A. Yu. Miroshnikov

Geochemical signature of bottom sediments in the mixing zones of Ob and Yenisei waters with Kara Sea water

This paper reports the results of a study of the geochemistry of bottom sediments from the zones of mixing between the freshwater of the Ob and Yenisei rivers and the saline water of the Kara Sea by means of neutron activation analysis. Using separate datasets for the sediments of the Ob and Yenisei estuaries accumulated under identical facies conditions, some characteristic features of the distribution of a number of chemical elements (mostly lithophile group elements) were established. The differences between them were attributed to distinctive regional geological and geochemical features of the catchments of the Ob and Yenisei, which are inherited by the geochemical characteristics of terrigenous material transported to the sea. The choice of the most informative indicator elements and their grouping on the basis of the character of behavior demonstrated that bottom sediments of the Ob or Yenisei origin can be identified in the marine region studied using the geochemical characteristics of a small group of samples.

Geoecological investigations of the Ob-Irtysh River Basin in the Khanty-Mansi Autonomous region: Yugra in 2006–2007

This paper reports the results of the investigations of 2006–2007 on the distribution and migration forms of artificial radionuclides and chemical elements in the Ob-Irtysh water system. Three regions were studied. One of them is a local segment of the Ob River upstream from the confluence with the Irtysh River; its investigation allowed us to estimate the general radioecological state of the aquatic environment affected by the activity of the Tomsk 7 plant. The second region is a local segment of the Irtysh River upstream from its confluence with the Ob River, where the influence of emissions from the NPO Mayak could be estimated. The third region is the water area of the Ob River after its confluence with the Irtysh River. It characterizes the real level of radioactive and chemical contamination of the middle reaches of the Ob River.In order to explain horizontal variations in the distribution of radionuclides in the upper layer of bottom sediments collected at various sites, the results of sorption-kinetic experiments with radioactive tracers in the precipitate-solution system were used. The investigation of the migration forms of trace elements and radionuclides occurring in river water was based on the method of tangential-flow membrane filtration.Chemical element contents were determined in 400-ml water samples. A set of Millipore polysulfone membranes with pore sizes of 8, 1.2, 0.45, 0.1, and 0.025 μm was employed. Taking into account the ultralow specific concentrations of radionuclides in the water, they were analyzed in 300–500 litre samples using Millipore polysulfone membranes with pore sizes of 0.45 μm and 15 kDa. This allowed us to estimate the percentages of cesium-137 and plutonium-239, 240 in the suspended particulate fraction, colloids, and dissolved species.

Isotope parameters (δD, δ18O) and sources of freshwater input to Kara Sea

The isotope characteristics (δD, δ18О) of Kara Sea water were studied for quantitative estimation of freshwater runoff at stations located along transect from Yamal Peninsula to Blagopoluchiya Bay (Novaya Zemlya). Freshwater samples were studied for glaciers (Rose, Serp i Molot) and for Yenisei and Ob estuaries. As a whole, δD and δ18O are higher in glaciers than in river waters. isotope composition of estuarial water from Ob River is δD =–131.4 and δ18O =–17.6‰. Estuarial waters of Yenisei River are characterized by compositions close to those of Ob River (–134.4 and–17.7‰), as well as by isotopically “heavier” compositions (–120.7 and–15.8‰). Waters from studied section of Kara Sea can be product of mixing of freshwater (δD =–119.4, δ18O =–15.5) and seawater (S = 34.9, δD = +1.56, δ18O = +0.25) with a composition close to that of Barents Sea water. isotope parameters of water vary significantly with salinity in surface layer, and Kara Sea waters are desalinated along entire studied transect due to river runoff. concentration of freshwater is 5–10% in main part of water column, and <5% at a depth of >100 m. maximum contribution of freshwater (>65%) was recorded in surface layer of central part of sea.

