Search

Scanning micro-X-ray fluorescence analysis with synchrotron radiation was applied to obtain the depth-variation profiles of element compositions of banded clays in Peyungda Lake (Krasnoyarsk krai, Evenkia) located 30 km southwest of the epicenter of the Tunguska event (1908). The age model was confirmed by a dated layer of anomalous thickness related to the fall and explosion of the Tunguska Cosmic Body (TCB). The variations in the element content in dated core layers were compared with the instrumental meteorological observation data over the last century. The regional average annual temperature and element compositions of the coeval bottom sediments (transfer function) were found to be interrelated. The approximation of the transfer function to the sampling depth of the sedimentary section made it possible to reconstruct the air temperature in the studied region over the past 1000 years. The average annual temperature reconstructions in the study area compared with the global temperature reconstructions in the Arctic region for the same period made it possible to reveal general trends and extreme values. [ABSTRACT FROM AUTHOR]

Long-term measurements show that the sedimentation dynamics of okenone (a carotenoid of purple sulfur bacteria) reflects the abundance of purple sulfur bacteria, the hydrogen sulfide content, and the stratification stability in the closed saline meromictic Shira Lake (Southern Siberia, Russia). The profile of fossil okenone in bottom sediments has been compared with the data on the water surface level in the lake over the last 100 years. The peaks of okenone correspond to lake transgressions, and the drops in the okenone content coincide with periods of stable or decreasing water level. Our observations show that fossil okenone may be used as a qualitative proxy of meromictic conditions and as a quantitative proxy of the water level dynamics in closed stratified lakes. Therefore, okenone can be used for qualitative reconstructions of the water balance and climate humidity in arid zones. [ABSTRACT FROM AUTHOR]

An anomalous layer enriched with chemical elements indicating the presence of terrigenous matter was discovered in the sediment core of Zapovednoe Lake located 60 km from the epicenter of the Tunguska event (1908) using synchrotron radiation X-ray fluorescence spectroscopy (SR–XRF). Radioisotope measurements indicate that the age of the layer is consistent with the date of the catastrophe. Apparently, the anomalous layer was formed as a result of an intense terrigenous matter inflow from the water catchment area due to massive forest falls and subsequent wildfires caused by the Tunguska event. Thus, it is established that targeted searches for microparticles of extraterrestrial origin can be carried out in the discovered and dated anomalous bottom sediment layer. [ABSTRACT FROM AUTHOR]

The tundra was divided into different classes depending on the temperature and precipitation in accordance with the Holdridge classification. Dry, moist, wet, and rainy tundras were distinguished. Datasets on climate variability were obtained from the Climatic Research Unit website (http://www.cru.uea.ac.uk/data) for the period from 2001 to 2017. The long-term (2001–2016) dynamics of phytomass for different tundra classes was studied on the basis of the Normalized Differential Vegetation Index (NDVI). The positive long-term dynamics of NDVI-vegetation for the tundra classes studied was revealed. This trend correlates with the positive dynamics of the mean annual biotemperature. It was shown that the impact of global climate change on vegetation of different tundra classes is ambiguous. For the dry tundra, the increase in NDVI in May and June was higher than for the rainy tundra. This correlates with the fact that the increase in the mean monthly temperatures in May and June on the territory of the dry tundra is greater than on the territory of the rainy tundra. [ABSTRACT FROM AUTHOR]

Abstract: Laboratory experiments were conducted in a hermetically sealed growth chamber with two soil samples obtained from the arctic tundra zone with different levels of moisture. Samples were maintained at a growing season typical of the region from which they were taken, and for the sample with a high level of moisture it was made twice: with the temperature in accord with natural conditions and one increased by 2°C. It has been shown that heating of the overmoistened tundra soil by 2°C can increased the average carbon dioxide emissions by almost two times (from 75 to 100-150 mg m-2 h-1). Upon the application of heat, no significant increase in methane emission was observed. [ABSTRACT FROM AUTHOR]

The validity of the competitive exclusion principle (the Gause’s principle) at one metabolic regulation factor is demonstrated for a general model of two-species community. The competitive exclusion principle postulates that a long-term coexistence of species is impossible if their number exceeds the number of density-dependent growth-regulating factors. Previously, this principle was proved for the stationary states in a general model of a community with any number of factors. In the dynamic modes, the number of species in a community may exceed the number of regulating factors. However, under the influence of one factor, only one species survives. [ABSTRACT FROM AUTHOR]

This study is devoted to investigating the content of uranium isotopes in water of the Yenisei River and its tributaries within the territories affected by the operation of Rosatom plants (mining chemical combine, and electrochemical plant). Long-term monitoring of the U content by mass spectrometry carried out in two institutes of the Siberian Branch of the Russian Academy of Sciences first revealed the multiple excess of U over the background content in different areas of the Yenisei River basin, such as the region of the Yenisei River near the effluents of the mining and chemical combine (MCC), and the territories of the Bol'shaya Tel' and Kan rivers. In these regions, the U content in water reaches 2.1-4.0 μg/l, which exceeds its content upstream from the MCC (0.3-0.6 μg/l) by almost an order of magnitude. The studies of the isotopic composition of uranium in water samples, which were carried out at the Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, showed the presence of a technogenic isotope of uranium U in the samples from the Bolshaya Tel' River and revealed the deviation of the isotope ratio U/U (167 ± 3 and 177 ± 3) from the equilibrium natural ratio (U/U = 138). These facts attest to the technogenic origin of part of the uranium in water of the Bol'shaya Tel' River connected with the activity of MCC. The excess uranium content in the Kan River requires additional studies to ascertain the fraction of uranium of technogenic origin connected with the activity of the electrochemical plant (ECP) (Fig. 1, Table 4). [ABSTRACT FROM AUTHOR]

Microbiological and isotopic-geochemical investigations of the brackish meromictic lakes Shira and Shunet were performed in the steppe region of Khakasia in winter. Measurements made with a submersed sensor demonstrated that one-meter ice transmits light in a quantity sufficient for oxygenic and anoxygenic photosynthesis. As in the summer season, in the community of phototrophic bacteria found in Lake Shira, the purple sulfur bacteria Amoebobacter purpureus dominated, whereas, in Lake Shunet, the green sulfur bacteria Pelodictyon luteolum were predominant. Photosynthetic production, measured using the radioisotopic method, was several times lower than that in summer. The rates of sulfate reduction and production and oxidation of methane in the water column and bottom sediments were also lower than those recorded in summer. The process of anaerobic methane oxidation in the sediments was an exception, being more intense in winter than in summer. The data from radioisotopic measurements of the rates of microbial processes correlate well with the results of determination of the isotopic composition of organic and mineral carbon (δ13C) and hydrogen sulfide and sulfate (δ34S) and suggest considerable seasonal variations in the activity of the microbial community in the water bodies investigated. [ABSTRACT FROM AUTHOR]