Showing papers in "Permafrost and Periglacial Processes in 2012"
TL;DR: Wang et al. as discussed by the authors provided an updated map of permafrost in China, including frozen ground area, and some suggestions are proposed for future mapping of permaffrost.
Abstract: Many permafrost maps in China have been compiled since the early 1960s. The scales of these maps range from the local (1:600 000) to the regional scale (1:10 000 000). The permafrost classification systems differ among these maps. The indices for permafrost classification used in these mapping projects include spatial continuity (areal extent) and thickness of the permafrost, air and ground temperatures and ground -ice content. All of those data have been retrieved, digitised and published in the Environmental and Ecological Science Data Center for West China. These maps represent the best understanding at the time regarding the distribution of permafrost in China and its changes over the past century. An updated map of permafrost in China, including frozen ground area, is also provided. The total area of permafrost in China is estimated at ~ 1.59 × 106 km2 (glaciers and lakes excluded), and the area of seasonally frozen ground (excluding instantaneous frozen ground) is ~ 5.36 × 106 km2. The total area of high-altitude (plateau and mountain) permafrost in China is ~ 1.35 × 106 km2, the area of mountain permafrost is ~ 0.30 × 106 km2 and the area of plateau permafrost is ~ 1.05 × 106 km2. The latitudinal permafrost is located in the northern part of northeastern China, and its area is ~ 0.24 × 106 km2. Additionally, some suggestions are proposed for future mapping of permafrost in China. Copyright © 2012 John Wiley & Sons, Ltd.
204 citations
TL;DR: In this article, four retrogressive thaw slumps (RTS) located on Herschel Island and the Yukon coast (King Point) in the western Canadian Arctic were investigated to compare the environmental, sedimentological and geochemical setting and characteristics of zones in active and stabilised slumps and at undisturbed sites.
Abstract: Four retrogressive thaw slumps (RTS) located on Herschel Island and the Yukon coast (King Point) in the western Canadian Arctic were investigated to compare the environmental, sedimentological and geochemical setting and characteristics of zones in active and stabilised slumps and at undisturbed sites. In general, the slope, sedimentology and biogeochemistry of stabilised and undisturbed zones differ, independent of their age or location. Organic carbon contents were lower in slumps than in the surrounding tundra, and the density and compaction of slump sediments were much greater. Radiocarbon dating showed that RTS were likely to have been active around 300 a BP and are undergoing a similar period of increased activity now. This cycle is thought to be controlled more by local geometry, cryostratigraphy and the rate of coastal erosion than by variation in summer temperatures. Copyright © 2012 John Wiley & Sons, Ltd.
93 citations
TL;DR: In this paper, the authors simulated changes in permafrost distribution on the Qinghai-Tibet Plateau (QTP) over the past 50 years (19602009) with a response model that uses data from a digital elevation model, mean annual air temperature (MAAT) and the vertical lapse rate of temperature.
Abstract: Decadal changes in permafrost distribution on the Qinghai-Tibet Plateau (QTP) over the past 50?years (19602009) were simulated with a response model that uses data from a digital elevation model, mean annual air temperature (MAAT) and the vertical lapse rate of temperature. Compared with published maps of permafrost distribution, the accuracy of the simulated results is about 85 per cent. The simulation results show: (1) with the continuously rising MAAT over the past 50?years, the simulated areas of permafrost on the QTP have continuously decreased; (2) through areal statistics, the simulated areas of permafrost were 1.60?x?106?km2, 1.49?x?106?km2, 1.45?x?106?km2, 1.36?x?106?km2 and 1.27?x?106?km2, respectively, in the 1960s, 1970s, 1980s, 1990s and 2000s; and (3) the rate of permafrost loss has accelerated since the 1980s, and the total area of degraded permafrost is about 3.3?x?105?km2, which accounts for about one-fifth of the total area of permafrost in the 1960s. Copyright (c) 2012 John Wiley & Sons, Ltd.
62 citations
TL;DR: In this article, the authors presented a high-resolution (30 x 30'm grid cells) probability model for the southern Yukon and northern British Columbia presented in this paper (regional model) is a combination of seven local empirical-statistical models, each developed from basal temperature of snow measurements in winter and ground-truthing of frozen-ground presence in summer.