Distribution of global fallouts cesium-137 in taiga and tundra catenae at the Ob River basin

The classification of soil catenae at the Ob River basin is developed and applied. This classification reflects the diverse geochemical conditions that led to the formation of certain soil bodies, their combinations and the migration fields of chemical elements. The soil and geochemical diversity of the Ob River basin catenae was analyzed. The vertical and lateral distribution of global fallouts cesium-137 was studied using the example of the four most common catenae types in Western Siberia tundra and taiga. In landscapes of dwarf birches and dark coniferous forests on gleysols, cryosols, podzols, and cryic-stagnosols, the highest 137Cs activity density and specific activity are characteristic of the upper soil layer of over 30% ash, while the moss-grass-shrub cover is characterized by low 137Cs activity density and specific activity. In landscapes of dwarf birches and pine woods on podzols, the maximum specific activity of cesium-137 is typical for moss-grass-shrub cover, while the maximum reserves are concentrated in the upper soil layer of over 30% ash. Bog landscapes and moss-grass-shrub cover are characterized by a minimum activity of 137Cs, and its reserves in soil generally decrease exponentially with depth. The cesium-137 penetration depth increases in oligotrophic histosols from northern to middle taiga landscapes from 10–15 to 40 cm. 137Cs is accumulated in oligotrophic histosols for increases in pH from 3.3 to 4.0 and in concretionary interlayers of pisoplinthic-cryic-histic-stagnosols. Cryogenic movement, on the one hand, leads to burying organic layers enriched in 137Cs and, on the other hand, to deducing specific activity when mixed with low-active material from lower soil layers.

Geochemical and radiation conditions in coastal landscapes of the Kara Sea Gulf (Novaya Zemlya Archipelago)

This work considers terrestrial coastal landscapes of Abrosimov and Stepovoi gulfs and Yuzhnii (Southern) Island in the Novaya Zemlya Archipelago in the Kara Sea. These areas are dominated by horizons of slightly acidic leptosols and lithic leptosols of 10 cm thick (Stepovoi Gulf) and those of weak skeleton acidic lithic leptosols of 10–15 cm thick (Abrosimov Gulf) covered by moss–shrub assemblages. Kaolinite is formed in a rhizosphere fine earth layer; illite is formed along the leptosol sequence. The studied coastal landscapes are characterized by low accumulation potential of chemical elements, including radionuclides, at higher contents of them. Elements such as Fe and Ti are dispersed in sols, whereas P, S, Cl, Cu, Pb, and Zn are accumulated in soils in minor amounts. Plants accumulate S, P, Cl, Sr, Zn, and 137Cs in minor amounts as well. Elements such as Ti, Mn, Fe, Cr, V, Co, Ni, Cu, Rb, Zr, Ba, Th, Y, Nb, Pb, and As are attributed to the group of weak biological adsorption. The specific 137Cs activity (Bq kg–1) amounts to 10–150 in plants, 10–300 in moor leptosol horizons, and 1–40 in mull horizons.

Geochemical recognition of terrigeneous material from the Ob and Yenisei rivers in bottom sediments of the eastern part of the Kara Sea

270 The continental runoff through the Ob and Yenisei river systems is the basic resource of bottom sediments in the eastern part of the Kara Sea. Various pollutants, including radionuclides, are transported to the sea together with many millions of tons of suspended min eral particles, organic detritus, and dissolved materi als. The global precipitation accumulated in land scapes of the water drainage areas and the active radi ochemical plants located in the upper reaches of the Ob and Yenisei rivers are the main sources of radioac tive pollution transported by the rivers [1–3]. Radio nuclides are mostly transported to the river estuaries and to the open part of the Kara Sea by suspended and colloid particles, which sorb significant portions of radioactive materials [1]. Rivers carry most of the sta ble chemical elements [4].

Radiocaesium distribution in the bottom sediments of the Kara Sea

The article presents the results of radiogeochemical studies carried out by the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, RAS (IGEM RAS), in the Kara Sea and the estuaries of the Ob and Yenisei rivers in 1995–2003. The studies were carried out onboard the Akademik Boris Petrov research vessel, belonging to the Institute of Geochemistry, RAS. Based on studies of circa 1500 samples of bottom sediments, taken from 172 marine and river stations, a map of 137Cs distribution in the surface sediments has been compiled. Four zones of radiocesium overactivity (>15 Bk/kg) have been identified: Novaya Zemlya Zone, Vaigach Zone, Ob Zone, and Yenisei Zone. The zones have different radiocesium concentration levels, as well as different input sources, but all of them have formed under the influence of complex geochemical barriers. Data from 47 sectioned cores of bottom sediments, sampled in Ob and Yenisei overactivity zones, demonstrate distinct differences in the vertical radiocesium distribution. These differences have been shown to be due to many-year oscillations of suspended silt discharge, which are main transfer agents of solvable and poorly solvable radiocesium forms and to be independent of sedimentation conditions and the geochemical characteristics of the deposition environment.

