Information is provided on a new project supported by the Ministry of Higher Education and Science of the Russian Federation, aimed at developing the scientific foundations of coastal operational oceanography and experimental implementation of its components at the Gelendzhik test site in the Black Sea.

The relative heat content (heat reserve) of the active layer of the sea and its variation in the warm period from April to November were estimated based on CTD data collected in 2010–2023 in the northeastern Black Sea at the Gelendzhik study site of the Shirshov Institute of Oceanology, Russian Academy of Sciences. The heat content of the upper mixed layer and the seasonal thermocline, which together make up the active layer, were calculated separately. The estimates based on real data were compared with calculations of the total heat flow based on the ERA5, NCEP CFSv2, and WHOI OAFlux reanalysis data. It was shown that the NCEP CFSv2 reanalysis data provide the result closest to the real data.

The vast majority of marine upwellings are widely examined because they are detected at the water surface. At the same time, there are poorly studied so-called "hidden" upwellings, where significant vertical water movements occur at depth. In the north-eastern Black Sea, high-frequency observations using a moored CTD and current meter profiler revealed hidden upwelling and downwelling beneath the seasonal thermocline over the continental slope. Anomalies in the depth of the indicative isopycnal sigma theta = 14.5 kg m(-3) relative to the annual mean values varied from -16 m (rising isopycnal) to +22 m (deepening). On average, the relative changes were -8.5 % and +7.2 %, respectively. In the layer 40-70 m below the photic zone, the turbulent diffusion coefficient (Kt) varied from 0.35 to 53 x 10(-5) m(2) s(-1). The diffusive nitrate flux (F-dif) depended on Kt but more strongly on gradient of nitrate (N-grad). However, variations in F-dif were smoothed by the inverse changes in Kt (increasing during downwelling) and N-grad (increasing during upwelling), yielding a nearly phase-independent upward flux. Changes in the advective nitrate flux (F-adv) were driven by equally short upwelling/downwelling phases (similar to 5.5 days). The mean F-adv and F-dif were 0.68 and 0.22 mmol N m(-2) day(-1), respectively. Estimated monthly means of new primary production ranged from 30 to 153 mg C m(-2) day(-1) with an average f-ratio of 0.31. The only visible biological response was the redistribution of the chlorophyll-a below the photic zone at high Kt. Such an impact means that, in addition to the positive effect on F-dif, and, therefore on new PP in the water column, high Kt can limit growth of deep phytoplankton assemblages.

Results of a laboratory experiment performed to test the fundamental mechanism of fine-structure stratification of a stratified fluid during turbulent mixing are described and analyzed [14, 15]. A series of experiments were carried out with mixing of aquatic environment with initially linear vertical salinity gradient using oscillating vertical rods, inducing uniform turbulent effect throughout the entire thickness of the water layer. At the same time, in each experiment, regular measurements of electrical conductivity (salinity) profiles were carried out and calculations of the vertical salt flux (mass) were performed. Under the condition of sufficiently strong density (salinity) gradient, the mass flux is described by a decreasing function of the density gradient, and this is the main condition for the formation of the fine structure, according to the proposed mechanism. The experimental results confirmed its realism and feasibility. The dependence of the vertical scale of the fine structure on the parameters of stratification and turbulent influence has also been established.

The paper is devoted to a brief description of the life path and work achievements of Sergey Vladimirovich Motyzhev, an outstanding engineer, innovator, scientist-organizer, who made a significant contribution to the development of drifter technologies for ocean research both in domestic and foreign science. The company “Marlin-Yug” created by him is a manufacturer of a wide class of autonomous surface buoys with satellite communications, designed to measure the parameters of the aquatic environment in various waters of the World Ocean, including icecovered Polar regions. His name will forever remain in the history of marine instrumentation aimed at the development of instrumental methods for operational long-term observations of the upper ocean layer and the near-water atmosphere.

