The goal of the work: assessment of summer oceanographic conditions of the Barents and Kara Seas.Materials and methods: the data presented in the work were obtained on the 96rd cruise of the R/V «Akademik Mstislav Keldysh» (July 25, 2024–August 31, 2024). During the expedition, hydrological and chemical characteristics (temperature, salinity, dissolved oxygen, silicates, mineral and organic forms of nitrogen and phosphorus and dissolved organic carbon) were measured from the surface to the bottom. Chemical analysis was carried out in the ship’s laboratory, according to certified methods for sea and fresh waters. Dissolved organic carbon samples were using a filtration through membrane filters (0.45 μn) and fixed with hydrochloric acid for further determination using high-precision TOC–L equipment in a stationary laboratory in Moscow. In total, 13 oceanological sections and 183 complex oceanological stations were completed.The practical significance of the research: assessment of the production potential of the economically significant seas of the European Arctic for Russia in the area of maximum climate changes, replenishment of the monitoring system of hydrological and biogeochemical characteristics based on ship observations in accordance with the Order of the Government of the Russian Federation of October 29, 2022 No. 3240-r.

Variability of the total heat balance (HB) of the Barents Sea during the cold period of the year has been studied. The cold period is that of cooling of the sea surface when the heat flux is permanently oriented towards the atmosphere. The contribution of two major components of the HB, i. e. sensible and latent heat fluxes, to the observed increase of the total winter heat transfer at the sea-atmosphere interface has been estimated. Data on short-wave and long-wave radiation fluxes, and sensible and latent heat values were obtained from the atmos-pheric reanalysis of the European Center for Medium-term Weather Forecasting ERA5. HB of the sea surface was calculated as a sum of short-wave and long-wave radiation fluxes and those of sensible and latent heat. The total HB, as well as the total flux of sensible and latent heat for the cold period were calculated by summing up the corresponding values between the start and end dates of the cooling season. Calculations demonstrated an increase in the sum of HB over the cold season for the northern part of the Barents Sea (up to 2000 MJ/m2 over 40 years), and a decrease in the southern part of the sea (up to 1000 MJ/m2 over 40 years). In the northern part of the sea, the contribution of sensible and latent heat fluxes decreases to 0,3-0,4. The observed trend of sum of HB over the cold season and its turbulent components could with high probability be explained by increasing difference between air temperature and sea surface temperature.

An inflow of warm and salty Atlantic origin waters (AW) from the Nordic Seas to the Arctic Ocean interior is in the list of the major external factors, which control the hydrologic regime of the East-Atlantic sector of the Arctic Ocean. Rapid decay of the sea ice cover in 2000–2010s raised questions on the possible changes in the fate of the inflow under present ice-depleted conditions: whether warm and salty AW will cool and freshen slower (due to less ice to be melted underway), or intensified heat loss to the atmosphere through the open surface will lead to the faster AW cooling on shorter distance? We present rare hydrologic data, collected during the late winter 2019 in the international expedition “Transarktika-2019” in the northern part of the Barents Sea and at the adjoining continental slope of the Nansen Basin. On the basis of field data, supported by the oceanic reanalysis product and numerical modelling we have studied the transformation of AW on its transit between Svalbard and Franz Joseph Land. We show that the observed cooling and desalination of the fraction of AW over the continental slope around this area is controlled by lateral mixing with colder and fresher waters, outflowing from cross-slope canyons, which cut the continental slope: Kvitøya Trough, Franz Victoria Trough and probably, the British Channel. The obtained results demonstrate more intensive transformation of AW on this transit compared to previous studies. Possible explanations of this contrast, which are supported by the earlier studies, may include: the season of the survey when dense water outflow through canyons is at its maximum and gradual “atlantification” of the East-Atlantic sector of the Arctic Ocean, which favours intensification of dense water formation in winter polynyas under conditions of increased seasonality of sea ice. In the latter case, faster cooling and desalination of AW en route in this part of the Arctic Ocean may be considered as a reasonable hypothesis, provided the atlantification of the Nansen Basin is progressing.

