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Nivation, the suite of weathering and transportation processes attributed to late-lying snowpatches, is linked to the formation of cryoplanation terraces (CTs). CTs resemble giant staircases arrang...

Cryoplanation terraces (CTs) are large (3000–800 000 m2) erosional landforms found in upland periglacial environments. Two hypotheses for the formation of CTs are supported in contemporary literature: (1) CT formation is controlled primarily by geologic structure; and (2) CTs are climatically controlled through nivation, a suite of erosional processes associated with late-lying snowbanks. A persistent question in periglacial geomorphology is whether nivation can produce CT-scale landforms. This paper examines the unusual deglaciation history of “Frost Ridge” on the Cathedral Massif, northwestern British Columbia, to estimate long-term denudation attributable to nivation processes active since the last glacial maximum. Frost Ridge forms one flank of an east–west-oriented glacial valley. During deglaciation, marginal drainage created V-shaped erosional notches on both valley walls. Minimization of solar radiation on the steep north-facing wall (Frost Ridge) allowed snowbanks to accumulate and persist in the marginal drainage features and nivation processes to erode the slope. Today, several large nivation hollows (incipient CTs) are present near the summit of Frost Ridge, while the V-shaped marginal drainage features are preserved at lower elevations and on the opposite, south-facing valley wall. A high-resolution survey using an unmanned aerial vehicle (UAV) allowed volumes of marginal drainage and incipient terrace features to be compared. Based on this volumetric comparison, denudation rates are estimated to range from 4.2 to 125.8 mm/kyr, which are comparable with relatively short-term nivation rates reported from Antarctica and mid-latitude alpine periglacial areas.

Cryoplanation terraces are prominent but enigmatic landforms found in present and past periglacial environments. Geomorphologists have debated for more than a century over processes involved in the formation of these elevated, step-like, bedrock features. Presented here are the first numerical surface exposure ages and scarp retreat rates from cryoplanation terraces in the Yukon-Tanana Upland (YTU) in Alaska, part of unglaciated eastern Beringia, obtained from terrestrial cosmogenic nuclides (TCN) in surface boulders. Ages comprise six 10Be TCN ages from two terrace treads near Eagle Summit and six 36 Cl ages from two treads on Mt. Fairplay. Based on these exposure ages, scarps at both locations were last actively eroding from 49 to 22.4 ka. Both locations exhibit time-transgressive development, particularly near scarp-tread junctions. Boulder exposure ages and distances between sampled boulder locations were used to estimate scarp retreat rates of 0.11 to 0.56 cm/yr. These numerical exposure ages presented here demonstrate that the cryoplanation terraces in the YTU are diachronous surfaces actively eroding during multiple cold intervals. With these results, hypotheses for cryoplanation terrace formation are discussed and evaluated for the YTU, including those based on geologic structure, nivation, and the influence of permafrost.