Abstract: Permafrost maps are needed for infrastructure planning, climatic change adaptation strategies and northern development but often lack sufficient detail for these purposes. The high-resolution (30 x 30 m grid cells) probability model for the southern Yukon and northern British Columbia presented in this paper (regional model) is a combination of seven local empirical-statistical models, each developed from basal temperature of snow measurements in winter and ground-truthing of frozen-ground presence in summer. The models were blended using a distance-decay power approach to generate a map of permafrost probability over an area of almost 500 000 km2 between 59°N and 65°N. The result is broadly similar to previous permafrost maps with an average permafrost probability of 58 per cent for the region as a whole. There are notable differences in detail, however, because the main predictive variable used in the local models is equivalent elevation, which incorporates the effects of gentle or inverted surface lapse rates in the forest zone. Most of the region shows permafrost distribution patterns that are non-linear, resembling those from continental areas such as Mongolia. Only the southwestern area shows a similar mountain permafrost distribution to that in the European Alps with a well-defined lower limit and a linear increase in probability with elevation. The results of the modelling can be presented on paper using traditional classifications into permafrost zones but given the level of detail, they will be more useful as an interactive online map. Copyright © 2012 John Wiley & Sons, Ltd.
61 citations
TL;DR: In this paper, soil organic carbon (SOC) contents were examined beneath two grassland vegetation communities and cold desert sites in permafrost areas of the central western part of the Qinghai-Tibet Plateau.
Abstract: Soil organic carbon (SOC) contents were examined beneath two grassland vegetation communities and cold desert sites in permafrost areas of the central western part of the Qinghai-Tibet Plateau. Mean SOC stocks in the top 150 cm were 7.73 kg m-2 for Stipa roborowskyi communities and 3.72 kg m-2 for Carex moorcroftii communities, but only 1.84 kg m-2 for cold alpine desert. More than 80 per cent of SOC stocks beneath the grasslands were in the top 100 cm. Correlation analyses showed that SOC stocks in the top 150 cm are linked to soil moisture content, and the vertical distribution of SOC is mainly affected by depth and soil moisture content. Moisture content and vegetation communities are therefore important factors associated with SOC content in this cold, arid area, while active-layer thickness, vegetation cover and topographical factors play non-significant roles in SOC distribution. Copyright © 2012 John Wiley & Sons, Ltd.
57 citations
TL;DR: In this paper, the authors identify research needs in four major areas and at the interfaces between them: rock temperature measurement and modelling; remote sensing of rock walls; process understanding of rock mass instability; and flow propagation models of rock-ice avalanches.
Abstract: Rock instability is believed to be causally linked to permafrost degradation, but it is difficult to demonstrate this directly because of the short record of slope failures in high mountains. While abductive scientific reasoning of ‘increasing permafrost-related instability’ based on the short time frame of recorded rockfall events in high mountains is still difficult, our deductive systemic understanding points toward a strong process linkage between permafrost degradation and rock instability. Enhanced technical understanding of coupled thermo-hydro-mechanical processes and systemic geomorphic understanding of rock slope adjustment in space and over (reaction/relaxation) time are required to accurately predict hazards associated with the impact of climate change on permafrost in bedrock. We identify research needs in four major areas and at the interfaces between them: rock temperature measurement and modelling; remote sensing of rock walls; process understanding of rock mass instability; and flow propagation models of rock-ice avalanches. This short communication identifies key interfaces between research directions to gain a better understanding of trajectories of destabilisation in time and space. We propose coordinated systemic research with respect to scale dependent and transient thermal behaviour, coupled thermo-hydro-mechanical understanding, enhanced remote inventorying of rock wall instability and integrated approaches for a better understanding and modelling of mixed avalanches. Copyright © 2012 John Wiley & Sons, Ltd.
56 citations
TL;DR: In this article, bathymetric data were collected for 28 thermokarst lakes across the Arctic Coastal Plain (ACP) of northern Alaska from areas with distinctly different surficial sediments and topography.
Abstract: Detailed bathymetric data were collected for 28 thermokarst lakes across the Arctic Coastal Plain (ACP) of northern Alaska from areas with distinctly different surficial sediments and topography. Lakes found in the low-relief coastal area have developed in marine silts that are ice-rich in the upper 6–10 m. The lakes tend to be shallow (~ 2 m), of uniform depth and lack prominent littoral shelves. Further inland on the ACP, lakes have formed in relatively ice-poor aeolian sand deposits. In this hilly terrain, average lake depth is less (~ 1 m) despite deeper (3–5 m) central pools. This bathymetry reflects the influence of broad, shallow littoral shelves where sand, eroded from bluffs at the lake margin, is deposited concurrently with deep penetration of the talik beneath the basin centre. Lakes in the ACP-Arctic Foothills transition zone to the south have developed in loess uplands. These yedoma deposits are extremely ice-rich, and residual lakes found inside old lake basins (alases) are generally 2–4 m deep, reflecting continued talik development and ground subsidence following drainage of the original lake. However, where the expanding lake encroaches on the flanks of the upland at actively eroding bluffs, near-shore pools develop that can be 6–9 m deep. It appears that thawing of ice-rich permafrost during lake expansion causes ground subsidence and formation of deep pools above ablating ice wedges. These data suggest that thermokarst lake morphometry largely depends on the characteristics of the substrate beneath the lake and the availability of sediments eroded at the lake margin. Copyright © 2012 John Wiley & Sons, Ltd.
