Search results

Filters

  • Journals
  • Authors
  • Keywords
  • Date
  • Type

Search results

Number of results: 130
items per page: 25 50 75
Sort by:

Abstract

The common and ecologically important cyanobacterial form-genus Leptolyngbya is widely distributed in numerous ecosystems over the Earth's biosphere. Several morphospecies dominate microbial communities in polar habitats, but their diversity and local ecological significance are little known. Several articles characterising strains isolated from Antarctic coastal habitats by molecular methods were published, but knowledge of their phenotype and ecological characters are indispensable for future detailed environmental studies. Distinct morpho- and ecotypes (ecologically important morphospecies) from maritime Antarctica are characterised in this article. Eight dominant Leptolyngbya types from subaerophytic and freshwater habitats were recognised, and four of them (L. borchgrevinkii, L. fritschiana, L. nigrescens and L. vincentii) are described as new distinct species.
Go to article

Abstract

The current climate warming results in a quick recession of glaciers on the northern slopes and valleys of the Lindströmfjellet-Hĺbergnuten mountain ridge in Nordenskiöld Land. The equilibrium line altitude has risen from c. 500-550 m in 1936 to c.750 m in 2001 and c. 800 m in 2006. The slopes, almost completely glaciated during the Little Ice Age, and even in 1936, have mostly been abandoned by glaciers afterwards. The upper parts of the glaciers undergo a clear retreat diminishing their accumulative (firn) fields. The lower parts of the active glacial tongues have been transformed into marginal zones built of dead ice covered with morainic and glacifluvial deposits. The surfaces of the marginal zones are progressively lowered due to ablation of dead ice. The state of the described glaciers is not balanced under the current climatic conditions. Thus, the landscape transformation of the mountain ridge will most certainly continue.
Go to article

Abstract

Traditional mass balance measurements by stake readings and snow surveying have been conducted annually since 1996 on the Waldemar Glacier (= Waldemarbreen) in northwest Spitsbergen, Svalbard. Several indirect methods were also used for estimating its mass balance. These methods were divided into two major groups: climatological and geodetic. A comparison of the latest map (2000) with that of 1978 and climatological records enable us to calculate the change in the mass balance of Waldemarbreen over 34 years. These methods include air temperature and degree-day (PDD) models. The average mass balance of Waldemarbreen, computed by climatological methods, was -0.42 m a-1 of water equivalent (w.e.) for the period 1970-2004, and -0.51 m w.e. for 1996-2004. These balances were compared with the glaciological balance for the period 1996-2004, -0.53 m w.e.. The mass balance was also computed using geodetic method, giving -0.52 m of w.e. from 1978 to 2000. It is suggested that, from these results, the approach used for Waldemarbreen might be also useful for estimation the mass balances of other small Svalbard glaciers which terminate on land.
Go to article

Abstract

Sphagnum riparium (Bryophyta) is recorded and described from the Wedel Jarlsberg Land on Spitsbergen, the Arctic Svalbard Archipelago. It is the northernmost known population of the species in the Northern Hemisphere. The distribution of the two known Sphagnum species in the Hornsund area, viz. S. riparium and S. squarrosum is mapped and described.
Go to article

Abstract

Eighty five faecal samples of the Svalbard reindeer inhabiting the coastal terrace of the northern side of Hornsund were collected in July 2005 and analyzed coprologically. The standard flotation method revealed a 97.6% prevalence of infection at an average intensity of 20 eggs in a single subsample. The quantitative, modified McMaster method helped to estimate the mean number of eggs in a gram of faeces (EPG) at 134.7. In the studied samples eggs of nematodes representing two species, i.e. Ostertagia gruehneri (97.6%, on average 20 eggs in a sample) and Marshallagia marshalli (2.3%, single eggs), were identified.
Go to article

Abstract

In 72 samples collected from various types of habitats of West Spitsbergen 150 algal taxa have been identified, including 100 taxa of Cyanoprokaryota, 40 of Chlorophyceae, and 10 of Xanthophyceae. Seventy-two species, mainly blue-green algae (55 taxa) are considered as new for Svalbard flora.
Go to article