Cryoplanation terraces (CTs) are large, staircase-like erosional features found in upland periglacial environments throughout the circum-Arctic region. They are ubiquitous in unglaciated Beringia. This presentation summarizes recent research on these features conducted in interior and western Alaska and northwestern British Columbia. The work falls into several categories:(1) Relative dating: Relative weathering indices (fracture counts, Cailleux roundness and flatness, Krumbein sphericity, rebound, and weathering rind thickness) were measured at a series of sites extending across eastern Beringia. Patterns of these indices indicate that inner treads were more recently exposed than distal locations. A model of time-transgressive CT development through nivation-driven scarp retreat addresses the removal of weathered material from terrace treads down side slopes through piping and gravity-driven mass-wasting processes.(2) Absolute dating: Several 10Be and 36Cl Terrestrial Cosmogonic Nuclide ages reveal that terrace scarps in the Alaskan Yukon-Tanana Upland were last actively eroding during the last glacial maximum (LGM). CT treads exhibit time-transgressive development. Boulder exposure ages and distances between sampled boulder locations were used to estimate rates of scarp retreat. The numerical exposure ages demonstrate that CTs are diachronous surfaces actively eroding during multiple cold intervals.(3) Landscape evolution: The unusual deglaciation history of “Frost Ridge” in northwestern British Columbia facilitates estimation of long-term denudation attributable to nivation processes since the LGM. Snowbanks accumulated and persisted in marginal drainage features on the ridge’s north-facing ridge flank, creating a series of CTs through nivation. Data obtained from an unmanned aerial vehicle were used to estimate the volumes of eroded material. Estimated erosion rates are comparable to short-term nivation rates reported from Antarctica and mid-latitude alpine periglacial areas.(4) Process monitoring: Soil thermal and moisture records, particle-size analysis, apparent thermal diffusivity calculations, and sediment-deposition patterns were used to examine periglacial processes operating on two active CTs. The coarse portions of sorted stripes function as underground channels (pipes) for sediment transportation across CT treads by flowing water. Late-lying snowbank environments are highly dynamic during warm weather, with large amounts of sediment transported over short periods.(5) Geomorphometry: Semi- and fully automated recognition algorithms (CTAR) were applied to high-resolution DEMs to identify the locations of CTs. CTAR achieved an overall accuracy of 90 percent. A strong linear relation exists between the size of CTAR-delimited terraces and those identified in a previous study. Hypsometric analysis was applied over extensive areas of eastern Beringia. Glaciated areas have hypsometric signatures distinctly different than those of cryoplanated terrain, across a spectrum of geographical scale. Results from fluvial morphometric analysis of a sorted-stripe field verifies the origins of such networks and their effectiveness for transporting water and suspended sediment across CT surfaces.(6) Climatic dependencies: Geospatial analysis involving nearly 700 CTs in eastern Beringia demonstrates that their elevation rises from Bering Sea islands to the Alaska-Canada border at rates nearly identical to those of Wisconsinan cirques, indicating close genetic links between the two classes of feature. Cryoplanation terraces can be considered the periglacial equivalent of glacial cirques.

The maximum depth of seasonal thaw is a critical design factor for civil infrastructure in permafrost regions. Although maps of active-layer thickness (ALT) have been created for localized areas in...

Palsa-scale frost mounds have great potential in paleoecological studies and for monitoring the effects of global change on permafrost in peatlands of the northern hemisphere. Incorporation of such applications into the larger scientific enterprise is jeopardized, however, by the overly complex and exotic terminology employed by periglacial geomorphologists. The term palsa should be used only in a morphologic context but can be modified adjectivally to communicate genetic information. Palsa-scale frost mounds can be divided into four genetic categories: ice-segregation, hydrostatic, hydraulic, and buoyant. Criteria for recognition of the genetic varieties include stratigraphy, ice fabrics, and patterns of ionic concentration and bubble inclusions. Palsas may be of aggradational or degradational origin, although these distinctions may be blurred in some cases.

Cryoplanation terraces are large erosional landforms common in cold, unglaciated mountainous environments. Terrace sequences are composed of alternating slope segments with gently sloping treads and steep rubble-covered risers, and culminate in extensive summit flats. Many unglaciated upland landscapes in eastern Beringia are dominated by these landforms. Indirect evidence indicates that they evolve through locally intensified weathering and mass-movement processes associated with late-lying snowcover. Geospatial analysis involving nearly 700 cryoplanation terraces in eastern Beringia demonstrates that their elevation rises from 175 to 350 masl on Bering Sea islands to median values > 1200 m near the Alaska-Canada border. The regional trends of cryoplanation terrace elevation are nearly identical to those of Wisconsinan cirques on several transects across Alaska. The consistency in the elevation trends of glacial cirques and cryoplanation terraces indicates close genetic links between the two classes of feature, involving topographic position, continentality gradients, and the mass balance of localized snow accumulations. Cryoplanation terraces can be considered the periglacial analogs of glacial cirques, and have greater potential as sources of paleoclimatic information than smaller periglacial features more sensitive to short-term climate variations. Process-oriented studies, age determinations, and high-resolution mapping are needed before the paleoenvironmental potential of these landforms can be realized fully.

