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TitleSpatial and temporal variability in permafrost thermal state and active layer thickness along the Mackenzie Valley transect, NWT Canada
AuthorSmith, S L; Duchesne, C; Ednie, M; Bonnaventure, P
SourceXI International Conference on Permafrost, book of abstracts; by Günther, F (ed.); Morgenstern, A (ed.); 2016 p. 491-492
Alt SeriesEarth Sciences Sector, Contribution Series 20150447
PublisherBibliothek Wissenschaftspark Albert Einstein (Potsdam, DE)
Meeting11th International Conference on Permafrost; Potsdam; DE; June 20-24, 2016
Mediaon-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS95H; 95I; 95J; 95N; 95O; 96C; 96D; 96E; 96F; 96L; 106I; 106J; 106N; 106O; 106P; 107B; 107C
AreaNorman Wells Pipeline; Mackenzie River; Fort Simpson; Wrigley; Norman Wells; Fort Good Hope; Inuvik; Tuktoyaktuk
Lat/Long WENS-136.0000 -120.0000 70.0000 61.0000
Subjectssurficial geology/geomorphology; permafrost; thermal regimes; ground temperatures; active layer thickness; Quaternary
ProgramEssential Climate Variable Monitoring, Climate Change Geoscience
LinksOnline - En ligne (PDF, 345 MB)
Permafrost is an important component of the landscape of the Mackenzie Valley NWT that influences both natural and socio-economic environments. Changes in the ground thermal regime and active layer conditions in response to a changing climate can lead to alterations in drainage and ground stability which has implications for environmental and infrastructure integrity. The active layer responds to shorter term fluctuations in climate compared to the thermal regime of deeper ground. Monitoring of two key cryospheric indicators (or essential climate variables), active layer thickness and permafrost thermal state allows an assessment of both inter annual variability and longer-term change in permafrost conditions. The Geological Survey of Canada has maintained a permafrost monitoring network in the Mackenzie Valley (Figure 1) since the mid 1980s that consists of a suite of sites representing the range of ecoclimatic conditions in the region. This paper describes the spatial variation in active layer thickness and permafrost thermal state and also documents the change that has occurred over time.
Study Sites and Instrumentation
The monitoring transect extends from the tundra environments of the Tuktoyaktuk peninsula to the boreal forest in the south. The terrain consists of lacustrine, moraine, fluvial and deltaic sediments. Extensive peatlands are found in the southern portion of the region where poor drainage resulted in thick accumulations of peat. Ice-rich fine-grained sediments such as lacustrine clays are common. Permafrost is continuous and several hundred metres thick on the Beaufort Coastal plain in the north and becomes thin and sporadic in the southern NWT. Field sites (Figure 1) were selected to be representative of the vegetation and terrain conditions in the region. The active layer monitoring network was initiated in 1991 and originally consisted of 66 sites with 45 still in operation. Thaw tubes are utilized to determine maximum summer thaw penetration and also maximum heave and subsidence of the ground surface. Details on instrumentation and site descriptions are available in Smith et al. (2009). Over 70 boreholes have been instrumented with thermistor cables connected to data loggers to measure ground temperatures to depths of 20 m. Some sites have been operational since the 1980s, but many were established between 2006 and 2008, during the International Polar Year (Smith et al. 2010). At many sites, instrumentation has also been installed to measure air and ground surface temperature. More information on the instrumented sites along with recent data collected can be found in Smith et al. (2015).
Current Conditions
Permafrost temperatures are above -2°C throughout a large portion of the region, especially within the discontinuous zone. Colder conditions are found within the continuous permafrost zone but permafrost temperatures are highly variable ranging from -6 to -7°C in the tundra uplands to higher than -2°C in wet areas or where vegetation promotes snow accumulation. Active layer thickness (ALT) ranges from about 0.5 m in the north to greater than 1 m in the south with ALT generally being less above treeline compared to that below treeline. Considerable spatial variability in ALT is observed particularly below treeline where high shrubs dominate and influence snow accumulation.
Temporal Variability
Long-term records of permafrost temperature indicate permafrost has generally warmed in the Mackenzie Valley since the mid 1980s, which is consistent with increases in air temperature (Smith et al. 2010). Although this warming has continued over the last decade, it has generally been at a lower rate. Since 2007, when many of the sites were established, permafrost temperatures have increased at most sites. Between 2007 and 2014, increases in permafrost temperature have ranged from less than 0.1°C to 0.2°C in the discontinuous zone and from 0.2 to 0.5°C in the continuous zone (Smith et al. 2015). At warmer permafrost sites, especially where ground temperatures are close to 0°C and soils are ice-rich, latent heat effects associated with phase change result in ground temperatures being less responsive to changes in climate (Smith et al. 2010). Greater interannual variability is observed in active layer records compared to ground temperature records and there has been no pronounced trend in ALT over the 1991-2014 record. At many sites the maximum ALT occurred in 1998 which was one of the warmest years on record. ALT generally decreased following the 1998 peak, but there has been an increase in ALT at many sites since 2005 which seems to coincide with a period of higher summer air temperatures. Although active layer development is influenced by summer air temperatures, the surface freezing index has decreased recently at some sites and the observed increase in ALT may also be partly due to warmer winter conditions.
Data from the permafrost monitoring network has enabled characterization of spatial and temporal variability in active layer thickness and permafrost thermal state in the Mackenzie Valley. Recent increases in ALT and permafrost temperature have been observed but the magnitude and rate of change varies spatially. The monitoring network generates essential information on permafrost in an important transportation/transmission corridor, which can inform land management decisions, infrastructure planning and adaptation to a changing climate.
Smith, S.L., Chartrand, J., Duchesne, C. and Ednie, M., 2015. Report on 2014 field activities and collection of ground thermal and active layer data in the Mackenzie Corridor, Northwest Territories, Geological Survey of Canada Open File 7935.
Smith, S.L., Riseborough, D.W., Nixon, F.M., Chartrand, J., Duchesne, C., and Ednie, M. 2009. Data for Geological Survey of Canada active layer monitoring sites in the Mackenzie valley, N.W.T., Geological Survey of Canada Open File 6287.
Smith, S.L., Romanovsky, V.E., Lewkowicz, A.G., Burn, C.R., Allard, M., Clow, G.D., Yoshikawa, K., and Throop, J. 2010. Thermal state of permafrost in North America - A contribution to the International Polar Year. Permafrost and Periglacial Processes, 21: 117-135.
Summary(Plain Language Summary, not published)
This presentation describes the spatial and temporal variability of permafrost thermal state and active layer thickness along the Mackenzie Valley, an important transportation/transmission corridor. Results are reported from a suite of sites representative of the range of ecoclimatic conditions in the region. In the north permafrost temperatures can be lower than -6°C with active layers about 0.5 m thick while in the south permafrost is warmer than -2°C and active layers can be 1 m or more in thickness. Warming of permafrost has occurred over the last 2-3 decades but permafrost temperatures have increased at a lower rate more recently with higher rates observed at northern sites with colder permafrost. No long-term trend in active layer thickness is apparent but since 2005, active layers have generally become thicker. Information is provided to characterize the range in permafrost conditions throughout an important transportation corridor and to improve prediction of future conditions and inform adaptation planning for a changing climate.