The results of analyzing the in-situ data of shear stratified flow measurements on the shelf of the Sea of Japan are presented. Study of critical zones and layers is performed in terms of the dimensionless Froude and Richardson numbers. It is shown that during the propagation of high-intensity internal bores, sufficiently long (up to several hours) time intervals occur, which are characterized by a supercritical Froude regime, when active generation of short-period internal waves of large amplitude is predicted and takes place. The statistics of the Richardson numbers shows that with the lower bound on the probability in the layer of flow measurements during the observation period, shear instability can occur in 15

The study is based on data from four moorings stretched out in the north-northwest – south-southeast direction across the isobaths in the southwestern Peter the Great Bay, the Sea of Japan, on 3–14 October, 2022. For this purpose, timeseries of vertical profiles of temperature and its gradient were expanded into empirical orthogonal functions; timescales were estimated using wavelet transform. In all cases, the leading mode captures vertical stratification variability related to the thermocline shoaling or deepening, manifesting itself by concerted oscillations of temperature and its vertical gradient, which occurred on the near-inertial, semi-diurnal and two-diurnal timescales. The near-inertial oscillations were the most intense during most of the time, while the semi-diurnal ones were the most intense on the fourth and fifth days. From the joint wavelet spectra it was found that temperature anomalies moved towards the shallower area and the speed was estimated as equal to 0.44–0.55 and 0.95–1.11 m/s for the near-inertial and semi-diurnal timescales, respectively. The speed on the two-diurnal timescale differs by an order of magnitude between the pairs of two deeper and two shallower moorings, equaling to 1.17 and 0.15 m/s, respectively. The results were interpreted as related to the near-inertial and semi-diurnal internal wave propagation from the continental slope towards the inner shelf and two-diurnal timescale was speculated to be a difference between them caused by non-linearity.

The propagation and disintegration of nonlinear internal waves at the hydrophysical test site of the Pacific Oceanological Institute FEB RAS on the shelf of the Sea of Japan have been studied in the summer-autumn period for a number of years. The mechanisms of generation and propagation of nonlinear internal wave trains due to internal tide decay have been determined by continuous measurements of the vertical temperature and velocity distribution at depths of 20–60 m using bottom stations and by a regular study of the distributions of the main hydrodynamic characteristics along selected paths. In addition, other short-period sources of thermocline deformation have been detected that can be attributed to the propagation of bottom and surface vortex structures. The high spatiotemporal resolution of the temperature field in the neighborhood of bottom stations made it possible to reveal the fine structure of wave perturbations of various types. Multilayer shallow-water models for wave-train propagation have been developed and verified using the results of field and laboratory experiments.

The paper considers a method for preprocessing (moderating) in situ hydrological data, which allows us to effectivety identify and eliminate noises of various nature. Registered data sometimes can contain abrupt surges and high-frequency pickup, caused by technology-related factors (operation nuances of the equipment used). They contradict the physical and space-time scales of hydrological wave processes, but at the same time they are not always obvious to a human operator conducting primary control. For the procedure of automatic moderation, the use of neural networks in combination with the methods of singular spectrum analysis (SSA) is proposed and the results of its practical application are demonstrated.