John Ross Mackay, President of the Association of American Geographers in 1969–1970, died peacefully on 28 October 2014. With his passing, the geographical and permafrost research communities lost one of their foremost scientists. Ross was an exemplary field observer, an insightful theoretician, a prodigious author, and an esteemed mentor.

Arctic earth surface systems are undergoing unprecedented changes, with permafrost thaw as one of the most striking examples. Permafrost is critical because it controls ecosystem processes, human activities, and landscape dynamics in the north. Degradation (i.e. warming and thawing) of permafrost is related to several hazards, which may pose a serious risk to humans and the environment. Thaw of ice-rich permafrost increases ground instability, landslides, and infrastructure damages. Degrading permafrost may lead to the release of significant amounts of greenhouse gases to the atmosphere and threatens also biodiversity, geodiversity and ecosystem services. Thawing permafrost may even jeopardize human health. Consequently, a deeper understanding of the hazards and risks related to the degradation of permafrost is fundamental for science and society.To address climate change effects on infrastructure and human activities, we (i) mapped circumpolar permafrost hazard areas and (ii) quantified critical engineering structures and population at risk by mid-century. We used observations of ground thermal regime, geospatial environmental data, and statistically-based ensemble methods to model the current and future near-surface permafrost extent at ca. 1 km resolution. Using the forecasts of ground temperatures, a consensus of three geohazard indices, and geospatial data we quantified the amount and proportion of infrastructure elements and population at risk owing to climate change. We show that ca. 70% of current infrastructure and population in the permafrost domain are in areas with high potential for thaw of near-surface permafrost by 2050. One-third of fundamental infrastructure is located in high hazard regions where the ground is susceptible to thaw-related ground instability. Owing to the observed data-related and methodological limitations we call for improvements in the circumpolar hazard mappings and infrastructure risk assessments.To successfully manage climate change impacts and support sustainable development in the Arctic, it is critical to (i) produce high-resolution geospatial datasets of ground conditions (e.g., content of organic material and ground ice), (ii) develop further high-resolution permafrost modelling, (iii) comprehensively map permafrost degradation-related hazards, and (iv) quantify the amount and economic value of infrastructure and natural resources at risk across the circumpolar permafrost area.

Ice cellars are a natural form of refrigeration constructed within permafrost. They are traditionally employed by indigenous Arctic peoples to store harvested wildlife. Recent reports from Alaska i...

In some regions underlain by ice-rich permafrost, a consistent, long-term increase in ALT under changing climatic conditions is not supported by observations. The apparent lack of ALT may be attributed to soil consolidation from thawing of the uppermost ice-rich permafrost and subsidence of the ground surface. Four plots established in 1962 at Barrow, Alaska, were re-instrumented in 2003 and surveyed annually using differential GPS technology, accompanied by active-layer probing. Elevation change from 1962 to 2003 was within the interannual variability of the 2003–15 period, indicating net stability in the area. Over the 2003–15 period, however, all four plots experienced subsidence trends of 0.4–1.0 cm/year, resulting in a net elevation change of 8–15 cm. Warmer winters and increased snow depth during this period decreased the potential for frost heave. Warmer summers resulted in thaw penetration into the ice-rich transient layer and ice wedges, leading to the net subsidence in recent years. Copyright © 2016 John Wiley & Sons, Ltd.

