Multidisciplinary studies of the bottom sediments–water column–atmospheric water layer system in the Barents and Pechora seas and Baydaratskaya Bay of the Kara Sea were carried out on the expedition European Arctic–2023: Geological Record of Environmental and Climate Change during the season of polar night and active development of autumn–winter thermal convection. Fundamentally new data on a number of areas of oceanology were obtained in the cruise.

Hydrophysical studies in 2004–2018 showed that the cyclonic gyre of the Middle Caspian Sea is not a year-round circulation. In the cold season, the current in the cyclonic gyre intensifies, while in the warm season, the circulation weakens and the directed current turns into a drift one, except for the western part, where the water is transferred from the Middle Caspian to the southern part of the sea due to the difference in the levels of the basins. It is shown that the current in the cyclonic circulation follows the contour above the slope of the Derbent Basin in the entire layer from the surface to the bottom. The seasonal boundaries of the annual intensification and weakening of the cyclonic circulation are revealed.

Contourite drifts were found for the first time on the SW Kara Sea shelf based on the analysis of bathymetry and seismoacoustic data obtained in the cruises 41 (2019) and 49 (2020) of R/V Akademik Nikolai Strakhov. These drifts are confined to a narrow NS depression with a depth of 240 m. They are separated from underlying sediments by the basal unconformity caused by the bottom current formed in the marine environment after melting of the Barents–Kara ice sheet during the Late Pleistocene–Holocene time. Hydrological measurements carried out in the cruise 89-1 (2022) of R/V Akademik Mstislav Keldysh made it possible to reveal the bottom current with a measured velocity of up to 10 cm/s.

Suspended particulate matter (SPM) as a main proxy of sedimentation conditions has potential to improve the study and monitoring of the consequences of rapid warming of the Arctic. In this study, we report the concentration of SPM and its major phase composition in the South Kara sedimentary basin in September 2022 as part of a climate experiment to investigate the composition of air and characteristics of the underlying surface in the Russian region of the Arctic and Siberia. In order to understand the sources, sinks, and hydrodynamic influences on SPM distribution in the South Kara Sea, three sections were carried out during cruise: longshore coastal section at the Priyamal shelf and two zonal sections through the center of the study area. These sections of SPM were overlain by salinity, temperature, turbidity, and chlorophyll-a fluorescence contours. Full depth profiles of SPM mass and volume concentrations obtained by a set of methods demonstrate layers of particle accumulation at density interfaces in the upper water column and widespread distribution of near bottom nepheloid layers. Particle composition and chlorophyll-a concentration analyzed from filtered samples throughout the water column aided considerably in determining the sources and distribution of SPM.

The study investigated vertical particle fluxes and associated environmental parameters in the southern part of the Kara Sea in September 2022 on the basis of a 5-day deployment of two moored Automatic Deep-Sea Sedimentation Observatories with sediment traps and CTD, currents and hydrooptical profilers.

The results of continuous year-long in situ observations of the circulation of currents and temperatures in the bottom Arctic regions of the energy-active zone of the Iceland Basin are presented. Data were obtained at flooded buoy stations at a section of 59.5° N at depths of about 50 m from the bottom during 2016–2017. The intra-annual variability of bottom currents and temperature was investigated. It was shown that during the entire period there was monotonous stationary movement of water at all stations, as well as an increase in temperature in bottom waters entering the basin, as well as in those leaving. At the same time, the annual temperature growth rate of the outlet stream was 1.5 times higher than the temperature increase of the inlet stream.

Data on the assessment of the dynamics of sedimentary waves over the western slope of the Caspian Sea are presented. The process of formation of the wave structure of sedimentary waves under the influence of hydraulic pressure jumps during the spreading of gravitational turbidity flows downslope is discussed.

