Characteristics and fate of isolated permafrost patches in coastal Labrador, Canada

Bodies of peatland permafrost were examined at five sites along a 300 km transect spanning the isolated patches permafrost zone in the coastal barrens of southeastern Labrador. Mean annual air temperatures ranged from C 1 degrees C in the south (latitude 51.4 ffi N) to 1 : 1 degrees C in the north (53.7 degrees N) while mean ground temperatures at the top of the permafrost varied respectively from 0 : 7 to 2 : 3 degrees C with shallow active layers (40-60 cm) throughout. Small surface offsets due to wind scouring of snow from the crests of palsas and peat plateaux, and large thermal offsets due to thick peat are critical to permafrost, which is absent in wetland and forested and forest-tundra areas inland, notwithstanding average air temperatures much lower than near the coast. Most permafrost peatland bodies are less than 5m thick, with a maximum of 10 m, with steep geothermal gradients. Onedimensional thermal modelling for two sites showed that they are in equilibrium with the current climate, but the permafrost mounds are generally relict and could not form today without the low snow depths that result from a heaved peat surface. Despite the warm permafrost, model predictions using downscaled global warming scenarios (RCP2.6, RCP4.5, and RCP8.5) indicate that perennially frozen ground will thaw from the base up and may persist at the southern site until the middle of the 21st century. At the northern site, permafrost is more resilient, persisting to the 2060s under RCP8.5, the 2090s under RCP4.5, or beyond the 21st century under RCP2.6. Despite evidence of peatland permafrost degradation in the study region, the local-scale modelling suggests that the southern boundary of permafrost may not move north as quickly as previously hypothesized.