Showing papers in "Permafrost and Periglacial Processes in 2011"

On the δ18O, δD and D-excess relations in meteoric precipitation and during equilibrium freezing: theoretical approach and field examples

Abstract: Analysis of the δD and δ18O composition of ice is commonly used to provide insight into the origin of ice bodies. However, studies have questioned the use of the co-isotope relationship to differentiate ground ice types. This study reviews the principles of fractionations affecting δD, δ18O and deuterium excess (d) in meteoric precipitation and during equilibrium freezing of water under changing freezing rates. Traditionally, regression slope values (SD-18O) between δD and δ18O of less than 6 have been used to suggest that ground ice was formed by freezing of liquid water but here it is shown that SD-18O values of less than 7.3 can be suggestive of freezing under equilibrium conditions. This maximum freezing SD-18O value falls within the range of many local meteoric water lines at sites in the Arctic, which can complicate proper identification of subsurface ice types. Many studies are starting to use the calculation of d to infer the origin of subsurface ice. However, d values do not provide much information on the origin of subsurface ice, as d is dependent on freezing conditions. To make proper use of d, its relation with D needs to be investigated, with no relation reflecting meteoric precipitation and a negative relation indicative of freezing. In all cases, it is recommended that stable O-H isotope measurements be supported by additional distinguishing tools (i.e. entrapped gases) when attempting to infer subsurface ice types. Copyright © 2011 John Wiley & Sons, Ltd.

Degrading Mountain Permafrost in Southern Norway: Spatial and Temporal Variability of Mean Ground Temperatures, 1999–2009

Abstract: A ten-year record (1999–2009) of annual mean ground surface temperatures (MGSTs) and mean ground temperatures (MGTs) was analysed for 16 monitoring sites in Jotunheimen and on Dovrefjell, southern Norway. Warming has occurred at sites with cold permafrost, marginal permafrost and deep seasonal frost. Ongoing permafrost degradation is suggested both by direct temperature monitoring and indirect geophysical surveys. An increase in MGT at 6.6–9.0-m depth was observed for most sites, ranging from ~0.015 to ~ 0.095°C a-1. The greatest rate of temperature increase was for sites having MGTs slightly above 0°C. The lowest rate of increase was for marginal permafrost sites that are affected by latent heat exchange close to 0°C. Increased snow depths and an increase in winter air temperatures appear to be the most important factors controlling warming observed over the ten-year period. Geophysical surveys performed in 1999 to delineate the altitudinal limit of mountain permafrost were repeated in 2009 and 2010 and indicated the degradation of some permafrost over the intervening decade. Copyright © 2011 John Wiley & Sons, Ltd.

Characteristics of Discontinuous Permafrost based on Ground Temperature Measurements and Electrical Resistivity Tomography, Southern Yukon, Canada

Abstract: Warm permafrost conditions (mean temperatures of −3°C to −0.1°C) were investigated in detail at 13 valley and mountain sites in the sporadic (10–50%) and extensive (50–90%) discontinuous permafrost zones in the southern half of the Yukon (60°N to 64°N), using a combination of ground temperature monitoring, electrical resistivity tomography (ERT), frost table probing and coring. Sites were selected to cover a wide range of substrates, vegetation types and ground ice contents. ERT profiling in the spring imaged both deep seasonal frost and perennially frozen ground. Deep active layers measured by probing at the end of summer were also detectable by ERT. Where ground temperatures indicated that the base of permafrost was at a depth of less than 25 m, vertical transitions in apparent resistivity were more sharply defined in coarse materials than in fine-grained deposits, probably because of differences in unfrozen moisture contents at temperatures just below 0°C. Apparent resistivity values related to excess ice fraction and ground temperatures were similar to those previously obtained in Mongolia and Iceland, but generally lower than in ice-rich rock glaciers in European studies. The observations revealed the complexity of site conditions where permafrost is discontinuous and the utility of ERT, in combination with other methods, to investigate permafrost thickness, spatial extent and ice content for infrastructure planning or climate change studies. Copyright © 2011 John Wiley & Sons, Ltd.

Advective Heat Transport in Frozen Rock Clefts: Conceptual Model, Laboratory Experiments and Numerical Simulation

Abstract: Advective heat transported by water percolating into discontinuities in frozen ground can rapidly increase temperatures at depth because it provides a thermal shortcut between the atmosphere and the subsurface. Here, we develop a conceptual model that incorporates the main heat-exchange processes in a rock cleft. Laboratory experiments and numerical simulations based on the model indicate that latent heat release due to initial ice aggradation can rapidly warm cold bedrock and precondition it for later thermal erosion of cleft ice by advected sensible heat. The timing and duration of water percolation both affect the ice-level change if initial aggradation and subsequent erosion are of the same order of magnitude. The surplus advected heat is absorbed by cleft ice loss and runoff from the cleft so that this energy is not directly detectable in ground temperature records. Our findings suggest that thawing-related rockfall is possible even in cold permafrost if meltwater production and flow characteristics change significantly. Advective warming could rapidly affect failure planes beneath large rock masses and failure events could therefore differ greatly from common magnitude reaction-time relations. Copyright © 2011 John Wiley & Sons, Ltd.