Abstract

A glacier lake outburst flood occurred on James Ross Island, Antarctic Peninsula region, during the 2004-2005 austral summer season. The source lake was located on the Lachman II ice-cored rock glacier, and formed prior to 1980. The size of the lake has been increasing gradually since the 1990s. The lake basin extended to approximately 220 m in length and 160 m in width by the end of February 2005. We observed that the lake had drained by February 2005, and found a deep gully on the south side of the lake rim. It appears that the lake level rose and water overflowed the lake rim here. James Ross Island contains a large number of debris-covered glaciers, ice-cored moraines, and rock glaciers with glacier lakes which are dammed by these features or which form upon them. As climatic warming has recently been reported for this region, further glacier lake outburst floods seem likely to occur.
Go to article

Abstract

This study used ground penetrating radar soundings to examine a tongue-shaped rock glacier (64°04’S 58°25’W) on James Ross Island, Antarctic Peninsula, in January 2005. The rock glacier studied has multiple well-developed transverse ridges and approximately 800 m long from the talus of its head to its frontal slopes and is 300 m wide in the middle. The longitudinal ground penetrating radar profile identified debris bands which dip up-glacier, similar to the thrust structures in the compression zone of a valley glacier. Transverse ground penetrating radar profiles indicated a layered structure which is inclined towards the central part of the rock glacier and which resembles the transverse foliation of a valley glacier. Consequently, the internal structure of the rock glacier is revealed as being similar to the “nested spoons” common in the interior of valley glaciers. We concluded that this rock glacier has been created by the deformation of a glacier ice core and a thick and continuous debris mantle.
Go to article

Abstract

Large-scale stone-banked lobes and terraces are distributed over an area of 1 km2 of gentle slope on Rink Plateau in the northern part of James Ross Island, Antarctic Peninsula region. Topographically, there are two main features: relatively high risers up to 5 m high and distinct frontal ridges. In order to understand the processes responsible for these lobes and terraces, the authors have monitored air and ground temperatures and movement of stones on the surface over the period 1995-2005. In February 2005, the subsurface structures were surveyed by ground penetrating radar and drilling. The ground penetrating radar profiles identified the bedrock surface. The surface morphology of the lobes corresponds closely with that of the bedrock. The relatively high risers of these lobes are presumed to be due to a cessation of frontal advance.
Go to article

Abstract

Mount Flora at Hope Bay, in northernmost part of Antarctic Peninsula, is a famous Jurassic flora locality. It has already been studied for a hundred years, but however, it is still possible to find there new taxa. Based on two species of liverworts found at Mount Flora (Schizolepidella gracilis and Schizolepidella birkenmajeri sp. nov.), the present study discusses affiliation of the genus Schizolepidella to liverworts. The new species Schizolepidella birkenmajeri is erected.
Go to article

Abstract

Trematomus newnesi (Nototheniidae), a bentho-pelagic fish, caught off Adélie Land (eastern Antarctic) was examined for the presence of internal parasitic worms. These fishes were infected with 11 species and larval forms of parasites: Digenea (Macvicaria pennelli, Neolebouria terranovaensis, Genolinea bowersi, and Elytrophalloides oatesi), larval Cestoda (two forms of tetraphyllidean metacestodes, bilocular form and trilocular form, and diphyllobothriid plerocercoids), Acanthocephala (Metacanthocephalus campbelli, M. johnstoni) and larval Nematoda (Contracaecum osculatum, C. radiatum). Larval cestodes were the dominant parasites, whereas acanthocephalans were relatively rare. Five species and larval forms were recorded also in fish caught in the Davis Sea. A check list of parasites of T. newnesi recorded in the eastern- and western Antarctic comprises 21 species and larval forms. Probably, T. newnesi plays an important role in life cycles of parasitic worms in the Antarctic.
Go to article

