Widespread and rapid thermokarst development in a region of very cold continuous permafrost in the Canadian High Arctic

Climate warming in regions of ice-rich permafrost can result in widespread thermokarst development which can have drastic impacts on ecosystem processes and human infrastructure. Numerous studies have demonstrated that local permafrost degradation is occurring in areas of relatively "warm" permafrost, yet few have acknowledged nor documented the vulnerability of cold permafrost to degradation. In this study we present the first dataset coupling observations of ice-wedge degradation and thermokarst development with on-site continuous ground temperature data. We show evidence of widespread permafrost degradation at three monitoring sites underlain by continuous permafrost, in the Canadian High Arctic (73 to 79°N). Across all sites, the lack of a substantial organic protective layer makes the permafrost vulnerable to increases in summer temperature. At the start of our ground observation period, ice wedges at each site showed little to no evidence of degradation, suggesting that this recent disturbance is unprecedented during the Holocene. During the last decade, at all sites, we observed a warming trend for climate and ground temperature, leading to an increase in active layer depth, ice-wedge melting, and subsequent ground subsidence. Between 2005 and 2013, active layer depth increased at Isachsen, Mould Bay and Green Cabin by up to 20, 30, and 40 cm respectively. This lead to trough deepening at Green Cabin and new development followed by further deepening of troughs at Mould Bay and Isachsen. To measure elevation changes caused by thermokarst development, and establish a baseline for future monitoring, we used structure from motion (SfM) photogrammetry to derive a high spatial resolution digital terrain model at each site. Local distribution of thermokarst landforms were quantified using high-resolution spectral satellite imagery at an annual resolution between 2010 and 2015 and indicate that ice-wedge trough development is widespread within at least a 1 km radius of each monitoring site. Our results illustrate the impact of widespread permafrost degradation on landscape topography and hydrology and highlight the vulnerability of high-arctic permafrost to climate change, especially in areas lacking substantial organic protective layers which act as a thermal buffer from top-down warming.