Antoni G. Lewkowicz

Slope sediment yield in arid lowland continuous permafrost environments, Canadian Arctic Archipelago

Abstract Surface wash erosion was measured at runoff plots on low to moderate slopes in clayey and sandy silts underlain by continuous permafrost on the Fosheim Peninsula, Ellesmere Island. Due to snow redistribution in winter, total precipitation on the plots varied from 34 to 150 mm, with corresponding surface runoff values of 0 to 102 mm. Where runoff occurred, at least 80% of it was derived from snowmelt. Suspended sediment removal was Plot data (precipitation, vegetation and surface grain-size) from the Fosheim Peninsula and Banks Island were used to develop a statistical model of suspended sediment removal by surface wash on undisturbed slopes. For any given grain-size, the model predicts a rise in erosion from zero precipitation (because of an absence of runoff) to a peak at about 50 mm, a decline as precipitation increases to 300 mm and a further increase in erosion beyond this inflection point. This non-linear response is due to the complex interaction of moisture (primarily snow) and vegetation cover. Erosion at any given precipitation value varies through three orders of magnitude depending on surface grain-size. The maximum erosion predicted is 1 kg m−2 a−1 for a runoff plot with 1100 mm of precipitation, a corresponding vegetation cover of 77% and a median surface grain-size of 7 φ.

SPATIAL AND THERMAL CHARACTERISTICS OF MOUNTAIN PERMAFROST, NORTHWEST CANADA

Lewkowicz, A.G., Bonnaventure, P.P., Smith, S.L. and Kuntz, Z., 2012. Spatial and thermal characteristics of mountain permafrost, northwest Canada. Geografiska Annaler: Series A, Physical Geography, ••, ••–••. doi:10.1111/j.1468‐0459.2012.00462.x ABSTRACT An extensive network of monitoring stations was used to develop a mean annual air temperature map for the complex mountainous terrain in the southern Yukon and northern British Columbia, Canada (latitude 59° to 65° N). Air temperature lapse rates measured at screen height from valley bottoms up to treeline are normal in the maritime extreme southwest, normal but weak in much of the region, and inverted in the highly continental northernmost sites. Relationships between air and ground surface temperatures, expressed as freezing and thawing n‐factors, vary significantly with vegetation type and hence elevational band, with the lowest values for the forested zone and the highest for non‐maritime alpine tundra. Equilibrium modelling carried out for one site in the southern part of the region and one in the northern part illustrates the impacts of the differing n‐factors on trends in mean ground surface temperature with elevation. Ground thermal regimes determined at borehole locations vary greatly due to these climatic controls but are also affected by substrate. Valley‐bottom permafrost in the south is scattered, at temperatures just below 0°C, has a depth of zero annual amplitude of 2–3 m (due to latent heat effects) and may be only a few metres in thickness. Permafrost on bedrock summits is cold, has active layers >5 m thick, is >50 m thick and may be locally continuous. Given the range of air temperatures and n‐factors, permafrost is possible throughout the Yukon but higher temperatures southward and stronger lapse rates mean that a lower elevational limit exists in northern British Columbia.

Multi-decadal degradation and persistence of permafrost in the Alaska Highway corridor, northwest Canada

Changes in permafrost distribution in the southern discontinuous zone were evaluated by repeating a 1964 survey through part of the Alaska Highway corridor (56° N–61° N) in northwest Canada. A total of 55 sites from the original survey in northern British Columbia and southern Yukon were located using archival maps and photographs. Probing for frozen ground, manual excavations, air and ground temperature monitoring, borehole drilling and geophysical techniques were used to gather information on present-day permafrost and climatic conditions. Mean annual air temperatures have increased by 1.5–2.0 ° C since the mid-1970s and significant degradation of permafrost has occurred. Almost half of the permafrost sites along the entire transect which exhibited permafrost in 1964 do so no longer. This change is especially evident in the south where two-thirds of the formerly permafrost sites have thawed and the limit of permafrost appears to have shifted northward. The permafrost that persists is patchy, generally less than 15 m thick, has mean annual surface temperatures >0 ° C, mean ground temperatures between −0.5 and 0 ° C, is in peat or beneath a thick organic mat, and appears to have a thicker active layer than in 1964. Its persistence may relate to the latent heat requirements of thawing permafrost or to the large thermal offset of organic soils. The study demonstrates that degradation of permafrost has occurred in the margins of its distribution in the last few decades, a trend that is expected to continue as the climate warms.

