Air temperature, snow cover, creep of frozen ground, and the time of ice-wedge cracking, western Arctic coast

1993 ◽  
Vol 30 (8) ◽  
pp. 1720-1729 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Snow Cover ◽  
Active Layer ◽  
Air Temperature ◽  
Thermal Stresses ◽  
Temperature Drop ◽  
Frozen Ground ◽  
Air Temperatures ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast

The time of ice-wedge cracking is examined for several sites with young and old ice wedges along the western Arctic coast. The correlation between sharp air temperature drops and ice-wedge cracking is highest where the snow cover is thin and least where the snow cover is thick. The favoured duration and rate of a temperature drop that results in cracking is about 4 days, at a rate of about 1.8°C/d. Such temperature drops have a minimal effect in cooling the top of permafrost wherever there is an appreciable snow cover. Since short duration temperature drops often result in ice-wedge cracking, the thermal stresses that trigger cracking probably originate more within the frozen active layer than at greater depth in permafrost. Although most ice wedges tend to crack during periods of decreasing air temperatures, about one third of those monitored have cracked during periods of increasing air temperatures. Long-term measurements show that the active layer and top of permafrost move differentially all year in a periodic movement. That is, creep of frozen ground occurs all year, irrespective of whether ice wedges crack or do not crack. The presence of a snow cover and the creep of frozen ground are two major factors that confound a simple application of conventional ice-wedge cracking theory to air temperature drops and the time of ice-wedge cracking.

Ice wedges on hillslopes and landform evolution in the late Quaternary, western Arctic coast, Canada

1995 ◽  
Vol 32 (8) ◽  
pp. 1093-1105 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Active Layer ◽  
Late Quaternary ◽  
Chronological Age ◽  
Bottom Slope ◽  
Thermally Induced ◽  
Landform Evolution ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
The Mean

In rolling to hilly areas of the western Arctic coast of Canada, anti-syngenetic wedges, which by definition are those that grow on denudational slopes, are the most abundant type of ice wedge. Through prolonged slope denudation, hilltop epigenetic wedges can evolve into hillslope anti-syngenetic wedges, and some bottom-slope anti-syngenetic wedges, by means of deposition from upslope, can evolve into bottom-slope syngenetic wedges. The axis of a hillslope wedge is oriented perpendicular to the slope, so the wedge foliation varies according to the trend of the wedge with respect to the slope. Because the tops of hillslope wedges are truncated by slope recession, the mean chronological age of anti-syngenetic wedge ice decreases with time, so the growth record for an old wedge is incomplete. Summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the troughs relative to the slope. Wedge-ice uplift, probably diapiric, has been measured. Some hillslope polygon patterns may predate the development of the present topography. Many Wisconsinan wedges, truncated and buried during the Hypsithermal period, have been reactivated by upward cracking.

The first 7 years (1978–1985) of ice wedge growth, Illisarvik experimental drained lake site, western Arctic coast

1986 ◽  
Vol 23 (11) ◽  
pp. 1782-1795 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Growth Rates ◽  
Linear Expansion ◽  
Temperature Dependent ◽  
Frozen Ground ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
Coefficient Of Linear Expansion ◽  
Lake Site ◽  
Crack Widths

A large lake, measuring 600 m × 300 m and with a depth of nearly 5 m, was artificially drained on 13 August 1978. Observations on the formation, width, and depth of thermal contraction cracks for the first 7 years show that the crack profiles and ice wedge growth rates differ markedly from those of old ice wedges reported in the literature. The first winter's cracks had box-like profiles, with surface widths to 10 cm and depths to 2.5 m. Some cracks continued to widen and deepen, once opened in early winter, and then narrowed or even closed completely in summer. Mean growth rates for the ice wedges for the first few years have been as much as 3.5 cm/year. Temperature gradients at the time of first cracking have been in the range of 10–15 °C/m. The growth rate of young ice wedges is site specific and temperature dependent, varying with factors such as the temperature gradient, vegetation, and snow cover, so an estimate of the age of an ice wedge from its width will usually be impossible. A study of crack widths indicates that the apparent coefficient of linear expansion of frozen ground may be several times that of ice. Upward cracking has been proven.