46 citations
TL;DR: In this article, the authors investigated and compared active layer characteristics determined from ground temperature measurements at ten borehole sites in various types of Alpine permafrost terrain, and found that the active layer thickness remained fairly constant at individual boreholes over the past five to 14 years, but was highly variable among the sites due to local terrain characteristics.
Abstract: This study investigates and compares active layer characteristics determined from ground temperature measurements at ten borehole sites in various types of Alpine permafrost terrain. Active layer thickness (ALT) remained fairly constant at the individual boreholes over the past five to 14 years, but was highly variable among the sites due to local terrain characteristics. To allow intra-site comparisons, a characteristic depth within the active layer was determined for each site. The temperature series either measured or interpolated for that depth were used to investigate different thermal stages during the annual thawing and refreezing cycle. The relation between air temperature thawing-degree days and ALT was investigated on an annual, seasonal and daily basis. The results show that at least daily data are required to establish the relevant characteristics of active layer development. Periods of slow advance of the thaw plane, interpreted as being due to the presence of ice-bearing layers within the active layer, are particularly important to the final ALT. Rapid active layer deepening, however, can occur due to the formation of taliks caused by lateral thermal disturbances below the active layer. Copyright © 2012 John Wiley & Sons, Ltd.
40 citations
TL;DR: Using in situ data and information from monitoring of a representative thermokarst lake in the Beiluhe Basin, the authors simulates the rate of talik development beneath the lake, the time taken for an open talik to form, and the time of permafrost lateral thaw after open-talik formation.
Abstract: Thermokarst lakes on the Qinghai-Tibet Plateau cause considerable thermal disturbance to the surrounding permafrost, giving rise to anomalous ground-temperature conditions and open-talik formation below some lakes. Using in situ data and information from monitoring of a representative thermokarst lake in the Beiluhe Basin, this study simulates the rate of talik development beneath the lake, the time taken for an open talik to form, and the rate of permafrost lateral thaw after open-talik formation. The simulation uses a simplified two-dimensional unsteady finite-element model for heat transfer with phase change under a cylindrical coordinate system. The results indicate that a bowl-shaped talik forms under the lake and that the talik thickness increases substantially over time. An open talik forms below the lake 733 years after the lake formed. The average maximum thaw rates at the top and bottom of permafrost beneath the lake before the open talik forms are 5.8 cm year-1 and 0.7 cm year-1, respectively. By 1100 years after lake formation, permafrost beneath the central deep pool and shallow nearshore zone of the lake thaws completely and the heat-source effect caused by the lake becomes very limited. The volume of the open talik beneath the lake still increases gradually with time 1500 years after lake formation, but the increase is very limited. Copyright © 2012 John Wiley & Sons, Ltd.
38 citations
TL;DR: In this article, the authors investigated the role of low-pressure weather systems in the occurrence of large-scale slush and wet-slab avalanches in High Arctic Svalbard.
Abstract: Mid-winter wet avalanche cycles in High Arctic Svalbard occurred during January 2010 and March 2011, allowing studies of slush and wet slab avalanche deposits. Both cycles represented extreme events in magnitude and frequency and were caused by the passage of low-pressure atmospheric systems with positive air temperatures, high wind speeds and 100-year record monthly rainfall. Slush avalanches were confined to river-cut gorges, with low starting-zone inclinations, and deposits consisting of flow lobes and levees. Wet slab avalanches were not confined topographically, started anywhere on open mountain slopes and displayed tongue-shaped debris deposits. During both of the two wet avalanche periods analysed, snowpack conditions favoured the release of slush avalanches, as the snowpack consisted of a coarse-grained middle section above a water-impermeable ice layer. Such snowpack conditions are typical for central Svalbard. The resulting slush and wet slab avalanches were extreme in their size and runout distances, crossing frequently used snowmobile tracks at 20 locations and posing a threat to traffic and infrastructure. Four additional potential large-scale slush avalanche periods were identified from analysis of the meteorological record from Longyearbyen (1912–2011). They cluster in the mid to early 1990s, with comparable meteorological conditions to the January 2010 and March 2011 wet avalanche cycles. It is concluded that the frequency and duration of low-pressure weather systems are the dominant controls on wet snow avalanches, and that mean snow season air temperature (October–May) is of little importance. Copyright © 2011 John Wiley & Sons, Ltd.
34 citations
TL;DR: The physical and chemical characteristics of two High Arctic lakes were investigated at the Cape Bounty Arctic Watershed Observatory on Melville Island, in response to large active-layer detachments generated by extreme summer temperatures in 2007 as mentioned in this paper.