Wide areas of the Siberian Arctic shelf are covered by freshened surface water layers, which are among the largest in the World Ocean. River discharge is the main freshwater source for formation of these layers; therefore, they are commonly referred to as river plumes (the Ob-Yenisei plume in the Kara Sea and the Lena plume in the Laptev and East Siberian seas). The contribution of sea ice meltwater (SIM) to the Ob-Yenisei and Lena plumes is pointed out to be small, albeit its actual volume remains unknown. In this study, we use a novel dataset of satellite-derived sea ice thickness in the Arctic Ocean during the melt period to quantify the annual volume of SIM, which was received by the Ob-Yenisei and Lena plumes during 2012–2020. We reveal that SIM is a significant source for the Lena plume providing, on average, 20% of total annual freshwater content. Moreover, the share of SIM in the Lena plume shows large inter-annual (14%–29%) variability, i.e., during certain years, SIM provides almost one-third of freshwater volume of the Lena plume. This variability is governed by inter-annual variability of ice thickness, as well as seasonal variability of sea ice melting conditions. Conversely, the contribution of SIM to the Ob-Yenisei plume is relatively low (8% on average), and its total annual share varies from 6% to 11% during the study period. This difference is mainly caused by significantly smaller area of the Ob-Yenisei plume as compared with the Lena plume. The forecasted earlier onset of ice melting in the Arctic Ocean in future decades due to climate change could decrease the contribution of SIM to the Ob-Yenisei plume, whereas its influence on the Lena plume remains unclear.

In this model study, we address the probability of rapid reorganization of thermohaline structure and circulation in the Arctic (AO) and North Atlantic (NA) oceans under the prolonged unidirectional atmospheric forcing over the AO. The relevance of such investigation is dictated by the presence of huge volume of surplus fresh water accumulated in the Beaufort Gyre (BG) of the Canada Basin for the past 30 years due to extremal sea ice melting and increased river runoff. In hypothetical case of rapid release to the NA, this fresh water volume may at least cause strong salinity anomaly similar to the Great Salinity Anomaly in the 1970s. Taking into account that the subpolar NA is the key locus of the deep water formation feeding the southward branch of the Atlantic Meridional Overturning Circulation (AMOC), the excess freshening at the ocean surface may negatively affect the AMOC intensity. To check up the validity of this hypothesis, we carried out the two idealized model experiments with opposite atmospheric forcings over the AO: the so-called “cyclonic” one, which favors intensive NA–AO water exchange, and the “anticyclonic” one, which impedes such an exchange. We chose the two actual years with extremal forcings (1989 as a cyclonic one, and 2004 as an anticyclonic one) and artificially applied them for the 10-year period assuming that such a duration is at the margin of physical realism. Our major finding, within the limitations of numerical experiments on the OGCM (Ocean General Circulation Model) INMOM (Institute of Numerical Mathematics Ocean Model), shows that anomalously long preservation of “cyclonic” forcing over the AO is able to substantially rearrange salinity in the upper ocean layer. However, it may not trigger massive “instant” outflow of freshwater through the Fram and Denmark Straits, since a large portion of accumulated in the BG freshwater spreads around the AO following the surface circulation pattern without reaching the Fram Strait. However, the tendency of the upper ocean layer freshening in the subpolar NA due to freshwater flushing from the AO is confirmed.

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.

Purpose. The paper represents a comparison analysis of water, heat and salt flows transported through Fram Strait and calculated using the data both of moorings in the strait and the GLORYS2v4, 2 v 4, ORAS5, 5, GloSea5 5 and C-GLORSv7 reanalysis. Methods and Results. The data obtained at the autonomous buoy stations were interpolated in the nodes of a regular grid with the resolutions 0.25 degrees degrees over longitude and 10 m over depth using the Ordinary Kriging. The algorithms unified both for the mooring and reanalysis data were applied to calculate the transport flows in 1997-2018. - 2018. The data of moorings and reanalysis constituted a base for obtaining the time series of heat and mass transport in the regular grid nodes at the cross- section in Fram Strait (8 degrees W, 8 degrees E). The mooring and reanalysis time series were compared, and the results were visualized. Conclusions. . It is shown that the reanalysis ensemble, on the whole, underestimates the transfer of water and heat volumes calculated using the observation data, by 25 %. The best agreement between the reanalysis products and the calculation results based on the observation data is obtained for the West Spitsbergen Current core which is most completely supplied with the observation data. It is revealed that the ensemble of models describes the observation data variability the best, and the FOAM and CGLO reanalysis - the greater part of temporal variability of the flows calculated by the autonomous buoy station data. The data consistency in the winter period (October - March) is shown to be higher than that in the summer one (April - September). That can be related both to the reanalysis imperfections (ice melt accounting) and the season, namely summer, when the autonomous buoy stations are usually replaced, which can result in additional errors in combining the time series.