Prior to development of the Circumpolar Active Layer Monitoring (CALM) programme, little attention was paid to formal spatial sampling designs for measuring active-layer thickness (ALT). This omission made the accuracy of many data-sets questionable, in part because spatial periodicities caused by landscape features such as ice-wedge polygons and thaw lakes can significantly influence the depth of thaw. Early in the development of CALM's protocols, ALT was sampled in the continuous permafrost zone in northern Alaska and simulated by computer, to determine how ALT could be measured accurately. The simulated and field data-sets were analysed by comparing the means, variances and frequency distributions obtained using four spatial sampling designs (random, systematic, systematic random and systematic stratified unaligned). By a small margin, systematic stratified unaligned sampling provided the most accurate results. Systematic designs can, however, provide adequate estimates of the statistical moments of ALT with significant savings in cost, time and ease of implementation. Based on these results, the CALM programme recommended use of 10 x 10, 100 x 100 or 1000 x 1000 m grids, with sampling intervals of 1, 10 and 100 m, respectively. Most probed CALM sites now employ this strategy, except in terrain with unusual landscape elements or other special constraints. Copyright © 2016 John Wiley & Sons, Ltd.

Ongoing climate change is causing fundamental changes in the Arctic, some of which can be hazardous to nature and human activity. In the context of Earth surface systems, warming climate may lead to rising ground temperatures and thaw of permafrost. This Data Descriptor presents circumpolar permafrost maps and geohazard indices depicting zones of varying potential for development of hazards related to near-surface permafrost degradation, such as ground subsidence. Statistical models were used to predict ground temperature and the thickness of the seasonally thawed (active) layer using geospatial data on environmental conditions at 30 arc-second resolution. These predictions, together with data on factors (ground ice content, soil grain size and slope gradient) affecting permafrost stability, were used to formulate geohazard indices. Using climate-forcing scenarios (Representative Concentration Pathways 2.6, 4.5 and 8.5), permafrost extent and hazard potential were projected for the 2041–2060 and 2061–2080 time periods. The resulting data (seven permafrost and 24 geohazard maps) are relevant to near-future infrastructure risk assessments and for targeting localized geohazard analyses.

[1] Observations in undisturbed terrain within some regions of the Arctic reveal limited correlation between increasing air temperature and the thickness of the seasonally thawed layer above ice-rich permafrost. Here we describe landscape-scale, thaw-induced subsidence lacking the topographic contrasts associated with thermokarst terrain. A high-resolution, 11 year record of temperature and vertical movement at the ground surface from contrasting physiographic regions of northern Alaska, obtained with differential global positioning systems technology, indicates that thaw of an ice-rich layer at the top of permafrost has produced decimeter-scale subsidence extending over the entire landscapes. Without specialized observation techniques the subsidence is not apparent to observers at the surface. This “isotropic thaw subsidence” explains the apparent stability of active layer thickness records from some landscapes of northern Alaska, despite warming near-surface air temperatures. Integrated over extensive regions, it may be responsible for thawing large volumes of carbon-rich substrate and could have negative impacts on infrastructure.

Increasing urbanization and development in the Arctic may exacerbate the local impacts of climate warming in areas underlain by permafrost. As part of the Barrow Urban Heat-Island Study (BUHIS), hourly air and near-surface soil temperatures (5 cm depth) were collected at 66 sites in and near Barrow, Alaska. Comparison of near-surface soil temperatures, categorized by land-cover type, revealed that urban temperatures in each category were higher than those in corresponding units of the surrounding undeveloped area. Mean summer soil-surface temperatures within comparable land-cover units were 0.3–2.3°C higher in the urban area. Active-layer thickness was greater by 15–40 cm at the urban sites than at locations with similar vegetation in the rural portions of the study area. Engineering criteria established from measurements made at ‘rural’ meteorological sites or from general maps of a large region may assume colder soils than are actually present, raising the possibility that inappropriate design ...

Increases in air temperature have occurred in most parts of the Arctic in recent decades. Corresponding changes in permafrost and the active layer have resulted in decreases in ground-bearing capacity, which may not have been anticipated at the time of construction in permafrost regions. Permafrost model was coupled with empirically derived solutions adopted from Soviet and Russian construction standards and regulations to estimate the bearing capacity of foundations under rapidly changing climatic conditions, in a variety of geographic and geologic settings. Changes in bearing capacity over the last 40 years were computed for large population and industrial centers within different physiographic and climatic conditions of the Russian Arctic. The largest decreases were found in city of Nadym, where the bearing capacity has decreased by more than 40%. A smaller, but considerable decrease of approximately 20% was estimated for Yakutsk and Salekhard. Spatial model results at a regional scale depict ...