Abstract

Zooplankton was investigated at fixed site in 24 hours in Kongsfjorden, a glacial fjord situated on the west coast of Spitsbergen (Svalbard) (79°N, 12°E), in order to unveil the level of diurnal variability in community composition and abundance. Parallel to zooplankton study water temperature and salinity were measured while information on local tides and winds was obtained from external sources. Observed changes did not exceed the range of variability regarded intrinsic, resulting from the nature of plankton. Because of this low variability we are of the opinion that the data presented can be regarded a valid measure of the natural heterogeneity of zooplankton communities in hydrologically dynamic Arctic coastal waters in summer. The observed changes in zooplankton were primarily induced by the complex dynamics of the fjord’s water masses. In spite of importance of tidal forcing, the variability in zooplankton did not demonstrate similar temporal fluctuations due to modification of the water movement by other irregular forces (local wind). Also, we have not found any indication of diel vertical migration in coastal water in the Arctic under the condition of midnight sun.
Go to article

Abstract

Saprotrophic filamentous microfungi were isolated by means of the soil dilution method from soil samples collected from four locations in the Bellsund region of Spitsbergen (77°33’N, 14°31’E) representing the following forms of surface micro-relief: an old stormbank, a sorted circle, a frost fissure between tundra polygons, and the central part of a tundra polygon. The fungal isolates were identified and screened for their ability to grow at low temperatures. The oligotrophy of psychrophilic and psychrotrophic strains was then determined as the ability of growth on silica gel without a C source added. Differences in some physico-chemical properties were found between the soils sampled from the four sites. A total of 89 taxa from 17 genera were isolated. Most of the isolates were species of Mortierella, Penicillium, Chrysosporium and Phialophora, and half of them were psychrophiles. Fungal communities isolated from a frost fissure between tundra polygons (site 3) and from the central part of a tundra polygon (site 4) were dominated by psychrophiles but those isolated from an old stormbank (site 1) and a sorted circle (site 2) were predominantly psychrotrophic. Oligopsychrophilic taxa accounted for 27% and oligopsychrotrophic for 20% of all the isolated taxa but only from 0.7% to 11.7% and from 1.2% to 6.3% of the total number of cfu (colony forming unit) isolated from an individual site, respectively. The results of the present study suggest that the abundance of fungi in Arctic soil is mostly affected by the content of organic matter in the A horizon and the plant cover, but other factors, such as the stage of soil development and the micro-relief of the surface, are more important for species richness of fungal communities.
Go to article

Abstract

The Bravaisberget Formation in Spitsbergen embraces an organic carbon-rich, clastic sequence that reflects a general shallow shelf development of the Middle Triassic depositional system in Svalbard . New observations and measurements of the type section of the formation at Bravaisberget in western Nathorst Land allow to present detailed lithostratigraphical subdivision of the formation, and aid to reconstruct its depositional history. The subdivision of the formation ( 209 m thick at type section) into the Passhatten, Somovbreen, and Van Keulenfjorden members is sustained after Mørk et al. (1999), though with new position of the boundary between the Passhatten and Somovbreen mbs. The Passhatten Mb is defined to embrace the black shale-dominated sequence that forms the lower and middle parts of the formation ( 160 m thick). The Somovbreen Mb ( 20 m thick) is confined to the overlying, calcite-cemented sequence of marine sandstones. The Van Keulenfjorden Mb ( 29 m thick) forms the topmost part of the formation composed of siliceous and dolomitic sandstones. The formation is subdivided into twelve informal units, out of which eight is defined in the Passhatten Mb (units 1 to 8), two in the Somovbreen Mb (units 9 and 10), and also two in the Van Keulenfjorden Mb (units 11 and 12). Units 1, 3, 5, 7 and 9 contain noticeable to abundant phosphorite, and are interspaced by four black shale sequences (units 2, 4, 6, and 8). Unit 9 passes upwards gradually into the main sandstone sequence (unit 10) of the Somovbreen Mb. The base of the Van Keulenfjorden Mb is a discontinuity surface covered by thin phosphorite lag. The Van Keulenfjorden Mb consists of two superimposed sandstone units (units 11 and 12) that form indistinct coarsening-upward sequences. The Bravaisberget Fm records two consequent transgressive pulses that introduced high biological productivity conditions to the shelf basin. The Passhatten Mb shows pronounced repetition of sediment types resulting from interplay between organic-prone, fine-grained environments, and clastic bar environments that focused phosphogenesis. The lower part of the member (units 1 to 5) contains well-developed bar top sequences with abundant nodular phosphorite, which are under- and overlain by the bar side sequences grading into silt- to mud-shale. The upper part of the member (units 6 to 8) is dominated by mud-shale, showing the bar top to side sequence with recurrent phosphatic grainstones in its middle part. Maximum stagnation and deep-water conditions occurred during deposition of the topmost shale sequence (unit 8). Rapid shallowing trend terminated organic-rich environments of the Passhatten Mb, and was associated with enhanced phosphogenesis at base of the Somovbreen Mb (unit 9). Bioturbated sandstones of the Somovbreen Mb (unit 10) record progradation of shallow-marine clastic environments. The sequence of the Van Keulenfjorden Mb (units 11 and 12) was deposited in brackish environments reflecting closure of the Middle Triassic basin in western Svalbard .
Go to article

