Sunlight, rather than microbes, plays a controlling role in the creation of carbon dioxide from material emitted by Arctic soils, a new study reveals.
According to the scientists, the finding was particularly important because climate change could affect when and how permafrost was thawed, which begins the process of converting the organic carbon into CO2.
Lead author Rose Cory from the University of Michigan said that converting soil carbon to carbon dioxide was a two-step process where first, the permafrost soil had to thaw and then bacteria must turn the carbon into greenhouse gases, carbon dioxide or methane. While much of this conversion process took place in the soil, a large amount of carbon was washed out of the soils and into rivers and lakes.
The research team measured the speed at which both bacteria and sunlight converted dissolved organic carbon into carbon dioxide in all types of rivers and lakes in the Alaskan Arctic, from glacial-fed rivers draining the Brooks Range to tannin-stained lakes on the coastal plain.
In virtually all of the freshwater systems they measured, however, sunlight was always faster than bacteria at converting the organic carbon into CO2.
Another factor limiting the microbial contribution was that bacteria grew more slowly in the cold, nutrient-rich waters.
The source of all of this organic carbon was primarily tundra plants, and it had been building up for hundreds of thousands of years, but doesn't completely break down immediately because of the Arctic's cold temperatures. Once the plant material got deep enough into the soil, the degradation stopped and became preserved.
The science community has not yet been able to accurately calculate how much organic carbon from the permafrost is being converted into CO2, and thus it would be difficult to monitor potential changes because of climate change, they acknowledge.
The study is published in the journal Science.