Cryogenic soil activity caused by differential soil movements during freeze-thaw cycles is of fundamental importance for Arctic ecosystem functioning, but its response to climate warming is uncertain. Eight proxies of cryogenic soil activity (including measurements of soil surface motion, vegetation and grey values of aerial photographs) were examined at eight study sites where non-sorted patterned ground spans an elevation gradient (400–1150 m asl) and a precipitation gradient (300–1000 mm yr-1) near Abisko, northern Sweden. Six proxies were significantly correlated with each other (mean |r| = 0.5). Soil surface motion increased by three to five times along the precipitation gradient and was two to four times greater at intermediate elevations than at low and high elevations, a pattern reflected by vegetation assemblages. The results suggest that inferences about how cryogenic soil activity changes with climate are independent of the choice of the proxy, although some proxies should be applied carefully. Four preferred proxies indicate that cryogenic soil activity may respond differently to climate warming along the elevation gradient and could be greatly modified by precipitation. This underlines the strong but spatially complex response of cryogenic processes to climate change in the Arctic. Copyright © 2013 John Wiley & Sons, Ltd.
Machine-learning regression tree models were used to extrapolate airborne electromagnetic resistivity data collected along flight lines in the Yukon Flats Ecoregion, central Alaska, for regional mapping of permafrost. This method of extrapolation (r = 0.86) used subsurface resistivity, Landsat Thematic Mapper (TM) at-sensor reflectance, thermal, TM-derived spectral indices, digital elevation models and other relevant spatial data to estimate near-surface (0–2.6-m depth) resistivity at 30-m resolution. A piecewise regression model (r = 0.82) and a presence/absence decision tree classification (accuracy of 87%) were used to estimate active-layer thickness (ALT) (< 101 cm) and the probability of near-surface (up to 123-cm depth) permafrost occurrence from field data, modelled near-surface (0–2.6 m) resistivity, and other relevant remote sensing and map data. At site scale, the predicted ALTs were similar to those previously observed for different vegetation types. At the landscape scale, the predicted ALTs tended to be thinner on higher-elevation loess deposits than on low-lying alluvial and sand sheet deposits of the Yukon Flats. The ALT and permafrost maps provide a baseline for future permafrost monitoring, serve as inputs for modelling hydrological and carbon cycles at local to regional scales, and offer insight into the ALT response to fire and thaw processes. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
]]>This review focuses on advances in applications of geophysical methods to permafrost terrain that have emerged in 2007–12. Improvements in the four main geophysical techniques presently used in permafrost research (i.e. electric, electromagnetic, seismic and radar methods) and new or resurrected methods for permafrost applications are discussed. Advances in geophysical monitoring and quantitative interpretation of geophysical survey results are presented, especially for ground ice and water content. Electrical resistivity is now used operationally for long-term monitoring of ice content, as well as for short-term process studies. Quantitative approaches to determine realistic ice and liquid water content values and their spatial and temporal variability exist, but need to be further refined to be widely applicable for geotechnical and numerical modelling purposes. Copyright © 2013 John Wiley & Sons, Ltd.
Knowledge of the thermal state of mountain permafrost has greatly increased since 2007 with the establishment of numerous new monitoring stations around the world. Data collected at these sites have pointed to longer-term changes in ground temperatures, which seem to have increased during the last two to three decades in cold permafrost, while in ground close to 0°C the near-surface ice content has restricted warming and similar trends are not apparent. Modelling of mountain permafrost has developed greatly, driven by general circulation models or gridded temperature maps, through both predictive methods and spatial equilibrium and transient approaches. The spatial resolution of climate parameters, which is normally much coarser than the spatial heterogeneity of alpine environments, presents a major problem for modelling studies. This is a fundamental challenge for future research. Copyright © 2013 John Wiley & Sons, Ltd.
