Methane uptake by Arctic soils may be higher than previously thought and increases under dry conditions and when labile carbon substrates are available. That’s the conclusion of a new study led by researchers from the University of Eastern Finland and the University of Montreal, Canada, published in Nature Climate Change. Arctic wetlands are known to be emitters of the powerful greenhouse gas methane (CH4), compared to well-drained soils that remove methane from the atmosphere.
In the arctic and boreal biomes, well-drained upland soils with a high potential for atmospheric methane consumption cover more than 80% of the land surface. Despite the large upland cover and its potential importance for methane uptake, the underlying mechanisms, environmental controls, and even the extent of methane uptake in Arctic soils are poorly understood. The study, on which researchers from Germany and the USA collaborated, was carried out mainly in Trail Valley Creek, a tundra in Canada’s western Arctic. The authors used a unique experimental setup consisting of 18 automated chambers to continuously measure methane fluxes.
There is no other automated camera system this far north of the Canadian Arctic, and there are few in the world above the Arctic Circle, most of which are installed at sites that emit methane. High-resolution measurements of methane uptake (more than 40,000 flow measurements) revealed previously unknown diurnal and seasonal dynamics of methane uptake: while methane uptake was higher in the afternoon in early and mid-summer, coinciding with the maximum soil temperature, methane uptake in late summer peaked at night. The underlying biogeochemical mechanisms are complex, but the study shows that peak methane uptake coincides with peak levels of ecosystem carbon dioxide (CO2) respiration.
Complementing the flow measurements at Trail Valley Creek with measurements from other Arctic locations in Canada and Finland showed that the availability of labile carbon substrates and nutrients can promote methane uptake in Arctic soils. On a larger scale, these results are of great importance for estimating the current Arctic methane budget and predicting the future response of Arctic soil methane uptake to a changing climate. According to the study, high-latitude warming, which is happening up to four times faster in the Arctic than in the rest of the world, will promote methane uptake into the atmosphere to a lesser extent than the associated large-scale drying.