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Active-layer and permafrost temperature data collected in the Mackenzie Delta, at Canadian Forces Station Alert and Baker Lake have been analyzed along with climatic data to determine the response of the active layer and the ground thermal regime to the anomalous warming associated with strong El Nino conditions of 1998. In the Mackenzie Delta region, early warming in 1998 resulted in earlier thaw of the active layer, warmer summer ground temperatures, and a longer thaw season which produced greater thaw penetration compared to previous years in the 1990s. At Baker Lake, warming was less pronounced and occurred later in the summer resulting in a slight extension of the thaw season into the fall. Warming was less extreme in the high Arctic but snow depths were greater at CFS Alert in 1998 and this appears to have resulted in higher shallow ground temperatures during the winter (February to April) of 1998. 2001-E5 S.L. Smith et al. 1 CURRENT RESEARCH RECHERCHES EN COURS 2001 Article Article Titles Titres Purchase Information Information pour acheter

IcewedgesonnorthernRichardsIsland,NorthwestTerritories,andalongtheYukonTerritorycoastlands,haverespondedtoincreasedthawdepths.Observationsmadein1999arecomparedtothoselastmadeintheseareasin1975and1984,respectively.Climatedataindicatethatairtemperaturesintheseareashavebeenwarmerthanaveragesince1978andthatwarmingin1998wasanextremeevent.Increasedthawinresponsetothiswarminghascausedadecreaseinthenumberofsecondaryandtertiaryicewedges,andisattributed to thaw truncation. Depths to the tops of ice wedges on Richards Island have increased, whereasdepths have decreased on the Yukon Territory coastlands due to thaw consolidation. Thaw-tube observa-tions indicate that 1998 thaw depths were the greatest since 1991 across the northern Mackenzie Deltaregion, with increases of as much as 21 cm.1 Resume : Lesfentesdeglacedanslenorddel’ileRichards(TerritoiresduNord-Ouest)etlelongdester-rains cotiers du Territoire du Yukon, ont reagi a l’accroissement de la profondeur de degel. On compare lesobservations faites en 1999 avec celles faites dans les memes regions en 1975 et en 1984, respectivement.Lesdonneesclimatiquesindiquentquedepuis1978,latemperaturedel’airdanscesregionsaetepluseleveeque la moyenne et qu’en 1998, le rechauffement a ete un evenement extreme. Suite a ce rechauffement, undegel plus profond a cause une diminution du nombre de fentes de glace secondaires et tertiaires et estattribuablealatroncatureparledegel.Laprofondeurjusqu’ausommetdesfentesdeglaceaaugmentedansl’ileRichardsalorsqu’elleadiminuelelongdesterrainscotiersduTerritoireduYukonenraisondelacon-solidation due au degel. Les observations dans les tubes de degel ont indique qu’en 1998, la profondeur depenetrationdudegelaetelaplusgrandedepuis1991danslenorddudeltaduMackenzie,avecdesaugmen-tations allant jusqu’a 21 cm.