Tundra lakes and permafrost, Richards Island, western Arctic coast, Canada

2002 ◽  
Vol 39 (8) ◽  
pp. 1281-1298 ◽  
Author(s):  
C R Burn
Keyword(s):  
Snow Cover ◽  
Active Layer ◽  
Open Water ◽  
Active Layer Thickness ◽  
Equilibrium Conditions ◽  
Lake Bottom ◽  
Near Shore ◽  
Western Arctic ◽  
Arctic Coast ◽  
Average Size

Lakes, of average size 33 ha, occupy a quarter of the surface area of Richards Island, Northwest Territories. Most of the lakes have a central pool deeper than the thickness of winter ice, and many have prominent, shallow, littoral terraces. The relatively warm lake bottoms cause considerable disturbance to the surrounding continuous permafrost. Water and lake-bottom temperatures, the configuration of permafrost, and active-layer thickness were measured at a tundra lake between 1992 and 1997. The lake is oval, 1.6 km long, 800 m wide, and as deep as 13 m. Sandy terraces, covered by less than 1 m of water, extend over 100 m from the shore. The terraces are underlain by permafrost, which terminates almost vertically at their edge. The annual mean temperature measured at lake bottom in the central pool ranged between 1.5°C and 4.8°C, depending on depth, and between –0.2°C and –5°C on the terraces, due to differences in snow cover and proximity to the central pool. In consequence, the temperature of permafrost at 7 m depth in the terraces also varied, from –2°C near shore to –5°C in mid-terrace. The active layer in the terraces was uniformly 1.4 m deep. Geothermal modelling of talik configuration indicates that there is no permafrost beneath the central pool of the lake. The modelling indicates that, under equilibrium conditions, about one quarter of the lakes on Richards Island have taliks that penetrate permafrost, and at least 10–15% of the island is underlain by talik. Short-term climatic changes predicted for the region imply a small increase in summer lake-water temperature and an extension of the open-water season, accompanied by thicker snow cover in winter. Following such changes, with longer freeze-up and warmer terrace temperatures in winter, permafrost may not be sustainable in the lake terraces.

scholarly journals Thermally induced movements in ice-wedge polygons, western arctic coast: a long-term study

2002 ◽  
Vol 54 (1) ◽  
pp. 41-68 ◽  
Author(s):  
J. Ross MacKay
Keyword(s):  
Active Layer ◽  
Term Study ◽  
Thermally Induced ◽  
Seasonal Movements ◽  
Long Term Study ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast

AbstractThermally induced seasonal movements of the active layer and subjacent permafrost have been measured in numerous ice-wedge polygons that have varied in age, type, crack frequency, and topographic location. The field observations show that, in winter, thermal contraction, which is inward, is constrained or vanishes at the polygon centres but, in summer, thermal expansion, which is outward, is unconstrained at the ice-wedge troughs. Therefore, there tends to be a small net summer transport of the active layer, to varying depths, into the ice-wedge troughs. The movement has been observed in all polygons studied. The slow net transport of material into the ice-wedge troughs has implications for: permafrost aggradation and the growth of syngenetic wedges in some troughs; the palaeoclimatic reconstruction of some ice- wedge casts; and the interpretation of polygon stratigraphy based upon the assumption that the polygon material has accumulatedin situ.

