Numerical experiment on the circulation in the Japan Sea

By using a two-dimensional barotropic model on a-plane, the effect of the bottom topography on the path of the Tsushima Current is investigated. The rectangular model ocean with continental slopes has two openings: one is located at the southern boundary and the other at the eastern boundary. In a steady state, most of the water supplied into the model ocean through the inflow opening, flows along the continental slope with the coast to the right. Continental shelf waves play an important role in the process of adjustment to a steady state. It is suggested that the nearshore branch of the Tsushima Current might be largely topographically controlled.     

Numerical experiment on the circulation in the Japan Sea

By using a rectangular basin of uniform depth with inflow and outflow openings, the circulation in the Japan Sea is investigated numerically. Heat flux through the sea surface is determined from the annual mean atmospheric conditions for the Japan Sea, but no wind stress is considered.In the transient state, the warm water supplied through an inflow opening travels cyclonically along the coast as a density-driven boundary current in a rotating system. In the quasi-steady state, the warm water flows northward as a western boundary current which corresponds to the East Korean Warm Current and gradually separates from the coast as it flows northward. No strong boundary current corresponding to the nearshore branch of the Tsushima Current exists.Under annual mean atmospheric conditions, formation of the deep water characteristic of the Japan Sea and of the thermal front corresponding to the Polar Front do not take place.     

Optimum design of the ocean acoustic tomography system for the Sea of Japan

An ocean acoustic tomography system covering the region of 800×1000 km with the spatial resolution of eddy-resolving scales has been designed on the basis of computer experiments using the hydrographic data collected in the Sea of Japan. The optimum number of acoustic sources required for 20 acoustic receivers was estimated as 13 by changing the source number. The spatial resolution for the optimum system was 41 km smaller than the dominant size of meso-scale eddies in the Sea of Japan. The effect of travel-time errors on tomographic maps is also quantified.     

Numerical experiment for strontium-90 and cesium-137 in the Japan Sea

A numerical experiment is carried out to reproduce distribution of concentration of ⁹⁰Sr and ¹³⁷Cs, estimate their total amount and verify their source in the Japan Sea. Model results are in good agreement with observational findings in the Japan Sea expeditions between 1997 and 2002 by the Japan Atomic Energy Agency. Vertical profiles of the concentration of ⁹⁰Sr and ¹³⁷Cs show exponential decreases with depth from the sea surface to the sea bottom. From the model and observational results, it is suggested that the concentration of ⁹⁰Sr and ¹³⁷Cs in the surface layer is approximately in the range of 1.0–1.5 Bq/m³ and 2.0–2.5 Bq/m3, respectively. On the other hand, it is found that the concentration in the intermediate and deep layer is higher than that observed in the northwestern Pacific Ocean, suggesting active winter convection in the Japan Sea. The total amount of ⁹⁰Sr and ¹³⁷Cs in the seawater is evaluated to be 1.34 × 10¹⁵ Bq and 2.02 × 10¹⁵ Bq, respectively, in the numerical experiment, which demonstrates an estimation by observational data obtained in the Japan Sea expeditions. The total amount of ⁹⁰Sr and ¹³⁷Cs changed during the second half of 20th century corresponding to deposition at the sea surface with the maximums of 4.86 × 10¹⁵ Bq for ⁹⁰Sr and 7.33 × 10¹⁵ Bq for ¹³⁷Cs, respectively, in the mid-1960s. The numerical experiment suggests that the main source of ⁹⁰Sr and ¹³⁷Cs has been global fallout, although there have been some potential sources in the Japan Sea.     

Acoustic monitoring using bamboo set net in the Southern Sea of Korea

High-temporal resolution profiles of acoustic backscatter were collected from a traditional bamboo set net along the coast of the Southern Sea, Korea, using sideward-looking multi-beam imaging sonar. These data were used to examine the impact of variations in tidal cycles and current speeds on the bamboo set net. The relatively high influx of fish during the nighttime compared to the low influx and high outflux of fish during the daytime suggests visual avoidance of the net by the fish during the daytime. The observed diel variation in the captured fish flux was significantly correlated with the current speed (day: r = 0.35, p = 0.002, night: r = 0.60, p < 0.001). The ratio of influx and outflux of fish, and current speed were correlated in a linear relationship (day: r = 0.45, p < 0.001; night: r = 0.56, p < 0.001). The fish activity of those inhabiting the bamboo set nets appears to be greatly influenced by day-night differences and current speed. The present study enhances understanding of fish behavior via utilization of a bamboo set net in the coastal zone.     

