Permafrost, tectonics, and past and future regional climate change, Yukon and adjacent Northwest Territories

Abstract

Late Tertiary changes in the general circulation of the atmosphere, regionally enhanced by uplift of the Wrangell -Saint Elias and Coast mountains, were sufficient to promote permafrost development in the western Arctic. Permafrost developed in Yukon Territory and adjacent Northwest Territories during early Pleistocene glacial periods, after continued tectonic activity led to further modification of regional climate, but degraded in the interglacials. Permafrost has been present in northem parts of the region since the Illinoian glaciation, but most ground ice in central Yukon formed in the Late Wisconsinan. The present interglacial is the only one with widespread evidence of permafrost, which is maintained in the valleys of central and southern Yukon by the Saint Elias Mountains blocking continental penetration of maritime air from the Gulf of Alaska. This reduces snow depth in winter, while cold-air drainage in the dissected terrain of the Yukon Plateaus enhances the nearsurface inversion, leading to continental minimum temperatures. General circulation models used to simulate climate represent the physiography of northwest Canada crudely. As a result, the simulations are unable to reproduce conditions responsible for the development and preservation of permafrost in the region.Le soulkement des massifs Wrangell, Saint Elias et de la chaine CBt2re amplifice de facon regionale des changements dans la circulation atmosphCrique gCnCrale qui eurent lieu au Tertiaire supCrieur. Ces changements furent suffisants pour provoquer le dCveloppement du pergelis01 dans la partie ouest de 1'Arctique. Le pergClisol s'est form6 dans le territoire du Yukon et les territoires du Nord-Ouest adjacents, durant les periodes glaciaires du PlCistocbne infkrieur, lorsque le climat rtgional fut modifiC davantage par une activitk tectonique continue, mais il s'est dBgrad6 durant les periodes interglaciaires. Le pergCliso1 Ctait prCsent dans la partie nord de la region depuis la glaciation Illinoienne, mais la majeure partie de la glace de sol du Yukon central s'est formte durant le Wisconsinien supCrieur. Seul l'interglaciaire actuel prCsente beaucoup d'Cvidences de pergCliso1, qui est conserv6 dans les vall6es du centre et le sud du Yukon par la barribre que forme le massif Saint Elias, qui empeche la pCnCtration sur le continent de l'air maritime en provenance du golfe d'Alaska. Ceci rkduit I'kpaisseur de neige en hiver alors que la dispersion d'air froid dans les terrains dissCquCs du plateau du Yukon favorise l'inversion en surface menant B des temp6ratures continentales minimales. Les mo&les de circulation atmosphCrique gkntrale, simulant les rCgimes climatiques, reprksentent de facon incomplbte la physiographie nord-ouest du Canada. Par conskquent, les simulations ne peuvent reproduire les conditions nCcessaires au dCveloppement et B la prCservation du pergklisol.

A middle Pleistocene paleosol sequence from Dawson Range, Central Yukon Territory

“…Burn (1994) presented evidence for progressively increasing continentality in central and southern Yukon during the late Pliocene and Pleistocene. He concluded that widespread permafrost in southern and central Yukon is unique to the Holocene interglaciation.…”

Impacts of mean annual air temperature change on a regional permafrost probability model for the southern Yukon and northern British Columbia, Canada

“…Scenario temperature changes in this paper are indicated in degrees Kelvin (K) in order to avoid confusion with MAATs which are stated in degrees Celsius. A scenario approach was favoured over applying global or regional climate model predictions which suffer from inadequate representation of the topography in the Yukon (see Burn, 1994). Permafrost conditions were also investigated under a cooler MAAT (−1 K) that may be representative of conditions during the Little Ice Age (LIA; Farnell et al, 2004).…”

Modelling climate change effects on the spatial distribution of mountain permafrost at three sites in northwest Canada

“…We investigated a Lewkowicz and Bonnaventure (2008) because values in the PISR field are corrected from those generated before the error in the Solar Analyst software was discovered (see text) range of warming values up to +5 K based on IPCC and ACIA predictions for the upcoming century. We chose this approach rather than using Global or Regional Climate Model predictions because of the problem of adequately representing the topography in the western Cordillera where our sites are located (see Burn 1994).…”