The overall spatial and temporal influence of shrub expansion on permafrost is largely unknown due to uncertainty in estimating the magnitude of many counteracting processes. For example, shrubs shade the ground during the snow-free season, which can reduce active layer thickness. At the same time, shrubs advance the timing of snowmelt when they protrude through the snow surface, thereby exposing the active layer to thawing earlier in spring. Here, we compare 3056 in situ frost table depth measurements split between mineral earth hummocks and organic inter-hummock zones across four dominant shrub–tundra vegetation types. Snow-free date, snow depth, hummock development, topography, and vegetation cover were compared to frost table depth measurements using a structural equation modeling approach that quantifies the direct and combined interacting influence of these variables. Areas of birch shrubs became snow free earlier regardless of snow depth or hillslope aspect because they protruded through the snow surface, leading to deeper hummock frost table depths. Projected increases in shrub height and extent combined with projected decreases in snowfall would lead to increased shrub protrusion across the Arctic, potentially deepening the active layer in areas where shrub protrusion advances the snow-free date.

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The Arctic is changing rapidly, leading to changes in habitat availability and increased anthropogenic disturbance. Information on the distribution of animals is needed as these changes occur. We examine seasonal presence of marine mammals in the western Canadian Arctic near Sachs Harbour, Northwest Territories, using passive acoustic monitoring between 2015 and 2016. We also examined the influence of environmental variables (ice concentration and distance, wind speed) on the presence of these species. Both bowhead whales (Balaena mysticetus) and beluga whales (Delphinapterus leucas) arrived in late April, and belugas departed in mid-August, while bowheads departed in late October. Bearded seal (Erignathus barbatus) vocalizations began in October, peaked from April through June, and stopped in early July. Ringed seals (Pusa hispida) vocalized occasionally in all months, but were generally quiet. Whales migrated in as the ice broke up and migrated out before ice formed in the autumn. Bearded seals started vocalizing as ice formed and stopped once ice was almost gone. Given the importance of sea ice to the timing of migration of whales and vocalization by bearded seals, the trends that we present here may change in the future due to the increasing ice-free season caused by climate change. Our study therefore serves as a baseline with which to monitor future change.Key words: climate change, conservation, passive acoustic monitoring, sea ice.Résumé : L'Arctique change rapidement, menant à des changements dans la disponibilité des habitats et l'augmentation des perturbations anthropiques. Les informations sur la répartition des animaux sont nécessaires à mesure que ces changements surviennent. Nous examinons la présence saisonnière de mammifères marins dans l'ouest de l'Arctique canadien près du havre Sachs, dans les Territoires du Nord-Ouest, en faisant de la surveillance acoustique passive entre 2015 et 2016. Nous avons aussi examiné les effets des variables environnementales (la concentration et la distance de la glace, la vitesse des vents) sur la présence de ces espèces. Tant les baleines boréales (Balaena mysticetus) que les bélugas (Delphinapterus leucas) sont arrivés à la fin avril et les bélugas sont repartis à la miaoût, tandis que les baleines boréales sont reparties à la fin octobre. Les vocalisations de phoques barbus (Erignathus barbatus) ont commencé en octobre, ont atteint un niveau maximal d'avril à juin et se sont arrêtées début juillet. Bien qu'ils aient été généralement silencieux, les phoques annelés (Pusa hispida) ont vocalisé de temps à autre au cours de tous les mois. Les baleines ont migré dans la région lorsque la glace s'est dispersée et ont migré hors

Ocean ambient noise is a crucial habitat feature for marine animals because it represents the lower threshold of their acoustically active space. Ambient noise is affected by noise from both natural sources, like wind and ice, and anthropogenic sources, such as shipping and seismic surveys. During the ice-covered season, ambient conditions in the Arctic are quieter than those in other regions because sea ice has a dampening effect. Arctic warming induced by climate change can raise noise levels by reducing sea ice coverage and increasing human activity, and these changes may negatively affect several species of marine mammals and other acoustically sensitive marine fauna. We document ambient noise off the west coast of Banks Island near Sachs Harbour, Northwest Territories, to provide baseline noise levels for the eastern Beaufort Sea. Noise levels were comparable to those found in other studies of the Canadian Arctic and Alaska and were typically much lower than levels reported farther south. Stronger wind increased noise, whereas greater ice concentration decreased it, dampening the effect of wind speed. Future work should expand monitoring to other locations in the Arctic, model the impact of increased human activities on ambient noise levels, and predict the impact of these changing levels on marine animals.

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Abstract. Envisat ASAR WS images, verified against mass balance, ice core, ground-penetrating radar and air temperature measurements, are used to map changes in the distribution of glacier facies zones across Devon Ice Cap between 2004 and 2011. Glacier ice, saturation/percolation and pseudo dry snow zones are readily distinguishable in the satellite imagery, and the superimposed ice zone can be mapped after comparison with ground measurements. Over the study period there has been a clear upglacier migration of glacier facies, resulting in regions close to the firn line switching from being part of the accumulation area with high backscatter to being part of the ablation area with relatively low backscatter. This has coincided with a rapid increase in positive degree days near the ice cap summit, and an increase in the glacier ice zone from 71 % of the ice cap in 2005 to 92 % of the ice cap in 2011. This has significant implications for the area of the ice cap subject to meltwater runoff.