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.

Purpose. The purpose of this work is to study the density of water in two ways in the suboxic layer of the Black Sea, to assess errors in calculating density using a standard method based on hydrophysical equipment data, to compare the results obtained with other characteristics of sea waters and to analyze the causes of these errors. Methods and Results. The waters of the Black Sea suboxic layer were studied in May 2021 and October 2022. Water density was measured with a high-precision laboratory density meter and calculated from the CTD probe data using electrical conductivity by the EOS-80 equation of state. The turbidity values were measured by a turbidimeter while sampling. The concentrations of major ions of the major ion-salt composition in the studied samples were determined by a potentiometric titration, and their difference from the standard sea water IAPSO was assessed in the laboratory. The assessing procedure showed that, as compared to the standard sea water, the contents of SO42- and HCO3- were higher onaverage by 0.2 and 0.6%, respectively, both K+ and Ca2+-by 0.2% , and the contents of Cl- and Na+ were lower on average by 0.4 and 0.3%, respectively. The content of Mg2+ was close to its content in standard sea water. It was found that within the range of conditional density (sigma(t)) 15.9-16.2 kg/m(3), the vertical distribution of major ions was not linear, especially in relation to chlorides and sulfates. Conclusions. As a result of determining the density of the waters of the suboxic layer of the Black Sea in two ways and comparing the obtained values, it was found that the errors in calculating the density according to the CTD probe data amount to 0.05-0.2 kg/m(3) and are due to variations in the ion-salt composition and the presence of a large suspension concentrations. The density gradient measured by a density meter is approximately twice as large as that measured by a CTD probe.

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.

О прибрежных апвеллингах и даунвеллингах, обусловленных вихревой динамикой вод в северо-восточной части Черного моря 1Зацепин А.Г., Подымов О

The results of the analysis of the variability of the concentration of dissolved oxygen and chlorophyll-a (Chl-a), as well as the values of apparent oxygen utilization (AOU), in a 5-mile transect perpendicular to the coastline of Golubaya Bay (Gelendzhik), in April–November 2012, are presented. It is shown that the maximum oxygen content during the study period in most cases is observed in the thermocline layer or immediately below it, and the minimal values of AOU (negative values reflecting the maximal photosynthetic oxygen release) are above the thermocline. The maximum content of Chl-a is most often at a depth of 10 to 20 m; i.e., in spring and summer, for the most part, it is located within the thermocline, and in autumn, above it. It is shown that the oxygen content in the upper water layer is largely determined by the solubility of the gas in the sea water at the given temperature and salinity. Biological processes of oxygen release and consumption (production and destruction of organic matter) have a lesser effect on its seasonal dynamics in the upper layer. In the water layer under the thermocline, the AOU can serve as an indicator of destructive processes.

Purpose. The paper is aimed at assessing salinity and temperature variability in the upper 300-meter layer of the northeastern part of the Black Sea based on the analysis of the archival and modern expeditionary data. Methods and Results. The data on the cross-sections “coast – sea center” (with the length of 70–110 nautical miles) performed from 1999 to 2009, as well as the results of regular ship monitoring in the shelf-slope zone of the northeastern part of the Black Sea carried out in 2010–2020 were used. It was found that salinity was progressively increasing in the upper 200-meter layer during the last decade. Salinity increase, on the average, constituted annually about 0.05–0.06 PSU. An increase of temperature was also observed below the layer of temperature minimum (core of the cold intermediate layer). In particular, the lower 8.7 °C isotherm rose annually, on the average, by 11 m from its annual average depth 242 m in 2010 up to 121 m in 2020. Salinity growth led to the corresponding changes in water density that resulted in elevation of the lower boundary of the oxygen-containing layer (potential density is 15.8) from the depth of 143 m in 2010 to 124 m in 2020. Conclusions. Climatic changes have led to a noticeable salinity increase in the upper 200-meter layer of the northeastern Black Sea, as well as to a temperature increase in the layers situated below the temperature minimum layer. Though the measurements were carried out in a certain area of the shelf-slope zone, there are reasons to assume that the observed dynamics can be attributed to the entire Black Sea. Physical reasons for the observed changes require a detailed research.

Thermohaline anomalies in the upper 300-m layer at stations of the so-called “hundred-mile” ship sections over the line “coastal zone of Gelendzhik–central part of the Black Sea,” were identified and analyzed using CTD-profiling data measured in 1997–2009 by the Southern Branch, Shirshov Institute of Oceanology, Russian Academy of Sciences. Thermohaline anomalies are understood as temperature and salinity inhomogeneities at isopycnals. Since the temperature and salinity anomalies at the same density level are related one-to-one to each other by the density ratio, the results of the analysis of only thermal inhomogeneities are presented. It was found that in the σθ density range 14.5–16.5 kg/m3, the amplitude of temperature anomalies rapidly decreases with increasing density; the anomalies almost disappear below σθ isopycnals 16.1–16.2 and do not exceed ±0.03°С. At the same time, in the upper part, they reach ±0.7–0.9°С. Seasonal variations in the amplitude of anomalies exist (in winter it is greater than in summer), and its pronounced variability along the sections is almost absent. Amplitudes of thermal anomalies at the isopycnals are compared with the amplitudes of thermal anomalies at the isobars. It is shown that the latter are two to four times greater than the former. No correlations were found between these anomalies. This does not mean, however, that isobaric thermal and salinity anomalies formed mainly due to the vertical displacement of isopycnals do not affect the formation of thermohaline anomalies at isopycnals. It is shown that the fine structure of water on temperature profiles has a predominantly inversion character in regions where the absolute value of the product ΔT [(ϕro – ϕT)2]1/2 is quite high. Here, ΔT is the value of the isopycnal temperature anomaly, and ϕro – ϕT is the angle of inclination of the isotherms to isopycnals.

