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Arctic lakes, through their ice cover phenology, are a key indicator of climatic changes that the high-latitude environment is experiencing. In the case of lakes in the Canadian Arctic Archipelago (CAA), many of which are ice covered more than 10 months per year, warmer temperatures could result in ice regime shifts. Within the dominant polardesert environment, small local warmer areas have been identified. These relatively small regions - polar oases - with longer growing seasons and greater biological productivity and diversity are secluded from the surrounding barren polar desert. The ice regimes of 11 lakes located in both polardesert and polar-oasis environments, with surface areas between 4 and 542 km², many of unknown bathymetry, were documented. In order to investigate the response of ice cover of lakes in the CAA to climate conditions during recent years, a 15-year time series (1997-2011) of RADARSAT- 1/2 ScanSAR Wide Swath, ASAR Wide Swath, and Landsat acquisitions were analyzed. Results show that melt onset occurred earlier for all observed lakes. With the exception of Lower Murray Lake, all lakes experienced earlier summer ice minimum and water-clear-of-ice (WCI) dates, with greater changes being observed for polar-oasis lakes (9-24 days earlier WCI dates for lakes located in polar oases and 2-20 days earlier WCI dates for polar-desert lakes). Additionally, results suggest that some lakes may be transitioning from a perennial/multiyear to a seasonal ice regime, with only a few lakes maintaining a multiyear ice cover on occasional years. Aside Lake Hazen and Murray Lakes, which preserved their ice cover during the summer of 2009, no residual ice was observed on any of the other lakes from 2007 to 2011. [ABSTRACT FROM AUTHOR]

In August 1978, a large tundra lake was drained to study the aggradation of permafrost into newly exposed lake-bottom sediments. Ice-wedge growth, which started in the first winter following drainage, had ceased in most of the lake bottom within about twelve years. The gradual cessation of thermal contraction cracking can be attributed to rapid vegetation growth, snow entrapment, an increase in winter ground temperatures, and a decrease in the linear coefficient of thermal contraction associated with freeze–thaw consolidation of the initially saturated lake-bottom sediments. The tilt and separation of markers in the active layer revealed gradual convergence towards the troughs even after ice-wedge growth had ceased. For the first few years the ice-wedge growth rate was up to 3 cm/a as determined by excavation, drilling, separation of the bottoms of benchmarks installed into permafrost, and divergence of free-floating inductance coils placed on the sides of ice wedges well below the bottom of the active layer. The vertical extent of most ice wedges was probably about 2 m, as deduced from the depths of ice-wedge cracks and the geometries of the wedge tops. Many thermal contraction cracks propagated upward to the ground surface from the tops of the ice wedges rather than downward from the ground surface. Small, upward facing, horizontal steps and vertical slickensided surfaces in permafrost on both sides of an excavated ice wedge near its top indicated that the adjacent permafrost had moved upward, relative to the wedge, from thermal expansion during the warming period.En août 1978, un grand lac de toundra a été drainé afin d'étudier l'extension du pergélisol dans des sédiments de fond de lac nouvellement exposés. La croissance des coins de glace, qui a débuté le premier hiver suivant le drainage, avait cessé dans presque tout le fond du lac après une douzaine d'années. La cessation graduelle de la fissuration par contraction thermique peut être attribuée à la croissance rapide de la végétation, la retenue de la neige, une augmentation de la température du sol en hiver et une décroissance du coefficient linéaire de contraction thermique associée à la consolidation par le gel–dégel des sédiments de fond de lac, initialement saturés. Le basculement et la séparation des marqueurs dans la couche active révèlent une convergence graduelle vers les fosses même après l'arrêt de croissance des coins de glace. Pour les quelques premières années, le taux de croissance des coins de glace était de 3 cm/a tel que déterminé par excavation, forage, séparation des fonds des repères installés dans le pergélisol et la divergence des bobines d'induction flottantes placées sur les côtés des coins de glace bien en dessous du fond de la couche active. L'étendue verticale de la plupart des coins de glace était probablement d'environ 2 m, tel que déduit à partir des profondeurs des fentes de glace et de la géométrie du haut des coins. Plusieurs fissures de contraction thermique se sont propagées vers le haut à la surface du sol, à partir du sommet des coins de glace, plutôt que vers le bas, à partir de la surface du sol. De petites marches horizontales à face vers le haut et des surfaces verticales de friction dans le pergélisol des deux côtés d'un coin de glace excavé à proximité de son sommet indiquent que, par rapport au coin, le pergélisol adjacent s'était déplacé vers le haut en raison de l'expansion thermique durant la période de réchauffement.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]