Upper Layer Of Permafrost Research Articles

Approaches for the complex assessment of polychemical pollution of permafrost-affected soils and the upper layer of permafrost.

The analysis of about 200 samples taken from 42 permafrost-affected soil profiles was carried out on four key sites in different regions of cryolithozone (West Siberia, Central, North, and North-East Yakutia) characterized by different active layer depths and soil lithology. The aim of the study was to determine the influence of different processes of cryogenic mass-exchange on the redistribution and accumulation of major pollutants such as petroleum products, acid-soluble forms of trace elements, polycyclic hydrocarbons, and technogenic radionuclides transferred via atmospheric transport or after the local anthropogenic impact in different soil horizons of Cryosols and in the upper layers of permafrost. Samples were analyzed using modern precise techniques (direct γ-spectrometric measurements with Ge(Li) and NaI(Tl) detectors; fluorometric method; reversed-phase high-performance liquid chromatography; spectrofluorimetric detection; atomic absorption spectrometry with flame atomization). The study has shown that processes (cryoturbations, frost heaving, gelifluction along with fluvial processes) that strongly affect Cryosols' profile structure can also lead to the active migration and accumulation of local and global pollutants in the middle and lowermost suprapermafrost soil horizons. The accumulation of some pollutants in suprapermafrost horizons of cryogenic soils and in the upper layers of permafrost (in particular, petroleum products and mobile forms of trace elements) can be associated with a combination of factors, such as the relatively light particle size distribution, relatively weak manifestation of cryoturbation processes, and low thickness of the active layer (about 40-60cm). The integral calculation of the geoaccumulation index values has shown that all of the groups of human-affected soil horizons are moderately to extremely polluted by petroleum hydrocarbons (and at a relatively lower level by trace elements) and the maximum pollution stands for the suprapermafrost horizons as well as in cryoturbated or buried fragments of organogenic matter in some cases. The maxima of the heavy PAH content in permafrost-affected soils can be confined to horizons enriched with anthropogenic inclusions and artifacts (for example, construction slag, coal) and to individual horizons of soils buried as a result of both cryogenic and alluvial processes. The specific activity of the technogenic radionuclide cesium in cryogenic soils revealed its association mainly with the surface organogenic and organomineral horizons of the studied profiles and rarely observed in the cryoturbated fragments of these horizons in the middle and suprapermafrost layers of soil profiles. The necessity of the complex analytical assessment of the permafrost-affected soils has been revealed especially in case of studying of the ecological state of the anthropogenically affected Cryosols.

Polychemical pollution of surface waters and permafrost-affected soils in Central and North Yakutia and in North-West Siberia

The concentration of main organic and inorganic pollutants (heavy metals, polyaromatic hydrocarbons, radionuclides) in surface waters and in water-soil solutions was analysed on three keysites within the permafrost zone: Tazovsky Peninsula (North-West Siberia), Kolyma Lowland (North Yakutia) and adjacent to Yakutsk (Central Yakutia). In the majority of sampling points that are not directly impacted by human activity, the pollutants accumulate in the uppermost organogenic and organo-mineral horizons of natural soils. At the human-affected keysites the major pollutants may accumulate not only in the superficial horizons of the disturbed soils due to the surface runoff but also in the central parts of the profile, in the material buried by cryogenic, solifluction or fluvial processes and in some cases – in the suprapermafrost horizons and in the upper layer of permafrost transported via suprapermafrost water runoff.

Patterns of spatial methane distribution in the upper layers of permafrost in Central Yakutia

The article presents the results of long-term field studies of methane in the upper part of permafrost for the different geomorphological levels of Central Yakutia. Patterns of spatial distribution of methane content across different landscapes were found. The highest concentrations of methane are found in alas deposits, the major role of methane in the conservation there goes to the moment of freezing the thermokarst lake draining. The difference in methane content in the sediments of the Late Pleistocene Ice Complex on the left and the right bank of the river Lena was identified. That is likely caused by the conditions of ice complex formation.

The influence of cryogenic mass exchange on the distribution of viable microfauna in cryozems

The role of cryogenic mass exchange in the distribution of the viable microfauna (ciliates, heterotrophic flagellates, and nematodes) in the profiles of cryoturbated cryogenic soils and in the upper layers of permafrost was revealed. The material for microbiological investigations was collected from the main horizons of cryozem profiles, including the zones with morphologically manifested processes of cryogenic mass exchange (the development of barren spots, cryoturbation, and suprapermafrost accumulation) and the zones affected by solifluction. The radiocarbon dating of the soil samples showed that the age of the organic cryogenic material and material buried in the course of solifluction varied from 2100 to 4500 years. Some zones with specific ecological conditions promoting the preservation of species diversity of the microfauna were found to develop in the cryozem profiles. A considerable part of the community (38% of ciliates, 58% of flagellates, and 50% of nematodes) maintained its viability in the dormant state, and in some cases, it could pass to the state of long-term cryobiosis in the upper layer of permafrost.

