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Permafrost and Periglacial Processes

Wiley Online Library : Permafrost and Periglacial Processes

Published: 2017-10-01T00:00:00-05:00


Long-term changes in the ground thermal regime of an artificially drained thaw-lake basin in the Russian European north


Long-term (1982–1995) observations of the ground thermal regime of a drained thaw-lake basin in the Pechora Lowlands of the Russian European north revealed a high spatial and temporal variability in the ground temperature response to artificial drainage. The thermal response was controlled by the atmospheric climate and by evolution of the landsurface following drainage. Observed changes in permafrost conditions were related to three climatic subperiods identified from air and ground temperature trends. The first (1982–1984) was characterized by gradual ground cooling associated with partial formation of permafrost patches under the initial stage of formation of marshy meadows. The second (1985–1987) involved strong ground cooling, resulting in the formation of a subsurface permafrost layer beneath most of the basin. The third (1988–1995) was marked by a gradual increase in annual mean ground temperature, promoting partial permafrost degradation under marshy meadows and willow stands. Initially, newly aggraded permafrost remained under peat mounds and tundra meadows. The spatial pattern of permafrost change can be attributed to heterogeneous landsurface evolution and variable snow thickness. Four distinct ground temperature regimes are distinguished: (i) thawed ground, (ii) deep permafrost, (iii) unstable permafrost and (iv) stable permafrost.

Erosion and sediment transfer processes at the front of rapidly moving rock glaciers: Systematic observations with automatic cameras in the western Swiss Alps


When connected to torrential channels, the fronts of active rock glaciers constitute important sediment sources for gravitational transfer processes. In this study, a 2013–16 time series of in situ webcam images from the western Swiss Alps was analyzed to characterize the erosion processes responsible for sediment transfer at the front of three rapidly moving rock glaciers and their temporal behavior. The main erosion processes comprised rock fall, debris slide, superficial flow and concentrated flow. These processes were induced by (i) changes of the frontal slope angle produced by rock glacier advance, and (ii) increases in water content of the sediments at the rock glacier front due to melt processes and rainfall. Erosion almost ceased during winter, when the front was frozen and snow-covered. The onset of snowmelt triggered an active period of high-frequency erosion events. After the melt period, sediment transfer continued as occasional rock falls, while other erosion processes occurred only during or following rainfall events. Intense regressive erosion phases that triggered debris flows were rare and occurred when enhanced snowmelt and/or recurring rainfall induced substantial groundwater flow on the debris slopes directly below the rock glacier fronts.

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No abstract is available for this article.

Vegetation Succession, Carbon Accumulation and Hydrological Change in Subarctic Peatlands, Abisko, Northern Sweden


High-resolution analyses of plant macrofossils, testate amoebae, pollen, mineral content, bulk density, and carbon and nitrogen were undertaken to examine the late Holocene dynamics of two permafrost peatlands in Abisko, Subarctic Sweden. The peat records were dated using tephrochronology, 14C and 210Pb. Local plant succession and hydrological changes in peatlands were synchronous with climatic shifts, although autogenous plant succession towards ombrotrophic status during peatland development was also apparent. The Marooned peatland experienced a shift ca. 2250 cal yr BP from rich to poor fen, as indicated by the appearance of Sphagnum fuscum. At Stordalen, a major shift to wetter conditions occurred between 500 and 250 cal yr BP, probably associated with climate change during the Little Ice Age. During the last few decades, the testate amoeba data suggest a deepening of the water table and an increase in shrub pollen, coinciding with recent climate warming and the associated expansion of shrub communities across the Arctic. Rates of carbon accumulation vary greatly between the sites, illustrating the importance of local vegetation communities, hydrology and permafrost dynamics. Multiproxy data elucidate the palaeoecology of S. lindbergii and show that it indicates wet conditions in peatlands. Copyright © 2017 John Wiley & Sons, Ltd.

Permafrost Thaw and Liberation of Inorganic Nitrogen in Eastern Siberia


The currently observed climate warming will lead to widespread degradation of near-surface permafrost, which may release substantial amounts of inorganic nitrogen (N) into arctic ecosystems. We studied 11 soil profiles at three different sites in arctic eastern Siberia to assess the amount of inorganic N stored in arctic permafrost soils. We modelled the potential thickening of the active layer for these sites using the CryoGrid2 permafrost model and representative concentration pathways (RCPs) 4.5 (a stabilisation scenario) and 8.5 (a business as usual emission scenario, with increasing carbon emissions). The modelled increases in active-layer thickness (ALT) were used to estimate potential annual liberation of inorganic N from permafrost soils during the course of climate change. We observed significant stores of inorganic ammonium in permafrost, up to 40-fold higher than in the active layer. The modelled increase in ALT under the RCP8.5 scenario can result in substantial liberation of N, reaching values up to the order of magnitude of annual fixation of atmospheric N in arctic soils. However, the thaw-induced liberation of N represents only a small flux in comparison with the overall ecosystem N cycling. Copyright © 2017 John Wiley & Sons, Ltd.

