To determine distributive provinces for the Late Paleozoic-Mesozoic sedimentary basins of South Verkhoyanye, U-Pb (LA-MC-ICPMS) isotope dating of 522 detrital zircon grains from five samples was made. It was established that during the late Paleozoic and Early Mesozoic there existed a major Paleo-Aldan river system that formed after Middle Paleozoic rifting (following the Early Carboniferous) and was traceable within South Verkhoyanye from south to north toward the Verkhoyansk passive continental margin. The main distributive provinces for sedimentary basins were the Siberian craton basement (Aldan shield and Okhotsk terrane), volcanites of the East Asian active continental margin, Precambrian terrigenous rocks of South Verkhoyanye, Angara-Vitim batholith, and Cisbaikalian Caledonides. Paleogeographic reconstructions of northeast Asia for Late Carboniferous, Permian, Early Triassic, and Early Jurassic times were compiled.

Modern geodynamics of the Lena-Aldan plateau, wherein the «Yakutsk city» agglomeration is located, is studied on the basis of seismotectonic and geophysical data as well as interpretation of aerial and space photos. A number of active faults are recognized (Yakutsk, Kangalassy, Tabaga, etc.), to which epicenters of earthquakes with an intensity of 4–6 are confined. Morphological-kinematic characteristics of these tectonic dislocations are given. Calculations of probable recurrence rate of strong (5–8 in intensity) seismic events in the area of Yakutsk are presented. The notion of seismic risk and methods of assessment of natural and technogenic disasters are considered that may arise during the economic development of the Lena River valley, which is associated with an increase of paces of construction and industrial pressure on the ecology of Tuymaada Valley, where Yakutsk is located. Priority measures necessary for risk reduction are proposed.

The Endybal Ore Mountain combines several forms of silver and gold as part of a major Endybal silver cluster in Western Verkhoyanye (Eastern Yakutia). This ore-magmatic system from North to South includes occurrences of silver Sterzhnevoy, Vostochniy, Verkhneendybalskiy and Nizhneendybalskiy. During all periods of exploration of this area, the main interest was concentrated around silver ores. The main ore body of the Nizhneendybalskiy manifestation consists of local zones of breccia with ore cement and numerous closely spaced cracks filled with carbonate, quartz, sulfides and silver sulphosalts. Measurements of elements of occurrence of ore cracks in stockwork contours showed directions from 60 to 135° at angles of incidence from 15° to almost vertical. Because of this, the exploration of this manifestation by core drilling is inefficient, the most optimal is large-volume testing. Several mineral types represent the ores: stratabound siderite – ankerite silver sulphosalt veinlets with minor galena; intersecting veinlets of galena with lenses of arsenopyrite, marmatite, pyrite, siderite and traces of pyrargyrite; the zones of breccias and vein-disseminated siderite-chalcopyrite-pyrite mineralization. Testing of spatially contiguous silver and copper ores from rock outcrops of the Nizneendybalskiy manifestation showed the presence of gold – the grade is up to 6 g/t. Gold and silver in the ores form a direct correlation, gold in the sample refers to electrum, and the ores to goldsilver ones.

In the paper, an analysis is carried out and evaluation of features of occurrence and thickness of permafrost section within the Vilyui syneclise is given on the basis of geothermal measurements and interpretation of standard well logging data on 46 exploration areas (112 deep wells). A significant heterogeneity of a geotemperature field, marked by intervals with different values and directions of a geothermal gradient is revealed. It is established that the thickness of the permafrost section within the structure varies from 45 to 820 m, and even within individual deposits, an amplitude of oscillations of a bottom of the permafrost section can reach 200 m. On the basis of the obtained studies, 3 regions are distinguished, differing by the features of the occurrence of the permafrost. Maps of the occurrence of a permafrost base and a series of the permafrost geothermal structures of the individual areas and the syneclise as a whole have been compiled.

Features of seasonal periodic changes of temperature and apparent resistivity of permafrost dispersed soil mass are shown based on results of field measurements of surface impedance in the 100–1000 kHz frequency range. It is shown a possibility of use of periodicity of changes in the apparent resistivity for an estimation of influence of surface air temperature and precipitation on a degree of freezing of permafrost soils. It is given a correspondence of characteristic changes of climatic factors and apparent resistivity of soils to certain periods of time. The apparent resistivity of the permafrost dispersed soil mass is shown to correspond to the degree of soil freezing. In addition, the seasonal changes of the apparent resistivity reflect four degrees of soil freezing: winter, spring, summer and autumn. Apart from the surface air temperature, the precipitation also has the significant influence on the condition of the soil, influencing it through climate elements such as thickness of snow cover and abundance of rainfall. The results of the analysis of the experimental data of observation of the changes of the apparent resistivity under the influence of the climatic factors in an annual cycle are given. Dependence of the degree of freezing of the permafrost soil mass in the summer period on its value during the preceding spring will allow predicting the state of the permafrost soils for rapid adoption of preventive measures to protect buildings and engineering structures in the cryolithozone under the conditions of a warming climate.

