Earth’s subterranean carbon blisters are starting to pop.
Carbon inside now-melting permafrost is oozing out, leaving scientists scrambling to figure out just how much of it is ending up in the atmosphere. Whether recent findings from research that attempted to help answer this question are good or bad climate news might depend on whether you see an Arctic river basin as half full of mud — or half empty.
Frozen soils known as permafrosts can be found across the planet, and they’re concentrated heavily in the Arctic, which has been warming since the 1980s at twice the global rate. Taken together, permafrosts contain more carbon than is already in the atmosphere. Their warming-induced breakdown is helping to fill the atmosphere with greenhouse gases. In a self-feeding cycle, that’s fueling the very climatic changes that are causing permafrost to waste away.
“What everyone’s really concerned about is how all this permafrost carbon is going to decompose,” said aquatic geochemist Rose Cory, an assistant professor at the University of Michigan. “If all of that gets turned into carbon dioxide, then we’ll more than double the amount of carbon dioxide in the atmosphere.”
A team of U.S. scientists led by Cory studied Arctic waterways and found that nearly half of the carbon that’s eroding from melting Arctic permafrost is flowing through rivers and lakes and ending up in the seas. Eventually, that sea-bound carbon is likely to be gobbled into aquatic food chains or to settle on ocean floors. The rest is being oxidized in waterways into carbon dioxide, floating into the skies instead of out to sea.
(Addtionally, soil microbes can oxidize carbon into carbon dioxide before the soil tumbles into water, and climate-changing methane can escape from thawing permafrost.)
The team took measurements and water samples at 135 lakes and 73 rivers around the Kuparuk River basin in Alaska’s North Slope during the summers of 2011, 2012, and 2013. The researchers wanted to know how much floating soil carbon was being oxidized into carbon dioxide by bacteria, how much was being oxidized through the effects of sunlight, and how much of the carbon was escaping both of these natural processes — and remaining in the water.
The good news from their analysis, the results of which were published last month in Science: About 45 percent of the soil carbon that’s eroding from permafrost and muddying Arctic waters was found to be remaining in the waterways.
The bad news? Looked at from another perspective, 55 percent of it is being oxidized into climate-changing carbon dioxide. The vast majority of that is caused by the effects of sunrays, which break apart chemical bonds that hold carbon molecules together, setting in motion reactions that can produce CO2.
The study was the first of its kind, and Cory said she hadn’t known what to expect. Some people who expected less carbon oxidation in the Arctic waterways “might be discouraged” by the findings, she said. But not her.
“Some have speculated that all the permafrost soil carbon would be rapidly released to the atmosphere as carbon dioxide once it flushed into rivers and lakes,” Cory said. “I think it’s encouraging that not all of this carbon that’s coming out of the soil gets turned into carbon dioxide. It’s producing this stuff that’s going to get washed from permafrost, which is one freezer, into the Arctic Ocean, which you can think of as another freezer.”
Arctic permafrost seen from a helicopter. Credit: Brocken Inaglory via Wikimedia Commons
The worrying news, no matter how you dice the de-icing permafrost findings? “There’s so much carbon stored in northern permafrost soils that even if, say, 10 percent of that carbon is released through the processes we studied, it would still have a big impact,” Cory said. She calculated that “conservative” scenario would raise atmospheric carbon dioxide levels by 75 to 80 parts per million — over and above the effects of continued fossil fuel burning and other causes. And that, she said, would lead to “a lot of warming.”
The research revealed the important role of sunlight in turning watery Arctic carbon into carbon dioxide, and the findings might be relevant for shallow rivers and lakes that drain permafrost soil elsewhere. “Our findings may be relevant in lots of freshwaters outside the Arctic,” Cory said. And that’s information that could help scientists improve their climate modeling and projections.
Compared with the role of bacteria, which can devour carbon and belch out carbon dioxide, Cory and her team found that sunlight produced three to 19 times more of the carbon dioxide that bubbles out of the Arctic rivers and lakes — depending on the site being studied. A Swedish research team published research earlier this year in the journal Global Biogeochemical Cycles that found sunlight was responsible for just 10 percent of the production of carbon dioxide from carbon in lower-altitude lakes; bacteria was blamed for the rest.
Uppsala University’s Birgit Koehler, one of the authors of the Swedish paper, said the two sets of findings are not contradictory. Arctic waterways are shallower than those in many other parts of the world, meaning sunlight can reach through a greater proportion of the water column. And cold conditions slow down microbes.
“A rather cold temperature and shallow water depth in their study area, both limiting microbial activity, may be a reason why sunlight played a larger role in these waters than in other areas of the world, and why microorganisms were less important,” Koehler said.
Now, Cory says she is running experiments aimed at determining how oxidation rates could change as the Arctic heats up further.
“As the Arctic continues to warm, and the permafrost thaw gets deeper, what happens then is you’re bringing out a different kind of carbon,” she said. “It has a different chemical signature.”