A solitary gravitational current over an inclined bottom is being investigated in the thermostratified laboratory tank of the SPb IO RAS. In the framework of a laboratory experiment close to real natural conditions, preliminary studies of complex, nonlinear processes of interaction of the bottom density flow, stratification and internal waves were carried out. The full life cycle of the formed vortex structures is considered: from their origin on a slope, development and propagation in a stratified environment, to their interaction with the field of internal waves. During the experiments, empirical data were obtained to verify a non-hydrostatic model with a spatial resolution that allows explicit reproduction of individual convective jets and vortices.

A detailed non-hydrostatic model of gravitational flow over an inclined bottom is being developed, which is capable of explicitly reproduce convective cells for future generalization and new parameterizations development. To minimize numerical noise, the method of an inclined computational domain and a regular rectangular grid are used. The properties of high-order accurate advection schemes are investigated. The fundamental possibility of explicitly numerical reproduction of relatively large (on the order of a meter or more) ocean turbulent structures, such as convective cells, is demonstrated. A high-resolution digital array of 3-dimensional velocity and tracer fields (active and passive) created based on a physical experiment for a range of Reynolds numbers of 30–300. This array will be used to develop new parameterizations for a large-scale ocean circulation model.

Regimes and limitations of the numerical solution method for hydrodynamic equations using the approximation of the near-surface velocity potential by the high-order Taylor expansion (High Order Spectral Method, HOSM) are investigated. This approach is considered in the context of simulation of large ensembles of sea surface displacement fields under finite-depth conditions. The main attention is paid to the description of strongly nonlinear waves and waves with a wide frequency spectrum. The study is performed in planar geometry.

Currently, the primary drivers of ice cover variability in the Barents Sea are the influxes of Atlantic water. This study examines advective heat and mass transfer across the western boundary of the Barents Sea over the period 1993–2023, using reanalysis data from ORAS5. The heat flux through the southern segment of the section (from Bear Island to Nordkapp Cape) is estimated at 60 TW, with a volumetric water flux of 2.1 Sv. Three current branches with elevated heat flux are identified in the southern part of the section.

A significant increase in heat and mass transfer over time is observed predominantly in the southern and central branches, correlating with trends in both current velocity and water temperature. The total heat flux into the Barents Sea basin is approximately 61 TW, showing a notable positive trend of 0.03 TW per month. Trend analysis indicates that over the 31-year period, heat transport in the southern part of the section increased by about 11 TW, while the northern part saw an increase of roughly 3 TW. Consequently, there has been a substantial shift in the spatial distribution of heat transfer toward the southern coastal region of the Barents Sea.

Wavelet analysis revealed quasi-7-year synchronous oscillations in water temperature and current velocity prior to 2008, contributing to an increase in heat flux. A shift in this pattern occurred during 2008–2010, followed by a desynchronization of these parameters from 2010 to 2023, which resulted in the stabilization of heat flux at a lower level. On an intra-annual scale, the southern branch of the heat flux exhibits high variability, driven primarily by current velocity, with a winter maximum and summer minimum associated with seasonal wind circulation patterns.

The dynamics and structure of the epilimnion largely determine the features of heat balance, gas emissions, turbulent mass transfer, chemical and biological processes occurring in the lake during the period of open water. This structure is formed under the influence of various external factors, which, as a rule, are periodic in nature. The response of the water column to such impacts occurs with some delay, and in some cases the thermal inertia of the water column leads to the occurrence of hysteresis effects. Along with seasonal and synoptic factors, external influences characterized by a daily period play an important role, in particular, night-time surface cooling and daily fluctuations in air temperature.

Using a thermocouple with highly sensitive sensors, an analysis of the temperature response at different depths to such influences was carried out. This response can, to a first approximation, be characterized as a temperature wave, the calculation of the parameters of which allows us to estimate the thickness of the thermally active layer, as well as the coefficient of turbulent diffusion. One of the advantages of this method is that these assessments can be carried out using a minimum number of temperature sensors.

At present, there are no quantitative estimates of the mean climatic annual course of bottom temperature parameters in Lake Ladoga that allow us to judge their interannual variations. A phenomenological model of the mean climatic annual variability of the Lake Ladoga bottom temperature depending on the depth of the limnic region is proposed. Based on analysis of a large array of temperature measurements for a century period, characteristic temperatures and dates of seasonal occurrence and dissipation of vertical stratification during the year in connection with variations in bottom temperature are determined. The dispersion and rate of change of near-bottom temperatures in different seasons were estimated.

Starting from a depth of 100 m, there are very small variations of the bottom temperature in Lake Ladoga during the summer period. In the winter season, these fluctuations are about 1.5 °C and largely depend on the date of occurrence and duration of the open water period of the water area and the intensity of vertical and horizontal convection. These indices can serve as a baseline for evaluating the response of real measured or modeled thermal parameters of Lake Ladoga to climate variations, as well as for comparison with other dimictic lakes of the world. The created empirical dependences of the near bottom temperature change on the floor depth for an average climatic year with ice cover and a warm year (with incomplete ice cover) has prognostic value.