Monitoring topographic changes in a periglacial high-mountain face using high-resolution DTMs, Monte Rosa East Face, Italian Alps

Abstract: This paper describes a remote sensing-based approach for detailed topographic investigations in steep periglacial high-mountain faces. The study was conducted at one of the highest periglacial rock faces in the European Alps, the permafrost-affected and partially glacierised east face of Monte Rosa. Strongly increased rock and ice avalanche activity on this rock wall has caused major topographic change in recent decades. A time series of high-resolution digital terrain models (DTMs) with a 2-m resolution was produced from digital aerial photogrammetry for 1956, 1988 and 2001 and from airborne LiDAR for 2005 and 2007. The DTM comparisons reveal a total volume loss of permafrost-affected bedrock and glacier ice of more than 20 × 106 m3 over the past 50 years, with the majority of the loss since 1988. Analysis of all unstable areas and detachment zones showed that the sequence of the main slope failures is spatially connected and that there is coupling between permafrost bedrock instability and the condition of adjacent hanging glaciers. Copyright © 2011 John Wiley & Sons, Ltd.

Origin and characteristics of massive ground ice on Herschel Island (western Canadian Arctic) as revealed by stable water isotope and Hydrochemical signatures

Abstract: Herschel Island in the southern Beaufort Sea is a push moraine at the northwestern-most limit of the Laurentide Ice Sheet. Stable water isotope (d 18 O, dD) and hydrochemical studies were applied to two tabular massive ground ice bodies to unravel their genetic origin. Buried glacier ice or basal regelation ice was encountered beneath an ice-rich diamicton with strong glaciotectonic deformation structures. The massive ice isotopic composition was highly depleted in heavy isotopes (mean d 18 O: � 33%; mean dD: � 258%), suggesting full-glacial conditions during ice formation. Other massive ice of unknown origin with a very large d 18 O range (from � 39 to � 21%) was found adjacent to large, striated boulders. A clear freezing slope was present with progressive depletion in heavy isotopes towards the centre of the ice body. Fractionation must have taken place during closed-system freezing, possibly of a glacial meltwater pond. Both massive ground ice bodies exhibited a mixed ion composition suggestive of terrestrial waters with a marine influence. Hydrochemical signatures resemble the Herschel Island sediments that are derived from nearshore marine deposits upthrust by the Laurentide ice. A prolonged contact between water feeding the ice bodies and the surrounding sediment is therefore inferred. Copyright # 2011 John Wiley & Sons, Ltd.

Palaeoclimatic information from stable water isotopes of Holocene ice wedges on the Dmitrii Laptev Strait, northeast Siberia, Russia

Abstract: The stable isotopic composition (δ18O, δD, d) of three Holocene-age ice wedges at the Dmitrii Laptev Strait, Russia (Oyogos Yar coast, 72.7°N, 143.5°E) was studied at high resolution (100 to 200 samples each) in order to develop palaeoclimatic records. AMS 14C ages of organic matter in the ice prove the Late Holocene age of the studied horizontal ice-wedge profiles and indicate syngenetic growth associated with sediment accumulation. Co-isotopic relationships of wedge ice close to the Global Meteoric Water Line point to a good suitability for palaeoclimate studies and all three profiles show similar isotopic features. A general Late Holocene winter warming trend is inferred from δ18O data changing from about −26‰ to values of −23‰ to −21‰, with periods of marked variability superimposed on the trend. This trend is accompanied by a shift in the d excess from 8‰–11‰ to 5‰–8‰, probably caused by varying proportions of differing moisture sources for precipitation. The highest winter temperatures and an increased influence of regional moisture in recent decades may reflect ongoing Arctic climate change. Copyright © 2010 John Wiley & Sons, Ltd.

Vegetation Canopy and Radiation Controls on Permafrost Plateau Evolution within the Discontinuous Permafrost Zone, Northwest Territories, Canada

Abstract: This study examines the links between the spatial distribution of three‐dimensional vegetation structural characteristics and historical permafrost plateau area changes using airborne light detection and ranging and aerial photography. The results show that vegetation is prone to reduced canopy fractional cover (by up to 50%) and reduced canopy heights (by 16−30%) at the edges of plateaus. Reduced biomass may cause a positive feedback, whereby diminished within‐ and below‐canopy shadowing (by 1h of shadow time per day) results in increased radiation incident on the ground surface (16% greater at open‐ vs closed‐canopy plateau sites) and increased longwave radiation losses (74% greater at open‐ vs closed‐canopy plateau sites). Increased incident shortwave radiation may result in augmented thawing of permafrost and increased meltwater runoff, which further inhibits vegetation and permafrost persistence. Edge influences on ground thaw cause vegetation to die over several years (confirmed using historical aerial photography), thereby exacerbating thaw and plateau area reduction (plateau area reduction=~27% over 60years). Permafrost degradation is also evidenced by the increasingly fragmented characteristics of the landscape. Copyright © 2011 John Wiley & Sons, Ltd.