The annual water temperature in the major water masses of the Barents Sea (BS) has significantly increased since the early 2000s. Advective heat transport from the neighboring water areas and heat exchange through the sea surface are the major factors, which shape the hydrological conditions in the BS. The paper estimates the contributions of heat exchange at the sea-atmosphere boundary and advective heat transport to changes in the average water temperature of the BS for the entire sea area. The average annual heat balance of the BS is calculated using atmospheric and oceanic reanalysis data. The change in the average temperature of the BS water is estimated taking into account the heat consumption for ice melting. The average surface heat balance from 1993 to 2018 was negative throughout the entire sea area: –70…–100 W/m2 in the south and –10…–20 W/m2 in the north. The advective heat supply was calculated for 9 straits with neighboring water areas. The determining source of advective heat is the influx of Atlantic waters from the Norwegian Sea between Cape Nordkapp and Bear Island. An average of 40.8 TW of advective heat is supplied through this margin. The calculations showed the predominance of annual heat influx due to advection over heat loss from the sea surface. This excess heat influx resulted in an estimated increase in the water temperature of the BS from 1993 to 2018 at a rate of 0.28 °C per year (taking into account the heat consumption for ice melting). In conclusion, it can be argued that the analysis has validated the hypothesis proposed in the article about compensation of heat losses from the surface of the BS by advective heat flow. The hypothesis is quantitatively confirmed by calculations on a simple box model (with an accuracy of up to an order of magnitude) based on atmospheric and oceanic reanalysis data. The ERA5 and GLORYS12V1 reanalysis data reliably describe the basic patterns of observed variability of ocean, sea ice and atmospheric parameters in the Barents Sea.

The results of assessing long–term changes in water temperature in the northern part of the Atlantic Ocean (0°–70° N, 8°–80° W) according to the data of ocean reanalyses and objective analyses for the periods of 1961–2011 and 1980–2011 are presented. The obtained estimates are based on the use of a nonparametric method of regression analysis (quantile regression) for the monthly mean ocean temperature for a quantile value of 0.5. In 1961–2011 the warming was mainly recorded in the upper 400-m layer in the region from the equator to 70° N. Over this 51-year period, the increase in the median monthly ocean temperature was ~0.5°C on average in the analyzed water area, while in the Gulf Stream–North Atlantic Current system, it was ~1°C. During the period of 1980–2011, the warming in the northern part of the Atlantic Ocean occurred mainly in the upper 1-km layer at high latitudes (50°–65° N). Over this 32-year period, the median monthly mean ocean temperature increased in the subpolar gyre in the upper 400-m layer by ~1°C.

Over the past 40 years, the Arctic, and the Barents Sea in particular, has undergone considerable changes in the state of the atmosphere, sea ice, and water column, which are presumably beginning start to affect the duration of the warm period (when the sea uptakes heat from the atmosphere) and the cold period of the year (when the sea loses heat to the atmosphere). This study considers the interannual variability of the onset dates and duration of the warm and the cold periods of the year. Data on short- and long-wave radiation, as well as on sensible and latent atmospheric heat fluxes from the ERA5 reanalysis were used. HDBSCAN cluster analysis method has made it possible to identify four regions (clusters) with synchronous dynamics of the dates of transition of the heat balance through zero. Several delineated regions are located on the pathway of the Atlantic origin water in the Barents Sea. A vast region has been distinguished in the northern part of the sea, where the inflow of the cold Arctic water occurs, providing cooling and freshening of Atlantic water transported from the Norwegian Sea. A shift in the date of heating onset in the southern and southeastern parts to later dates (4–5 days per 10 years) and a shift to earlier dates in the northern and northeastern parts of the sea (4–5 days per 10 years) have been detected. For heating termination dates, the opposite situation shift compared to the heating onset dates is observed. In the southern part, there has been a shift to earlier dates (1–2 days per 10 years), and in the northern part, to later dates (4–5 days per 10 years).

The multiyear variability of ice conditions in the Russian Arctic seas and the ice area of the Arctic Ocean (AO) is analyzed. It is shown that the ice conditions of the Russian Arctic seas are largely determined by large-scale atmospheric processes and the development of ice cover in the AO. It is shown that there are significant changes in the nature of the variability of the ice coverage of the Russian Arctic seas, which make it possible to distinguish two different periods: 1946–2004 and 2005–2021. It is found that in the past 17-year period, the frequency of complete cleansing of the water area of the Russian Arctic seas has significantly increased compared to previous periods.

