Nav: Home

Carbon emission from permafrost soils underestimated by 14%

June 15, 2020

Picture 500 million cars stacked in rows. That's how much carbon--about 1,000 petagrams, or one billion metric tons--is locked away in Arctic permafrost.

Currently, scientists estimate that 5-15% of the carbon stored in surface permafrost soils could be emitted as the greenhouse gas carbon dioxide by 2100, given the current trajectory of global warming. This emission, spurred by microbial action, could lead to 0.3 to 0.4 degrees Celsius of additional global warming.

But this estimation is missing a crucial path that carbon dioxide may be entering the atmosphere: sunlight.

According to a University of Michigan study, organic carbon in thawing permafrost soils flushed into lakes and rivers can be converted to carbon dioxide by sunlight, a process known as photomineralization.

The research, led by aquatic geochemist Rose Cory, has found that organic carbon from thawing permafrost is highly susceptible to photomineralization by ultraviolet and visible light, and could contribute an additional 14% of carbon dioxide into the atmosphere. Her team's study is published in the journal Geophysical Research Letters.

"Only recently have global climate models included greenhouse gases from thawing permafrost soils. But none of them contain this feedback pathway," said Cory, an associate professor of earth and environmental sciences.

"To get a number on how much carbon could be released from permafrost soils through oxidation, we have to understand what are the processes and what is the timescale: maybe this carbon is just so resistant to oxidation that, even if thawed out, it would just flow into the Arctic ocean and be buried in another freezer."

This pathway has been debated because measuring how sunlight degrades soil carbon is difficult. Each wavelength of light has a different effect on soil organic carbon, as does the level of iron in the soil. To precisely measure how carbon dioxide is emitted when organic carbon is exposed to sunlight, Cory's co-corresponding author Collin Ward, a scientist at Woods Hole Oceanographic Institution and U-M alum, developed a method to measure each wavelength's effect on soil organic carbon. To do this, he built a new instrument that uses LED lights to mimic different wavelengths of the sun.

"This new LED-based method makes it far easier and cheaper to figure out how light-driven reactions vary for different wavelengths of the sun," Ward said. "After I built the instrument I immediately called Rose and told her that I wanted to first use it on permafrost samples."

The researchers placed organic carbon leached from soil samples from six Arctic locations in the instrument, and then subjected the samples to the LED light. After the light exposure, they extracted the carbon dioxide cryogenically and used a mass spectrometer to measure the age and amount of carbon dioxide given off by the soil carbon.

They found that not only did the wavelength of sunlight impact the amount of carbon dioxide released, the amount of iron in the sample did as well. Iron acted as a catalyst, increasing the reactivity of the soil.

"What we have long suspected is that iron catalyzes this sunlight-driven process, and that's exactly what our results show," Cory said. "As the total amount of iron increases, the amount of carbon dioxide increases."

Cory's team also used carbon dating to age the soil organic carbon and the carbon dioxide emitted from it to demonstrate this oxidation was happening to ancient permafrost, not just soil that thaws annually. This is important because soil that thaws annually would release a much smaller amount of carbon dioxide than what's available in permafrost.

The researchers found that it was between 4,000 and 6,300 years old, and by demonstrating how old the soil is, they show that permafrost carbon is susceptible, or labile, to oxidation to carbon dioxide.

"Not only do we have the first wavelength specific measurement of this sunlight-driven reaction but we have verification that it's old carbon that is oxidized to carbon dioxide," Cory said. "We can put to rest any doubt that sunlight will oxidize old carbon and we show what is controlling this process--it's the iron that catalyzes the sunlight oxidation of ancient (or old) carbon."

Including the U-M team's finding into climate change models means that--conservatively--there could be a release of 6% of the 100 billion metric tons of carbon currently stored in Arctic permafrost. If 6% doesn't sound like much, consider that's the carbon equivalent of approximately 29 million cars evaporating into the atmosphere.
-end-
Earth and environmental sciences graduate student Jennifer Bowen was first author of the study, which also included George Kling, professor of ecology and evolutionary biology. Bowen was supported by a National Ocean Sciences Accelerator Mass Spectrometry graduate student internship program. Ward received internal support from Woods Hole Oceanographic Institution.


University of Michigan

Related Permafrost Articles:

Siberia's permafrost erosion has been worsening for years
The Arctic is warming faster than any other region on the planet.
Alaska is getting wetter. That's bad news for permafrost and the climate.
Alaska is getting wetter. A new study spells out what that means for the permafrost that underlies about 85% of the state, and the consequences for Earth's global climate.
Plant roots increase carbon emission from permafrost soils
A key uncertainty in climate projections is the amount of carbon emitted by thawing permafrost in the Arctic.
Stocks of vulnerable carbon twice as high where permafrost subsidence is factored in
Twice as much carbon in permafrost is vulnerable to microbial respiration when researchers from Northern Arizona University accounted for subsidence, the gradual sinking of terrain caused by loss of ice and soil mass.
Carbon emission from permafrost soils underestimated by 14%
Picture 500 million cars stacked in rows. That's how much carbon -- about 1,000 petagrams, or one billion metric tons - -is locked away in Arctic permafrost.
Nitrogen in permafrost soils may exert great feedbacks on climate change
A new Sino-German scientific collaboration investigating nitrogen in the soils of China's melting permafrost aims to get to the bottom of why emissions of nitrous oxide -- an often overlooked greenhouse gas -- are greater than they are supposed to be.
Patterns in permafrost soils could help climate change models
A team of scientists spent the past four summers measuring permafrost soils across a 5,000 square-mile swath of Alaska's North Slope.
Here be methane: Skoltech scientists investigate the origins of a gaping permafrost crater
Researchers from Skoltech and their colleagues spent more than two years studying a 20-meter wide and 20-meter deep crater in the Yamal Peninsula in northern Russia that formed after an explosive release of gas, mostly methane, from the permafrost.
How horses can save the permafrost
Permafrost soils in the Arctic are thawing. In Russia, experiments are now being conducted in which herds of horses, bison and reindeer are being used to combat this effect.
Arctic permafrost thaw plays greater role in climate change than previously estimated
Abrupt thawing of permafrost will double previous estimates of potential carbon emissions from permafrost thaw in the Arctic, and is already rapidly changing the landscape and ecology of the circumpolar north, a new CU Boulder-led study finds.
More Permafrost News and Permafrost Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.