The frequency of ice-wedge cracking (1967–1987) at Garry Island, western Arctic coast, Canada

1992 ◽  
Vol 29 (2) ◽  
pp. 236-248 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Air Temperature ◽  
Classification System ◽  
Environmental Reconstruction ◽  
Wide Range ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
The Common ◽  
A Site ◽  
Observation Period

The frequency of ice-wedge cracking has been studied at Garry Island, Northwest Territories, for the 1967–1987 period. Sites have included low-centre polygons, intermediate-centre polygons, and polygons that do not fit any classification system. Analyses of crack frequency have included trough characteristics, polygon characteristics, and ice-wedge types. The results show that crack frequencies are highly variable within one site and also between two adjacent sites. The correlation between crack frequency and a low air temperature is poor. Crack frequencies for a site with 59 wedges ranged from 8 to 42% between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75% between 1967 and 1987. In view of the wide range in crack frequencies at a given site, the use of mean ice-wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous. The data show that the common twofold classification into active and inactive wedges is difficult to apply because crack frequencies are gradational and dependent on such factors as the number of ice wedges being monitored, the size of the area, the types of ice wedges, and the length of the observation period. A system for classifying crack frequency is proposed.

Permafrost

2021 ◽  
Keyword(s):  
Active Layer ◽  
Air Temperature ◽  
Ground Surface ◽  
Rooting Depth ◽  
Permafrost Degradation ◽  
Frozen Ground ◽  
Air Temperatures ◽  
Discontinuous Permafrost ◽  
Deep Infiltration ◽  
Mean Annual Air Temperature

Permafrost is permanently frozen ground that remains continuously below 0 °C for two or more years. The upper level of permafrost, the permafrost table, can occur within a centimeter of the ground surface or at a depth of several meters. The active layer, which thaws each summer, overlies permafrost. Permafrost underlies about a quarter of the northern hemisphere and can form in sediment or bedrock and on land or under the ocean. Permafrost forms incrementally and, in the regions where it is up to 1 km thick, permafrost can represent thousands of years of formation. Permafrost is present at high latitudes and high altitudes. In these regions, permafrost can be described as continuous, discontinuous, sporadic, or isolated. Continuous permafrost forms at mean annual air temperatures below -5 °C and is laterally continuous, regardless of surface aspect or material. Discontinuous permafrost forms where the mean annual air temperature is between -2 and -4 °C, allowing permafrost to persist in 50 to 90 percent of the landscape. Permafrost is sporadic where 10 to <50 percent of the landscape is underlain by permafrost and mean annual air temperature is between 0 and -2 °C. Permafrost is considered isolated where less than 10 percent of the landscape is underlain by permafrost. When it is present, permafrost creates unique conditions. Permafrost forms an impermeable layer beneath the active layer, for example, which limits the rooting depth of plants and prevents infiltration by water during the summer. The lack of deep infiltration can facilitate formation of extensive wetlands in high-latitude areas that receive relatively little precipitation. Permafrost degradation (thaw) creates diverse environmental hazards, including instability of the ground surface that affects infrastructure and fluxes of water, sediment, and organic matter entering rivers, lakes and oceans. Permafrost degradation releases frozen microbes, some of which are pathogens, and organic carbon. Permafrost degradation also influences the geographic range of plants and animals and thus ecosystem processes and biotic communities. The greatest concern with permafrost degradation at present, however, is the potential for releasing significant carbon into the atmosphere. Globally, soils are the largest terrestrial reservoir of carbon and permafrost soils are the single largest component of the carbon reservoir. Carbon released by degrading permafrost can enter the atmosphere as the greenhouse gases carbon dioxide and methane, or the carbon can be taken up by plants or transported by rivers to the ocean and buried in marine sediments. The balance among these different pathways is largely unknown, but carbon release to the atmosphere presents a serious threat as a mechanism to enhance global warming.

scholarly journals Satellite observations of changes in snow-covered land surface albedo during spring in the Northern Hemisphere