Представлены данные наблюдений за придонной циркуляцией течений и температуры в арктической части Атлантического океана, полученные на притопленных буйковых станциях по разрезу 59,5 сев. шир. в течение 2016–2017 гг. Показана внутригодовая изменчивость придонной скорости, температуры и энергии течений. Сделано предположение, что существующая межгодовая изменчивость океанологических полей возможно связана с долгопериодными климатическими изменениями Земли, в том числе и с Эль Ниньо. The article presents data on observations of near-bottom circulation of currents in the Arctic part of the Atlantic Ocean, obtained from submerged buoy stations in the 59.5o N section. during 2016–2017 years. The intra-annual variability of the velocity and energy of the near-bottom currents is shown. It is assumed that the current interannual variability of oceanological fields, which is possibly associated with long-term climatic changes of the Earth, including El Niño.

First results of the multidisciplinary expedition onboard the R/V Akademik Nikolaj Strakhov in the Barents Sea in August–September 2018 are presented. Hydrophysical sounding has been carried out on 41 stations, sampling of bottom sediments has been done using both grab and gravity corer. As a result of the geophysical investigations, areas with manifestations of current dangerous natural processes are identified. Four seismic bottom stations have been installed in the Pechora Sea.

Based on time series of near-bottom current velocities and temperatures obtained in the period June, 2016 to July, 2017, at three points in the Atlantic Subarctic Front, along with the use of multi-year (since 1993 up to now) satellite ocean surface sounding data, multi-scale fluctuations of ocean surface and near-bottom flows over the western and eastern flanks of the Reykjanes ridge, as well as near Hatton Rise, on the Rokoll plateau, are studied. Hydrological profiles were carried out from the ocean surface to the bottom with readings every 10 m, when setting and retrieving the buoy stations. Using data from the Bank of hydrological stations (WOD13), SST satellite arrays (Pathfinder), long-term sea level and geostrophic velocities time series (AVISO), and bottom topography (model ETOPO-1), features of longterm cyclical fluctuations of SST, sea level, geostrophic currents on the ocean surface were defined in the sub-polar North Atlantic. It is shown that, in accordance with the large-scale thermohaline structure of the Subarctic front, two branches of the North Atlantic Current are detected on the ocean surface.One is directed from the Hatton towards the Icelandic-Faroese Rise, and the other – alomg the western flank of the Reykjanes Ridge toward Iceland. For the first branch, which is the main continuation of the North Atlantic Current, the average (for 25 years) water drift at a speed of 9.1±0.1 cm/s is determined to the northeast. The second branch, which forms the eastern part of the Subarctic cyclonic gyre, has the average water drift at a speed of 4.0±0.1 cm/s is directed north-northeast, along the western flank of the Reykjanes Ridge. In the intermediate waters of the frontal zone, an average water flow is observed at a speed of 2.7±0.1 cm/s to the north-northeast, along the eastern slope of the Reykjanes ridge.Due to the multy-scale components of the total variability, the average kinetic energy densities(KED) of total currents (109, 45, 97, (±3) erg/cm3, at station points from east to west) are much greater than the mean drift KED. The near-bottom flows on the Reykjanes ridge flanks are opposite to the direction of the North Atlantic Current. Outside the Subarctic gyre, the direction of average transport is maintained from the ocean surface to the bottom. The average (per year) KED of near-bottom currents are 31, 143, 27 (±3 erg/cm3), for three stations from east to west, respectively. In the intermediate waters of the frontal zone, above the eastern slope of the Reykjanes Ridge, there is a powerful reverse (relative to the North Atlantic Current) near-bottom water flow to the south-west, with a high average speed of ~ 15 cm/s. The KED of the currents during the year varies widely from zero to ~ 600 erg/cm3. The overall variability is due to cyclical variations and intermittency (“flashes”) of currents. Perennial cycles, seasonal variations, synoptic fluctuations with periods in the range of 30–300 days, as well as inertial oscillations and semi-diurnal tidal waves are distinguished. The intermittency of oscillations is partly due to changes in low-frequency flows, which can lead to a dopler frequency shift in the cyclic components of the spectrum. The amplitude of temperature fluctuations in the bottom layer for the year was (0.07–0.10) ± 0.01°C by the standard deviation. The seasonal changes of the bottom temperature are not detected. However, a linear trend with a warming of ~ (0.10–0.15) ± 0.01°С per year is noticeable.