В статье представлены результаты гидрологических исследований на шельфе залива Петра Великого Японского моря в июле – августе 2012, июле – августе 2017, августе 2019 и августе 2021 годов. Пространственная изменчивость полей температуры и скорости звука, характерная для региона, проанализирована по результатам гидрологических CTD-зондирований и долговременных измерений заякоренными вертикальными термогирляндами. В ходе измерений было зарегистрировано прохождение тайфунов Болавен (28–29 августа 2012 года), Нору (7–8 августа 2017 года), Кроса (16 августа 2019 года), Мирина (7–9 августа 2021 года), Лупит (8–9 августа 2021 года), Омаис (10–11 августа 2021 года) у побережья Приморья Российской Федерации. Показано значительное изменение гидрологической ситуации в заливе под воздействием экстремальных внешних факторов. В спокойных метеорологических условиях в заливе наблюдается до трех слабовыраженных термоклина, расположенных на глубинах 8–15 м, 30–35 м и 45–60 м. Во время прохождения тайфунов три термоклина объединяются в один мощный на глубине примерно 50–60 м, а в некоторых случаях термоклин с большим градиентом находился на глубинах 30–40 м. Перепад температуры в термоклине, сформированным под действием тайфунов, составил примерно 12–15°C на 10 м глубины. По-видимому, усиления волнения и нагон прогретой поверхностной воды в заливе Петра Великого, вызванные сильными южными и юго-западными ветрами, приводят к появлению ярко выраженного придонного подводного звукового канала. Поскольку такие изменения влияют на распространение акустических сигналов, их особенно важно исследовать при работе с автономными подводными объектами, осуществлении их позиционирования и связи с ними.

n this work we applied machine learning methods in the field of hydrological measurements to recover (to predict) missing or damaged data. Field measurements of temperature field that were taken as a typical example, were carried out on the Sea of Japan shelf (the Peter the Great Bay) in October 2021 using a vertical moored thermostring. Recording of one of its sensors was partly deleted in manual way. To recover the missing part, we used the method of averaging the readings of the nearest sensors, as well as one-dimensional and two-dimensional Long Short-Term Memory (LSTM) neural network models. The results were compared with real data; recovery quality was assessed using the Root Mean Square Error (RMSE) of the prediction. The study showed that two-dimensional LSTM provides more accurate data recovering, with a minimum RMSE of 0.014 ± 0.006. The simulation results prove that multidimensional recovering can significantly increase the length of the predicted series while maintaining acceptable accuracy and compensate for the error accumulation effect that is observed with one-dimensional recovering. We believe that multidimensional data recovery method based on the LSTM neural network is very promising for non-stationary time series.

В статье представлены результаты гидрологических исследований на шельфе залива Петра Великого Японского моря в июле – августе 2012, июле – августе 2017, августе 2019 и августе 2021 годов. Пространственная изменчивость полей температуры и скорости звука, характерная для региона, проанализирована по результатам гидрологических CTD-зондирований и долговременных измерений заякоренными вертикальными термогирляндами. В ходе измерений было зарегистрировано прохождение тайфунов Болавен (28–29 августа 2012 года), Нору (7–8 августа 2017 года), Кроса (16 августа 2019 года), Мирина (7–9 августа 2021 года), Лупит (8–9 августа 2021 года), Омаис (10–11 августа 2021 года) у побережья Приморья Российской Федерации. Показано значительное изменение гидрологической ситуации в заливе под воздействием экстремальных внешних факторов. В спокойных метеорологических условиях в заливе наблюдается до трех слабовыраженных термоклина, расположенных на глубинах 8–15 м, 30–35 м и 45–60 м. Во время прохождения тайфунов три термоклина объединяются в один мощный на глубине примерно 50–60 м, а в некоторых случаях термоклин с большим градиентом находился на глубинах 30–40 м. Перепад температуры в термоклине, сформированным под действием тайфунов, составил примерно 12–15°C на 10 м глубины. По-видимому, усиления волнения и нагон прогретой поверхностной воды в заливе Петра Великого, вызванные сильными южными и юго-западными ветрами, приводят к появлению ярко выраженного придонного подводного звукового канала. Поскольку такие изменения влияют на распространение акустических сигналов, их особенно важно исследовать при работе с автономными подводными объектами, осуществлении их позиционирования и связи с ними. The paper presents the results of hydrological studies which we carried out on the shelf of the Peter the Great Bay of the Sea of Japan in July – August 2012, July – August 2017, August 2019 and August 2021. We have analyzed spatial variability of temperature and sound velocity fields, peculiar to the region, on the basis of hydrological CTD-data and the results of long-term measurements with anchored vertical thermostrings. In the course of measurements, we registered the following typhoons during theirpassageoff the coast of the Primorsky Territory of Russia: Bolaven (August 28–29, 2012), Noru (August 7–8, 2017), Krosa (August 16, 2019), Mirinae (August 7–9, 2021), Lupit (August 8–9, 2021), Omais (August 10–11, 2021). A significant change in the hydrological situation in the bay under the influence of extreme external factors is shown. Up to three mild thermoclines are observed in the bay in calm meteorological conditions. Its are located at depths of 8–15 m, 30–35 m, and 45–60 m in some cases, a thermocline with a large gradient was located at depths of 30–40 m. The temperature difference in the thermocline formed under the influence of typhoons was approximately 12–15°C per 10 m of depth. Apparently, the intensification of waves and surge of heated surface water in the Peter the Great Bay, caused by strong southerly and southwesterly winds, lead to the appearance of a pronounced near-bottom underwater sound channel. Since such changes affect the propagation of acoustic signals, they are especially important to study when working with autonomous underwater objects, their positioning and communicating with them.