The first record of stable isotopes through a complete sequence of ice within an open-system pingo in northwestern Mongolia indicates a complex history of ice formation and pingo growth. A continuous section of ice 32 m long was cored through the centre of Mongot Pingo, and ice cores were analysed for stable isotopes and chemical composition. Two different stable isotope patterns in separate ice sections are identified: open-system freezing and semi-closed system (or closed system) freezing. Discharge measurements were observed in 2009 after drilling through pingo ice to artesian sub-pingo water and compared with data collected from the same pingo in 1968. Approximately 850–950 m3 of sub-pingo water discharged within 120 h during drilling in both 1968 and 2009, a volume equivalent to about 10 per cent of the current pingo ice volume. Between 1968 and 2009, permafrost (pingo ice) thickened by about 60 cm (1.46 cm per year), from 32.0 to 32.6 m, due to the decrease in sub-pingo artesian water pressure after water release from the 1968 drilling. The major mechanism for ice formation at this pingo is groundwater artesian pressure, though not continuously. Four major stages of pingo growth after 8790 yr BP are inferred. Copyright © 2013 John Wiley & Sons, Ltd.
The relationships between thermokarst activity, limnogeological processes and climate change in the Siberian Arctic are not well understood. The objective of this paper is to identify the factors controlling the patterns of deposition, using grain size distribution, organic content, elemental composition and mineralogical composition of a 137-cm long sediment core with a maximum age of ~ 10.9 cal. kyr BP from Lake El'gene-Kyuele in the tundra of northeastern Siberia. Eight fine sand layers are attributed to depositional events associated with thaw slump activity acting upon orthogonally oriented patterns of ice-wedge networks in the ice-rich permafrost on the NW margin of the lake catchment. Sr/Rb ratios, which correspond to the total feldspar and illite content, serve as high-resolution grain size proxies. The Br content relates to the total organic carbon content, and the Fe/Mn ratio reflects the degree of oxidisation. Our results indicate a relationship between repeated phases of fine sand input and retrogressive thaw slumping dependent on hydroclimate variability and orthogonally oriented ice-wedge networks within the catchment. Copyright © 2013 John Wiley & Sons, Ltd.
The Stefan equation is one of the simplest approximate analytical solutions for the thaw-freeze problem. It provides a useful method for predicting the depth of thawing/freezing in soils when little site-specific information is available. The limited number of parameters in the Stefan equation makes possible its application in a multi-layered system. We demonstrate that a widely used algorithm (JL-algorithm), which has been frequently used in permafrost regions, was derived by an incorrect mathematical method. It will inevitably result in systematic errors in the simulation if this algorithm is used in a multi-layered soil.
We present another simple thaw-freeze algorithm (XG-algorithm) for multi-layered soils. The new algorithm can be used to determine the freeze/thaw front in multi-layered soils no matter how thick each layer is and how many layers the soil profile contains. Simulation results of the JL-algorithm and the XG-algorithm are compared using hypothetical soil profiles, and the XG-algorithm is also used to simulate the thaw depth at three permafrost monitoring sites on the Qinghai-Tibet Plateau and one on the Loess Plateau, China. These applications show that the XG-algorithm could be readily used to analyse the factors that affect active-layer thickness. It can also be coupled with hydrological or land surface models to simulate the freeze-thaw cycles in permafrost regions and for related engineering applications. Copyright © 2013 John Wiley & Sons, Ltd.
This paper reviews contributions to permafrost isotope geochemistry published between 2007 and 2012 and proposes future research directions. It focuses on: (1) the origin and age of ground ice; (2) geochemistry and water movement in the active and transient layers; and (3) geochemistry and water movement in deep permafrost. The use of isotope geochemistry to study permafrost-related processes has grown significantly over the last few years. These processes have been elucidated by combining geochemical and isotope measurements from different components of permafrost. Such combination has yielded new insights, for example, into the water source and transfer processes that lead to the formation of ground ice, as well as groundwater movement and residence time in permafrost. Permafrost isotope geochemistry has a promising future and should provide valuable tools for the study of a rapidly changing permafrost environment. Copyright © 2013 John Wiley & Sons, Ltd.
CryoGRID 1.0 provides an equilibrium model of permafrost distribution in Norway at a spatial resolution of 1 km2. The approach was forced with gridded data on daily air temperature and snow cover. Ground thermal properties for different bedrock types and sediment covers were derived from surveys and geological maps to yield distributions of thermal conductivity, heat capacity and water content. The distribution of blockfields was derived from satellite images adapting a newly developed classification scheme. The model was evaluated using measured ground surface and ground temperatures, yielding a realistic description of the permafrost distribution in mainland Norway.
