Sunlight, Not Microbes, Control Carbon Release in the Arctic

A vast amount of carbon stored in Arctic permafrost is being converted into carbon dioxide (CO2) once it enters freshwater systems - a process that is worrying experts tracking climate change. This process was long thought to be enabled by microbial activity, but a new study identifies that sunlight itself might be the true culprit.

Traditional permafrost is frozen water trapped in soil in a region that never warms enough to the point that the ground will thaw. However, in the wake of a changing climate, parts of the Arctic are suddenly experiencing heightened temperatures, melting permafrost and loosening frozen ground.

During thawing, melt water interacts with carbons in the soil to create and release worrying levels of carbon dioxide and methane. Until now, researchers believed that bacteria were largely responsible for this conversion.

However, a study published in the journal Science details how this process can occur even without the help of microbes, at least when the trapped carbon reaches a freshwater source.

"Our results suggest that sunlight, rather than biological processes, controls the fate of carbon released from thawing permafrost soils into Arctic surface waters," Rose Cory, an aquatic geochemist and the first author of the study, said in a statement.

According to co-author Bryon Crump, understanding that carbon release can occur even without the help of microbial life "represents a major change in thinking about how the carbon cycle works in the Arctic."

"It turns out, that in Arctic rivers and lakes, sunlight is faster than bacteria at turning organic carbon into CO2," Cory said. "This new understanding is really critical because if we want to get the right answer about how the warming Arctic may feedback to influence the rest of the world, we have to understand the controls on carbon cycling."

"In other words, if we only consider what the bacteria are doing, we'll get the wrong answer about how much CO2 may eventually be released from Arctic soils," she added.

Still, it's important to note that this initial carbon release is just half of a very complex process. Lakes of melted permafrost, called thermokarst lakes, are of course seen as short-term climate warmers. However, other recent research has found that these lakes actually become climate coolers in the long run - as long as they refreeze - absorbing and trapping more carbon than they ever released.