Permafrost Thaw Mechanisms and Talik Function in Discontinuous Permafrost Peatlands

Abstract:

Climate warming in fragile discontinuous permafrost peatlands is causing permafrost loss and changes in ecosystem dynamics at unprecedented rate. Though rates of permafrost loss and landscape change have been widely documented based on remote sensing and field measurements, the mechanisms of permafrost degradation remain under-studied. In the discontinuous permafrost region, the formation of a talik (perennially thawed soil) between the base of the active layer and the top of the permafrost table signals the beginning of permafrost degradation. A coupled mass and heat transfer 1-D finite volume model of cryotic soils identified soil moisture and surface temperature (a combination of surface albedo and incoming radiation) as the major drivers of talik formation, while advection through existing taliks accelerated permafrost degradation rates. Data collected over three decades of research at the Scotty Creek Research Station in the southern Northwest Territories of Canada was analyzed to determine the hydrologic, thermodynamic and geophysical function of taliks in different parts of the landscape. This data points to a pattern of talik evolution and permafrost degradation beginning with the formation of an isolated talik, which expands to link with existing permafrost-free wetland features, and then forms perennial flow paths between adjacent wetlands. Once flow is established, advection leads to more rapid thaw, and the flow path expands eventually resulting in the wetland features merging. This trajectory for landscape evolution is supported by geospatial analyses which use remote sensing data and a space-for-time approximation to document landcover changes in discontinuous permafrost peatlands. This work has established the mechanisms and drivers of permafrost thaw in discontinuous permafrost peatlands, clearing the path for predictions of thaw rates and subsequent expected changes in the hydrology and ecosystems in this landscape.