The model results show that permafrost underlies sites mainly with exposed bedrock or covered by coarse-grained sediments, such as blockfields and coarse tills. In northern Norway, palsa mires are abundant and organic material and vegetation strongly influence the ground thermal regime. Modelling suggests that permafrost in equilibrium with the 1981–2010 climate presently underlies between 6.1 per cent and 6.4 per cent of the total area of mainland Norway, an area significantly smaller than that modelled for the Little Ice Age climate (14%). CryoGRID 1.0 was subsequently forced using output from a regional climate model for the 2071–2100 period, which suggests that severe permafrost degradation will occur, leaving permafrost beneath an area of just 0.2 per cent of mainland Norway. Copyright © 2013 John Wiley & Sons, Ltd.
Since 2002, ground and ground surface temperatures have been systematically measured in the mountains of Troms and Finnmark, northern Norway. These data were used to calibrate and validate a transient heat flow model and a spatial permafrost model, to address ground thermal development since the end of the Little Ice Age, as well as possible permafrost responses to anticipated future climate changes. Approximately 20 per cent of the land area is underlain by permafrost, and in Finnmark, permafrost in palsa mires seems to dominate. Both observations and modelling show that the present permafrost is mainly ‘warm’, with mean ground temperatures above -3 °C. Permafrost has warmed during the last century, and at one site our ground temperature observations show the degradation of permafrost over the intervening decade. The study identifies three major permafrost regions in northern Norway: (1) maritime mountain permafrost in western Troms; (2) continental permafrost above the treeline and in bogs in Finnmark; and (3) Low Arctic permafrost on the peninsula of Varangerhalvøya, forming a transition between the Scandinavian mountain-dominated permafrost in the south and the arctic permafrost towards the north and east. Copyright © 2013 John Wiley & Sons, Ltd.
GPR is applied to image subsurface structures below non-sorted polygons in Kapp Linné, Svalbard, where ice and active-layer soil wedges co-exist within a small area. Two-dimensional GPR images ice wedges as hyperbolic reflections extending down from the frost table. However, some ice-wedge signals are obscured or masked by similar hyperbolic reflections produced by stones or active-layer soil wedges. Three-dimensional GPR images ice wedges as linear amplitude anomalies, which excludes the possibility of misinterpretation and offers more reliable results. GPR investigations show that ice wedges are distributed sporadically in lower (younger) beach ridges, but not in higher (older) ones.
Inter-site monitoring of ground temperature, soil moisture, slow ground deformation and cracking during 2004–09 and the determination of near-surface soil texture and stratigraphy suggest that snow cover and soil thermal properties determine the distribution of ice wedges. Most ice wedges are considered to be inactive due to relatively high permafrost temperatures. Shock loggers and extensometers detected shallow (soil wedge) cracking in sandy sediments, when the ground surface temperature dropped to −12°C and the thermal gradient in the upper 20 cm of ground reached −10°C m−1. Copyright © 2013 John Wiley & Sons, Ltd.
Eight segmented PVC columns (Rudberg pillars) inserted vertically in the treads of three vegetation-covered (‘turf-banked’) solifluction lobes at altitudes of 912–1031 m in the Fannich Mountains of NW Scotland were exhumed 35 years after insertion, and downslope displacement of each segment was measured to derive velocity profiles for each site. Data from these profiles yielded average surface velocities of 7.8–10.6 mm a-1 (mean 8.8 mm a-1), average volumetric velocities of 8.3–13.3 cm3 cm-1 a-1 (mean 10.5 cm3 cm-1 a-1) and maximum displacement depths of 290–445 mm (mean 390 mm). Measured volumetric velocities for these maritime periglacial sites are fairly similar to those recorded in high alpine environments, but markedly less than most reported rates for solifluction in areas of warm permafrost or deep seasonal freezing. Movement affects only the uppermost parts of individual lobes, and the measured volumetric velocities imply either very slow advance of lobe fronts (~ 0.7 mm a-1) or slow thickening and steepening of stationary lobe risers. Velocity profiles decline approximately exponentially with depth over the depth range 50–400 mm, consistent with movement by frost creep alone or frost creep plus gelifluction. Comparison with measured rates of periglacial mass transport elsewhere on British mountains suggests (1) that, contrary to traditional views, surface velocities are similar to (and may exceed) those of ploughing boulders in the same area, and (2) that both surface velocities and volumetric velocities are markedly less than at unvegetated sites where needle ice creep is the dominant component of solifluction. Copyright © 2012 John Wiley & Sons, Ltd.
