Central Baikal Research Articles

Chemical hydrogeodynamics of the Kultuk groundwater reservoir vs. paragenetically related large earthquakes in the central Baikal Rift System, Siberia

Chemical hydrogeodynamics of the Kultuk groundwater reservoir vs. paragenetically related large earthquakes in the central Baikal Rift System, Siberia

Серия ОВП-импульсов подземных вод побережья Байкала 20–27 марта 2024 г.: вероятная связь с магнитными бурями

A short (8-day) series of ORP pulses begins with low-amplitude (about 1 mV) oscillations, partially smoothes out, and progresses to deep minima reaching 138 mV. The series differs from the pulses covering the full (30-day) tidal lunar-solar cycle in February–early March 2024. It is suggested that variations in ORP pulses are temporally related to magnetic storms. Also, for generation of powerful ORP pulses, the spring lunar-solar tide is considered as a favorable factor. The March series of pulses is accompanied by decreasing background ORP values. Similar ORP decrease, but without pulses, characterizes the January episodes of earthquakes in the central Baikal Rift System.

THREE-DIMENSIONAL VELOCITY STRUCTURE OF THE CRUST IN CENTRAL LAKE BAIKAL FROM LOCAL SEISMIC TOMOGRAPHY

This work deals with the importance of studying seismicity and deep structure of the Earth’s crust in the region of the Baikal rift zone. The study presents a three-dimensional velocity structure of the Earth’s crust in the central part of Lake Baikal, obtained from the results of tomographic inversion of the travel times of P- and S-waves from more than 800 seismic events. Synthetic tests provide substantiation for the resolution of the tomographic inversion algorithm. The seismic structure of the crust was obtained to a depth of 35 km and has a direct relationship with the geological structure. The three-dimensional distributions of seismic P- and S-wave velocity anomalies are in good agreement with each other.The sharp contrast between the anomalies may indicate a difference in the material composition of the basement of the Central Baikal basin. At a 15-km depth below the Selenga River delta, there is observed a strong low-velocity anomaly which confirms the presence of a thick sedimentary cover therein. In the basement (at depths of 20 km or greater), to the northeast of the intersection between the Delta fault and the Fofanov fault, there occurs a high-velocity anomaly elongated towards the Olkhon Island. This anomaly is probably related to a rigid block in the earth’s crust. The same depths, on the western side of the Baikal-Buguldeika fault, show a reduced Vp/Vs ratio: 1.56–1.65 versus 1.70–1.75 in the adjacent areas. This indicates another type of basement rock composition and the presence of consolidated matter there.Besides, there has been made a more accurate hypocenter determination for further comparison between seismic events and active fault structures. For the central part of Lake Baikal, the distribution of seismicity mainly corresponds to depths of 10–22 km. The situation is different below the Selenga Delta – the only area where seismicity is observed at depths greater than 22 km, – which can be attributed to complex fault interactions.The velocity anomalies discussed herein are confined to reliably identified active faults and correlate well with the distribution of seismicity and gas hydrate structures.

Long-term dynamics of dominant diatom species abundance of spring phytoplankton in three basins of the pelagic zone of Lake Baikal in 1964-1984 and 2007-2016

Abstract. Analysis of long-term observations of dominant diatom species of spring phytoplankton of Lake Baikal Synedra acus subsp. radians, Aulacoseira baicalensis, Aulacoseira islandica, Stephanodiscus meyeri and Nitzschia graciliformis was demonstrated. It is shown, how the abundance of these species varied in Southern, Central and Northern Baikal in 2007-2016 compared to other observation periods in 1964-1968 and 1969-1984. It is found out that, species ratio changed in 2007-2016. The abundance of S. acus subsp. radians increased in Southern and Central Baikal, while for other species - A. baicalensis, A. islandica, N. graciliformis and S. meyeri, it significantly decreased. In Northern Baikal, the ratio of species in 2007-2016 was comparable to 1969-1984. Despite the change in the ratio of species over the past decade, the contribution of these five dominant species to the total abundance of spring phytoplankton of Lake Baikal has comparable values in all studied periods.

