The results of studying the process of stirring of a sinking thermal (small volume of denser water) with surrounding water are presented. The analysis of laboratory flows in a hydroflume has been allowed to identify the main peculiarities of the stirring of the thermal and the surrounding water. The essence of one of these features concluded in the presence of many high-gradient layers in the density field. The phase of an advective-rotational nature of the stirring of thermal waters with different density has been identified. Detailing of the evolution of the flow density structure was performed using the calculated flows on a 2d-nonlinear model of the dynamics of a fluid that is inhomogeneous in density. Features of the density structure are revealed using the values of local density gradients for the internal nodes of the computational grid. The density gradients along and across the streamlines were calculated. Quantitative estimates of the repeatability of high-gradient layers have shown significant variability in the flow density field. An analysis of the potential stability of the selected local regions of the flow has been carried out. The calculation of the Reynolds (Re) and Richardson (Ri) numbers has been allowed to assume a laminar nature of the flow, with the exception of two small zones in the back part of the sinking thermal. The role of the baroclinic mechanism of vorticity generation as a structure-forming factor in the formation of a distinguished stage of advective-vortex movement within interpenetration of thermal with surrounding water has shown.

One of the factors of wind wave impact on vertical distributions in atmosphere surface layer is the flux of momentum produced by the wave-produced fluctuations. Wave surface are supposed to be a dynamically rough and effects of the molecular viscosity are neglected. In this paper impact of wave momentum fluxes with values of wind velocity which lead to dynamically smooth ocean surface is estimated. The well-known theoretical aspects and results of experimental research are applied. Dependence of dimensionless thickness of viscosity layer on dimensionless roughness of smooth surface is analyzed. The equations of motion are formed taking into account the manifestation of three factors: molecular, turbulent and wave momentum flux. The models based on these equations are described.
The choice of constant coefficients that are set in calculations with this model is considered. Results of calculations and analysis of vertical profiles of wind speed and the dependence of the drag coefficient on wind velocity under various wave age.

Particle trajectories and average settling and drift velocities of microplastic particles under wave action were studied in a linear wind-wave channel. A wave-maker and an airflow above the water surface created various hydrodynamic conditions. Particles of various shapes (isometric, flat, elongated) were used. The paper provides a brief overview of the theoretical approaches (dimensional analysis) used to study the transport of microplastics in the presence of surface waves and currents. Based on this, a characteristic of wave regimes and sets of experimental particles is given. Terminal settling velocities of the particles in a quiet fluid are 1.0–3.8 cm/s. They were obtained experimentally and may be of independent interest. The settling trajectories of 13 types of particles in 4 wave regimes were obtained and analyzed. According to Welch’s t-criterion (p < 0.05), the average particle settling rate in the presence of waves differs slightly from the terminal settling velocity, which is consistent with other works. The results indicate that the average horizontal (drift) velocity follows the velocity of the mean current. The presence of wind enhances horizontal transport due to the induction of drift current and drastically increases particle dispersion.

This study introduces the development and implementation of a regional numerical finite-volume model FESOM–C, specifically designed to accurately compute barotropic tidal dynamics in the Pacific waters adjacent to the southeastern region of the Kamchatka Peninsula. The dynamics of principal harmonics of the semidiurnal M2 and diurnal K1 tidal constituents are replicated, as well as the total tide, which encompasses 12 constituents. The computed results, obtained using a detailed unstructured grid, are interpreted through the Long-wave approach. The FESOM–C regional model revealed the variability of harmonic constants of tide and current characteristics within the shelf and canyon-cut continental slope, due to topographic scattering of tidal waves. The assessment includes the estimation of maximum currents and eddy structures associated with residual tidal circulation on the shelf and continental slope. To investigate the influence of varying open boundary conditions, sensitivity experiments have been conducted using data from two state-of-the-art global tidal models FES2014 and TPXO9. The findings reveal that the regional model’s solution exhibits only minimal dependency on this choice, and it aligns well with the limited available tidal data. Interestingly, the global models themselves demonstrate significant disparities in the tidal currents. Furthermore, we assess the accuracy of global tidal model solutions in a broader region encompassing the Sea of Okhotsk, as well as the Pacific waters along the Kuril Islands and the Kamchatka Peninsula. This assessment utilizes a verified database of tidal harmonic constants derived from the Soviet and British tide tables. While the average errors in tidal heights calculations remain minor and closely approximate officially declared values, certain areas within the region exhibit notable discrepancies in the outputs of the global models. These discrepancies are site-specific and vary depending on the particular model and tidal harmonic under consideration. This underscores the need for caution when applying results from global tidal models at the regional scale. Meanwhile, the importance of advancing regional tidal dynamics modeling remains evident.

Dynamics of acidification of the Arctic Ocean through 1993–2021 and predictions of further tendencies of this process until the end of 2100 were assessed making use of both the GLODAPv.2021 and the Global Ocean Biogeochremistry Hindcast (GOBH) reanalysis data on pH. The projections of pH were performed by CMIP6 models for four scenarios of rates of socio-economic and agricultural development and emissions of greenhouse gases: SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5.

The tendencies of pH decline over the last 27 years (1993–2019) as determined from the GLODAP in situ and the reanalysis data over 1993–2021 proved to be, respectively –0.9% (from 8.18–8.11) and –0.7% (from 8.10–8.05). Thus, the annual acidification rate as assessed from both data sources proved to be –0.03%.

