Excess Ice Content Research Articles

Vertical distribution of excess ice in icy sediments and its statistical estimation from geotechnical data (Tuktoyaktuk Coastlands and Anderson Plain, Northwest Territories)

Excess ice, found as massive ice and within icy sediments, is an important variable to quantify as it is a dominant control on the terrain and geotechnical response to permafrost thaw. A large amount of permafrost borehole data are available from the Tuktoyaktuk Coastlands; however, field geotechnical assessments typically only involve the estimation of visible ice. To add significant value to these data sets, a cryostratigraphic data set collected along the Inuvik–Tuktoyaktuk Highway (566 boreholes) is used to develop a beta regression model which predicts the excess ice content of icy sediments based on interval depth, visible ice content, material type, and Quaternary deposits. The resulting predictions are compared to recorded massive ice intervals and show that ground ice within icy sediments can contribute up to 65% of the excess ice and potential thaw strain within the first 10 m from the surface in this area. This study shows the general applicability of this approach and indicates that comparable, quantitative data on ground ice conditions should be collected with drilling programs to derive geotechnical variables and reduce modelling uncertainties so that ground ice data are available for quantitative analysis.

Numerical Assessments of Excess Ice Impacts on Permafrost and Greenhouse Gases in a Siberian Tundra Site Under a Warming Climate

Excess ice that exists in forms such as ice lenses and wedges in permafrost soils is vulnerable to climate warming. Here, we incorporated a simple representation of excess ice in a coupled hydrological and biogeochemical model (CHANGE) to assess how excess ice affects permafrost thaw and associated hydrologic responses, and possible impacts on carbon dioxide and methane (CH4) fluxes. The model was used to simulate a moss-covered tundra site in northeastern Siberia with various vertical initializations of excess ice under a future warming climate scenario. Simulations revealed that the warming climate induced deepening of the active layer thickness (ALT) and higher vegetation productivity and heterotrophic respiration from permafrost soil. Meanwhile, excess ice temporarily constrained ALT deepening and thermally stabilized permafrost because of the highest latent heat effect obtained under these conditions. These effects were large under conditions of high excess ice content distributed in deeper soil layers, especially when covered by moss and thinner snow. Once ALT reached to the layer of excess ice, it was abruptly melted, leading to ground surface subsidence over 15–20 years. The excess ice meltwater caused deeper soil to wet and contributed to talik formation. The anaerobic wet condition was effective to high CH4emissions. However, as the excess ice meltwater was connected to the subsurface flow, the resultant lower water table limited the CH4efflux. These results provide insights for interactions between warming climate, permafrost excess ice, and carbon and CH4fluxes in well-drained conditions.

Projecting circum-Arctic excess-ground-ice melt with a sub-grid representation in the Community Land Model

Abstract. To address the long-standing underrepresentation of the influences of highly variable ground ice content on the trajectory of permafrost conditions simulated in Earth system models under a warming climate, we implement a sub-grid representation of excess ground ice within permafrost soils using the latest version of the Community Land Model (CLM5). Based on the original CLM5 tiling hierarchy, we duplicate the natural vegetated land unit by building extra tiles for up to three cryostratigraphies with different amounts of excess ice for each grid cell. For the same total amount of excess ice, introducing sub-grid variability in excess-ice contents leads to different excess-ice melting rates at the grid level. In addition, there are impacts on permafrost thermal properties and local hydrology with sub-grid representation. We evaluate this new development with single-point simulations at the Lena River delta, Siberia, where three sub-regions with distinctively different excess-ice conditions are observed. A triple-land-unit case accounting for this spatial variability conforms well to previous model studies for the Lena River delta and displays markedly different dynamics of future excess-ice thaw compared to a single-land-unit case initialized with average excess-ice contents. For global simulations, we prescribed a tiling scheme combined with our sub-grid representation to the global permafrost region using presently available circum-Arctic ground ice data. The sub-grid-scale excess ice produces significant melting of excess ice under a warming climate and enhances the representation of sub-grid variability of surface subsidence on a global scale. Our model development makes it possible to portray more details on the permafrost degradation trajectory depending on the sub-grid soil thermal regime and excess-ice melting, which also shows a strong indication that accounting for excess ice is a prerequisite of a reasonable projection of permafrost thaw. The modeled permafrost degradation with sub-grid excess ice follows the pathway that continuous permafrost transforms into discontinuous permafrost before it disappears, including surface subsidence and talik formation, which are highly permafrost-relevant landscape changes excluded from most land models. Our development of sub-grid representation of excess ice demonstrates a way forward to improve the realism of excess-ice melt in global land models, but further developments require substantially improved global observational datasets on both the horizontal and vertical distributions of excess ground ice.

Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave Geological Province, Northwest Territories, Canada

Abstract. The central Slave Geological Province is situated 450–650 km from the presumed spreading centre of the Keewatin Dome of the Laurentide Ice Sheet, and it differs from the western Canadian Arctic, where recent thaw-induced landscape changes in Laurentide ice-marginal environments are already abundant. Although much of the terrain in the central Slave Geological Province is mapped as predominantly bedrock and ice-poor, glacial deposits of varying thickness occupy significant portions of the landscape in some areas, creating a mosaic of permafrost conditions. Limited evidence of ice-rich ground, a key determinant of thaw-induced landscape change, exists. Carbon and soluble cation contents in permafrost are largely unknown in the area. Twenty-four boreholes with depths up to 10 m were drilled in tundra north of Lac de Gras to address these regional gaps in knowledge and to better inform projections and generalizations at a coarser scale. Excess-ice contents of 20 %–60 %, likely remnant Laurentide basal ice, are found in upland till, suggesting that thaw subsidence of metres to more than 10 m is possible if permafrost were to thaw completely. Beneath organic terrain and in fluvially reworked sediment, aggradational ice is found. The variability in abundance of ground ice poses long-term challenges for engineering, and it makes the area susceptible to thaw-induced landscape change and mobilization of sediment, solutes and carbon several metres deep. The nature and spatial patterns of landscape changes, however, are expected to differ from ice-marginal landscapes of western Arctic Canada, for example, based on greater spatial and stratigraphic heterogeneity. Mean organic-carbon densities in the top 3 m of soil profiles near Lac de Gras are about half of those reported in circumpolar statistics; deeper deposits have densities ranging from 1.3–10.1 kg C m−3, representing a significant additional carbon pool. The concentration of total soluble cations in mineral soils is lower than at previously studied locations in the western Canadian Arctic. This study can inform permafrost investigations in other parts of the Slave Geological Province, and its data can support scenario simulations of future trajectories of permafrost thaw. Preserved Laurentide basal ice can support new ways of studying processes and phenomena at the base of an ice sheet.

Factors controlling near surface ground-ice characteristics in a region of warm permafrost, Beiluhe Basin, Qinghai-Tibet Plateau

Ground ice is a key component of permafrost, and its melt induced by climate change and anthropogenic disturbance has been causing increased ground surface subsidence, thermal erosion, and engineering problems. However, the distribution and quantity of ground ice in permafrost have yet to be investigated in detail on the Qinghai-Tibet Plateau (QTP), and consequently, an assessment of the nature of impacts associated with permafrost degradation is challenging. In this study, variation in near-surface ground ice content of the upper 2–3 m of the permafrost layer was examined by drilling 72 boreholes at eight sites in Beiluhe Basin, QTP, an area with relatively warm (near 0 °C) permafrost. High ground ice contents occur at most sites, but visible ice was absent at one site, where the vegetation cover has transitioned from a meadow to a sparsely-covered grassland. The moisture content within the active layer (surface to 2 m depth) increases with depth at most sites, and the higher moisture contents were associated with greater near-surface ground ice contents. The gravimetric moisture content (Mg) in permafrost typically ranged from 8% to 500%, and ~76% of samples were classified as ice rich (Mg ≥ 20%). The mean excess-ice content in near-surface permafrost was ~19% for all boreholes. At six flat sites, the minimum mean excess-ice content was about zero, and the mean maximum was ~22% at an alpine grassland site. The mean excess-ice content at a sunny sloping site was much higher (~27%) than at a north-facing shady site (10%) and the ice was distributed differently with depth. The mean subsidence ratio at the eight sites was from 0.05 to 0.44. The volumetric ice content varied from 1% to 70% in samples from the different sites, with an average value of ~16%. Topographically controlled moisture availability, slope direction, and fine-particle content are important controls on ground ice content in Beiluhe Basin. This study provides fundamental information about the spatial distribution of ground ice on QTP, which is important for future assessments of thermal erosion potential and infrastructure instability in the region.

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 analyzed 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 characterized as a medium sand, which classifies them as low to non-frost susceptible. 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 paleo-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.

Distribution and origin of ground ice in University Valley, McMurdo Dry Valleys, Antarctica

AbstractGround ice is one of the most important and dynamic geologic components of permafrost; however, few studies have investigated the distribution and origin of ground ice in the McMurdo Dry Valleys of Antarctica. In this study, ice-bearing permafrost cores were collected from 18 sites in University Valley, a small hanging glacial valley in the Quartermain Mountains. Ground ice was found to be ubiquitous in the upper 2 m of permafrost soils, with excess ice contents reaching 93%, but ground ice conditions were not homogeneous. Ground ice content was variable within polygons and along the valley floor, decreasing in the centres of polygons and increasing in the shoulders of polygons towards the mouth of the valley. Ground ice also had different origins: vapour deposition, freezing of partially evaporated snow meltwater and buried glacier ice. The variability in the distribution and origin of ground ice can be attributed to ground surface temperature and moisture conditions, which separate the valley into distinct zones. Ground ice of vapour-deposition origin was predominantly situated in perennially cryotic zones, whereas ground ice formed by the freezing of evaporated snow meltwater was predominantly found in seasonally non-cryotic zones.