Abstract: The physical and chemical characteristics of two High Arctic lakes were investigated at the Cape Bounty Arctic Watershed Observatory on Melville Island, in response to large active-layer detachments generated by extreme summer temperatures in 2007. In the two years following the permafrost disturbances, there was an elevated loading of total dissolved solids into both lakes, but no concomitant increase in suspended sediment levels. The physical dynamics of one lake were significantly altered by an internal sediment input, which was not directly related to watershed processes. The results indicate that localised permafrost disturbance in the watersheds resulted in changes to chemical conditions in these relatively deep, large lakes, while increased sediment transport from disturbances did not have a sustained impact. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, phase-contrast synchrotron micro-computed tomography (μCT) is used to study the microstructure of frozen soil, and two modes of crack formation are identified: micro-cracks between soil particles and longer, well-developed cracks that follow along ice-soil particle boundaries and span across the ice between particles.
Abstract: Phase-contrast synchrotron micro-computed tomography (μCT) is well suited to studying the microstructure of frozen soil. To take advantage of the high-resolution three-dimensional images that can be generated using μCT, a specialised in-situ rig was designed and commissioned. This miniature temperature-controlled oedometer is capable of controlling soil sample thermal gradients and applying uniaxial deformation while measuring stress. This system was used to apply repeated freeze-thaw cycles to water-saturated samples of Leighton Buzzard sand, Reigate sand and spherical glass ballotini (an idealised soil). High-resolution images were obtained using a monochromatic, parallel beam of x-rays generated on Beamline I12 of the Diamond synchrotron. Cracking in the ice was directly measured utilising the phase-contrast fringes generated by ice-air interfaces. Examination of these images revealed two modes of crack formation in the ice phase of frozen soil: micro-cracks between soil particles, and longer, well-developed cracks that follow along ice-soil particle boundaries and span across the ice between particles. Both crack types were orientated parallel to the freezing front (normal to the heat flow), affecting both the frozen soils' mechanical behaviour, and we hypothesise that these cracks are potential initiation sites for ice lens development. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors explored the spatial variables which affect the surface thermal regime in a valley in a high-altitude catchment of the Andes of Santiago, and used linear mixed-effects models to quantify the effects of site characteristics on mean MGST and ground surface thermal regimes.
Abstract: The spatial variables which affect the surface thermal regime are explored in a valley in a high-altitude catchment of the Andes of Santiago. Two one-year (2009 - 10 and 2010 - 11) ground surface temperature (GST) time series are analysed separately and linear mixed-effects models are used to quantify the effects of site characteristics on mean GST (MGST) and ground surface thermal regimes. The effect of snow cover onset and disappearance dates on MGST is further examined in a sensitivity analysis. Elevation has the strongest effect on MGST (1C/100 m), 30 additional days of snow cover suppress MGST by an estimated 0.1 to 0.6 C and openwork boulder surfaces are cooler by an estimated 0.6 to 0.8 C. The sensitivity analysis corroborates the effect of late snow cover in the linear models, which can overwhelm the spatial differences in radiative effects. A positive MGST found on active rock glaciers would suggest negative thermal offsets probably related to the presence of coarse blocky material at the surface, and which may also be present outside rock glaciers. We suggest that spatial patterns of MGST can serve as a proxy for spatial patterns in the lower limit of permafrost occurrence
TL;DR: In this article, the authors examined the thermal conditions in seven rock glaciers in the Retezat Mountains using ground surface temperature, bottom temperature of snow (BTS) and late-summer water temperature at springs.
Abstract: Thermal conditions in seven rock glaciers (RGs) in the Retezat Mountains were examined using ground surface temperature, the bottom temperature of snow (BTS) and late-summer water temperature at springs. Direct current resistivity profiles were used to detect ice-rich layers and to estimate RG volume. These parameters were supplemented by measurements of RG surface movement and morphological characteristics in order to develop a RG typology. RG activity is suggested based on BTS values and the mean annual surface temperature. The lower altitudinal limits for permafrost occurrence and the activity of RGs were found to be at 2000 m and 2100 m asl, respectively. The two highest and most active RGs are younger than 8 ka and developed following a cold climate event at 8.2 ka when a last isolated glacial episode occurred in their hosting cirques, while the remaining RGs date from 11.5–8.7 ka. Calculated rockwall denudation rates to produce these forms range from 0.8–1.1 mm/yr. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, water temperature profile measurements were made in 12 thermokarst lakes along a 150 km long north-south transect across the Arctic Coastal Plain of northern Alaska.
