Permafrost response to vegetation greenness variation in the Arctic tundra through positive feedback in surface air temperature and snow cover

Abstract

The permafrost response to variations in Arctic vegetation remains controversial. We investigated the consequences of Arctic vegetation greenness variation over the past three decades using a coupled land-atmosphere model and found that it induces air temperature perturbation, which is further amplified by snow cover variation and eventually leaves a footprint on soil temperature. Compared to the atmospheric impacts of vegetation, local shading of vegetation canopy has relatively minor effects on soil temperature. Significant soil warming was observed along the summer snowline between the Low and High Arctic, indicating the direct impact of snow cover variation led by vegetation changes. In the Low Arctic, the winter snowpack insulates the soil from colder air, resulting in less permafrost. In the High Arctic, snow persists for more than 330 d per year and has a strong protection effect on the permafrost as it insulates soil from warmer summer air and reflects solar radiation.

Monitoring 13 years of drastic catchment change and the hydroecological responses of a drained thermokarst lake

“…Water chemistry later in the record did not return to lower spring 2007 values, owing to the altered abiotic and biotic conditions produced by increased shrub vegetation. We found temperatures at the ground surface to be 2-3 åC higher under deeper snowpack among tall shrub vegetation compared to open and spruce-covered sites, which is generally consistent with other findings in northwestern North America (Sturm et al 2001;Myers-Smith and Hik 2013;Roy-Léveillée et al 2014;Wang et al 2019b;Wilcox et al 2019). The thermal properties of deeper snow among tall shrub vegetation have been associated with deeper active layer thaw depths (e.g., in OCF, Turner, unpublished data; Cameron and Lantz 2016), especially in drained thaw-lake basins , and near-surface permafrost temperature (Roy-Léveillée et al 2014).…”

Tundra shrub expansion may amplify permafrost thaw by advancing snowmelt timing

“…Hummock height had the largest effect on hummock frost table depth after sample date, but snow-free date has a similarly strong influence on frost table depth based on the standardized path coefficients from the structural equation model (0.13 and −0.11, respectively). Snow-free date has been shown to control active layer thickness in large-scale modeling studies (Lawrence and Swenson 2011;Bonfils et al 2012;Wang et al 2018); however, the direct effect of snow-free date on frost table depth has not been reported at the plot scale previously. Our results indicate that the effect of shrub shading is not a dominant control on frost table depth at the Siksik Creek watershed, as areas of birch and channel shrubs had significantly deeper hummock frost table depths than tundra areas, whereas alder and tundra frost table depths did not differ significantly.…”

“…In addition, patches of tall shrubs can trap blowing snow (Pomeroy et al 1997), which in turn increases wintertime ground temperatures as deeper snow insulates the ground more effectively (Sturm et al 2001;Hinkel and Nelson 2003;Myers-Smith and Hik 2013). Deeper snow also requires longer to melt and delays the beginning of active layer thaw (Wang et al 2018).…”

Scientific Cooperation: Supporting Circumpolar Permafrost Monitoring and Data Sharing

“…The active layer will freeze again in the autumn. Changing climatic conditions affect the state of permafrost in direct and indirect ways: among the factors that influence a frozen ground are rising air temperatures, changing snow regimes, and condition of vegetation [19][20][21]. A typical classification, first developed in 1927 [22], recognizes continuous permafrost (underlying 90-100% of the landscape), discontinuous permafrost (50-90%), and sporadic permafrost (0-50%).…”