Effects of excess ground ice on projections of permafrost in a warming climate

In permafrost soils, ‘excess ice’, also referred to as ground ice, exists in amounts exceeding soil porosity in forms such as ice lenses and wedges. Here, we incorporate a simple representation of excess ice in the Community Land Model (CLM4.5) to investigate how excess ice affects projected permafrost thaw and associated hydrologic responses. We initialize spatially explicit excess ice obtained from the Circum-Arctic Map of Permafrost and Ground-Ice Conditions. The excess ice in the model acts to slightly reduce projected soil warming by about 0.35 °C by 2100 in a high greenhouse gas emissions scenario. The presence of excess ice slows permafrost thaw at a given location with about a 10 year delay in permafrost thaw at 3 m depth at most high excess ice locations. The soil moisture response to excess ice melt is transient and depends largely on the timing of thaw with wetter/saturated soil moisture conditions persisting slightly longer due to delayed post-thaw drainage. Based on the model projections of excess ice melt, we can estimate spatially explicit gridcell mean surface subsidence with values ranging up to 0.5 m by 2100 depending on the initial excess ice content and the extent of melt.

A model for co-isotopic signatures of evolving ground ice in the cold dry environments of Earth and Mars

The basics of the model (REGO) are summarized including diffusive water vapor transport, ice content, adsorption and the isotopic ratios of the various water species. Inclusion of a temperature and stress–strain solution is also described as are the effects of cracking when the tensile breaking strengths are exceeded. Cracking is viewed as a multi-scale phenomena, whereby the larger cracks are produced by chaining together smaller ones. After some validation, the model is applied to the upper University Valley (Antarctic Dry Valleys) data and to the Phoenix landing site at lat. 69N on Mars. For the University Valley, the model when forced by measured diurnal temperature cycles and known relative humidity reproduces some of the complex the ice content and isotope structure found in the upper University Valley ground ice cores. The model takes a few hundred years to fill the pores just under the ice table. The excess ice observed in the University Valley cores can be produced by thermal cracking combined with the diurnal temperature cycle. Time taken to achieve the observed excess ice content is of order 104years. There is limited subsurface data for the Phoenix site, but there are measured ice table depths, surface thermal properties and Met variables. There is enough to do diurnal and seasonal runs of the REGO model. As with the University Valley, the upper few tens of centimeters icing are controlled by the diurnal temperatures, largely in the warmer part of the year. The observed ubiquitous pore full ice right at the ice table could be produced from a dry soil in about 103a and the nearly pure ice patches could be produced by the cracking-diffusion mechanism in about million years, if shear stresses are included. Emplacement of ice down to ∼10m is possible using the seasonal temperature cycle and cracking. Excess ice in the upper meter could produced by the model in about 6×106a if the temperature at the Phoenix site was 10–20deg warmer.

Physical and temporal factors controlling the development of near-surface ground ice at Illisarvik, western Arctic coast, Canada

Near-surface permafrost was sampled in summer 2010 at 26 sites in the Illisarvik drained-lake basin and nine sites in the surrounding tundra on Richards Island, NWT, to investigate the growth of segregated near-surface ground ice. Permafrost and ground ice have developed in the lake basin since drainage in 1978. The lake bed soils are predominantly silts of varying moisture and organic-matter contents, with sandier soils near the lake margins. Excess-ice contents in the basin were also variable, and ice enrichment was observed to a maximum depth of 60 cm below the 2010 permafrost table. Shrub-covered, wet areas had the highest mean excess-ice content in the top 50 cm of permafrost (10%), while grassy, dryer areas (4%) and poorly vegetated marginal areas (<1%) were less enriched with ice. Site wetness was the most important variable associated with near-surface excess-ice content in the lake basin. Silt content was a secondary variable. Mean excess-ice content in the top 50 cm of permafrost at tundra sites (25%) was much greater than in the basin, with ice enrichment to greater depths, likely a result of the time available for permafrost aggradation since the early Holocene climatic optimum.

