Vol 273

Antarctica is the least studied continent on the planet. Extreme climate conditions, ice cover, and the lack of permanent infrastructure make it difficult to conduct field and stationary research. Nevertheless, interest in Antarctica as a unique natural laboratory is steadily growing, which is confirmed by a stable increase in the number of scientific publications covering a wide range of topics from geodynamics and glaciology to applied engineering solutions.

One of the priority areas of scientific research in Antarctica is the study of its deep structure. Most of the continent is covered with a thick ice sheet, so the main geoscientific data are acquired using geophysical methods, among which magnetotelluric (MT) ones have the greatest penetration depth and insignificant environmental impact. The possibility of acquiring high-quality MT data in the conditions of the sixth continent has long been questioned. The work is aimed at studying the specifics of magnetotelluric survey in Antarctica. The following tasks were set: to summarize the world experience of studying Antarctica using MT sounding methods; to identify factors that negatively affect the high-quality data acquisition; to determine methods for minimizing the influence of these factors. The article analyses geophysical studies conducted by the magnetotelluric sounding method in the Antarctic region from 1964 to the present. The application of the method is complicated by the following: extremely low temperature affects the drop in the batteries capacity, freezing of the non-polarizing electrodes solution, and changes in the strength properties of materials. Electromagnetic noise occurs during strong winds; proximity to the magnetotelluric field source can violate the plane wave principle on which the method is based. The ice sheet covering most of Antarctica does not allow acquiring optimal values of the contact resistance of the electrode grounding; the extended coastline distorts the acquired data. Studies of the influence of factors complicating the MT sounding method in the coastal and central parts of Antarctica made it possible to formulate recommendations for preparing equipment and adapting the work procedure, modifying the processing flow and a set of measures to ensure safety, the implementation of which will both allow safe performance of geophysical investigations and high-quality data acquisition.

The article presents the findings from research conducted at Vostok Station during the 69th Russian Antarctic expedition. The primary goal of the research is to perform a thorough investigation of the snow-firn layer using both direct (drilling and core analysis) and indirect (georadiolocation and seismic exploration) methods. As part of the research, fundamental tasks related to the study of the structure and dynamics of the upper part of the ice sheet were addressed, as well as applied tasks aimed at justifying the depth of explosive charge placement for seismic work with the goal of conducting a detailed study of Lake Vostok and selecting the point for drilling access to the lake. Data on the microstructure and physical properties of the snow-firn layer were collected. The findings will allow for future improvements to the firn densification model, which is required to understand the evolution of ice grains during the early stages of metamorphism. The study's findings aided in the understanding of the structural features of the ice sheet's surface layer, allowing for more precise determination of the structural and physical characteristics of the snow-firn layer and ice, potentially leading to a better understanding of climatic and geological processes in Antarctica.

The paper deals with geodynamic reconstructions of Australia and Antarctica (using the GPlates program) 79, 68-61, 48, 44, and 40 Ma based on the comparison of conjugate single-age magnetic anomalies. The relevance of the present study is determined by the increased scientific interest in the problems of Gondwana break-up and the influence of lithospheric block tectonics on the processes of riftogenesis and ocean opening. The early stage of oceanic opening between Australia and Antarctica is characterised by a series of distinct linear magnetic anomalies. Oceanic spreading occurred in an ultra-slow to slow regime with rates of 20-26 mm/year between 33o and 21u anomalies (80-48 Ma) and 40 mm/year between 21u and 18o anomalies (48-40 Ma). According to the studies, there is a clear correlation between the change in spreading rate and the position of the rotation poles. Between 80 and 48 Ma, the rotation pole was located to the west, in the Kerguelen Plateau region, and Australia shifted westward relative to Antarctica. About 48 million years ago, the rate of seafloor spreading almost doubled (from ultra-slow to slow), and Australia began to migrate northwards. The rotation pole was near the southern edge of Tasmania and continued to move southeast towards the Pacific Ocean. The separation of Australia and Antarctica was associated with the advance of the spreading axes of the Indian and Pacific oceans towards each other, with orthogonal inter-section of the ancient lithospheric blocks of the two continents, and was determined by the geometry of the marginal rift structures.

