Peculiarities of oceanographic processes in the north-western Black Sea

The paper examines how various factors affect the intensity of photosynthesis and oxidation reaction in the north-western part of the Black Sea. In the course of the evolution of the basin, natural aspects were widely changing; therefore their role is evaluated by the content of organic matter and diatoms in the bottom sediments. The influence of anthropogenic factors is determined by the current tendencies in the variation of physico-chemical and biological characteristics of the basin. The main factor upsetting steady functioning of the north-western Black Sea ecosystem is the large biogenic influx to the sea. The possible changing of the ecosystem during the nearest few decades is assessed. Translated by Vladimir A. Puchkin.     

Investigation of the development of a hydrodynamic instability of currents in the north-western Black Sea

In terms of a two-layer model, the current instability problem is solved in a linear statement with velocity shear, seafloor relief, and water stratification being considered. Numerical experiments were carried out using parameters characteristic of the north-western part of the Black Sea during the summer and winter seasons.Translated by Vladimir A. Puchkin.     

Current field in the north-western Black Sea and its role in the distribution of hydrological characteristics

The data derived from the observation of current profiles and hydrophysical features, carried out in the north-western Black Sea in August 1992, are considered. The main features of the currents' structure have been identified; they are consistent with the distribution of the basic characteristics computed from the distributions of the hydrological elements (dynamic heights, cold content, density of the accessible potential energy). A relationship between the thickness of the cold intermediate layer (CIL) and the Richardson numbers near the layer core distinctly manifested itself in the convergence zone over the shelf edge. The average correlation coefficient between these quantities was equal to 0.877, and the range of sampling variability with a probability of 0.95 varied from 0.9 to –0.79.Translated by Vladimir A. Puchkin.     

Upwelling in the north-western Black Sea during the period of summer-time warming

A numerical multilevel model based on primitive equations of sea thermohydrodynamics is applied to investigate the development of near-shore upwelling zones in the north-western Black Sea. Analysed are the results of eight numerical experiments on mapping the areas of upwelling and downwelling, depending on wind direction. The acquired data are matched up with the observations by the NOAA-11 satellite designed to measure sea surface radiation temperature twice a day. The numerical calculations are shown to agree with the remotely-sensed data. Translated by Vladimir A. Puchkin.     

Modelling of the propagation and transformation of riverine waters over the north-western shelf and in the abyssal part of the Black Sea

To study the propagation and transformation of riverine waters in the framework of a multilayer model based on primitive equations, the method of through counting is suggested, involving two types of grids, namely, a fine grid in the north-western shelf area and a large-sized grid in the deep sea. It has been shown that, in the absence of wind, riverine waters propagate over the shelf and along the western coast of the sea. North-easterly wind presses this flow against the shore, thus intensifying it; as a result of this, brackish waters turn out to be nearly entirely driven from the north-western shelf area and concentrate in the western section of the open sea where they form a layer that is quasi-homogeneous, in terms of salinity. Due to the forcing of the north-westerly wind, riverine waters penetrate into the interior of the shelf area and then move southward toward the open sea, mixing up with the upwelling abyssal saltier waters and forming a tongue of relatively brackish waters in the central part of the western half-basin. Translated by Vladimir A. Puchkin.     

Numerical model and calculation of the water circulation in the north-western Black Sea

A multilevel model based on primitive equations and a monotonic finite-difference scheme is applied to study the fluid dynamics over the north-western Black Sea shelf. Wind-generated currents and currents induced by river discharge are simulated in terms of the barotropic version. The effects of the bottom topography, the rigid-lid approximation, and the interaction of wind and river discharge-induced flows are examined.Translated by Vladimir A. Puchkin.     

Some peculiarities of the Black Sea inertial currents

By treating observations involving long-term buoy moorings, numerical characteristics of the periods, amplitudes, phases and orbits of inertial currents in some Black Sea areas have been obtained. The inertial component's contribution to the total velocity field and turbulent exchange has been determined. As a result, the maximal heights of the internal waves generated by the inertial currents have been estimated. Translated by Vladimir A. Puchkin.     

