Contribution of Retrogressive Thaw Slumps to the Near Shore Carbon Budget along the Yukon Coast, Canada

The mechanism of carbon dioxide and methane release to the atmosphere in permafrost regions is not solely restricted to the progressive thawing of the upper part of the ground by warmer air temperatures. Organic carbon and nutrients are released to streams, rivers or coasts by abrupt processes such as thermokarst, thermal erosion and simply river bank or coastal erosion. Thermo-erosion, as a mechanism of rapid permafrost thaw, reshapes Arctic coasts and has a clear impact on the mobilization and distribution of carbon and nitrogen in permafrost terrains. Retrogressive thaw slumps are one specific and highly dynamic landform, which results from thermo-erosion of ice-rich permafrost and leads to the displacement of large volumes of sediments. Studies reporting on the occurrence and evolution of retrogressive thaw slumps over the Arctic show that in varied Arctic areas, slumps have increased over the last decades. While the processes responsible for the initiation of retrogressive thaw slumps are well defined, little research has been done on a regional scale to define the terrains on which they occur, and to measure the volumes of sediments eroded through their development. There are currently no estimates of the contribution of these permafrost degradation landforms to the carbon budget, therefore thermo-erosional features are not yet accounted in the carbon models. With this study, we highlight the important contribution of retrogressive thaw slumps to the nearshore carbon cycle in the eastern part of the Beaufort Sea by 1) calculating the amount of sediments eroded through the development of RTSs, 2) estimating the amount of carbon mobilized and potentially transported from the land to the nearshore zone of the Beaufort Sea. We used a large set of high-resolution multispectral satellite images from 2011 (GeoEye-1 and WorldView-2) we manually digitized coastal retrogressive thaw slumps along a 235 km coastline. We gathered additional observations during fieldwork in July and August 2015 on the current development stage of retrogressive thaw slumps and classified them between active and stable. We extrapolated the eroded surfaces using a digital elevation model. Based on available literature on carbon stocks in the area, we estimated the amounts of mobilized particulate organic carbon and nitrogen. This model allowed us to measure the contribution of retrogressive thaw slumps to the near shore carbon budget in the area