Разработка Листвянского, Бугульдейского и Ольхон-Приольхонского мониторинговых полигонов на Байкале: обзорное изучение микроэлементов и изотопов U в речных и подземных водах

The results of prospecting studies of trace elements and activity ratio 234U/238U (АR4/8) in surface waters and groundwaters from the Listvyanka, Buguldeyka, and Olkhon-Priolkhonye polygons of integrated monitoring, organized since 2020, are presented. At the Listvyanka polygon, wide interval of АR4/8 from 1.67 to 2.5 is obtained for groundwater in the Bolshie Koty village, at the Buguldeyka and Olkhon-Priolkhonye polygons that are located in the zone of the Primorsky fault – an interval of AR4/8 from 1.25 to 2.70. These values is general characteristic of large active faults of the central Baikal Rift Zone. Water from the Buguldeyka River differs in terms of both trace element compositions and AR4/8 values from those of its tributary Kurtun due to location of these rivers basins in rocks of the exposed basement of the Siberian Platform and its sedimentary cover, including evaporate carbonate sediments. On the Olkhon island, determined is groundwater that differs in elemental composition from the deep Baikal water.

Fault Zones and Stress Fields in the Sedimentary Fill of Lake Baikal: Tectonophysical Approach for Seismic and Hydroacoustic Data Interpretation

Abstract —This paper presents a schematic summary of comprehensive analysis of seismic, reflection profiling, and hydroacoustic data on faults which caused sediment deformation in the central segment of the Central Baikal basin. According to the tectonophysical analysis results, the fault pattern within sediment fill has been recognized as zone-block, i.e., it represents a network of high-density fracture zones limiting weakly deformed blocks. The structure of large NE-trending fault zones (Olkhon, Beregovoy, Gydratny, and Svyatoy Nos) is controlled by main fault planes (or their segments) bounded by subsidiary faults. Geomorphic expression of NW cross faults in the sedimentary cover as broad zones of smaller-scale fractures accounts for early stages of the evolution of basement faults. In a longitudinal direction, they divide the basin into large fragments. The zone–block structure of the sedimentary strata was developed in different stress regimes: strike-slip and extension at the early and late orogenic rifting stages, respectively. At the modern stage of tectogenesis, the established network of fault zones controls the gaseous (including hydrate formation) and seismic activity expression in the subsurface. Hydrate-bearing mud volcanoes and seeps are confined to major faults, while earthquake epicenters are confined to fault zones and form clusters at junctions of large NE-trending faults with NW-oriented extension zones and E–W left-lateral strike-slip faults.

Current State of Deep Oil Seepage Near Cape Gorevoi Utes (Central Baikal)

Abstract —We present data, collected in 2016, on the concentration of n-alkanes and polycyclic aromatic hydrocarbons in water and bottom sediments as well as the abundance and composition of the cultured microbial community in the area of the oil seepage near Cape Gorevoi Utes. Since its discovery in 2005, the development dynamics of the oil seepage has demonstrated a decrease in the total concentration of normal hydrocarbons and polycyclic aromatic hydrocarbons in oil slicks and bottom sediments, partial degradation of oil entering the water surface, and an increase and subsequent reduction in the number of microorganisms in water and bottom sediments with the maintained structure of the cultured microbial community. From 2006 to 2016, there was a low total concentration and a narrow range of detected concentrations of n-alkanes and polycyclic aromatic hydrocarbons in the water column, which indicates the preservation of water purity in the lake near the oil seepage.

The Ust’-Barguzin Transfer Zone (Central Baikal): Seismological Evidence on the Transtensive Stress Field of the Crust

According to seismological and geodetic data, the central part of the South Baikal basin is under an extension regime of the Earth’s crust. This study presents for the first time seismological evidence of a transtensive stress field in a local area adjacent to the eastern side of the Central Baikal subbasin. Two independent approaches to determining the orientation of the principal stress axes show a subhorizontal orientation of the axes of stresses of minimum and maximum compression, which results in a strike–slip component in the focal mechanisms of the earthquakes. The area under consideration is a part of the Ust’-Barguzin transfer zone, in which the transfer of deformations between South Baikal and the Barguzin basin takes place. The results obtained are in agreement with the geological and structural data and may indicate the contribution of horizontal displacements in the transfer of deformations between the segments of the rift zone.

Assessment of water pollution near the deep oil seep in Lake Baikal

Water purity was assessed at the site of a deep oil seepage near Cape Gorevoy Utes (Central Baikal). Polycyclic aromatic hydrocarbons (PAHs) and n-alkanes were determined in different types of oil-containing samples collected at this section of Lake Baikal. The set of studied samples included: (i) samples of water from the surface water layer; (ii) samples of water from different depths; (iii) oil on the water surface; (iv) oil from a sediment core. In the surface water layer and the water column, the total concentration of n-alkanes ranged from 0.2 to 5.3 µg/L and did not exceed the 0.1 maximum permissible concentration (MPCfish = 50 µg/L) established for hydrocarbons in water bodies of fishery importance. PAHs with carcinogenic properties were less than 0.1 ng/L. The total concentration of PAHs found in the water column did not exceed 110 ng/L; toxic equivalent (TEQ) values ranged from 0.001 to 0.110 ng/L. The distribution of petroleum hydrocarbons from the seepage site was limited, and water pollution was localised. The low level of water pollution is associated with natural mechanisms in the Baikal ecosystem. Microbiological community and phytoplankton make a decisive contribution to the purity of Baikal water, and oil fractionation during deep discharge contributes to the bioavailability of petroleum hydrocarbons.