Debris ridges in New Zealand are routinely assumed to be ‘moraines’ and used as key Southern Hemisphere paleoclimatic sites without detailed evaluation of ridge origin. Here we assess the origin of a debris ridge adjacent to Dundas Ridge in the Tararua Range, North Island, New Zealand, through measurements of ridge morphology and sedimentary properties. The ridge has a steep c. 35° distal slope (height 18 m), compared with the c. 19° proximal slope (height 6 m), and on all transects the distal slopes contain the coarsest material (median b-axis clast widths of 0.18-0.25 m), compared to distal samples (0.34-0.37 m). Clast shape (C40 range 40-60%) and angularity (RA>65%) indicate typically angular and ‘slabby’ clasts, and along with the lack of fines, and the ca. 40-m-distance between the ridge crest and the foot of the backwall, lead us to reject a glacial (moraine) origin for the ridge. The single ridge morphology precludes a protalus rock glacier origin, while the lack of a broad hillslope scar and debris apron beyond the ridge excludes a landslide origin. Instead, we interpret the ridge as a pronival (protalus) rampart formed by supranival debris supply–from the ca. 200 m-high southeastern slopes of Dundas Ridge–across a snowbed. Re-distribution of snow by prevailing westerlies from Mt Dundas Ridge into the basin would have nourished the snowbed, which is likely to have formed during the interval 24-18 ka BP, when a minor alpine-style glaciation affected sectors of the Tararua Range. This is the first pronival rampart detailed in New Zealand, raising the possibility that debris ridges of pronival origin may also be present elsewhere in New Zealand's mountains. Copyright © 2012 John Wiley & Sons, Ltd.
High-resolution satellite remote sensing analysis (n = 637 lakes) and field measurements (n = 29 lakes) of two peat plateau areas in northeast European Russia were carried out to investigate lake morphology, map shoreline erosion indicators and assess possible orientation patterns in lake and shore morphology. The study includes the first detailed characterisation of the shape and size of thermokarst lakes in organic terrain. The area covered by lakes is 7.0 per cent and 13.6 per cent, and median lake size is 184 m2 and 265 m2, respectively, for the two study areas. In both areas, most lakes have a similar northwest to southeast orientation, and shores most commonly face northeast or southwest. The shores are generally steeper and have more cracks and lake depths are greater along shores facing northeast or southeast, and along the shorelines of larger lakes. Shores with a peat substrate are more heterogeneous than those with a mineral substrate in terms of steepness, cracks and water depths. Since the lakes are generally small, the shoreline/area ratio is high and a large part of the peat plateau areas can potentially be affected by shoreline erosion. Copyright © 2012 John Wiley & Sons, Ltd.
The monograph summarises radiocarbon and stable isotope research on syngenetic ice wedges. The southern boundary of active and inactive ice wedges in Russian permafrost is re-evaluated and revised. A new model of cyclical growth of syngenetic ice wedges is proposed, involving three cycles in ice-wedge development: micro-, meso- and macrocycles. Direct dating of syngenetic ice wedges can be carried out by accelerator mass spectrometry (AMS) radiocarbon dating of organic microinclusions and pollen concentrates from ice-wedge ice. Dating reveals vertical and lateral variation in the age of yedoma at Duvanny Yar (NE Yakutia), one of the key syngenetic permafrost exposures in Eurasia. Radiocarbon ages and oxygen and deuterium isotopic values of syngenetic ice wedges in northern Russia and North America provide insights into palaeoenvironmental history and palaeogeocryology. Syngenetic ice wedges sometimes show complex cryostratigraphic relationships with other types of ice, including massive ice, icing ice and pingo ice. Comparison of isotope records from syngenetic ice wedges with those from Greenland ice cores reveals evidence for Dansgaard-Oeschger (D/O) events preserved in Siberian permafrost. Copyright © 2013 John Wiley & Sons, Ltd.