Internal Structure and Environmental Significance of a Perennial Snowbank, Melville Island, N.W.T.

A perennial snowbank located in the continuous permafrost zone was cored to obtain details of its internal structure and history. In spring the snowbank is up to 10 m thick and composed of deep snow accumulated during the previous winter, overlying ice developed by basal ice accretion over many years. The perennial ice exhibits a layered structure with alternating clear and milky bands and contains randomly oriented, variably shaped bubbles. Horizons of aeolian and mudflow deposits occur at irregular intervals and correspond to periods of aggradation and thaw truncation of the snowbank. Tritium concentrations in a core from the deepest portion of the snowbank indicate that the basal 2 m of ice pre-dates 1957. Other layers of ice likely represent precipitation that fell between 1958 and 1962, between 1968 and 1976, and after 1983. Ice developed during the 1963 atmospheric tritium peak is no longer present. Energy balance measurements indicate that potential climatic warming is unlikely to eliminate the perennial portion of the snowbank unless accompanied by substantially less snow drifting at the site.Key words: snowbank ice, tritium, climate changeMots clés: glace de congère, tritium, changement de clima

Salinization of Permafrost Terrain Due to Natural Geomorphic Disturbance, Fosheim Peninsula, Ellesmere Island

Efflorescences (surface salt accumulations) are common on the Fosheim Peninsula and elsewhere in the Canadian Arctic Archipelago, especially at elevations below the Holocene marine limit, and cover up to 9% of the terrain in the vicinity of lower Hot Weather Creek. They are most extensive on naturally disturbed slopes and in floodplain locations. More than 75% of efflorescences are related to geomorphic disturbances (active-layer detachment sliding, retrogressive thaw slumping, and gullying), which initiate the causal chain of (1) surface erosion; (2) local degradation of permafrost; (3) contact between supra-permafrost groundwater and soluble ions previously held within frozen sediments; (4) increase in total dissolved-solids concentrations in slope surface runoff; and (5) depending on the degree of channelization of drainage and the slope profile, transport of dissolved solids directly to the stream system or their redistribution and accumulation downslope. Concentrations of Na+ in surface runoff reached almost 5 g/l during summer 1996 at a recent (1988) detachment slide scar in marine sediments. These concentrations are sufficiently high to negatively affect most terrestrial arctic plant species. Soluble Na+ levels within the active layer suggest that concentrations in slope runoff will remain elevated for several decades. Climatic warming, if it causes an increase in annual thaw depths or in the frequency and extent of geomorphic disturbances, could also result in active layer salinization within areas of salt-rich permafrost, such as in marine surficial deposits.On trouve couramment des efflorescences (accumulations de sel en surface) dans la presqu'île de Fosheim et à d'autres endroits dans l'archipel Arctique canadien, en particulier à des hauteurs situées sous la limite marine de l'holocène. Ces efflorescences couvrent jusqu'à 9 p. cent du terrain aux environs du cours inférieur de Hot Weather Creek. On les trouve en grande quantité sur des pentes ayant subi une perturbation naturelle et dans des zones où sont situées des plaines d'inondation. Plus de 75 p. cent des efflorescences sont reliées à des perturbations géomorphiques (glissement d'un décollement de la couche active, décrochement dû à la fonte régressive et ravinement), qui sont à l'origine de la chaîne causale suivante: 1) érosion de surface; 2) dégradation locale du pergélisol; 3) contact entre la nappe d'eau du suprapergélisol et les ions solubles contenus précédemment dans les sédiments gelés; 4) augmentation de la concentration totale de solides en suspension dans l'eau de ruissellement de surface sur les pentes; et 5), dépendant du degré de canalisation du drainage et du profil de la pente, transport direct des solides en suspension dans l'eau des ruisseaux ou leur redistribution et accumulation plus bas sur la pente. Les concentrations en Na+ dans l'écoulement de surface atteignaient presque 5 g/l durant l'été 1996 sur une niche de décollement récente (1988) dans des sédiments marins. Ces concentrations sont suffisamment élevées pour affecter de façon négative la plupart des espèces végétales terrestre de l'Arctique. Les niveaux de Na+ en suspension au sein de la couche active suggèrent que les concentrations dans l'écoulement de la pente resteront élevées pendant encore plusieurs dizaines d'années. Le réchauffement climatique, s'il est responsable de l'augmentation de la profondeur du dégel annuel ou de la fréquence et de l'étendue des perturbations géomorphiques, pourrait aussi amener une salinisation de la couche active dans des régions où le pergélisol est riche en sel, comme c'est le cas pour les dépôts marins superficiels

Northern Hemisphere permafrost map based on TTOP modelling for 2000-2016 at 1 km²scale