Heave, settlement and fracture of chalk during physical modelling experiments with temperature cycling above and below 0 °C

To elucidate the early stages of heave, settlement and fracture of intact frost-susceptible rock by temperature cycling above and below 0°C, two physical modelling experiments were performed on 10 rectangular blocks 450mm high of fine-grained, soft limestone. One experiment simulated 21cycles of bidirectional freezing (upward and downward) of an active layer above permafrost, and the other simulated 26cycles of unidirectional freezing (downward) of a seasonally frozen bedrock in a non-permafrost region. Heave and settlement of the top of the blocks were monitored in relation to rock temperature and unfrozen water content, which ranged from almost dry to almost saturated.In the bidirectional freezing experiment, heave of the wettest block initially occurred abruptly at the onset of freezing periods and gradually during thawing periods (summer heave). After the crossing of a threshold marked by the appearance of a macrocrack in the upper layer of permafrost, summer heave increased by an order of magnitude as segregated ice accumulated incrementally in macrocracks, interrupted episodically by abrupt settlement that coincided with unusually high air temperatures. In the unidirectional freezing experiment, the wet blocks heaved during freezing periods and settled during thawing periods, whereas the driest blocks showed the opposite behaviour. The two wettest blocks settled progressively during the first 15 freeze-thaw cycles, before starting to heave progressively as macrocracks developed.Four processes, operating singly or in combination in the blocks account for their heave and settlement: (1) thermal expansion and contraction caused heave and settlement when little or no water-ice phase change was involved; (2) volumetric expansion of water freezing in situ caused short bursts of heave of the outer millimetres of wet rock; (3) ice segregation deeper in the blocks caused sustained heave during thawing and freezing periods; and (4) freeze-thaw cycling caused consolidation and settlement of wet blocks prior to macrocracking in the unidirectional freezing experiment. Rock fracture developed by growth of segregated ice in microcracks and macrocracks at depths determined by the freezing regime. Overall, the heave, settlement and fracture behaviour of the limestone is similar to that of frost-susceptible soil.

Polycyclic aromatic hydrocarbons in soil and surface marine sediment near Jubany Station (Antarctica). Role of permafrost as a low-permeability barrier

Although Antarctica is still considered as one of the most pristine areas of the world, the growing tourist and fisheries activities as well as scientific operations and their related logistic support are responsible for an increasing level of pollutants in this fragile environment. Soils and coastal sediments are significantly affected near scientific stations particularly by polycyclic aromatic hydrocarbons (PAHs). In this work sediment and soil were sampled in two consecutive summer Antarctic expeditions at Potter Cove and peninsula, in the vicinity of Jubany Station (South Shetland Islands). Two- and 3-ring PAHs (methylnaphthalene, fluorene, phenanthrene and anthracene) were the main compounds found in most sites, although total PAH concentrations showed relatively low levels compared with other human-impacted areas in Antarctica. Pattern distribution of PAHs observed in samples suggested that low-temperature combustion processes such as diesel motor combustion and open-field garbage burning are the main sources of these compounds. An increase in PAH concentrations was observed from surface to depth into the active soil layer except for a unique sampling site where a fuel spill had been recently reported and where an inverted PAH concentration gradient was observed. The highest level was detected in the upper layer of permafrost followed by a sharp decrease in depth, showing this layer is acting as a barrier for downward PAH migration. When PAH levels in soil from both sampling programs were compared a significant decrease (p<0.01) was observed in summer 2005 (range at 75-cm depth: 12+/-1-153+/-22 ng/g) compared to summer 2004 (range at 75-cm depth: 162+/-15-1182+/-113 ng/g) whereas concentrations in surface sediment collected nearby the station PAHs increased drastically in 2005 (range: 36+/-3-1908+/-114 ng/g) compared to 2004 (range: 28+/-3-312+/-24 ng/g). Precipitation regime and water run off suggest that an important wash out of soil-PAHs occurred during the interval time between samplings. Results showed that the present PAH contamination level of Jubany Station is relatively low compared to other reported cases in Antarctica but also suggests that an increase in rain and in thawing processes caused by the global warming could result in an important soil-associated PAH mobilization with unpredictable consequences for the biota of Potter Cove.

Soil organic carbon content in northern Canada: A database of field measurements and its analysis

Arctic and sub-arctic soils contain a large amount of organic carbon in their topsoil horizons and in the upper layers of permafrost. There is concern that climate warming could release this soil organic carbon (SOC) to the atmosphere as greenhouse gases. However, information about the profile features and spatial distribution of SOC in northern ecosystems are far less than for other regions. In this study, we compiled all the available field measurements of SOC in northern Canada and developed a database. Including our recent measurements, the database contains 438 profiles with 1473 soil horizons. We analyzed the profile features and the regional patterns of SOC in northern Canada based on this database. The results show that the SOC content of subsurface soils is relatively high in northern regions because of the alternate freeze-thaw actions. In the top 100 cm of soils, 40% of the SOC is located in the 50- to 100-cm layer. The SOC content is lower in northern Arctic and in mountainous regions. The average upland SOC content in northern Canada is higher than in other world biomes (i.e., croplands, temperate forest, tropical savannas, and tropical forest) except temperate grasslands and boreal forest. Key words: Soil organic carbon, northern Canada, database, arctic and sub-arctic.

Measurements of Atmospheric Pollution in the Siberian Arctic.

Atmospheric concentrations of aerosol chemical species and SO2 have been measured at Tiksi, Yakutsk and Norilsk in Siberia from 1993. Concentrations of SO42-, Pb, Cu, Ni and V at Tiksi increase in winter and spring, and decrease in summer. Soil, moss and larch leaf samples were collected at Norilsk and Yakutsk, and soil samples at Tiksi. Concentrations of SO42-, Ni and Cu in the moss and larch leaf samples decreased with the distance from nickel and copper smelters in Norilsk. Moss and larch leaf, thus, can be used as bio-monitor of the air pollution. Concentrations of pollutants in the surface soil were higer than those in the soil 20-30cm below in Norilsk and Tiksi. It suggests that the long range transported atmospheric pollutants deposit on the surface and accumulate in the upper layer of permafrost in the Siberian Arctic.