Showing papers on "Permafrost published in 1997"

Effects of climate change on the freshwaters of arctic and subarctic north america

Abstract: Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Central northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass changes will play an important role in precipitation changes associated with climate warming. The snow season in the region is prolonged resulting in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall usually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models are in close agreement for this region and predict temperature increases as large as 4°C in summer and 9°C in winter for a 2 × CO2 scenario. Palaeoclimate indicators support the probability that substantial temperature increases have occurred previously during the Holocene. The historical record indicates a temperature increase of > 1°C in parts of the region during the last century. GCM predictions of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnitude. Precipitation change is as important as temperature change in determining the water balance. The water balance is critical to every aspect of hydrology and limnology in the far north. Permafrost close to the surface plays a major role in freshwater systems because it often maintains lakes and wetlands above an impermeable frost table, which limits the water storage capabilities of the subsurface. Thawing associated with climate change would, particularly in areas of massive ice, stimulate landscape changes, which can affect every aspect of the environment. The normal spring flooding of ice-jammed north-flowing rivers, such as the Mackenzie, is a major event, which renews the water supply of lakes in delta regions and which determines the availability of habitat for aquatic organisms. Climate warming or river damming and diversion would probably lead to the complete drying of many delta lakes. Climate warming would also change the characteristics of ponds that presently freeze to the bottom and result in fundamental changes in their limnological characteristics. At present, the food chain is rather simple usually culminating in lake trout or arctic char. A lengthening of the growing season and warmer water temperature would affect the chemical, mineral and nutrient status of lakes and most likely have deleterious effects on the food chain. Peatlands are extensive in region 2. They would move northwards at their southern boundaries, and, with sustained drying, many would change form or become inactive. Extensive wetlands and peatlands are an important component of the global carbon budget, and warmer and drier conditions would most likely change them from a sink to a source for atmospheric carbon. There is some evidence that this may be occurring already. Region 2 is very vulnerable to global warming. Its freshwater systems are probably the least studied and most poorly understood in North America. There are clear needs to improve our current knowledge of temperature and precipitation patterns; to model the thermal behaviour of wetlands, lakes and rivers; to understand better the interrelationships of cold region rivers with their basins; to begin studies on the very large lakes in the region; to obtain a firm grasp of the role of northern peatlands in the global carbon cycle; and to link the terrestrial water balance to the thermal and hydrological regime of the polar sea. Overall, there is a strong need for basic research and long-term monitoring. © 1997 John Wiley & Sons, Ltd.

The deep cold biosphere: facts and hypothesis

Abstract: Deep subterranean layers may be regarded as the most stable environment for microorganisms where possible fluctuations should be explained by geological events only. The analysis of the total amount of microorganisms has revealed that in sedimentary deposits their number is only one order of magnitude lower than the same parameter in soil. Taking into account the depth of sediments the microbial biomass in subterranean rocks has to be considerably larger than that in soils. Permafrost is the most constant and stable environment among deep habitats. Microbial communities survive in permafrost for at least some millions of years. The diversity of organisms and of microbial activities after permafrost thawing displays distinct differences to those in soils. The abundance of the bacterial biomass assumed is comparable in frozen and unfrozen sediments. Therefore, the permanently low temperature in permafrost is a stabilizing factor that sustains life in deep cold biotopes. Studies of microbial communities in permafrost sediments of different lithology and age suggest that the level of subzero temperature and the duration of its influence define the ratio between the hypometabolic cells, readily reversible to proliferation, and the so-called viable but non-culturable cells (deep resting cells). To a certain extent, cell aggregates in the extracellular matrix may be regarded as an additional survival mechanism supporting the hypometabolic state of cells. There is indirect evidence for adaptive physiological and biochemical processes in microorganisms during the long-term impact of cold.