Purpose. The work is purposed at investigating the underwater ridge impact on the motion of anticyclonic eddies over a sloping bottom as result of the topographic beta-effect in the laboratory conditions. Methods and Results. The experiments are carried out in a cylindrical tank located on a rotating platform. A cone is placed into the tank so that its base coincides with the cylinder lower base. The cone height is less than the base radius. Before the start of each experiment, the tank is filled with fresh or salt water of certain salinity. The fluid layer height exceeds that of the cone in the tank. The anticyclonic eddies are generated using a local constant source of a blue-colored fresh water flow. The source is located directly below the water layer surface at a distance equal to a half of the tank's radius from its center. Having achieved the critical diameter, the generated eddies drift along the isobaths in the "western" direction ("north" is at the cone top in the tank center) due to the topographic beta-effect. The experiments were carried out over the cone with a smooth surface, and over the cone with a ridge on its side whose height was significantly smaller than that of the cone located on the path of the eddy drift. In the experimental runs with the ridge, the drift both of barotropic (fresh water in the tank) and baroclinic (salt water in the tank) eddies slowed down as compared to the eddy drift velocities in the absence of the ridge. After crossing the ridge, the orbital velocity of the eddies also decreased significantly. Conclusions. Field observations and numerical modeling of the Sevastopol anticyclonic eddy in the Black Sea moving over the continental slope along the isobaths in the southwestern direction showed that the eddy motion slowed down in the area of the underwater ridge formed by a local rise in the bottom relief between two canyons - the Danube and the Western Dnieper paleochannels. The results of the laboratory experiment have confirmed the data of field observations and numerical modeling on a slowdown of the Sevastopol eddy motion and a decrease in its orbital velocity while crossing the underwater ridge due to the topographic beta-effect.

The article describes the design and operational principles of the MDS-II bottom multimodem station, located in the coastal zone (depth of location 25 m) of the northeastern Black Sea at the Gelendzhik test site of the Shirshov Institute of Oceanology, Russian Academy of Sciences. The station is connected to the coastal center by a bottom fiber optic cable, through which power is supplied to the station, and online transmission of measurement data takes place. The station is an underwater server to which one can connect a measuring device and get a real-time access to it, as well as remotely control on its operation. The design of an automatic stationary station for vertical sounding (SSVS) of the water column, which is also used at the Gelendzhik test site, is described as well. This station is moored close to the MDS-II multimodem station and is connected to one of its modems. The station consists of a bottom electric winch installed on the seabed and a floating module (probe) on a cable line wound around the winch drum. When the command “sounding” is given, the cable unwinds and the floating module, equipped with temperature and pressure sensors, floats and measures the water temperature profile from the bottom layer to the sea surface. Then the cable is wound on a drum, and the floating module returns to the bottom layer. A prototype of a new SSVS is being developed, which will allow sounding of the water layer with a thickness of up to 100 m. It will be equipped with a multiparameter probe that makes joint measurements of hydrophysical and biooptical parameters.

On June 8, 2024, the life of Lydia Vasilievna Moskalenko, candidate of geographical sciences, senior researcher of the Laboratory of Hydrophysics and Modeling of the Southern Branch of the Institute of Oceanology of the Russian Academy of Sciences (SB IO RAS), ended. Lydia Vasilievna was a major scientist and a remarkable person who devoted her entire life to oceanology. Her work yielded important scientific results that made it possible to clarify the patterns of formation of the hydrological structure and dynamics of the waters of the Mediterranean and Black Seas. The article briefly reflects the life path of L. V. Moskalenko and notes her main achievements in Russian oceanology.