The article analyzes results of geochemical monitoring of snow cover at the geocryological station «Tuymaada». Transformation parameters of snow (temperature, height, density, moisture reserve) and peculiarities of migration of moisture and matter during destruction of the snow cover in a spring period are studied. A volume of accumulation of chemical components in the snow cover is calculated. A nature of a change in the density of the salt composition of the snow cover makes it possible to distinguish three phases of a process of washing out the chemical components. It was found that in the spring period the maximum loss of soluble components by the snow cover is observed for Clions and nitrogen compounds, with which the last portions of melt water are enriched. A ratio of a lost stock of chemical elements has the form: Cl > N

> S > Ca > C. By the end of April, immediately to melting of the snow cover, 30–70 % of the ions were washed from the snow. At the same time, the water equivalent in snow decreased only by 30 %. In the period of the destruction and melting of the snow cover in early May, the soil cover remains frozen and the bulk of snow moisture is transferred to the final drainage basins: city lakes and the Lena River, contributing to desalination of water bodies and streams.

In the article features of the syntaxonomic classification and succession dynamics of spruce forests in a valley of the Middle Lena are considered. Forestry-geobotanical studies and analysis of the successions were carried out in accordance with traditional methods and the latest approaches. There are 4 associations from 2 groups Mixtoherbosa and Hylocomiosa: Piceetum obovatae mixtoherbosum (spruce with various grasses), P.o. mixtoherboso-pyrolosum, P.o. pyroloso-rhytidiosum and P.o. vaccinioso-rhytidiosum. Forests of the Mixtoherbosa group are characterized by high constancy and a significant abundance of xeromezophilic and mesophilic grasses, lack of arctoboreal shrubs, ground mosses and lichens. In the moss cover of Hylocomiosa forests, xeromesophilic Rhytidium rugosum often dominates, which is caused by significant drying of near-surface soil layers in the middle of the growing season. A principal scheme of the successions of the spruce forests is presented, driving factors of dynamics are analyzed. Near settlements, the spruce forests do not reach their potential diversity due to many years of anthropogenic pressure. In specific zonal-intrazonal conditions of the first and second terraces above flood-plain of the valley, the spruce forests can be recognized as the quasi-climax forests. In these landscape parts, the favorable hydrothermal soil conditions and practical absence of fires determine relative stability of spruce forests.

The article presents results of research work devoted to study germination and sprouting process of 46 rare, endangered and endemic species and subspecies of spontaneous flora of Yakutia. Germination and sprouting patterns were determined in freshly collected seeds (on the day of collection) and after 6 months of storage at room temperature of 23 ± 1 °C. The studies were based on the collection of the spontaneous flora of the Yakutsk Botanical Garden. According to a seed sprouting classification proposed by I.V. Borisova (1996), 10 rare species (IB) are characterized by high germination capacity and fast seed sprouting. The seeds with slow sprouting (II) are represented by 20 taxa, 16 species of which are with the maximum number of the germinated seeds at the beginning of sprouting – IIA. The seeds with fast germination of types IA and IB as well as IIA and high germination are common for taxa, which are decreasing in number and the rarity of which is not caused by their biological features but by external factors. The seeds with the low laboratory germination, primary dormancy of different duration and germinating after ripening and with the zero germination are represented by 16 species (III). Pre-sowing procedures have been suggested in order to derive the latter from the resting condition. After 6 months storage, the pattern of seed germination remains for most species, but it changes for some species, both in the direction of accelerating and decelerating, their laboratory germination capacity can also vary, more often it increases. The problematic seed germination of some rare species with small ranges in the territory of Yakutia suggests that the quality of seeds is one of the factors limiting their wider distribution.

In past decades, tundra ecosystems in the Arctic rapidly changed. Greenhouse gases emission from frozen organic carbon after permafrost thaw have the higher potential to increase effect of climate change in this region. Thawing and degradation of permafrost have been observed in many circumpolar research sites. The analysis of the multiyear complex observations of vegetation and permafrost dynamics in the tundra station «Chokurdakh» of SakhaFluxNet were carried out in this study. Carbon dioxide and methane fluxes in the typical tundra ecosystem in the Indigirka river lowlands in the Northeast of Russia were measured. The net carbon dioxide fluxes were higher compared to other sites, with a net ecosystem gas exchange (NEE) = –92 gCm⁻²yr⁻¹, which is composed of soil respiration of the ecosystem (Reco) = 141 gCm⁻²yr⁻¹ and gross primary production of tundra vegetation (GPP) = –232 gCm⁻²yr⁻¹. This large carbon sink could be explained by the continental climate of the site with low winter soil temperatures (–14°C) that decrease the respiration rates, and short, but relatively warm summers (10.4°C), stimulating high photosynthesis rates. The methane flux was 28 gC-CO2m⁻²yr⁻¹, so that the greenhouse gas balance was −64 gCCO2m⁻²yr⁻¹. The methane fluxes were highly sensitive to hydrological conditions and vegetation composition of the site. The importance of the vegetation composition and surface topography for protection of the active layer of permafrost and direction of the carbon flux were investigated. The strong vulnerability of the Arctic tundra even to small-scale changes of vegetation cover was shown. The development of a thaw pond after removing the shrub shifted the plots in our experimental site from a sink of methane into a source. The representative data for the tundra ecosystems, interannual and seasonal variability of the carbon balance are analyzed for the purpose of identification of trends. Nowadays, the tundra ecosystems are weak stock of carbon in comparison with the permafrost forest ecosystems of the Northeast of Russia. According to our long-term eddy-covariance data, the annual carbon sink in the tundra – 0.7 ± 0.2 tCha^-1yr^-1, in the larch forest is 2.0 ±0.5 tCha^-1yr^-1. An approximation of the long-term data of eddy-covariance indicates the positive trend of an increase in the accumulation of carbon in the future in the tundra ecosystems owing to the climate change and expansion of an area of growth of tree and shrub species to the North.