Since the mid-1990s, there has been a marked decrease in the sea ice extent (SIE) in the Arctic Ocean. After reaching an absolute minimum in September 2012, the seasonal variations in the SIE have settled at a new level, which is almost one-quarter lower than the average climatic norm of 1979–2022. Increased melting and accelerated ice export from marginal seas ensure an increase in the open water area, which affects the lower atmosphere and the surface layer of the ocean. Scientists are cautiously predicting a transition to a seasonally ice-free Arctic Ocean as early as the middle of this century, which is about 50 years earlier than was predicted just a few years ago. Such predictions are based on the fact that the decrease in sea ice extent and ice thinning that occurred at the beginning of this century, initially caused by an increase in air temperature, triggered an increase in the thermal and dynamic contribution of the ocean to the further reduction in the ice cover. This paper reviews published evidence of such changes and discusses possible mechanisms behind the observed regional anomalies of the Arctic Sea ice cover parameters in the last decade.

This paper is devoted to the features of seismological observations in the Arctic seas, which are complicated by harsh climatic conditions, the presence of ice cover, stamukhi and icebergs, and limited navigation. Despite the high risk of losing expensive equipment, the deployment of local networks of bottom seismographs or stations installed on ice is still necessary for studying the seismotectonic characteristics and geodynamic processes of the region under consideration, the deep structure of the crust and upper mantle, seismic hazards, and other marine geohazards. Various types of seismic stations used for long-term and short-term deployments in the Russian sector of the Arctic Ocean, as well as various schemes and workflows for their deployment/recovery, are described. The characteristics of seafloor seismic noise and their features are also considered. The results of deployments demonstrate that the characteristics of the stations make it possible to reliably record earthquake signals and seismic noise. Based on the experience gained, it was concluded that the preferred schemes for deploying ocean-bottom seismographs are those in which their subsequent recovery does not depend on their power resources. Usually, such schemes allow for the possibility of dismantling stations via trawling and are suitable for the shelf depths of the sea. The advantages of such schemes include the possibility of installing additional hydrophysical and hydrobiological equipment. When using pop-up ocean-bottom seismographs, special attention should be paid to the careful planning of the recovery because its success depends on the possibility of a passage to the deployment site, which is not always possible due to changing meteorological and ice conditions. Seismic records obtained on the seafloor are characterized by a high noise level, especially during periods of time when there is no ice cover. Therefore, it is recommended to install bottom stations for periods of time when ice cover is present. The frequency range of the prevailing noise significantly overlaps with the frequency range of earthquake signals that must be taken into account when processing bottom seismic records.

In this model study, we address the feasibility of rapid shutdown or, at least, substantial weakening of the Global Circulation Conveyor (GCC) caused by massive discharge of freshwater to the northern North Atlantic (NA). The source of this freshwater excess is the permanently ice-covered Arctic Ocean (AO), while its release may be caused by ice melting and intensified river runoff due to global warming. To check up the validity of this hypothesis, we carried out the two idealized experiments with opposite atmospheric forcings over the AO: the so-called "cyclonic" one, which favors intensive water exchange between the AO deep interior and the Nordic Seas (NS), and "anticyclonic" one, which impedes this exchange. We chose the two actual years with extremal forcings (1989 as cyclonic one, and 2004 as anticyclonic one) and artificially applied these forcings during the 10-year period assuming that such a duration is at the margin of physical realism. Our major finding, within the limitations of numerical experiments on the OGCM (Ocean General Circulation Model) INMOM (Institute of Numerical Mathematics Ocean Model), shows that anomalously long preservation of "cyclonic" forcing over the AO is able to substantially rearrange salinity in the upper ocean layer. However, it may not trigger massive "instant" outflow of freshwater through the Fram and Denmark Straits, since a large portion of accumulated in the Beaufort Gyre freshwater spreads around the AO following the circulation without reaching the Fram Strait. However, the tendency of the upper ocean layer freshening in the northern NA due to flushing of freshwater from the AO is confirmed in consistency with the basic concept of the GCC hiatus.

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use.