Mineral composition of soils and bottom sediments in bays of Novaya Zemlya

We have analyzed the specific features of the mineralogical composition of bottom sediments of Blagopoluchiya, Tsivol’ki, and Abrosimov bays and soils on Cape Zhelaniya and the coasts of Abrosimov and Stepovoi bays. The data were obtained during two scientific expeditions of the R/V Professor Shtokman in 2014 (cruise 128) and R/V Akademik Mstislav Keldysh in 2015 (cruise 63). These investigations revealed patterns in the transportation of terrigenous material in the coastal zone of the bays: a decrease in the share of nonclay minerals and an increase in that of clay minerals with distance from shore. The increase in kaolinite and smectite content in soil horizons is related to biochemical weathering, while illite is mainly formed as a result of physical weathering.

Radioecological investigations on the Northern Novaya Zemlya Archipelago

Multidisciplinary investigations carried out in the Cape Zhelaniya area and on the Severny ice dome of Severny Island in the Novaya Zemlya Archipelago during cruise 63 of the R/V Akademik Mstislav Keldysh in September 2015 included a study of the environmental radiation level. The landscape‒geochemical and radiation‒glaciological data show that the Severny ice dome serves as a secondary source of radionuclides on the surface of the ice sheet; this source originated from past nuclear weapons testing in the atmosphere over the Severnaya Zemlya test site. Some samples taken from the periglacial zone near the edge of the Severny ice dome yielded specific activity levels of radioactive cesium of 450–650 Bq/kg. The study of ice cores obtained by shallow (up to 5.4 m) drilling of three boreholes revealed no significant activity values. At the same time, glaciological investigations made it possible to obtain the first data on the previously unexamined glacier, which indicate that the radioactively contaminated layer is located at a depth of 15‒20 m at the boundary of the glacier alimentation zone. No similar investigations had been conducted earlier either by Russian or international scientific teams.

Isotope (δD, δ18О) systematics in waters of the Russian Arctic seas

Oxygen and hydrogen isotope analysis was performed to study the processes of distribution of water masses and modification of their salinity in the Russian Arctic seas. A wealth of new isotopic data was obtained for freshwater (river runoff, Novaya Zemlya glaciers) and seawater samples collected along a set of extended 2D profiles in the Barents, Kara, and Laptev Seas. The study presents the first δD values measured for the Northeast Atlantic Deep Water NEADW dominated the water column of the Barents Sea (S = 34.90 ± 0.05, δD = +1.55 ± 0.4‰, δ18O = +0.26 ± 0.1‰, n = 44). This water mass is present in the Kara Sea and western Laptev Sea. The relationship between δD, δ18О, and salinity data was used to calculate the fractions of waters of different origin, including the fractions of continental runoff in waters of the Barents, Kara, and Laptev Seas. It was shown that the relationships between the isotopic parameters (δD, δ18О) and salinity in waters of the Kara and Laptev Seas is controlled by the intensity of continental runoff and sea ice processes. Sea ice formation is the main factor controlling the formation of the water column on the Laptev Sea shelf, whereas the surface waters of the middle Kara Sea are dominated by the contribution of river runoff. A very strong stratification in the Kara Sea is caused by the presence of a relatively fresh surface layer mostly contributed by estuarine water inputs from the Ob and Yenisei Rivers. The contribution of river waters reaches 40–60% in the surface layer in the central part of the sea and decreases to a few percent down 100 m water depth. Stratification in the western part of the Laptev Sea is controlled by the contribution of freshwater input from the Lena River and modification of salinity by sea ice formation.