Multi-scale Evidence of Large CO2 and CH4 Emissions from Permafrost During Spring Thaw in Northern Alaska
Thursday, 17 December 2015: 13:55
2004 (Moscone West)
Arctic warming will amplify climate change especially if thawing tundra emits increasingly greater amounts of CO2 and CH4 due to rising temperatures in the coming decades. However, uncertainties about flux rates and sources limit the prediction of these feedbacks. The few observations of tundra carbon fluxes during snowmelt suggest that there may be large releases during spring thaw, but little is known about the underlying mechanisms and whether emissions of greenhouse gases are widespread enough to influence atmospheric concentrations. To address this question we employed a multi-scale approach, including ecosystem-scale measurements, a mechanistic soil-core thawing experiment, and airborne observations of atmospheric carbon concentrations. We show that fluxes during the 2-week period of snow and surface-ice melt in 2014 near Barrow, Alaska, reduced the net snow-free season uptake of CO2 by 46% and added 6% to the CH4 emissions. A controlled laboratory experiment revealed that when frozen permafrost was exposed to warming temperatures, it released an immediate, large pulse of CO2 and CH4 that had been trapped under the surface ice. While the Alaskan North Slope was undergoing snowmelt, changes in the concentrations of CO2 and CH4 measured by aircraft were correlated to fluxes of CO2 and CH4 measured by eddy-covariance. Airborne measurements from the aircraft reflected local observations, and confirmed that the pulse had influence on regional atmospheric concentrations. This research suggests that the Arctic carbon spring pulse is a result of a delayed release of biogenic production in fall, and that this pulse is widespread and large enough to offset a significant fraction of the moderate Arctic tundra carbon sink.