Tundra Underlain by Thawing Permafrost Persistently Emits Carbon to the Atmosphere Over Fifteen Years of Measurements

Abstract:

Warming of the Arctic can stimulate microbial decomposition and release of permafrost soil carbon as greenhouse gases, and thus has the potential to influence climate change. At the same time, plant growth can be stimulated and offset carbonrelease. The interaction between increased resource availability to plants and soil microbes coupled with the life histories of these organisms will determine the net response of the ecosystem C cycle to changes in climate. This study presents a 15-year time series of chamber and eddy covariance measurements of net ecosystem C exchange in a tundra ecosystem in Alaska where permafrost has been degrading due to regional warming. The site was, on average, a carbon dioxide source to the atmosphere of 52.2 g C m^-2 year^-1, representing a cumulative total loss of 781.6 g C m^-2 over the study period. Both gross primary productivity and ecosystem respiration were already likely higher than historical levels such that increases in ecosystem respiration losses overwhelmed gross primary productivity gains in most years. This shift to a net carbonsource to the atmosphere likely started in the early 1990s when permafrost was observed to warm and thaw at the site. Shifts in the plant community occur more slowly and are likely to constrain future gross primary productivity increases as compared to more rapid shifts in the microbial community that contribute to increased ecosystem respiration. Observed rates suggest that cumulative net soil C loss of 4.18 to 10.00 kg C m^-2 —8-20% of the current active layer soil carbonpool— could occur from 2020 to the end of the century. This amount of permafrost carbon loss to the atmosphere represents a significant accelerating feedback to climate change if it were to occur at a similar magnitude across the permafrost region.