The results of sound scattering studies in the Sea of Japan and the Sea of Okhotsk in various years are presented. The relevance of the research is related to the need to create operational methods to assess the variability of the structure of the marine environment during the continuous movement of the vessel. This circumstance is especially important near the frontal zones and flow boundaries, when the characteristics of the medium change over a short distance and therefore no contact methods allow for a detailed spatial survey of the structure of the medium near such boundaries. An effective acoustic method based on sound scattering has been developed, which allows studying the structure of sound-scattering layers, including bubbles, plankton, underwater gas flares, at various frequencies. Sound scattering coefficients were measured during the course of the vessel and at individual stations at frequencies from 12 to 100 kHz. Estimates of plankton biomass along traces based on sound scattering have been carried out. Studies of sound scattering in underwater gas flares found at the shelf boundary in the Sea of Japan are presented. The presented theoretical models made it possible to estimate the concentration of gas in the bubbles forming gas flares, as well as to estimate the total amount of gas escaping from the discovered gas flares on the shelf of the Sea of Japan.

The acoustic properties of real liquids are largely related to the phase inclusions contained in them, of which gas bubbles are the most common. The aim of the work was to find the relationship between the nonlinear acoustic parameter and the cavitation strength of the liquid with the distribution of bubbles in the liquid, which has so far been poorly studied. The theoretical studies of the parameter of acoustic nonlinearity and the cavitation strength of a liquid with bubbles were carried out within the framework of the homogeneous approximation of a micro-homogeneous liquid; the relationship of these parameters with the bubble distribution function was established, and the typical values of these parameters for different concentrations of bubbles were calculated. Experimental measurements of the parameter of acoustic nonlinearity and the cavitation strength in the upper layer of seawater were carried out; these measurements were consistent with the theoretical estimates. A connection was established between the thresholds of acoustic and optical cavitation—the optical breakdown of a liquid by laser radiation. The results obtained can find practical application in the measurement of the cavitation strength of seawater at great depths in the sea, and the use of an optoacoustic method associated with the use of optical cavitation is proposed.

We demonstrate some of the capabilities of the automated complex, which allow it to be quickly used in field and laboratory conditions with high sensitivity of analysis. The operation of the complex is based on the use of ultrasound, which allows you to create an aerosol from the liquid under study and simultaneously generate an optical breakdown with the registration of atomic lines of carbon, sodium, calcium, and magnesium. It is shown that combined laser and ultrasonic exposure leads to an increase in the sensitivity of spectroscopy of the elemental composition of various substances in seawater. The obtained results made it possible to create an automated LIBS complex for the operational assessment of the characteristics of water masses. The automated complex was used in voyage No. 81 of the RV “Professor Gagarinsky” from 1.08.22 to 14.08.22 in the Sea of Japan.

Results of a joint Russian-Brazilian expedition to study the dynamics of continental river runoff in the ocean associated with the Amazon plume are presented. The stations of the study region covered the seaward part of the Amazon plume. The work was carried out in the dry season (November). The data of in situ measurements and satellite data show that the most desalinated and rich in suspended particulate matter and chlorophyll-a waters were localized on the shallow inner shelf. The horizontal and vertical structure of the thermohaline fields indicates the presence of a well-pronounced river plume about 15 m thick. The decrease in salinity in the plume relative to the background values exceeded 6 PSU even at 300–400 km from the river mouth. The plume waters were characterized by increased concentrations of suspended matter. The best approximation to the in situ measurements is provided by the SMOS satellite salinity data and reanalysis GLORYS12. Chemical determinations in the surface layer in the area of the plume reveal elevated concentrations of silicates, phosphates, and nitrites compared to the seaward part.

Practically important properties of real liquids, including seawater, are their nonlinear properties, which include a nonlinear acoustic parameter, as well as cavitation strength – a rupture of the continuity of a liquid at high intensities in an acoustic wave. The manifestation of nonlinear effects is greatly facilitated by the presence of various nuclei in the liquid – gas bubbles, foreign particles, and other inclusions of various origins. For practical applications, it is important to study the properties of real liquids with inclusions in them. Due to the difficulties of measuring cavitation strength by acoustic methods, other methods are being sought. It is proposed to use an optoacoustic method associated with the use of laser radiation that causes optical breakdown - optical cavitation, that accompanied by a strong sound generation effect. The connection between optical breakdown thresholds and acoustic cavitation thresholds has been established, which can later be used to identify cavitation thresholds at high static pressures (at great depths in the sea), where the use of acoustic emitters is extremely difficult. The paper studies the bubble size distribution function in seawater, combined with studies of the acoustic nonlinearity parameter and cavitation strength at various depths. The interrelation of these characteristics for seawater is shown.

The work is devoted to the study of acoustic effects accompanying an optical breakdown in a liquid generated by focused laser radiation during interaction with the liquid surface. It is proposed to use an optical-acoustic method associated with the use of laser radiation that causes optical breakdown—optical cavitation, accompanied by a strong sound generation effect. A connection was established between optical breakdown thresholds and acoustic cavitation thresholds, which can subsequently be used to determine cavitation thresholds at high static pressures (at great depths in the sea), where the use of acoustic emitters is extremely difficult. A model is proposed describing the experimentally observed occurrence of optical breakdown in a liquid by laser pulses at a relatively low energy by the mechanism of breakdown formation associated with the existence of pre-threshold nanoscale nuclei of a new phase in the liquid.

The possibilities of detection and operational analysis of chemical elements in seawater using ultrasonic spark spectroscopy are demonstrated. This study was carried out using a specially designed automated complex for spectral and hydrophysical studies, which was successfully tested for many days in field conditions in the Sea of Japan (cruise 81 of the R/V Professor Gagarinskii ) and in the Atlantic Ocean (cruise 52 of the R/V Akademik Boris Petrov ). New data on the distribution of dissolved chemical elements and the state of seawater have been collected with high spatial resolution along long routes and on multi-day study sites in the Sea of Japan and Atlantic Ocean. The complex and the methods used can be recommended for in-situ studies of the state of natural water basins.