Rapid rise of salinity is observed in the Black Sea in recent years, with the largest positive trend (0.07 ps mu per 10 years) detected in the pycnocline. We use long-term hydrological measurements for 1985 -2019 to show that salinity of pycnocline has intense seasonal and interannual variability modulated by the mechanical and convective mixing. In the warm period of a year, shear turbulence driven by strong winds and intense geostrophic currents causes the penetration of warm waters into the lower density layers. This is accompanied by the rise in their salinity, the source of which is the deep saline waters situated below the halocline. This process is most intense in the areas of downwelling and intensifies in the autumn period, when thermal stratification is relatively weak. Another important reason is the entrainment of salty Mediterranean waters in the upper part of the Black Sea halocline, which is modulated by the deepening of the seasonal thermocline near the Bosphorus strait and mechanical mixing. The increase of salinity is compensated during cold winters, when convective mixing transports fresher water influenced by river discharge into lower density layers of the basin and causes a decrease in pycnocline salinity. This process is most intense in the center of the cyclonic gyres, where pycnocline is located closer to the surface and winter temperature reaches minimal values. Due to the long-term warming of the Black Sea, the process of freshening of deep layers now is observed only in rare cold years. At the same time, an intensification of wind speed, vorticity, and geostrophic circulation processes promote the blurring of the halocline and the rise of the salinity of the Black Sea upper layers. Such rise begins after 2007 in the upper part of Black Sea halocline (depth 50 -100 m) and is traced down to 250 m by 2020.

The paper is commemorating Vladimir Grigorievich Krivosheya (1934–2011), a renowned scientist from the Southern Branch of SIO RAS. V. G. Krivosheya was a head of Hydrophysical Department, Ph.D. in Geography, researcher and explorer, whose studies of hydrology and water dynamics of the Mediterranean and Black Seas had significantly improved our understanding of hydrophysical features of these two basins. The paper provides a brief reflection of V. G. Krivosheya’s biography and describes his major achievements in Russian oceanography.

This paper is concerned with the analysis of the long-term regular time series of current velocity and conductivity, temperature, and depth (CTD) profiles, measured with the moored autonomous profiler Aqualog over the upper part of the continental slope at a fixed geographical location in the Northeastern Black Sea. This study focuses on the fine structure of the density profiles to show that the fine-structure Cox number (C) is a power function of the Richardson number (Ri). A similar inverse power relationship with the same exponent was found earlier for the coefficient of vertical turbulent mass exchange (Kρ) and Ri. Based on those results, the analysis indicated a statistically significant correlation between C and Kρ, which suggests that the estimations of Kρ could be conducted from the CTD data only.

Cyclonic eddies in the ocean often increase primary production and phytoplankton biomass. The main mecha-nism is the rise of the nutricline in the cyclone's core, which determines the intensification of the ascending flow of deep nutrients into the photic layer. However, some cyclones suppress primary productivity, and the natural processes underlying them are little studied and are of great fundamental interest. In August 2021, a vast cyclonic zone with two mesoscale cyclones occupied the Black Sea deep-water basin. A powerful quasi-tropical atmospheric vortex amplified one of the cyclones, which increased the Ekman pumping and led to strong sea surface cooling by 4 degrees C. However, the inflow of thermocline water into the euphotic layer and higher nutricline gradients did not lead to elevated depth-integrated concentration of chlorophyll a (Chl) and phytoplankton biomass. Moreover, the surface Chl and the average primary production was less than in the outside waters. The proposed Stratification-Lock hypothesis explains this phenomenon. A combination of several factors led to its appearance. The drastic water cooling, followed by calm weather and vigorous summer heating, led to strong thermal stratification, dampening turbulent mixing in the near-surface layer. At the same time, the velocity and shear of current in and below the thermocline were low in the entire cyclonic zone, which prevented substantial diapycnal mixing generated at depth. As a result, a 'stratification lock' appeared in the entire water column, suppressing nutrients' upward flux. The proposed hypothesis is consistent with the effect of thermal stratification on primary productivity revealed in the entire cyclonic zone. The higher was the thermal stratification the lower was the depth-integrated total phytoplankton biomass and primary production. Also, diatoms developed in the upper layer in waters with weaker thermal stratification. The described stage lasted two weeks and was inter-rupted by strong wind mixing, which destroyed the 'stratification lock' and caused an increase in Chl at the sea surface. This stage of the cyclone life cycle occurs under a strictly defined combination of hydro-meteorological conditions, suggesting a relatively rare occurrence. Nevertheless, some evidence of the similar effect of a cyclone on primary productivity can be found in other studies, indicating that this natural mechanism, consisting of a complex weather-current-eddy combination, can operate in various marine areas.