Acoustic monitoring of gas emissions from the seafloor. Part II: a case study from the Sea of Marmara

A rotating, acoustic gas bubble detector, BOB (Bubble OBservatory) module was deployed during two surveys, conducted in 2009 and 2011 respectively, to study the temporal variations of gas emissions from the Marmara seafloor, along the North Anatolian Fault zone. The echosounder mounted on the instrument insonifies an angular sector of 7° during a given duration (of about 1 h). Then it rotates to the next, near-by angular sector and so forth. When the full angular domain is insonified, the “pan and tilt system” rotates back to its initial position, in order to start a new cycle (of about 1 day). The acoustic data reveal that gas emission is not a steady process, with observed temporal variations ranging between a few minutes and 24 h (from one cycle to the other). Echo-integration and inversion performed on the acoustic data as described in the companion paper of Leblond et al. (Mar Geophys Res, 2014), also indicate important variations in, respectively, the target strength and the volumetric flow rates of individual sources. However, the observed temporal variations may not be related to the properties of the gas source only, but reflect possible variations in sea-bottom currents, which could deviate the bubble train towards the neighboring sector. During the 2011 survey, a 4-component ocean bottom seismometer (OBS) was co-located at the seafloor, 59 m away from the BOB module. The acoustic data from our rotating, monitoring system support, but do not provide undisputable evidence to confirm, the hypothesis formulated by Tary et al. (2012), that the short-duration, non-seismic micro-events recorded by the OBS are likely produced by gas-related processes within the near seabed sediments. Hence, the use of a multibeam echosounder, or of several split beam echosounders should be preferred to rotating systems, for future experiments.     

Acoustic telemetry for ocean acoustic tomography

Very low data rate burst telemetry for long-range deep-ocean applications is discussed. Energy efficiency, propagation coherence, and waveform coding, together with transmitter constraints, influenced the design of proposed buoy-to-buoy and buoy-to-shore systems.     

Tidal ice drift in the White Sea: Results of a numerical experiment

The tidal ice drift is considered as an element of the tidal dynamics in a sea covered with ice. The appropriate problem is solved with the use of a combination of a simple viscoelastic continuum model of the tidal ice drift with the QUODDY-4 three-dimensional finite-element hydro-thermodynamical model. The combined model is used for simultaneous calculations of the tidal regime and the tidal ice drift in the White Sea. The calculated distributions of the characteristics of the semidiurnal (M₂ wave) tidal ice drift such as the ice drift velocity and the tidal variations of the ice concentration and the pressure of the ice compression are discussed. The distributions are used for detecting the zones of the quasi-steady tidal compression and extension of ice and regions of ridging of ice floes. Particular attention is paid to the residual tidal ice drift, a phenomenon that has remained almost unnoticed so far.     

应用Hyperion图像监测渤海海冰

对所获取的2008年冬季的辽东湾西岸海域含有海冰的Hyperion高光谱图像进行了大气校正,得到了反射率图像。用ISODATA(Iterative Self-Organizing Data Analysis Technique)聚类分析方法对反射率图像进行计算机自动分类,并结合实测的同时期的海冰反射率光谱确定了不同海冰类型的分布范围。根据不同类型海冰的厚度特征,得到了海冰厚度分级分布图和海冰厚度图。结果表明,Hyperion图像可以区分光谱有区别的冰型,无法区分浮冰和固定冰,可以更清晰地显示出海冰的光谱反射率,与实测光谱曲线更加相似,优于MODIS多光谱图像。同时,用主成分分析方法对海冰Hyperion图像进行了分析。海冰Hyperion图像中,各个波段之间的相关系数都较大,光谱维信息冗余度较大,其中30波段贡献率最高。     

Variability of Sea Surface Circulation in the Japan Sea

Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.     

Phosphorites of the Sea of Japan

The lithology and geochemistry of the Miocene concretional phosphorites recovered from four submarine rises in the Sea of Japan (the North and South Yamato, the East Korean, and the Krishtofovich) were examined by means of analytical electron microscopy and ICP-MS chemical and microchemical elemental analysis. The microstructural studies and the data on the distributions of the 57 major and trace elements in these phosphorites revealed their close similarities to the Late Quaternary nodular phosphorites from the Namibian shelf, as well as phosphorites from other parts of the world, thus suggesting a common genetic affinity. Unlike the Namibian phosphorites, our samples collected from the Sea of Japan display a number of geochemical signatures indicative of volcanic and hydrothermal activity. This is supported by the presence of positive Ce and Eu anomalies in some samples and the Ga enrichment in a sample from the Chentsov Volcano.     

Acoustic model-based matched filter processing for fadingtime-dispersive ocean channels: theory and experiment

It is shown that the performance of a conventional matched filter can be improved if the reference (replica) channel compensates for the distortion by the ocean medium. A model-based matched filter is generated by correlating the received signal with a reference channel that consists of the transmitted signal convolved with the impulse response of the medium. The channel impulse responses are predicted with a broadband propagation model using in situ sound speed measured data and archival bottom loss data. The relative performance of conventional and model-based matched filter processing is compared for large time-bandwidth-product linear-frequency-modulated signals propagating in a dispersive waveguide. From ducted propagation measurements conducted in an area west of Sardinia, the model-based matched filter localizes the depths of both the source and receiving array and the range between them. The peak signal-to-noise ratio for the model-based matched filter is always larger than that of the conventional filter     