The paper presents brief results of integrated studies of the northern part of the Sea of Okhotsk close to of the Kuril arc, obtained on cruise 92 of the R/V Akademik M.A. Lavrentiev in April–May 2021. The relief was refined and the distribution of geophysical and gas-geochemical fields was obtained. Volcanic edifices hidden in the sedimentary layer were discovered. A large array of data was obtained on the distribution of temperature and salinity of surface waters, as well as the concentrations of methane, carbon dioxide, and atomic mercury in the near-water atmosphere along the route of the vessel.

This paper develops the study of the effect of powerful ultrasound on the laser breakdown of liquids and a comparative study of the possibilities of acoustic and optical diagnostics of breakdown. The method of laser-induced breakdown spectroscopy (LIBS) for elemental analysis of liquids, along with high efficiency, continues to be less sensitive compared to traditional chemical methods. The paper develops a method of using additional ultrasound irradiation of the laser breakdown area in order to increase the efficiency of LIBS. Using the developed technique, spectral lines of chemical elements such as potassium, manganese, sodium, calcium, etc. were obtained for the first time depending on the frequency and power of ultrasound. It is shown that a sharp increase in the intensity of spectral lines of elements in water during laser breakdown is observed in the field of high-power ultrasound. It indicates an increase in the sensitivity of the combined method of ultrasonic LIBS. Along with the optical spectrum, the spectral and energy characteristics of acoustic emission were studied. An automated complex for hydrophysical and spectral studies is described, which was tested in the Sea of Japan during the voyage No. 81 of the research vessel RV "Professor Gagarinsky" in August 2022.

In this paper, we show the possibility of using nonstationary and nonlinear sound scattering for diagnosing bubbles in a liquid. Nonstationary sound scattering arises due to transient processes of bubble swinging under the action of acoustic pulses. It was previously used for bubble spectroscopy in seawater using parametric emitters. Transient processes cause the coherent swinging of bubble eigenoscillations by high-frequency phase-shift keyed pulses, which are realized at certain ratios between values of high- and low-frequency resonance for the bubble and are refined by phase manipulation in the pulse. The nonlinear scattering of high-frequency pulses at difference frequencies for a monotonic bubble size distribution function g ( R ) is shown to be mainly determined by bubble resonance at the pumping frequency rather than at the difference frequency, regardless of the pulse duration. The use of nonstationary nonlinear scattering is justified in the case of a nonmonotonic size distribution of bubbles. Nonstationary nonlinear spectroscopy of bubbles is if that the pumping frequency corresponds to bubbles on the descending branch of g ( R ) for small sizes, while the difference frequency corresponds to large bubbles on the other side of the maximum of the g ( R ) function. We demonstrate that the use of nonlinear nonstationary scattering by colliding beams will allow remote spectroscopy of bubbles in a liquid that are formed in natural and technological processes and to correctly estimate the gas content in bubble structures.

The paper presents brief results of comprehensive studies of the water area of the Tatar Strait and Sea of Japan obtained on cruise 61 of the R/V "Akademik Oparin" in November-December 2020. The bottom relief and geophysical and gas-geochemical fields were refined, and new features of the geochemistry and mineralogy of bottom sediments were revealed.

The results of studying the spectra of optical breakdown plasma under two-pulse and single-pulse excitation in an ultrasound field are reported. It is shown that the efficiency of using ultrasound for recording the trace concentrations of chemical elements in a liquid under one-pulse excitation of the liquid is comparable to the efficiency under a two-pulse optical breakdown.

Abstract —The paper gives brief results of comprehensive studies in the South China Sea obtained from a joint Russian–Vietnamese expedition in November 2019 (cruise 88 of the R/V “Akademik M.A. Lavrentyev”). The set of methods included acoustics, geophysics, geology, mineralogy,geochemistry, paleogeography, geomicrobiology, hydrooptics and hydrology. The seafloor relief, geophysical and gasgeochemical fields have been refined; new features of the geochemistry and mineralogy of the continental shelf of Vietnam and the adjacent deep-sea basins have been revealed.

Представлены результаты исследования спектров плазмы оптического пробоя при двухимпульсном и одноимпульсном возбуждении в поле ультразвука. Показана эффективность использования ультразвука для регистрации следовых концентраций химических элементов в жидкости при одноимпульсном возбуждении жидкости, сравнимая с эффективностью при двухимпульсном оптическом пробое. Ключевые слова: оптический пробой, лазерно-искровая спектроскопия, спектральные линии, оптоакустические эффекты, ультразвук.

Представлены результаты исследований нелинейного акустического параметра воды в верхнем слое океана. Метод измерений основан на использовании параметрической генерации звука на различных разностных частотах при бигармоническом излучении высокочастотной накачки. Измерения нелинейного акустического параметра проводились в различные годы в приповерхностном слое в северо-западной части Тихого океана, в верхнем слое до глубины 100 м в Индийском океане, а также на шельфе Японского моря, в бухте Витязь залива Петра Великого. The results of studies of the nonlinear acoustic parameter of water in the upper layer of the ocean are presented. The measurement method is based on the use of parametric sound generation at different difference frequencies under biharmonic radiation of high-frequency pumping. Measurements of the nonlinear acoustic parameter were carried out in various years in the near-surface layer in the North-Western Pacific Ocean, in the upper layer up to a depth of 100 m in the Indian ocean, as well as on the shelf of the Sea of Japan, in the Vityaz Bay of Peter the Great Bay.