Air and Ground Temperature Variations Observed along Elevation and Continentality Gradients in Southern Norway

Abstract: The coupling between air and ground temperatures in the mountains of southern Norway was examined using 12 shallow boreholes drilled in August 2008. Three borehole arrays (at Juvvass, Jetta and Tron), each with boreholes at different elevations, were established along a continentality gradient. At the least continental site (Juvvass), the transect includes boreholes with shallow seasonal frost to continuous permafrost, while at Jetta and Tron, the arrays covered the transition from relatively deep seasonal frost to marginal permafrost. On the north slope of Tron, however, ground surface temperatures indicate more widespread permafrost conditions, apparently due to the negative thermal anomaly associated with an openwork block field. The surface offsets (mean ground surface temperature (MGST) minus mean air temperature (MAT)) ranged from < 1 °C for unvegetated wind-scoured sites to up to 4.5 °C for sites with a thick, prolonged snow cover. Active-layer thicknesses at the borehole sites close to the lower limit of mountain permafrost were up to 10 m in bedrock, even under a low thermal diffusivity sediment cover. The mean ground temperature at 10-m depth differed significantly from the MGST, mainly due to the 3D thermal effects of the varying snow cover. Our air temperature measurements do not support the inference that the observed decrease in the lower elevational limit of mountain permafrost with continentality is mainly due to lower MAT. Rather, the pattern fits with an eastwards decrease in the lower limit of block fields and snowfall amounts. Copyright © 2011 John Wiley & Sons, Ltd.

Automated Time‐lapse ERT for Improved Process Analysis and Monitoring of Frozen Ground

Abstract: A new automated electrical resistivity tomography (A-ERT) system is described that allows continuous measurements of the electrical resistivity distribution in high-mountain or polar terrain. The advantages of continuous resistivity monitoring, as opposed to single measurements at irregular time intervals, are illustrated using the permafrost monitoring station at the Schilthorn, Swiss Alps. Data processing was adjusted to permit automated time-effective handling and quality assessment of the large number of 2D electrical resistivity profiles generated. Results from a one-year dataset show small temporal changes during periods with snow cover, and the largest changes during snowmelt in early summer and during freezing in autumn, which are in phase with changes in either near-surface soil moisture or subsurface temperature. During the snowmelt period, spatially variable infiltration processes were observed, leading to a rapid increase in soil moisture and corresponding decrease in electrical resistivity over a period of a few days. This infiltration led to the onset of active-layer thawing long before the seasonal snow cover vanished. Statistical analyses showed that both spatial and temporal variability over the course of one year are similar, indicating the significance of spatial heterogeneity regarding active-layer dynamics. As a result of its cost-effective ability to monitor freezing and thawing processes even at greater depths, the new A-ERT system can be widely applied in permafrost regions, especially in the context of long-term degradation processes. Copyright © 2011 John Wiley & Sons, Ltd.

Internal structure of the Green Lake 5 rock glacier, Colorado Front Range, USA

Abstract: Information about the internal structure of rock glaciers is needed to understand their reaction to ongoing climate warming. Three different geophysical techniques—shallow seismic refraction, ground-penetrating radar (GPR) and electrical resistivity tomography—were used to develop a detailed subsurface model of the Green Lake 5 rock glacier in the Colorado Front Range, USA. Below a thin zone of fine sediments and soils (0.7 – 1-m thickness; 0 – 20 kΩm and 320 – 370 m s−1), a 1 – 3-m thick zone with low p-wave velocities (790 – 820 m s−1) and high electrical resistivity (20 – 100 kΩm) is interpreted as the ice-free, blocky active layer with large void spaces. The data corroborate strong reflections of the GPR signals which travel at this depth at 0.11 m ns−1. A third layer that extends from depths of 1 – 3 m to about 5 m is characterised by lower electric resistivities (5 – 20 kΩm) and has lower electromagnetic wave velocities (0.65 m ns−1), representing unfrozen, finer and wetter sediments. At around 5-m depth, the measured physical parameters change drastically (vp = 3200 – 3300 m s−1, 50 – 150 kΩm, vGPR = 0.15 m ns−1), showing an ice-rich permafrost zone above the bedrock. This model of the internal structure was used to evaluate an existing hydrological flowpath model based on the hydrochemical properties of water outflow from the rock glacier. Copyright © 2011 John Wiley & Sons, Ltd.