Tectonic control of modern fluid discharge at the bottom of Lake Baikal: the Class@Baikal Project data report

Lake Baikal is a part of large intracontinental rift zone. Baikal sedimentary infill is more than 7 km thick and was developed under predominantly extensional tectonics. Large number of faults of different geometry is imaged by several seismic surveys carried out in the region. The fault systems serve as fluid discharge pathways from deep sources to surface. A number of active seepage structures were mapped and studied during the Class@Baikal expeditions along the major fault system of the Central Baikal basin, which extends in SE-NW direction over 40 km and was named recently as the Gydratny Fault. Irregular distribution of these seeps, differences in their morphology and activity rate imply a variable permeability of the fault and different characteristics of migration pathways along its segments.

Current state of phytoplankton in the littoral area of Lake Baikal, spring 2017

To assess the current state of phytoplankton in the littoral area of Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the 44 littoral and 3 pelagic stations covering all three basins of the lake. The study examined chemical parameters of water (NH4+, NO2−, NO3−, PO4−3, Si, COD), species composition, abundance, and biomass of phytoplankton in Lake Baikal during late spring 2017. Sharp spatial heterogeneity was observed in the distribution of phytoplankton biomass along the western (399 ± 72 mg/m3) and eastern (1319 ± 220 mg/m3) shores of the lake. The phytoplankton were diverse, with 79 species; dominant algae were different from site to site and from south to north throughout the lake. In Southern and Central Baikal, we recorded an intense bloom of the diatom Synedra acus subsp. radians (28–1400 cells/mL), similar to that observed for the past 10 years, while the chrysophyte Dinobryon cylindricum dominated in Northern Baikal. The diatoms Aulacoseira baicalensis, A. islandica, and Stephanodiscus meyeri that were dominant in the 1960s–1990s were not numerous in 2017 (0.5–10 cells/mL). This change in dominant species indicates structural changes in the phytoplankton of Lake Baikal, which have led to the disappearance of the main distinctive feature of the Baikalian phytoplankton – the alternation of extremely high (with the algal biomass over 1000 mg/m3) and extremely low (less than 100 mg/m3) productivity years. The ecological equilibrium appears to have shifted towards a new steady state.

Morphotectonic and paleoseismological studies of Late Holocene deformation along the Primorsky Fault, Baikal Rift

The Baikal Rift is the largest Cenozoic continental rift in Asia and has developed at the boundary between the Siberian craton and a collage of microplates composing the Amurian lithospheric plate. GPS data show that the Amurian plate moves southeastward at a rate of 3–4 mm/yr with respect to stable Eurasia but the slip rates along the main faults that control the opening of basins within the Baikal Rift System, are still poorly quantified. The recent graben system of the Olkhon region of the central Baikal Rift is a key example for studying of synrift faulting. We discovered a previously unknown paleoseismic structure in the course of our morphometric study of the Primorsky fault scarp, one of the youngest grabens within the Baikal Rift. Detailed topographic mapping of the deformation area and trenching across the fault scarp revealed two paleoseismic events responsible for scarp formation. Dating of organic remnants found in the trench walls allowed us to estimate a late Holocene age for the paleoearthquakes and bracket the vertical slip rates along the Primorsky Fault to between 0.5 ± 0.1 mm/yr (min) and 0.9 ± 0.2 mm/yr (max) over the last ~2.5 kyr. The geomorphological and paleoseismological data, in combination with the analysis of recent seismicity and horizontal geodetic rates, suggest that the Primorsky Fault has accumulated elastic stress with the potential for a ~M 6.6 earthquake. Large earthquakes of this magnitude have occurred at least twice on the investigated fault segment during the last ~1.4 kyr.