Accumulation of Excess Ground Ice in an Age Sequence of Drained Thermokarst Lake Basins, Arctic Alaska

ABSTRACTThe excess ice content of near‐surface permafrost near Barrow, Alaska, was estimated using cores collected from 57 drained thermokarst‐lake basins and additional cores from a nearby landform unaffected by thaw‐lake processes. The excess ice content, estimated using soil cryostructures, increased with surface age: from 20 per cent in young basins < 50 years in age to 40 per cent in ancient basins that drained 2000–5500 years ago. The frequency of ice wedges encountered during coring increased from 0 per cent in young basins to 50 per cent in ancient basins. These results indicate that the volume of ground ice increases rapidly immediately following lake drainage, as permafrost aggrades into unfrozen basin sediments. Ice enrichment continues over time by incorporating meteoric water as ice veins and lenses, and expanding networks of ice wedges. To test the efficacy of visually estimating excess ice content, the ice content was measured on a subsample of cores; measured volumetric values were strongly correlated (r2 = 0.72; p < 0.001) to the estimated excess ice content. The results of this study have important implications for estimating soil organic carbon content of soils with abundant excess ice, and for evaluating the susceptibility of these soils to thermokarst. Copyright © 2012 John Wiley & Sons, Ltd.

Advance mechanisms of rock glaciers

Rock glacier advance is believed to be the result of the advection of frozen debris to and over the front, (partial) melt-out of ice, and incorporation and subsequent overriding of the mass at the base of the rock glacier. In this contribution, an approach to measure mass balance and transport within rock glacier fronts is presented. The technique is applied to Gruben and Suvretta rock glaciers, Swiss Alps. The results confirm a ‘conveyor belt’-like advance mechanism for both features. At the Gruben rock glacier front, an average excess ice content of approximately 65% was detected, 15% more than at Suvretta rock glacier. The frontal part of Suvretta rock glacier turned out to have a linear velocity profile over the entire thickness. At Gruben rock glacier, the horizontal mass transport is, for the most part, concentrated in a 5–10 m thick surface layer. Copyright © 2005 John Wiley & Sons, Ltd.

Semi-quantitative geophysical investigation of permafrost in northern Québec

Both continuous and discontinuous permafrost occur in northern Québec. In contrast with permafrost in western Canada and Alaska, permafrost in eastern Canada contains no massive ice because of the regionally different climatic conditions and soil compositions. Site investigations related to infrastructures such as building foundations, airports, and roads frequently require a knowledge of the spatial distribution of ice content in permafrost since differential thawing can significantly affect the mechanical behavior of the soil. Delineation of permafrost ice content in northern Québec is difficult because of its diffusion into the various unconsolidated deposits. Electrical and gravity surface surveys are appropriate methods for determining the horizontal and vertical extent of such permafrost conditions because the resistivity, IP chargeability, and density parameters are directly affected by the volume ice content and the amount of unfrozen water in the permafrost. This integrated surface geophysical approach was applied at three test sites in the Kangiqsualujjuaq (George River) area to yield a semi-quantitative volumetric estimate rather than a discrete spatial distribution of the excess ice content. The selected test sites at which this integrated method was demonstrated are representative of continental and supratidal cryogenic mounds of different dimensions in which negative residual gravity anomalies, large electrical resistivity contrasts, and near-zero IP chargeability were combined to delineate and characterize the excess ice zones. The relative magnitudes of these parameters are interpreted to yield a semi-quantitative estimate of the ice content in the anomalous regions. Test drill holes at the surveyed sites indicate that the integrated approach can provide useful geotechnical assessments of the integrity of foundations and other structures subject to permafrost environments.

Pile load tests in saline permafrost at Clyde River, Northwest Territories

Significant salt content in the pore phase of permafrost causes dramatic reduction in strength or bearing capacity. Previous experience with laboratory tests and limited field testing discussed in the Soviet literature indicate that creep rates can be accelerated many times and foundation bearing capacities reduced by factors of 2–3 if pore water salinities exceed 10–20 ppt. At Clyde River on the northwest coast of Baffin Island, pile load tests were carried out in 1982. A combination of high salinities and significant excess ice contents at some locations suggested that a limited program of pile load testing should be carried out to confirm or modify the initial pile loadings based on previously published material. No fully documented case history was available to support initial pile design loads.Three piles were subjected to loads of five different magnitudes for different durations. Creep settlement was initiated and persisted in all cases. Continuous curve fitting was carried out by computer, and the resulting smoothed strain rate plotted with time. The minimum settlement rates were compared with earlier predictions. They were generally somewhat faster than results from previous laboratory saline creep testing combined with theoretical pile design based on creep settlement.The tests highlight the dramatic reductions in foundation bearing capacity and acceleration in pile creep rates that can be expected in permafrost exhibiting significant pore water salinity. A simplified testing procedure suitable for laboratory or field testing is described. Key words: permafrost, saline, piles, load tests, laboratory, field, in situ, capacity, creep, creep rate, salinity test.