Equivalent Elevation: A New Method to Incorporate Variable Surface Lapse Rates into Mountain Permafrost Modelling

Abstract: Permafrost is present at multiple elevations with no de! ned lower limit in the southern Yukon Territory, Canada. Empirical statistical modelling of permafrost probability in the region required the development of equivalent elevation, a new variable that re" ects measured differences between surface air temperature lapse rates below and above treeline. In areas where surface lapse rates are negative (normal) but gentle up to the altitudinal treeline, equivalent elevation results in a compressed elevational range. Where surface lapse rates are positive (inverted) in the forest due to the strength of winter inversions, equivalent elevations calculated for valley " oors are higher than those at treeline. There is a strong relationship between the magnitude and sign of surface lapse rates below treeline and the annual amplitude of monthly air temperatures at nearby climate stations, which permits prediction of equivalent elevation for the entire region. Permafrost probability modelling using equivalent elevation produced statistically signi! cant results in several study areas whereas actual elevation values did not. The concept is of particular use where forestedareasareunderlainbypermafrostandmaybetransferabletoareaswithsimilarterrainandclimatesuchasthose in the Canadian Northwest Territories, Alaska and Mongolia. Copyright © 2011 John Wiley & Sons, Ltd.

On the Connection between Debris Flow Activity and Permafrost Degradation: A Case Study from the Schnalstal, South Tyrolean Alps, Italy

Abstract: The possible influence of permafrost degradation on the formation of debris flows in an area of the South TyroleanAlps, Italy, was examined by comparing debris flow activity since 1983 with the modelled contemporary permafrostdistribution. The study focused on the spatial congruence of new initiation zones and potentially marginalpermafrost, which should be especially sensitive to climatic change and is presumed to be currently degrading. Theresults show that distinct changes in the spatial position of debris flow initiation areas mainly occurred at elevationsabove this marginal zone. Consequently, the changes detected in debris flow activity do not appear to have beeninfluenced by atmospheric warming‐induced degradation of permafrost. However, a link may exist to the thickeningof the active layer caused by the melting of a glacier. Copyright © 2011 John Wiley & Sons, Ltd. KEY WORDS : periglacial debris flows; mapping; permafrost degradation; spatial modelling INTRODUCTIONAreasofmountainpermafrostareexpectedtobesignificantlyaffected by current climate warming (Haeberli and Gruber,2009). Mountainous areas are also subject to increasinglyintense use and development (Haeberli et al., 1997). Thus,the possible increase in hazard potential−especially in theEuropean Alps−has generated considerable research on thelinks between atmospheric warming, permafrost degradationand slope instability (e.g. Schlyter et al., 1993; Davies et al.,2001; Harris et al., 2001; Kneisel et al., 2007; Noetzli et al.,2007;Allen etal.,2010;Keileretal.,2010).Thepresentstudyfocuses on debris flows, which are common mass‐wastingprocesses in the changing alpine environments and thus posesignificant hazards to life and infrastructure.Recent progress in measurement techniques and model-linghasimprovedourknowledgeoftherelationshipbetweenpermafrost and rock face stability (e.g. Harris et al., 2009),but the possible role of climatically induced permafrostdegradation in the initiation of debris flows is not yet wellunderstood. One reason for this is an inadequate compre-hension of the evolution of permafrost beneath moderatelyinclined slopes where debris and snow cover act as complexinterfaces between the atmosphere and the subsurface(Luetschg et al., 2004; Gruber and Haeberli, 2009). Thiscreates a significant challenge for modelling the thermalcondition and spatial distribution of permafrost. Further-more, permafrost in unconsolidated materials generally hashigh ice contents, which retard potential thawing by theuptake of latent heat (Noetzli et al., 2007). Permafrost soilsthus may respond to climate forcing over several decades tocenturies (cf. Haeberli, 1992) and the effects of permafrostdegradation on debris flows may be difficult to detect withinone or two decades. Finally, debris flows themselves arehighlycomplexgeomorphicprocesses.Ourunderstandingoftheir initiation, resulting from the temporal and spatialconcurrence of several highly variable factors includingdebris availability and the occurrence of transient triggeringevents, and their overall sensitivity to changes in climaticparameters, is still incomplete (cf. Rebetez et al., 1997;Zimmermann et al., 1997; Jomelli et al., 2004, 2007). Yet,climatically induced thawing of alpine permafrost isexpected to significantly affect the hydraulic and geotech-nical properties of perennially frozen unconsolidated

Biogeochemical and geocryological characteristics of wedge and thermokarst-cave ice in the CRREL permafrost tunnel, Alaska†