Abstract: In summer 2010, water temperature profile measurements were made in 12 thermokarst lakes along a 150-km long north–south transect across the Arctic Coastal Plain of northern Alaska. In shallow lakes, gradual warming of the water column to 1–4°C begins at the lake bed during decay of the ice cover in spring. Rapid warming follows ice-off, with water temperature responding synchronously to synoptic weather variations across the area. Regionally, ice-off occurs 2–4 weeks later on lakes near the coast. Inland lakes are warmer (13°C) in mid-summer than those near the coast (7°C), reflecting the regional climate gradient and the maritime effect. All lakes are well mixed and largely isothermal, with some thermal stratification (< 2°C) occurring during calm, sunny periods in deeper lakes. In deep (6–9 m) lake-bed depressions that are likely ice-wedge troughs, water cools by conduction to the colder sediments below, while concurrent warming occurs in the upper water column. A spatially dense sample of near-surface temperature measurements was collected from one lake over a short period and shows warmer (2–3°C) temperatures on the upwind, sheltered end of the lake. This study demonstrates that climatic gradients, meteorological conditions and basin characteristics impact lake temperature dynamics. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, a new database of 12 705 measurements of vertical water content and bulk soil properties from 98 permafrost and non-permafrost cores collected in raised bogs and peat plateaus across the region, together with in-situ measurements of surface moisture and thaw depth, botanical descriptions of dominant surface vegetation species assemblage, and field notes.
Abstract: Russia's West Siberian Lowland (WSL) contains the most extensive peatlands on Earth with many underlain by permafrost. We present a new database of 12 705 measurements of vertical water content and bulk soil properties from 98 permafrost and non-permafrost cores collected in raised bogs and peat plateaus across the region, together with in-situ measurements of surface moisture and thaw depth, botanical descriptions of dominant surface vegetation species assemblage, and field notes. Data analyses reveal significant contrasts (p < 0.01 to p < 0.0001) between permafrost and non-permafrost sites. On average, permafrost WSL peatlands exhibit drier surfaces, shallower depth, lower organic matter content and higher bulk density than do non-permafrost sites. Peat bulk density and ash-free density increase with depth for non-permafrost but not for permafrost sites. Gravimetric water content averages 92.0% near the surface and 89.3% at depth in non-permafrost, but 81.6% and 85.4%, respectively, in permafrost, suggesting that the disappearance of permafrost could produce moister surfaces across the WSL. GIS extrapolation of these results suggests that WSL peatlands may contain ~1200 km3 of water and ice, a large storage equivalent to ~2-m average liquid water depth and approximately three times the total annual flow in the Ob' River. A global estimate of ~6900-km3 subsurface water storage for all northern peatlands suggests a volume comparable to or greater than the total water storage in northern lakes. The database is freely available as supplementary material for scientific use at http://onlinelibrary.wiley.com/doi/10.1002/ppp.735/suppinfo. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, the role of thermal contraction-crack polygons (sublimation polygons) in modulating sublimation of buried glacier ice in Antarctica is assessed.
Abstract: To assess the role of thermal contraction-crack polygons (sublimation polygons) in modulating sublimation of buried glacier ice in Antarctica, we applied a 2D numerical model using COMSOL Multiphysics that calculates the rate and spatial variability of vapour diffusion through porous media. Specifically, we examined vapour transport through Granite drift, a dry supraglacial till marked with thermal contraction-crack polygons that rests on glacier ice reportedly ≥8-million years in age. The model results show that sublimation varies with drift texture and surface topography. Initially, the rates are highest beneath relatively coarse-grained sand-wedge deposits at polygon margins, creating deep, surface troughs. As troughs approach ~1-m depth, the cooler atmospheric and soil temperatures that arise from solar shielding reduce the rates of ice sublimation to levels below that at polygon centres, preventing runaway ice loss at polygon margins. Including the effects of a salt-cemented horizon at 10 − 15-cm depth (porosity 20%) and a rocky surface pavement (75% ground coverage), our modelled ice loss at polygon centres, for example, is 0.022 mm a−1, an order of magnitude lower than previous estimates (0.14 mm a−1). This finding highlights the importance of including field-based data for drift texture, topography and microclimate variation in modelling ice sublimation. The results also suggest that stable conditions (no ice loss) at polygon centres are possible with either a 1.9°C decrease in mean annual atmospheric temperature or a 12 per cent increase in mean annual relative humidity. These results indicate that the preservation of buried, multi-million-year-old ice is plausible in the coldest and driest regions of Antarctica. Copyright © 2011 John Wiley & Sons, Ltd.
TL;DR: In this paper, a conceptual model for epikarst morphogenesis for the chalk karst of Lublin Upland is proposed, involving three stages, in the absence of permafrost, precipitation water infiltrates unconsolidated glaciogenic deposits.