Purpose. The study is purposed at calculating and analyzing the characteristics of short-period internal wave (IW) packages based on the long-term measurements of vertical temperature distributions by a cluster of three moored thermoresistor chains spaced apart from each other and placed on the Black Sea shelf in the Golubaya Bay area (the Southern Branch of IO RAS, Gelendzhik). Methods and Results. Measurements were carried out in 2018-2020. A cluster of three thermoresistor chains at the moored buoy stations supplied with the submerged buoys was located at a distance of about 1300 m from the coast and connected to a multi-modem station, through which the data was transmitted online to the onshore data server via a fiber optic cable. The moored buoy stations with the thermoresistor chains were installed several times at the depths 24-28 m in the corners of a triangle with the sides that varied from setting to setting in the range from 40 to 130 m. Frequent (every 10 s) temperature measurements were performed by highly sensitive sensors spaced vertically at a distance of about 1 m from each other. Data processing made it possible to identify more than 50 recorded cases of IW packages with the 1-10 m amplitude of oscillations, at that they were observed most often in spring (during the thermocline development). The values of the IW oscillation period, phase velocity of their propagation (magnitude and direction), length and amplitude, and also their number in a package were calculated. Conclusions. It was revealed that the IW packages propagate mainly from the deep part of the sea to the coast. They are often observed in the frontal zones related to the intrusion of warmer or colder waters to the thermoresistor chains location area. The IW phase velocity was established to be in a statistically significant dependence on the temperature stratification parameters as well as on the IW nonlinearity parameter.

The paper analyzes quasiperiodic upwellings and downwellings on the shelf and upper part of continental slope of the northeastern Black Sea. It is shown that these processes are related to changes in intensity and direction of alongshore current and the following geostrophic adjustment of the density field. The source of such changes is the meandering of the Black Sea Rim Current (RC). It leads to a quasiperiodic change in direction of the alongshore current, from northwestern (cyclonic RC meander) to southeastern (anticyclonic RC meander, or eddy). These cycles, or phases, have an average duration of about 10 days. During the northwestern phase, the permanent Black Sea pycnohalocline (hereafter pycnocline) and seasonal thermocline descend, their thickness increases, and so does the thickness of the upper mixed layer (UML). During the southeastern phase, both the pycnocline and seasonal thermocline ascend and become thinner, along with the UML, which also becomes thinner. In both phases, isopycnals in the pycnocline and isotherms in the thermocline demonstrate quasi-in-phase vertical oscillations, which have a good correlation with the speed and direction of the alongshore current. These correlations allow estimation of the magnitude of upwellings and downwellings in the shelf–slope area of the northeastern Black Sea using data series of current velocity profiles.

The basic aim of the investigation is to study the regularities of fine structure layering of the stratified fluid (i.e., the oceanic pycnocline) under vertically homogeneous turbulent stirring. By means of physical (laboratory) modeling turbulent exchange through the density (salinity) interface, as well as the structure of this interface between two quasi-homogeneous layers of different salinity is investigated. The layers are continuously stirred by a system of horizontally oscillating vertical rods, passing through both layers. The rods produce vertically homogeneous turbulent stirring of a two-layered fluid media. During every experimental run the salinity in the upper layer is measured with the four electrode conductometer. In a part of experiments vertical profiles of salinity are periodically measured using a single-electrode conductivity microsensor. These measurements are used to calculate the turbulent flux of salt (mass) between layers and to relate these measurements with the structure of the density interface, as well as to determine the dependences of the mass flux and thickness of the interface on the defining dimensionless parameter—the Richardson number. It is shown that the interface with a decrease in the Richardson number first sharpens and then expands (diffuses). In this case, the mass flux between the layers reaches a maximum at a sharpened interface between the layers just before the interface begin to sharpen.