The active layer plays an important role in the functioning of environmental ecosystems and affects many human activities in the polar regions. Regional assessments and predictions of this parameter are critical for many physical and social applications. Large heterogeneity in near-surface permafrost characteristics, including the active layer, even over small distances, creates serious constraints to their evaluation across large geographic extents. Discrepancies between modeled climatic fields add to the uncertainties associated with predicting active-layer thickness (ALT) at regional scales. This study uses a stochastic approach, in combination with an equilibrium permafrost model, to map the geographic distribution of ALT and near-surface permafrost temperature on the North Slope of Alaska. GIS techniques are used to determine the spatial variabilityof ecosystem factors controlling the ground thermal regime within each grid cell of the permafrost model. To incorporate the uncertainty associated with t...

A climate-monitoring network was implemented in a large private preserve along the southern shore of Lake Superior. The network uses a dense sampling design to assess the spatial and temporal influence of a large, cold body of water on adjacent terrestrial surfaces. Based on a 3-year record, near-shore sites are 1–2°C cooler than sites 5 km inland in spring and summer, and 1°C warmer in winter. Near the shore, winds are from the NNW most of the year, and are much stronger in winter. Inland, southwesterly flow is typical and overall wind velocity is lower and more consistent. This decoupling is attributable to the influence of the Huron Mountains, a topographic barrier that restricts the lake effect to a narrow coastal zone. A 2-year record of hourly air temperature measurements from 26–30 sites across the study area demonstrates that the mean daily temperature can differ by as much as 11°C, but the average difference is 2.5–3.0°C.

A significant portion of the Tibetan Plateau is underlain by permafrost, and is highly sensitive to climate change. Observational data from recent Chinese investigations on permafrost degradation and its environmental effects in the Tibetan region indicate that a large portion of the Tibetan Plateau has experienced significant warming since the mid-1950s. The air temperature increase is most significant in the central, eastern, and northwestern parts of the Plateau. The warming trend in the cold season was greater than that in the warm season. The duration of seasonal ground freezing has shortened due to the air temperature increase in winter. Numerical simulations indicate that air temperature on the Plateau will continue to increase in the 21st century. Significant warming has resulted in extensive degradation of permafrost. Over the last 30 years, a 25 m increase in the lower altitudinal occurrences of permafrost has taken place in the north. In the south the increase is 50–80 m over the past 20 years. Active-layer thickness and mean annual ground temperature have increased by 0.15–0.50 m during 1996–2001 and by 0.1–0.5 °C during the last 30 years on the Tibetan Plateau, respectively. Widespread permafrost degradation has already caused environmental deterioration. Extensive desertification processes are apparent in the eastern and western portions of the Tibetan Plateau, with the area occupied by desert increasing annually by about 1.8%. With rapid retreat and thinning of permafrost, large carbon pools sequestered in permafrost could be released to increase net sources of atmospheric carbon, creating a positive feedback and accelerated warming. Damage to human infrastructure is also caused by frost heave, thaw settlement, and thaw slumping in the permafrost-affected region. The impact of permafrost degradation on energy and water exchange processes between the ground and atmosphere require further examination. Large-scale intensive monitoring networks, remote sensing investigations, and models for frozen soil are needed to clarify regional details of climate change, permafrost degradation, and their environmental effects.

Ground-penetrating radar (GPR) has considerable potential for the detection and identification of sediment-filled wedges and relict polygonal patterns in mid-latitude areas. Relict cryogenic macrostructures have been described previously both within and outside the maximum extent of the Late Wisconsinan glacial border in many regions of the USA. The features were formed under climatic conditions associated with permafrost and periglacial conditions and provide evidence of climate change. In this study, buried relict cryogenic macrostructures were identified with GPR. On some two-dimensional GPR (2D GPR) records, boundaries with the host materials are indistinguishable or blurred resulting in the features being overlooked, misinterpreted and/or imprecisely delineated. Three-dimensional GPR (3D GPR) was able to delineate buried networks of sediment-filled wedges and provided more meaningful information than 2D radar records. When supplemented with adequate ground-truth observations, GPR offers considerable potential for imaging, interpreting and mapping near-surface cryogenic macrostructures in former periglacial environments. Copyright © 2009 John Wiley & Sons, Ltd.