Abstract: Pocket forms several decimetres in diameter, 0.5–1.5 m deep and infilled mainly with glaciogenic sands, silts and clays of Saalian age are commonly developed on the top of the karstified chalk massif of the Lublin Upland, eastern Poland. Analysis of lithofacies, particle-size distribution and micromorphology of three pocket infills in the Chelm chalk quarry reveals a prominent clay cortex between the host chalk and the glaciogenic infill and suggests that periglacial processes have played a considerable role in the formation of the pockets and in the redistribution of their primary glaciogenic infill. A conceptual model for epikarst morphogenesis for the chalk karst of Lublin Upland is proposed, involving three stages. Stage I: In the absence of permafrost, precipitation water infiltrates unconsolidated glaciogenic deposits. Stage II: Periglacial transformation with underlying permafrost. Primary cryoturbation structures became protokarst forms, and then epikarst forms. Stage III: Degradation of the permafrost, with increased carbonate dissolution and development of a clay karst cortex. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors describe one such mound, identified as a lithalsa, which had been eroded so as to expose almost its entire vertical cross-section, revealing its internal structure.
Abstract: Perennial frost mounds are present near the edges of ponds located on the terrace between the mountain flank and a valley-bottom lake in the Akkol valley of the Russian Altai Mountains. These mounds are 10–50 m in diameter and 3–6 m in height. We describe one mound, identified as a lithalsa, which had been eroded so as to expose almost its entire vertical cross-section, revealing its internal structure. The frozen core consisted mainly of soil segments suspended in reticulate ice lenses with a mean thickness of 11–48 mm and a maximum thickness of about 160 mm. The shapes of the soil segments matched their neighbours. Other features included soil segments suspended in the ice veins shaped like ‘En echelon gash veins’, and the presence of a radial structure of ice-rich and sediment-rich frozen bands. These features all suggest the greater importance of a differential stress field during heaving of the mound and after ice segregation, compared to the thermal gradient and water supply. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: Spatial point pattern analysis (SPPA) as discussed by the authors has been used to quantify overall network geometries based on the randomness or regularity exhibited by the spatial arrangement of polygon-bounding trough intersections.
Abstract: Polygon networks are usually described qualitatively as becoming more regular through time, but such a concept has yet to be demonstrated numerically. The aim of this study is to address this question quantitatively in order to determine if polygonal terrain networks actually become more regular as they develop. Spatial point pattern analysis (SPPA), which can quantify overall network geometries based on the randomness or regularity exhibited by the spatial arrangement of polygon-bounding trough intersections, was used at three ice-wedge polygon sites in the Canadian High Arctic. SPPA was applied in two ways: (i) on the present-day networks observed in the field; and (ii) on historical arrangements derived by distinguishing primary from secondary troughs. In all cases, the polygonal networks had undergone a statistically significant regularisation over the course of their development. Although the method was applied only to terrestrial ice-wedge polygons, such an approach may also be useful for interpreting the evolution of Antarctic sublimation polygons and geometrically similar polygonal networks on Mars. Copyright © 2012 John Wiley & Sons, Ltd. and Her Majesty the Queen in Right of Canada.
TL;DR: In this paper, a 15 km section of the Fishing Branch River, Yukon causing open water during winter and numerous discrete springs near Bear Cave Mountain, was analyzed using three groundwater chemistry groups and variability in surface water chemistry.
Abstract: Perennially flowing groundwater discharges along a 15-km section of the Fishing Branch River, Yukon causing open water during winter and numerous discrete springs near Bear Cave Mountain. Groundwater flow occurs in karstified marine carbonate rocks as well as in alluvial river talik(s). The PCO2 and δ13C indicate groundwater dissolves CO2 during recharge in organic soils and weathers limestone in the aquifer. These analyses show three groundwater chemistry groups and variability in surface water chemistry. The variations in water chemistry are related to differences in the rocks exposed in the recharge area. The δ18O and δ2H results show that groundwater represents approximately the annual average of precipitation based on samples collected in the region. Noble gases were used to determine that the recharge temperature lies between 0 and 5 °C which suggests that recharge happens during the summer. Groundwater ages, calculated using 3H-3He dating, were found to be between 0 and 17.7 years. River discharge was measured during spring and summer under different water-level conditions. Winter baseflow was calculated based on summer discharge measurements and the width of the river channel in winter. Although river flow decreases in winter, groundwater discharge maintains open water. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors demonstrate the ability of light detection and ranging (LiDAR) to map wet terrain within an area of discontinuous permafrost adjacent to the Northwest Territories Highway 3, located west of Yellowknife, Canada.