The paper presents analysis of geological-geophysical data, both from archives and collected in recent expeditions by Shirshov Institute of Oceanology, RAS (SIO RAS) together with satellite data. The interpretation shows modern rise of fluid dynamic activity on North Caspian. Based on summary of previous data, it is possible to recognize ryithmostratigraphic and seismostratigraphic complexes. Side sonar data shows many reflexing objects on the sea bottom. One of the most prominent features of Northern and Central Caspian is great number of pipe-like vertical bodies, they were discovered by SIO RAS expeditions with high-resolution seismic methods. These “pipes” go down beyond seismic section data. All specified seismic anomalies and bottom microrelief can be considered as evidence of vertical migration of gas and water via sediments and its escaping to water by gas and water grifons. Satellite images of North and Central Caspian show great amount of sliks and oil signs on the sea surface, and some of them present constantly on the same place, so it is possible to claim the sub-bottom fluid escape theory. The paper shows connection between bottom structures and grifon activity via satellite images (spatial-time grouping of oil slicks) of 2011–2019.

Приведены первые результаты комплексной экспедиции на научно-исследовательском судне «Академик Николай Страхов» в Баренцево море в августе–сентябре 2018 г. Проведено гидрофизическое зондирование на 41 станции, отобраны пробы донных осадков как с помощью дночерпателя, так и грунтовой трубкой. В результате геофизических исследований выявлены участки с проявлениями современных опасных природных процессов. Установлены 4 сейсмостанции в Печорском море.

The experimental data given in the article show a perturbation of currents in the northeastern Caspian Sea near Peschanomysskoe uplift, which is caused by the interaction between cyclonic circulation and the southern slope of the uplift. This interaction results in that the water of the cyclonic circulation forks into lower and upper branches. The lower, bottom branch is reflected southwestward by the uplift, where, at the head of the uplift, it meets water flowing southeastward over the bed of the Yuzhno-Buzachinskii depression, while the upper branch, consisting of the surface and intermediate cold water, is pushed upward and flows over the uplift. The rise of cold water forms upwelling in the top layer, which extends over the entire northeastern part of the sea.

Results of field observations of current dynamics in the frontal zone of the western Middle Caspian are given. The cyclonic circulation over the western slope in winter is shown to be a unidirectional intense current with velocities up to 100 cm/s. In summer, the current slows down and separates into branches—it turns southwestward and westward at the slope depth down to 150 m, southward and southeastward at the depth of ~100–350 m, and eastward at larger depths. In summer, shelf currents interact with the flow of Middle Caspian cyclonic circulation, resulting in that anticyclonic vortices reach the shelf.

The results of an investigation into water mass dynamics in the northeastern sector of the middle Caspian Sea are presented. High variations of currents are observed in this region of the sea, which are caused by the influence of the Peschanomysskoye Rise (PMR) on the cyclonic gyre. This bottom elevation is an obstacle to the currents of the gyre. The Yuzhno-Buzachinskii Deflection also influences the currents. Part of the dense and cold waters from the northern Caspian Sea flows along this deflection to the Derbent Basin. This basin is also a sink for the cold waters transported on the Peschanomysskoye Rise and those that overflow it. Observations in May 2015 over a cross-shaped survey at the western basement of the PMR showed that the currents in May in the western part of the survey in the entire water column from the surface to the bottom are organized in layers in the form of an anticyclonic spiral: the bottom current is directed to the south, the middle current is directed to the west, and the surface current is directed to the north. Lenses of warm water are observed in the bottom layer.

On the basis of in-situ hydro-physical one year long time series, acquired in June, 2016 -July, 2017, in the North Atlantic Subpolar Gyre, along with the use of up to date satellite data, detailes of long term variability of surface and near-bottom flows over Reykjanes Ridge flanks and near the Hatton Bank (Rockall Plateau) are presented.