Tundra vegetation affects thaw depth response to soil temperature

• Main Authors: Grünberg, Inge, Wilcox, Evan J., Zwieback, Simon, Marsh, Philip, Boike, Julia
• Format: Conference Object
• Language: unknown
• Published: 2020
• Subjects: Northwest Territories; Canada; Valley Creek; Trail Valley Creek; Active layer thickness; Arctic; permafrost; taiga; Tundra
• Online Access: https://epic.awi.de/id/eprint/53653/; https://epic.awi.de/id/eprint/53653/1/poster_ac_inge.pdf; https://hdl.handle.net/10013/epic.806ec818-592b-43b0-858f-0cfb3c2eaf76; https://hdl.handle.net/

As a result of recent climate warming, permafrost thaw changes landscape hydrology and threatens infrastructure in the north. Topsoil temperature is an important indicator of how surface conditions translate to active layer thickness and permafrost temperatures. We measured topsoil temperature at 1-3cm depth at 68 locations within 0.5km²? at the Trail Valley Creek study site in the tundra-taiga transition zone, Northwest Territories, Canada. The sensors recorded temperature below six different vegetation types for two years (2016-2018). Topsoil temperature was highly spatially variable even within vegetation types and with mean annual temperatures between -3.7 and 0.1°C. Winter and spring topsoil temperatures clearly depended on the snow distribution, which was influenced by vegetation. On the other hand, summer and autumn temperatures were less variable in space and only weakly related with vegetation type or height, making vegetation a poor proxy for summer soil warming. Vegetation played a crucial part in the link between topsoil temperature and thaw depth. Cold winter temperature was associated with deep active layers in the following summer beneath lichen and dwarf shrub tundra, while we observed the opposite beneath tall shrubs and tussocks. Summer topsoil temperature was not important for thaw depth, in particular at tall shrub and tussock locations. Only beneath lichen and dwarf shrub tundra, we could observe a tendency towards deeper active layers at locations with higher cumulative positive degree days. Our study elucidates how vegetation mediates between above ground processes and permafrost thaw, likely in combination with soil properties and soil moisture. We highlight the importance of complex feedback mechanisms and spatial variability within a few meters for the overall permafrost response. Therefore, reliable estimates of permafrost vulnerability based on permafrost models or remote sensing observations will need to incorporate vegetation-permafrost interactions.