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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]

On the border of China and North Korea, there is the only active stratovolcano in the eastern part of Asia: Mount Paektu (other names are Baitoushan and Changbaishan). It is widely known for one of the largest eruptions in the historical era, which occurred in the 10th century AD. On the volcanic-activity scale, the event is rated at seven points, this is the largest eruption in the last millennium. Modern research shows that the eruption of the Paektu volcano occurred in late autumn–winter 946 AD. This dating is supported by data obtained from the study of an ice core from North Greenland, in which traces of volcanic ash were found. At a depth of 860 mm (the age according to the calculation of annual layers is 942 AD ± 26 years), a layer 2–3 mm thick was found, which differed sharply in color and texture from the rest of the core material. Using a module of confocal X-ray microscopy, an optical section containing an anomalous layer was studied. 2D scanning with a focused beam of synchrotron radiation 20 µm in diameter was carried out. A large amount of microparticles with a high content of zirconium and yttrium was found inside the layer. The possibility of finding traces of the eruption of the Paektu volcano is discussed. [ABSTRACT FROM AUTHOR]

The distribution of charcoal particles >100 µm in size, which are indicators of plant combustion in ambient territories, are analyzed in sediments of Shira and Uchum lakes located in southern Siberia in the steppe zone of the North Minusinsk Basin (Republic of Khakasiya and Krasnoyarsk krai). The age of the lakes is to 1400 and 500 years, respectively. The lacustrine sediments contain charcoal particles of three types. Particles of group 1 have elongated morphology and are interpreted as remnants of grassy plants and/or conifers. Particles of group 2 look like thin plates similar to relics of leaves and bark of trees. Group 3 is composed of various irregular volumetric particles, which are probably relics from wood and coal combustion. The particles of group 1 are mostly indicators of natural fires, and their amount is almost constant in the current period. The amount of charcoal particles of groups 2 and, mostly, 3 has strongly increased in past 100 years, which reflects an increase in the amount of artificially combusted wood and coal in the vicinities of the lakes in the present-day industrial period. An increase in the contribution of the charcoal particles to lacustrine sediments over the past 100 years has been detected for the first time for this region, which is unprecedented for the period of study. This is evidence of the anthropogenic impact on the dynamics of charcoal particles in lacustrine sediments. Our data can be useful for reconstruction of the dynamics of natural fires and the paleoclimate in southern Siberia in the Late Holocene. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070279 [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 possibility of distinguishing layer boundaries through lithological and geochemical indicators (Rb/Sr ratio) is shown by a case study of bottom sediments from Lake Kucherlinskoe (Altai). Based on the data from scanning synchrotron radiation–induced XRF microanalysis and isotope studies, a record of the Tunguska event of 1908 is found in the bottom sediments of Lake Zapovednoye, forty kilometers from the explosion's epicenter. An anomalous layer in the sediments is associated with an increase in the terrigenous drift in the catchment area due to massive forest outfall and subsequent fires. The possibility of a targeted search for microparticles of extraterrestrial origin in lake sediments is demonstrated. [ABSTRACT FROM AUTHOR]

Frozen upper layers of the bottom sediment of Lake Shira are selected using special sampling equipment. Frozen samples and solid samples prepared from the upper layers of a sediment core are examined by means of X-ray fluorescence at the Local and Scanning X-Ray Fluorescence Elemental Analysis Station of the Siberian Synchrotron and Terahertz Radiation Center's Shared Resource Center. Analytical data on the initial frozen and processed solid samples demonstrate the good repeatability of the results. Quantitative estimates of the sedimentation regimes are obtained, and geochemical indicators of the change in redox conditions are determined from the analysis data. Lithological and geochemical records are synchronized with regional seasonal and annual variations in weather and climate, and with the hydrological regime of the lake for the last 50 years. [ABSTRACT FROM AUTHOR]

