The oceanographic observations in the Okhotsk Sea were made on board the patrol ship “Soya” in the prevailing period of drift ice in 1964, 1965 and 1966. The older data obtained by the Hydrographic Office of Japan from 1935 to 1940 were also examined.
It was ascertained that the Open Water, that is ice-free area always existed in the southern part of the Okhotsk Sea. This open water is maintained ice-free by the inflow of warm water from the Pacific Ocean through the straits between the Kurile Islands.
The movement of water flowing in and out between the islands was investigated and the amount of water transport was estimated.
The results are as follows:
1) There exists throughout the year the West Kamchatka Current, (a tentative name), which flows northwards into the Okhotsk Sea between the Kurile Islands. In winter season, this current suppresses drift ice which flows down to south, and makes ice-free open water area. The area of this open water is about 0.2-0.5 × 10⁶ km², which is one fifth of the total area of the Okhotsk Sea.
2) The main ocean current system in the Okhotsk Sea is composed of the West Kamchatka Current which flows toward north along the west coast of the Kamchatka Peninsula and the East Sakhalin Current which flows toward south off the east coast of the Sakhalin, and several counter currents and vortices between them.
3) The water flux of 15.0 × 10⁶ m³/sec, on the average, flow in and out between the Kurile Islands from winter to spring.
4) Through the North Uruppu Sound, which is the largest channel between the Kurile Islands, the large flux flows out toward south in the upper layer and is estimated to be about 5.0 × 10⁶ m³/sec.

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The movement of the cold Oyashio water and the occurrence of the cold water mass in Kumanonada were discussed through the distribution of four cold-water copepods, Calanus plumchrus, Calanus cristatus, Eucalanus bungii bungii, and Metridia lucens, in the waters off east-central Honshu. The selected copepods which are known to be most dominantly distributed in the shallow layer of the Oyashio area, north of 40°N in general, were found in the present area in the depths greater than 400 m where the temperature was lower than 10°C. Their distribution seemed to agree with the layers where the Pacific Intermediate Water exists.
Great differences were observed between C. cristatus obtained in the present area and that from the Oyashio area on comparing their composition of developmental stages, population, and body weight. These facts indicated that the reproduction of the cold-water copepods does not occur in the present area but they are only supplied from the Oyashio area. It is evident from their distribution pattern that the Oyashio water sinks and spreads widely to southward at the levels between 400 m and 1, 000 m, and furthermore it extends westerly as far west as about 138°E after passing over the Izu ridge. Probably, the water finally reaches Kumanonada.
There might exist two branches of the submerged Oyashio water. One flows along the coast of Honshu, north of the Kuroshio, and the other runs in offshore area, south of the Kuroshio. The appearance of the copepods suggested that the former retains the characteristics of the Oyashio water rather than the latter.

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By means of an analytical method used in previous papers, some numerical computations are carried out in order to examine in detail VALEMBOIS' experimental and theoretical result that a rectangular hydraulic resonator installed on one side of a straight channel of uniform depth and of semi-infinite or infinite length (cf. Figs. 1 and 2) can almost perfectly reflect incident periodic waves, without obstructing the passage, if its length equals one-quarter the wave length. It seems that our result agrees fairly well with his experimental result. The resonator reflects, in fact, the greater part of the incident waves for some periods, which, however, do not exactly satisfy the above relation between the wave length and the length of the resonator. Nevertheless, the amplitudes in the rear of it are strikingly increased at the immediate vicinity of these periods. Since the waves are generally not monochromatic, such a structure, though very effective if tuned to waves of certain particular periods, should be rather inconvenient to the practical purpose.

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To estimate the amount of nutrients brought up from the nutrient-rich, stablystratified deep-water into the surface layer by the convective currents which are generatedfrom a maintained source of heat placed on the bottom of the sea or in the deep water. Forthe sake of simplicity, the density gradient in the deep water is taken to be constant and noallowance is made for the motion of the ambient water.

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