Recent Increases in Permafrost Thaw Rates and Areal Loss of Palsas in the Western Northwest Territories, Canada


Decay of palsas can indicate permafrost status, particularly in regions where air temperatures have increased rapidly in recent decades. Using weather data, annual surveys of active-layer thickness, and analyses of high-resolution aerial imagery from the eastern Selwyn/western Mackenzie Mountains, NT, Canada, we show that permafrost temperatures have increased, active layers have deepened, and palsa areal extents have decreased considerably since the 1940s. High-altitude palsas thawed quickly from the 1940s to the 1980s, although some low-altitude palsas have recently decreased rapidly in areal extent due to peat-block calving. The linear rate of increasing active-layer thickness may not be congruent with the non-linear rate of areal loss of palsas. The rapid and episodic collapse of palsas at some sites highlights the necessity to consider hydrology, vegetation cover, landscape position, and morphology in palsa dynamics in addition to a warming climate. Copyright © 2017 John Wiley & Sons, Ltd.

Utilising a Suite of Isotopic and Elemental Tracers to Constrain Cryoturbation Rates and Patterns in a Non-sorted Circle


The empirical quantification of rates of material movement in cryoturbated soils has lagged behind the physical and chemical characterisation of these materials. We applied a novel suite of elemental (C, Hg), stable isotope (13C) and radioisotope (137Cs, 210Pb, 14C, 10Be) tracers in conjunction with analytical and numerical models to constrain the rates and patterns of soil movement due to cryoturbation in a non-sorted circle (NSC) near Abisko, Sweden. We present the first observations of the variability of 10Be across a patterned-ground feature, which facilitate the interpretation of subsurface peaks in soil organic carbon, Hg and 13C and provide constraints on the surficial histories of cryoturbated materials. Apparent rates of surficial lateral movement across the NSC estimated from 137Cs and 210Pb (0–2.55 cm year−1) decreased with distance from its centre and were an order of magnitude greater than rates of subduction and subsurface movement estimated from 14C (0.04–0.27 cm year−1). Novel estimates of the original surficial residence times of cryoturbated parcels based on excess 10Be and Hg inventories ranged from 238 to 3940 years. Our results demonstrate the utility of the spatially explicit application of elemental and radioisotopic tracer suites to constrain cryoturbation rates in Arctic patterned ground. Copyright © 2017 John Wiley & Sons, Ltd.

Cryostratigraphy and the Sublimation Unconformity in Permafrost from an Ultraxerous Environment, University Valley, McMurdo Dry Valleys of Antarctica


The cryostratigraphy of permafrost in ultraxerous environments is poorly known. In this study, icy permafrost cores from University Valley (McMurdo Dry Valleys, Antarctica) were analysed for sediment properties, ground-ice content, types and distribution of cryostructures, and presence of unconformities. No active layer exists in the valley, but the ice table, a sublimation unconformity, ranges from 0 to 60 cm depth. The sediments are characterised as a medium sand, which classifies them as low to non-frost susceptible. Computed tomography (CT) scan images of the icy permafrost cores revealed composite cryostructures that included the structureless, porous visible, suspended and crustal types. These cryostructures were observed irrespective of ground-ice origin (vapour deposited and freezing of snow meltwater), suggesting that the type and distribution of cryostructures could not be used as a proxy to infer the mode of emplacement of ground ice. Volumetric ice content derived from the CT scan images underestimated measured volumetric ice content, but approached measured excess ice content. A palaeo-sublimation unconformity could not be detected from a change in cryostructures, but could be inferred from an increase in ice content at the maximum predicted ice table depth. This study highlights some of the unique ground-ice processes and cryostructures in ultraxerous environments. Copyright © 2017 John Wiley & Sons, Ltd.