During the expeditionary research of 2023-2024 in the conditions of thick Antarctic ice sheet, the medium- and low-frequency ground penetrating radars (GPR) OKO-3 with a 150 MHz antenna and Triton-M with an extendable 25-50-100 MHz antenna (LOGIS LLC, Russia) improved and adapted for glacier investigations were tested for the first time. An example of the ice sheet study in the Schirmacher Oasis area showed that the OKO-3 GPR allows obtaining detailed information on the internal structure of the ice sheet to depths of about 200 m and successfully solving glacial stratigraphy issues. The Triton-M GPR has proven itself well for mapping the roof of underlying rocks to depths of 250-300 m. The article presents new data on the glacier structure in the Novo Runway area, as well as information on the glacier thickness and the subglacial rock base topography near the Schirmacher Oasis (Novolazarevskaya and Maitri stations). Typical structures of the glacier strata in this area are gently sloping layers and steep folds that replace them, complicated by crevasses. The subglacial topography to the south of the oasis is quite gentle. Individual uplifts and depressions do not exceed 30 m. The interface between the ice and the rock base was recorded over a distance of 4.5 km to the south of the oasis. In the east, about a kilometre from the last rock outcrop, the oasis is limited by a sharp depression in the bed. New data opens up the possibility of constructing the ice sheet models, studying its dynamics and evolution, and finding patterns in the crevasse formation.

New geophysical data have revealed a large number of narrow and deep depressions in the ice sheet bed in various areas of Antarctica with depths of up to 3500 m below sea level (Denman Depression). These depressions have all the features of Cenozoic rifting – steep sides, the greatest depths on land, strong negative gravity anomalies in free air (–100 mGal and less) and high heat flow. The continuation of rifting after the glaciation of Antarctica with almost complete cessation of sedimentation under the ice explains the great depth and steep sides of the depressions with increased heat flow and mass deficit. Important features of the coastal depressions of the ice bed are their retrograde slopes, characteristic only of Antarctica. The subglacial relief of the basins on the approach to the continental coast sharply flattens out, which indicates sedimentation in the transition zone during periods of ice melting and subsequent marine regressions-transgressions in the Late Cenozoic. Increased heat flow can lead to melting of the glacier base and promote their accelerated sliding from the bedrock into the ocean. Another factor affecting the rate of glacier sliding into the ocean is the friction force with the bedrock. The presence of soft young sediments reduces friction and promotes the sliding of ice sheets into the ocean under the influence of gravity. Fast-moving ice sheets in Antarctica are mainly confined to areas of rift basins. Acceleration of glacier runoff along retrograde slopes into the ocean has a positive feedback and creates a potential hazard of global sea level rise. The geodynamic mechanism responsible for the Cenozoic activation of Antarctic rift zones is due to the action of local upper mantle plumes beneath Antarctica during and after the breakup of Gondwana. Further reactivation of extension along weakened zones in the lithosphere is associated with the general acceleration of global mantle convection that began in the Miocene. Numerical three-dimensional geodynamic models of the formation of the Transantarctic Mountains and the uplift of the Gamburtsev intraplate orogen in the Cenozoic are proposed.

The paper focuses on the technique and results of an aeromagnetic survey conducted using a fixed-wing unmanned aerial system (UAS) in East Antarctica at the Bunger Hills and Highjump Archipelago (Wilkes Land) during the 69th Russian Antarctic Expedition. The above survey was carried out at a 250-meter distance between flight lines (scale 1:25,000) over the area of 600 km2 to increase the geological knowledge of the area. The magnetic anomaly map obtained after data processing is more detailed than any of known published geological maps of the area. The size of anomalies detected varies from dozens of meters up to large, kilometer-scale structures traced within the entire area under survey. The data analysis shows that the surveyed region is characterized by morphological heterogeneity and amplitude variability of anomalous magnetic field. Along with relatively calm zones one can observe strong gradient ones. Even the fluent analysis of aeromagnetic survey results proves their high information content. The UAS-based survey results demonstrate that the technique implemented is an important tool of applied geophysics and can effectively solve tasks of geological mapping in harsh weather conditions of Antarctica. It can adequately replace conventional aeromagnetic surveys that are now done using manned aircraft.