Abstract: Surface hydrology is an important aspect of northern environments on account of the thermal influence of water on permafrost. In this study, we demonstrate the ability of light detection and ranging (LiDAR) to map wet terrain within an area of discontinuous permafrost adjacent to the Northwest Territories Highway 3, located west of Yellowknife, Canada. Wet terrain was identified from LiDAR intensity measurements beneath forest canopies and across vegetated surfaces, including peatlands, fens, flooded black spruce and birch forests, and terrain adjacent to the highway embankment. Surface water pathways representing hydrological connections between water bodies and wet terrain were also identified at locations otherwise indiscernible from optical imagery. Statistical separability between terrain types, and thus the ability to map them, was improved by integrating LiDAR all-return and bare-earth intensity with colour orthophotos. The average classification accuracy for wet terrain was 93 per cent. These results indicate that LiDAR intensity can be used for local-scale mapping of wet terrain, as required by northern engineers and scientists. Future integration of LiDAR intensity and elevation measurements may be used to assess changes in surface hydrological conditions impacting permafrost. Copyright © Her Majesty the Queen in Right of Canada 2012.
TL;DR: In this article, the excess ice content of near-surface permafrost near Barrow, Alaska was estimated using cores collected from 57 drained thermokarst-lake basins and additional cores from a nearby landform unaffected by thaw-lake processes.
Abstract: The excess ice content of near-surface permafrost near Barrow, Alaska, was estimated using cores collected from 57 drained thermokarst-lake basins and additional cores from a nearby landform unaffected by thaw-lake processes. The excess ice content, estimated using soil cryostructures, increased with surface age: from 20 per cent in young basins < 50 years in age to 40 per cent in ancient basins that drained 2000–5500 years ago. The frequency of ice wedges encountered during coring increased from 0 per cent in young basins to 50 per cent in ancient basins. These results indicate that the volume of ground ice increases rapidly immediately following lake drainage, as permafrost aggrades into unfrozen basin sediments. Ice enrichment continues over time by incorporating meteoric water as ice veins and lenses, and expanding networks of ice wedges. To test the efficacy of visually estimating excess ice content, the ice content was measured on a subsample of cores; measured volumetric values were strongly correlated (r2 = 0.72; p < 0.001) to the estimated excess ice content. The results of this study have important implications for estimating soil organic carbon content of soils with abundant excess ice, and for evaluating the susceptibility of these soils to thermokarst. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, the relative contributions of thaw consolidation and slope-parallel seepage to the generation of overall porewater pressure and resultant potential changes in slope stability are determined in two case studies of thaweding soils.
Abstract: The relative contributions of thaw consolidation and slope-parallel seepage to the generation of overall porewater pressure and resultant potential changes in slope stability are determined in two case studies of thawing soils. The first study concerns experimental slopes of frozen silt inclined at 12° and 24° that thawed during scaled centrifuge modelling reported by Harris et al. (2008). The second study concerns a natural slope near Pontresina, eastern Swiss Alps, of coarse-grained talus inclined at 37° and overlying fine-grained soil that contains the permafrost table. In both cases, seepage parallel to the slope was found to contribute much more to the excess porewater pressures in the thawing soils than did thaw consolidation. This suggests that the effects of thaw consolidation on the stability of alpine talus slopes in mountain permafrost may have only minor significance. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, an experiment in a climate chamber at the University of Western Ontario was designed to freeze and thaw four peat cores 60 cm in diameter and evaluated their ability to maintain one-dimensional change in soil moisture and temperature profiles.
Abstract: Large climate chambers are suitable to simulate, at or close to field scale, the annual freezing and thawing of layered peat in subarctic active layers above permafrost. An experiment in a climate chamber at the University of Western Ontario was designed to freeze and thaw four peat cores 60 cm in diameter. This paper describes the climate chamber and experimental setup, and evaluates their ability to maintain one-dimensional change in soil moisture and temperature profiles. Preliminary results on soil water content (liquid and total) indicate that active-layer freezing resulted in an upward movement of water towards a freezing front that propagated downward. The physical simulations will contribute towards improving conceptual and mathematical hydrological models for permafrost regions. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, it was shown that hummocks are composed of frost-susceptible silty soil (modal grain size 10−100 µm) with occasional clasts and exhibit no evidence for cryoturbation or diapirism.
Abstract: Extensive fields of vegetated, dome-shaped earth hummocks 5–35 cm high and typically 80–200 cm in diameter occur on slopes of up to 15° at elevations of 320–440 m asl on Dartmoor, SW England, but are limited to terrain underlain by metasedimentary rocks and dolerite, and absent from granite areas. Hummocks occur within archaeological sites, implying formation within the last ~ 3000 years and ruling out development over permafrost. The hummocks are composed of frost-susceptible silty soil (modal grain size 10–100 µm) with occasional clasts, but exhibit no evidence for cryoturbation or diapirism. Hummock size and spacing are fairly consistent at particular sites but vary between sites. Hummock age, distribution and characteristics are incompatible with non-frost action origins and most proposed frost action origins (cryostatic pressure, soil circulation, permafrost aggradation, soil injection), but regular spacing and granulometry favour initiation by differential frost heave under conditions of periodic shallow (0.2–0.4 m) seasonal ground freezing. We suggest that hummock growth may reflect migration of silt in advance of inclined freezing planes until equilibrium is achieved with soil loss down hummock sides. Our results confirm that hummock formation by frost action occurs on silty soils in humid cool temperate climates with only limited seasonal frost penetration. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors used a regional-scale atmospheric model to downscale global climate model output, and then stepwise multiple regression to develop an equation that provides a best-fit prediction of site-specific observational data using bilinearly interpolated output from the atmospheric model.