The spatio-temporal organization of the bacterial community inhabiting the chemocline of the stratified meromictic Lake Shunet (Khakassia, Russia) was investigated from May to September 2005 by means of microscopy, analysis of photosynthetic pigments, and PCR-DGGE with subsequent 16S rDNA analysis. The samples were collected with a multisyringe stratification sampler, sampling being performed every 5 cm. It was demonstrated that, during the period of investigation, there were no large changes in the bacterial community of the chlemocline, at least among the detected forms. During the whole period of study, purple sulfur bacteria related to Lamprocystis purpurea ( Chromatiaceae) were predominant in the chemocline. Beneath the layer of purple bacteria, green sulfur bacteria were revealed that were phylogenetically distant from strain ShN Pel02, which was previously isolated from this lake. Development of phytoflagellates of the genus Cryptomonas was observed in the upper zone of the chemocline. In the chemocline of Lake Shunet, the numbers of picoplankton cyanobacteria of the genus Synechococcus increased from May to September. It was demonstrated that the application of universal bacterial primers for DGGE resulted in the same qualitative distributional pattern of predominant species as microscopic studies. [ABSTRACT FROM AUTHOR]

The anoxygenic phototrophic bacterial community of the brackish meromictic Lake Shira (Khakassia) was investigated in August 2001, July 2002, and February–March 2003. In all the periods of investigation, the prevailing microorganisms were purple sulfur bacteria similar to Lamprocystis purpurea in morphology and pigment composition. Their highest number (3 × 105 cells/ml) was recorded in July 2002 at the depth of 15 m. According to 16S rRNA gene analysis, the strain of purple sulfur bacteria isolated in 2001 and designated Sh Am01 exhibited 98.6% similarity to the type strain of Thiocapsa roseopersicina and 97.1–94.4% similarity to the type strains of Tca. pendens, Tca. litoralis, and Tca. rosea. The minor microorganisms of the anoxygenic phototrophic bacterial community within the period of investigation were nonsulfur purple bacteria phylogenetically close to Rhodovulum strictum (98.3% similarity, strain Sh Rb01), Ahrensia kielensis (of 93.9% similarity, strain Sh Rb02), Rhodomicrobium vannieli (of 99.7% similarity, strain Sh Rmc01), and green sulfur bacteria, phylogenetically close to Chlorobium limicola (of 98.7% similarity, strain Sh Cl03). [ABSTRACT FROM AUTHOR]

The biogeochemical and molecular biological study of the chemocline and sediments of saline meromictic lakes Shira and Shunet (Khakasia, Russia) was performed. A marked increase in the rates of sulfate reduction and methanogenesis was revealed at the medium depths of the chemocline. The rates of these processes in the bottom sediments decreased with depth. The numbers of the members of domains Bacteria, Archaea, and of sulfate-reducing bacteria (SRB) were determined by fluorescence in situ hybridization with rRNA specific oligonucleotide probes labeled with horseradish peroxidase and subsequent tyramide signal amplification. In the chemocline, both the total microbial numbers and those of Bacteria were shown to increase with depth. The archaea and SRB were present in almost equal numbers. In the lake sediments, a drastic decrease in microbial numbers with depth was revealed. SRB were found to prevail in the upper sediment layer and archaea in the lower one. This finding correlated with the measured rates of sulfate reduction and methanogenesis. [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]

Microbiological and biogeochemical studies of the meromictic saline Lake Shira (Khakasia) were conducted. In the upper part of the hydrogen-sulfide zone, at a depth of 13.5–14 m, there was a pale pink layer of water due to the development of purple bacteria (6 × 105 cells/ml), which were assigned by their morphological and spectral characteristics to Lamprocystis purpurea (formerly Amoebobacter purpureus). In August, the production of organic matter (OM) in Lake Shira was estimated to be 943 mg C/(m2 day). The contribution of anoxygenic photosynthesis was insignificant (about 7% of the total OM production). The share of bacterial chemosynthesis was still less (no more than 2%). In the anaerobic zone, the community of sulfate-reducing bacteria played a decisive role in the terminal decomposition of OM. The maximal rates of sulfate reduction were observed in the near-bottom water (114 μg S/(l day)) and in the surface layer of bottom sediments (901 μg S/(dm3 day)). The daily expenditure of Corg for sulfate reduction was 73% of Corg formed daily in the processes of oxygenic and anoxygenic photosynthesis and bacterial chemosynthesis. The profile of methane distribution in the water column and bottom sediments was typical of meromictic reservoirs. The methane content in the water column increased beginning with the thermocline (7–8 m) and reached maximum values in the near-bottom water (17 μl/l). In bottom sediments, the greatest methane concentrations (57 μl/l) were observed in the surface layer (0–3 cm). The integral rate of methane formation in the water column and bottom sediments was almost an order of magnitude higher than the rate of its oxidation by aerobic and anaerobic methanotrophic microorganisms. [ABSTRACT FROM AUTHOR]