Evolution of Northern Wetlands in Response to Permafrost Thaw

Wetlands are vegetated regions that are inundated with water on a permanent, seasonal or intermittent basis. These ecosystems play an important role in the carbon cycle: wetlands take up and store carbon, and release carbon dioxide and methane throught the decomposition of organic matter. More than 50 % of wetlands are located in the high northern latitudes, where permaforst also prevails and exerts a strong control on wetland hydrology. Permafrost degradation is linked to changes in Arctic lakes: between 1973 and 2004, the abundance of lakes increased in continuous permafrost zones, but decreased in other zones. Here, I use a global climate model to examine the influence of permafrost thaw on the prevalence of high-latitude northern wetlands, under four emissions scenarios. I show that as permafrost degrades, the areal extent of wetlands declines; I found a net loss in wetland extent in the three highest emissions scenarios. I also note an initial increase in the number of days of the year conducive to wetland formation, owing to an increase in the unfrozen surface moisture resulting from a lengthening of the thaw season. This is followed by a dramatic decline in the number of wetland-conducive days, owing to a deepening of the permafrost surface, and drainage of near-surface soil moisture to deeper soil layers. I suggest that a reduction in the areal extent and duration of wetlands will influence high-latitude carbon emissions.