We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using a high-resolution array of 7 oceanographic moorings, deployed across the Eurasian continental slope north of Severnaya Zemlya in 2015-2018. In particular, we quantified transports and individual water masses based on temperature and salinity recorders and current profilers. The highest velocities (>0.30 ms-1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 ms-1 in the deep basin. The ABC shows strong seasonal variability with velocities two times higher in winter than in summer. Compared to the upstream conditions north of Svalbard, the water mass distribution changed significantly within 20 km from the shelf edge due to mixing with- and intrusion of shelf waters. Further offshore, Atlantic Waters remained largely unmodified. The ABC transported 4.2±0.1 Sv across the region with 63-71% of the volume transport constrained within 30-40 km of the shelf edge. Water mass transport was 0.52±0.13, 0.9±0.27, 0.9±0.33 and 0.9±0.35 Sv for Atlantic Waters (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW), respectively. A seasonality in TAW and BSBW transport was linked with temperature changes, where maximum transports coincided with minimum temperatures. Our results highlight the importance of the Barents Sea for the ABC along the Siberian slopes, and indicate that a continuing Barents Sea warming would directly translate to reductions in the TAW and BSBW cooling effect and thus lead to warmer oceanic conditions in the ABC pathway.

Sea ice in the Arctic is one of the main dynamic elements in the interacting atmosphere–ice–ocean system. Currently, theoretical and experimental studies of drifting and soldered ice are used to develop predictive models of the mechanical state of sea ice. This paper presents the results of an experimental study of physical and mechanical processes on the surface of the Arctic Ocean. Field work was carried out using the spatial placement of autonomous seismic stations directly on the drifting ice. Data on surface gravitational waves of the ocean, accompanied by periodic deformations of bending and shear in the ice, have been obtained. On the basis of amplitude spectra, the features of the process of propagation of storm waves of swell in the ice cover are considered and a comparative analysis with map of maximum heights of sea waves is performed. A significant factor is the use of microseismic oscillations recorded at coastal stations of the Greenland Sea to determine the time and place of a powerful storm. The spectrum of the wave field in the ice sheet indicates an increase in the frequency of oscillations due to the dispersion of the wave field. New data have been obtained on the large-scale mechanics of the occurrence of cracks in the ice cover and discrete flexural-gravity waves as one of the main indicators of ice destruction. The results of the study are important for improving weather and climate forecasting models, as well as for solving engineering problems on the Arctic shelf.

The article is dedicate to the study of ice age categories composition in the East Siberian Sea. The calculation results showed that thick first-year ice (over 120 cm) prevails in drifting ice and fast ice in the sea by the end of the winter period (May). The transition of ice from one age gradation to an older one in fast ice occurs earlier than in drifting ice, by ten-day period 2–4. In the western part, thick first-year ice forms on average a month earlier than in the eastern part. The amount of drifting thick first-year ice in the East Siberian Sea in May was about 50%.

In the Arctic Ocean (AO) of today, there are noticeable changes in the composition and structure of biological communities inhabiting the water-ice environment. Over the past two decades, a decrease in the number of species of the sea ice flora and fauna has been noted in the central regions of the AO due to the changing physical environment of their habitat. In view of the current climatic instability in the AO, it is important to monitor and evaluate their composition, structure and dynamics of development. It is also important to preserve the methods of processing the materials collected in order to compare the state of the water-ice biota on similar spatial and temporal scales of the basin. In the present study, centric and pennate diatoms dominating in ice floristic communities were selected as indicators of changes. The aim of the work is to analyze the physical state of the water-ice environment and the species composition of ice diatoms based on the materials of the expeditions within the NABOS program at the Research Vessel (R/V) “Akademik Treshnikov” in the Arctic Basin in 2018 and 2021. The field work included observations of the state of the sea-ice cover in the area of the expeditions, the selection of ice cores to assess the salt composition and species composition of the algae, as well as CTD-sounding of the under ice — water layer. The analysis of the materials collected showed significant differences in the species composition and abundance of algae between the seasons, which indicates the formation of independent floristic communities in the current conditions of unstable physical environment in the central regions of the AO, which confirms the previously obtained results in the period 2007–2015. The materials under discussion were obtained in a short period of time and in limited spaces in the zones of production of annual ice in the waters of the shelf seas and zones of removal to the central regions of the AO. At the same time, short-term observations provide “instant” information about the qualitative and quantitative state of sea-ice biological communities. In order to obtain reliable estimates, long-term observations are needed, which may be organized in the near future based on new logistical approaches to the study of the marine Arctic.