Abstract: The paper presents a combined analysis of the lithological, granulometric and mineralogical composition of unconsolidated sediments in the Sentsa River basin (Oka Plateau, Eastern Sayan, Russia). Complex analytical studies and drilling operations were aimed at studying the lake, river and moraine sediments that fill the river valley in order to reconstruct the conditions of their accumulation. Granulometric analysis, performed using sieve and laser diffraction methods, made it possible to establish the sequence of sediment accumulation in this dammed paleoreservoir and the position of the paleotable of the permafrost (at depths of 1.2 and 2.1 m). The mineralogical composition of alluvial sands confirmed the predominantly quiet water regime of their accumulation (in lake and lake-marsh conditions). The composition of moraine sediments and the structure of moraine ridges indicate the activity of water flows during the melting of the glacier, which formed a ‶layer cake″ of a terminal moraine ridge, as well as a stadial moraine with a thick sandy layer (more than 3.0 m) in the middle stream of the Sentsa River. Deep drilling allowed to establish for the first time the structure of the vertical section of the river valley and the permafrost thickness, which amounted to 44 m. A borehole with a depth of 45.1 m penetrated a section composed of frozen silts, clayey silts, clays and sands, as well as sub-permafrost groundwater. The cryotextures of unconsolidated sediments are predominantly massive and rare schlieren, with lenses and layers of ice up to 8-10 cm thick at different depths. Radiocarbon dating of a core sample taken from a depth of 1.5 m showed an age of 3510±120 years and confirmed the existence of an open water reservoir in the late Holocene in the Sentsa River valley.

Keywords: Oka Plateau, radiocarbon dating, moraine sediments, sedimentation rate, lithological composition, cryogenic texture, mineralogical composition, permafrost thickness, granulometric composition, unconsolidated sediments

Abstract: This research is focused on quantitative assessment of salinity influence on predictions of permafrost temperature on a regional scale. The relevance is determined by the intensive economic development of the Yamal Peninsula and the observed climate change in the Arctic. Reducing the uncertainty in forecast predictions of the permafrost temperature helps to reduce the value of the safety margin when designing the ground foundations of buildings and structures, avoiding the development of negative geoprocesses during their construction and operation. The object of the study is the permafrost of the Yamal Peninsula, which is continuously distributed and forms the foundation of the majority of buildings and structures in operation. The temperature of the saline permafrost is the subject of the study. The methods used combine thermodynamic and mathematical modelling and climate change consideration. The mean annual ground temperature by mid-century is predicted for three regions of the peninsula – north-western and western Yamal as well as the lower course of the Ob River. The temperature of the permafrost was determined by two independent approaches. In the first case, we used the heat-exchange characteristics of rocks which are constant for the forecast period, and in the second case – those that change with the transformation of the water-ionic composition of pore solutions. The minimum difference between the obtained temperature values is 0.1–0.2 °C in the north-western Yamal. The largest discrepancy between the modelling results is observed for the lower Ob River and reaches 0.5–0.6 °С. Neglecting the salinity of the permafrost and its properties for the period of geocryological forecasting leads to an error in determining the mean annual ground temperature of up to 20%. With the increase of pore solution salinity from 35 to 150 g/l, the difference in calculations increases by 15–20%. The mean annual ground temperature obtained with constant heat transfer characteristics turn out to be underestimated in comparison with the results of the problem with time-varying characteristics. Improving the geocryological forecast methodology will make it possible to more reasonably approach the assessment of the future thermal state of saline permafrost under climate change.

Keywords: Yamal Peninsula, autoretrospective analysis, climate change, QFrost, mathematical modelling, Freezbrine, thermodynamic modelling, water-ionic composition, geocryological forecast, saline permafrost

Abstract: The subject of the study is the cryostructures of Pleistocene sediments uncovered by a 30-m borehole in the Churapcha village and the distribution of stable oxygen and hydrogen isotopes in the schlieren ice and thin ice lenses. The research was located in the area of continuous permafrost distribution, the vertical thickness of which reaches 400–500 m here. The average annual temperature of rocks ranges from -4.6 to -6.2 °C, in river valleys the temperatures are increased to about –2 to –1°C. Permafrost sediments in the Churapcha area are characterized by relatively high iciness, from 26 to 47%. Ice is found in deposits as interlayers that form a layered (as well as lenticular and braided) cryostructure. During the fieldwork, frozen cores opened by a drilling hole at a depth of 30 meters were studied. Drilling was carried out using a large-sized drilling rig (PBU-2) based on a Kamaz truck. A core drilling pipe with a diameter of 146 mm was used. Sampling was carried out from the frozen core. The well-uncovered permafrost deposits, which have mainly dark brown and gray colors, especially bluish-gray shades characteristic of heavy loams and clays. The seasonally active layer has a sandy loam composition, and below, at depths from 1.5 to 6.0 m, the deposits are loamy. At depths of 6.0–20.0 m, alternating layers of loams and clays of different thickness are observed, and below there is a sharp change in the lithological composition to medium and fine sand (20.75–24.0 m), including a large number of layers of organic matter. The distribution of δ18O and δ2H values was examined in structured ice up to a depth of 17.7 meters. In the upper 12 m, the isotopic composition is significantly more negative: δ18O values vary from –29.44 to –34.35‰, while δ2H values range from –213.5 to –253.6‰. In the 12-17.7 m range, δ18O oscillates between –25.94 and –28‰, whereas δ2H ranges from –195.3 to –214.3‰. Analysis of data on the isotopic composition of structure ice in the yedoma deposits of Yakutia showed a close range of values with the ice of unit 1 from the borehole in Churapcha that we studied. The heavier isotopic composition of ice of unit 2 is probably explained by another source of water and the influence of isotopic fractionation during the interaction of clay particles with water. As for the contrast of the isotopic characteristics of unit 1 and unit 2, we note that such a ratio, when the isotopic composition in the upper unit is on average consistently 3-5‰ lower than in the lower unit, is quite rare in permafrost. The water for the formation of segregation ice from the borehole could have been formed to a greater extent from melted winter snow and was less subject to evaporation. Contrasting values in the ice of the two studied units may indicate different water sources; for the ice in unit 1, the water source could have been, to a greater extent, winter precipitation (surface water formed from melted snow); the presence of a negative peak in the vertical distribution of isotopic values may indicate two-sided freezing (from above and below) and isotopic fractionation during freezing. The deposits of unit 2 are represented by heavy loams, probably lacustrine. It can be assumed that the saturation of these deposits under these conditions occurred with lake water, which consisted of a mixture of precipitation from both winter and summer seasons and was characterized by higher values of the isotopic composition. Freezing of these loams could have begun already when the lake became shallow. In any case, for now the probable explanation for the heavier isotopic composition of unit 2 is isotopic fractionation in water during interaction with clay particles and a different water source than in unit 1.