The research aims to study the resonant properties of the water area of the Peter the Great Gulf, in the Sea of Japan. The coast of the gulf is exposed to the threat of tsunamis due to relatively high seismic activity in the Sea of Japan. On May 26, 1983, a tsunami hit several bays of the gulf with wave heights reaching 5 m. As a response, the coasts were equipped with three sophisticated sea level measuring stations. Field measurements with installation of autonomous pressure gauges were carried out August 18–26, 2016, to study the peculiarities of free surface oscillations in the western part of the Peter the Great Gulf. Spectral analysis of the recorded data and the data obtained from the Posyet automated post of the Russian Tsunami Warning Service showed, in particular, that there were several clearly pronounced peaks at periods of 40, 48, 79 and 89 min. These oscillations are coincident for the Sea of Japan and the studied water area with a wide entrance. A finite-volume numerical model was used to calculate free oscillations in the computational domain covering the Sea of Japan region. We performed model calculations with an irregular triangular grid. This allowed us to describe both the outer water area of the Sea of Japan and separate small-scale relief elements in the water area under study, which are important for the formation of local seiches. Isophases and spatial patterns of several resonant oscillations spectra at 15–105 min periods were obtained for the Peter the Great Gulf area. Model calculations carried out in this work showed an evident spatial structure of resonant oscillations. Such research, including field measurements in adjacent coastal waters, is required to identify and monitor potentially hazardous coastal areas. The amplification of resonant oscillations depends on how effectively the specific atmospheric disturbance generates corresponding eigenmodes of the Sea of Japan. In some bays, the amplitudes of the Sea of Japan eigen oscillations can increase due to resonant properties of coastal water areas, even with a low quality factor. If the amplitudes are large, such a double resonance can lead to a meteorological tsunami.

На основе инструментальных и спутниковых наблюдений рассматриваются характерные особенности локального апвеллинга, наблюдавшегося в октябре 2011 г. в юго-западной части залива Петра Великого Японского моря. Кроме того, приведены результаты численного моделирования, выполнявшегося при помощи Regional Ocean Model System (ROMS) со свободной поверхностью. При вычислениях использовались метеорологические наблюдения за неоднородностями поля ветра и инструментальные измерения гидрологической структуры воды. Анализ данных натурных измерений и их сравнение с результатами моделирования развития апвеллинга выявили, что пространственный и временной масштаб явления определялся силой, продолжительностью и направлением воздействующего ветра. Неоднородность поля скорости ветра, тесно связанная с особенностями береговой орографии, приводит к усилению апвеллинга у некоторых частей побережья и формированию температурных фронтов и струй холодной воды, поперечных основному течению, идущему вдоль шельфа.