The article analyses the results of geophysical studies of rift structures in East Antarctic, direct geological surveying of which is impossible due to a thick ice sheet. A model is proposed for the formation of Lake Vostok depression suggesting its emplacement within the regional transtensional zone. The Lake basin includes the southern longitudinal graben forming along the main shear and the northwestern basin, which is estimated as a pull-apart structure. Based on results of the gravity and magnetic field interpretation proposed in the article, the identification and parameters of the interblock suture zone in the basement of the coastal part of the subglacial Lake Vostok are substantiated. Similarities in the structure of the Earth’s crust of regional and local structures containing Lakes Vostok and Baikal have been recorded for a large number of features: spatial correlation with position of regional shear zones; geniculate morphology of lake basins composed of linear longitudinal depressions parallel to direction of the shear zone and depressions controlled by diagonal fault displacements; relief of adjacent structures; steepness of coasts; high seismicity with earthquakes localized along the main axes of fault displacements as well as the Earth’s crust structure of geostructures controlling these basins. The formation model of rift structures of East Antarctic localized along subparallel shear zones is presented. To explain the geodynamic nature of rift systems, the model of the upper mantle convective cell is used. The Vostok, Scott, Aurora, Concordia, Adventure, Wilkes, and Astrolabe depressions form an extensive tectonic zone approximately 2,000 km long and 1,500 km wide. Tectonic schemes showing localization of the East Antarctic rift system as well as depressions of the Mesozoic West Transbaikal rift area and the Cenozoic Baikal-Stanovoi rift zone are presented.

The paper studies seismicity of the South Polar Region from the South Pole to the 50th parallel of south latitude. During the observation period, earthquakes of various genesis with a magnitude of M > 8 occurred in seismically hazardous zones of the Southern Ocean – the South Sandwich subduction zone, the Macquarie Ridge and the Antarctic Ridge. These events can cause significant tsunamis. The Macquarie Ridge is characterized by a shear mechanism of the earthquake source, while different mechanisms were obtained for the Sandwich subduction zone region. During the instrumental observation period, weak intracontinental seismicity of Antarctica was recorded, which refutes the position of aseismicity of this continent. Seismicity is observed at the boundaries of tectonic blocks or is confined to coastal areas. In the continental intraplate region of Antarctica, earthquakes occur in several settings. The events in the Transantarctic Mountains and some subglacial rift basins, as well as isolated events in the central part of the continent, are probably tectonic. Seismicity in the coastal zone and on the continental margin may be related to glacial isostatic adjustment with a regional tectonic component in some places. The seismicity observed in Antarctica is low compared to other continental intraplate regions. The strongest events within the continent have a magnitude of 5-6. The authors identified intracontinental areas of increased seismicity. A correlation between intracontinental seismicity and subglacial basins of East Antarctica is shown. Some events with magnitudes below the threshold are not recorded. In addition, seismicity is partially suppressed by a thick ice cover.

In the course of seasonal work of the 70th Russian Antarctic expedition (RAE) in 2024-2025, as part of the field geological and geophysical studies by researchers of Empress Catherine II Saint Petersburg Mining University on the Broknes Peninsula (Larsemann Hills, East Antarctica), areal ground magnetic survey was accomplished at 1:10,000 scale. The study area is characterized by a high exposure degree of Cambrian and Precambrian rocks with localization in certain parts of magnetite-bearing complexes. The work included experimental and methodological research, surveying in two modes (discrete and continuous) with data quality control as well as subsequent processing and initial interpretation of the results. A detailed map of the total magnetic intensity covering an area of 17.5 km2 and maps of the field transformations – vertical derivative, absolute horizontal gradient, etc., were compiled. Qualitative interpretation allowed identifying morphologically homogeneous zones in the study area characterized by different features of anomalous magnetic field. Results of the studies will be used in future for geological interpretation of anomalies and compilation of the structural tectonic map of the region.

This paper presents new data on various types of pegmatites from the Larsemann Hills oasis (Princess Elizabeth Land, East Antarctica), collected during the 70th Russian Antarctic Expedition in 2024-2025. As a result of comprehensive geological and geophysical investigations, all pegmatite occurrences in the area belonging to different stages of the Pan-African orogeny have been described, analyzed, and systematically classified in a unified context for the first time. In addition to previously known pegmatites associated with deformation stages D2-3, D4, and post-D4, a further subdivision is proposed based on mineralogical-geochemical characteristics and the content of natural radionuclides. These include borosilicate D2-3 pegmatites, rare-metal D4 pegmatites, muscovite-bearing post-D4 pegmatites, as well as two newly identified types not previously described in the region: K-feldspar D4' pegmatites and miarolitic rare-metal post-D4' pegmatites, which differ in morphology, mineralogy, and geochemical features. Special attention is given to the structural-tectonic control of pegmatite bodies, their geological setting, zoning patterns, and the results of gamma spectrometric and magnetic surveys. Pegmatitic formations containing rare typomorphic minerals – such as tourmaline, boralsilite, grandidierite, and chrysoberyl – are also examined. The results indicate a significant diversity of pegmatite formation conditions, help refine the PT parameters and timing of the initial and final stages of the Pan-African metamorphic event, and confirm the genetic link between pegmatite development and D2-D4 deformation stages. These findings contribute to the reconstruction of Early Paleozoic pegmatite-forming stages during anatectic processes in the geodynamic evolution of East Antarctica and Gondwana.