Properties and Classification of Cold Desert Soils from Antarctica

Abstract: Eight pedons representing three climatic zones and parent materials ranging from Holocene to Pliocene were characterized from the Dry Valleys region of Antarctica. All of the sows contain abundant watersoluble salts, including NaCI in coastal regions, NaNO 3 along the polar plateau, and Na 2 SO 4 in intermediate areas. The salts originate primarily from atmospheric deposition and accumulate linearly with time. Based on a comparison of salt input by precipitation and the salt content of the profiles, minimal leaching of salts has occurred during the past 3 million yr in soils along the polar plateau. Chemical weathering generally is restricted to oxidation of Fe-bearing minerals and some clay authigenesis. Some of the soils contain ice-cemented permafrost; however, many of the older soils with <5% moisture content have dry permafrost. Although the soils bear many features of Aridisols, they fail to meet the requirements of an aridic soil moisture regime because of the very cold temperatures. They could be classified as Cryids if the Aridisols suborder were expanded to include soils with temperatures that never exceed 5 or 8°C. In the proposed Gelisols order for permafrost-affected soils, the soils are classified as Natric, Glacic, and Typic Anhyturbels (evidence of cryoturbation) and Salic and Petrosalic Anhyhaplels (no cryoturbation).

Global warming and active-layer thickness: results from transient general circulation models

Abstract: The near-surface thermal regime in permafrost regions could change significantly in response to anthropogenic climate warming. Because there is only a small lag between these two processes, the impact of warming on the active layer can be investigated using relatively simple climate-driven models. A formulation attributable to Kudryavtsev was used to study the potential increase of active-layer thickness in the permafrost regions of the Northern Hemisphere, where warming is predicted to be more pronounced than elsewhere. Kudryavtsev's solution was validated using contemporary data, and successfully reproduced the actual depths of frost and thaw at widely spaced locations in North America and Eurasia. Modern climatic data and scenarios of climate change for 2050, derived from three transient coupled ocean-atmosphere general circulation models (GCMs), were used in conjunction with the thaw-depth solution to generate hemispheric maps showing contemporary active-layer thickness for several soil types and moisture conditions, and its relative changes over the next century. The simulations indicate a 20–30% increase of active-layer thickness for most of the permafrost area in the Northern Hemisphere, with the largest relative increases concentrated in the northernmost locations.

Small‐scale polygonal features on Mars: Seasonal thermal contraction cracks in permafrost

Abstract: A time-dependent viscoelastic model of thermal stress in Martian ice-rich permafrost is developed to test the hypothesis that small-scale polygonal features observed from orbit and by the Viking Lander 2 are the result of thermal contraction cracking, as commonly occurs in terrestrial permafrost. Results indicate that significant tensile stress occurs in Martian ice-rich permafrost as a result of seasonal cycles in the ground temperature. Using conservative rheological parameters appropriate for ice at low temperatures, tensile stresses poleward of about 20° to 30° latitude easily exceed the tensile strength (assumed to be 2 to 3 MPa) and fractures should readily form. In the equatorial regions, special conditions may allow tensile stresses to approach the tensile strength. These results support a thermal contraction origin of observed small-scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice.

Hydrograph separations in an arctic watershed using mixing model and graphical techniques

Abstract: Storm hydrographs in the Upper Kuparuk River basin (142 km2) in northern Alaska were separated into source components using a mixing model and by recession analysis. In non-Arctic regions, storm flow is commonly dominated by old water, that is, water that existed in the basin before the storm. We suspected that this may not be true in Arctic regions where permafrost diminishes subsurface storage capacity. Streamflow during the snowmelt period was nearly all new water. However, all summer storms were dominated by old water. Storms in a neighboring basin were dominated by new water but much less than was the snowmelt event. Thus a large increase in old water contributions occurred following the snowmelt period. This increase continued moderately through the summer in 1994 but not in 1995. We credit the seasonal changes in old water contributions to increased subsurface storage capacity due to thawing of the active layer.

Effects of Climate on the Active Layer and Permafrost on the North Slope of Alaska, U.S.A.

