Distribution of the anoxic water mass in the eastern part of Hiuchi-Nada was investigated from 1981 to 1983. A cold water mass was found on the bottom of the area concerned in summer, and a second (i.e. lower) thermocline appeared just above the cold water mass. The anoxic water was observed below a second thermocline. The horizontal distribution of the cold water mass coincided with that of the anoxic water mass, and also with a region of high concentration of organic matter in the sediment. These results suggest two important effects of the second thermocline on the generation of the anoxic water mass. Firstly, it prevents supply of dissolved oxygen from the upper to bottom layer of the water column. Secondly, it accelerates settling of particulate material resulting in a large accumulation of organic matter in the bottom water and the sediment which leads to an increase in the rate of oxygen consumption. The net oxygen consumption rate in the bottom layer in this sea was much smaller than that in Mikawa Bay where anoxia occurs at almost the same level as in Hiuchi-Nada. This finding also suggests the important role of the second thermocline.

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Temporal variation of the anoxic water mass in Hiuchi-Nada was investigated. Vertical diffusivities at the thermoclines and oxygen consumption rates in the middle and lower layers were estimated by box model analysis using the results of field observations. On the basis of the obtained diffusivities and consumption rates, the time scale for anoxia and the degree of anoxia were examined for various conditions. It was revealed that the time scale for anoxia is about a week in the case where serious anoxia occurs and the degree of anoxia is sensitive to the diffusivity at ‘the second thermocline’. The anoxia which occurred frequently in the 1960's and 1970's is deduced to be caused by oxygen consumption rates a few times larger than the average at present and by diffusivities a few tens of per cent smaller than those under normal conditions.

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Avoiding the subject for fish accumulation, the traditional view in fish population dynamics has ascribed immigration and emigration of fish to dispersal of fish. The main purpose of this paper is to find a quantity that represents the time rate of accumulation-dispersal of marine organisms, and also has some relation to the horizontal convergence of current velocity of the surrounding water. For this, the accumulation-dispersal coefficient is introduced not in the form of diffusion, but in the same form as the convergence. Since the accumulation-dispersal of organisms is a factor that changes its distribution density, all factors causing the change are first classified to locate the position occupied by the accumulationdispersal. Each factor corresponds to each coefficient appearing in a linearized equation describing the rate of change in the density, averaged over a region or a group. The immigration-emigration coefficient is divided into three coefficients of passage, accumulationdispersal and diffusion velocity. For the organisms ranging in a nearly horizontal layer, the accumulation-dispersal coefficient is shown to equal the area-averaged horizontal convergence of organismal velocity relative to land, which is the sum of the area-averaged horizontal convergences of swimming velocity relative to water and of current velocity. However, the area-averaged convergence of current velocity associated with the accumulation-dispersal coefficient for a region is shown to be somewhat different from the usual one.

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An attempt is made to find a relation between K, the absolute value of accumulation-dispersal coefficient of marine organisms referred to a region or a group (Kawai, 1986a), and L, the square root of the area of the region or the group over which the distribution density of organisms is averaged. K is estimated as shown below. For appropriate sampling time-intervals, K becomes greater than other coefficients such as population growth coefficient. Using this result, an order of magnitude of K dependent on L is estimated from various data of temporal change in density. With the aid of a dependence Q∝L^-2/3 (Kawai, 1985b), a relation K∝L^-2/3 is predicted for 30 cm≤30 km, where Q and K are the root-mean-square values of area-averaged horizontal divergence of near-surface flows and of the accumulationdispersal coefficient, respectively. The reason why K tends to have the order of magnitude of weak or medium Q is discussed. The doubling-halving time of the distribution density due to accumulation-dispersal, T, is related to K byT=(log_e2)/K∝L^2/3. Finally, sampling time-intervals to estimate accumulation-dispersal coefficients are referred to.

