Purpose. Spatio-temporal variability of the mixed layer depth (MLD) in different areas of the Black Sea in 1985-2017, its relationship with basin dynamics and atmospheric forcing are studied. Methods and Results. The study is based on the hydrological data archive for 1985-2017 including the measurements of the ship expeditions, the Argo buoys and the moored buoy "Aqalog". Seasonal and interannual variability of the mixed layer depth was determined using the density criterion (dr = = 0.07kg/m(3)) between the surface layers and the base of the upper mixed layer. Conclusions. In January - March, the large-scale and mesoscale dynamics significantly affects the mixed layer depth variability Minimum monthly average values of the mixed layer depth in winter are observed in the mesoscale cyclonic eddies and in the center of the sea (20-30 m), the moderate values - on the periphery of the basin (40-45 m) and the maximum ones - in the mesoscale anticyclones (60-70 m). Several times the mixed layer depth values exceeding 150 m were detected in the downwelling areas of the basin. Analysis of the whole period (1985-2017) shows that the mixed layer density was never more than 1015 kg/m(3). This isopycnal limits the maximum possible depth of the upper mixed layer. The impact of wind velocity on the spatial and temporal variability of the mixed layer thickness is the largest in spring and autumn when the seasonal thermocline is weak. It is less important in summer when solar heating stabilizes the upper layer, and in winter when the mixed layer depth is large. Rise of the mixed layer depth in summer is observed in recent years that is associated with rise of the wind speed in a warm period of a year.

A possible approach to, and preliminary results of, amplitude calibration of acoustic signals backscattered from an ADCP moored at the bottom of the near-shelf zone of the Black Sea is considered. The aim of this work is to obtain vertical profiles of acoustic scattering signal levels, showing the real characteristics of the volume content of suspended sediments in sea water in units of conventional acoustic turbidity for a given signal frequency. In this case, the assumption about the intervals of maximum acoustic transparency and vertical homogeneity of the marine environment in long-term series of ADCP measurements is used. According to this hypothesis, the intervals of the least values of acoustic backscattered signals are detected, an empirical transfer function of the ADCP reception path is constructed, and it is calibrated. Normalized sets of acoustic backscattered signals relative to a signal from a level of conventionally clear water are obtained. New features in the behavior of vertical profiles of an acoustic echo-signal are revealed due to the calibration. The results of this work will be used in subsequent analysis of the vertical and time variations in suspended sediment content in the near-shelf zone of the Black Sea.

Modeling results of the Black Sea deep-water current reconstruction are considered.Computations are provided by applying the nonlinear z-coordinate model developed in Marine Hydrophysical Institute (MHI).Climatic atmospheric forcing and the atmospheric reanalysis data (ALADIN, Era-Interim) obtained for 2006, 2010 and 2013 are taken into account in different numerical experiments.The Black Sea climatology experiment is performed with a spatial grid step equal to 5 km, and in other experiments the 1.6 km grid step is used.Three-dimensional structure of the Black Sea currents on 45 levels within the surface horizon (2.5 m) and the bottom one (2100 m) is reconstructed.The anticyclonic current (countercurrent) extending along the Black Sea continental slope in direction opposite to the Rim Current is detected at about 1000 m and deeper.In the climatic fields the countercurrent exists in spring and summer in the northern part of the basin.In the experiments that included the reanalysis forcing, the countercurrent is revealed as separate streams in various continental slope areas and in different seasons.Its mean velocity is about 5 cm/s, the highest one is equal to 10 cm/s.In the overlying layer in the northeastern part of the Black Sea, the countercurrent is also detected by modeling as well as it is revealed by CTD and ADCP measurements.

The results of a test experiment comparing quasi-synchronous data of three adjacent acoustic Doppler current profilers (ADCPs) deployed on the shelf bottom of the Black Sea in September 2014 are considered. The direct aim of the experiment was quantitative comparison of data from different ADCPs placed in maximally similar conditions to simultaneously measure the sea current parameters at one geographic point. The goals and the scheme of the experiment, methods for processing the measurement results, main results, and their interpretations and analysis, including practical results and conclusions, are described.

