Characteristics Of Ground Ice Research Articles

Rapid transformation of tundra ecosystems from ice-wedge degradation

Ice wedges are a common form of massive ground ice that typically occupy 10–30% of the volume of upper permafrost in the Arctic and are particularly vulnerable to thawing from climate warming. In assessing the patterns and rates of ice-wedge degradation in northeastern Alaska, we found degradation was widespread and rapidly transforming the microtopography, hydrology, soils, ground ice, and vegetation of tundra ecosystems through a sequence of degradation and stabilization stages. Across an extensive mapping area (30 km2), thermokarst troughs and pits with open water (degradation-advanced) covered 0.7% overall and 1.6% in the oldest terrain in 2018. Within an area (0.5 km2) of concentrated thermokarst, undegraded and degraded ice wedges together covered 29% of the area, and all degradation stages combined increased from 2% in 1950 to 19% area in 2018. Initial degradation peaked at 9% in 2000 and initial stabilization was trending upward at 12% area in 2018, indicating slowing degradation and a transition to stabilization. Integration and reorganization of the drainage network as troughs expanded and connected reduced impounded surface water and helped slow degradation. Degradation created large changes in microtopography, trough widths, water depths, depth to wedge ice, pH, soil and ground ice characteristics, and thermal regimes among stages. Community composition completely shifted from dominance of deciduous and evergreen shrubs in tussock tundra in the undegraded stage to dominance of aquatic mosses and forbs in flooded depressions in degradation-advanced stage. Soil slumping along trough margins and rapid colonization by aquatic mosses halted the degradation, and aquatic sedges became dominant in the stabilization-initial stage. In stabilization-advanced, aquatic mosses persisted and the diversity of wet-adapted forbs, sedges, and mosses increased. Recovery back to tussock tundra, however, is unlikely. This decadal-scale transformation has major implications for arctic land cover, tundra productivity, lake expansion and drainage, soil‑carbon balance, trace-gas emissions, and caribou and bird populations.

Spatial and stratigraphic variation of near‐surface ground ice in discontinuous permafrost of the taiga shield

AbstractThe acceleration of permafrost thaw due to warming, wetting, and disturbance is altering circumpolar landscapes. The effect of thaw is largely determined by ground ice content in near‐surface permafrost, making the characterization and prediction of ground ice content critical. Here we evaluate the spatial and stratigraphic variation of near‐surface ground ice characteristics in the dominant forest types in the North Slave region near Yellowknife, Northwest Territories, Canada. Physical variation in the permafrost was assessed through cryostructure, soil properties, and volumetric ice content, and relationships between these parameters were determined. Near‐surface ground ice characteristics were contrasted between forest types. In black spruce forests the top of the permafrost was ice‐rich and characterized by lenticular and ataxitic cryostructures, indicating the presence of an intermediate layer. Most white spruce/birch forests showed similar patterns; however, an increase in the active layer thickness and permafrost thaw at some sites have eradicated the transition zone, and the large ice lenses encountered at depth reflect segregated ground ice developed during initial downward aggradation of permafrost. Our findings indicate that white spruce/birch terrain will be less sensitive than black spruce forests to near‐surface permafrost thaw. However, if permafrost thaws completely, white spruce/birch terrain will probably be transformed into wetland–thaw lake complexes due to high ground ice content at depth.

