, which at 320 miles north of the Arctic Circle is the United States’ northernmost city. It’s a region that already feels acute pressure from climate change. According to Bockheim, temperatures around Barrow have risen by as much as 2 degrees Celsius during the past 20 to 30 years, nearly four times the rate of warming for the planet as a whole. Thawing soils have put houses, roads and even the Alaskan oil pipeline at risk of collapse. But the changes in Barrow have implications that reach far beyond the Arctic, says Bockheim.

In Barrow, Bockheim and Kao-Kniffin are trying to glimpse into the future of polar soils by learning from their past. Working with a team of international scientists, they have been digging into the soils of former lake basins, which drained anywhere between 50 and 8,000 years ago, to get a view of how different soils have developed over time. Once emptied of water, Bockheim explains, the basins fill with grasses, sedges and willows, attracting animal life and creating changes in soil composition. Older beds contain more carbon, for instance, and they also harbor more ice, due to repeated seasons of snow and rain trickling into upper layers of soil.

The scientists’ interest is not only in the soil itself, but also in the microbes that call it home—specifically, how those resident microbes metabolize sources of carbon in the soil. One of the main concerns about the warming Arctic soils is that as once-frozen organic matter thaws, resident microbes will start churning out carbon, releasing potentially large quantities back into the atmosphere. But it’s also possible that the soil nutrients won’t be suitable to support the microbial community.

“We know the rate of carbon sequestration in these lakes, but we don’t know anything about decomposition rates and the different forms of carbon that exist,” says Bockheim, whose study of polar soils began with a trip to Antarctica in 1969.

Kao-Kniffin, a microbiologist who recently became an assistant professor at Cornell University, is now in the process of characterizing the microbial community that lives in the Alaskan soils. She will analyze fatty acids and DNA of the soil microbes to get a clearer picture of their metabolic function, using stable isotope tracers to follow the path of carbon through the system.

“The lab component is easy,” says Kao-Kniffin, compared to the physical ordeal of drilling and collecting cores from the Alaskan tundra. Once samples were collected, the scientists returned to a small Quonset hut backdropped by the frozen Arctic Ocean to measure and prepare them for lab analysis. At one point, as newly thawed soil samples dried in an oven, a whiff of a mushroom-like aroma wafted through the hut, a sign of the fungi and other microbes in the soil. It was a small reminder of the suspended life harbored within those frozen soils—and the potential consequences once that life is awakened.