GEOSCAN, résultats de la recherche

Menu GEOSCAN


TitrePermafrost-ecological relations within the northern Great Slave region, Northwest Territories, Canada
AuteurMorse, P D; Wolfe, S A; Kokelj, S V; Gaanderse, A J
SourceCANQUA-CGRG Biannual Meeting, abstracts; 2013 p. 1
Année2013
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130143
ÉditeurUnivesity of Alberta
RéunionCANQUA-CGRG Biannual Meeting; Edmonton; CA; août 18-22, 2013
Documentlivre
Lang.anglais
Mediapapier; numérique
Formatspdf (Adobe® Reader®)
ProvinceTerritoires du Nord-Ouest
SNRC85J; 85K
RégionBehchoko; Tibbitt Lake; Grand lac des Esclaves
Lat/Long OENS-118.0000 -114.0000 63.0000 62.0000
Sujetspergélisol; glace fossile; caractéristiques périglaciaires; écologie; analyses thermiques; regimes thermiques; végétation; climat; dépôts organiques; tourbières; sols; sediments; temperature; températures au sol; trous de mine; humidité du sol; neige; analyses statistiques; conductivité thermique; changement climatique; forêt; géologie des dépôts meubles/géomorphologie; géologie de l'environnement; Nature et environnement
ProgrammeGéosciences de changements climatiques, Infrastructures terrestres
Diffusé2013 08 01
Résumé(disponible en anglais seulement)
This study reports on the ground thermal regime of permafrost occurring within distinct ecological settings of the Great Slave Lowland and Upland High Boreal Ecoregions, which lie within the extensive discontinuous permafrost zone. Permafrost distribution has commonly been associated with peatlands, but is also associated with coniferous (black-spruce dominant) and deciduous (white-birch dominant) forests, although is generally absent beneath fens, sandy jack-pine forest, and bedrock outcrops. This terrain mosaic leads to abrupt transitions in the occurrence of permafrost that are associated with changes in ground ice content. Disturbance or warming climate can thaw permafrost, leading to terrain instability if there are high ground-ice contents; however the potential response of permafrost is not well understood as there are few data on variation of the ground thermal regime in this region.
A 2010-13 field program was conducted to examine permafrost conditions at undisturbed peatland and spruce and birch forest sites on a 170 km transect of the Great Slave Lowland and Upland, along the north shore of Great Slave Lake, between Behchoko and Tibbitt Lake. Field data included eight air temperature sites, 19 near-surface ground temperature sites, nine deep ground temperature sites, 14 boreholes, ecological descriptions at 48 sites (vegetation cover, active-layer thickness, soil moisture, and organic-layer thickness), and 50 snow depth sites. The 1981-2010 mean annual air temperature at Yellowknife Airport was -4.1°C. At the study sites, annual mean air temperature was -4.3°C in 2010-11, but was 2°C higher in 2011-12 mainly due to higher winter air temperatures. Regression analysis of air temperature data indicated regionally consistent air temperatures, and a +0.5°C bias at Yellowknife Airport. Annual mean surface temperatures (2010-12) ranged from -0.5 to 3.2°C, and were about 1°C higher in peatlands than at forested sites. Conversely, annual mean temperatures at 100-cm depth were at least 1°C lower in peatlands than at forested sites, and ranged overall from -3.7 to -0.1°C. Permafrost occurred at sites with thermal offsets ranging from -6.1 to 0.1°C. Annual mean ground temperatures (5 to 10 m depths) at peatlands and forested sites ranged from -0.98 to -0.42°C and each site was approximately isothermal. Compared with peatland sites, deciduous forest sites had deeper, drier active layers with thin surface organic layers. Data for coniferous forest sites was intermediate between those of peatlands and deciduous forest. Median late-March (2013) snow depths ranged from 39 cm in deciduous forest to 47 cm at peatlands, close to the Yellowknife median annual late-winter maximum snow depth of 45 cm.
On an annual basis, ground-surface temperature variation was influenced mainly by differences in substrate materials, particularly the moisture content and thermal conductivity of the freezing/thawing layer. Higher surface temperatures at peatlands were due mainly to freezing season conditions of the active layer, with greater than 1.5 times the amount of latent heat released from freezing the soil compared with forested sites, but once frozen, icy peat has a high thermal conductivity that facilitates ground cooling. Conversely, the average winter surface temperatures at forested sites were lower, likely due to drier soil and less latent heat released from active-layer freezing. At forested sites, temperatures at 100-cm depth remained close to 0°C, likely due to the relatively low thermal conductivity of the active layer and high thermal inertia associated with phase change of unfrozen water content at the top of permafrost. As the permafrost beneath forested sites was isothermal, increased surface temperature would direct energy toward thawing, rather than warming. Preliminary data suggest thermal conditions differ amongst the various soil and vegetation types in the region, and indicate the possibility of combining field data and remote sensing to create predictive maps of permafrost conditions.
Sommaire(Résumé en langage clair et simple, non publié)
Nous diffusons la température du sol en zone de pergélisol (sol qui demeure gelé toute l¿année) dans divers contextes écologiques dans la région de Great Slave, dans les Territoires du Nord-Ouest. Tandis que la température du sol près de la surface dans les tourbières est plus élevée qu¿en forêt, elle l¿est moins en profondeur (p. ex., à 100 cm de profondeur). Nous attribuons cet écart de température du sol au taux d¿humidité et à la conductivité thermique (capacité qu¿ont les sols de transmettre la chaleur) du sol. Ces données indiquent qu¿avec le réchauffement, les sites boisés pourraient être plus vulnérables à la fonte que les tourbières. Les résultats de notre étude pourraient servir à établir des cartes prévisionnelles de l¿état du pergélisol dans cette région.
GEOSCAN ID292789