Permafrost is a key element of the cryosphere and an essential climate variable in the Global Climate Observing System. There is no remote-sensing method available to reliably monitor the permafrost thermal state. To estimate permafrost distribution at a hemispheric scale, we employ an equilibrium state model for the temperature at the top of the permafrost (TTOP model) for the 2000–2016 period, driven by remotely-sensed land surface temperatures, down-scaled ERA-Interim climate reanalysis data, tundra wetness classes and landcover map from the ESA Landcover Climate Change Initiative (CCI) project. Subgrid variability of ground temperatures due to snow and landcover variability is represented in the model using subpixel statistics. The results are validated against borehole measurements and reviewed regionally. The accuracy of the modelled mean annual ground temperature (MAGT) at the top of the permafrost is ±2 °C when compared to permafrost borehole data. The modelled permafrost area (MAGT 0) is around 21 × 106 km2 (22% of exposed land area), which is approximately 2 × 106 km2 less than estimated previously. Detailed comparisons at a regional scale show that the model performs well in sparsely vegetated tundra regions and mountains, but is less accurate in densely vegetated boreal spruce and larch forests

Variability and change in the Canadian cryosphere

Abstract During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing systems and retrieval algorithms for satellite measurements facilitated development of a snapshot of current cryospheric conditions, providing a baseline against which future change can be assessed. Key findings include: 1. surface air temperatures across the Canadian Arctic exhibit a warming trend in all seasons over the past 40 years. A consistent pan-cryospheric response to these warming temperatures is evident through the analysis of multi-decadal datasets; 2. in recent years (including the IPY period) a higher rate of change was observed compared to previous decades including warming permafrost, reduction in snow cover extent and duration, reduction in summer sea ice extent, increased mass loss from glaciers, and thinning and break-up of the remaining Canadian ice shelves. These changes illustrate both a reduction in the spatial extent and mass of the cryosphere and an increase in the temporal persistence of melt related parameters. The observed changes in the cryosphere have important implications for human activity including the close ties of northerners to the land, access to northern regions for natural resource development, and the integrity of northern infrastructure

Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands

Permafrost stores globally significant amounts of carbon (C) which may start to decompose and be released to the atmosphere in form of carbon dioxide (CO 2 ) and methane (CH 4 ) as global warming promotes extensive thaw. This permafrost carbon feedback to climate is currently considered to be the most important carbon-cycle feedback missing from climate models. Predicting the magnitude of the feedback requires a better understanding of how differences in environmental conditions post-thaw, particularly hydrological conditions, control the rate at which C is released to the atmosphere. In the sporadic and discontinuous permafrost regions of north-west Canada, we measured the rates and sources of C released from relatively undisturbed ecosystems, and compared these with forests experiencing thaw following wildfire (well-drained, oxic conditions) and collapsing peat plateau sites (water-logged, anoxic conditions). Using radiocarbon analyses, we detected substantial contributions of deep soil layers and/or previously-frozen sources in our well-drained sites. In contrast, no loss of previously-frozen C as CO 2 was detected on average from collapsed peat plateaus regardless of time since thaw and despite the much larger stores of available C that were exposed. Furthermore, greater rates of new peat formation resulted in these soils becoming stronger C sinks and this greater rate of uptake appeared to compensate for a large proportion of the increase in CH 4 emissions from the collapse wetlands. We conclude that in the ecosystems we studied, changes in soil moisture and oxygen availability may be even more important than previously predicted in determining the effect of permafrost thaw on ecosystem C balance and, thus, it is essential to monitor, and simulate accurately, regional changes in surface wetness

Northern Hemisphere permafrost map based on TTOP modelling for 2000–2016 at 1 km2 scale

Permafrost is a key element of the cryosphere and an essential climate variable in the Global Climate Observing System. There is no remote-sensing method available to reliably monitor the permafrost thermal state. To estimate permafrost distribution at a hemispheric scale, we employ an equilibrium state model for the temperature at the top of the permafrost (TTOP model) for the 2000–2016 period, driven by remotely- sensed land surface temperatures, down-scaled ERA-Interim climate reanalysis data, tundra wetness classes and landcover map from the ESA Landcover Climate Change Initiative (CCI) project. Subgrid variability of ground temperatures due to snow and landcover variability is represented in the model using subpixel statistics. The results are validated against borehole measurements and reviewed regionally. The accuracy of the modelled mean annual ground temperature (MAGT) at the top of the permafrost is ±2 °C when compared to permafrost borehole data. The modelled permafrost area (MAGT 0) is around 21 × 106 km2 (22% of exposed land area), which is approximately 2 × 106 km2 less than estimated previously. Detailed comparisons at a regional scale show that the model performs well in sparsely vegetated tundra regions and mountains, but is less accurate in densely vegetated boreal spruce and larch forests

Permafrost is warming at a global scale

Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007-2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged