Abstract
Abstract. 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 +1 ∘C in the south (latitude 51.4∘ N) to −1.1 ∘C in the north (53.7∘ N) while mean ground temperatures at the top of the permafrost varied respectively from −0.7 to −2.3 ∘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 5 m thick, with a maximum of 10 m, with steep geothermal gradients. One-dimensional 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.
Highlights
Global and regional models project that the southern boundary of permafrost will shift northwards over the century as the climate warms (e.g. Koven et al, 2013; Zhang et al, 2008a, b)
We describe field measurements of air temperature, ground temperature and the spatial extent of permafrost patches using frost probing and electrical resistivity tomography (ERT), and the results of numerical modelling to assess the fate of these isolated bodies of perennially frozen ground as the climate warms
We modelled the thermal dynamics for borehole WJD02 at Cartwright and borehole WJD03 at Blanc-Sablon using the Northern Ecosystem Soil Temperature (NEST) model (Zhang et al, 2003)
Summary
Global and regional models project that the southern boundary of permafrost will shift northwards over the century as the climate warms (e.g. Koven et al, 2013; Zhang et al, 2008a, b). Global and regional models project that the southern boundary of permafrost will shift northwards over the century as the climate warms In the zone of isolated patches, permafrost underlies less than 10 % of the landscape and is mainly present in frozen peatlands (Smith and Riseborough, 2002). Peatland permafrost is considered to be vulnerable to thaw in response to projected regional warming, which may modify ecosystem properties and change landscape development processes (Tarnocai, 2006, 2009). Most field-based studies of changes in peatland permafrost have focused on the sporadic and extensive discontinuous zones A better understanding of the current distribution and characteristics of bodies of permafrost located in the zone of isolated patches is needed to assess the likelihood of their persistence or degradation in the face of climate warming
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