Abstract: Thermal regimes of the active layer and permafrost and their relations to the present-day climatic conditions on the north slope of Alaska, U.S.A. were investigated by using data collected over six years and by numerical modelling. The thickness of the active layer increases from the Arctic coast to the foothills of the Brooks Range and is directly proportional to summer air temperatures and thawing index. Within about 120 km from the Arctic coast, mean annual air temperature for the period from 1987 through 1992 was nearly constant at about −12.4±0.4°C, while the mean annual ground surface and permafrost surface temperatures increased more than 4°C. Variations in the length of thaw season and thawing index are the major factors which influence permafrost temperatures during the summer. Interactions of wind, microrelief, vegetation and seasonal snow cover and variations of physical (such as density and structure) and thermal properties of snow are the major factors affecting permafrost temperatures during the winter. The insulating effect of the seasonal snow cover could be either positive or negative on a daily basis depending upon the synoptic weather processes and on a monthly basis depending upon the time of year. On an annual basis, seasonal snow cover could increase the mean annual ground surface temperature by 2 to 7°C. Over a decade, snow cover also shows a strong effect on permafrost temperatures. Modelling results show that the depth hoar fraction of the seasonal snow cover varies from about 0.31 along the coast to about 0.57 inland. Higher permafrost temperatures along the foothills of the Brooks Range are the results of warm winters due to the impact of less strong atmospheric temperature inversion. © 1997 John Wiley & Sons, Ltd.

Analysing the creep of mountain permafrost using high precision aerial photogrammetry: 25 years of monitoring Gruben rock glacier, Swiss Alps

Abstract: Aerophotogrammetrical monitoring of Gruben rock glacier over the period 1970 to 1995 results in a unique time series documenting the three-dimensional surface kinematics of creeping mountain permafrost. In places, the area under study is aAected by historical fluctuations of the polythermal Gruben glacier. Changes in elevation and surface velocities were measured over five consecutive five-year periods using an advanced photogrammetric monoplotting technique of multitemporal stereo models. The measurements are based on a regular grid with a mesh width of 25 metres and have an accuracy of a few centimetres per year. Although surface lifting occurred in places and within individual time intervals, surface subsidence predominated at an average rate of a few centimetres per year in the ‘periglacial’ part of the rock glacier and of a few decimetres per year in the ‘glacier-aAected’ part of the rock glacier which still contains some dead glacier ice in permafrost. Fluctuations in horizontal surface velocities seem to correlate with temporal changes in surface elevation. Analysing flow along principal trajectories and interpreting the advance rate of the front leads to an age estimate of the rock glacier of a few millennia. Dynamic eAects of three-dimensional straining within the creeping permafrost as computed from the measured surface velocity field are estimated to potentially contribute to surface heave or subsidence in the same order of magnitude as the observed vertical changes. Temporal variations of surface altitudes at Gruben rock glacier show distinct similarities with mass balance and surface altitude variations determined on nearby glaciers but at a greatly reduced amplitude. This similarity may indicate that the same climatic forcing (summer temperatures?) could possibly have a predominant influence on permafrost aggradation/degradation as well as on glacier mass balance in mountain areas. #1997 John Wiley & Sons, Ltd.

Permafrost zonation and climate change in the northern hemisphere: results from transient general circulation models

Abstract: Numerous studies have demonstrated that both global patterns and local details of permafrost distribution are highly responsive to climatic fluctuations, at several temporal and spatial scales Permafrost currently underlies about one fourth of the land area of the northern hemisphere, and many qualitative predictions have been made for a severe reduction of this area in response to global warming A map of permafrost distribution compiled using the ‘frost index’, a dimensionless number that can be related to the zonal arrangement of permafrost, shows very good correspondence with a recently published empirical map The frost index was used in conjunction with three transient general circulation models to compile maps of permafrost zonation for conditions in the mid-21st century Although regional patterns and local details differ substantially between the three scenarios, all result in reductions in the area occupied by each permafrost zone Localized expansions of the area underlain by permafrost are apparent from two of the scenarios Reductions in the areal extent of equilibrium permafrost predicted from two of the three transient models are much less than those indicated by runs using 2 × CO models

A full-scale field experiment (1978-1995) on the growth of permafrost by means of lake drainage, western Arctic coast: a discussion of the method and some results