Tomographic Pn Velocity and Anisotropy Structure in Mongolia and the Adjacent Regions

AbstractWe present new high‐resolution Pn velocity and anisotropy models beneath Mongolia and the adjacent regions by inverting 169,406 Pn arrivals. The data are selected from 786 permanent stations and 106 portable seismographs recently deployed in Mongolia and China's Inner Mongolia. The availability of new data acquired has allowed us to explore the uppermost mantle structures in great detail in this region, and the 2° × 2° model resolution is capable of distinguishing small‐scale geological features. Pn average velocity is 8.18 km/s, substantially faster than the global average. Distinct contrast in the velocity of the uppermost mantle is observed between the central part and two ends of the Baikal Rift, with the presence of higher velocities under the Central Baikal Rift, indicating strong variation of lithospheric thinning across the entire Baikal Rift. Low velocity beneath the Hangay Dome implies partial melting of mantle reflected by asthenospheric upwelling. Azimuthal anisotropy in the upper and lower mantle lid is measured by grouping the travel time data into two phases by epicenter distance. The obvious depth dependence of Pn anisotropy beneath the Hentey Mountains suggests different origins of fabrics. The lower anisotropy may origin from asthenospheric flow, while the shallower fabric may exhibit the preserved lattice preferred orientation anisotropy in the uppermost mantle. Meanwhile, depth‐dependent anisotropic structures and significantly low velocity are found beneath Tien Shan, most possibly suggesting that the lithospheric mantle thinning is experienced by either delamination or local asthenospheric upwelling.

Current Trends in Upper Water Layer Temperature in Coastal Zones of Baikal

Based on the data from 17 meteorological stations, we have analysed the characteristics of the temperature change within the surface water layer (0.2–0.5 m) in the coastal zone of Lake Baikal. It was determined that during 1970–2016, the average temperature trend in May–September was increasing from Southern Baikal to Central and Northern Baikal due to a combination of physical– geographical features (heat from the sun, orography of the coastal mountains and underwater slopes, wind conditions, and water dynamics) in the lake basin. It was established that the low value of the trend in Southern Baikal is due to a relatively poor protection of its water area by the Primorskii Ridge (approximately 800 m high) from strong winds of the western quarter. It was found that an increased wind activity causes a more pronounced wind–wave mixing in the upper layers as well as more frequent upwellings/downwellings which also involve the waters from the deeper layers in the exchange with the upper water layers. In the Central Baikal basin, the influence of the water mass on the atmospheric circulation in the surface layer is the most obvious. Its consequence implies high atmospheric transparency and decreased cloudiness over the lake leading to an increase in incident solar radiation in the upper water layers. The high temperature trends, compared to the other parts of Baikal, correspond to the Northern Baikal basin best protected from the strong westerly winds by the Baikalskii Ridge (up to 2500 m high). Over the past two decades (1994–2016), the trend of warming of the surface water layer has decreased significantly, along with an increase in the warming rate of Central and Southern Baikal. Using data of deep–water temperature monitoring in Southern Baikal, we estimated the spatial scales of the identical response of the surface temperature and the lake water column to climate change.

Genetic diversity of Microsporidia in the circulatory system of endemic amphipods from different locations and depths of ancient Lake Baikal.

Endemic amphipods (Amphipoda, Crustacea) of the most ancient and large freshwater Lake Baikal (Siberia, Russia) are a highly diverse group comprising >15% of all known species of continental amphipods. The extensive endemic biodiversity of Baikal amphipods provides the unique opportunity to study interactions and possible coevolution of this group and their parasites, such as Microsporidia. In this study, we investigated microsporidian diversity in the circulatory system of 22 endemic species of amphipods inhabiting littoral, sublittoral and deep-water zones in all three basins of Lake Baikal. Using molecular genetic techniques, we found microsporidian DNA in two littoral (Eulimnogammarus verrucosus, Eulimnogammarus cyaneus), two littoral/sublittoral (Pallasea cancellus, Eulimnogammarus marituji) and two sublittoral/deep-water (Acanthogammarus lappaceus longispinus, Acanthogammarus victorii maculosus) endemic species. Twenty sequences of the small subunit ribosomal (SSU) rDNA were obtained from the haemolymph of the six endemic amphipod species sampled from 0–60 m depths at the Southern Lake Baikal’s basin (only the Western shore) and at the Central Baikal. They form clusters with similarity to Enterocytospora, Cucumispora, Dictyocoela, and several unassigned Microsporidia sequences, respectively. Our sequence data show similarity to previously identified microsporidian DNA from inhabitants of both Lake Baikal and other water reservoirs. The results of our study suggest that the genetic diversity of Microsporidia in haemolymph of endemic amphipods from Lake Baikal does not correlate with host species, geographic location or depth factors but is homogeneously diverse.

