Karst caves, formed by the erosion of soluble carbonate rocks, provide unique ecosystems characterized by stable temperatures and high humidity. These conditions support diverse microbial communities, including wall microbial fouling, aquatic biofilms, and planktonic communities. This study discloses the taxonomic diversity of protists in aquatic biotopes of Shulgan-Tash Cave, a culturally significant site and popular tourist destination, by 18S rRNA gene metabarcoding. Our findings reveal the rich protist communities in the cave’s aquatic biotopes, with the highest diversity observed in Blue Lake at the cave entrance. In contrast, Distant Lake in the depth of the cave was inhabited by specific communities of plankton, mats, and pool fingers, which exhibited lower richness and evenness, and were adapted to extreme conditions (cold, darkness, and limited nutrients). High-rank taxa including Opisthokonta, Stramenopiles, and Rhizaria dominated all biotopes, aligning with observations from other subterranean environments. Specific communities of biotopes inside the cave featured distinct dominant taxa: amoeboid stramenopile (Synchromophyceae) and flagellates (Choanoflagellatea and Sandona) in mats; flagellates (Choanoflagellatea, Bicoecaceae, Ancyromonadida) and amoeboid protists (Filasterea) in pool fingers; flagellates (Ochromonadales, Glissomonadida, Synchromophyceae), fungi-like protists (Peronosporomycetes), and fungi (Ustilaginomycotina) in plankton. The specificity of the communities was supported by LEfSe analysis, which revealed enriched or differentially abundant protist taxa in each type of biotope. The predominance of Choanoflagellatea in the communities of cave mats and pool fingers, as well as the predominance of Synchromophyceae in the cave mats, appears to be a unique feature of Shulgan-Tash Cave. The cold-tolerant yeast Malassezia recorded in other caves was present in both plankton and biofilm communities, suggesting its resilience to low temperatures. However, no potentially harmful fungi were detected, positioning this research as a baseline for future monitoring. Our results emphasize the need for ongoing surveillance and conservation efforts to protect the fragile ecosystems of Shulgan-Tash Cave from human-induced disturbances and microbial invasions.

This study presents the results of a long-term investigation of the microclimatic conditions in Shulgan-Tash Cave (Southern Urals, Russia), which hosts the largest assemblage of Upper Paleolithic paintings (ca. 16.3–19.6 ka) in Eastern Europe. The cave exhibits two distinct seasonal ventilation regimes – winter and summer – differentially influence its two levels of galleries. In the Lower Level, which contains 83% of the images, near-atmospheric CO2 concentrations persist year-round, and temperature variations associated with seasonal infiltration events are minimal (1.0–1.3°C). By contrast, the Upper Level, including the decorated Hall of Paintings, is affected by downdrafts of CO2-rich air during summer, resulting in elevated concentrations (up to 0.2–0.3% vol.). These conditions reflect the position of this sector beneath a densely forested massif and the degassing of phreatic waters. The principal threats to the preservation of the cave art include: (i) summer condensation, mitigated by the use of air-circulation screens; (ii) cyclic CO2 fluctuations, which drive alternating dissolution and degassing in water films on decorated walls; and (iii) rapid degassing of infiltrating waters, leading to calcite deposition over the paintings. These processes variably affect the decorated chambers, highlighting the need for site-specific conservation measures. Given the cave's recent inscription on the UNESCO World Heritage List, these findings provide an essential basis for developing effective long-term preservation strategies for this unique cultural heritage site.