Through the percentile method-based comparison of consistency of historical observation data on pH with GBH model hindcast four best models were identified: MPI-ESM1–2-LR, NorESM2-MM, NorESM2-LM, and CMCC-ESM2. The projection results strongly indicate that the Arctic Ocean acidification will continue till the end of this century. The highest rates of pH decrease (–4.9% and –6.2%) were forecasted, respectively, for scenarios SSP3–7.0 and SSP5–8.5 that implied the global mean temperature increases by 3.6 °C and 4.4 °C, respectively. A comparison of the results obtained with the previously made assessments is indicative that by the end of the current century the rate of acidification (i. e. pH decrease) in the Arctic should be expected to be higher than that averaged over the World Oceans: the difference for each of the SSP scenarios proved to be –0.1.

The aim of this work was to study the properties of vertical fluorescence intensity (FI) profiles of phytoplankton pigments (chlorophyll-a, phycocyanin, phycoerythrin, and beta-carotene) using data on the phytoplankton species composition obtained during the cruise 114 of the R/V ‘Professor Vodyanitsky’. The analysis of covariance matrices of phytoplankton pigment FI profiles in the upper 50-meter layer of the Black Sea indicates that the pigment composition of phytoplankton changes with depth, which may be associated with changes in its species composition. At the same time, 80 % variability of phytoplankton pigment FI profiles in the upper 20-meter layer is described by the first eigenvector. It agrees well with direct observations of the phytoplankton species composition, indicating the dominance of one phytoplankton division in the 20-meter layer. In addition, there are regional peculiarities: for example, the average FI values of the phytoplankton pigments in the Sea of Azov are significantly higher than those in the Black Sea, which is associated with a higher concentration of phytoplankton in the Sea of Azov.

The results of oceanographic research in the marginal ice zone of the Barents Sea near the ice cover boundary, carried out from the R/V Dalnie Zelentsy from April 27 to May 6, 2023, are presented. The position of the frontal zones recorded from contact observations on hydrological meridional transects along 33°30′, 40°, 45°, and 50° E are considered. The transects were made from the fields of finely broken annual ice southward towards the open water area of the Barents Sea. High-gradient zones expressed in the temperature and salinity fields at different distances from the ice field edge were detected on all transects. It was shown that during the research period the frontal zone was located at a distance from 25 to 180 km from the ice field edge, the temperature gradients varied from 0.021 to 0.067 °C/km, the salinity — from 0.002 to 0.012 psu/km, the width of the frontal zone did not exceed 28 km. The maximum values of chlorophyll-a and dissolved oxygen were observed in the area of the frontal zone boundary.

The article presents a solution to the problem of the phase transition of methane hydrate — methane-gas + ice in porous hydrate-containing sediments at a negative Celsius temperature in the medium. The numerical solution of the resulting system of differential equations of piezoand thermal conductivity makes it possible to effectively simulate the change in pressure and temperature in both time and space in a medium of any dimension during its heating or decompression. In this case, the medium is not subdivided into parts with varying phase states of methane hydrate. Instead, its sediment substance is considered as a single entity, with its physical properties changing in magnitude when the hydrates undergo phase transformation. As an example, the problem of the thermobaric regime of a heating spherical cavern containing ice, hydrate and free methane has been solved. This cavern is situated within a continuous gas-tight underground ice. The solution shows that although the temperature of the sphere surface increases considerably, the decomposition of hydrate only occurs in an extremely thin shell located directly between the surface and the displaced inward phase boundary.
Over time, the stability conditions of hydrates establish anew but at a higher gas pressure and medium temperature. This phenomenon of severely limited decomposition of the hydrate in a closed gas-insulated space, nevertheless leading to an increase in pressure in it, is, apparently, the basic process that provides the “self-preservation” of methane hydrates.

A lidar survey of the western part of the Kara Sea was carried out in September 2022. The shipborne radiometric (profiling) lidar PLD-1 was used. The lidar optical unit was located on the 8th deck of the R/V ‘Akademik Mstislav Keldysh’ at an altitude of 15 m above the water surface. Lidar sounding was carried out at stations and underway. The vessel route passed through water areas characterized by a wide range of changes in hydrooptical characteristics. Lidar measurements were accompanied by synchronized measurements of hydrooptical and hydrological characteristics. These measurements were carried out using submersible instruments at stations and using a flow-through measuring complex along the ship's route. The hydrooptical characteristics vertical distribution uniformity in the upper ten-meter layer was controlled remotely using underway lidar data.
Good agreement between the spatial distributions of the lidar echo signals parameters, of the hydrooptical and of the hydrological characteristics (coincidence of the locations of various distribution features, local maxima, minima and frontal zones) was demonstrated. A large volume of measurement data has been obtained, which allows for further statistical processing in order to find relationships between the parameters of lidar echo signals and hydrooptical characteristics recorded by contact methods.

The main optical characteristics of phytoplankton and colored dissolved organic matter are described. The necessity of simultaneous registration of fluorescence of phytoplankton pigments and colored dissolved organic matter in seawater in situ is substantiated. Commercial recording devices, realizing registration of signals of phytoplankton fluorescence intensity in situ, are considered. This paper presents the developed experimental probing autonomous multichannel multichannel meter of fluorescence and light scattering in seawater (FR1). The paper presents the functional scheme of the developed meter, describes its main assemblies and principles of its operation. The developed meter allows quasi-simultaneous registration of a large set of parameters: excitation spectra of phytoplankton fluorescence, fluorescence intensity of phytoplankton pigments (chlorophyll-a, phycoerythrin, phycocyanin, β-carotene), as well as fluorescence intensity of colored dissolved organic matter and spectra of light scattering index at an angle of 90°. Registration of all these parameters is carried out from one measuring volume, where the same composition of suspended matter is located in the process of probing at each specific moment of time. The paper presents the results of approbation of the developed meter and suggests the direction of further research using it.