Abstract: Partially eroded ice wedges and lenticularly shaped bodies of massive thermokarst-cave ice in ice-rich syngenetic permafrost (yedoma) are exposed in the CRREL tunnel near Fairbanks, Alaska The ice wedges, which formed 25 000 − 40 000 years ago, were subsequently affected by localised thermal erosion, resulting in underground cavities that filled with surface water infiltrating through a network of conduits This water froze inward from the walls of the cavity We report the biogeochemical characteristics of one of these thermokarst-cave ice features and four nearby ice wedges The thermokarst-cave ice has 30 times the dissolved organic carbon concentration, 20 times the total dissolved nitrogen concentration and five to 20 times the inorganic solute concentrations of the surrounding (original) ice wedge material Based on these results we present a schematic model to describe how the thermokarst-cave ice was formed and preserved and what processes led to its current biogeochemical characteristics Current estimates of soluble solutes stored in permafrost may underestimate the total carbon and nutrient load where wedge material has been extensively replaced by surface water rich in organic carbon, nutrients or inorganic solutes Published in 2011 by John Wiley & Sons, Ltd

Effects of Ice Content on the Thermal Erosion of Permafrost: Implications for Coastal and Fluvial Erosion

Abstract: The effects of ice content and water flow on thawing and erosion of non‐cohesive permafrost banks were investigated through laboratory experiments. A critical ice content was identified as associated with turbulent flows (20% and 80% for Reynolds numbers of 15 900 and 12 700, respectively), above which thermal erosion results in ablation and a decrease in ice content increases ablation. Below the critical value, the ablation model over‐estimates the erosion rate as the removal of thawed sediments occurs episodically, possibly due to the imbrication of sand grains. The ablation model applies to rivers with non‐cohesive banks, high ice contents and subject to high‐velocity water flows. The model may explain differential erosion that results in massive ice layers in relief. At other sites, however, the retreat rate increases with ground ice content. This behaviour can be explained for sandy permafrost with a relatively low ice content and heterogeneous sand sizes and shapes subject to relatively low‐velocity water flow. These results apply only to perenially frozen sands, as even a small percentage of cohesive material would modify the relationships described. Copyright © 2011 John Wiley & Sons, Ltd.

The Development of Frost‐weathering Microstructures on Sand‐sized Quartz Grains: Examples from Poland and Mongolia

Abstract: Quartz grains, 0.25−1.0 mm in diameter, taken from Pleistocene sands and a palaeo-active layer in Poland (Łodź Teofilow) and from silty-clayey sediments of the contemporary active layer near Ulaanbaatar (Mongolia) were analysed using a scanning electron microscope (SEM). Other analyses included granulometric composition, and frosting and rounding of quartz grains. The effects of frost weathering comprise several microstructures, such as breakage blocks (>10 µm and <10 µm), surface coating and scaling, among which breakage blocks <10 µm are apparently the most common. Two types of frost weathering were distinguished. Weathering of the P type is mainly initiated on convex fragments of grains as the result of ice segregation. Weathering of the F type is linked to the volumetric expansion of ice and usually observed within concave linear microstructures. A frost action index (FAI) was developed based on the frequency of occurrence of microstructures from frost weathering. The FAI value varies between 0 and 3, and the higher the value, the more intensive the frost weathering. The value of the FAI in sediments from the Polish study site is relatively low with a maximum barely exceeding 1. The FAI values from the Ulaanbaatar site are higher in all of the sediment samples with a maximum of 2. Copyright © 2011 John Wiley & Sons, Ltd.

The Role of Interannual Climate Variability in Controlling Solifluction Processes, Endalen, Svalbard

Abstract: A continuous record is presented of active layer processes at Endalen, Svalbard, over the period 2005–08. The monitored slope has a gradient of around 7° and in 2005, active layer depth was 94 cm, but this increased by around 14 cm over the next three years. The presence of an ice-rich transient layer proved highly significant in determining the timing and profiles of solifluction movement. Frost heaving was 4.2 cm in 2005–06, 6.6 cm in 2006–07 and 3.2 cm in 2007–08, but thaw settlement exceeded frost heave in each year, giving a net total ground surface lowering of 6.2 cm. In winter, segregation ice was concentrated within the upper and lower active layer, leaving the central parts ice-poor. During the summers of 2006 and 2008, thawing of the transient layer was associated with artesian pore pressures at 90 cm depth and basal soil shearing, but in 2007, when the thaw front failed to reach the ice rich basal zone, pore pressures during thaw were sub-hydrostatic and no basal shearing was observed. Solifluction shear strain during thaw settlement resulted in downslope surface displacements of 2.3 cm in 2005–06, 1.2 cm in 2006–07 and 1 cm in 2007–08. Copyright © 2011 John Wiley & Sons, Ltd.