Abstract

This paper describes the weather conditions on the NE coast of Sørkappland (South Spitsbergen) during August 2005, and considers them in the context of the general synoptic situation over the North Atlantic . A comparison of local climates features for the East and West coast of southern Spitsbergen shows that the general atmospheric circulation and direct solar radiation in summer are the decisive factors affecting weather on the East coast. Foehn effects were observed during the study period. In the East, these were triggered by the westerly cyclonic situation and, in the West, by the easterly. The differences in the intensity of foehn effects may be explained by a specific relief of the Sørkappland peninsula.
Go to article

Abstract

The general objective of this research has been to identify the factors and conditions of migration of CaCO3 within glaciers and their marginal zones in Svalbard . Special attention has been paid to the cryochemical processes responsible for precipitation of calcium carbonate in icing (naled ice) formed near fronts of polythermal glaciers during winter. Estimates of the importance of those processes in respect of the general mineral mass transfer in the glacier system are attempted here. Field studies concerning the carbonate contents in proglacial sediments and icing fields were carried out in the Werenskioldbreen and the Elisebreen basins (S and NW Spitsbergen respectively). A functional model of CaCO3 migration in a glacier system is proposed which indicates the various paths of the mineral mass flow. Considerations on intensity of glacial processes permitted quantitative estimation of the particular components in respect to the Werenskioldbreen basin. Cryochemical processes do not appear to be of overriding importance in such migration but, clearly, they play a specific role in retaining CaCO3 in the proglacial zone on land. The crystalline forms present in the icings, which have many lattice defects, are very easily re-dissolved or removed by wind.
Go to article

Abstract

Twelve glaciers, representing various types, were investigated between 2000 and 2005, in a region adjacent to the northern reaches of Billefjorden, central Spitsbergen ( Svalbard ). On the basis of measurements taken using reference points, DGPS and GPS systems, analyses of aerial photographs and satellite images, geomorphological indicators and archival data their rates of deglaciation following the “Little Ice Age” (LIA) maximum were calculated variously on centennial, decadal and annual time scales. As most Svalbard glaciers have debris-covered snouts, a clean ice margin was measured in the absence of debris-free ice front. The retreat rates for both types of ice fronts were very similar. All studied glaciers have been retreating since the termination of the Little Ice Age at the end of 19th century. The fastest retreat rate was observed in the case of the Nordenskiöldbreen tidewater glacier (mean average linear retreat rate 35 m a-1). For land-terminating glaciers the rates were in range of 5 to 15 m a-1. Presumably owing to climate warming, most of the glacier retreat rates have increased several fold in recent decades. The secondary factors influencing the retreat rates have been identified as: water depth at the grounding line in the case of tidewater glaciers, surging history, altitude, shape and aspect of glacier margin, and bedrock relief. The retreat rates are similar to glaciers from other parts of Spitsbergen . Analyses of available data on glacier retreat rates in Svalbard have allowed us to distinguish four major types: very dynamic, surging tidewater glaciers with post-LIA retreat rates of between 100 and 220 m a-1, other tidewater glaciers receding of a rate of 15 to 70 m a-1, land terminating valley polythermal glaciers with an average retreat of 10 to 20 m a-1 and small, usually cold, glaciers with the retreat rates below 10 m a-1.
Go to article

