Reduction in areal extent of high-latitude wetlands in response to permafrost thaw

Abstract

Wetlands are vegetated regions that are inundated with water on a permanent, seasonal or intermittent basis¹. These ecosystems play an important role in the carbon cycle: wetlands take up and store carbon, and release carbon dioxide and methane through the decomposition of organic matter². More than 50% of wetlands are located in the high northern latitudes³, where permafrost also prevails and exerts a strong control on wetland hydrology⁴. 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 zones⁵. Here, we use a global climate model to examine the influence of permafrost thaw on the prevalence of high-latitude northern wetlands, under four emissions scenarios. We show that as permafrost degrades, the areal extent of wetlands declines; we found a net loss in wetland extent in the three highest emissions scenarios. We also note an initial increase in the number of days of the year conducive to wetland formation, owing to an increase in 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 moisture to deeper soil layers. We suggest that a reduction in the areal extent and duration of wetlands will influence high-latitude carbon emissions.