Isotope characterisation of ground ice in northern Canada

Abstract: This paper reviews isotopic research on the characterisation and identification of various types of ground ice throughout the Canadian Arctic, including buried glacier ice, massive segregated ice, segregated ice lenses and offshore ice-rich permafrost, as well as ice related to other cold-region phenomena such as ice wedges, icings (aufeis), frost blisters and pingos. The formational age of ground ice bodies ranges from recent (seasonal ice in the active layer) to tens of thousands of years, when the region experienced widespread continental-scale glaciation. Modern ice lenses generally have 18O/16O ratios of -18 to -22‰, while modern ice wedges usually range from -22 to -25‰. δ18O values as high as -14‰ are representative of the Hypsithermal period (4000 to 8000 years BP), while glacial-age ice has been measured with 18O/16O ratios as low as -36‰. Buried glacier ice often preserves climatic variations from the time of snow deposition. Other massive ground ice bodies contain isotopic signatures (18O and 2H) that indicate variable fractionation of the isotopes during freezing of the source water at stationary freezing fronts in either open or closed systems. Placing the ice bodies into a time frame can be accomplished either through age dating of the enclosing sediments and encased organics, or by direct dating of the ice utilising tritium (3H) for relatively young ice and radiocarbon (14C) analysis of contained gas bubbles for older ice. Copyright © 2011 John Wiley & Sons, Ltd.

Investigation of ice-wedge infilling processes using stable oxygen and hydrogen isotopes, crystallography and occluded gases (O2, N2, Ar)

Abstract: The source and mechanism of infill of ice wedges of various ages (modern to Pleistocene) were examined for sites in the western Arctic. Several techniques were employed, including stable O-H isotope and crystallographic analyses of the ice, and gas composition (O2, N2 and Ar) analyses of air entrapped in the ice. The results indicate that climatic and site-specific conditions may influence the source of infilling during ice-wedge growth, so that wedge ice in wet and dry environments exhibits different characteristics. For example, Vault Creek tunnel (Alaska) ice wedges, dating from the Late Pleistocene, a cold and dry period, preserved stable O-H isotopes and gas compositions similar to those expected for ice formed by snow densification. In contrast, ice wedges from the Old Crow region (Yukon), dating from the Late Holocene, preserved isotopic and gas compositions more comparable with those expected for ice formed by the freezing of liquid water. In both ice-wedge types, the δ(O2/Ar) values are much lower than both dissolved and atmospheric values, which may be due to the respiration of microorganisms living within ice bubbles or interstitial water at the grain boundaries. The elevated δ18OO2 (up to 16‰) of the occluded gases supports the occurrence of microbial respiration. However, the δ(N2/Ar) values do not appear to have been affected by biological processes, and as such are reflective of the infilling processes. Copyright © 2010 John Wiley & Sons, Ltd.

Isotopic composition and thermal regime of ice wedges in northern Victoria Land, East Antarctica

Abstract: Ice wedges, with tops located 27 to 55 cm below the ground surface, were studied over several summers between 1998 and 2006 at three sites with differing elevations in northern Victoria Land, East Antarctica. The thermal regime, based on data-logger measurements over five years, exhibits very low temperatures, an inferred absence of snow, and high temperature gradients between the ground surface and the top of the ice wedge that may trigger cracking. A co-isotopic study of the wedge-ice oxygen (δ18O) and hydrogen (δD) isotopic values shows extremely negative deuterium excess values and a strong divergence from the expected precipitation. These values and observations of hoarfrost crystals in ice-wedge cracks during summer field surveys indicate that sublimation processes control the formation of ice in wedges, especially at high elevations within this region. Copyright © 2010 John Wiley & Sons, Ltd.

Permafrost thermal regime from two 30-m deep boreholes in southern victoria land, Antarctica

Abstract: Two 30-m deep permafrost temperature-monitoring boreholes were installed in bedrock, one at Marble Point and one in the Wright Valley, in the Ross Sea region of Antarctica. A soil climate-monitoring station in till is located near each borehole. The ground surface temperature (GST) was highly correlated with the air temperature at both sites in 2008. Thermal offsets were small (< 1 °C) in the till and negligible in the boreholes. The active layer was thicker in the boreholes than in the till, presumably because of the higher thermal diffusivity of the rock. The measured depth of zero annual temperature amplitude was around 27 m at Wright Valley and 25 m at Marble Point. Permafrost thickness was estimated at about 680 m at Wright Valley and 490 m at Marble Point. The GST history, reconstructed using an inversion procedure, suggests a slight cooling from 1998 to 2003 followed by a slight warming to 2008. Longer temperature records or deeper boreholes would be required to establish if long-term climate change has occurred. Copyright © 2011 John Wiley & Sons, Ltd.

