ABSTRACT: The impact of recent warming on permafrost in Nunavik.

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Abstract

As the worse cases climate warming scenarios now seem likely to materialize in this beginning of the 21st Century, the climate shift that occurred between 1992 and 2003 in Nunavik generated impacts in permafrost terrain that provideexcellent examples of what may lie ahead. After a generally cooling trend since about 1950, the atmospheric temperature started to rise in 1993 and went above the long term mean around 1995-1998. For instance, the mean annual air temperatures went up from around -6.8 °C in 1993 to -3.4 °C in 1999 in Kuujjuaq; since then they oscillate around -4 °C. This increase was also felt in Salluit, with temperatures rising from – 9 °C in 1990 to -5.7 °C in 2005. Theresulting shifts in ground temperature profiles and associated changes in active layer depth were recorded across Nunavik from a network of more than 45 thermistor cables located in 12 sampling sites in nearly all soil types (bedrock, till, sand, clay, peat), under airport runways, in communities, and in the natural environment. Active layer depth increased by more than 2 m in most bedrock sites. It went down from about 45 cm to nearly 1 m in clay soils in Salluit. Under several runways where the permafrost table was originally contained within the embankment (as designed during construction), the active layer now penetrates to depth of 30-50 cm in the underlying soil and thaw settlement has begun to occur at sites built on ice-rich soils, necessitating more frequent and costlier maintenance. In the discontinuous permafrost zone east of Hudson Bay, comparisons of high resolution satellite images (Ikonos) taken in 2005 with aerial photographs from 1957 show that permafrost inwetlands contained in palsas that accounted for 12 % of the surface area of the landscape now accounts for only 5.8 %, for a total area reduction of 51%.Permafrost decay provokes the incipience of thermokarst lakes and favours the expansion of shrub vegetation. Both in the natural environment and around built infrastructures, snow cover accumulation by wind drifting is an important factor of localized warming that increases permafrost thawing rates and accelerates the general impact of climate warming. This is particularly so around decaying palsas, on roadsides and along runways. Correlation coefficients between maximum snow depth and mean annual soil surface temperature were calculated at several sites. These values will have to be considered for the thermal design of new or repaired infrastructures. Theimpacts of warming to come will possibly be mitigated though careful land use planning based on new permafrost sensitivity maps that are just being finishedfor the Nunavik communities. In the natural environment, important impacts related to geomorphological changes, creation of GHGgenerating wetlands and disturbance of hydrographic networks are predictable.

Bibliography of Canadian Geomorphology