Effect of Climate on Morphology and Development of Sorted Circles and Polygons


Sorted circles and polygons are widespread features of periglacial landscapes, but the controls on their development remain poorly understood, impeding their use as palaeoenvironmental indicators. We investigate the relationship of sorted circles and polygons to altitude in the northern Billefjorden area, central Svalbard. The patterns occur in two distinct elevation zones, below 200–250 m asl and above 600 m asl. The higher-elevated patterns have smaller diameters and shallower sorting depths due to a thinner active layer at higher elevations, suggesting that sorted patterns can indicate climate conditions and ground thermal state when the patterns initiated. Geology is believed to be of less importance for pattern morphology in the study area, causing only its fine-scale variations. The pattern diameter-to-sorting depth ratios have a median value of 3.57, consistent with previous studies and theoretical models of patterned-ground formation involving circulation mechanisms. Large-scale sorted patterns may develop over centennial timescales in this high-Arctic environment. They are probably not in equilibrium with present-day climate conditions and have probably formed throughout the Holocene. Copyright © 2017 John Wiley & Sons, Ltd.

Factors Controlling Velocity Variations at Short-Term, Seasonal and Multiyear Time Scales, Ritigraben Rock Glacier, Western Swiss Alps


This study analyses the factors controlling variations in short-term, seasonal and multiyear deformation velocity of an alpine rock glacier from data obtained over periods of 1–20 years. The Ritigraben rock glacier, in the western Swiss Alps, was monitored using tacheometry, terrestrial laser scanning, an in situ global positioning system and borehole deformation measurements. Rock glacier stratigraphy and ground temperature data were obtained from boreholes, and long-term meteorological data (temperature, precipitation, snow water equivalent) from nearby weather stations. Shearing within a distinct water-bearing layer represents the major component of the displacement. Short-term accelerations and seasonal velocity patterns of the rock glacier deformation appear to have been triggered by water supply to this layer. A long-term acceleration of the rock glacier was probably also caused by increased water supply. Permafrost temperature in the rock glacier has increased slightly since 2002, yet no direct causality could be established between this limited warming and rock glacier acceleration. Copyright © 2017 John Wiley & Sons, Ltd.

State of High-Altitude Permafrost on Tropical Maunakea Volcano, Hawaii


One of the most unusual occurrences of sporadic permafrost is on the summit plateau of Maunakea volcano on Hawaii Island, where permafrost was documented in two cinder-cone craters in the 1970s. To investigate the state of this permafrost, we acquired multi-year ground temperature data and conducted electrical resistivity and ground penetrating radar surveys. The two ice bodies still exist, but one has shrunk in volume by an order of magnitude and is expected to disappear soon. The other is still more than 50 m wide. We also prospected the summit region for additional permafrost bodies, based on insolation modelling, temperature probing and geomorphological indicators, but none was found. Permafrost occurs preferentially in the interiors of craters with a closed basin, even though there are exterior slopes that receive less solar radiation annually. Copyright © 2017 John Wiley & Sons, Ltd.

Path-Dependent Frost-Wedging Experiments in Fractured, Low-Permeability Granite


To investigate the mechanism of frost wedging in fractured low-porosity bedrock, we monitored the opening of an artificial 4 mm wide and 80 mm deep crack, cut 20 mm from the end of a rectangular granite block. Two freezing protocols were employed – top-down and bottom-up, the former consisting of short- and long-term variants, lasting 1 and 53 days, respectively. Our results demonstrate that (i) in 1-day experiments, maximum crack widening during top-down freezing is around 0.11 mm, while bottom-up freezing produces only 0.02 mm of deformation; (ii) neither ice nor water pressure causes measurable irreversible crack widening during 1-day tests; (iii) irreversible crack widening is only observed following the 53-day experiment under top-down freezing. Based on these results, we suggest (i) freezing direction plays a key role in determining the magnitude of crack widening; and (ii) freezing duration could be essential for crack propagation. The fracturing is both time-dependent and subcritical; thus, persistent freezing in winter could actually be the active period of crack propagation. This allows us to propose a simplified method to calculate ice pressure according to crack widening. Here we show how freezing direction and duration in ice-filled cracks control the path-dependent efficacy of frost-wedging. Copyright © 2017 John Wiley & Sons, Ltd.