A Century (1910–2008) of Change in a Collapsing Pingo, Parry Peninsula, Western Arctic Coast, Canada

Abstract: An isolated, eroding pingo at the southern end of Parry Peninsula, N.W.T., Canada was first photographed in about 1910. The photograph allows examination of a century of landform change. Since 1910, the pingo crater pond has drained, the north side of the pingo has become well vegetated, the serrated crest has been smoothed, and the lake bottom has become colonised by willows and other vegetation. The height of the feature was over 100 ft (30 m) in 1910 and is now about 50 ft (15–17 m). The erosion of the pingo has probably been dominated by the strong southerly katabatic winds in the area, as the vegetation on the south side of the pingo is poorly developed in comparison with the north side. A secondary cause of erosion has been the numerous excavations by ground squirrels (Spermophilus parryii) and foxes (Vulpes lagopus) on the slopes of the pingo. It is unusual to detect change of collapsed pingos near the western Arctic coast of Canada unless ground ice is exposed in the core or on the sides of the pingo. The increases since 1996 in height and cover of willows are the first record of such change from western Arctic Canada. Copyright © 2011 John Wiley & Sons, Ltd.

Isotopic composition of syngenetic ice wedges and palaeoclimatic reconstruction, western Taymyr, Russian Arctic

Abstract: Recent, Holocene and Late Weichselian (Sartan) generations of syngenetic ice wedges developed in loess-like and alluvial sediments were investigated along the coast of the Yenisey Bay from Sopochnaya Karga Cape (71°88'N, 82°68'E) to Dikson (73°31'N, 80°34'E). Ages of about 3.4 − 4.6 ka BP were determined for peat layer and wood fragments in ice-rich deposits surrounding ice wedges near Dikson. The isotopic composition of these wedges reflects relatively cold winter temperatures in the Holocene. The lightest isotope composition characterises older ice wedges near Dikson and Sopochnaya Karga Cape. A warming trend between ice wedges of different generations was indicated by a distinct increase in O (4 − 5 ‰) and H (35 − 40‰) stable isotopes. Palaeotemperature reconstruction based on the data shows that winter temperatures during the formation of older generation ice wedges were lower than Holocene winter temperatures, indicating that they developed in the Late Weichselian (MIS2). The presence of syngenetic ice wedges strongly suggests that the coast of western Taymyr was not ice-covered at this time. Copyright © 2011 John Wiley & Sons, Ltd.

Holocene Chemical Weathering, Surface Lowering and Rock Weakening Rates on Glacially Eroded Bedrock Surfaces in an Alpine Periglacial Environment, Jotunheimen, Southern Norway

Abstract: Indices of the rate of Holocene chemical weathering of pyroxene-granulite gneiss and peridotite are estimated from bedrock surfaces deglaciated c. 9700 years ago. A mean surface lowering rate for pyroxene-granulite gneiss of 4.8 ± 1.0 mm ka−1 is estimated from the mean height of upstanding quartz veins, and Schmidt hammer R-values are used to validate the reference-surface method. Microrelief development and crack-widening rates for peridotite are 2.6 ± 1.1 mm ka−1 and 1.8 ± 0.4 mm ka−1, respectively. Well-developed weathering rinds indicate a mean rind development rate for peridotite of 0.6 ± 0.1 mm ka−1. New indices of rock surface weakening (IRW) and the rock surface weakening rate (WR) are defined in relation to Schmidt hammer mean R-values. IRW values from weathered and unweathered surfaces of known age are 38.7 per cent for gneiss and 34.1–59.2 per cent (depending on the texture of the weathered rock surface) for peridotite: corresponding WR values are 2.7 R-units ka−1 and 2.1–3.7 R-units ka−1, respectively. Our methods and results are evaluated, particularly in relation to previous research and other rock types in Scandinavia. The various indices, being affected in different ways by biochemical and biological mechanical weathering and micro-erosion, are regarded as complementary aids in the investigation of both the effects of chemical weathering and its rate. Copyright © 2010 John Wiley & Sons, Ltd.

Utility of Classification and Regression Tree Analyses and Vegetation in Mountain Permafrost Models, Yukon, Canada

Abstract: Classi! cation and regression tree (CART) analyses were undertaken to test the usefulness of including vegetation variables in mountain permafrost distribution models for ! ve widely spaced study areas in the Yukon. Digital elevation model (DEM)! derived variables, ! eld! derived vegetation variables and satellite imagery! derived vegetation variables were employed individually to classify sites into permafrost probable, permafrost improbable and permafrost ‘uncertain’ categories. The vegetation variables were subsequently combined with the DEM! derived set to see if they could improve the latter’s accuracy. Overall training accuracies for the probable and improbable permafrost categories for 102 sites ranged from 81% to 92%. Remotely sensed imagery alone had the lowest overall training (81%) and testing (50%) accuracies. The CART that combined imagery and DEM! based variables produced high overall accuracy for training (90%) and the highest for testing (77%), had few nodes classi! ed as ‘uncertain’ and could be used to create permafrost probability maps of the study areas. CART analyses appear useful for predicting permafrost distribution because they can incorporate non! linear relationships between independent variables and the presence of permafrost. Remotely sensed variables relating to vegetation, speci! cally a normalised difference vegetation index, improved the DEM! based results, but required considerable additional effort for data collection and processing. Copyright © 2011 John Wiley & Sons, Ltd.