Long‐term recovery patterns of arctic tundra after winter seismic exploration

In response to the increasing global demand for energy, oil exploration and development are expanding into frontier areas of the Arctic, where slow-growing tundra vegetation and the underlying permafrost soils are very sensitive to disturbance. The creation of vehicle trails on the tundra from seismic exploration for oil has accelerated in the past decade, and the cumulative impact represents a geographic footprint that covers a greater extent of Alaska's North Slope tundra than all other direct human impacts combined. Seismic exploration for oil and gas was conducted on the coastal plain of the Arctic National Wildlife Refuge, Alaska, USA, in the winters of 1984 and 1985. This study documents recovery of vegetation and permafrost soils over a two-decade period after vehicle traffic on snow-covered tundra. Paired permanent vegetation plots (disturbed vs. reference) were monitored six times from 1984 to 2002. Data were collected on percent vegetative cover by plant species and on soil and ground ice characteristics. We developed Bayesian hierarchical models, with temporally and spatially autocorrelated errors, to analyze the effects of vegetation type and initial disturbance levels on recovery patterns of the different plant growth forms as well as soil thaw depth. Plant community composition was altered on the trails by species-specific responses to initial disturbance and subsequent changes in substrate. Long-term changes included increased cover of graminoids and decreased cover of evergreen shrubs and mosses. Trails with low levels of initial disturbance usually improved well over time, whereas those with medium to high levels of initial disturbance recovered slowly. Trails on ice-poor, gravel substrates of riparian areas recovered better than those on ice-rich loamy soils of the uplands, even after severe initial damage. Recovery to pre-disturbance communities was not possible where trail subsidence occurred due to thawing of ground ice. Previous studies of disturbance from winter seismic vehicles in the Arctic predicted short-term and mostly aesthetic impacts, but we found that severe impacts to tundra vegetation persisted for two decades after disturbance under some conditions. We recommend management approaches that should be used to prevent persistent tundra damage.

A prelanding assessment of the ice table depth and ground ice characteristics in Martian permafrost at the Phoenix landing site

We review multiple estimates of the ice table depth at potential Phoenix landing sites and consider the possible state and distribution of subsurface ice. A two‐layer model of ice‐rich material overlain by ice‐free material is consistent with both the observational and theoretical lines of evidence. Results indicate ground ice to be shallow and ubiquitous, 2–6 cm below the surface. Undulations in the ice table depth are expected because of the thermodynamic effects of rocks, slopes, and soil variations on the scale of the Phoenix Lander and within the digging area, which can be advantageous for analysis of both dry surficial soils and buried ice‐rich materials. The ground ice at the ice table to be sampled by the Phoenix Lander is expected to be geologically young because of recent climate oscillations. However, estimates of the ratio of soil to ice in the ice‐rich subsurface layer suggest that that the ice content exceeds the available pore space, which is difficult to reconcile with existing ground ice stability and dynamics models. These high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity, initially high‐porosity soils, or the migration of water along thin films. Measurement of the D/H ratio within the ice at the ice table and of the soil‐to‐ice ratio, as well as imaging ice‐soil textures, will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable.

Permafrost in Svalbard: a review of research history, climatic background and engineering challenges

This paper reviews permafrost in High Arctic Svalbard, including past and current research, climatic background, how permafrost is affected by climatic change, typical permafrost landforms and how changes in Svalbard permafrost may impact natural and human systems. Information on active layer dynamics, permafrost and ground ice characteristics and selected periglacial features is summarized from the recent literature and from unpublished data by the authors. Permafrost thickness ranges from less than 100 m near the coasts to more than 500 m in the highlands. Ground ice is present as rock glaciers, as ice-cored moraines, buried glacial ice, and in pingos and ice wedges in major valleys. Engineering problems of thaw-settlement and frost-heave are described, and the implications for road design and construction in Svalbard permafrost areas are discussed.

Genetic types and characteristics of ground ice in Northeast China

The southern limit of permafrost in northeast China oversteps that in the other regions of Eurasia by a few degrees of latitude. There are 11 types of ground ice found within the studied region, including vein ice, massive bedrock ice, lava caves ice and so on. The water for the formation of the ground ice comes from various sources: precipitation, surface water, soil water, and ground water. The ground ice types coexist with the surrounding environment. The correlation and distribution features of the original types of ground ice, their surrounding environments are analyzed for the theoretical study of ground ice formation, engineering control of hazards in ice-rich areas and the prediction of changing conditions.