The first data on the creation of the subsatellite polygon on the Black Sea shelf and continental slope in the Gelendzhik area (designed in order to permanently monitor the state of the aquatic environment and biota) and the plans for maintaining and developing this polygon are presented. The autonomous measuring systems of the polygon in the composition of bottom stations with acoustic Doppler current profilers (ADCP), Aqualog robotic profilers, and thermo-chains on moored buoy stations should make it possible to regularly obtain hydrophysical, hydrochemical, and bio-optical data with a high spatial-time resolution and transmit these data to the coastal center on a real-time basis. These field data should be used to study the characteristics and formation mechanisms of the marine environment and biota variability, as well as the water-exchange processes in the shelf-deep basin system, ocean-atmosphere coupling, and many other processes. These data are used to calibrate the satellite measurements and verify the water circulation numerical simulation. It is assumed to use these data in order to warn about the hazardous natural phenomena and control the marine environment state and its variation under the action of anthropogenic and natural factors, including climatic trends. It is planned to use the polygon subsatellite monitoring methods and equipment in other coastal areas, including other Black Sea sectors, in order to create a unified system for monitoring the Black Sea shelf-slope zone.

Представлены первые результаты по созданию и планы работы по поддержанию и развитию подспутникового полигона на шельфе и континентальном склоне Черного моря в районе г. Геленджик, предназначенного для перманентного мониторинга состояния водной среды и биоты. Размещаемые на полигоне автономные измерительные системы в составе донных станций с акустическими доплеровскими профилографами скорости течения (ADCP) автоматических зондов-профилографов “Аквалог” и термокос на заякоренных буйковых станциях должны обеспечивать регулярное получение гидрофизических, гидрохимических и биооптических данных с высоким пространственно-временнм разрешением и их оперативную передачу в береговой центр. Эти натурные данные необходимы для исследования характеристик и механизмов формирования изменчивости морской среды и биоты, водообменных процессов в системе “шельф–глубоководный бассейн”, взаимодействия океан–атмосфера и многих других. Они востребованы для калибрации спутниковых измерений, верификации результатов численного моделирования циркуляции вод. Их предполагается использовать в целях предупреждения об опасных природных явлениях, а также для контроля экологического состояния морской среды и его изменения под влиянием антропогенных и природных факторов, включая климатические тренды. Планируется распространение методов и средств полигонного подспутникового мониторинга водной среды на другие прибрежные акватории, в том числе на другие сектора Черного моря с целью создания единой системы мониторинга шельфово-склоновой зоны Черного моря. м разрешением и их оперативную передачу в береговой центр. Эти натурные данные необходимы для исследования характеристик и механизмов формирования изменчивости морской среды и биоты, водообменных процессов в системе “шельф–глубоководный бассейн”, взаимодействия океан–атмосфера и многих других. Они востребованы для калибрации спутниковых измерений, верификации результатов численного моделирования циркуляции вод. Их предполагается использовать в целях предупреждения об опасных природных явлениях, а также для контроля экологического состояния морской среды и его изменения под влиянием антропогенных и природных факторов, включая климатические тренды. Планируется распространение методов и средств полигонного подспутникового мониторинга водной среды на другие прибрежные акватории, в том числе на другие сектора Черного моря с целью создания единой системы мониторинга шельфово-склоновой зоны Черного моря.

Field studies performed at the Shirshov Institute of Oceanology, Russian Academy of Sciences (SIO RAS), Black Sea hydrophysical polygon in 2012 are illustrated. The variations in the vertical distribution of the hydrophysical characteristics (water temperature, salinity, and density, as well as current velocity) in the upper 200-m layer of the Black Sea above the continental slope in the cold season, obtained using an Aqualog autonomous profiler on a moored buoy station, have been analyzed. It has been established that the position of the permanent pycno-halocline and the hydrosulphuric zone upper boundary intensively oscillate with a characteristic period of 5–10 days. These oscillations cause short-period variations in the thickness of the oxigenated layer by 20–40 m, which reaches one-third of the total thickness of the layer. Measurements performed with autonomous stations (bottom ADCP, thermochain) at the experimental subsatellite polygon in the Gelendzhik coastal zone, as well as meteorological, ship, and satellite data obtained during the catastrophic rains and flooding on July 6–7, 2012, and afterward, have been simultaneously analyzed. It has been established that a catastrophic flow of turbid fresh water into the sea caused the formation of a belt of freshened (by 1.0–2.7 psu) less dense water with a high suspension concentration on the shelf and the upper continental slope. This water formed a quasi-geostrophic northwestward along-shore current, the velocity of which reached 40–50 cm/s. Therefore, the freshened and turbid water mostly escaped from the Gelendzhik region northwestward for two days after the flood, and the remaining water became free of suspension owing to its settlement during approximately the same period. The fields of the current velocity and suspension concentration in a submesoscale cyclonic eddy, identified on the satellite image, were measured at the hydrophysical polygon. It has been established that a high (when compared to the background values) suspension concentration in the surface-water layer in an eddy is related to intense upwelling at the eddy center and the rising of suspension (apparently phytoplankton) from the thermocline layer, where the suspension concentration is maximal.