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The metal load into sediments and the change in the sedimentaryenvironment of Osaka Bay in the Seto Inland Sea have been studied through geochemical analysis of core sediments, using both Pb-210 dating and a selective chemical leabhing technique. Analytical results from a 6-m core of sediment show that copper and zinc pollution started in the late 1800's and the present enrichment ratios of copper and zinc, relative to background levels (20mg kg^-1 for Cu and 94mg kg^-1 for Zn), are 2.8 and 4. 1, respectively. The present anthropogenic copper and zinc loads into Osaka Bay sediments, are 47 and 368 ton yr^-1, while natural copper and zinc loads are 40 and 186 ton yr^-1, respectively. Osaka Bay sediment at the present day is considered to be seriously polluted by zinc, now. The vertical profiles of copper and zinc in four successively separated fractions (10% acetic acid soluble fraction: F-HAC, 0.1M hydrochloric acid-soluble fraction: F-HCl, hydrogen peroxide-soluble fraction: F-H₂0₂ and hydrofluoric acid-soluble fraction: F-HF) from the core sediments indicate that enrichments of copper and zinc in the upper layer of the sediment are dependent on increases in the metal contents of the F-HAC, F-HCl and F-H₂0₂ fractions. Copper in F-HAC, and zinc in F-HAC and F-HCl, seem to be of anthropogenic origin.
Results of sequential studies of the whole Seto Inland Sea can be summarized as follows: At the present time, the sedimentary loads of copper and zinc over the whole Seto Inland Sea area are 630 and 3, 500 ton yr^-1, respectively, while the natural and anthropogenic loads are 320 and 310 ton yr^-1 for copper and 1, 800 and 1, 700 ton yr-1 for zinc, respectively.

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Deep currents measured by moored current meters over the shelf-slope off Cape Shiono-misaki, Kii Peninsula during the period from 28 April, 1981 to 4 May, 1982 are analyzed to determine characteristics of the deep current before and after the large meander of the Kuroshio formed. The observed deep currents show some different characteristics between the periods before and after the formation of the large meander of the Kuroshio, i.e.:
1. The mean current direction over the shelf slope changed to westward after the meander was formed, though it was eastward at two offshore stations before the meander was formed.
2. The eddy kinetic energy, ke ((u¹²+v¹²)/2) became large at all stations after the meander formed.
3. It appears that there were current variations in the period band shorter than 10 days which propagated offshore before the meander formed but inshore after the meander formed.
4. After the meander formed, the current variations with a period of 0 (25 days) were amplified at two of the three stations. The current variations in this period band showed high coherence among the three stations.

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The energy flux of the Japan Sea Tsunami of May 26, 1983 radiated offshore causing the destruction of ships in Shimane Prefecture, the fourth worst area hit. In 1960, a tsunami from Chile attacked the Pacific coast from the Ryukyu Islands to Adak Island, Alaska. The energy flux of the latter was similar to that of the former. The angle formed at the origin off the Chilean coast by the energy flux was 68°48'or possibly slightly larger. The coincidence between the angle given by this process and that by the directivity theory of Miyoshi (1977) is good. The Sanriku District is located approximately on the center line of this angle. Judging from the fact that the Sanriku District was attacked most severely in 1960, it can be suspected that the energy flux was a little more sharply directed than estimated by the theory. The equivalent angle in the case of the Japan Sea Tsunami, which attacked the area from the tip of the Noto Peninsula to the east coast of the Korean Peninsula, was only 45°30' and the smaller angle can be explained as a refraction effect of the Yamato Bank. The above information should be useful for warnings of future tsunamis.

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An internal wavetrain, generated by a tidal current in superposition with the Tsushima Warm Current, has been observed by use of an acoustic echo-sounder upstream of the ‘Shichiri-Ga-Sone’ Seamounts in the East Tsushima Strait of the Japan Sea. The sea surface above the internal wavetrain was simultaneously observed and was found to be undulated at the wavelength of the internal wave.

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