Singular spectrum analysis (SSA), among other methods of decomposition based on empirical orthogonal functions (EOF), expands opportunities for statistical analysis of data fields. The authors suggest using two-dimensional version of SSA (2D-SSA) for processing in-situ hydrological data and prove that this method is applicable for this purpose. The authors consider key features and advantages of this approach as well as its procedural sequence and offer physical interpretation of the results based on full understanding of contribution of various factors to the hydrological situation. The examples of processing of the field measurements carried out in the shelf zone of the Sea of Japan are presented in the paper. The first dataset contained the data of profiling for one-and-a-half-hours with the intervals of two minutes at one observation point. The second consisted of the data of a single profile section along which observations were made three times several weeks apart. In both cases, the singled out two-dimensional structures were ordered according to the degree of their influence on the general hydrological picture. The filtration carried out this way made it possible in the first case to consider wave dynamics in detail, and in the second case to clarify the features of spatial geometry of the currents and vertical convection. In general, the use of 2D-SSA made it possible to interpret the results of the survey with a high degree of accuracy.

An instrumental package for monitoring hydrophysical processes (internal and surface gravity waves, including tides, seiches, and wind waves) in the shallow part of the ocean shelf is described as well as methods and approaches.

The goal of this research is to consider placer deposits allocation on the shelf on the example of the territory of Russia is given. A specification on fields of the useful minerals (tin, gold, platinum, minerals of Ti, Fe, Zr and amber) is given for mentioned placer deposits. The map of placement of underwater objects in shelf regions of Russia is submitted. In article the description of a new efficient magnetoacoustic method of searches in a shelf zone which principle of application is based on studying of change of magnetic properties of a deposit at local reorganization of its structure due to dynamic influence is also given. The essence of a method consists in carrying out primary and repeated high-precision hydromagnetic survey on the same object of researches. Retakes are carried out by results of seismoacoustic monitoring, which serves for fixing of geodynamic influence. The special attention is paid to deposits of black ore minerals as the most widely developed in coastal and shelf zones of the seas. The magnetoacoustic method will keep not only the considerable financial, human and time expenses for placer accumulation identification, but also health and longevity of people.

Spatiotemporal variability of the internal gravity waves in the Sea of Japan shelf zone (in the Peter the Great Bay) is analyzed basing on the results of the experimental data processing. It is shown that, as for autumn water structure, the tidal internal waves moving towards the coast are transformed due to the non-linear effects and may reach significant amplitudes (of about 10 meters). Such waves are usually referred to as strongly non-linear. The main characteristics of such intense waves were estimated. An example of the disintegration of solitary temperature depression into the package of short-period intense internal waves is given.

Materials of bottom sampling and drilling on Ebelyakh Bay, the Cape Svyatoi Nos area, and southern part of the Dmitry Laptev Strait by researchers from VNIIOkeangeologiya during the past 60 years and data on the geological setting of the Chokhchur–Chokurdakh zone (Ebelyakh Bay included) were also examined. The geology and lithology of Cenozoic sediments in the water area of the bay and adjacent land were scrutinized to elucidate mineral resources in the Earth’s interior in the study area. Analysis of the Upper Jurassic–Holocene summary section shows that terrigenous material was derived from (i) coastal zones composed of granitoid or contact metamorphic rocks, (ii) Quaternary friable sediments of marine terraces and beaches, (iii) submarine rises, and (iv) river discharge. It is shown that cassiterite is associated with the Pliocene–lower Pleistocene Serkino horizon and Holocene sediments. New promising cassiterite areas have been revealed. The results suggest that prospecting for tin placers should be continued at Ebelyakh Bay.

We present the results of hydroacoustic experiments carried out in 2010 in the Peter the Great Bay, the Sea of Japan, using low-frequency emitters (26 and 33 Hz). These studies are conducted in the waters where the information on geological conditions in the upper sediment layer have been obtained before and the geoacoustic sediment model has been built. An example of the influence of large inhomogeneities in bottom sediments on the acoustic signal propagation along the route is given.