Abstract: Assessing possible permafrost degradation related to engineering projects, climate change and land use change is of critical importance for protecting the environment and in developing sustainable designs for vital infrastructure in cold regions. A major challenge in modelling the future degradation of permafrost is finding ways to constrain changes in the upper thermal boundary condition over time and space at appropriate scales. Here, we report on an approach designed to predict time series of air, ground surface and shallow ground temperatures at a spatial scale on the order of 102 m2 for engineering design of a railway or highway project. The approach uses a regional-scale atmospheric model to downscale global climate model output, and then stepwise multiple regression to develop an equation that provides a best-fit prediction of site-specific observational data using bilinearly interpolated output from the atmospheric model. This approach bridges the scale difference between atmospheric climate models and permafrost thermal models, and allows for a wider range of factors to be used in predicting the thermal boundary condition. For a research site located in Beiluhe, China, close to the Qinghai-Tibet Railway, a comparison of model predictions with observational data not used in the construction of the model shows that this method can be used with a high degree of accuracy to determine the upper boundary condition for a permafrost thermal model. Once a model is constructed, it can be used to predict future changes in boundary condition parameters under different greenhouse emission scenarios for climate change. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors examined how soil nitrogen transformations differ between PGFs and the surrounding inter-PGF tundra along an arctic latitudinal gradient, showing that spatial heterogeneity at several scales can influence soil nitrogen dynamics, and therefore an important influence on arctic ecosystem function.
Abstract: Small patterned-ground features (PGFs) in the Arctic have unique soil properties that vary with latitude and may greatly affect tundra biogeochemistry. Because nitrogen availability can strongly limit arctic vegetation growth, we examined how soil nitrogen transformations differ between PGFs and the surrounding inter-PGF tundra along an arctic latitudinal gradient. We collected soils at eight sites from the Alaskan Low Arctic to the Canadian High Arctic. The soils were incubated for 21days at 9 C and 15 C and analysed for changes in total inorganic nitrogen, nitrate and extractable organic nitrogen (EON). We found greater nitrogen immobilisation in the surrounding inter-PGF soils than in the PGF soils. Along the latitudinal gradient, differences in net nitrogen mineralisation and EON cycling between PGF and inter-PGF soils were strongly influenced by the presence of a pH boundary within the Low Arctic and the transition between the High and Low Arctic, with greater immobilisation in the nonacidic and Low Arctic sites, respectively. Incubation temperature affected EON flux but did not affect net nitrogen mineralisation or nitrification. These results show that spatial heterogeneity at several scales can influence soil nitrogen dynamics, and is therefore an important influence on arctic ecosystem function. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this paper, a series of systematic shear tests were performed using an inclinable shear box containing a coarse-grained active layer overlying a finegrained permafrost layer, a stratigraphy observed in the field.
Abstract: A series of systematic shear tests were performed using an inclinable shear box containing a coarse-grained active layer overlying a fine-grained permafrost layer, a stratigraphy observed in the field. The angle of mobilised interface friction Φmob was determined as depending on the grain size of the active layer and the permafrost, the water content of the active layer and the ice content of the permafrost. Φmob was found to be 8° lower for ice-free permafrost compared to permafrost containing ice. This result implies a possible long-term decrease of active-layer slope stability on scree slopes in Alpine permafrost terrain under warming conditions. Copyright © 2012 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors measured the thermal characteristics of an apparently static cave, with limited connections to the external environment other than through the cave entrance, for three years, and found that the cave demonstrated the thermal properties of a static cold trap.
Abstract: Air temperatures internal and external to a talus cave (‘ice mine’) in central Pennsylvania were measured hourly for three years. Despite its location near the base of a talus slope, the cave demonstrated the thermal characteristics of an apparently static cave, with limited connections to the external environment other than through the cave entrance. Congelation ice that lasted until late spring formed as drip or flowstone and ponded ice from the limited influx of infiltrating water during late winter/early spring. A closed period of thermal stratification and slow warming of cave air was followed by an open period in winter months during which the cave was cooled by the influx of cold dry air. Unlike the occasionally strong and localised cooling induced by the flow of cold air from vents at the base of talus slopes, static cold traps retain their cold air and have little apparent effect on surrounding biota, instead providing potential refugia for organisms that prefer colder temperatures. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.