Приводятся результаты натурных наблюдений, выполненных на черноморском гидрофизическом полигоне ИО РАН в 2012 г. Проанализированы данные об изменчивости вертикального распределения гидрофизических характеристик (температура, соленость, плотность воды и скорость течения) в верхнем 200-метровом слое Черного моря над континентальным склоном в холодный период года, полученные благодаря использованию автономного профилографа “Аквалог” на заякоренной буйковой станции. Установлено наличие интенсивных колебаний положения перманентного пикно-халоклина и верхней границы сероводородной зоны с характерным периодом 5–10 суток. Эти колебания вызывают короткопериодные изменения толщины кислородосодержащего слоя на 20–40 м, что составляет до одной трети его общей толщины. Проведен совместный анализ данных измерений, выполненных автономными станциями (донный ADCP, термокоса) на экспериментальном подспутниковом полигоне в прибрежной зоне г. Геленджик, метеоданных, судовой и спутниковой информации в период катастрофического ливня и наводнения 6–7 июля 2012 г. и после него. Установлено, что в результате бурного стекания мутной пресной воды в море, в области шельфа – верхней части континентального склона образовался пояс опресненных (на 1.0–2.7 psu) менее плотных вод с высокой концентрацией взвеси. Эти воды образовали квазигеострофическое вдольбереговое течение северо-западного направления, скорость которого достигала 40–50 см/c. Благодаря этому значительная часть опресненной и мутной воды за двое суток после окончания наводнения “утекла” из геленджикского района на северо-запад, а оставшаяся часть примерно за то же время очистилась от взвеси, благодаря ее оседанию на дно. На акватории гидрофизического полигона осуществлена съемка полей скорости течения и концентрации взвешенного вещества в субмезомасштабном циклоническом вихре, идентифицированном на спутниковом изображении. Установлено, что высокое (по сравнению с фоновыми значениями) содержание взвешенного вещества в приповерхностном слое вод в вихре связано с интенсивным апвеллиногом в его ядре и подъемом взвешенного вещества (по-видимому, фитопланктона) из слоя скачка температуры, где его содержание максимально.

The influence of the winter atmospheric forcing on the interannual variability of the Black Sea’s active layer’s thermohaline structure during 1982–2008 is investigated. The results are based on the combined analysis of the hydrological measurements from a ship, satellite measurements of the sea’s surface temperature (SST), and the NCEP/NCAR reanalysis data for the surface air temperature (SAT). A high correlation between the variability of the winter mean SST/SAT and the thermohaline characteristics of the active layer during the following warm season was found. It is shown that the winter atmospheric forcing significantly affects the variability of the temperature, salinity, and density down to the 150–200 m depth, and this has to be considered in the analysis of the interannual and long-term variability of the Black Sea’s active layer.

A poorly known mechanism of formation of a warm coastal current by spatially nonstationary and nonuniform wind forcing in the northeastern part of the Black Sea is described. Owing to the blocking influence of the Caucasian Mountains, the northeasterly wind (nordost) west and east of Tuapse is characterized by a spatially nonuniform speed distribution over the Russian sector of the sea. In the first half of the year, during the nordost wind, the intense wind forcing upon the upper quasi-homogeneous layer (UQL) leads to its fast cooling due to the turbulent entrainment of cold waters from the shallow seasonal thermocline. Satellite data and measurements from ships obtained at the end of June-beginning of July 2006 showed that, during two days, the temperature of the UQL west of Tuapse dropped by 7–10°C, whereas, east of Tuapse where the wind was weak, it practically did not change. As a result, a narrow frontal zone between the warm (less dense) and cold (denser) upper layer waters oriented quasi-normally to the shore was formed. A hydrodynamic analysis showed that, in such situation, an intense jet of a near-shore density current is developed that transports warm waters to the northwest at a velocity of 40–60 cm/s. This estimate agrees well with satellite data and observations from ships. The satellite data allowed us to find that this jet reached the Kerch Strait region in a few days. During the time of its existence (approximately 2 weeks), the jet transports a large volume of water and can change the functioning regime of the coastal ecosystem. The mechanism of the near-shore current formation revealed may also function in other seas and oceanic regions.

Работа выполнялась в рамках Госконтракта № 11.519.11.5020 «Черноморский экспериментальный подспутниковый полигон в целях мониторинга состояния и исследования прибрежной экосистемы» с Минобрнауки России (2011-2013 гг.), Программы 23 РАН «Фундаментальные проблемы океанологии: физика, геология, биология, экология», Программы сотрудничества РАН – НАН Украины «Черное море как имитационная модель океана» и грантов РФФИ №11-05-00830, 13-05-92608, 13-05-00777.