Abstract

During the late 2007 austral summer, 20 sediment samples were collected in Admiralty Bay (King George Island, South Shetlands, West Antarctica) from 8 down to 254 m water-depth (mwd). The samples yielded abundant assemblage of monothalamous benthic foraminifera, belonging to at least 40 morphospecies. They constituted the first such collection from Antarctic Peninsula fjords and provided a new insight into this group’s diversity and distribution. Among organic-walled taxa, Psammophaga sp., Allogromia cf. crystallifera, and three morphotypes of Gloiogullmia were especially abundant. Agglutinated forms were dominated by Hippocrepinella hirudinea, Psammosphaera spp., Lagenammina spp., and various mudballs. Although, the majority of the morphotypes were known from other high-latitude locations, some were reported for the first time. Our quantitative data (>125 µm) showed the greatest differences between monothalamous foraminifera assemblages at shallowest water depths above 50 mwd. The deepest assemblages from between 179 and 254 mwd, were most similar, suggesting uniform near-bottom conditions at ~200 mwd throughout the Admiralty Bay.
Go to article

Abstract

The main objective of this work is to provide a closed formula for the backward and symmetric solution of the 2-D implicit Roesser model. The relative forward and backward fundamental matrix is of fundamental importance in our approach. An algorithm for the determination of the backward fundamental matrix sequense is also given.
Go to article

Abstract

In this work synthesis, sintering processes and properties of three groups of perovskite-type ceramics utilized in chosen electronic applications are briefly described. The first group includes high permittivity dielectrics based on relaxor ferroelectrics and new leadfree ceramics, destined for bulk and thick film capacitors. The second group comprises ceramics for low and high temperature thermistors and the third one nonstoichiometric conducting compounds containing doped SrMnO3 and SrCoO3, tested as electrode materials for solid state cells.
Go to article

Abstract

The paper presents the results of numerical simulation of processes aimed at production of nanostructures with the use of oil emulsions in water. The appropriate molecular models of water and oil, as well as the model of the substance which would sediment at the water – oil interface, are looked for. Such substance, after suitable solidification, would become the main component of the produced material. For the described simulations, the Molecular Dynamics method has been used throughout this paper.
Go to article

Abstract

Effects of confinement on mechanical, structural and thermodynamic properties of uniform fluids are very well understood. In contrast, a general theory based on statistical thermodynamics for confined nonuniform and non-isotropic phases, such as the lamellar phase, is in its infancy. In this review we focus on the lamellar phase confined in a slit or in a pipe in order to illustrate various effects of confinement. We limit ourselves to the results obtained by M. Tasinkevych, V. Babin and the author for lamellar phases in oil-water-surfactant mixtures within a generic semi-microscopic model, using a mean-field approximation. We show that compared to isotropic fluids the excess grand potential contains additional terms associated with structural deformations. These terms depend on the type of the confining walls, the shape of the container and on the thickness of the lamella. As a result of the dependence of the structure of the confined lamellar phase on the shape of the container, capillary lamellarization and capillary delamellarization is found in slits and in pipes respectively.
Go to article

Abstract

The paper deals with the problem of electromagnetic field analysis for linear, cylindrical and spherical electromechanical converters at synchronous state of work. There are considered synchronous motor with windings on moving part (rotor, carriage) and with permanent magnets thereon. The electromagnetic field is determined analytically with the help of separation method proposed for each problem. The boundary conditions are formulated for electromechanical converters linear, cylindrical and spherically shaped. The results obtained can be used as benchmark for electromagnetic field numerical analysis and force/torque calculations.
Go to article

Abstract

The paper discusses the stability problem for continuous time and discrete time positive systems. An alternative formulation of stability criteria for positive systems has been proposed. The results are based on a theorem of alternatives for linear matrix inequality (LMI) feasibility problem, which is a particular case of the duality theory for semidefinite programming problems.
Go to article

This page uses 'cookies'. Learn more