Pleistocene Involutions and Patterned Ground in France: Examples and Analysis Using a GIS Database


A georeferenced database is used to analyse the distribution of Quaternary soft-sediment deformation structures across France. They include features visible in aerial photographs (soil stripes and cells) and features described in cross-section (involutions). Overall, there is no clear relation between the distribution of features and the locations of known faults and earthquakes in available databases. In contrast, the distribution agrees with that of Pleistocene periglacial structures. Most of the soil stripes and cells are located north of 47.5°N, i.e. in the zone of ice-wedge pseudomorphs, and can be interpreted as deformation structures of an active layer in permafrost terrain. The height of the involutions is influenced by the nature of the filling, the substrate and latitude. Deformation structures are larger in coarse material, reflecting the role of drainage and thermal conductivity. Their height increases northward to ca. 2 m at 48°N. This is thought to reflect the increase in thickness of the layer subjected to freeze–thaw cycles. Bowl-shaped structures separated by coarse pillars, which correspond to soil stripes seen in section, have formed on slopes in settings unfavourable to the generation of high pore-water pressure. Their genesis is probably related to differential frost heave. Ball-and-pillow structures and diapirs are common in flat and poorly drained terrain, and formed by liquefaction and sometimes fluidisation in a periglacial setting. Copyright © 2017 John Wiley & Sons, Ltd.

Palaeoenvironmental Proxies for Permafrost Presence During the Younger Dryas, Central Poland


Involutions and small frost fissures have been recorded over a wide area of the lower terrace of the Warta River valley (central Poland). They developed at the lithological boundary between an organic-rich deposit with a thin peat layer (unit b) and an underlying fluvial sandy deposit (unit a). Most of the involutions are products of a reversed density gradient and loading, or developed under the influence of cryohydrostatic pressure. Among them are drop-like and flat-bottomed structures, diapirs, flame-like and fold structures and irregular involutions. Some frost fissures have also been recorded in the same stratigraphic position. The sedimentological properties and formative mechanism of the involutions, together with environmental data (lithology, groundwater conditions, snow cover and vegetation), reveal their origin as periglacial. Radiocarbon dating indicates that the structures formed during the Younger Dryas. Overall, the involutions and frost fissures indicate that permafrost re-aggraded in this region of central Poland during the Younger Dryas. Copyright © 2017 John Wiley & Sons, Ltd.

Microtextural Inheritance on Quartz Sand Grains from Pleistocene Periglacial Environments of the Mazovian Lowland, Central Poland


Sand grains from Quaternary glacial, aeolian and fluvial deposits in the Mazovian Lowland, central Poland, were examined to characterize the effects of different Quaternary processes on sand-grain surfaces that experienced repeated cycles of intense polar-desert-like conditions during the Middle and Late Pleistocene. A cold, dry and windy periglacial environment prevailed here at least twice between the Saalian (Marine Isotope Stage (MIS) 6) and Holocene (MIS 1) stages. Because the surface characteristics of quartz sand grains can provide important palaeoenvironmental information, we examined grains extracted from sediment samples in different landforms to determine their surficial features from scanning electron microscope images. The grain surfaces were dominated by microtextures characteristic of aeolian-induced grain transformation, indicated by a high percentage of well-rounded, low-relief-worn grains with dish-shaped depressions, bulbous edges and upturned plates. Although remnants of previous sedimentary cycles were occasionally observed, aeolian effects were dominant even in glacial and fluvial settings. Quartz microtextures indicated that none of the examined grains represented their original setting, but rather suggested remobilisation under periglacial conditions. Copyright © 2017 John Wiley & Sons, Ltd.

Very Large Cryoturbation Structures of Last Permafrost Maximum Age at the Foot of Qilian Mountains (NE Tibet Plateau, China): a Discussion


Intensely cold conditions occurred during part of the last major glaciation of the mountains and Qinghai–Tibet Plateau in northeast China but their chronology is constrained by few limiting ages. At the Mengyuan section, on the northeastern margin of the Qilian Mountains, sandy silt provided three OSL ages that suggest deposition during a very cold, dry period in northeastern China between c. 29 and 19 ka (early part of marine isotope stage (MIS) 2). Load-casting into the underlying outwash gravel occurred during climate amelioration. In some cases, the sandy silt infilled the spaces left by underlying thawing blocks of ice without collapse of the surrounding gravel. The gravel must therefore be older than c. 30 ka and was probably deposited by outwash from glaciers on the higher parts of the Qilian Mountains during MIS 3. Included in them were buried contemporaneous or remnant blocks of glacial ice. Subsequently the surface became flat by unknown processes and was finally covered by a thin loess dating from 2.7 ka, indicating it was deposited in the first warmer period in the Neoglacial sequence of events. Thus, the last major cold event spanned the period through isotope stages 2 and 3 in this area (57 to c. 19 ka), during which the dominant effects of glaciation of the mountain tops were replaced by intensely dry, cold permafrost conditions for c. 10 ka. Copyright © 2017 John Wiley & Sons, Ltd.