Abstract: On 13 August 1978, a lake on the western Arctic coast was artificially drained, in a multidisciplinary experiment on the growth of permafrost on the unfrozen bottom of the drained lake. A bowl-shaped talik (unfrozen basin) with a maximum depth of about 32 m underlay the lake bottom prior to drainage. In the first winter after drainage, downward freezing started on the exposed lake bottom and upward freezing from permafrost beneath the talik. After drainage, the soft lake-bottom sediments hardened from water loss and freeze–thaw consolidation. Gradual thinning of the active layer at many sites was accompanied by ground uplift and the growth of aggradational ice. Downward and upward freezing has resulted in solute rejection, freezing-point depressions, pore-water expulsion from the freezing of the saturated lake-bottom sands, and convective heat transfer from groundwater flow in an open hydrologie system. The increasingly saline intrapermafrost groundwater, flowing at an increasingly negative temperature be...

Methane emissions from wetlands in the zone of discontinuous permafrost: Fort Simpson, Northwest Territories, Canada

Abstract: We examined the influence of water table position, temperature, vegetation, and CH 4 storage on CH 4 flux at 22 wetland sites located in the zone of discontinuous permafrost, near Fort Simpson, Northwest Territories. Sites ranged from frozen peat plateaux and palsas with collapse scars to fens and bogs and ponds. Mean summer CH4 emissions ranged from -1.3 to 255 mg m -2 d -1 , and the variation among sites was best explained by mean water table position (r 2 = 0.62, n = 19). Large CH 4 fluxes (>30 mg m -2 d -1 ) and high water tables occurred in ponds and graminoid sites, whereas small fluxes ( < 30 mg m -2 d -1 ) and low water tables occur in shrub and woody sites. These relationships were upheld across several northern boreal regions, based on water table depth and broad ecological criteria. CH4 turnover times were generated by comparing surficial fluxes and storage within the saturated portion of the peat profile. Graminoid sites had CH 4 turnover times from 1 to 4 days, whereas shrub or woody sites had longer turnover times, ranging from weeks to years. We estimated an overall flux of ∼ 18 mg m -2 d -1 for the landscape around Fort Simpson. This CH 4 flux may increase with the onset of global warming, owing to the fragility of permafrost, resulting in the formation of collapse scars with high CH 4 emission rates.

The impact of permafrost thawing on the carbon dynamics of tundra

Abstract: There is debate on the potential release of the tundra's immense carbon stocks into the atmosphere in response to global warming. We present here results obtained with a model of CO2 exchanges, coupled to a model of the soil thermal and hydrological regime in the tundra. We show that, because of the partial thawing of permafrost and subsequent increase in nutrient availability, the ecosystem's response to warming may be a long-lasting increase in C accumulation, following a temporary increase in CO2 emissions. Our study also provides a consistent picture of CO2 exchanges in tundra ecosystems, reconciling the short-term experimental response to warming, recent field measurements, and Holocene C accumulation estimates.

Carbon storage along a latitudinal transect in Alaska

Abstract: Global warming is anticipated to have a significant impact on high-latitude ecosystems which store large amounts of C in their soils and have a predominance of permafrost. The purpose of this study was to estimate the total C storage of different ecosystems along a north-south transect in Alaska. Soil pedons from three Alaska climate zones were studied. These zones were the arctic slope with continuous permafrost and vegetation predominantly tussock tundra and coastal marsh, Interior Alaska with discontinuous permafrost and vegetation predominantly spruce forest on the upland and tundra or bog in the lowland, and Southern Alaska free of permafrost with the vegetation predominantly mixed hardwood and conifers with moss bogs. Soil samples were taken from the representative ecosystems of these zones for carbon storage analysis. In the Arctic and Interior Alaska zones, many soils are cryoturbated and as a result the horizons are warped and often broken. These conditions made it impractical to use the common method for estimating C storage that is used for soils with roughly parallel horizons. For this study the linear proportion of each horizon in the cryoturbated pedon was digitized by using a Geographic Information System (GIS) and the irregular horizons were collapsed to form a simulated profile with parallel horizons. The carbon content of each pedon was then calculated based on the linear proportions. These carbon stores based on the whole soil (1 m deep) approach were compared to other available estimates from the literature. Calculations for pedons from selected ecosystems in Alaska ranged from 169 MgC/ha to 1292 MgC/ha. The organic carbon storage of the arctic coastal marsh pedon amounted to 692 MgC/ha, and that of the arctic tundra pedon amounted to 314 and 599 MgC/ha. The carbon storage of interior forest pedons was 169 and 787 MgC/ha, and the associated organic soil stored nearly 1300 MgC/ha. The carbon storage in the mixed forest and coastal forest pedons was 240 and 437 MgC/ha, respectively. The bog associated with the mixed and coastal forest stored 1260 MgC/ha. Soils with the thickest organic layers were bogs associated with the tundra and boreal forest. These soils had the largest carbon storage. Carbon stores estimated from the whole pedon approach are 30 to 100% higher than those from the literature from the same zones. These data suggest that the global carbon storage estimates based in part on literature values from the N. latitudes, may be underestimated.