Optimal statistical estimates of the vertical current velocity in the north-western Black Sea

The paper discusses a method for the statistical evaluation of the vertical current velocity componentV _z(z) using data provided by profilers. The calculation of theV _z(z) profiles involves the determination of the root-mean-square deviation of the error of determination of the vetical current velocity component at each level and the RMS deviation of the sample statistical variability of this quantity's estimates. ProfilesV _z(z) have been computed for the north-western Black Sea using three surveys, with the involvement of an OLT profiler. The computations have shownV _z(z) to have a two-layer structure, with zero being crossed in the main pycnocline. Such structure of the current velocity vertical component is consistent with the hydrodynamic model of the field of currents induced by buoyancy fluxes through the lateral boundaries of the basin. The availability of the zero values of the vertical current velocity in the pycnocline yields a tool for gaining insight into the mechanism controlling the emergence of the oxic/anoxic interface and areas with sharp vertical gradients of chemical and hydro-optical characteristics. Translated by Vladimir A. Puchkin.     

Peculiarities of the Black Sea rim current near the Crimean coast

This paper discusses the quasi-stationary Black Sea rim current velocity field observed at seven points of the shelf area and continental slope in the vicinity of South Crimea from 6 June to 15 July, 1991. Current velocity fluctuations conditioned by the difference in atmospheric pressures over the eastern part of the sea and the western one, with the wind speed being 5 cm s⁻¹, have been studied. Inertial and seiche flows are described numerically. The peculiarities of the kinematics of the Black Sea rim current’s regular component have been scrutinized. Translated by Vladimir A. Puchkin.     

Vertical structure of currents in the upper part of the continental slope of the Black Sea in the Region of Gelendzhik

The results of a joint analysis of the synchronous-profile ensemble of density and current velocity measured using the autonomous moored Aqualog profiler at the Gelendzhik experimental site of the Shirshov Institute of Oceanology in 2013–2015 are presented. The distribution of probability density of current velocity by directions reveals the presence of two well-pronounced maxima in the southeastern and northwestern sectors at all depths of measurements, which confirms the bimodal direction of the currents in the study site. We consider in detail the vertical structure of the density stratification and the current velocity corresponding to the modes determined from the maximum of the probability density distribution of the current velocity by directions. The averaged profiles of the kinetic, potential, and total energies are given. The results of isopycnic averaging over the entire ensemble of profiles indicate that possible self-similarity exists in the dependence of the vertical distribution of density and kinetic energy.     

Peculiarities in the distribution of hydrocarbons in the southeastern part of the Baltic Sea

Data on the contents and compositions of the hydrocarbons (HCs)—aliphatic (AHCs) and polycyclic aromatic (PAHs)—are provided in comparison with the contents of the total organic carbon (C_org), the lipids in the particulates, and the C_org in bottom sediments. Particular attention has been paid to the distribution of the HCs in the water area of the Kravtsov oil field. It has been established that the concentrations of AHCs in the water are governed by the content of particulates, and the elevated AHC concentrations are confined to the coastal areas. In the water area of platform D-6, the sandy bottom sediments were notable for the great variability of the HC concentrations, both laterally and from year to year. In the summer of 2010, the content of AHCs averaged 40 μg/g (19% in the C_org), and that of PAHs, 23 ng/g. Natural seepage from the sediment mass is considered to be a source of HCs along with oil contamination.     

A numerical model of online forecasting Black Sea currents

A numerical three-dimensional nonlinear model of the hydrophysical fields of the Black Sea is presented. The properties of model discrete equations are described. The results of test experiments on the choice of model finite-difference approximations and parameters (as applied to the online forecasting of currents) are given. The results of prognostic calculations of the hydrophysical fields of the Black Sea are given for the period of March 31, 2005, to September 26, 2006. These results show that this numerical model with consideration for real atmospheric forcing can yield a satisfactory forecast of the parameters of the upper layers of the sea for 18 months of model time.     

Fine vertical structure of currents and hydrological elements in the Black Sea

Data on the fine vertical structure of currents and hydrological elements in the Black Sea, obtained through the use of a hydrophysical OLT profiler, are examined. Vertical exchange coefficients are evaluated, whose distribution is characterized by the occurrence of minima in the seasonal pycnocline and main halocline, a maximum in the core of the cold intermediate layer (CIL), and relatively steady values within the 300–500 m layer. The vertical exchange coefficient values, are consistent with the data acquired through other techniques, and the profiles of this parameter vertically are more detailed.Translated by Vladimir A. Puchkin.     