2015 ◽  
Vol 9 (5) ◽  
pp. 1879-1893 ◽  
Author(s):  
K. Atlaskina ◽  
F. Berninger ◽  
G. de Leeuw
Keyword(s):  
Snow Cover ◽  
Northern Hemisphere ◽  
Air Temperature ◽  
Land Surface ◽  
Surface Albedo ◽  
Vegetation Index ◽  
Precipitation Amount ◽  
Snow Cover Fraction ◽  
Air Temperatures ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. Thirteen years of Moderate Resolution Imaging Spectroradiometer (MODIS) surface albedo data for the Northern Hemisphere during the spring months (March–May) were analyzed to determine temporal and spatial changes over snow-covered land surfaces. Tendencies in land surface albedo change north of 50° N were analyzed using data on snow cover fraction, air temperature, vegetation index and precipitation. To this end, the study domain was divided into six smaller areas, based on their geographical position and climate similarity. Strong differences were observed between these areas. As expected, snow cover fraction (SCF) has a strong influence on the albedo in the study area and can explain 56 % of variation of albedo in March, 76 % in April and 92 % in May. Therefore the effects of other parameters were investigated only for areas with 100 % SCF. The second largest driver for snow-covered land surface albedo changes is the air temperature when it exceeds a value between −15 and −10 °C, depending on the region. At monthly mean air temperatures below this value no albedo changes are observed. The Enhanced Vegetation Index (EVI) and precipitation amount and frequency were independently examined as possible candidates to explain observed changes in albedo for areas with 100 % SCF. Amount and frequency of precipitation were identified to influence the albedo over some areas in Eurasia and North America, but no clear effects were observed in other areas. EVI is positively correlated with albedo in Chukotka Peninsula and negatively in eastern Siberia. For other regions the spatial variability of the correlation fields is too high to reach any conclusions.

The Influence of Uncertainty in Air Temperature and Albedo on Snowmelt

1991 ◽  
Vol 22 (2) ◽  
pp. 95-108 ◽  
Author(s):  
G. Blöschl
Keyword(s):  
Snow Cover ◽  
Air Temperature ◽  
Meteorological Data ◽  
Model Parameters ◽  
Local Effects ◽  
Austrian Alps ◽  
Air Temperatures ◽  
Basin Scale ◽  
Simulation Results

Extrapolating meteorological data to the basin scale represents a major problem of spatial snowmelt modelling in alpine terrain. Within this study errors in air temperature introduced by regionalization are analyzed for the Sellrain region in the Austrian Alps. Albedo is simulated using a range of model parameters representing different snow cover conditions. The influence on snowmelt is assessed by simulating water equivalent at the site scale using estimated air temperatures and albedoes. Simulation results indicate that a bias in measured temperatures as produced by local effects may be significantly more important than interpolation errors. Uncertainty in albedo appears to affect snowmelt to a higher degree than air temperature.

Pingo collapse and paleoclimatic reconstruction

1988 ◽  
Vol 25 (4) ◽  
pp. 495-511 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Soviet Union ◽  
Field Studies ◽  
Normal Faults ◽  
Paleoclimatic Reconstruction ◽  
Air Temperatures ◽  
The Soviet Union ◽  
Long Time ◽  
Western Arctic ◽  
Arctic Coast ◽  
Time Required

Long-term field studies of contemporary pingo growth, collapse, and rampart formation along the western Arctic coast of Canada provide criteria that may be helpful in the identification of pingo ramparts in nonpermafrost environments. Such criteria include the volume of the ramparts, which should approximate that of the enclosed depressions from which the rampart materials were derived; peripheral deposits associated with mass wasting, streamflow, and debris flow; casts of dilation crack ice trending across the ramparts; and high-angle peripheral normal faults. The conventional method of correlating the present mean annual air temperature with the present pingo distribution to establish warm-side limiting temperatures for paleoclimatic reconstruction is unsound, because most pingos in North America and the Soviet Union commenced growth hundreds to thousands of years ago under mean annual air temperatures that may have differed greatly from those of the present. Some other factors to be considered in paleoclimatic reconstruction are the thermal offset; site availability; the differing requirements for the growth of large pingos as compared with small pingos; and the long time required for pingos to grow to full size.

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