At the Black Sea research site Gelendzhik of the Shirshov Institute of Oceanology (IO RAS), a technique has been established for joint current velocity profile measurements using towed ADCP and periodic CTD soundings from on board of the mini R/V Ashamba with high spatiotemporal resolution. In this case, CTD soundings are taken from the sea surface to the bottom layer according to an original method recently proposed by V.T. Paka and tested by him and his colleagues on the Baltic Sea. Simultaneous measurements of this kind are important due to the insufficient knowledge of the effect of submesoscale eddies on the hydrological structure and vertical mixing processes. On the other hand, a promising aspect of fast joint ADCP and CTD surveys from the mini R/V is that their measurements can be automatically recorded to the ship's server in real time. It's connected transmitter can relay measurement data to a coastal data center, and they can be assimilated into numerical models for now- and hindcast calculations of the state of the marine environment. Thus, in the future, this technique can be considered an operational oceanograpic tool, the development of which is one of the main tasks being solved at the Gelendzhik research site.

С целью получения более детальных знаний о вертикальной структуре мезомасштабных температурных аномалий, наблюдаемых на поверхности моря из космоса, а также уточнения механизмов их формирования проведён совместный анализ спутниковой температуры поверхности моря над северо-восточной частью Чёрного моря и данных гидрологических разрезов, полученных с борта НИС «Акванавт» в 1998-2007 гг.Сравнение спутниковой температуры поверхности моря c температурой воды, измеренной CTD-зондом на глубине порядка 1 м, показало, что расхождение данных в зимние месяцы ночью при небольшом временном лаге практически отсутствует и сопоставимо с точностью спутниковых измерений.Дневной прогрев верхнего слоя зимой в среднем даёт разницу в 0,25 °C в пользу спутниковой температуры.В летние месяцы наиболее близкие к судовым измерениям значения спутниковой температуры получаются при квазисинхронных ночных измерениях.Значительное превышение спутниковой температуры над судовыми измерениями (до 3 °C) наблюдается в дневные часы летом и вызвано развитием суточного термоклина.В среднем расхождение между спутниковой и зондовой температурой летом в 2-4 раза больше, чем зимой.При прочих равных условиях степень совпадения спутниковой и зондовой температуры приповерхностного слоя вдоль судового разреза зависит от интенсивности Основного черноморского течения (ОЧТ) и степени выраженности мезомасштабной изменчивости температуры приповерхностного слоя

A possible ventilation mechanism of the aerobic zone in the Black Sea may exist, caused by a descent of oxygen-containing water down the bottom slope in the Ekman boundary layer. To study this theory three long-term (1.5-2 months) installations of automatic bottom stations were carried out in 2018-2019 on the Black Sea shelf/continental slope in the depth range from 80 to 243 m. The stations were placed on a coastal cross section on the beam of the Tolstyi Cape (the Gelendzhik Bay). They recorded the hydrophysical (temperature and salinity of water, pressure and flow rate) and hydrochemical (dissolved oxygen concentration) parameters at 0.5-2.5 m from the bottom. The acquired data were used to estimate the spatiotemporal scales of water transfer in the bottom layer along the slope. Our analysis had confirmed the existence of the bottom water transport normal to the shore. A downward flow was observed in the case of an intensive north-western alongshore current. This type of water movement corresponds to both the geostrophic adjustment and the dynamics of the bottom Ekman boundary layer. However, changes in water density in the bottom layer, which occur due to the water movement up and down the slope, were of the same range as those observed in the water column at the same depth. This fact casts doubt on the efficiency of the Ekman transport in the bottom layer as the ventilation mechanism for water of the upper continental slope of the Black Sea.

