A purpose of the work is to study the interaction between surface semidiurnal tides in the system of the Barents and Kara Seas. Using the 3D finite-element hydrostatic model QUODDY-4, we have carried out two numerical experiments. In the first of them it is assumed that the tides in the Barents and Kara Seas are free to interact with each other, whereas in the second one it is supposed that there is no interaction of tides in these seas (an impervious rigid wall, that prevents a horizontal wave flux of barotropic tidal energy between the seas, is placed here). It is shown that the tidal interaction does not lead to a qualitative reorganization of their spatial structure, although its quantitative changes are noticeable. An interaction domain covers the north-eastern part of the Barents Sea only, while outside this domain the averaged (over a tidal cycle) rms absolute vector difference between the tidal sea elevations obtained with and without tidal interaction is almost everywhere less than the corresponding error of the tidal predictions, thereby indicating that it lies in the model noise.

A three-dimensional mathematical ecosystem model has been combined with a circulation and a sea-ice models of the Barents Sea. The ecosystem model describes the interaction of phytoplankton, zooplankton, dissolved inorganic nitrogen, total inorganic carbon, alkalinity, organic and inorganic parts of detritus. The paper presents the results of calculations of the chlorophyll-a concentration in the period of maximum spring phytoplankton bloom in the Barents Sea, as well as the results of calculations of CO2 flux between the atmosphere and the sea under various conditions. The correspondence between the zones of the intensive growth of phytoplankton during the bloom period and the position of the Polar Front has been demonstrated. The estimation of the ocean-atmosphere CO2 exchange intensity in the presence and absence of the biological CO2 pump has been carried out. For the case without taking into account the oceanic biological uptake of atmospheric carbon dioxide it was found that the maximum values of CO2 flux can be observed in the areas of the ice edge. Taking into account the oceanic biological uptake of atmospheric CO₂ leads to the spatial correspondence of the zones of maximal CO₂ flux from the atmosphere and the zones of high primary production in the ocean surface layer. The results of the present study show that the spatial variability of the carbon dioxide flux from the atmosphere to the ocean is determined by the spatial variability of the primary production to a much greater extent than by the variations in the sea surface temperature.

The coefficients of horizontal turbulent viscosity and their variability with the depth depending on the averaging period of flow rates are calculated on the basis of an increased flow velocity measurement data performed in the heavy areas of the White Sea. The technique of sliding averaging was used to eliminate the orderly movement in the velocity field, and the selection of local effects was carried out on the basis of wavelet analysis. The results indicated the possibility of release the time interval scale inflow of energy from the energy-ordered motions in the White Sea (fluctuations with the tidal frequencies M2, M4 and M6, the mechanism of the regular adjustment of currents, bottom friction), and unstable external sources (baroclinic currents, the disintegration of the internal tide, short-period internal waves). It was found that the anisotropy increases with the averaging period. Under certain extent of smoothing the flow velocity, mainly for the central regions of the flow field, the field of pulsations of a horizontal vector of speed is isotropic. Taking into account the exclusion of influence of external sources of energy in the flow structure and the surface wind and wave processes the values of eddy viscosity coefficients along the flow was 102—105 sm2⁄s, and in a direction normal to the flow the exchange ratio was 1—3 times smaller.

The main difference between the hydroacoustic field and other physical fields is significant and complicated dependence of signal propagation law on the hydroacoustic conditions (HC). Therefore, algorithms for solving the most practical problems of hydroacoustics, which, as a rule, are inverse problems, should take into account current hydroacoustic conditions, i.e., must be consistent with the environment of propagation of hydroacoustic signals and interference. The purpose of the paper is to review practical applications of hydroacoustics, based on the use of algorithms, agreed with the environment. Such applications include: tomography of the ocean; detection of sea objects at greater distances; classification of sea objects; a joint solution of classification and ranging problems; underwater sound communication. The quality of solution of these problems depends largely on the accuracy of the parameters of the waveguide. Researches to improve this accuracy must be fulfilled in two directions: development of methods and devices of in-situ measurement of current parameters of the environment; development of adequate models of the waveguide, oriented to the solution of practical problems and considered the possibilities of these methods and devices.

The problem of determination of hydro-physical marine environment characteristics by fixed values of known emitted and received reflected acoustic signals from the natural scatters without direct characteristics modification by the ship dipping probes is actual. Impact assessment of the vertical sound speed distribution from the surface to the bottom in the sea waveguide is made immediately before the use of various ship sonar equipment. The ability to use information about the hydro-physical waveguide propagation characteristics of acoustic signals when underwater target detecting can significantly improve the efficiency of the ship sonar equipment. We consider an algorithm for solving inverse problems of restoring the vertical sound speed distribution from ship probing acoustic sound diffusers in natural water environment in the volume limited by directional characteristics of ship antennas, sea surface and the bottom. The sound speed at different horizons is determined by propagation time difference of (between) the emitted acoustic signals and is found by phase difference of the received signals with different frequencies. Sea trials of designed experimental equipment led to the conclusion about the possibility of the construction of the vertical sound speed distribution from the ship at its speed up to 5 knots.

An investigation of the peculiarities in shaping of lidar images of nonlinear internal waves is performed in the conditions approaching the actual. The analysis of the dependence of internal wave images structure on the character the attenuation coefficient stratification is made (surface and bottom turbid layers, linear stratification, fine structure of the attenuation coefficient). It is shown that the conditions for obtaining contrast images of nonlinear internal waves are existent in coastal zones of the Barents Sea. The relative variations of the echo-signal power in the internal wave field may run to ten decibel. The maximum variation of the echo-signal is observed with a turbid layer in a pycnocline region, in this case the vertical displacements of the turbid layer in the internal wave field are effectively manifests. The shadow image of the internal wave is formed with essential distinctions in fluid transparence over and under pycnocline, the contrast sign of this image depends on the polarity of soliton and the fact of what layer (upper or lower) is more turbid. In the case of linear stratification of the attenuation coefficient the spatial variations of the echo-signal power reproduce the field of vertical displacements in the internal wave. These results can be used for solution the problems of lidar remote sensing of internal waves.

A quantitative assessment of the quality and informational content of the Earth's magnetic field’s model is provided to get an idea of its navigation informational content inventories and possibilities of its application for autonomous navigation in the ocean. The indicators of the informational content of the Earth's magnetic field vector’s module, which are used as the statistical characteristics of the anomalies of inventories in the control interval in the sliding mode, are calculated. The results of the evaluation of the navigation informational content of the module of the Earth's magnetic field’s vector according to the model of St.-Petersburg Filial of the Pushkov institute of terrestrial magnetism, ionosphere and radio wave propagation of RAS of era 2015 as an example of the experimental waters of the Atlantic Ocean are submitted. On the basis of the research it is shown that the higher informational content has combined navigation descriptiveness of the Earth's magnetic field anomalies in the form of dispersion, correlation interval and gradient index. The division of the World’s ocean into parts to increase saturation the Earth's magnetic field navigational landmarks is proposed. It allows determine the current location depending on the specifics of spreading zones. This provides meaningful information content navigation parameters of the Earth's magnetic field for correlation-extreme autonomous navigation in the ocean basins.