June 11, 2013
As Arctic Permafrost Melts And Decomposes, More Greenhouse Gases Released
Brett Smith for redOrbit.com - Your Universe Online
Conditions within Arctic permafrost soils prevent dead plants and animals from decomposing, resulting in layer upon layer of organic carbon being sequestered just beneath the topsoil. However, rising Arctic temperatures are causing these soils to thaw at unprecedented rates, and NASA scientists are currently looking into just how much greenhouse gas is being released through soil decomposition.
Using NASA´s C-23 Sherpa aircraft, scientists from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) have been flying at extremely low altitudes over the Alaskan Arctic to measure greenhouse gases. About two dozen scientists from 12 institutions are involved in the program.
"Some of the methane and carbon dioxide concentrations we've measured have been large, and we're seeing very different patterns from what models suggest," said CARVE scientist Charles Miller of NASA's Jet Propulsion Laboratory in Pasadena, California.
"We saw large, regional-scale episodic bursts of higher-than-normal carbon dioxide and methane in interior Alaska and across the North Slope during the spring thaw, and they lasted until after the fall refreeze,” Miller said. “To cite another example, in July 2012 we saw methane levels over swamps in the Innoko Wilderness that were 650 parts per billion higher than normal background levels. That's similar to what you might find in a large city."
Arctic soils have typically sequestered more carbon than they release. If the Arctic becomes warmer and drier, however, scientists predict most of the sequestered carbon will be released as carbon dioxide. If it gets warmer and wetter, carbon will tend to be released in the form of methane.
The CARVE scientists are currently analyzing data from the program´s first full year of flights. According to Miller, the early findings are both surprising and troubling.
"Permafrost soils are warming even faster than Arctic air temperatures — as much as 2.7 to 4.5 degrees Fahrenheit in just the past 30 years," he said. "As heat from Earth's surface penetrates into permafrost, it threatens to mobilize these organic carbon reservoirs and release them into the atmosphere as carbon dioxide and methane, upsetting the Arctic's carbon balance and greatly exacerbating global warming."
While the C-23´s pilots refer to it as "a UPS truck with a bad nose job," its ability to reliably fly about 500 feet above the ground level allows the on-board team to test the lower levels of the atmosphere for greenhouse gases, which is quite different that other carbon-checking airborne flights.
"CARVE shows you need to fly very close to the surface in the Arctic to capture the interesting exchanges of carbon taking place between Earth's surface and atmosphere," Miller noted. "We are showing the power of using dependable, low-cost prop planes to make frequent, repeat measurements over time to look for changes from month to month and year to year."
In addition to testing for atmospheric carbon, CARVE is also studying the impact of wildfires on the regional carbon cycle. Arctic fires accelerate the thawing of permafrost, and historical records show the average annual number of Alaskan wildfires has grown over the past 70 years. CARVE scientists plan to use measurements of greenhouse gases to determine how much carbon is released by these fires.
The scientists also say they hope to find out if an irreversible “tipping point” for permafrost may be near at hand.
"We hope CARVE may be able to find that 'smoking gun,' if one exists," Miller said.