Statistical Analyses of Active Patterned Ground Occurrence in the Taillon Massif (Pyrénées, France/Spain)

Abstract: Statistical approaches were used to describe and explain the presence or absence of active patterned ground features in a mid‐latitude alpine area. The relative rarity of these landforms can be problematic for such analyses but this issue was resolved by a novel spatial sampling strategy that considers only terrain within circles drawn around each observed patterned ground feature, which is then subdivided into a grid. This strategy focuses only on fields with potential patterned ground occurrence and can be used for all statistical studies concerning the occurrence of scattered features over extensive areas. These data were examined using factor analyses (multiple correspondence analysis and hierarchical ascendant classification) blended with a complementary bivariate method to associate patterned ground occurrence with eight environmental variables (elevation, exposure, height‐distance ratio, drift, glacier influence, vegetation cover, slopewash and lithology). The absence of active patterned ground is associated with low elevation, glacier absence, no slopewash, a low height‐distance ratio and talus fans. Zones where active patterned ground features are present are divided into three homogeneous subzones and are mostly associated with glacier influence, a large height‐distance ratio and an absence of vegetation. Their location is controlled by the presence of till from different glacial sequences so that the former and current presence of glaciers favours the development of patterned ground features at the landscape scale. Copyright © 2011 John Wiley & Sons, Ltd.

Internal structure and geological context of ramparted depressions, Llanpumsaint, Wales

Abstract: In Europe, ramparted depressions have traditionally been interpreted as the relict forms of periglacial ground-ice mounds. In many cases, however, such interpretations have been based on limited subsurface evidence. We present detailed sedimentological and geophysical investigations of ramparted depressions from Llanpumsaint, Wales. These data are used to establish internal structure and to evaluate possible mechanisms for landform formation. Borehole and geophysical data have revealed a thick (∼30 m) sequence of glaciolacustrine sediments beneath the study site. The geological context (drainage of a large proglacial lake) would have been conducive to the formation of: (i) permafrost-related ground-ice mounds, at times when exposed frost-susceptible glaciolacustrine sediments were subject to permafrost aggradation; and (ii) craters associated with the in-situ meltout of blocks of glacier ice grounded in the lake during periods of falling water levels. Rampart deformation structures are consistent with both models, but units of sand and gravel within the ramparts favour a hypothesis that these landforms represent the collapsed remains of ground-ice mounds. This study highlights the importance of recognising and evaluating all possible (periglacial and non-periglacial) models for the development of ramparted depressions. We recommend that future studies carefully consider all possible mechanisms of formation, particularly where subsurface information is limited. Copyright © 2011 John Wiley & Sons, Ltd.

Shallow ground temperatures and periglacial processes on Iztaccíhuatl volcano, Mexico

Abstract: Shallow ground temperatures and the extent of periglacial processes were examined and modelled on Iztaccihuatl volcano (19°10′20″N, 98°38′30″W, 5230 m asl). Air and ground temperatures (to 0.6 m depth) were measured at five sites from 4137 m to 5020 m asl on the southwest slope of the volcano between 2001 and 2007. Snow lies on the ground for only a few days each year and has almost no effect on periglacial process distribution. Daily freeze-thaw cycles at the ground surface are numerous at the summit (around 212 days annually), but cycles cease only a few centimetres below the surface, so that frost action does not occur below 60 cm depth. Permafrost is present at 4900 m asl on north-facing slopes with a 60 cm thick active layer. Copyright © 2011 John Wiley & Sons, Ltd.

Sulfur and carbon isotopes within atmospheric, surface and ground water, snow and ice as indicators of the origin of tabular ground ice in the Russian Arctic

Abstract: Field sampling of tabular ground ice (TGI) was undertaken at a number of geological sections along the Russian Arctic coast. 34 S in sulfate ion and 13 C in organic matter were analysed in ground ice and enclosing deposits, and in reference samples from snowpacks, atmospheric precipitation, surface waters and glaciers. The scatter in the stable isotope data obtained indicates the heterogeneity of moisture sources for TGI formation. There is a notable difference in the sulfur and carbon isotopic structure between TGI and atmospheric and continental moisture. TGI and its enclosing deposits have a heavier isotopic composition of sulfur and carbon than buried snow and glacial ice. This is considered to be evidence of an essential contribution of marine moisture and sediments to TGI formation. Copyright # 2011 John Wiley & Sons, Ltd.