Subject. The aim of the work is to study the mechanism and sources of water formation, as well as the peculiarities of carbonate mineralization in the aquifer of the Kyndyg thermal water deposit. Materials and methods. The samples of water (8) and deposited carbonates (15), collected at different seasons at three sites, characterized by different temperatures and distances from the source, were investigated. pH, Eh, and electrical conductivity were determined by an electrochemical method. For the determination of HCO³ – , Cl– , SO₄ ²–, titrimetric, mercurymetric and turbidimetric methods were used. Trace element composition was determined by ICP-MS (NexION 300S); strontium isotopic composition – by MC-ICP-MS (Neptune Plus) using the bracketing technique after Sr chromatographic separation. Results. The chloride-calcium hydrochemical type prevails in the studied waters. A number of trace elements in water exceeds the clarke concentrations for groundwater in the supergene zone of mountain landscapes. ⁸⁷Sr/⁸⁶Sr isotope ratios (0.7065–0.7072) in thermal waters suggest that their composition is determined rather by the isotopic characteristics of the rocks through which water drains than by the influence of sea water. Among the newly formed carbonates, aragonite prevails. In contrast to thermal water, the concentrations of most metals in carbonates are below the clarke values; only Sr and Se are increased, which content is significantly increased in water as well. Deposited carbonates are characterized by ⁸⁷Sr/⁸⁶Sr values (0.7028–0.7074), which are lower than in the source thermal waters. Conclusions. On the basis of hydrogeological, hydrochemical and geochemical data, it can be assumed that the waters of this aquifer complex are formed mainly due to fresh fractured karst waters of lower Cretaceous limestones with submerged monocline dipping into the zone of slow circulation and mixing with sedimentogenic sodium chloride waters. The geochemical data and the presence of scandium anomaly suggest that the underlying Jurassic volcanogenic rocks also participate in water exchange.

Speleogenesis in hypogene karst settings may be closely tied to regional tectonic dynamics and concomitant hydrochemical evolution of karst waters. However, placing temporal constraints on these processes can require a wider array of field observations and techniques than for typical karst systems. Herein, we present a comprehensive study of Novoafonskaya Cave (Western Caucasus, Abkhazia). The updated speleogenetic history of the cave comprises four stages: (1) the most ancient, a low-T hydrothermal (ca. 40–50°C) priming stage; (2) the main stage enabled by mixing of upwelling thermomineral and locally recharged common karst waters; (3) the late sulfuric-acid speleogenesis (SAS) stage, which left significant mineralogical overprint (gypsum and a suite of minerals resulting from the alteration of silicate sediments) but did not alter the morphology of the cave appreciably; and (4) the contemporary stage, occurring predominantly in the phreatic and epiphreatic zones. Ages of speleogenetic stages were constrained by radiometric dating (230Th-U and 40Ar/39Ar) and paleomagnetic data, alongside the Quaternary geological history of the region and paleodynamics of the Black Sea level. Conditions for the low-T hydrothermal karstification occurred from Miocene – Middle Pliocene. The main stage, which created the main volumes of the cave, took place from Late Pliocene – Middle Pleistocene. The cave emerged from the phreatic into the vadose zone after ca. 400 ka ago, due to the combined effect of the Black Sea regression and intensification of tectonic uplift in the Caucasus. The presence of sulfidic waters during dewatering led to the development of transient SAS processes during Middle to Late Pleistocene. Dating of calcite underlying SAS-associated overgrowths constrains the cessation of this SAS activity to within the last 147 ka. In its present state, the cave has no connection with thermomineral waters; however, such waters are found deeper in the southern parts of the karst massif (based on the hydrochemistry of Psyrtskha spring), implying that hypogene karstification, primarily driven by mixing corrosion, may still be active deep in the phreatic zone.

Pendant 24 ans, de 1934 à 1958, A.V. Rumin, docteur en biologie et spécialiste en zoologie, a élaboré une théorie de l’existence de l’art paléolithique dans les grottes de l’Oural méridional, supportée par deux collègues et amis : le paléontologue I.A. Efremov et l’archéologue A.Y. Brusov. Les recherches d’Alexandre Rumin sur le Paléolithique ont été couronnées de succès à partir du mois de janvier 1959, quand les premiers dessins et peintures anciennes murales, peintes à l’ocre (ours, loup, lion, cheval) ont été découvertes dans la grotte de Kapova (Choulgan-Tach). Cet article présente les descriptions de la faune du Paléolithique ainsi représentée. Une biographie de l’auteur est réalisée.