Long-term changes in the meiobenthos of the eastern part of the Black Sea

The results of meiobenthic surveys undertaken in 1991, 1999, and 2005 off the Caucasian coasts of the Black Sea are presented. During the period of 1991 to 1999, the number of free-living nematodes increased significantly at all the sampling stations. The mean nematode abundance values grew from 85 ind./10 cm² in 1991 to 1167 ind./10 cm² in 1999. Proportionally, the total metazoan meiofauna density increased from 171 to 1283 ind./10 cm². The abundance of other meiofaunal groups including harpacticoid copepods did not change significantly. As a result of these changes, the ratio of nematodes to copepods (the nematodes-copepods index) increased from 2.5: 1 in 1991 to 26: 1 in 1999 and to 70: 1 in 2005. The number of foraminifers increased twofold. In 1991, they were found only at five stations out of 25. In 1999, foraminifers were presented at all ten stations with a mean density of 212 ind./10 cm². Such changes in the meiobenthic communities could have resulted from cascade transformations of the ecosystem leading to among other changes to a decline in the macrobenthos biomass and the release of nonutilized organic matter in the bottom ecosystems. The differences in the procedures of the sampling and the samples’ processing in the different years may be responsible for the 20–30% variation in the assessment of the meiobenthos’ number.     

Characteristics of trapped topographic waves in the northwest part of the Black Sea

We study trapped baroclinic topographic waves in the northwest shelf of the Black Sea for the actual slopes of the bottom and stratification. The time scales of trapped waves are determined. The space scales of the amplitude of oscillations are computed. It is shown that the vertical distribution of the amplitude of oscillations is in qualitative agreement with the experimentally observed distribution. The energy of topographic waves trapped by the sloping bottom is concentrated in the bottom layer, which agrees with the data of measurements. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 44–52, September–October, 2006.     

Short-range forecast of hydrophysical fields in the eastern part of the Black Sea

On the basis of an analysis of the results of modeling and a forecast of the basic hydrophysical fields in the easternmost part of the Black Sea for 2010–2012, the features of annual variability of regional circulating processes in this part of the sea basin are investigated. A forecast of a hydrological mode is made on the basis of the regional forecasting system developed at the Institute of Geophysics at Javakhishvili State University in cooperation with the oceanographic centers of the Black Sea riparian countries within the frame-work of the ARENA and ECOOP EU international scientific and technical projects. The regional system is one of the components of the Black Sea basin-scale Nowcasting/Forecasting System. The analysis of the material cumulated for the registered period shows that the easternmost water area of the Black Sea is a dynamically active zone where there is a continuous formation of different circulating processes considerably distinguished from each other.     

Analysis of the nitrate distribution in the Black Sea density field

The paper discusses the results derived from the analysis of the vertical distribution of nitrates in the Black Sea density field during the winter of 1994. It has been shown that in the absence of winter-time convective mixing of waters, the vertical structure of nitrates is isopycnically defined. Maximum nitrates concentration persists throughout the warm period, normally changing from 5 to 9 μmol in the deep-water part of the area, and has not altered, in comparison with the 1980 data. Translated by Vladimir A. Puchkin.     

On numerical modelling of currents over the north-west shelf of the Black Sea

Water circulation in the north-west part of the Black Sea during the summer period is calculated by means of a complete non-linear thermohydrodynamic model. We have also studied the contribution of wind forcing, the thermohaline regime, the coastline configuration, and the bottom topography to the generation and transformation of a flow field. It has been shown that the thermohaline regime and wind forcing account for 30 and 70% of the total circulation, respectively. Variation in the nature of circulation at weak winds is due to thermohaline factors. Vertical motion plays a crucial role in theT, S- andH ₂ S-field formation.Translated by V. Puchkin.     

Statistical characteristics and the variability of currents over the western Black Sea shelf

Statistical characteristics and the parameters of the temporal variability of currents are analysed using data on current measurements conducted by five moored autonomous buoy stations over Bulgaria's shelf. Estimates of the specific contribution to the variability of synoptic (60%) and mesoscale (40%) oscillations are derived. The qualitative spectrum of the currents is defined, constituted by synoptic oscillations, short-period synoptic oscillations, inertial oscillations, and internal waves. Estimates of periods and oscillation amplitudes are also derived. The kinetic energy of the currents is calculated and the specific contribution of the energy of different-scale oscillations and their interrelations are determined.Translated by V. Puchkin.