Aufeis of the Firth River Basin, Northern Yukon, Canada: insights into permafrost hydrogeology and Karst

Abstract: The 31-km2 aufeis ice sheet of the upper Firth River holds a wealth of information on groundwater hydrology in periglacial environments. Baseflow recession calculations, corrected for aufeis storage (12% of basin discharge), indicate specific groundwater recharge rates of up to 100 mm yr-' (up to 50% of runoff), suggesting a significant proportion of drainage from karst. The upper Firth River aufeis is a composite aufeis, with discrete baseflow contributions from different watersheds. Since the late Pleistocene, annual growth of the aufeis has exerted a strong control on lateral erosion and the local river channel geomorphology. Two groundwater recharge processes are distinguished on the basis of carbonate geochemistry and 8'3C: (1) Methanogenic groundwaters, with '3CDI Up to -3.3%,, are recharged through saturated soils underlain by permafrost; conditions which support anaerobic consumption of dissolved organic carbon (DOC) and produce up to 700 Ipg-CH4 L-' (calculated), and (2) Karst groundwaters, with '3C-depleted DIC, recharged through unsaturated soils and circulate through fissured talik in the carbonate bedrock. Most drainage from the region shows varying contributions of these two groundwaters, although a greater contribution from the methanogenic groundwaters occurs in north-facing watersheds. The 8'3C values for cryogenic calcite precipitates in the ice indicate that the karst groundwaters are the major contribution to aufeis growth. The combined use of s'3CDIC and geochemistry may be a useful tool to quantify methanogenesis in northern watersheds.

Ecology of Arctic Environments

Abstract: Arctic Soils And Permafrost Microbial Ecology, Decomposition And Nutrient Cycling The Role Of Bryophytes And Lichens In Polar Ecosystems Habitat Fragility As An Aid To Long Term Survival In Arctic Vegetation The Role Of Arctic Vegetation In Ecosystem And Global Processes Life Strategies Of Arctic Terrestrial Arthropods Environmental Fluctuations In Arctic Marine Ecosystems As Reflected By Variabilty In Reproduction Of Polar Bears And Ringed Seals Trophic Interactions In Arctic Ecosystems And The Occurrence Of A Terrestrial Trophic Cascade Pathways And Effects Of Contaminants In The Arctic Effects Of Acid Deposition On Arctic Vegetation Effects Of Enhanced UV-B Radiation On Subarctic Vegetation Effects Of CO2 And Climate Change On Arctic Ecosystems

Climatic and physiographic controls on wetland type and distribution in manitoba, canada