The article presents the laboratory results of formation and breaking of water and organosilicon fluid emulsions, as well as formation and dissociation of nitrogen hydrates under PT conditions close to the conditions at the interface of a glacier and subglacial Lake Vostok using the Gas Hydrate Autoclaves GHA 350 complex. The studied organosilicon fluid was polydimethylsiloxane WACKER AK-10 (in the Russian classification according to GOST 13032-77, PMS-10) with a density of 0.9359 g/cm3 and a kinetic viscosity of 10 mm2/s. We found that a decrease in the emulsion temperature leads to an increase in the time of its breaking, the formation of microemulsions and multiple emulsions of the “oil – in water – in oil” type. This is especially evident at temperatures ≤10 °C. The average emulsion breaking time was 107 s. The minimum emulsion breaking time was observed at a minimum mixer rotation speed of 100 rpm and a maximum temperature of 60 °C, and the maximum emulsion breaking time was observed at a mixer rotation speed of 500 rpm and a temperature of –2.8 °C. We found that nitrogen hydrates were formed at a pressure of 35.0±0.5 MPa and a temperature of ≤ –1 °C.

The article presents the results of experimental drilling of congelation ice in the branch hole 5G-5 at the Vostok Station (Antarctica) using the KEMS-135 coring drill in the PMS-3 organosilicon fluid. The studies were conducted during the 70th Russian Antarctic Expedition and were aimed at assessing the technology efficiency in deep glacier drilling and opening of subglacial reservoirs, as well as at determining rational drilling parameters. Borehole preparation included extraction of drilling fluid, a body of geophysical studies, and wellbore reaming. The PMS-3 was delivered to the bottomhole using a specialized device called “Slonik”. Experimental drilling of congelation ice was conducted by the KEMS-135 coring drill. Two drilling runs were performed with core sampling of 1.10 and 1.14 m long, drilling depth 3595.15-3597.39 m. The presence of PMS-3 at the bottomhole was monitored by geophysical studies and sampling. Particular attention was given to analysing drilling modes, including mechanical speed, cuttings properties, and the effect of PMS-3 on the drilling equipment elements. The results of experimental drilling showed an increase in the mechanical drilling speed in the PMS-3 organosilicon fluid environment by 15-20 % compared to the used drilling fluid (kerosene + dichlorofluoroethane), as well as the absence of crown plugging and improved lubricating properties of the fluid. The article describes the promising areas of further research related to the drill design optimization for operation in the PMS-3 environment and the study of the long-term impact on subglacial ecosystems.

Construction of a new wintering complex at the Antarctic Vostok Station required prompt delivery of builders and mechanics to Progress Station to move them further to the work area. To solve this major logistical issue, a new landing site, later named Zenit, certified for accommodating heavy wheeled aircraft, was prepared in the Progress Station area from March to August 2022. Its snow pavement slab with a total area of 350 thousand m2 is from 100 to 120 cm high. It was made by applying snow layers with their subsequent compaction by a specially designed compaction platform for snow airfields suitable for heavy wheeled aircraft. As a result, the pavement has a surface hardness of at least 1 MPa. The layer from 30 to 60 cm has a hardness of at least 0.8 MPa, and the bottom layer at least 0.6 MPa. The first Il-76TD-90VD aircraft of the Russian company Volga-Dnepr was accommodated to the new runway on 7 November 2022. The aircraft landed in normal mode. The depth of the chassis wheels track after landing did not exceed 3 cm. The research provided in-depth understanding of the mechanisms for forming the supporting base of the runway from snow and ice in Antarctica. The experience gained can be used to solve similar issues in the Far North.