Factors Influencing the Spatial and Temporal Occurrence of Thermo-erosional Landforms along the Yukon Coast, Canada

Processes associated with permafrost degradation in the arctic coastal zone are highly dynamic and account for significant amounts of organic carbon released to the Arctic Ocean. Thermo-erosion, as a mechanism of rapid permafrost thaw, reshapes arctic landscapes and has a clear impact on the mobilization and distribution of carbon and nitrogen in permafrost terrains. However, few studies report on the diversity of thermo-erosional landforms or assess the factors involved in their development. This study highlights the diversity of thermo-erosional drainage pathways -- including gullies and valleys -- and specific thermokarst features such as retrogressive thaw slumps and active layer detachments, and determines the prevailing factors accounting for their distribution and driving their expansion over the last 60 years along the Yukon coast. With the software OrthoEngine from PCI Geomatica we used a large set of high resolution satellite images from 2011 (GeoEye-1 and WorldView-2) for geocoding aerial photographs from the 1950s. The aerial photographs come from the National Air Photo Library, Canada. This dataset allowed us to manually digitize and classify thermo-erosional gullies, valleys, retrogressive thaw slumps and active layer detachments for the 1950s and 2011 using ArcGIS 10.3. We gathered additional observations during fieldwork in July and August 2015 on gully and valley morphologies, and on the current development stage of retrogressive thaw slumps. Based on remote sensing, we calculated and compared the surface area occupied by slumps in 1950s and in 2011 as well as the types, number and lengths of thermo-erosional drainage pathways over the same period. We coupled these information with additional datasets related to climate, geology and topography, and performed multivariate statistical analyses using the software R. Over this time span, we observed an important spatial heterogeneity in the landform dynamics among the different geological units. The number and the surface area of retrogressive thaw slumps increased on average. We did not detect a specific increase in the length of thermo-erosional drainage pathways over the whole area, however, in some specific geological units they decreased in length due to important coastal erosion. This dataset will be complemented by soil organic carbon data collected across several thermo-erosional landforms during fieldwork conducted in 2015 in order to understand the processes of carbon mobilization within specific thermo-erosional landforms