Changes in mass, extent, duration, and physical properties of snow are key elements for studying associated climate change feedbacks in northern regions. In this study, we analyzed snowpack physical properties along a 'mega' transect from 47°N to 83°N (4,000 km) in northeastern Canada, which includes marked transitions between ecozones from boreal forest to subarctic and arctic ecosystems. Our unique dataset of 391 detailed snowpits acquired over the last 20 years, complemented with snow data from weather stations, shows that snowpack properties such as snow water equivalent, snow depth, density, grain size and basal depth hoar fraction (DHF) are strongly linked to vegetation type. Based on these results, we propose an updated classification of snow types in three classes: boreal forest snow (47-58°N), tundra snow (58-74°N) and polar desert snow (74-83°N), which is more appropriate to the study area than the general north hemisphere classification commonly used. We also show that shrub presence along the transect contributes to a significant increase in DHF development which contributes most strongly to the thermal insulation properties of the snowpack. Overall, our analysis suggests that snow-vegetation interactions have a positive feedback effect on warming at northern latitudes. RÉSUMÉLes changements dans la masse, l'étendue, la durée et les propriétés physiques du manteau neigeux sont des éléments clés pour l'étude des rétroactions du changement climatique dans les environnements nordiques. Dans cette étude, nous avons analysé les propriétés physiques du couvert nival le long d'un « méga » transect de 47°N à 83°N (4000 km) dans le nord-est du Canada, comprenant des transitions marquées entre l'écozone de la forêt boréale et les écosystèmes subarctiques et arctiques. Notre ensemble de données uniques de 391 puits de neige détaillés, acquis au cours des 20 dernières années, enrichi de données de neige provenant de stations météorologiques, montre que les propriétés du manteau neigeux telles que l'équivalent
The geothermal record for 1977-2014 from a 29 m deep borehole in permafrost on Mont Jacques-Cartier, in southeastern Canada, shows substantial decadal fluctuations and an overall warming trend. An extremely thin winter snow cover on the wind-blown summit favours the presence of permafrost. As a consequence, the instability of the thermal regime was found to be a direct response to air temperature variations modelled from data produced by the National Center for Environmental Prediction and National Center for Atmospheric Research. At a depth of 14 m, an increase of 0.4°C from 1979 to 1984 was followed by a decrease of 0.7°C over the next decade, and then by a marked, but irregular increase of 1°C up to 2013. Since 2008, diurnal data, refined by a one-dimensional, transient heat transfer model, indicate an active layer averaging 8.6 m in depth, but whose thickness is sensitive to fluctuations in annual mean ground surface temperatures. For a permafrost body already close to the thawing point, the continuation of the overall warming trend of the last 37 years would lead to its rapid degradation, and the permafrost would then become relict, thinning progressively both from the base and the surface.
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