The Fukuoka Prefectural Fisheries Experimental Station has been carrying out oceanographic observations on a fixed line in the East Tsushima Strait since 1913. Seasonal and secular changes in water temperature were investigated based on these data from 1919 to 1979. The deviations from the mean water temperature were large in summer, especially in the thermocline layer at 50m. Abnormally high temperatures appear from spring to autumn whereas abnormally low temperature appears from autumn to spring. The secular variation of water temperature in the East Tsushima Strait shows a 6-or 8-year periodicity from 1919 to 1943 and a 6-year periodicity after 1948.

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In the consideration of safety it is required that packages containing radioactive wastes when dumped at sea should keep their integrity and retain their contents until they reach the seabed. Packages containing simulated radioactive wastes (non-radioactive) were tested by a free-fall method at depths ca. 4, 300 m in an area for dumping industrial waste off Shikoku Island. Since the weight of the largest package was 4, 300 kg, special attention was paid to the connection of a buoyancy system with mooring rope. Descent and ascent velocities of the free-fall system were calculated prior to the experiment. A free-fall experiment with an extremely heavy object, heavier than ever previously reported, was accomplished without trouble by using the free-fall system. Recovery of a camera, flash-light, and other components was successful in each of the three experiments. Successive photographing of the package during descent was made and its integrity was observed using the photographs taken by the recovered camera. The packages remained intact during descent and at least for a short time after arrival on the seabed.

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The relation between the intensity of breaking of individual wind-wave crests and parameters of wave size and wave form (e. g., height, period, steepness and skewness) is examined, and the process of change of these parameters is studied in a wind-wave tank (reference wind speed 15 m sec^-1, fetch 16m) Distributions of the wave form parameters are different for breaking and nonbreaking waves. Fully breaking waves seem to hold the relation H ∝ T², where H is the individual wave height and T is the period. The condition of breaking is not simply determined by the simple criterion of Stokes' limit. Wave height and steepness of a breaking wave are not always larger than those of a nonbreaking wave. This suggests the existence of an overshooting phenomenon in the breaking wave. The wave form parameters are found to change cyclically in a statistical sense during the wave propagation. The period of the cycle in the present case is estimated to be longer than four wave periods. An intermittency of wave breaking is associated with this cyclic process. Roughly speaking, two or three succeeding breaking-waves sporadically exist among a series of nonbreaking waves along the fetch.

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Sedimentation rates in ten sediment cores from Hiroshima Bay in the Seto Inland Sea of Japan were determined with the ²¹⁰Pb technique, and heavy metals were analyzed. The sedimentation rates vary from 0.18 to 0.33g cm^-2 yr^-1. The highest sedimentation rates were observed in the northern part of the bay at the mouth of Ota River, while lower sedimentation rates not more than 0.20g cm^-2 yr^-1 were observed at stations close to narrow waterways, or where water depth was shallow. The contents of copper and zinc in the sediment cores began to increase around 1930 as a result of increased human activity, and have remained almost unchanged since 1970 possibly because of regulation of pollutant discharge. The natural background values of copper and zinc in the sediment of this bay range from 16 to 27 mg kg^-1 and 70 to 105mg kg^-1, respectively. The total amounts of anthropogenic copper and zinc deposited in the sediments since about 1930 are estimated to be 0.5-2.7 ton km^-2 and 2. 2-14. 5 ton km^-2, respectively. At the present-day, the anthropogenic loads of copper and zinc to the sediments of the whole bay are 26 ton yr^-1 and 183 ton yr^-1, and these values constitute 39 % and 48 % of the total sedimentary loads at the present-day, respectively.

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The horizontal circulations caused by the combined effect of the bottom oscillatory boundary layer (Stokes layer) and a sloping bed have been investigated both theoretically and experimentally. The generating mechanism is analogous to that for horizontal circulation induced by wind or by density variation. This horizontal circulation canaccount for a part of the tidal residual current observed in a tidal hydraulic model.

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The principal character of the tidal exchange process is neither diffusion nor advection, but a third category of transport, “Massenaustausch”, which appears in the space/time averaged transport. The exchange process can be divided into four fluxes: the flux of standing eddies, the flux of tidal exchange, the flux of tidal eddies and the flux of local eddies. The results of observations at the entrance channel of Kumihama-Bay show a typical example of transport dominated by tidal exchange.
The tidal exchange ratio defined by Parker et al.(1972) applies to the process of exchange between the outflowing watermass and the surrounding watermass outside of the bay mouth, but this should also be considered as being coupled with the ratio for the process of exchange between the inflowing watermass and the surrounding watermass inside of the bay mouth. These two exchange ratios can be combined into a single exchange ratio which describes the exchange process between the outer watermass and the bay water.

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Kinetic studies have been carried out on the dissolution of 10 μm beads of silica and of the siliceous tests of two species of diatoms (Thalassiosira fluviatus and Skeletonema costatum) in sea water at 10-50°C and over the pH range 6-9. At all temperatures dissolution of the biogenous silica occurred most rapidly at pH 8 and most slowly at pH 6. First order kinetics were closely followed when the silica was present in a considerable excess over that required for saturation, the rate being proportional to the area of the silica. Apparent deviation from this type of kinetics occurred when there was insufficient silica to bring about saturation. This was undoubtedly due to the progressive decrease in the surface area which takes place as the particle dissolves. Application of the rather simplistic model developed by Kamatani et al.(1980), which makes allowance for this decrease, gave a close correspondence with the data until-90 % of the silica had dissolved.

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The origin of a western boundary current as a jet is accounted for by a transfer of potential energy to kinetic energy, and poleward changes along the western boundary are directly correlated to variation in Coriolis parameter.

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It is indeed my great honor to receive the Okada Prize (1983) for my studies on the population dynamics and production of inshore marine copepods. This article summarizes the lecture I gave under the above title.
It has long been postulated that there is some mechanism whereby a species can repopulate after its disappearance from the plankton, since the appearance of many temperate marine copepods clearly occurs on a seasonal basis. During the last decade, evidence of resting egg production has been found for more than 20 species belonging to Temoridae, Centropagidae, Pontellidae, Acartiidae and Tortanidae. In the Inland Sea of Japan, a summer-fall copepod Tortanus forcipatus lays diapause (obligatory resting) eggs in the fall, which overwinter in the sediment on the sea floor until the following summer when water temperature reaches ca. 15°C. On the other hand, in Onagawa Bay, Acartia clausi is perennial and produces only subitaneous eggs, many of which, however, sink to the bottom and undergo quiescence (facultative resting eggs) due to adverse environmental conditions (e. g. low temperature, deoxygenation, darkness). There are a large quantity (0.5-2.0 × 10⁶ eggs m^-2) of A. clausi resting eggs in the sediments of Onagawa Bay, which may play an important role in maintaining a more constant planktonic population.
The parameters of population dynamics, i.e. the rates of egg production, recruitment and mortality, have been analyzed for A. clausi in Onagawa Bay, by an integration of field and laboratory studies. Recruitment into the planktonic population older than NIII only accounts for 10-20% of egg production. This apparent loss of eggs, which coincides with the benthic resting phase, may be a characteristic feature of the population dynamics of this species. Stage-specific mortality is generally similar in most of the stages, although CI and CVI suffer more severe mortality, possibly as a result of great morphological change in the former stage and heavy predations in the latter. The seasonal change in daily production by A. clausi has also been investigated, its annual production being 2.45 gC m^-2. Daily production and biomass (P: B) ratios increase linearly with temperature. Estimated values of production for other inshore marine copepods are reviewed in relation to P: B ratios and the ratio between secondary and primary production.

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