Keywords: Central Yakutia, Lena-Aldan interfluve, Churapcha, hydrogen stable isotopes, oxygen stable isotopes, cryostructure, ground ice, Late Pleistocene, borehole, permafrost

Abstract: The subject of the study is the ionic composition of syngenetic Late Pleistocene ice wedges: IW-17 and IW-20, located in Batagay yedoma. Both ice wedges consist of ultra-fresh ice with concentrations of major ions from 20 to 40 mg/L. For samples from ice, a method was used to measure the mass concentration of Ca2+, Mg2+, Na+, K+, NH4+ cations in samples of drinking, mineral, natural and waste water by ion chromatography FR.1.31.2005.01738. The range of detectable concentrations is 0.10-20.00 mg/L, and for the determination of anions, the method of measuring the mass concentration of Cl-, SO4-, NO3- in samples of drinking, mineral, natural and wastewater by ion chromatography FR.1.31.2005.01724 was used. The range of detectable concentrations is 0.10-20.00 mg/L and the method of measuring the mass concentration of ions in samples of natural, drinking and wastewater by ion chromatography HDPE F 14.1:2:4. 132-98 was used, the range of detectable concentrations for cations is 0.10-150.00 mg/L. Measuring instruments: ion chromatographic system "Stayer", detection limit for chloride ion 0.02 mg/L. The main results of the conducted research are, as follows: Sodium and calcium soluble cations significantly predominate in the ionic composition of IW-17, reaching 24.15 and 53.16 mg/L, respectively. In the same sample, chlorine anions reach 34.51 mg/L. The average concentration of sulfate soluble anions is 2-3 mg/L. Sodium and calcium cations significantly predominate in the ionic composition of IW-20, reaching 7.27 and 50.0 mg/L, respectively. In the same sample, chlorine anions reach 13.72 mg/L. The average concentration of sulfate anions is 2-4 mg/L, reaching 22.24 mg/L. The content of calcium soluble cations is 6-20 mg/L (calcium soluble cations rarely reaching 42-53 mg/L), the concentration of potassium cations is 0.7-3 mg/L. Sodium and calcium cations significantly predominate in the ionic composition of IW-20, reaching 7.27 and 50.0 mg/L, respectively, in one sample. In the same sample, chlorine anions reach 13.72 mg/L. The average concentration of sulfate anions is 2-4 mg/L, reaching 22.24 mg/L. The content of calcium soluble cations is 6-20 mg/L (rarely reach 42-53 mg/L), the concentration of potassium cations is 0.7-3 mg/L.

Keywords: north of Yakutia, Batagay, yedoma, major soluble ions, ionic composition, cryogeochemistry, ice wedge, Late Pleistocene, radiocarbon age, permafrost

Abstract: The aim of the work is to create a dynamic picture of the development of the forms of research of the USSR Academy of Sciences in Yakutia in 1947-1991. The initial chronological boundary is connected with the organization of the Yakut base of the USSR Academy of Sciences. The final boundary is due to the reformatting of the USSR Academy of Sciences into the Russian Academy of Sciences. The research is based on the involvement of documents from the archives of the Yakut Scientific Center of the Siberian Branch of the Russian Academy of Sciences, the Archive of the P.I. Melnikov Permafrost Institute of the Siberian Branch of the Russian Academy of Sciences, the Current Archive of the Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy of the Siberian Branch of the Russian Academy of Sciences (Yakutsk), the Scientific Archive of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk), the Archive of the Russian Academy of Sciences (Moscow), as well as information presented in the available scientific literature. When processing the accumulated materials, special historical methods of scientific cognition were used (the principle of historicism, historical-typological, historical-comparative and historical-genetic methods, etc.). For the first time in historiography, a characteristic of the development of forms of organization of academic research in Yakutia in the period 1947–1991 is presented. It is noted that during the period considered in the article, the forms of organization of academic research in Yakutia have received significant development. The expedition surveys of the staff of the USSR Academy of Sciences were continued, which were carried out with greater intensity than before. An important place was occupied by stationary research, which unfolded on a network of hospitals in various parts of Yakutia. In addition, experimental and design work carried out in academic institutions established in the region was characterized by a number of achievements. This state of affairs has allowed the academic center to conduct a complex of largely unique research focused not only on obtaining fundamental, but also applied, of serious practical importance, results.

Keywords: North, experimental work, design work, expeditions, stationary surveys, scientific research, The USSR Academy of Sciences, Yakutia, Arctic, academic institutions