Japan Shelf Research Articles

Estimation of Seawater Hydrophysical Characteristics from Thermistor Strings and CTD Data in the Sea of Japan Shelf Zone

The knowledge of salinity in a specific sea area with high accuracy is required to solve several acoustic and hydrophysical problems on the ocean shelf. Unlike temperature, which can be measured continuously for a long time, with, for example, thermistor strings (thermostrings), salinity values of required accuracy can be obtained only using CTD profiling. This is why methods of estimating salinity from temperature could be helpful. In this paper, the authors propose using the regression method for solving this type of problem and demonstrate the efficiency of this method using examples of temperature measurements from anchored thermostrings. For the correct construction of regressions, the authors analyzed the errors of CTD measurements and suggested a method for the dynamic correction of raw CTD data. From CTD profiling datasets of 12 years (2011–2022), after their dynamic correction, the authors obtained regression polynomial formulas for calculating salinity from temperature and studied data stability in space and time at the hydrophysical test site, located in the shelf zone of the Sea of Japan. The authors consider this method efficient and applicable in solving a variety of acoustic and hydrophysical problems.

Registration of Nonlinear Hydrophysical Disturbances—Rogue Waves in Full-Scale Conditions

In the paper, we discuss the results of processing and analysis of field data obtained from a laser-based supersensitive detector during the registering of hydrosphere pressure variations on the seabed at various points of the Sea of Japan shelf. The main focus is the study of physical mechanisms of the occurrence of nonlinear hydrophysical disturbances in the range of gravity and infragravity sea waves classed as rogue waves, the amplitudes of which are more than twice the amplitudes of the bordering signals in this range of periods. It has been established that in the range of gravity/wind sea wave periods (2–20 s), similar disturbances were registered by the supersensitive detector of hydrosphere pressure variations. The paper explains the appearance of such nonlinear disturbances. In addition to single large-amplitude nonlinear perturbations, classical nonlinear disturbances, related to the “one sister”, “two sisters”, and “three sisters” rogue wave types were discovered. Their occurrence is associated with the interaction of gravity and infragravity sea waves in the zone of the recording equipment location. In the course of spectral processing of the obtained field data, the main modes of wind waves and infragravity sea waves responsible for the formation of the observed rogue waves were identified. The intermodal energy transfer in the observed wave packet resembles in its behavior the modified Fermi–Past–Ulam recurrence. In the lower frequency range, non-linear hydrophysical disturbances of the “sea hole” and “crest” type were found; the origin of which is associated with atmospheric processes.

Method of Hydrological Time Series Recovery Using Neural Network Technologies

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.

Dynamics and Transformation of Sea Surface Gravity Waves at the Shelf of Decreasing Depth

This paper reviews the results of the processing of synchronized data on hydrosphere pressure variations and the Earth’s crust deformation in the microseismic range (5–15 s), obtained over the course of numerous experiments, using a coastal laser strainmeter and laser meters of hydrosphere pressure variations installed in various points of the Sea of Japan shelf. Interpreting the results, we have discovered new regularities in the dynamics of surface progressive gravity waves, and their transformation into primary microseisms, when waves move at the shelf of decreasing depth. For example, we found non-isochronous behavior of progressive waves, which manifests itself in a decrease in the periods of gravity waves due to the transformation of a part of their energy into the energy of primary microseisms. Furthermore, when processing the synchronous fragments of the records, made by laser strainmeters and laser meters of hydrosphere pressure variations, we identified approximate zones of the most effective transformation of the energy of gravity progressive waves into the energy of primary microseisms, which start from the depth of less than a half-wavelength and stretch to the surf zone.

Features of the geological structure and oil and gas content of the shelves of the Far Eastern Seas

Russian shelf is one of the most important areas for hydrocarbon forecast and mineral resources development. The main features of the geological structure of the shelves of the Far Eastern seas are discussed in the paper. The most promising basins on the Okhotsk shelf are located around Sakhalin island where the majority of the hydrocarbon fields have been discovered. The Bering and the Japan shelf has not been sufficiently studied by now but nevertheless has high oil and gas potential. The main focus is made on the geological and geophysical data, licensing, lithological and stratigraphic structure, seismic interpretation, oil and gas fields distribution. The structural-tectonic zoning of the entire Far Eastern region has been done in order to identify zones of deep troughs with thick sedimentary cover to predict the sources of hydrocarbon generation.

Fluctuations of the Sea Level, Caused by Gravitational and Infra–Gravitational Sea Waves

In the article we analyzed the results of processing experimental data of the range of surface gravity sea wind waves (2–20 s) and the range of infra-gravitational sea waves (30 s–10 min), obtained on the laser meter of hydrosphere pressure variations. The laser meter of hydrosphere pressure variations was installed for a long time on the bottom at different points of the Sea of Japan shelf. This paper presents the results of the analysis of swell waves caused by the KOMPASU typhoon, which passed over the Sea of Japan on 2–3 September 2010. Several mechanisms of the generation and propagation of waves with different periods during the typhoon movement are considered. In the course of the analysis, we studied the connection between variations of the main periods of gravitational sea waves with the dispersion and the Doppler effect, variations of speed and direction of the wind in a typhoon zone. The nonlinearity of the process of wave period change caused by dispersion is estimated. In the combined analysis of variations of hydrosphere pressure in the ranges of gravitational and infra-gravitational sea waves, we studied their energy relationships and determined regional infra-gravitational sea waves, which make a significant contribution to the energy of the infra-gravitational range.