Heat budget in the Japan Sea

The long-term mean (31-year mean) surface heat fluxes over the Japan Sea are estimated by the bulk method using the most of the available vessel data with the resolution of 1^o×1^o. The long-term annual mean net heat flux is about –53 W m^–2 (negative sign means upward heat flux) with the annual range from 133 W m^–2 in May to –296 W m^–2 in December. The small gain of heat in the area near Vladivostok seems to indicate the existence of cold water flowing from the north. In that area in winter, the mean loss of heat attains about 200 W m^–2, and the Bowen's ratio is over the unity. The largest insolation occurs in May in the Japan Sea, and the upward latent heat flux becomes the largest in November in this area. The heat flux of Haney type is also calculated, and the result, shows that the constantQ ₁ has the remarkable seasonal and spatial variation, while the coefficientQ ₂ has relatively small variation throughout all seasons. Under the assumption of constant volume transport of 1.35×10⁶ m³s^–1 through the Tsugaru Strait, the long-term averages of the volume transport through the Tsushima and Soya Straits are estimated to be about 2.20 and 0.85×10⁶ m³s^–1 from the result of the mean surface heat flux, respectively.     

Lead-210 in the Japan Sea

This is the first detailed study on the distribution of lead-210 in the Japan Sea water. The content of lead-210 ranged from 9.3±2.1 dph/l in the surface water to 3.4+-0.8 dph/l in the deep water—a quite low content as compared to that in the deep water of the North Pacific. Vertical profiles show that the content of lead-210 abruptly decreases below the seasonal thermocline (10–20 m in depth) and nearly uniform in the deep water. It is suggested that a significant amount of air-borne lead-210 deposited over the Japan Sea is transported along with the Tsushima Current to the open ocean. The budget of lead-210 is calculated by using a simple box-model and the mean residence time of lead-210 in the Japan Sea is estimated to be 15 yr.     

Abyssal circulation in the Japan Sea

Journal of Oceanography - The water below a depth of 1,000 m in the Japan Sea was found to consist of two water masses, the upper layer (the Deep Water) and the lower layer (the Bottom Water). The...     

Radium-228 in the Japan Sea

The distribution of²²⁸Ra in surface and subsurface waters in the Japan Sea was studied. The concentrations of²²⁸Ra in surface waters were around 100 dpm/1000l which were much higher than those reported for Pacific surface waters. The concentrations of²²⁸Ra decreased with increasing depth to less than 10 dpm/1000l in the Japan Sea Proper Water. Based on the comparison between observed values of²²⁸Ra and calculated profile through the near-surface water mass and the underlying main water mass in the Japan Sea, the apparent vertical eddy diffusion coefficient was estimated to be about 2 cm² s^–1.     

Geomagnetic anomaly pattern of the Japan Sea

Using all available geomagnetic data, including those obtained in a detailed survey conducted by the authors in 1970, the geomagnetic anomaly pattern if the Japan Sea has been studied. It has been established that sublinear magnetic anomalies run subparallel to the general trend of the Japanese Islands. The peak to peak amplitudes of most of these anomalies are less than 300y, their wavelengths 20 to 40 km. The anomalies are much less distinct in linearity than those found in the northwestern corner of the Pacific basin off northeastern Honshu. The linear trend is better developed in the deeper basin areas and less recognizable in the Yamato- and Kitayamato-areas. The anomaly pattern appears to support the view that the Japan Sea floor evolved through a spreading process from numerous spreading centers. A definite conclusion about the genesis of the Japan Sea, however, must await further investigation.     

黄海冷水团声层析监测数值模拟

海洋冷水团是海洋学家关注多年的问题 ,其监测方法亟待解决。本文将简正波波数层析法用于冷水团监测 ,并对简正波波数层析用于反演黄海冷水团声速剖面进行了数值模拟。数值模拟结果表明 ,简正波波数层析可以用于反演平均声速剖面 ,特别在监测与距离有关海洋环境的声速结构方面大有潜力。     

XBT monitoring of a meridian section across the western Mediterranean Sea

During the Thetis-2/MAST-2 tomography experiment, T7-XBT calibrated (accuracy ∼0.05°C) probes were launched ∼28 km apart between France and Algeria, twice a month from Feb. to Sep. 1994. Combined with infrared images, altimetric data and ship drifts, they provide definite information on the structure, drift and role of the eddy-like mesoscale phenomena generated by the Algerian Current instability. When embedded in this alongslope current, these phenomena generally propagate downstream at a few km/day and are markedly asymmetrical. Because of the topography in the eastern part of the Algerian Basin, they separate from the current, become more symmetrical and follow an anticlockwise circuit in the open basin. These phenomena are deeper than ∼750 m and entrain seaward pieces of the Levantine Intermediate Water (LIW) vein flowing along the Sardinian slope, thus being responsible of the large spatial and temporal variability of the LIW distribution in the open basin. The non-existence of a LIW vein flowing westward across the Algerian Basin is definitely demonstrated. In the Gulf of Lions, new insights are provided into the formation and spreading of the Winter Intermediate Water (WIW), which is the Western Mediterranean counterpart of LIW. Considering the large amount of WIW formed during this mild winter, it is clear that this water has not received enough attention yet, and is certainly a major component of the Mediterranean outflow at Gibraltar. Finally, the XBT data account for the eastward flow of the Western Mediterranean Deep Water (WMDW) off Algeria.