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

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.