Thawing permafrost and the resulting microbial decomposition of previously frozen organic carbon (C) is one of the most significant potential feedbacks from terrestrial ecosystems to the atmosphere in a changing climate. In this article we present an overview of the global permafrost C pool and of the processes that might transfer this C into the atmosphere, as well as the associated ecosystem changes that occur with thawing. We show that accounting for C stored deep in the permafrost more than doubles previous high-latitude inventory estimates, with this new estimate equivalent to twice the atmospheric C pool. The thawing of permafrost with warming occurs both gradually and catastrophically, exposing organic C to microbial decomposition. Other aspects of ecosystem dynamics can be altered by climate change along with thawing permafrost, such as growing season length, plant growth rates and species composition, and ecosystem energy exchange. However, these processes do not appear to be able to com...

An increase in snow cover on the Tibetan Plateau has been observed over the past 50 years. The frequency of snow disasters on the Plateau has also increased. Much of the Qinghai-Xizang (Tibetan) Plateau is underlain by permafrost. Some observation sites of the GEWEX Asian Monsoon Experiment (GAME)-Tibet are located in the Naqu-Anduo

Three-dimensional ground-penetrating radar (3D GPR) was used to investigate the subsurface structure of ice-wedge polygons and other features of the frozen active layer and near-surface permafrost near Barrow, Alaska. Surveys were conducted at three sites located on landscapes of different geomorphic age. At each site, sediment cores were collected and characterised to aid interpretation of GPR data. At two sites, 3D GPR was able to delineate subsurface ice-wedge networks with high fidelity. Three-dimensional GPR data also revealed a fundamental difference in ice-wedge morphology between these two sites that is consistent with differences in landscape age. At a third site, the combination of two-dimensional and 3D GPR revealed the location of an active frost boil with ataxitic cryostructure. When supplemented by analysis of soil cores, 3D GPR offers considerable potential for imaging, interpreting and 3D mapping of near-surface soil and ice structures in permafrost environments. Copyright © 2007 John Wiley & Sons, Ltd.

Locational data for 96 allochthonous blockfields distributed throughout the Appalachian Mountains of eastern USA were obtained using TerraServer, an online resource for viewing air-photo and satellite imagery. The elevation of Appalachian blockfields south of the Last Glacial Maximum (LGM) border parallels regional gradients of contemporary mean July, summer and annual temperature. Mean July temperature reductions inferred from palaeoecological studies indicate that the median elevation of blockfields throughout the Appalachians lay at or above timberline during the LGM. Palaeotemperatures calculated using known Appalachian lapse rates and published LGM temperature departures indicate that most blockfields in the study area were formed under climatic conditions conducive to permafrost. Allochthonous blockfields in the Appalachians appear to be constituent elements of periglacial ‘form communities’. Internet-based map products can be used to create generalised reconnaissance-level geomorphic data bases over large areas. Complementary use of these resources and spatial-analytic techniques holds considerable potential for addressing the broad-scale problems with which traditional climatic geomorphology is concerned. Copyright © 2007 John Wiley & Sons, Ltd.