Abstract: Wetlands represent a substantial part of Manitoba’s terrestrial landscape, covering 233,340 km2 or 43% of the province; peatlands represent 90% of all wetlands. A wetland inventory for Manitoba is presented following a classification scheme grounded in wetland function, vegetation, and landform. The province is subdivided into twelve wetland regions each having distinctive wetland types and abundances. A hybrid Detrended Canonical Correspondance Analysis (DCCA) indicates that wetland distribution in the province is largely controlled by allogenic factors of climate and physiography. The first canonical axis represents the variance in wetland distribution occurring along a north-to-south gradient within the province. In northern Manitoba, permafrost bogs dominate, replaced southwards by bogs without permafrost and fens with and without internal lawns. Farther south, peatlands are replaced by non-peat-accumulating wetlands. This wetland distributional gradient is most strongly correlated to mean annual temperature, with thermal seasonal aridity, annual precipitation, and moisture deficit (precipitation-potential evaporation) also significant. Significant allogenic variables correlated to the first canonical axis are not restricted to climate alone. The type of bedrock geology in the area also plays an important role in determining wetland distribution, with bogs occurring preferentially in areas of acidic bedrock, while fens are found on calcareous bedrock. The second canonical axis represents a surface-water flow gradient, with patterned fens and marshes having relatively large amounts of surface-water flow on one end and nonpermafrost bogs and swamps with low amounts of surface-water flow on the other. Texture of the subsurface is the most important variable explaining the second axis, with sediments having high hydraulic conductivity correlated to wetlands with high surface-water flow, while sediments with low hydraulic conductivity are related to wetlands with low surface-water flow. Annual precipitation is also a statistically significant variable explaining the variance in wetland distribution along the second axis.

Distribution, Characteristics, and Use of Earth Dens and Related Excavations by Polar Bears on the Western Hudson Bay Lowlands

Abstract: Polar bears fasting on land along the western coast of Hudson Bay during the open water period, from late July through early November, excavate three different types of structures, which we termed pits, deep dens, and shallow dens. Pits were shallow excavations found on the tops of banks or beach ridges, whereas both deep and shallow dens were dug into frozen peat banks. Pits were used as temporary resting places. The function of shallow dens is less clear, although some bears have been observed resting in them. Deep dens, which have an entrance tunnel and an enlarged inner chamber, are similar in size and structure to maternity dens dug in snow by female poplar bears elsewhere in their range. Deep and shallow dens are primarily occupied by lone females, most of which are pregnant, while pits are generally occupied by adult males and are used more during summer than in autumn. Pregnant polar bears in western Hudson Bay give birth between mid-November and mid-December, by which time snowdrifts suitable for the construction of maternity dens have not yet formed in most years. Thus, because earth dens represent the only consistently suitable environment available at the time of parturition, we suggest most cubs in western Hudson Bay are born in them. Consequently, the availability of suitable habitat for the construction and use of earth dens is probably critical to the survival of the polar bear population in Western Hudson Bay. Secondary benefits of earth dens to pregnant females, and to other bears during the warm weather in late summer, are that they help the bears to conserve energy by remaining cool and to avoid insect harassment.

Principal features of evaporite karst in Canada

Abstract: Outcrops of sulfate and mixed sulfate-carbonate rocks are common every where in Canada outside of the Shield province. Interstratal salt deposits are abundant in the interior lowlands. Types of karst that occur are determined chiefly by relations between (i) formation thickness and purity, (ii) regional topography and hydraulic gradient, (iii) effects of receding Wisconsinan and earlier glaciers, and (iv) extent of modern permafrost.

Canada Stream: A Glacial Meltwater Stream in Taylor Valley, South Victoria Land, Antarctica

Abstract: The McMurdo Dry Valleys of South Victoria Land, Antarctica, form the largest of the desert oases found along the coast of Antarctica Although this region is an extreme cold desert, glacial meltwater streams, which flow for 6-10 wk during the austral summer, are a prominent feature of the landscape Canada Stream is in Taylor Valley and is one of 3 major streams draining Canada Glacier The surrounding landscape is characterized by an absence of plant life, an underlying permafrost at a depth of 05 m, and prominent "patterned ground" features, which are large (3-5 m across) polygonal patterns formed through freeze/thaw cycles In contrast to the barren landscape, many of the streams contain perennial algal mats and mosses, illustrating that the presence of liquid water allows for a photosynthetically based ecosystem even under the harshest conditions Canada Stream is one of 10 streams that flow into Lake

The chronology of speleothem deposition in northern Yukon and its relationships to permafrost

Abstract: In the northern Yukon there is a significant group of limestone caves in an area that was not glaciated during the Quaternary. Permafrost appears to have played an important role in restricting calcite speleothem deposition in the caves. U/Th dating and stable isotopic studies indicate that the deposits form two distinct groups, a first group younger than 350 ka, and a second group older than the 350 ka BP limit of the conventional U/Th alpha spectrometric dating method. Two large samples from the second group yield sequences of magnetic declinations and inclinations with reversed and normal polarity, perhaps from the Tertiary. The pollen content of five speleothems, the modes of calcite deposition, and stable isotopic analyses indicate that the speleothems were deposited under a cold regime. It is suggested that the ancient speleothems were deposited at a time when permafrost was absent, during the later Tertiary or at the beginning of the Quaternary period. The establishment and maintenance of permafros...