Quantitative estimates of the Lake Ladoga ecosystem response to changes in climatic atmospheric forcing and external nutrient loads were obtained for the period 1980–2020. The estimates were obtained using the MITgcm three-dimensional hydrothermodynamic model combined with the SPBEM biogeochemical module adapted to the phosphorus-limited conditions of the lake.

Numerical experiments were conducted using the following three scenarios: 1) a reference scenario with realistic changes in the external nutrient load and atmospheric forcing for 1980–2020, 2) with realistic changes in the external nutrient load and the “average” intra-annual course of atmospheric forcing for this period, and 3) with realistic changes in atmospheric forcing and a constant external nutrient load equal to the average value for the period under consideration.

The results of the study demonstrate a pronounced dominance of the external nutrient load as the main factor determining the dynamics of the lake ecosystem characteristics in 1980–2020. The contribution of climate change to the highly deterministic linear trends of the change in winter phosphate concentrations, summer phytoplankton biomass, and annual phytoplankton production in the photic layer amounted to only 24 %, 10 %, and 21 %, respectively. According to the calculation results, there is a noticeable decrease in these characteristics of the lake ecosystem in the second half of the considered period 1980-–2020. At the same time, a noticeable (more than 20 %) compensating effect of climate change is noted for phytoplankton production, leveling out part of the effect of the decrease in nutrient load.

It is shown that non-diatoms, which make the main contribution (63 %) to the total phytoplankton production, strongly respond to climatic changes in water temperature in the considered period. Diatoms show less dependence on climate change, maintaining a close relationship with winter phosphate reserves.

The work examines the drift of pollock eggs and larvae in the Pacific Ocean region adjacent to the southeastern coast of the Kamchatka Peninsula and the northern Kuril Islands. A model approach is used, combining particle trajectory calculations using the ICHTHYOP software, ocean reanalysis data, and the results of a regional tidal model. The eggs and larvae are considered as passive tracers, and their transport from the main spawning ground of the East Kamchatka pollock in the deep-water canyon of the Avacha Bay was calculated for one month in 2024 and 2025, starting from the observed spawning date in April.

The main objective of the modelling was to determine the influence of various dynamic factors on particle transport and the likely locations of their accumulation, where egg development and larval hatching may occur. Identifying these locations through ichthyoplankton surveys is very difficult. The model calculations did not take into account a number of factors related to the mortality of eggs and larvae under the influence of environmental changes and predation, larval activity during development, and other processes of physical and biological interaction. The transport of tracers after their ascent to the surface in the spawning area was analyzed using background surface currents and those averaged over the upper sea layer.

The simulation results show that the predicted horizontal particle trajectories depend not only on the different hydrodynamic conditions for the two years, but also on the consideration of tidal drift. A hypothesis has been put forward regarding the dynamic conditions favorable for the development and survival of pollock eggs and larvae, under which their drift does not lead to their transport from the shelf water into the open ocean. Potential areas of particle accumulation in coastal waters have been identified.

This study derives analytical formulas for estimating the loads exerted by a bore and a solitary wave on a fixed, partially immersed body. These estimates are required in the design and operation of coastal structures. The formulas are obtained by fitting results from extensive numerical simulations spanning variations in body submergence, body length, and incident-wave amplitude. We consider runup heights on the front and back sides of the body, as well as the horizontal and vertical components of the resultant wave force. The bore and solitary-wave problems are solved using one-dimensional shallow water models based on the first and second long-wave approximations, respectively. We report the average and maximum relative errors of the formulas and compare their predictions with results from previous studies. These comparisons demonstrate that the proposed formulas are applicable across the parameter ranges considered.

A small-sized spectroradiometer (SSR) developed at the Shirshov Institute of Oceanology of the Russian Academy of Sciences based on a miniature AIOX 2000–02 spectrometer for deck measurements of the spectral remote sensing reflectance Rrs(λ), the parts of which are mainly made by 3D printing, is described. The advantage of the new spectroradiometer is its significantly lower weight and dimensions compared to the previously developed deck spectroradiometer, as well as the convenience of measuring in deck conditions, including during pitching, due to both its weight and size characteristics and the lack of the need to use a cuvette with clean water and manually install a cuvette and a gray screen during measurements. The Rrs(λ) spectra obtained using this instrument are compared with the results of other spectroradiometers. It is shown that the relative mutual error of measuring the spectral coefficient of remote sensing reflectance between the data of the described spectroradiometer and other instruments does not exceed 15 %, which can be considered a good match between their data. The results of processing the Rrs(λ) curves obtained on the described device using the GIOP algorithm are in good agreement with independent data on bio-optical characteristics got by independent methods at the time of measurements.