Arctic’s carbon reserves in danger

About 50 percent of the world’s organic carbon stored in the soil is locked down in the frigid northern reaches of the Arctic, below an icy permafrost cap and in rich peat lands. If all that carbon were released, atmospheric CO2 concentrations could go up a whopping 660-870 parts per million.

Global warming is gradually unlocking these Arctic carbon reserves. In a paper published recently in the Journal of Geophysical Research, University of Alaska, Fairbanks geophysicist Guido Grosse and colleagues tease out two forces acting on the Arctic carbon reserve. “Press” disturbances present a slow, persistent force on the carbon reserves. And “pulse” disturbances present rapid and extreme releases. The result is a complicated web of environmental implications for the Arctic and the globe.

At Point Hope, Alaska, the tundra is gradually succombing to the effects of warming. Photo: Josh Kellogg.

Among the most important “press” disturbances is the continual melt of Arctic permafrost, which until now has kept deep layers of carbon-rich soil intact. By the year 2100, an estimated 20 percent of all the permafrost will be seasonal only, which has dramatic ramifications on the soil ecology. Warming soils will change the biological processes (enzyme kinetics) of plant and microbial communities, the authors write. More Nitrogen will be released, spurring plant productivity and also providing fertile ground for microbes to digest and decompose organic matter in the soil. That in turn will release carbon from the soil.

Meanwhile, with less ice cover and more coastal storms, erosion rates will increase. In the American Arctic, exposed soils from formerly covered permafrost ground are eroding at a rate sometimes exceeding 20 meters a year, resulting in substantial carbon releases into the ocean.

Pulse impacts like tundra wildfires can release massive amounts of carbon into the atmosphere, both from the soil and from vegetation. Furthermore, melting permafrost can create dramatic changes in the landscape in the form of thermokarst terrain, which when exposed can increase the thawing of permafrost.

The paper presents a dire picture of how Arctic carbon reserves may eventually be depleted.