Beaver Damming and Palsa Dynamics in a Subarctic Mountainous Environment, Wolf Creek, Yukon Territory, Canada

Abstract The growth, longevity, and decay of mineral-cored palsas at an altitudinal treeline site in the southern Yukon all appear to be significantly affected by the activities of beaver (Castor canadensis). The palsas are composed of stratified, fine-grained, organic-rich, frost-susceptible deposits, which are interpreted as originating from sedimentation in beaver ponds. Peat development, which is a precondition for mound formation, takes place in the adjacent wetland, in part due to poor drainage because of dams. Palsa degradation over the past 55 yr preferentially followed flooding due to dam construction. Drainage of ponds by dam breach was succeeded by mound formation in aggrading permafrost. Unlike previous studies, therefore, it is impossible to infer a clear climate signal from palsa dynamics at this location.

LAKE‐ICE BLISTERS, TERRA NOVA BAY AREA, NORTHERN VICTORIA LAND, ANTARCTICA

Abstract. Ice blisters, typically 0.2–0.8 m high and 5–20 m long, develop annually on perennially frozen lakes in Northern Victoria Land. They are believed to be caused by hydrostatic pressures generated through progressive freezing of solute‐rich water beneath the lake‐ice cover during winter. Lake‐ice blisters in the study area differfrom icing blisters described from the northern hemisphere. The latter are caused by hydraulic pressures and are found at locations such as river beds or spring sites on sloping terrain. The Antarctic lake‐ice blisters reflect the occurrence of dry‐based perennially frozen lakes with high salt contents in an extremely cold and arid environment.

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 +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. 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.

Active Layer Detachment Slides and Retrogressive Thaw Slumps Susceptibility Mapping for Current and Future Permafrost Distribution, Yukon Alaska Highway Corridor

The Yukon portion of the Alaska Highway Corridor traverses the discontinuous permafrost zone. Air-photos and high resolution satellite imagery were used to produce an updated landslide inventory (2013) that identified 1,600 landslides in the corridor. Landslide susceptibility models were developed for the corridor for two types of landslides triggered in permafrost, active layer detachment slides (ALD) and retrogressive thaw slumps (RTS), which comprise about 3 % of the inventory. A qualitative heuristic approach was used to combine data layers for slope, vegetation, surficial geology unit, slope aspect, and permafrost distribution. ALD and RTS susceptibility maps were produced for present day permafrost distribution and also equilibrium permafrost distribution resulting from air temperature increases of 1–5 °C. The resulting susceptibility maps indicate that with warming and reduced permafrost extent, there will be fewer zones of high susceptibility. The maps for warmer conditions give a “snapshot” of a potential decrease in zones of high landslide susceptibility, but they do not show the potential landslide occurrence as permafrost warms and thaws. It is expected that as permafrost warms and thaws, ALD and RTS activity will increase until conditions stabilize as permafrost disappears.

Why Permafrost Is Thawing, Not Melting

As global climate change is becoming an increasingly important political and social issue, it is essential for the cryospheric and global change research communities to speak with a single voice when using basic terminology to communicate research results and describe underlying physical processes. Experienced science communicators have highlighted the importance of using the correct terms to communicate research results to the media and general public [e.g., Akasofu, 2008; Hassol, 2008]. The consequences of scientists using improper terminology are at best oversimplification, but they more likely involve misunderstandings of the facts by the public.