This study is presented against the background that climate warming is predicted to continue in much of the Arctic through the next century and that small greenhouse chambers have been used widely to warm tundra communities in order to forecast climate-related changes. It reports results from up to 8 years of experimental warming with ∼1 m2 open-top chambers (OTCs) at four tundra communities near Barrow (71°18′N, 156°40′W) and Atqasuk (70°29′N, 157°25′W) in northern Alaska. Between 1994 and 2002 the OTCs increased the mean growing season air temperature by between 0.6 and 2.2°C, depending on the site and year. The change in average July soil temperature recorded over 3 years at 10 cm depth due to the OTCs varied between −0.8 and 0.7°C, depending on the site. Changes in soil temperature did not result in detectable differences in thaw depth at any site. This is interpreted to be the result of the small size of the OTCs and possibly changes in vegetation. The differences in warming profiles between...

The Arctic climate is changing. Permafrost is warming, hydrological processes are chang- ing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates con- vincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and pro- cesses influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show

The dominant landscape process on the Arctic Coastal Plain of northern Alaska is the formation and drainage of thaw lakes. Lakes and drained thaw-lake basins account for approximately 75% of the modern surface expression of the Barrow Peninsula. The thaw-lake cycle usually obliterates lacustrine or peat sediments from previous cycles, which could otherwise be used for paleoecological reconstruction of long-term landscape and vegetation changes. Several possible erosional remnants of a former topographic surface that predates the formation of the thaw lakes have been tentatively identified. These remnants are characterized by a higher elevation, a thick organic layer with very high ground ice content in the upper permafrost and a plant community somewhat atypical of the region. Ten soil cores were collected from one site, and one core was intensively sampled for soil organic carbon content, pollen analysis and 14C dating. The lowest level of the organic sediments represents the earliest phase of plant growth and dates to ca. 9000 cal BP. Palynological evidence indicates the presence of mesic shrub tundra (including sedge, birch, willow and heath vegetation), and microfossil indicators point to wetter eutrophic conditions during this period. Carbon accumulation was rapid due to high net primary productivity in a relatively nutrient-rich environment. These results are interpreted as the local response to ameliorating climate during the early Holocene. The middle Holocene portion of the record contains an unconformity, indicating that between 8200 and 4200 cal BP sediments were eroded from the site, presumably in response to wind activity during a drier period centered around 4500 cal BP. The modern vegetation community of the erosional remnant was established after 4200 cal BP and peat growth resumed. During the late Holocene, carbon accumulation rates (CARs) were greatly reduced in response to the combined effects of declining productivity associated with climatic cooling, and increased nutrient stress as paludification and permafrost aggradation sequestered mineral nutrients.

Research treating permafrost-climate interactions is traditionally based on a two-layer conceptual model involving a seasonally frozen active layer and underlying perennially frozen materials. This conceptualization is inadequate to explain the behaviour of the active-layer/permafrost system over long periods, particularly in ice-rich terrain. Recent research in North America supports earlier Russian conclusions about the existence of a transition zone that alternates in status between seasonally frozen ground and permafrost over sub-decadal to centennial time scales. The transition zone is ice-enriched, and functions as a buffer between the active layer and long-term permafrost by increasing the latent heat required for thaw. The existence of the transition zone has an impact on the formation of a cryogenic soil structure, and imparts stability to permafrost under low-amplitude or random climatic fluctuations. Despite its importance, the transition zone has been the focus of relatively little research. The impacts of possible global warming in permafrost regions cannot be understood fully without consideration of a more realistic three-layer model. The extensive data set under development within the Circumpolar Active Layer Monitoring (CALM) program will provide a significant source of information about the development, characteristics, behaviour, and extent of the transition zone. This paper is focused on the uppermost part of the transition zone, which joins the active layer at sub-decadal to multi-centennial time scales. This upper part of the transition zone is known as the transient layer. Copyright © 2005 John Wiley & Sons, Ltd.

