Wednesday, September 10, 2008

Arctic soil reveals climate change clues

Newly published UAF research shows that frozen arctic soil contains nearly twice as much organic material that gives rise to planet-warming greenhouse gases as was previously estimated.

School of Natural Resources & Agricultural Sciences Soil Sciences Professor Chien-Lu Ping published his latest findings in the Nature Geoscience and Scientific American websites, after conducting extensive examinations of a wide range of landscapes across Alaska. Ping and his team of scientists took soil samples at 117 sites. Rather than testing to a depth of only 40 centimeters, as previous researchers had done, the team consistently dug down to more than one meter at each site. Similarly conducted Canadian research was added to Ping’s study.

Wielding jackhammers, the scientists discovered that underneath the surface, there is a second layer of organic matter (carbon) accumulation right on top and in the upper part of permafrost, ranging from 60 to 120 centimeters deep. This “buried” organic matter is produced on the surface of the tundra soils, where it accumulates and is then dragged down because of frost heave and patterned ground formation. Due to the turbulent nature of the arctic landscape, arctic tundra soils are characterized by warped, broken, and distorted soil horizons. Movement is routinely caused by cracking of the Earth’s surface during freezing and thawing cycles, transporting organic matter to the lower active layers and upper permafrost.

The resulting patterned ground plays a key role in determining tundra vegetation and the dynamics of carbon storage and release, Ping found. When temperatures warm and the arctic soil “churns,” less carbon from the surface gets to the deeper part of the soil, and the carbon stored in the deeper part of the soil is released into the atmosphere as carbon dioxide, methane, and other gases.

Ping predicted that with even a two to three degree rise in air temperatures the arctic tundra would switch from a carbon sink (area that absorbs more carbon dioxide than it emits) to a carbon source (area that emits more carbon dioxide than it absorbs). The greater the carbon store the greater the impact of any future releases, Ping stated.

“The distribution of the Arctic carbon pool with regard to the surface, active layer and permafrost has not been evaluated before, but is very relevant in assessing changes that will occur across the Arctic system,” Ping wrote in his study. “Where soil organic carbon is located in the soil profile is especially relevant and useful to climate warming assessments that need to evaluate effects on separate soil processes that vary with temperature and depth throughout the whole annual cycle of seasons.”

Since earning his doctorate at Washington State University in 1976, Ping has been researching soil, particularly permafrost soils, volcanic soils, organic carbon dynamics, and soil climate and its application in land-use interpretations.

Colleagues on the project were Gary Michaelson, UAF Agricultural and Forestry Experiment Station; Mark Jorgenson, Alaska Biological Research; John Kimble, professional soil scientist; Howard Epstein, University of Virginia Department of Environmental Sciences; Vladimir Romanovsky, University of Alaska Fairbanks Geophysical Institute; Donald Walker, UAF Institute of Arctic Biology.

Contact Chien-Lu Ping at the Palmer (Alaska) Research and Extension Center. 907-746-9462. E-mail:

Further reading:
"Not-So-Permafrost: Big Thaw of Arctic Soil May Unleash Runaway Warming" by David Biello, Scientific American, 8-26-2008.

"Global warming time bomb trapped in Arctic soil: study", published 8-24-2008 by

•Fairbanks Daily News-Miner article, "Permafrost study reveals larger global warming problem"

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