This article describes a new tethered profiler Winchi designed as a compact, easily deployed device for measurements of aquatic parameters from 60 m depth to air-water boundary. The profiler is capable of working from subsurface buoy or bottom anchor. It can obtain the long time series of the depth profiles of aquatic parameters during 6 months if measured once per day. Preliminary results of the profiler’s evaluation are also presented.

The study considers the formulation of the problem and performs a numerical experiment for a short-term forecast of hydrological parameters using the data of two thermohaline surveys on September 14 and 16, 2019, at the test site of the Southern Branch of the Shirshov Institute of Oceanology, Russian Academy of Sciences (IO RAS) at Gelendzhik. Due to the small spatial scale of the survey area (about 15 × 15 km), a forecast as a solution to the Cauchy problem is impossible due to the large time gap between surveys. Therefore, the authors attempted to solve the forecast problem using the technique of a priori nonadiabatic sources, reflecting the temporal variability of the sought characteristics contained in the field data of the first survey. Essentially, this technique assumes a persistent trend of temporal variability of hydrological processes during the transition to the second survey. In this case, the problem of forecasting with nonadiabatic sources is divided into two stages using a quasi-hyperbolic system of equations. At the first stage, the problem of analysis with assimilation of the first survey data is considered, in the solution of which the required nonadiabatic sources are found. At the second stage, the forecast problem is solved by calculating nonadiabatic a priori sources. Comparison of the forecast results with the data of the second survey in this case yields satisfactory results.

Biogeochemical cycles of carbon transformation throughout the euphotic zone of the sea are controlled by physical processes, e.g., daily thermocline, variation in solar irradiance, thermohaline convection, and intermittent mixing. These processes should be regularly observed with sufficient time resolution at fixed geographical locations. This study provides a brief overview of the carbon observational site in the Northeastern Black Sea. The focus is on the design of a new tethered profiler Winchi for the inner continental shelf part of the site. The profiler hull and two outriggers comprise an open trimaran platform that is positively buoyant and tends to maintain a horizontal position in the water. The lower end of the winch wire is secured to the bottom anchor. By unwinding/winding the wire, the profiler ascends/descends while measuring the depth profiles of marine environment parameters ranging from the seafloor to air–sea interface. After surfacing, the profiler determines its location using the Global Positioning System (GPS) and transmits data to (and from) a server on land through the Global System for Mobile Communications (GSM). Initial field tests with the Winchi profiler at the Northeastern Black Sea shelf exhibited promising results. We report these early tests to demonstrate the use of Winchi.

In this study, a laboratory experiment was conducted to investigate quantitatively turbulent exchange between two quasi-homogeneous layers of equal thickness and different density (salinity), as well as the fine structure of the density transition zone (interface) between the layers. The fluid was continuously stirred by a system of horizontally oscillating vertical rods, piercing through both layers and producing vertically homogeneous turbulent impact in a two-layered fluid. In every experimental run, the stirring process was carried out continuously from certain initial state up to the complete mixing of the layers. The buoyancy flux between the layers was estimated using the data on time changes of the salinity in both upper and lower layers. The fine structure of density interface was measured by vertically profiling conductivity microprobe. The results were presented in a dimensionless form and analyzed depending on two dimensionless parameters as follows: the Richardson number, Ri, and Reynolds number, Re. It was found that if Ri>Ri∗Re where Ri∗ is the critical Richardson number, the interface exists in “sharpening” mode and in “eroding” (diffusive) mode if Ri<Ri∗Re. The maximum mixing efficiency was achieved at critical Richardson number, when the density interface was in a transition state between the sharpening and diffusive modes.