Melting Permafrost (Part 3)

Melting permafrost is in the news! Check out this great slide show and article:

• Josh Hane, Hunting for clues to global warming, New York Times, 16 December 2011.

• Justin Gillis, As permafrost thaws, scientists study the risks, New York Times, 16 December 2011.

They track Katey M. Walter Anthony, an assistant professor at the Water and Environmental Research Center at the University of Alaska Fairbanks, as she studies methane bubbling up from lakes—as shown above.

These lakes form in an interesting way. Permafrost is permanently frozen soil lying beneath a layer 0.6 to 4 meters thick of soil that thaws in the summer and refreezes in the winter: the active layer. The permafrost itself can be much thicker—up to 1500 meters in parts of Siberia!

As far as I can tell, talik is permanently unfrozen soil on top of, amid or beneath the permafrost.

Permafrost is rock-hard and solid. Liquid water does not pass through it, so permafrost environments tend to be poorly drained and boggy. But when permafrost starts to melt, it becomes soft. Soil sinks down into marshy hollows separated by small hills, forming a kind of terrain called thermokarst.

Trees in this terrain can lean crazily as their roots sink, creating drunken forests.

On flat ground, melted water can pool into a thermokarst lake. On slopes, water pours downhill and the land can rip open in a thermokarst failure. Here are Breck Bowden and Michael Gooseff exploring a thermokarst failure in Alaska:

For more on this, see:

• Emily Stone, When the ground collapses like a soufflé: Studying the effect of thermokarst on the Arctic, Field Notes: the Polar Field Services Newsletter

All these are natural processes that are widespread at the end of each glacial period. Here’s a surprisingly delightful book which discusses this in detail:

• Evelyn C. Pielou, After the Ice Age: the Return of Life to Glaciated North America, U. Chicago Press, Chicago, 1991.

So, please don’t misunderstand: I’m not trying to say that thermokarst lakes, drunken forests and the like are signs of disaster. However, as the Earth warms, new regions of permafrost are melting, and we’ll see these phenomena in new regions. We need to understand how they work, and the positive and negative feedbacks. For example, thermokarst lakes are darker than their surroundings, so they absorb more sunlight and warm the area.

Most importantly, as permafrost thaws, it releases trapped carbon in the form of carbon dioxide and methane, which are both greenhouse gases. Since there are roughly 1.7 trillion tons of carbon in northern soils, with about 90% locked in permafrost, that’s a big deal.

At least once so far, the tundra has even caught fire:

One day in 2007, on the plain in northern Alaska, a lightning strike set the tundra on fire.

Historically, tundra, a landscape of lichens, mosses and delicate plants, was too damp to burn. But the climate in the area is warming and drying, and fires in both the tundra and forest regions of Alaska are increasing.

The Anaktuvuk River fire burned about 400 square miles of tundra, and work on lake sediments showed that no fire of that scale had occurred in the region in at least 5,000 years.

Scientists have calculated that the fire and its aftermath sent a huge pulse of carbon into the air — as much as would be emitted in two years by a city the size of Miami. Scientists say the fire thawed the upper layer of permafrost and set off what they fear will be permanent shifts in the landscape.

Up to now, the Arctic has been absorbing carbon, on balance, and was once expected to keep doing so throughout this century. But recent analyses suggest that the permafrost thaw could turn the Arctic into a net source of carbon, possibly within a decade or two, and those studies did not account for fire.

“I maintain that the fastest way you’re going to lose permafrost and release permafrost carbon to the atmosphere is increasing fire frequency,” said Michelle C. Mack, a University of Florida scientist who is studying the Anaktuvuk fire. “It’s a rapid and catastrophic way you could completely change everything.”

By the way, if you click on these scientists’ portraits, you’ll see where they work. If you’re a student looking for an interesting career, consider these options! For example, Michelle C. Mack—shown above—runs a lab, and you can see her postdocs and grad students, and what they do.

For previous posts in this series, see:

• Melting Permafrost (Part 1).

• Melting Permafrost (Part 2).