Landsat-7 ETM + scenes were acquired for the western Arctic Coastal Plain of Alaska extending from 152° to 162° W longitude. A segmentation algorithm was used to classify lakes and drained thaw lake basins (DTLBs) exceeding 1 ha in size. A total of 13,214 lakes and 6539 DTLBs were identified. Several indices were obtained from the image processing software and used for a comparative analysis of lakes and basins including object size, goodness of elliptic fit, shape complexity, shape asymmetry, and orientation of the major axis. Nonparametric statistical analyses indicate that lakes and basins share similar orientation only. Three subregions of the western Arctic Coastal Plain were identified based on landscape age, as demarcated by ancient shorelines. The surfaces become progressively older inland and include the Younger Outer Coastal Plain, the Outer Coastal Plain, and the oldest Inner Coastal Plain. Lakes and basins in all subregions have statistically similar orientation, indicating that summer wind direction has not changed appreciably over the past several thousand years. Basin orientation is less clustered than lake orientation. Lakes are highly elliptical, while basins have more complex shapes. Lake coverage (%) is fairly constant across the three subregions, while DTLB coverage decreases on older surfaces. Lake and basin size decreases on progressively older surfaces, but the number of features per unit area increases. It is uncertain if surface age is responsible for differences in regional metrics as an analysis of the Inner Coastal Plain demonstrates significant internal variation. Distance from the coast, ground ice content, surficial sediments, and local relief may also influence lake morphometry. Copyright © 2005 John Wiley & Sons, Ltd.

The coastal village of Barrow, Alaska (71.3° N, 156.5° W) is the northernmost settlement in the United States. With 4000 residents, it is also the largest native community in the circumarctic region. Installation of the 67-site Barrow Urban Heat Island Study network in 2001 facilitated a detailed examination of the spatial characteristics of summer air temperature within a 150 km 2 area incorporating Barrow and its surroundings. Although the summers of 2001 and 2002 were climatologically unusual, the record clearly illustrates the control of a local maritime gradient, as well as a close correspondence between temperature distribution and wind regime. In contrast to the situation in winter, the effects of local urban infrastructure on air temperatures were relatively minor during these summers, compared to those of maritime and wind influences.

Wedge-like sedimentary structures at two sites in northern Delaware USA are located at the erosional surface of, and extend into, channel deposits of the fluvial, mid-Pleistocene Columbia Formation. The wedges are 0.25–0.60 m wide at the top, 1.0–1.5 m in vertical extent, contain moderate to poorly sorted, and vertically-stratified sediment, and are overlain unconformably by a layer of wind-blown silt. Several hypotheses for the formation and infill of the wedges were evaluated using detailed physical, stratigraphic, and sedimentological information. The most likely explanation for the features is that they are relict cryogenic structures formed by thermal-contraction cracking in permafrost, and filled with wind-blown sediments derived from the Columbia Formation. The wedges are believed to have formed in the tundra environment that existed in northern Delaware, south of the Laurentide Ice Sheet, during the coldest parts of the Wisconsinan glaciation. Copyright © 2004 John Wiley & Sons, Ltd.

Samples of fabric data collected from periglacial solifluction lobes in central Alaska show a systematic, positive relation between clast axial ratio and fabric strength. Samples composed of clasts with low a:b axial ratios have relatively low fabric strength. Restricting sampling to clasts with axial ratios of 1.5:1 or higher increases fabric strength and decreases its variability. To enhance comparability between fabric studies and the utility of fabric interpretation, sampling should be restricted to clasts with relatively large (≥ 1.5:1) axial ratios.

Thaw lakes and drained thaw lake basins are ubiquitous on the Arctic Coastal Plain of Alaska. Basins are wet depositional environments, ideally suited for the accumulation and preservation of organic material. Much of this soil organic carbon (SOC) is currently sequestered in the near-surface permafrost but, under a warming scenario, could become mobilized. The relative age of 77 basins on the Barrow Peninsula was estimated using the degree of plant community succession and verified by radiocarbon-dating material collected from the base of the organic layer in 21 basins. Using Landsat-7+ imagery of the region, a neural network classifying algorithm was developed from basin age-dependent spectra and texture. About 22% of the region is covered by 592 lakes (>1 ha), and at least 50% of the land surface is covered by 558 drained lake basins. Analysis of cores collected from basins indicates that (1) organic layer thickness and the degree of organic matter decomposition generally increases with basin ...