Thickness and stratigraphy of reddish brown clay were compiled from lithologic descriptions of various types of cored surface sediments in the western North Pacific. Thin brown clays usually overlie gray clay in hemipelagic depositional environments and the thickness of the brown clay increases offshore, as results of the decreasing rate of sedimentation of terrigenous organic matter. The hemipelagic gray clay disappears in pelagic environments and several tens of meters of pelagic red clay overlies the basement sedimentary sequences of bedded chert and chalk in the pelagic seafloor. In the boundary region of the hemipelagic and pelagic sequences at the outer open floor of the trench basin, the pelagic facies of the red clay-bedded chert-chalk assemblage underlie the hemipelagic gray clay. This stratigraphy might indicate subduction of pelagic facies below the hemipelagic sequences.

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“Siome”, which was firstly defined by Uda (1938): is a line of convergence on the sea surface. There are many kinds of siome in the sea. I propose in this paper that siome should be classified into “streak” and “front”. Streak is defined as “the convergence within the same water mass” and front “the convergence between two different water masses”. Streaks and fronts are classified into more details on the basis of their mechanisms of generation. The proposed classification will be useful for understanding the dynamics of siome and should help to promote interdisciplinary studies around siome regions.

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The run-up height reached by the tsunami of 1896 at the former Ryohri Village had been erroneously recognized as high as only 21.9 m. Our study (1983) renewed the figure of 38.2 m (Matsuo, 1933), which is now officially recognized.
In 1980, we selected the spot, Raga, Tanohata Village, and, using a hand level, pointed out the decisive underestimation of the run-up height in Igi's report (1897). Our study, however, provided only circumstantial evidence that the maximum runup at the former Ryohri Village might be 38.2 m. In 1986, we directly studied the run-up height at the saddle point at Ohkubo, the former Ryohri Village using hand levels, and confirmed that it was at least as high as 36 m. Countermeasures for future tsunamis need major revisions, a part of which is the consideration on the combination of the large V-shaped Ryohri Bay and a neighboring small (V+U)-shaped bay. This consideration becomes essential and we show that the (V+U)-shaped bay is of the worst shape, basing on the survival ratios of individual small subhamlets, which have been recently ready for use (Yamashita, 1982).

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By measuring the maximum water level of thetraces attained by the Japan Sea Tsunami on 26 May 1983, we obtained the distribution along the west coast of the northeast Japan. The level reaches a maximum at the coast eastward of the epicenter and decreases with the relationship 8.6 e^-0.017x (m) with distance x (km) measured from the coast nearest to the epicenter. A small increase of levels was observed at coasts to the south of the tsunami source having distance larger than 200 km. With the aid of tide gauge records we revealedan excitation of edge wave which brought about the small increase of levels at the southern coast. In comparison with the decrease with distance obtained on the coasts of the main islands of Japan, some noticeable peaks were observed at several small islands. It is suggested that the reason why a short period component is predominant for the initial wave motion of tsunami is that the source region has depth of 3, 000meters. The feature of wave period is discussed in comparison with that of the 1964 Niigata Tsunami.

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We indentify three different types of Lagrangiancoordinate systems that are used in oceanography. These are: true Lagrangian coordinates (TLC), Lagrangian coordinates (LC), and averaged Lagrangian coordinates (ALC). The diffusion process is studied in each of these coordinate systems. At “large” scales the eddydiffusivity is proven to be independent of molecular diffusivity, providing the spectrum of turbulent kinetic energy varies as scale raised to a power less than 4¹/₃. The shear effect is examined using solutions to the averaged Lagrangian diffusion equation obtained by Okubo et al.(1983). In Eulerian coordinates both advection and diffusion are necessary for the occurrence of the shear effect, while in ALC timedependent dispersion coefficients are necessary for the process. In TLC we use the method of Taylor (1921) to study the dispersion of material by a velocity field, that from the Eulerian perspective, consists of turbulent motion across a uniform shear. The transformation of the above Eulerian velocity field into TLC results in a uniform deformation field and turbulent motion both along and across the shear. This work shows how dispersion of material is related to the turbulent Eulerian velocity and uniform velocity gradients. The instantaneous rate of change of variance of a spreading patch of material is completely specified by the instantaneous divergence obtained over the area occupied by the patch (Kawai, 1976). This relationship is shown to depend upon the fact that at any particular instant it is possible to define TLC that are equivalent to the Eulerian coordinates. In order to describe patch spreading from divergence measured over longer periods it is also necessary to consider other dispersive processes.

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The evolution of an isolated meso-scale eddy near a coast is studied numerically. In particular, it is found that the translation speed of the adjusted eddy is estimated well by the mutual induction mechanism adapted to a rotating stratified fluid. The nonlinear Kelvin wave excited during the adjustment process is also discussed in connection with the “Kyucho”, the sudden warming of coastal waters associated with swift currents.

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For the audience or readers to deepen understanding of fisheries oceanography, especially physical fisheries oceanography, this lecture reviews my research work, including clues, failures and management problems encountered during the course of my studies. The contents of this lecture are:(1) introduction, (2) hydrographical feature in and around the Perturbed Area between the Kuroshio and Oyashio Fronts and its fluctuation, (3) conservative properties along a streamline or a trajectory and observation planning, (4) the Kuroshio south of Japan and warm and cold eddies pinched off from the Kuroshio meanders, (5) convergence-divergence of currents and accumulation-dispersal of marine organisms, (6) the Japan Sea (and a part of the East China Sea), and (7) conclusion: approaches to research in fisheries oceanography.

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