Communities of insectivorous and rodents of Yakutsk were investigated. 3338 cone-days, 106 days of exposure of glue traps were worked out in summers of 2017–2018, and 414 specimens of small mammals were caught. For comparison, materials collected in the same area in 1993–1997 (4000 cone-days and 700 specimens of small mammals) were used. A population of small mammals of undeveloped urban lands and suburban area of Yakutsk includes 14 species. Investigations in 2017–2018 expanded the list by catching Sorex roboratus and Apodemus peninsulae. The communities of the suburban area are typical for natural biotopes of the region: Clethrionomys rutilus and Sorex caecutiens dominate in forest stations, Microtus oeconomus, M. gregalis and S. tundrensis in meadows and bushes. In the undeveloped parts of the city there was a decrease in the number and species diversity of taiga species and an increase in the proportion of inhabitants of meadows. Among eusynanthropes outside of buildings in the city only Mus musculus was caught, immigration of the eusynanthropes to the natural habitats was not registered. At the fauna level, the communities of urban and suburban areas differ, as a rule, by only 1 or 2 species, which does not exceed interannual differences within landscape sites. At the same time, the communities of small mammals in the undeveloped areas of the city differ sharply in composition and structure from the communities of surrounding biotopes and are close to the floodplain ones in terms of the average number of species, indices of species diversity and dominance, which are indexes of community sustainability. The similarity of the population of the undeveloped areas of the city with the floodplain communities indicates the ecological instability of the urban communities.

A review of studies of low-molecular weight compounds of lichens, ensuring their successful ex- istence in extreme environmental conditions is given. The paper discusses features of lichen physiology in terms of adaptation to low temperatures and dehydration. Existing hypotheses about mechanisms that ensure stability of lichens at the biochemical level are considered. The degree of knowledge of lichen metabolites with cryo- and osmoprotective function is present. The special role of polyols in the formation of lichen sta- bility during hypothermia and anhydria was noted. The necessity for further comprehensive study of the poly- saccharides and low-molecular weight compounds of lichens was actualized. They will significantly enrich the knowledge of the adaptation mechanisms of the lichen biota and contribute to the development of lichen- ology, cryobiology and hypobiology.

During development of new elastomeric materials, it is promising to use environmentally friendly additives of natural origin, for example, products of hydrolysis of various proteins, which improve operational properties of the new materials. In this study, collagen hydrolysates obtained from the swim bladder of northern fish species using the alkali-salt method followed by lyophilization were used as a modifying additive. The hydrolysates were used in rubbers based on frost-resistant epichlorohydrin rubber (GECO) HYDRIN T6000 and nitrile butadiene rubbers. It was found that the modifying additive leads to an increase of curing rate, reduction of the technological cycle of production of rubber products and gives the rubbers higher relaxation properties while retaining other characteristics. The protein nature of the collagen hydrolysates and structural changes occurring during rubber modification, which consist in the chemical interaction of the hydrolysate with rubber macromolecules, have been confirmed by FTIR spectroscopy. Using the nitrile-butadiene rubber, it has been shown that the presence of collagen hydrolysate leads to a denser network of vulcanization bonds of the elastomeric material.

The work is devoted to study of the process of fatigue fracture in samples of heat-treated struc- tural steel 40X13 under gigacycle regime. The gigacycle tests were carried out on an ultrasound resonant machine with a loading frequency of 20 kHz. As part of the work, in order to avoid an effect of overheating of the sample under the influence of high-frequency load, a system to maintain the temperature of the sample during the test was developed. Features of evolution of fracture under the influence of an alternating magnet- ic field on the sample by means of the original magnetization system of the sample are considered. The struc- tural analysis of the tested samples by electron scanning microscopy was carried out. The analysis shows the effect of the alternating magnetic field on the size of zones of slow crack growth. It is shown that in the sam- ples tested under the action of the alternating magnetic field the area of the zone of slow crack growth is re- duced in comparison with the samples tested under normal conditions.