Specifics of the Deepwater Reception of Pseudo-Random Pulse Signals Propagating from the Shelf towards the Deep Ocean

The results of an experiment conducted in September 2017 are considered with regard to the applicability of the acoustic “mudslide” effect for positioning autonomous underwater vehicles (AUV) operating substantially deeper than the axis of the deep sound channel (DSC). The results of the experimental study and numerical analysis of the effect of focusing acoustic energy in the bottom layer on the Sea of Japan shelf and transitional zone with the deep water (up to 500 m deep) for summer-autumn hydrological conditions are presented. Mathematical modeling of the propagation of acoustic waves in a waveguide reproducing the experimental conditions using the parabolic equation method has been performed. The effective propagation velocities of the signal are explained in terms of the modal-analysis method.

On intense internal waves in the coastal zone of the Peter the Great Bay (the Sea of Japan)

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.

The role of the Commission on the Limits of the Continental Shelf (CLCS) and extended continental shelf of Japan

The role of the Commission on the Limits of the Continental Shelf (CLCS) and extended continental shelf of Japan

Effect of a sloping bottom on sound propagation

The paper presents the results of field measurements of acoustic fields generated in autumn hydrological conditions of the Sea of Japan shelf by a TON-320Hz autonomous signal emitter, moored in the sea at a depth of 34 m, as well as by a low-frequency pulsed pneumoemitter lowered from from a ship to a horizon of 10 m. Reception was via a hydrophone moored at a depth of 41 m from a digital radio-hydroacoustic buoy and the hydrophone of an autonomous acoustic recorder lowered together with an autonomous hydrological sonde from a drifting ship. Sound propagation from these sources was simulated by a wide-angle parabolic equation taking into account the elastic properties of rocks making up the bottom, as well as by a 3-D mode parabolic equation in the adiabatic approximation for a “fluid” bottom.

Initial spread of <sup>137</sup>Cs from the Fukushima Dai-ichi Nuclear Power Plant over the Japan continental shelf: a study using a high-resolution, global-coastal nested ocean model

Abstract. The 11 March 2011 tsunami triggered by the M9 and M7.9 earthquakes off the Tōhoku coast destroyed facilities at the Fukushima Dai-ichi Nuclear Power Plant (FNPP) leading to a significant long-term flow of the radionuclide 137Cs into coastal waters. A high-resolution, global-coastal nested ocean model was first constructed to simulate the 11 March tsunami and coastal inundation. Based on the model's success in reproducing the observed tsunami and coastal inundation, model experiments were then conducted with differing grid resolution to assess the initial spread of 137Cs over the eastern shelf of Japan. The 137Cs was tracked as a conservative tracer (without radioactive decay) in the three-dimensional model flow field over the period of 26 March–31 August 2011. The results clearly show that for the same 137Cs discharge, the model-predicted spreading of 137Cs was sensitive not only to model resolution but also the FNPP seawall structure. A coarse-resolution (∼2 km) model simulation led to an overestimation of lateral diffusion and thus faster dispersion of 137Cs from the coast to the deep ocean, while advective processes played a more significant role when the model resolution at and around the FNPP was refined to ∼5 m. By resolving the pathways from the leaking source to the southern and northern discharge canals, the high-resolution model better predicted the 137Cs spreading in the inner shelf where in situ measurements were made at 30 km off the coast. The overestimation of 137Cs concentration near the coast is thought to be due to the omission of sedimentation and biogeochemical processes as well as uncertainties in the amount of 137Cs leaking from the source in the model. As a result, a biogeochemical module should be included in the model for more realistic simulations of the fate and spreading of 137Cs in the ocean.

Mathematical modeling and evaluation of bioinvasion status of barnacles on the shelf of Japan

The results of a statistical analysis of spatiotemporal distribution of the barnacles Amphibalanus improvisus, A. amphitrite, and A. eburneus on the shelf of the Sea of Japan are presented for the period of 1935–2000. The locations of barnacle finds coincide with the areas of huge sea ports and electric power plants. The empirical patterns of barnacle bioinvasion to the Sea of Japan are described under the statistical analysis of sampling data. The computational model of barnacle invasion is developed and analyzed. This model takes into account empirical data and suggested parametric factors, such as natural population growth, intra- and interspecific competition, sea environmental conditions, and natural settling activity, and anthropogenic factors, such as navigation intensity anthropogenic load. The algorithms of population dynamics and evaluation of model adequacy are suggested. Significant concordance between model and field data is obtained.

Application of pseudorandom signals for underwater distance measurement on a shelf

In this paper, the results of experiments conducted on the Sea of Japan shelf are applied and discussed. The aim of these experiments was to study regularities in the formation of impulse characteristics for wave conductors under variable hydrological conditions. It has been shown that, in order to determine the distance and coordinates of underwater devices precisely when working on a shelf, one should identify the first and last impulses in impulse characteristics for the wave conductor, measure their arrival times, and multiply them to calculate the values of effective sonic velocity along the propagation routes of these impulses.

Experimental studies of seasonal variation for temperature fields on the Sea of Japan shelf by acoustical methods

The results of experimental studies are given for the pulsed characteristic of an underwater channel on the Sea of Japan shelf depending on the seasonal variation of a temperature field.

Distribution and origin of subaqueous dunes on the shelf of Japan

Subaqueous dunes are found on the shelf around the Japanese Islands, mainly in the straits between the islands. Some of the dunes are formed by ocean currents, and others by tidal currents. Combined flows also produce shoreparallel coarse-grained bands and medium dunes on the inner shelf. The dynamics of these bedforms was examined using repeated observations of bedforms and by comparing the hydraulic conditions required to form the bedforms with the existing oceanographic conditions. The study indicates that most of bedforms are active but the volumes of sediment transported are too small to form the sand bodies which underlay the large dunes. Seismic records show these sand bodies occur on the erosional surfaces formed after the last glacial maximum. It is suggested that most of the sand bodies were formed during the postglacial transgression.