In a study published today in Nature Climate Change, an international team of scientists demonstrates the importance of soil moisture as a critical factor in determining the amount and form of carbon produced from thawing permafrost. The team was led by Northern Arizona University Research Prof. Christina Schädel and includes co-author and WHRC Associate Scientist Susan Natali.
Arctic permafrost is like a vast underground storage tank of carbon, holding almost twice as much as the atmosphere, and small changes in how the carbon is released will have big effects on the climate. The scientists’ meta-analysis of 25 laboratory experiments of arctic soils found that both temperature and soil conditions affected the quantity and form of carbon released from thawing permafrost. Understanding the form and quantity of carbon released into the atmosphere is important because it could accelerate rates of warming. Methane packs 34 times the climate change punch of carbon dioxide
A 10°C increase in soil temperature released twice as much carbon into the atmosphere, and drier, aerobic soil conditions released more than three times more carbon than wetter, anaerobic soil conditions.
“Permafrost drives soil moisture in the Arctic by restricting water flow and by providing ground structure,” says Dr. Natali. “When permafrost thaws, soils can become saturated as a result of ground collapse or dryer as a result of drainage. Understanding future changes in soil moisture is critical,” she adds, “because the changes affect the form and magnitude of carbon released to the atmosphere, which will ultimately determine the effect of permafrost thaw on global climate.”
As permafrost thaws, the increased microbial activity produces either carbon dioxide or methane, depending on soil conditions.
The ratio of carbon dioxide to methane gas released by this process affects the strength of the permafrost carbon feedback loop: greenhouse gases released due to thawing permafrost cause temperatures to rise, leading to even more thawing and carbon release.
The researchers zeroed in on two factors: soil temperature and the availability of oxygen. Soils were incubated in a lab at a range of warmer temperatures projected for the future. The availability of oxygen is important because it determines the activity of soil microbes. Oxygen-rich, or aerobic, conditions are found in dry soils and produce carbon dioxide. Oxygen-poor, or anaerobic, conditions are found in wet soils and produce both carbon dioxide and methane. The lab incubations mimicked both wet and dry conditions. Most of the carbon produced was in the form of carbon dioxide, mixed with smaller amounts of methane under oxygen-free conditions.
Will wet or dry soils dominate the future arctic permafrost zone? The answer to this question is a big unknown. This study, however, will strengthen existing models of permafrost ecosystem response to a warming climate. The work also highlights the need to monitor moisture changes associated with permafrost thaw.
Woods Hole Research Center is an independent research institute where scientists investigate the causes and effects of climate change to identify and implement opportunities for conservation, restoration and economic development around the world.