The preliminary results of an experimental study of a mechanism of the Black Sea anoxic layer ventilation related with the descent of oxygen-containing water down the bottom slope in Ekman boundary layer are presented. To study this mechanism, several automatic measuring stations were installed at the bottom of the shelf-continental slope zone in the depth range from 80 to 243 m, on the cross-section abeam of the Gelendzhik Bay. The observations that lasted for 1.5–2 months were fulfilled during two periods in the beginning and the end of 2018. The stations were registering hydrophysical (temperature, salinity, pressure and current velocity) and hydrochemical (dissolved oxygen concentration) parameters at a 0.5–2.5 m distance from the bottom. The acquired data are suitable for estimation of spatio-temporal parameters of water transfer in the bottom layer up and down the slope, depending on direction and intensity of alongshore current. Preliminary analysis of the first installation data confirmed the presence of bottom water transfer along the slope perpendicular to the shore. Also, in case of intense alongshore north-western current, a descent of the bottom layer water was observed. Such manner of water transfer conforms to both geostrophic adjustment and dynamics of the bottom Ekman boundary layer. However, variability of water density in the bottom layer, caused by vertical water transport, had about the same range as density fluctuations in the water column on the same depths. This fact disputes the effectiveness of Ekman transfer in the bottom layer as a water ventilation mechanism for the upper part of continental slope of the Black Sea (Zatsepin et al., 2007; Elkin, Zatsepin, 2017).

The paper presents an overview of the existing hypotheses about the formation areas and the distribution mechanisms of the cold intermediate layer (CIL) in the Black Sea. The testing of the statistical hypothesis about the relationship of the CIL parameters in the shelf-slope zone of the Black Sea Northeastern part with the temperature of the atmosphere surface layer in the central part of the eastern cyclonic gyre is performed. The obtained high values of the correlation coefficients (~0.98) confirmed the dependence of the CIL parameters during its formation period from the air temperature over the Northeastern part of the Black Sea. One of the concepts of the “convective-advective” hypothesis by Ovchinnikov and Popov (1987) about approximately 2 months time shift between the processes of cold air masses invasion into the water area of the Black Sea and the developed CIL waters appearance in the coastal zone of the Gelendzhik area is also confirmed.

In order to understand of the processes controlling phytoplankton successions in the NE Black Sea, long-term data series are needed. We compiled 15 years (2002-2017) of measurements from which the existence emerges of a tight link between phytoplankton species dominance and nutrients concentrations. The latter is strongly influenced by wind direction. The link between algal dominance and nutrients is mediated by the growth strategy adopted by algal species. In spring, when nutrients are abundant, small diatoms such as Pseudo-nitzschia pseudodelicatissima, with a "rapid growth strategy", prevail. In late spring and early summer, when N is low and P and Si are high, coccolithophorids such as Emiliania huxhleyi dominate, thanks to an "affinity growth strategy". Large diatoms, especially Pseudosolenia calcar-avis, dominate in summer and autumn, when their "storage growth strategy" allows the exploitation of discontinuous upwelling of nutrients. These seasonal changes of dominant species influence the structure of the food web.

Estimates of vertical turbulent diffusion coefficient (K t ) in the Black Sea pycnohalocline have been obtained from data of simultaneous observations of seawater temperature, salinity, density, and horizontal current velocity, obtained in the northeastern part of the Black Sea during 2013–2014 with a moored Aqualog profiler. A Munk and Andersson (1948) type parameterization, adapted for the Black Sea environment, is proposed for calculating K t . Strong short-period (several days) variability of turbulent exchange is revealed, induced by vertical shear variations of the current velocity.

The work demonstrates the results of the 6-years complex ship-borne monitoring of coastal zone in the north-eastern part of the Black Sea, carried out by the Southern Branch of P.P.Shirshov Institute of Oceanology, RAS, on a marine cross-section at the Blue Bay (Gelendzhik) beam 1-2 times per month. Climatic changes and eutrophication exert a significant impact on the sea water at the coastal area. In case of the Black Sea these factors pile up with a permanent hydrogen sulphide contamination of the sea water below 80-200 meters depth (depending on the season and distance from the shore). Strong pycno-halocline at the depths from 70 to 160 meters, formed due to the inflow of high salinity water from the Marmara Sea, inhibits the mixing between the water layers and, as a result, also limits the oxygen transport into the deeper layers. The winter cooling reduces the pycno-halocline and enriches the top active layer, down to the cold intermediate layer (CIL), with oxygen and nutrients, which subsequently lead to a vernal phytoplankton bloom. Formation of the thermocline and upper quasi-homogeneous layer (UQL), caused by the water warming in spring, at large extent determines a thickness of phytoplankton-rich layer during the spring and summer seasons. The work demonstrates seasonal and interannual dynamics of the UQL, thermocline, CIL and hydrogen sulphide boundary position in the coastal zone of the north-eastern part of the Black Sea.

Laboratory experiments on the dynamics of a downwelling coastal current over a sloping bottom were conducted in a tank on a rotating platform. The current was generated by a source of stable water flow of the same density (barotropic case) or of lesser density (baroclinic case) compared with the surrounding water in the tank. It was found that even in the case of the baroclinic current, a less dense water downflow in the bottom Ekman layer was formed under certain conditions. At some moment, this downflow undergoes convective instability. Taking into account the results of the experiment, the parameters of the bottom Ekman layer on the continental shelf/slope of the Black Sea were preliminarily estimated and the possible sinking depth of less dense water was calculated.