Neoglacial Climate Control of Subarctic Picea abies Stand Dynamics and Range Limit in Northern Sweden

Abstract: The study focused on the performance of the spruce (Picea abies [L.] Karst.) range limit in northern (subarctic) Sweden during the Neoglacial period of the Holocene, mainly after the climax of the Little Ice Age. Subfossil wood remains suggest that the geographic spruce tree limit has remained fairly stable for slightly more than the past 2000 14C yr. Previous postulates about delayed immigration and continual spread are contradicted in favor of a dynamic climate/spruce equilibrium. The mechanism restricting the spruce distribution was inferred to be severe annual ground frost characterizing this climatically continental and snowpoor region, which is crossed by the limit of discontinuous permafrost. An extensive (landscape scale) age structure analysis showed near-exponential population build-up over the past 100 yr or so. This manifested as densification of outlying stands and sparse range limit advance by some tens of kilometers. These responses clearly related to increased snowfall during the early (December) and late winter (March). In consequence, annual ground frost and permafrost declined in general, which made the least ground frost prone sites equable for establishment and persistent growth (less risk of winter desiccation) of spruce. These inferences are strengthened by tendencies for decreased spruce regeneration and vitality during the past decades, coincident with some exceptionally cold and snow-poor early winters. It is speculated that the structure and performance of the studied system, i.e. outliers checked by severe ground frost, is a small-scale analogy to the situation preceding the general late Holocene expansion of spruce in Fennoscandia.

Numerical simulation of permafrost evolution as a part of sedimentary basin modeling: permafrost in the Pliocene–Holocene climate history of the Urengoy field in the West Siberian basin

Abstract: Present-day temperature profile may be used as an important constraint for reconstruction of the thermal regime in sedimentary basin modeling. This type of profile is significantly non-steady state, especially for basins located at high and middle latitudes. However, estimations of past thermal regimes are indefinite and often limited by knowledge of past glaciations and by the simple two-layer model usually employed. In this paper, permafrost modeling was carried out as a continuation of basin modeling of the sedimentary section of Urengoy field of the West Siberian basin (66°N, 77°E). Consideration of surface temperatures beginning with the Triassic, a refined initial temperature distribution, permafrost modeling for the past 3.4 Ma, and use of a real lithological cross section distinguish this approach from previous studies. Depth and time variations in thermophysical parameters of rocks (heat conductivity, heat capacity, unfrozen water content, salt content, and porosity) had a considerable influence ...

The Contribution of Geoelectrical Investigations in the Analysis of Periglacial and Glacial Landforms in Ice Free Areas of the Northern Foothills (Northern Victoria Land, Antarctica)

Abstract: All periglacial and glacial landforms investigated in the Northern Foothills have a very thin active layer (0.1-0.3 m thickness) overlying a thin permafrost layer, characterised by electrical resistivities ranging between 13 and 50 kΩm and by different thicknesses. Below this surficial layer, different types of ground ice (with a resistivity range from 8000 to 0.1 kΩm) were detected. These different types of ground ice permitted ice-cored rock glaciers to be distinguished from ice-cemented rock glaciers, subsea permafrost to be identified in some raised beaches, and other interpretations to be suggested about a debris-covered glacier. These results have been obtained by vertical electrical soundings (VES) carried out in ice-free areas of the Northern Foothills, near Terra Nova Bay Station during the tenth national Italian expedition in Antarctica (1994-1995). In these areas on the basis of previous geomorphological research, some landforms such as rock glaciers, raised beaches with patterned ground and debris-covered glaciers were chosen to carry out the VES. The electrical prospection can be considered a good means for understanding the origins of landforms in ice-free areas of Antarctica and for making a contribution to the palaeoenvironmental reconstruction of this continent.