Authigenic rhodochrosite from a gas hydrate-bearing structure in Lake Baikal

Early diagenetic carbonates are rare in Lake Baikal. Siderite (Fe carbonate) concretions in the sediments were discovered only recently. Here, we discuss the first finding of rhodochrosite concretions (Mn carbonate) discovered in the near-bottom sediments of the gas hydrate-bearing seepage structure St. Petersburg-2 in the deep water environment of the Central Baikal Basin. The crystal lattice of rhodochrosite contains iron and calcium substituting to manganese. Based on pore water geochemistry and of δ13C values of rhodochrosite (− 23.3 and − 29.4‰), carbon dioxide (+ 3.8 to − 16.1‰) and methane (− 63.2 to − 67.8‰), we show that carbonate crystallization most likely occurred during microbial anaerobic oxidation of organic matter, and that part of the oxygen making up the rhodochrosite seems to be derived from the 18O-rich water released from dissociating gas hydrates.

Cyanobacteria Nostoc Punctiforme from Abyssal Benthos of Lake Baikal: Unique Ecology and Metabolic Potential.

A strain of Nostoc punctiforme was isolated from the bottom sediments of the oil seep at Gorevoy Utes (Central Baikal) at a depth of 890m. The Baikal strain is highly similar (98-99%) to the N. punctiforme CCAP 1453/9 strain and the typical N. punctiforme PCC 73103 strain isolated from soil ecotopes. Based on the analysis of functional genes and mass spectrometry data, we determined that the strain can produce bioactive peptides and polyketides, but does not produce known cyanobacterial toxins, saxitoxin or its analogs, or microcystins. The peptides aeruginosinamide, aeruginosin 606, aeruginosin 98-A, kasumigamide C, and microginin 91-D were recorded in the metabolic profile of the strain. The major ion found in the MALDI mass spectrum is most likely to be an ion of a polyketide substance with unknown function.

MIDDLE NEO-PLEISTOCENE GEODYNAMICS OF THE NORTH-EASTERN MARGIN OF THE BAIKAL RIFT ZONE

The Neo-Pleistocene tectonic activity in the north-eastern margin of the Baikal Rift Zone differed from that of the central Baikal sector. The neotectonic uplifts of the rift valleys mountain surround in the Stanovoi upland occurred in the Middle Neo-Pleistocene, which was confirmed by the results of palynological analysis and thermoluminescent dating. The regime of lacustrine sedimentation arose here more than once up to the Late Neo- Pleistocene. During the Late Neo-Pleistocene stage, the formation of the valley meso-landforms was caused mainly by climatic factors.

Jelly-like Microbial Mats over Subsurface Fields of Gas Hydrates at the St. Petersburg Methane Seep (Central Baikal)

Jelly-like microbial mat samples were collected from benthic surfaces at the St. Petersburg methane seep located in Central Baikal. The concentrations of certain ions, specifically chloride, bromide, sulphate, acetate, iron, calcium, and magnesium, were 2–40 times higher in the microbial mats than those in the pore and bottom water. A large number of diatom valves, cyanobacteria, and filamentous, rod-shaped and coccal microorganisms were found in the samples of bacterial mats using light, epifluorescence and scanning microscopy.Comparative analysis of a 16S rRNA gene fragment demonstrated the presence of bacteria and archaea belonging to the following classes and phyla: Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Verrucomicrobia, Cytophaga-Flavobacteria-Bacteroidetes, Cyanobacteria, and Euryarchaeota. The chemical composition and phylogenetic structure of the microbial community showed that the life activity of the mat occurs due to methane and its derivatives involved. Values of δ13C for the microbial mats varied from −73.6‰ to −65.8‰ and for animals from −68.9‰ to −36.6‰. Functional genes of the sequential methane oxidation (pmoA and mxaF) and different species of methanotrophic bacteria inhabiting cold ecosystems were recorded in the total DNA. Like in other psychroactive communities, the destruction of organic substances forming formed as a result of methanotrophy, terminates at the stage of acetate formation in the microbial mats of Lake Baikal (1,400 m depth). Its further transformation is limited by hydrogen content and carried out in the subsurface layers of sediments.

Microbial oxidation of methane in the sediments of central and southern Baikal

Methane levels and methane oxidation rates were determined in the sediments from geochemically different areas in the central and southern parts of the low-mineral Lake Baikal. At different stations, integral rates of methane oxidation varied from 60 to 6592 μmol m−2 day−1. Typically, two distinct peaks of methane oxidation rates were revealed, located in the oxic and anoxic sediment horizons. In most cases, the rates of aerobic and anaerobic methane oxidation were comparable. Due to low sulfate concentration in pore water (<0.15 mM), a mechanism different from reverse methanogenesis, which involves methanotrophic archaea and sulfate-reducing bacteria and is common in marine sediments, was probably responsible for this process in Lake Baikal reduced sediments. The possible alternative mechanisms and electron acceptors are discussed.